The advent and development of organocatalysis

An Organic Molecular Mimetic Metal-Free Heterogeneous Catalyst for Electrocatalytic Alkyne Semihydrogenation

The direct construction of metal-free catalysts on conductive substrates for electrocatalytic organic hydrogenation reactions is significant but still unexplored. Here, learning from the homogeneous molecular catalysts, an organic molecular mimetic metal-free heterogeneous catalyst is designed and constructed in situ on a graphite flake electrode via a mild electrochemical oxidation-reduction relay strategy. The as-prepared -COOH- and -OH-functionalized metal-free catalyst exhibits an electrocatalytic alkyne semihydrogenation performance with a 72 % Faradaic efficiency, 99 % selectivity and 96 % yield of the alkene product, which is comparable to that of noble metal catalysts. The removal of these oxygen-containing groups leads to negligible activity. The experimental and calculation results reveal that the origin of the high activity can be assigned to the -COOH and -OH groups on graphite. A flow electrolytic cell delivers ten grams of hydrogenated products with 81 % Faradaic efficiency. This metal-free catalyst is also suitable for gas-phase acetylene semihydrogenation and other electrocatalytic hydrogenation reactions.

New Entries in Organocatalysts from an Alkaloid Library; Development of Aminal Catalysis for a Michael Reaction Based on Calycanthine

Natural products have historically been actively evaluated for their biological activity in the development of pharmaceuticals, while their evaluation as asymmetric catalysts has rarely been explored. In this study, we evaluated the catalytic activity of the natural product library. Three naturally occurring alkaloids, gardnerine, spiradine A, and calycanthine, were found to catalyze an asymmetric Michael reaction using oxindole and nitrostyrene. We further studied (+)-calycanthine, which is characterized by its aminal structure. Concise synthetic and extraction protocols were developed to provide both enantiomers of calycanthine. Further derivatization of this alkaloid led to improved enantioselectivity in a model reaction. Computational studies suggested that the aminal moiety of the catalyst activated nucleophiles and electrophiles through multiple hydrogen bonding interactions, including nonclassical hydrogen bonds between carboxylic acid and the aminal C-H.

Direct Enantioselective α-C-H Conjugate Addition of Propargylamines to α,β-Unsaturated Ketones via Carbonyl Catalysis

Direct asymmetric α-C-H conjugate addition of propargylamines to α,β-unsaturated ketones remains a great challenge due to the low α-amino C-H acidity of propargylamines and the nucleophilic interference of the NH2 group. Utilizing a new type of pyridoxals featuring a benzene-pyridine biaryl skeleton and a bulky amide side chain as carbonyl catalyst, we have accomplished direct asymmetric α-C-H conjugate addition of NH2-unprotected propargylamines to α,β-unsaturated ketones. The adducts undergo subsequent in situ intramolecular cyclization, delivering a wide range of chiral polysubstituted 1-pyrrolines in high yields (up to 92%) with excellent diastereo- and enatioelectivities (up to >20:1 dr and 99% ee). This work has demonstrated a straightforward approach to access pharmaceutically important chiral 1-pyrrolines, and it has also provided an impressive instance of direct asymmetric functionalization of inert C-H bonds enabled by biomimetic organocatalysts.

Catalyst Control over S(IV)-stereogenicity via Carbene-derived Sulfinyl Azolium Intermediates

Stereoselective synthesis utilizing small-molecule catalysts, particularly N-heterocyclic carbene (NHC), has facilitated swift access to enantioenriched molecules through diverse activation modes and NHC-bound reactive intermediates. While carbonyl derivatives, imines, and "activated" alkenes have been extensively investigated, the exploration of heteroatom-centered analogues of NHC-bound intermediates has long been neglected, despite the significant potential for novel chemical transformations they offer once recognized. Herein, we disclose a carbene-catalyzed new activation mode by generating unique sulfinyl azolium intermediates from carbene nucleophilic addition to in situ-generated mixed sulfinic anhydride intermediates. Combined experimental and computational mechanistic investigations pinpoint the chiral NHC-catalyzed formation of sulfinyl azolium intermediate as the enantio-determining step. The novel "S"-based carbene reactive intermediate imparts high efficiency for the catalytic construction of sulfur-stereogenic compounds, giving rise to sulfinate esters with high yields and enantioselectivities under mild conditions. Notably, distinct from most of the NHC-catalyzed enantioselective transformations focusing on the "C" central chiral products, our study realizes a unique carbene-catalyst control over chiral "S" stereocenters via direct asymmetric S-O bond formation for the first time. Furthermore, these sulfinyl-containing products could serve as versatile synthetic platforms for enantioenriched S-stereogenic functional molecules and exhibit remarkable antibacterial activities against rice plant pathogens, which is valuable for the development of novel agrochemical agents.

Visible-light-induced redox-neutral difunctionalization of alkenes and alkynes

The twelve principles of green chemistry illuminate the pathway in the direction of sustainable and eco-friendly synthesis, marking a fundamental shift in synthetic organic chemistry paradigms. In this realm, harnessing the power of visible light for the difunctionalization of various skeletons without employing any external oxidant or reductant, specifically termed as redox-neutral difunctionalization, has attracted tremendous interest from synthetic organic chemists due to its low cost, easy availability and environmentally friendly nature in contrast to traditional metal-catalyzed difunctionalizations. This review presents an overview of recent updates on visible-light-induced redox-neutral difunctionalization reactions with literature coverage up to May 2024.

Expedited Proton Relay in Enzyme-Inspired Cobaloximes Facilitate Organic Transformations

Developing a water-soluble, oxygen-tolerant, and acid-stable synthetic H2 production catalyst is vital for renewable energy infrastructure. To access such an effective catalyst, we strategically incorporated enzyme-inspired, multicomponent outer coordination sphere elements around the cobaloxime (Cl-Co-X) core with suitable axial coordination (X). Our cobaloximes with axial imidazole or L-histidine coordination in photocatalytic HAT including the construction of anilines via a non-canonical cross-coupling approach is found superior compared to commonly used cobaloxime catalysts. The reversible Co(II)/Co(I) process is influenced by the axial N ligand's nature. Imidazole/L-histidine with a higher pKa promptly produces H2 upon irradiation, leading to the improved reactivity compared to previously employed axial (di)chloride or pyridine analogue.

