Hydrodecarboxylation of Carboxylic and Malonic Acid Derivatives via Organic Photoredox Catalysis: Substrate Scope and Mechanistic Insight

Direct C-H amidation of 1,3-azoles: light-mediated, photosensitiser-free vs. thermal

We have developed one thermal and one light-mediated method for direct Minisci-type C-H amidation of 1,3-azoles, which are applicable to thiazoles, benzothiazoles, benzimidazoles, and for the first time, imidazoles. The new visible light-mediated approach can be rendered photosensitiser/photocatalyst-free and likely proceeds via an electron donor-acceptor (EDA) complex, the first direct Minisci-type amidation to do so.

Titanium in photocatalytic organic transformations: current applications and future developments

Titanium, as an important transition metal, has garnered extensive attention in both industry and academia due to its excellent mechanical properties, corrosion resistance, and unique reactivity in organic synthesis. In the field of organic photocatalysis, titanium-based compounds such as titanium dioxide (TiO2), titanocenes (Cp2TiCl2, CpTiCl3), titanium tetrachloride (TiCl4), tetrakis(isopropoxy)titanium (Ti(OiPr)4), and chiral titanium complexes have demonstrated distinct reactivity and selectivity. This review focuses on the roles of these titanium compounds in photocatalytic organic reactions, and highlights the reaction pathways such as photo-induced single-electron transfer (SET) and ligand-to-metal charge transfer (LMCT). By systematically surveying the latest advancements in titanium-involved organic photocatalysis, this review aims to provide references for further research and technological innovation within this fast-developing field.

Disulfide Bonds as Functional Tethers in Metal-Organic Frameworks

The functionality of metal-organic frameworks (MOFs) is often encoded by specific chemical moieties found within these architectures. As such, new techniques to install increasingly more complex functionalities in MOFs are regularly being reported in the literature. One such functional group is the disulfide bond. The redox behavior of this covalent linkage renders MOFs responsive to stimuli, often under reducing conditions. Here, we review examples in which disulfide-containing MOFs are deployed in applications including drug delivery, therapeutic ferroptosis, exfoliation, energy storage, sensing, and others.

Stereoselective Synthesis of Baloxavir Marboxil Using Diastereoselective Cyclization and Photoredox Decarboxylation of l-Serine

Baloxavir marboxil (1; BXM) is a potent drug used for treating influenza infections. The current synthetic route to BXM (1) is based on optical resolution; however, this method results in the loss of nearly 50% of the material. This study aimed to describe an efficient and simpler method for the synthesis of BXM. We achieved a stereoselective synthesis of BXM (1). The tricyclic triazinanone core possessing a chiral center was prepared via diastereoselective cyclization utilizing the readily available amino acid l-serine. The carboxyl moiety derived from l-serine was removed via photoredox decarboxylation under mild conditions to furnish the chiral tricyclic triazinanone core ((R)-14). The synthetic route demonstrated herein provides an efficient and atomically economical method for preparing this potent anti-influenza agent.

Acridine photocatalysis enables tricomponent direct decarboxylative amine construction

Amines are centrally important motifs in medicinal chemistry and biochemistry, and indispensable intermediates and linchpins in organic synthesis. Despite their cross-disciplinary prominence, synthetic access to amine continues to rely on two-electron approaches based on reductions and additions of organometallic reagents, limiting their accessible chemical space and necessitating stepwise preassembly of synthetic precursors. We report herein a homogeneous photocatalytic tricomponent decarboxylative radical-mediated amine construction that enables modular access to α-branched secondary amines directly from the broad and structurally diverse chemical space of carboxylic acids in a tricomponent reaction with aldehydes and aromatic amines. Our studies reveal the key role of acridine photocatalysis acting in concert with copper and Brønsted acid catalytic processes in facilitating the previously inaccessible homogeneous photocatalytic reaction and provide a streamlined segue to a wide range of amines and nonproteinogenic α-amino acids.