Enantioselective Michael addition of 3-hydroxy-2-pyridone to nitroolefins using cinchona-derived bifunctional organocatalysts

Despite the extensive use of N-heteroarenes in pharmaceuticals and natural products, efficient methods for selective alkylation at the C-4 position of 2-pyridone are scarce. We developed an enantioselective Michael addition of 3-hydroxy-2-pyridone to nitroolefins at the C-4 position using cinchona-derived bifunctional squaramide organocatalysts, achieving up to 95% yield and >99% ee. This selectivity is driven by the bifunctional organocatalysts' hydrogen bonding interactions with 3-hydroxy-2-pyridone and nitroolefins under mild conditions. This method demonstrates the Michael reaction's versatility with various nitroolefins, providing a sustainable approach for synthesizing chiral N-heteroarenes with high enantioselectivity and regioselectivity under environmentally friendly conditions.

Organocatalytic enantioselective construction of Si-stereocenters: recent advances and perspectives

Silicon-stereogenic chiral organosilanes have found increasing applications in synthetic chemistry, medicinal chemistry, and materials science. In this context, various asymmetric catalytic methods have been established for the diverse synthesis of silicon-stereogenic silanes. In particular, asymmetric organocatalysis is emerging as an important and complementary synthetic tool for the enantioselective construction of silicon-stereocenters, along with the rapid development of chiral-metal catalyzed protocols. Its advent provides a powerful platform to achieve functionalized silicon-stereogenic organosilanes with structural diversity, and should lead to great development in chiral organosilicon chemistry. In this Tutorial Review, we highlight these latest achievements from two aspects: desymmetrizations of prochiral tetraorganosilanes and dynamic kinetic asymmetric transformations of racemic organosilanes by employing five organocatalytic activation modes. The advantages, limitations and synthetic value of each protocol, as well as the synthetic opportunities still open for further exploration, are also discussed.

Skeletal Transformations Observed in the Reaction of a Tricyclic Thymine Nucleoside with Dicarbonyl Compounds

Some intriguing skeletal transformations were observed in the reaction of α-hydroxypyrrolidine thymine nucleoside 2 with different dicarbonyl compounds. In these reactions, unusual ring systems, together with new C-C bonds and stereogenic centers of defined configuration, were formed in a single step. These reactions were initiated by the nucleophilic attack of the NH of the pyrrolidine ring, present on 2, on one of the carbonyl moieties of a dicarbonyl reagent and seem to proceed through an enamine-iminium mechanism. The present methodology is particularly attractive because no catalyst or aggressive conditions are needed. The new polycyclic nucleosides obtained from 2 can be good scaffolds for diversification. In fact, modification and derivatization can be achieved by performing further chemical transformations of the functional groups present in some of them. This may lead to the formation of new highly functionalized nucleosides. Our results show the high synthetic potential of 2 to construct complex systems in an efficient way. On the other hand, the enamine chemistry involved in the particular reactivity of the α-hydroxy pyrrolidine ring present in 2 has no connection with the nucleobase and could be extended to simple glycosides preserving this essential ring system.

N-Heterocyclic Carbene Enabled Functionalization of Inert C(Sp3)-H Bonds via Hydrogen Atom Transfer (HAT) Processes

Developing methods to directly transform C(sp3) -H bonds is crucial in synthetic chemistry due to their prevalence in various organic compounds. While conventional protocols have largely relied on transition metal catalysis, recent advancements in organocatalysis, particularly with radical NHC catalysis have sparked interest in the direct functionalization of "inert" C(sp3) -H bonds for cross C-C coupling with carbonyl moieties. This strategy involves selective cleavage of C(sp3) -H bonds to generate key carbon radicals, often achieved via hydrogen atom transfer (HAT) processes. By leveraging the bond dissociation energy (BDE) and polarity effects, HAT enables the rapid functionalization of diverse C(sp3)-H substrates, such as ethers, amines, and alkanes. This mini-review summarizes the progress in carbene organocatalytic functionalization of inert C(sp3)-H bonds enabled by HAT processes, categorizing them into two sections: 1) C-H functionalization involving acyl azolium intermediates; and 2) functionalization of C-H bonds via reductive Breslow intermediates.

Is the E/Z Iminium Ratio a Good Enantioselectivity Predictor in Iminium Catalysis?

Developing new enantioselective reactions is an important part of chemical discovery but requires time and resources to test large arrays of potential reaction conditions. New techniques are required to analyse many different reactions quickly and efficiently. Mass spectrometry is a high-throughput method; when combined with ion-mobility spectrometry, this technique can monitor diastereomeric reaction intermediates and thus be a handle to study enantioselective reactions. Through this technique and others, it was noted before that in the organocatalytic 1,4-addition to α,β-unsaturated aldehydes, the abundance of initial diastereomeric intermediates correlates strongly to that of the final enantiomeric products. This work determines isomeric abundance for various catalysts and aldehydes and uses it to predict the enantiomeric excess of two control reactions. The prediction matches well for one reaction but does not predict the obtained results for the second. This finding confirms that the E/Z ratio of the iminium intermediates can be used as a predictor for some reactions, but the kinetics of the following steps can dramatically change the true enantioselectivity.

The Diversity and Evolution of Chiral Brønsted Acid Structures

The chemical space of chiral Brønsted acid catalysts is defined by quantity and complexity, reflecting the diverse synthetic challenges confronted and the innovative molecular designs introduced. Here, we detail how this successful outcome is a powerful demonstration of the benefits of utilizing both local structure searches and a comprehensive understanding of catalyst performance for effective and efficient exploration of Brønsted acid properties. In this concept article we provide an evolutionary overview of this field by summarizing the approaches to catalyst optimization, the resulting structures, and functions.

Highly Selective O-Phenylene Bisurea Catalysts for ROP: Stabilization of Oxyanion Transition State by a Semiflexible Hydrogen Bond Pocket

Organocatalyzed ring-opening polymerization (ROP) is a versatile technique for synthesizing biodegradable polymers, including polyesters and polycarbonates. We introduce o-phenylene bisurea (OPBU) (di)anions as a novel class of organocatalysts that are fast, easily tunable, mildly basic, and exceptionally selective. These catalysts surpass previous generations, such as thiourea, urea, and TBD, in selectivity (kp/ktr) by 8 to 120 times. OPBU catalysts facilitate the ROP of various monomers, achieving high conversions (>95%) in seconds to minutes, producing polymers with precise molecular weights and very low dispersities (Đ ≈ 1.01). This performance nearly matches the ideal distribution expected from living polymerization (Poisson distribution). Density functional theory (DFT) calculations reveal that the catalysts stabilize the oxyanion transition state via a hydrogen bond pocket similar to the "oxyanion hole" in enzymatic catalysis. Both experimental and theoretical analyses highlight the critical role of the semirigid o-phenylene linker in creating a hydrogen bond pocket that is tight yet flexible enough to accommodate the oxyanion transition state effectively. These new insights have provided a new class of organic catalysts whose accessibility, moderate basicity, excellent solubility, and unparalleled selectivity and tunability open up new opportunities for controlled polymer synthesis.

A Simple Organo-Electrocatalysis System for the Chlor-Related Industry

Consuming a substantial quantum of energy (~165 TW h), the chlor-alkali industry garners considerable scholarly and industrial interest, with the anode reaction involving the oxidation of chloride ions being a paramount determinant of reaction rates. While the dimensionally stable anode (DSA) displays commendable catalytic activity and longevity, they rely on precious metals and exhibit a non-negligible side reaction in sodium hypochlorite (NaClO) production, underscoring the appeal of metal-free alternatives. However, the molecules and systems currently available are characterized by intricate complexity and are not amenable to large-scale production. Herein, we have successfully developed an economical and highly efficient molecular catalyst, demonstrating superior performance compared with the former organic molecules in the chloride ion oxidation process (COP) for the production of both chlorine gas (Cl2) and NaClO. The molecule of 2N only needs 92 mV to reach a current density of 1000 mA cm-2, with a small cost of only 0.002 $ g-1. Furthermore, we propose a novel mechanism underpinned by non-covalent interactions, serving as the foundation for an innovative approach to the design of efficient anodes for the COP.

Ionic Hydrogen Bond-Assisted Catalytic Construction of Nitrogen Stereogenic Center via Formal Desymmetrization of Remote Diols

The control of noncarbon stereogenic centers is of profound importance owing to their enormous interest in bioactive compounds and chiral catalyst or ligand design for enantioselective synthesis. Despite various elegant approaches have been achieved for construction of S-, P-, Si- and B-stereocenters over the past decades, the catalyst-controlled strategies to govern the formation of N-stereogenic compounds have garnered less attention. Here, we disclose the first organocatalytic approach for efficient access to a wide range of nitrogen-stereogenic compounds through a desymmetrization approach. Intriguingly, the pro-chiral remote diols, which are previously not well addressed with enantiocontrol, are well differentiated by potent chiral carbene-bound acyl azolium intermediates. Preliminary studies shed insights on the critical importance of the ionic hydrogen bond (IHB) formed between the dimer aggregate of diols to afford the chiral N-oxide products that feature a tetrahedral nitrogen as the sole stereogenic element with good yields and excellent enantioselectivities. Notably, the chiral N-oxide products could offer an attractive strategy for chiral ligand design and discovery of potential antibacterial agrochemicals.

Redox-Active Carboranyl Diphosphine as an Electron and Proton Transfer Agent

In this work, we report the first example of the PCET reactivity for a boron cluster compound, the zwitterionic nido-carboranyl diphosphonium derivative 7-P(H)tBu2-10-P(H)iPr2-nido-C2B10H10. This main-group reagent efficiently transfers two electrons and two protons to quinones to yield hydroquinones and regenerate a neutral closo-carboranyl diphosphine, 1-PtBu2-2-PiPr2-closo-C2B10H10. As we have previously reported the conversion of this closo-carboranyl diphosphine into the zwitterionic nido- derivative upon reaction with main group hydrides, the transformation reported herein represents a complete synthetic cycle for the metal-free reduction of quinones, with the redox-active carboranyl diphosphine scaffold acting as a mediator. The proposed mechanism of this reduction, based on pKa determination, electrochemical studies, and kinetic isotope effect determination, involves the electron transfer from the nido- cluster to the quinone coupled with the delivery of protons.

Integrating chemistry knowledge in large language models via prompt engineering

This paper presents a study on the integration of domain-specific knowledge in prompt engineering to enhance the performance of large language models (LLMs) in scientific domains. The proposed domain-knowledge embedded prompt engineering method outperforms traditional prompt engineering strategies on various metrics, including capability, accuracy, F1 score, and hallucination drop. The effectiveness of the method is demonstrated through case studies on complex materials including the MacMillan catalyst, paclitaxel, and lithium cobalt oxide. The results suggest that domain-knowledge prompts can guide LLMs to generate more accurate and relevant responses, highlighting the potential of LLMs as powerful tools for scientific discovery and innovation when equipped with domain-specific prompts. The study also discusses limitations and future directions for domain-specific prompt engineering development.

Design, Preparation, and Implementation of Axially Chiral Benzotetramisoles as Lewis Base Catalysts for Asymmetric Cycloadditions

Developing novel catalysts with potent activity is of great importance in organocatalysis. In this study, we designed and prepared a new class of benzotetramisole Lewis base catalysts (AxBTM) that have both central and axial chirality. This unique feature of these catalysts results in a three-dimensional microenvironment with multi-layers of chirality. The performance of the developed catalysts was tested in a series of cycloaddition reactions. These included the AxBTM-catalyzed (2+2) cycloaddition between α-fluoro-α-aryl anhydride with imines or oxindoles, and the sequential gold/AxBTM-catalyzed (4+2) cycloaddition of enynamides with pentafluorophenyl esters. The interplay between axial and central chirality had a collaborative effect in regulating the stereochemistry in these cycloadditions, leading to high levels of stereoselectivity that would otherwise be challenging to achieve using conventional BTM catalysts. However, the (2+2) and (4+2) cycloadditions have different predilections for axial and central chirality combinations.

Radical meta-C-H Halogenation of Azines via N-Benzyl Activation Strategy

Regioselective halogenation of six-membered N-heteroarenes is crucial for precise functional derivatization. We present a meta-selective halogenation method for pyridines, quinolines, and isoquinolines via electrophilic halogen radical addition utilizing an N-benzyl activation strategy. This method achieves C3- and C5-dihalogenation in pyridines, C3- and C6-dihalogenation in quinolines, and C3-monohalogenation in isoquinolines. The feasibility and potential applications of this method were validated through scale-up reactions and the bromination of quinoline derivatives with biomolecular fragments.