Redox-Neutral Multicatalytic Cerium Photoredox-Enabled Cleavage of O-H Bearing Substrates

The need for synthetic methodologies capable of rapidly altering molecular structure are in high demand. Most existing methods to modify scaffolds rely on net exothermicity to drive the desired transformation. We sought to develop a general strategy for the cleavage of C-C bonds β to hydroxyl groups independent of inherent substrate strain. To this end we have applied a multicatalytic cerium photoredox-based system capable of activating O-H bonds in lactols to deliver formate esters. The same system is also capable of effecting hydrodecarboxylation and hydrodecarbonylation reactions. Initial mechanistic probes demonstrate atomic chlorine (Cl⋅) is generated under the reaction conditions, but substrate activation through cerium-alkoxides or -carboxylates cannot be ruled out.

Multimodal Acridine Photocatalysis Enables Direct Access to Thiols from Carboxylic Acids and Elemental Sulfur

Development of photocatalytic systems that facilitate mechanistically divergent steps in complex catalytic manifolds by distinct activation modes can enable previously inaccessible synthetic transformations. However, multimodal photocatalytic systems remain understudied, impeding their implementation in catalytic methodology. We report herein a photocatalytic access to thiols that directly merges the structural diversity of carboxylic acids with the ready availability of elemental sulfur without substrate preactivation. The photocatalytic transformation provides a direct radical-mediated segue to one of the most biologically important and synthetically versatile organosulfur functionalities, whose synthetic accessibility remains largely dominated by two-electron-mediated processes based on toxic and uneconomical reagents and precursors. The two-phase radical process is facilitated by a multimodal catalytic reactivity of acridine photocatalysis that enables both the singlet excited state PCET-mediated decarboxylative carbon-sulfur bond formation and the previously unknown radical reductive disulfur bond cleavage by a photoinduced HAT process in the silane-triplet acridine system. The study points to a significant potential of multimodal photocatalytic systems in providing unexplored directions to previously inaccessible transformations.

Asymmetric synthesis of the fully functionalized six-membered A-ring of siphonol A

A synthetic study toward the construction of the fully functionalized six-membered A-ring of siphonol A is described. The salient features include the introduction of a six-membered ring system through a HWE reaction, the construction of a stereocenter at C5 via a hetero-Diels-Alder reaction, and the installation of the fully functionalized six-membered A-ring of siphonol A through photolytic decarboxylation.

Photocatalyzed hydrodecarboxylation of fatty acids: a prospective method to produce drop-in biofuels

A direct and practical method for photocatalyzed hydrodecarboxylation of fatty acids is reported herein. The catalytic system consists of a commercially available acridinium salt as the photocatalyst and thiophenol as the Hydrogen Atom Transfer (HAT) co-catalyst. Results evidenced that Cn-1 alkanes were obtained in yields up to 77%. Furthermore, the protocol was employed for a complex mixture of fatty acids bio-derived from a real sample of licuri oil to obtain hydrocarbons in the range of C9-C17 with high selectivity and excellent conversion (>90%). This work provides a powerful strategy for producing drop-in biofuels under mild conditions. Finally, an energetic assessment of our proposed protocol (∼22.9 kW h) reveals the benefit of a sustainable production of renewable hydrocarbons.

Unified Strategy Enables the Collective Syntheses of Structurally Diverse Indole Alkaloids

Natural products and their analogues are significant sources of therapeutic lead compounds. However, synthetic strategies for generating large collections of these molecules remain a significant challenge. The most difficult step in their synthesis is the design of a common intermediate that can be easily transformed into natural products belonging to different families. This study demonstrates the evolution of synthetic tactics designed to assemble the functionalized piperidines present in indole alkaloids from a common intermediate. More importantly, we also report a previously unknown Ir- and Er-catalyzed dehydrogenative spirocyclization reaction that enables direct access to spirocyclic oxindole alkaloids. As a practical application, the asymmetric total syntheses of 29 natural alkaloids belonging to different families were accomplished by following a uniform synthetic route. The proposed methodology extends the capability of the iridium-catalyzed dehydrogenative coupling reaction to the realm of indole-alkaloid synthesis and provides new opportunities for the efficient preparation of natural product-like molecules.

Visible Light-Mediated Selective Aerobic Oxidation of Alcohols Catalyzed by Disulfide in Batch and Flow

Selective aerobic oxidation of alcohols in batch and flow can be realized under light irradiation, utilizing disulfide as the photocatalyst, and a variety of primary and secondary alcohols were converted to the corresponding aldehydes or ketones in up to 99% yield and high selectivity. The reaction efficiency could be increased even further by combining a continuous-flow strategy. Detailed mechanistic studies have also been achieved to determine the role of oxygen and disulfides in this oxidation.

Direct conversion of carboxylic acids to free thiols via radical relay acridine photocatalysis enabled by N-O bond cleavage

Carboxylic acids and thiols are basic chemical compounds with diverse utility and widespread reactivity. However, the direct conversion of unprotected acids to thiols is hampered due to a fundamental problem - free thiols are incompatible with the alkyl radicals formed on decarboxylation of carboxylic acids. Herein, we describe a concept for the direct photocatalytic thiolation of unprotected acids allowing unprotected thiols and their derivatives to be obtained. The method is based on the application of a thionocarbonate reagent featuring the N-O bond. The reagent serves both for the rapid trapping of alkyl radicals and for the facile regeneration of the acridine-type photocatalyst.

Photocatalytic Hydrodecarboxylation of Fatty Acids for Drop-in Biofuels Production

A mild, practical, and environmentally friendly method for the hydrodecarboxylation of fatty acids using an acridine-based photoredox catalyst and thiophenol was developed. Cn-1 alkanes were synthesized in good to excellent yields (up to 99 %) from C10-C18 saturated fatty acids under visible light irradiation (405 nm). The developed protocol was employed for a mixture of fatty acids obtained from the hydrolysis of Licuri oil, affording a mixture of C9-C17 hydrocarbons in quantitative yield, which demonstrates the potential application of the method to produce drop-in biofuels.

Kinetically-driven reactivity of sulfinylamines enables direct conversion of carboxylic acids to sulfinamides

Sulfinamides are some of the most centrally important four-valent sulfur compounds that serve as critical entry points to an array of emergent medicinal functional groups, molecular tools for bioconjugation, and synthetic intermediates including sulfoximines, sulfonimidamides, and sulfonimidoyl halides, as well as a wide range of other S(iv) and S(vi) functionalities. Yet, the accessible chemical space of sulfinamides remains limited, and the approaches to sulfinamides are largely confined to two-electron nucleophilic substitution reactions. We report herein a direct radical-mediated decarboxylative sulfinamidation that for the first time enables access to sulfinamides from the broad and structurally diverse chemical space of carboxylic acids. Our studies show that the formation of sulfinamides prevails despite the inherent thermodynamic preference for the radical addition to the nitrogen atom, while a machine learning-derived model facilitates prediction of the reaction efficiency based on computationally generated descriptors of the underlying radical reactivity.

Improbable Rotaxanes Constructed From Surrogate Malonate Rotaxanes as Encircled Methylene Synthons

We have developed a new approach for the synthesis of "improbable" rotaxanes by using malonate-centered rotaxanes as interlocked surrogate precursors. Here, the desired dumbbell-shaped structure can be assembled from two different, completely separate, portions, with the only residual structure introduced from the malonate surrogate being a methylene group. We have synthesized improbable [2]- and [3]rotaxanes with all-hydrocarbon dumbbell-shaped components to demonstrate the potential structural flexibility and scope of the guest species that can be interlocked when using this approach.