Direct flipping dynamics and quantized enrichment of chirality at single-molecule resolution

Chirality is an important aspect of nature, and numerous macroscopic methods have been developed to understand and control chirality. For the chiral tertiary amines, their flexible flipping process makes it possible to achieve high chiral controllability without bond formation and breaking. Here, we present a type of stable chiral single-molecule devices formed by tertiary amines, using graphene-molecule-graphene single-molecule junctions. These single-molecule devices allow real-time, in situ, and long-time measurements of the flipping process of an individual chiral nitrogen center with high temporal resolution. Temperature- and bias voltage-dependent experiments, along with theoretical investigations, revealed diverse chiral intermediates, indicating the regulation of the flipping dynamics by energy-related factors. Angle-dependent measurements further demonstrated efficient enrichment of chiral states using linearly polarized light by a symmetry-related factor. This approach offers a reliable means for understanding the chirality's origin, elucidating microscopic chirality regulation mechanisms, and aiding in the design of effective drugs.

Organocatalysis as an enabling tool for enantioselective ring-opening reactions of cyclopropanes

The rich reactivity profile of cyclopropanes has been extensively explored to trigger new organic transformations that enable unusual disconnective approaches to synthesize molecular motifs that are not easily reached through conventional reactions. In particular, the chemistry of cyclopropanes has received special attention in the last decade, with multiple new approaches that capitalize on the use of organocatalysis for the activation of the cyclopropane scaffold. This situation has also opened the possibility of developing enantioselective variants of many reactions that until now were only carried out in an enantiospecific or diastereoselective manner. Our group has been particularly active in this field, focusing more specifically on the use of aminocatalysis and Brønsted acid catalysis as major organocatalytic activation manifolds to trigger new unprecedented transformations involving cyclopropanes that add to the current toolbox of general methodologies available to organic chemists for the enantioselective synthesis of chiral compounds.

Arginine Acts as both Co-Solvent and Catalyst in Regioselective Eutectic-Mediated Dimerization of Levulinic Acid

A simple, solvent-free arginine-catalyzed aldol dimerization of levulinic acid was achieved via the simultaneous formation of a eutectic mixture. Dimers of levulinic acid are valued as biomass-derived fine chemical precursors, with potential to upgrade to bio-jet fuels or N-containing functional chemicals. Typically, these dimers are produced as isomeric mixtures using high temperatures and a variety of solid inorganic catalysts or mineral acids. In this study, an organocatalytic and regioselective dimerization was achieved at 22 % conversion on either a bench or kilogram scale using mild temperatures and only L-arginine as both a co-solvent and catalyst. The intricate H-bonding network comprising the eutectic solvent was harnessed to produce only one product, minimizing side reactivity and preserving the reactants for recycling.

A New Age of Biocatalysis Enabled by Generic Activation Modes

Biocatalysis is currently undergoing a profound transformation. The field moves from relying on nature's chemical logic to a discipline that exploits generic activation modes, allowing for novel biocatalytic reactions and, in many instances, entirely new chemistry. Generic activation modes enable a wide range of reaction types and played a pivotal role in advancing the fields of organo- and photocatalysis. This perspective aims to summarize the principal activation modes harnessed in enzymes to develop new biocatalysts. Although extensively researched in the past, the highlighted activation modes, when applied within enzyme active sites, facilitate chemical transformations that have largely eluded efficient and selective catalysis. This advance is attributed to multiple tunable interactions in the substrate binding pocket that precisely control competing reaction pathways and transition states. We will highlight cases of new synthetic methodologies achieved by engineered enzymes and will provide insights into potential future developments in this rapidly evolving field.

Electrochemical Asymmetric Radical Functionalization of Aldehydes Enabled by a Redox Shuttle

Aminocatalysis is a well-established tool that enables the production of enantioenriched compounds under mild conditions. Its versatility is underscored by its seamless integration with various synthetic approaches. While the combination of aminocatalysis with metal catalysis, photochemistry, and stoichiometric oxidants has been extensively explored, its synergy with electrochemical activation remains largely unexplored. Herein, we present the successful merger of electrochemistry and aminocatalysis to perform SOMO-type transformations, expanding the toolkit for asymmetric electrochemical synthesis. The methodology harnesses electricity to drive the oxidation of catalytically generated enamines, which ultimately partake in enantioselective radical processes, leading to α-alkylated aldehydes. Crucially, mechanistic studies highlight how this electrochemical strategy is enabled by the use of a redox shuttle, 4,4'-dimethoxybiphenyl, to prevent catalyst degradation and furnishing the coveted compounds in good yield and high enantioselectivity.

An Artificial Enzyme for Asymmetric Nitrocyclopropanation of α,β-Unsaturated Aldehydes-Design and Evolution

The introduction of an abiological catalytic group into the binding pocket of a protein host allows for the expansion of enzyme chemistries. Here, we report the generation of an artificial enzyme by genetic encoding of a non-canonical amino acid that contains a secondary amine side chain. The non-canonical amino acid and the binding pocket function synergistically to catalyze the asymmetric nitrocyclopropanation of α,β-unsaturated aldehydes by the iminium activation mechanism. The designer enzyme was evolved to an optimal variant that catalyzes the reaction at high conversions with high diastereo- and enantioselectivity. This work demonstrates the application of genetic code expansion in enzyme design and expands the scope of enzyme-catalyzed abiological reactions.

Enantioselective Hydroaminoalkylation of Azaaryl Ketones through Asymmetric Photoredox Catalysis

An enantioselective hydroaminoalkylation of azaaryl ketones under a transition-metal-free asymmetric photoredox catalysis platform is reported. A series of valuable azaarene-functionalized 1,2-amino alcohols featuring attractive quaternary carbon stereocenters have been synthesized in high yields with good to excellent enantioselectivities. The viability of readily accessible N-aryl glycines as reaction partners facilitates the conjugate modification of these products into important derivatives, thereby enhancing the synthetic utility of the current approach.

N-Heterocyclic carbene/palladium synergistic catalysis in organic synthesis

The cooperation of two distinct catalytic cycles to activate different reactive centers leading to a chemical transformation has been classified as synergistic catalysis. The synergistic combination of NHC with palladium catalysis has emerged as a powerful strategy in the last few years. Merging the ability of NHCs to inverse the polarity of a functional group with the unique reactivity of palladium enables transformations that cannot be accomplished by either of these catalysts alone. Despite the associated challenges, such as quenching of catalysts, reactivity mismatch etc., significant development has been achieved in the field of NHC/Pd synergistic catalysis. The recent incorporation of photoredox catalysis with NHC/Pd synergistic catalysis has further advanced this area. This review highlights the developments made in the area of NHC/Pd synergistic catalysis.