Red-light-mediated Barton decarboxylation reaction and one-pot wavelength-selective transformations

In organic chemistry, selecting mild conditions for transformations and saving energy are increasingly important for achieving sustainable development goals. Herein, we describe a red-light-mediated Barton decarboxylation using readily available red-light-emitting diodes as the energy source and zinc tetraphenylporphyrin as the catalyst, avoiding explosive or hazardous reagents or external heating. Mechanistic studies suggest that the reaction probably proceeds via Dexter energy transfer between the activated catalyst and the Barton ester. Furthermore, a one-pot wavelength-selective reaction within the visible light range is developed in combination with a blue-light-mediated photoredox reaction, demonstrating the compatibility of two photochemical transformations based on mechanistic differences. This one-pot process expands the limits of the decarboxylative Giese reaction beyond polarity matching.

Nickel-Catalyzed Asymmetric Decarboxyarylation with NHP Esters of α-Amino Acid to Chiral Benzylamines

A nickel-catalyzed asymmetric decarboxyarylation of NHP esters via reductive cross-coupling has been established. Utilizing the NHP of amino acid esters as radical precursors furnishes a new protocol in which structurally diverse chiral benzylamines could be accessible. This method has demonstrated excellent catalytic efficiency, high enantioselective control, mild conditions, and good functional group tolerance, thus enabling the late-stage modification of bioactive molecules and pharmaceuticals.

Direct decarboxylative Giese amidations: photocatalytic vs. metal- and light-free

A direct intermolecular decarboxylative Giese amidation reaction from bench stable, non-toxic and environmentally benign oxamic acids has been developed, which allows for easy access to 1,4-difunctionalised compounds which are not otherwise readily accessible. Crucially, a more general acceptor substrate scope is now possible, which renders the Giese amidation applicable to more complex substrates such as natural products and chiral building blocks. Two different photocatalytic methods (one via oxidative and the other via reductive quenching cycles) and one metal- and light-free method were developed and the flexibility provided by different conditions proved to be crucial for enabling a more general substrate scope.

Recent Developments on Photochemical Synthesis of 1,n-Dicarbonyls

1,n-dicarbonyls are one of the most fascinating chemical feedstocks finding abundant usage in the field of pharmaceuticals. Besides, they are utilized in a plethora of synthesis in general synthetic organic chemistry. A number of 'conventional' methods are available for their synthesis, such as the Stetter reaction, Baker-Venkatraman rearrangement, oxidation of vicinal diols, and oxidation of deoxybenzoins, synonymous with unfriendly reagents and conditions. In the last 15 years or so, photocatalysis has taken the world of synthetic organic chemistry by a remarkable renaissance. It is fair to say now that everybody loves the light and photoredox chemistry has opened a new gateway to organic chemists towards milder, more simpler alternatives to the previously available methods, allowing access to many sensitive reactions and products. In this review, we present the readers with the photochemical synthesis of a variety of 1,n-dicarbonyls. Diverse photocatalytic pathways to these fascinating molecules have been discussed, placing special emphasis on the mechanisms, giving the reader an opportunity to find all these significant developments in one place.

Synthesis of Thioureas, Thioamides, and Aza-Heterocycles via Dimethyl-Sulfoxide-Promoted Oxidative Condensation of Sulfur, Malonic Acids, and Amines

Malonic acid and derivatives have been well-known to undergo monodecarboxylation under relatively mild conditions and have been exclusively used as a C2 synthon. We report herein their new application as a C1 synthon via double decarboxylation promoted by sulfur and dimethyl sulfoxide. In the presence of amines as nucleophiles, a wide range of thioureas and thioamides as well as N-heterocycles were obtained in good to excellent yields under mild heating conditions.