Bicarbonate-binding catalysis for the enantioselective desymmetrization of keto sulfonium salts

Herein, an enantioselective desymmetrization of cyclic keto sulfonium salts through enantioselective deprotonation/ring opening process by anion-binding catalysis is presented. We report a squaramide/HCO3- complex as catalytic active species which is able to stereo-differentiate two enantiomeric protons, triggering the ring opening event taking advantage of the great tendency of sulfonium salts to act as leaving groups. Thus, this desymmetrization methodology give rise to β-methylsulfenylated sulfa-Michael addition type products with excellent yields and very good enantioselectivities. The bifunctional organocatalyst has been demonstrated to be capable of activating simultaneously the base and the keto sulfonium salt by DFT calculations and experimental proofs.

Deprotonated 2-thiolimidazole serves as a metal-free electrocatalyst for selective acetylene hydrogenation

Metal-free catalysts offer a desirable alternative to traditional metal-based electrocatalysts. However, metal-free catalysts, featuring defined active sites, rarely show activities as promising as metal-based materials. Here we report 2-thiolimidazole as an efficient metal-free catalyst for selective electrocatalytic hydrogenation of acetylene into ethylene. Under alkaline conditions, the sulfhydryl and imino groups of 2-thiolimidazole are spontaneously deprotonated into dianions. Deprotonation thus enriches the negative charges of pyridinic N sites in 2-thiolimidazole to enhance the adsorption of electrophilic acetylene through the σ-configuration. Ethylene partial current densities show a volcano relationship with the negative charges of the pyridinic N sites in various imidazole derivatives. Consequently, the deprotonated 2-thiolimidazole exhibits an ethylene partial current density and faradaic efficiency competitive with metal-based catalysts like Cu and Pd. This work highlights the tunability and promising potential of metal-free molecules in electrocatalysis.

Bifunctional iminophosphorane organocatalyst with additional hydrogen bonding: Calculations predict enhanced catalytic performance in a michael addition reaction

A new iminophosphorane-thiourea superbase was rationally designed and investigated as an organocatalyst for the enantioselective Michael addition reaction of nitromethane to 4-phenylbut-3-en-2-one. Starting from an iminophosphorane-thiourea organocatalyst structure already known, we have used theoretical calculations to determine the structures of transition states involved in the carbon-carbon bond formation step and carried out structural modifications to accelerate the reaction rate and to increase the enantioselectivity. The effective structural modification was adding a rigid hydroxyl group able to make an additional hydrogen bond to the transition state, producing a substantial decrease of the ΔG‡ by 7 kcal mol-1. The enantiomeric excess is predicted to be above of 97% using the reliable M06-2X and ωB97M - V functionals. The determination of the complete reaction mechanism and free energy profile was followed by a detailed microkinetic analysis. The present study points out a new direction for structural modifications on this kind of organocatalyst.

Secondary Amine Catalysis in Enzyme Design: Broadening Protein Template Diversity through Genetic Code Expansion

Secondary amines, due to their reactivity, can transform protein templates into catalytically active entities, accelerating the development of artificial enzymes. However, existing methods, predominantly reliant on modified ligands or N-terminal prolines, impose significant limitations on template selection. In this study, genetic code expansion was used to break this boundary, enabling secondary amines to be incorporated into alternative proteins and positions of choice. Pyrrolysine analogues carrying different secondary amines could be incorporated into superfolder green fluorescent protein (sfGFP), multidrug-binding LmrR and nucleotide-binding dihydrofolate reductase (DHFR). Notably, the analogue containing a D-proline moiety demonstrated both proteolytic stability and catalytic activity, conferring LmrR and DHFR with the desired transfer hydrogenation activity. While the LmrR variants were confined to the biomimetic 1-benzyl-1,4-dihydronicotinamide (BNAH) as the hydride source, the optimal DHFR variant favorably used the pro-R hydride from NADPH for stereoselective reactions (e.r. up to 92 : 8), highlighting that a switch of protein template could broaden the nucleophile option for catalysis. Owing to the cofactor compatibility, the DHFR-based secondary amine catalysis could be integrated into an enzymatic recycling scheme. This established method shows substantial potential in enzyme design, applicable from studies on enzyme evolution to the development of new biocatalysts.

Transesterification of Dimethyl Carbonate with Ethanol Catalyzed by Guanidine: A Theoretical Analysis

Density-functional theory (DFT) was performed to investigate the mechanistic features of different guanidine-based catalysts, namely, 1,1,3,3-tetramethyl guanidine (TMG) and 1,5,7-triaza-bicyclo-[4.4.0]dec-5-ene (TBD), for the transesterification reaction of dimethyl carbonate (DMC) with ethanol (EtOH). Different possible pathways were suggested in which these catalysts act as either nucleophile or base within a homogeneous system. The DFT results allowed not only the study of the thermochemistry aspects of all elementary reactions featured in the two different activation modes but also the accurate calculation of the free energy barriers for each case. Our findings showed that the catalyzed reaction proceeded through simultaneous activation of DMC and EtOH, facilitated by hydrogen bonding for both catalysts. This feature led to the formation of a stable intermediate with a relatively low free energy barrier. TBD exhibited a potentially more efficient mechanism, owing to its planar structure and dual-activation mode. The free energy barrier of the rate-limiting step, identified as the formation of a zwitterionic complex, then declined by approximately 50% when compared with the reaction without catalysts. Overall, the DFT approach provides good insight into the reactivity of both catalysts and helps to find possibilities for further enhancing the mechanistic features of both catalysts for this type of transesterification reaction.

Catalytic Strategies for the Cycloaddition of CO2 to Epoxides in Aqueous Media to Enhance the Activity and Recyclability of Molecular Organocatalysts

The cycloaddition of CO2 to epoxides to afford versatile and useful cyclic carbonate compounds is a highly investigated method for the nonreductive upcycling of CO2. One of the main focuses of the current research in this area is the discovery of readily available, sustainable, and inexpensive catalysts, and of catalytic methodologies that allow their seamless solvent-free recycling. Water, often regarded as an undesirable pollutant in the cycloaddition process, is progressively emerging as a helpful reaction component. On the one hand, it serves as an inexpensive hydrogen bond donor (HBD) to enhance the performance of ionic compounds; on the other hand, aqueous media allow the development of diverse catalytic protocols that can boost catalytic performance or ease the recycling of molecular catalysts. An overview of the advances in the use of aqueous and biphasic aqueous systems for the cycloaddition of CO2 to epoxides is provided in this work along with recommendations for possible future developments.

Deciphering Photoinduced Catalytic Reaction Mechanisms in Natural and Artificial Photosynthetic Systems on Multiple Temporal and Spatial Scales Using X-ray Probes

Utilization of renewable energies for catalytically generating value-added chemicals is highly desirable in this era of rising energy demands and climate change impacts. Artificial photosynthetic systems or photocatalysts utilize light to convert abundant CO2, H2O, and O2 to fuels, such as carbohydrates and hydrogen, thus converting light energy to storable chemical resources. The emergence of intense X-ray pulses from synchrotrons, ultrafast X-ray pulses from X-ray free electron lasers, and table-top laser-driven sources over the past decades opens new frontiers in deciphering photoinduced catalytic reaction mechanisms on the multiple temporal and spatial scales. Operando X-ray spectroscopic methods offer a new set of electronic transitions in probing the oxidation states, coordinating geometry, and spin states of the metal catalytic center and photosensitizers with unprecedented energy and time resolution. Operando X-ray scattering methods enable previously elusive reaction steps to be characterized on different length scales and time scales. The methodological progress and their application examples collected in this review will offer a glimpse into the accomplishments and current state in deciphering reaction mechanisms for both natural and synthetic systems. Looking forward, there are still many challenges and opportunities at the frontier of catalytic research that will require further advancement of the characterization techniques.

Manganese(I)-Catalyzed Enantioselective C(sp2)-C(sp3) Bond-Forming for the Synthesis of Skipped Dienes with Synergistic Aminocatalysis

Mn(I)-catalyzed enantioselective C-C bond-forming reactions represent a great challenge in homogeneous catalysis primarily due to a limited understanding of its mechanistic principles. Herein, we have developed an interesting catalytic strategy that leverages a synergistic combination of a dimeric manganese(I) catalyst and a chiral aminocatalyst to address this issue. A range of conjugated dienals and trienals can exclusively proceed 1,4-hydroalkenylation by using readily available aromatic and aliphatic alkenyl boronic acids as coupling partners, producing a rich library of skipped diene aldehydes in synthetically useful yields and high levels of enantioselectivities. Notably, downstream transformations of these products can not only afford a concise approach to construct enantioenriched skipped trienes but also realize enantioselective total synthesis of analogues to (-)-Blepharocalyxin D in four steps. DFT calculations suggest the 1,4-hydroalkenylation is kinetically more favorable than 1,6-hydroalkenylation.

NHC-Catalyzed Enantioselective Transformations Involving α-Bromoenals

α-Haloenals, especially, α-bromoenals considered as one of the important building blocks in organic synthesis. They can participate in various (3+2)-, (3+3)-, (3+4)-, and (2+4)-annulation reactions with other organic molecules in the presence of an NHC catalyst to produce enantioenriched carbo-, and heterocyclic compounds. Herein, we have described NHC-catalyzed enantioselective transformations of α-bromoenals in the synthesis of various heterocycles, and carbocycles, as well as acyclic organic compounds.

Enantioselective organocatalytic strategies to access noncanonical α-amino acids

Organocatalytic asymmetric synthesis has evolved over the years and continues to attract the interest of many researchers worldwide. Enantiopure noncanonical amino acids (ncAAs) are valuable building blocks in organic synthesis, medicinal chemistry, and chemical biology. They are employed in the elaboration of peptides and proteins with enhanced activities and/or improved properties compared to their natural counterparts, as chiral catalysts, in chiral ligand design, and as chiral building blocks for asymmetric syntheses of complex molecules, including natural products. The linkage of ncAA synthesis and enantioselective organocatalysis, the subject of this perspective, tries to imitate the natural biosynthetic process. Herein, we present contemporary and earlier developments in the field of organocatalytic activation of simple feedstock materials, providing potential ncAAs with diverse side chains, unique three-dimensional structures, and a high degree of functionality. These asymmetric organocatalytic strategies, useful for forging a wide range of C-C, C-H, and C-N bonds and/or combinations thereof, vary from classical name reactions, such as Ugi, Strecker, and Mannich reactions, to the most advanced concepts such as deracemisation, transamination, and carbene N-H insertion. Concurrently, we present some interesting mechanistic studies/models, providing information on the chirality transfer process. Finally, this perspective highlights, through the diversity of the amino acids (AAs) not selected by nature for protein incorporation, the most generic modes of activation, induction, and reactivity commonly used, such as chiral enamine, hydrogen bonding, Brønsted acids/bases, and phase-transfer organocatalysis, reflecting their increasingly important role in organic and applied chemistry.

Organocatalytic desymmetrization provides access to planar chiral [2.2]paracyclophanes

Planar chiral [2.2]paracyclophanes consist of two functionalized benzene rings connected by two ethylene bridges. These organic compounds have a wide range of applications in asymmetric synthesis, as both ligands and catalysts, and in materials science, as polymers, energy materials and dyes. However, these molecules can only be accessed by enantiomer separation via (a) time-consuming chiral separations and (b) kinetic resolution approaches, often with a limited substrate scope, yielding both enantiomers. Here, we report a simple, efficient, metal-free protocol for organocatalytic desymmetrization of prochiral diformyl[2.2]paracyclophanes. Our detailed experimental mechanistic study highlights differences in the origin of enantiocontrol of pseudo-para and pseudo-gem diformyl derivatives in NHC catalyzed desymmetrizations based on whether a key Breslow intermediate is irreversibly or reversibly formed in this process. This gram-scale reaction enables a wide range of follow-up derivatizations of carbonyl groups, producing various enantiomerically pure planar chiral [2.2]paracyclophane derivatives, thereby underscoring the potential of this method.

Organoboron-mediated polymerizations

The scientific community has witnessed extensive developments and applications of organoboron compounds as synthetic elements and metal-free catalysts for the construction of small molecules, macromolecules, and functional materials over the last two decades. This review highlights the achievements of organoboron-mediated polymerizations in the past several decades alongside the mechanisms underlying these transformations from the standpoint of the polymerization mode. Emphasis is placed on free radical polymerization, Lewis pair polymerization, ionic (cationic and anionic) polymerization, and polyhomologation. Herein, alkylborane/O2 initiating systems mediate the radical polymerization under ambient conditions in a controlled/living manner by careful optimization of the alkylborane structure or additives; when combined with Lewis bases, the selected organoboron compounds can mediate the Lewis pair polymerization of polar monomers; the bicomponent organoboron-based Lewis pairs and bifunctional organoboron-onium catalysts catalyze ring opening (co)polymerization of cyclic monomers (with heteroallenes, such as epoxides, CO2, CO, COS, CS2, episulfides, anhydrides, and isocyanates) with well-defined structures and high reactivities; and organoboranes initiate the polyhomologation of sulfur ylides and arsonium ylides providing functional polyethylene with different topologies. The topological structures of the produced polymers via these organoboron-mediated polymerizations are also presented in this review mainly including linear polymers, block copolymers, cyclic polymers, and graft polymers. We hope the summary and understanding of how organoboron compounds mediate polymerizations can inspire chemists to apply these principles in the design of more advanced organoboron compounds, which may be beneficial for the polymer chemistry community and organometallics/organocatalysis community.