Photocatalytic Transformation of Biomass and Biomass Derived Compounds-Application to Organic Synthesis

Biomass and biomass-derived compounds have become an important alternative feedstock for chemical industry. They may replace fossil feedstocks such as mineral oil and related platform chemicals. These compounds may also be transformed conveniently into new innovative products for the medicinal or the agrochemical domain. The production of cosmetics or surfactants as well as materials for different applications are examples for other domains where new platform chemicals obtained from biomass can be used. Photochemical and especially photocatalytic reactions have recently been recognized as being important tools of organic chemistry as they make compounds or compound families available that cannot be or are difficultly synthesized with conventional methods of organic synthesis. The present review gives a short overview with selected examples on photocatalytic reactions of biopolymers, carbohydrates, fatty acids and some biomass-derived platform chemicals such as furans or levoglucosenone. In this article, the focus is on application to organic synthesis.

Regioselective Radical Alkylation of Arenes Using Evolved Photoenzymes

Substituted arenes are ubiquitous in molecules with medicinal functions, making their synthesis a critical consideration when designing synthetic routes. Regioselective C-H functionalization reactions are attractive for preparing alkylated arenes; however, the selectivity of existing methods is modest and primarily governed by the substrate's electronic properties. Here, we demonstrate a biocatalyst-controlled method for the regioselective alkylation of electron-rich and electron-deficient heteroarenes. Starting from an unselective "ene"-reductase (ERED) (GluER-T36A), we evolved a variant that selectively alkylates the C4 position of indole, an elusive position using prior technologies. Mechanistic studies across the evolutionary series indicate that changes to the protein active site alter the electronic character of the charge transfer (CT) complex responsible for radical formation. This resulted in a variant with a significant degree of ground-state CT in the CT complex. Mechanistic studies on a C2-selective ERED suggest that the evolution of GluER-T36A helps disfavor a competing mechanistic pathway. Additional protein engineering campaigns were carried out for a C8-selective quinoline alkylation. This study highlights the opportunity to use enzymes for regioselective radical reactions, where small molecule catalysts struggle to alter selectivity.

Visible Light Thiyl Radical-Mediated Desilylation of Arylsilanes

A straightforward, visible-light triggered desilylation of arylsilanes by thiyl radicals is presented. Silyl groups are often used to block a reactive position in multi-step organic synthesis, for which a mild cleavage at a late-stage will provide new possibilities and disconnection routes by C_Ar -Si cleavage/deprotection. In this work, commercially available and cheap disulfides are employed for the first time in this type of C(sp² )-Si bond cleavage reactions. Thus, upon irradiation with visible-light, homolytic cleavage of the disulfide give rise to the corresponding thiyl radical that allows for a radical chain mechanism. This methodology represents a mild, fast and simple approach suitable for a broad variety of simply substituted arylsilanes. Moreover, the procedure could be easily extended to natural products and therapeutic derivatives, showing its robustness and synthetic application potential.

Benzophenone as a cheap and effective photosensitizer for the photocatalytic synthesis of dimethyl cubane-1,4-dicarboxylate

The key intramolecular [2 + 2] photochemical cycloaddition step in the synthesis of dimethyl cubane-1,4-dicarboxylate is performed with substoichiometric amounts of the photosensitizer benzophenone. The reaction proceeds via a Dexter energy transfer process between the triplet excited state benzophenone and a well-known cubane precursor diene. The use of the cheap and widely available benzophenone as the photosensitizer enables lower energy light to be used than the traditional photochemical process.

Regioselective Radical Alkylation of Arenes Using Evolved Photoenzymes

Substituted arenes are ubiquitous in molecules with medicinal functions, making their synthesis a critical consideration when designing synthetic routes. ^1,2 Regioselective C-H functionalization reactions are attractive for preparing alkylated arenes, ^3-5 however, the selectivity of existing methods is modest and primarily governed by substrate electronic properties. ^6,7 Here, we demonstrate a biocatalyst-controlled method for the regioselective alkylation of electron-rich and electron-deficient heteroarenes. Starting from an unselective 'ene'-reductase (ERED) (GluER-T36A), we evolved a variant that selectively alkylates the C4 position of indole, an elusive position using prior technologies. Mechanistic studies across the evolutionary series indicate that changes to the protein active site alter the electronic character of the charge transfer (CT) complex responsible for radical formation. This resulted in a variant with a significant degree of ground state change transfer in the CT complex. Mechanistic studies on a C2 selective ERED suggest that the evolution of GluER-T36A helps disfavor a competing mechanistic pathway. Additional protein engineering campaigns were carried out for a C8 selective quinoline alkylation. This study highlights the opportunity to use enzymes for regioselective reactions where small molecule catalysts struggle to alter selectivity.

Copper-Catalyzed Decarboxylative Elimination of Carboxylic Acids to Styrenes

A copper-catalyzed decarboxylative elimination reaction of (hetero)aromatic propionic acids to vinyl (hetero)arenes has been developed. This method furnishes alkenes from carboxylic acids without the need for stochiometric Pb or Ag additives or expensive or specialized photocatalysts. A series of mechanistic experiments indicate that the reaction proceeds via benzylic deprotonation and subsequent radical decarboxylation; a pathway that is distinct from the single-electron-transfer mechanisms implicated in related decarboxylative elimination reactions.

Chemoselective Decarboxylative Protonation Enabled by Cooperative Earth-Abundant Element Catalysis

Decarboxylative protonation is a general deletion tactic to replace polar carboxylic acid groups with hydrogen or its isotope. Current methods rely on the pre-activation of acids, non-sustainable hydrogen sources, and/or expensive/highly oxidizing photocatalysts, presenting challenges to their wide adoption. Here we show that a cooperative iron/thiol catalyst system can readily achieve this transformation, hydrodecarboxylating a wide range of activated and unactivated carboxylic acids and overcoming scope limitations in previous direct methods. The reaction is readily scaled in batch configuration and can be directly performed in deuterated solvent to afford high yields of d-incorporated products with excellent isotope incorporation efficiency; characteristics not attainable in previous photocatalyzed approaches. Preliminary mechanistic studies indicate a radical mechanism and kinetic results of unactivated acids (KIE=1) are consistent with a light-limited reaction.

Multi-Resonant Thermally Activated Delayed Fluorescent (MR-TADF) Compounds as Photocatalysts

Donor-acceptor (D-A) thermally activated delayed fluorescent (TADF) compounds, such as 4CzIPN, have become a widely used sub-class of organic photocatalysts for a plethora of photocatalytic reactions. Multi-resonant TADF (MR-TADF) compounds, a subclass of TADF emitters that are rigid nanographene derivatives, such as DiKTa and Mes₃ DiKTa, have to date not been explored as photocatalysts. In this study both DiKTa and Mes₃ DiKTa were found to give comparable or better product yield than 4CzIPN in a range of photocatalytic processes that rely upon reductive quenching, oxidative quenching, energy transfer and dual photocatalytic processes. In a model oxidative quench process, DiKTa and Mes₃ DiKTa gave increased reaction rates in comparison to 4CzIPN, with DiKTa being of particular interest due to the lower material cost (£0.94/mmol) compared to that of 4CzIPN (£3.26/mmol). These results suggest that DiKTa and Mes₃ DiKTa would be excellent additions to any chemist's collection of photocatalysts.

Direct Aroylation of Olefins through a Cobalt/Photoredox-Catalyzed Decarboxylative and Dehydrogenative Coupling with α-Oxo Acids

A photoredox/cobalt dual catalytic procedure has been developed that allows benzoylation of olefins. Here the photoredox catalyst effects the decarboxylation of α-ketoacids to form benzoyl radicals. After addition of this radical to styrenes, the cobalt catalyst abstracts a H-atom. Hydrogen evolution from the putative cobalt hydride intermediate allows a Heck-like aroylation without the need for a stoichiometric oxidant. Mechanistic studies reveal that electronically different styrenes lead to a curved Hammett plot, thus suggesting a change in product-determining step in the catalytic mechanism.