Cinchona-Based Hydrogen-Bond Donor Organocatalyst Metal Complexes: Asymmetric Catalysis and Structure Determination

In this study, we describe the synthesis of cinchona (thio)squaramide and a novel cinchona thiourea organocatalyst. These catalysts were employed in pharmaceutically relevant catalytic asymmetric reactions, such as Michael, Friedel-Crafts, and A3 coupling reactions, in combination with Ag(I), Cu(II), and Ni(II) salts. We identified several organocatalyst-metal salt combinations that led to a significant increase in both yield and enantioselectivity. To gain insight into the active catalyst species, we prepared organocatalyst-metal complexes and characterized them using HRMS, NMR spectroscopy, and quantum chemical calculations (B3LYP-D4/def2-TZVP), which allowed us to establish a structure-activity relationship.

Synthesis of γ-Oxo-phosphonates via N-Heterocyclic Carbene-Catalyzed Acylphosphorylation of Alkenes

In this study, we present an N-heterocyclic carbene-catalyzed method for the radical acylphosphorylation of alkenes. Electrochemical investigations were employed to identify an appropriate class of oxime phosphonates capable of undergoing a single-electron transfer (SET) with Breslow enolates. The resulting phosphoryl radicals were effectively coupled with diverse styrenes and aldehydes to yield a variety of γ-oxo-phosphonates. Both radical clock experiments and electrochemical studies support our reaction design, and a plausible mechanism for the organocatalytic transformation is proposed.

Modeling the alkylation of amines with alkyl bromides: explaining the low selectivity due to multiple alkylation

CONTEXT

Nucleophilic substitution reactions of aliphatic amines with alkyl halides represent a simple and direct mechanism for obtaining higher-order aliphatic amines. However, it is well known that these reactions suffer from low selectivity due to multiple alkylations, which is attributed to the higher reactivity of the newly formed amine. In order to provide a detailed explanation for this kind of system, we have investigated the reactivity of primary and secondary amines with 1-bromopropane and 2-bromopropane. The free energy profile in acetonitrile solution was obtained and a detailed microkinetic analysis was needed to analyze this complex reaction system. We have found that the product of the first alkylation is an ion pair corresponding to the protonated secondary amine and the bromide ion, which can transfer the proton to the reactant primary amine. Then, the newly formed secondary amine can also react, leading to a second alkylation to produce a tertiary protonated amine. Our modeling points out that both the proton transfer equilibria and the similar reactivity of the primary and secondary amines produce reduced selectivity. The proton transfer equilibria also contribute to slowing down the kinetics of the first alkylation.

METHODS

The exploration of the mechanism was done by geometry optimization using the CPCM/X3LYP/ma-def2-SVP method, followed by harmonic frequency calculation at this same level of theory. A composite approach was used to obtain the free energy profile, using the more accurate ωB97X-D3/ma-def2-TZVPP level of theory for electronic energy and the SMD model for the solvation free energy. These calculations were performed with the ORCA 4 program. The detailed microkinetic analysis was done using the Kintecus program.

Merging gold plasmonic nanoparticles and L-proline inside a MOF for plasmon-induced visible light chiral organocatalysis at low temperature

Light-driven asymmetric photocatalysis represents a straightforward approach in modern organic chemistry. In comparison to the homogeneous one, heterogeneous asymmetric photocatalysis has the advantages of easy catalyst separation, recovery, and reuse, thus being cost- and time-effective. Here, we demonstrate how plasmon-active centers (gold nanoparticles - AuNPs) allow visible light triggering of chiral catalyst (proline) in model aldol reaction between acetone and benzaldehyde. The metal-organic framework UiO-66-NH2 was used as an advanced host platform for the loading of proline and AuNPs and their stabilization in spatial proximity. Aldol reactions were carried out at a low temperature (-20 °C) under light illumination which resulted in 91% ee with a closed-to-quantitative yield, 4.5 times higher than that without light (i.e. in the absence of plasmon triggering). A set of control experiments and quantum chemical modeling revealed that the plasmon assistance proceeds through hot electron excitation followed by an interaction with an enamine with the formation of anion radical species. We also demonstrated the high stability of the proposed system in multiple catalytic cycles without leaching metal ions, which makes our approach especially promising for heterogeneous asymmetric photocatalysis.

Investigating the efficacy of green solvents and solvent-free conditions in hydrogen-bonding mediated organocatalyzed model reactions

In this study, we have delved into various reactions conducted using green solvents or under solvent-free conditions, employing hydrogen bonding organocatalysis to advance more sustainable practices in chemical synthesis. The outcomes suggest that cyclopentyl methyl ether could potentially replace non-polar organic solvents such as hexane and toluene with comparable enantioselectivity and yields. The non-polar nature of liquefied or supercritical CO2 restricts its application to reactions that require non-polar solvents. Furthermore, pursuing solvent-free conditions, even without liquid substrates, might result in similar conversion rates with reduced catalyst loading. These findings highlight the potential of exploring solvent-free conditions when enantioselectivity is not of concern. Based on the results, solvent-free conditions and bio-based solvents can serve as viable alternatives to conventional organic solvents without compromising performance. This is expected to influence the way chemists approach reaction optimisation within method development in the field, fostering a broader adoption of environmentally friendly approaches.

Organocatalyst Supported by a Single-Atom Support Accelerates both Electrodes used in the Chlor-Alkali Industry via Modification of Non-Covalent Interactions

Consuming one of the largest amount of electricity, the chlor-alkali industry supplies basic chemicals for society, which mainly consists of two reactions, hydrogen evolution (HER) and chlorine evolution reaction (CER). Till now, the state-of-the-art catalyst applied in this field is still the dimensional stable anode (DSA), which consumes a large amount of noble metal of Ru and Ir. It is thus necessary to develop new types of catalysts. In this study, an organocatalyst anchored on the single-atom support (SAS) is put forward. It exhibits high catalytic efficiency towards both HER and CER with an overpotential of 21 mV and 20 mV at 10 mA cm-2 . With this catalyst on both electrodes, the energy consumption is cut down by 1.2 % compared with the commercial system under industrial conditions. Based on this novel catalyst and the high activity, the mechanism of modifying non-covalent interaction is demonstrated to be reliable for the catalyst's design. This work not only provides efficient catalysts for the chlor-alkali industry but also points out that the SACs can also act as support, providing new twists for the development of SACs and organic molecules in the next step.