Direct Minisci-Type C–H Amidation of Purine Bases

A method for the C–H carboxyamidation of purines has been developed that is capable of directly installing primary, secondary, and tertiary amides. Previous Minisci-type investigations on purines were limited to alkylations and arylations. Herein, we present the first method for the direct C–H amidation of a wide range of purines: xanthine, guanine, and adenine structures, including guanosine- and adenosine-type nucleosides. The Minisci-type reaction is also metal-free, cheap, operationally simple, scalable, and applicable to late-stage functionalizations of biologically important molecules.

Visible-light-induced alkylation of 2-iminochromene

A metal-free, photochemical protocol for C-4 alkylation of 2-iminochromene has been developed by employing the naturally abundant feedstock carboxylic acid. Selective C-4 alkylation under photoredox conditions to access C-4 alkylated 2-iminochromene in up to 81% yield was achieved. In addition, biologically relevant chromophores can be easily incorporated under this protocol.

Photomediated Hydro- and Deuterodecarboxylation of Pharmaceutically Relevant and Natural Aliphatic Carboxylic Acids

Herein, we report a photomediated hydro- and deuterodecarboxylation of different primary, secondary, and tertiary carboxylic acids catalyzed by an organic pyrimidopteridine photoredox catalyst. The reaction was optimized by a statistical design of experiment (DoE). Under optimized reaction conditions, the conversion of commercially available nonsteroidal anti-inflammatory drugs (NSAIDs) in tablet form and on gram scale was realized. The scope of the application comprises primary, secondary, and tertiary aliphatic biologically active carboxylic acids. A deuterium incorporation of up to 95% by using D₂O as inexpensive deuterium source was achieved. A sensitivity assessment as well as experiments aiding the elucidation of the reaction mechanism are discussed.

Aliphatic C-H Functionalization Using Pyridine N-Oxides as H-Atom Abstraction Agents

The alkylation and heteroarylation of unactivated tertiary, secondary, and primary C(sp3)-H bonds was achieved by employing an acridinium photoredox catalyst along with readily available pyridine Noxides as hydrogen atom transfer (HAT) precursors under visible light. Oxygen-centered radicals, generated by single-electron oxidation of the Noxides, are the proposed key intermediates whose reactivity can be easily modified by structural adjustments. A broad range of aliphatic C-H substrates with electron-donating or -withdrawing groups as well as various olefinic radical acceptors and heteroarenes were well tolerated.

Radical 1,2,3-tricarbofunctionalization of α-vinyl-β-ketoesters enabled by a carbon shift from an all-carbon quaternary center

Herein, we report an intermolecular, radical 1,2,3-tricarbofunctionalization of α-vinyl-β-ketoesters to achieve the goal of building molecular complexity via the one-pot multifunctionalization of alkenes. This reaction allows the expansion of the carbon ring by a carbon shift from an all-carbon quaternary center, and enables further C-C bond formation on the tertiary carbon intermediate with the aim of reconstructing a new all-carbon quaternary center. The good functional group compatibility ensures diverse synthetic transformations of this method. Experimental and theoretical studies reveal that the excellent diastereoselectivity should be attributed to the hydrogen bonding between the substrates and solvent.

Organocatalyzed Cross-Nucleophile Couplings: Umpolung of Catalytic Enamines

ConspectusThe concept of umpolung, or polarity reversal, introduced by Seebach and Corey nearly half a century ago, ushered a new paradigm into synthetic chemistry. Novel connections were able to be forged among functional groups that were typically inaccessible. Conceptually, an umpolung reaction is identified only upon retrosynthetic analysis. Stoichiometric examples have served as a platform to develop and refine elegant methodologies into catalytic processes. The advent of these unconventional arrangements of canonical synthons into new points of diversity has expanded the repertoire of the synthetic toolbox. Within this context, asymmetric organocatalyzed methodologies remain rare, and there are even fewer aminocatalyzed variants.Recent years have witnessed a renaissance in α-functionalizations of aldehydes, specifically in the context of oxidative umpolung strategies. Unlike previous open-shell approaches, application of a quinone-based oxidant in conjunction with an aminocatalyst leads to a discrete, substitutionally labile quinone adduct. These have proven to be valuable building blocks toward polar reactivity─auguring the advent of new avenues to construct tetrasubstituted tertiary stereocenters through the application of conventional nucleophiles to form C-C, C-N, C-O, and C-S bonds through an organocatalyzed cross-nucleophile coupling (organo-CNC) reaction. The resulting nonepimerizable stereocenter demonstrates high optical fidelity and provides a significant advancement in many applications that suffer from racemization, such as in vivo studies.This strategy harnesses a trifunctional aminocatalyst to promote an unusual S_N2 reaction at a highly congested center. The selection of the quinone oxidant and nucleophile converges to a continuum of reactivity ranging from enantioselective oxidation to stereoselective substitution. A remarkable aspect of these developments is the identification of an asymmetric S_N2 dynamic kinetic resolution (S_N2-DKR) manifold. These organo-CNC reactions are highly modular and demonstrate complete stereocontrol from the catalyst with minimal influence from incoming chiral nucleophiles. Leveraging this facet, these technologies have been extended to peptidic bioconjugations bearing bio-orthogonoal linker molecules.This Account aims to highlight the progress, from an internal perspective, toward directing the initial result into established methodologies. Within this construct, the underlying principles of each reaction will be disseminated with specific content on inherent challenges and opportunity. Combined, these will serve as an instructive tool to stimulate applications in cross-disciplinary interfaces.

9-Cyano-10-methoxycarbonylanthracene as a Visible Organic Photoredox Catalyst in the Two-Molecule Photoredox System

Visible-light-induced decarboxylative and deboronative reactions using two-molecule organic photoredox catalysts, namely, phenanthrene (Phen) and biphenyl (BP), as electron donors and 9-cyano-10-methoxycarbonylanthracene 1a as an electron acceptor were achieved. The high solubility of 1a significantly improved the reaction efficiency and product yield. In addition, the facile tuning of the oxidation potential of the electron-donor molecule via the replacement of Phen with BP enabled the application of the two-molecule photoredox system to a wide range of substrates.

Silver-catalysed double decarboxylative addition-cyclisation-elimination cascade sequence for the synthesis of quinolin-2-ones

An atom-efficient silver-catalysed double carboxylative strategy for the one-step synthesis of quinolin-2-ones via an addition-cyclisation-elimination cascade sequence of oxamic acids to acrylic acids, mediated either thermally or photochemically, is reported. The reaction was applicable to the synthesis of a broad range of quinolin-2-ones and featured a double-disconnection approach that constructed the quinolin-2-one core via the formal and direct addition of a C(sp²)-H/C(sp²)-H olefin moiety to a phenylformamide precursor.

Decarboxylative tandem C-N coupling with nitroarenes via SH2 mechanism

Aromatic tertiary amines are one of the most important classes of organic compounds in organic chemistry and drug discovery. It is difficult to efficiently construct tertiary amines from primary amines via classical nucleophilic substitution due to consecutive overalkylation. In this paper, we have developed a radical tandem C-N coupling strategy to efficiently construct aromatic tertiary amines from commercially available carboxylic acids and nitroarenes. A variety of aromatic tertiary amines can be furnished in good yields (up to 98%) with excellent functional group compatibility under mild reaction conditions. The use of two different carboxylic acids also allows for the concise synthesis of nonsymmetric aromatic tertiary amines in satisfactory yields. Mechanistic studies suggest the intermediacy of the arylamine–(TPP)Fe(III) species and might provide a possible evidence for an S_H2 (bimolecular homolytic substitution) pathway in the critical C-N bond formation step.

Aromatic tertiary amines are versatile building blocks in organic synthesis. In this article, the authors report on an iron-catalysed reaction for the decarboxylative C-N coupling from carboxylic acids and nitroarenes, leading to non-symmetric tertiary aromatic amines.