Creating Remarkably Moisture- and Air-Stable Macromolecular Lewis Acid by Integrating Borane within the Polymer Chain: A Highly Active Catalyst for Homo(co)polymerization of Epoxides

Borane-based Lewis acids (LA) play an indispensable role in the Lewis pair (LP) mediated polymerization. However, most borane-based LPs are moisture- and air-sensitive. Therefore, development of moisture and air-stable borane-based LP is highly desirable. To achieve this goal, the concept of "aggregation induced enlargement effects" by chemically linking multiple borane within a nanoscopic confinement was conceived to create macromolecular LA. Accordingly, an extremely moisture and air stable macromolecular borane, namely, PVP-1B featuring poly(4-vinylphenol) backbone, was constructed. The concentration of borane active site is greatly higher than average concentration due to local confinement. Therefore, an enhanced activity was observed. Moreover, the local LA aggregation effects allow its tolerance to air and large amount of chain transfer agent. Consequently, PVP-1B showed remarkable efficiency for propylene oxide (PO) polymerization at 25 °C (TOF=27900 h-1 ). Furthermore, it enables generation of well-defined telechelic poly (CHO-alt-CO2 ) diol (0.6-15.3 kg/mol) with narrow Đs via copolymerizing cyclohexene oxide and CO2 at 80 °C. This work indicates unifying multiple borane within a polymer in a macromolecular level shows superior catalytic performance than constructing binary, bi(multi)functional systems in a molecular level. This paves a new way to make functional polyethers.

Enabling High Throughput Kinetic Experimentation by Using Flow as a Differential Kinetic Technique

Kinetic data is most commonly collected through the generation of time-series data under either batch or flow conditions. Existing methods to generate kinetic data in flow collect integral data (concentration over time) only. Here, we report a method for the rapid and direct collection of differential kinetic data (direct measurement of rate) in flow by performing a series of instantaneous rate measurements on sequential small-scale reactions. This technique decouples the time required to generate a full kinetic profile from the time required for a reaction to reach completion, enabling high throughput kinetic experimentation. In addition, comparison of kinetic profiles constructed at different residence times allows the robustness, or stability, of homogeneously catalysed reactions to be interrogated. This approach makes use of a segmented flow platform which was shown to quantitatively reproduce batch kinetic data. The proline mediated aldol reaction was chosen as a model reaction to perform a high throughput kinetic screen of 216 kinetic profiles in 90 hours, one every 25 minutes, which would have taken an estimated continuous 3500 hours in batch, an almost 40-fold increase in experimental throughput matched by a corresponding reduction in material consumption.

Ligating Catalytically Active Peptides onto Microporous Polymers: A General Route Toward Specifically-Functional High Surface Area Platforms

A versatile post-synthetic modification strategy to functionalize a high surface area microporous network (MPN-OH) by bio-orthogonal inverse electron-demand Diels-Alder (IEDDA) ligation is presented. While the polymer matrix is modified with a readily accessible norbornene isocyanate (Nor-NCO), a series of functional units presenting the robust asymmetric 1,2,4,5-tetrazine (Tz) allows easy functionalization of the MPN by chemoselective Nor/Tz ligation. A generic route is demonstrated, modulating the internal interfaces by introducing carboxylates, amides or amino acids as well as an oligopeptide d-Pro-Pro-Glu organocatalyst. The MPN-Pz-Peptide construct largely retains the catalytic activity and selectivity in an enantioselective enamine catalysis, demonstrates remarkable availability in different solvents, offers heterogeneous organocatalysis in bulk and shows stability in recycling settings.

Using the phospha-Michael reaction for making phosphonium phenolate zwitterions

The reactions of 2,4-di-tert-butyl-6-(diphenylphosphino)phenol and various Michael acceptors (acrylonitrile, acrylamide, methyl vinyl ketone, several acrylates, methyl vinyl sulfone) yield the respective phosphonium phenolate zwitterions at room temperature. Nine different zwitterions were synthesized and fully characterized. Zwitterions with the poor Michael acceptors methyl methacrylate and methyl crotonate formed, but could not be isolated in pure form. The solid-state structures of two phosphonium phenolate molecules were determined by single-crystal X-ray crystallography. The bonding situation in the solid state together with NMR data suggests an important contribution of an ylidic resonance structure in these molecules. The phosphonium phenolates are characterized by UV-vis absorptions peaking around 360 nm and exhibit a negative solvatochromism. An analysis of the kinetics of the zwitterion formation was performed for three Michael acceptors (acrylonitrile, methyl acrylate, and acrylamide) in two different solvents (chloroform and methanol). The results revealed the proton transfer step necessary to stabilize the initially formed carbanion as the rate-determining step. A preorganization of the carbonyl bearing Michael acceptors allowed for reasonable fast direct proton transfer from the phenol in aprotic solvents. In contrast, acrylonitrile, not capable of forming a similar preorganization, is hardly reactive in chloroform solution, while in methanol the corresponding phosphonium phenolate is formed.

Nucleophilicity of 4-(Alkylthio)-3-imidazoline Derived Enamines

Imidazolidine-4-thiones (ITOs) are cyclic, secondary amines that were considered as potential prebiotic organocatalysts for light-driven α-alkylations of aldehydes by bromoacetonitrile (BAN). Recent studies showed that the initially supplied ITOs represent the pre-catalyst because they undergo S-alkylation with BAN to give 4-(alkylthio)-3-imidazolines (TIMs). Given that the same reagent mix that undergoes light-driven α-alkylations is also effective in the dark, we synthesized ten ITO- or TIM-derived enamines of aldehydes and characterized their nucleophilic reactivities by kinetic studies in acetonitrile. The experimental second-order rate constants k2 for reactions of enamines with benzhydrylium ions (reference electrophiles) were evaluated by the Mayr-Patz equation, lg k2 (20 °C)=sN (N+E). The determined nucleophilicities N (and sN ) reveal the reactivity profiles of these enamines under prebiotically relevant conditions as well as their potential for use in organocatalytic synthesis.