Frustrated Lewis Acid/Brønsted Base Catalysts for Direct Enantioselective α-Amination of Carbonyl Compounds

Mechanochemical Thiolation of α-Imino Ketones: A Catalyst-Free, One-Pot, Three-Component Reaction

Herein, we report an efficient mechanochemical synthesis of α,α-amino thioketones involving a one-pot, three-component milling of 2-oxo aldehydes, amines, and thiols. Unlike previous methods, this protocol does not require any catalyst or oxidizing additive. The reaction proceeds through the thiolation of in situ formed α-imino ketones by liquid-assisted grinding. We have successfully extended this protocol to synthesizing benzothiazoles, thiazoles, and quinoxalines, demonstrating its efficiency and potential in the field. Importantly, we have shown the gram-scale synthesis, synthetic applications, and substrate scope of this protocol, instilling confidence in its practicality.

Biocatalytic Synthesis of α-Amino Esters via Nitrene C-H Insertion

α-Amino esters are precursors to noncanonical amino acids used in developing small-molecule therapeutics, biologics, and tools in chemical biology. α-C-H amination of abundant and inexpensive carboxylic acid esters through nitrene transfer presents a direct approach to α-amino esters. Methods for nitrene-mediated amination of the protic α-C-H bonds in carboxylic acid esters, however, are underdeveloped. This gap arises because hydrogen atom abstraction (HAA) of protic C-H bonds by electrophilic metal-nitrenoids is slow: metal-nitrenoids preferentially react with polarity-matched, hydridic C-H bonds, even when weaker protic C-H bonds are present. This study describes the discovery and evolution of highly stable protoglobin nitrene transferases that catalyze the enantioselective intermolecular amination of the α-C-H bonds in carboxylic acid esters. We developed a high-throughput assay to evaluate the activity and enantioselectivity of mutant enzymes together with their sequences using the Every Variant Sequencing (evSeq) method. The assay enabled the identification of enantiodivergent enzymes that function at ambient conditions in Escherichia coli whole cells and whose activities can be enhanced by directed evolution for the amination of a range of substrates.

Exploring the Impact of Elements on the Reactivity of a Straightforward Procedure for Generating Vinyl-Carbazole Derivatives via a Frustrated Lewis Pair Mechanism

The effect of chemical element on the reactivity for carbazolation reaction of phenylacetylene utilizing G13(C6F5)3 (Lewis acid) and G15-carbazole (Lewis base) was theoretically investigated using density functional theory (M06-2X-D3/def2-TZVP), where G13 represents Group 13 elements and G15 represents Group 15 elements. Through activation strain model (ASM) analysis, it is apparent that the reactivity of the entire carbazolation reaction is chiefly governed by the structural strain energy of the alkyne fragment. In other words, if G13(C6F5)3 or G15-carbazole features an atomic radius that is either too small (e.g., B atom) or too large (e.g., Tl or Bi atom), it results in inadequate orbital overlap between the reactants due to the impact of steric effects. This, in turn, results in an elevation of the activation energy for such reactions, thereby impeding the alkyne from undergoing the carbazole catalytic reaction. In light of the above analyses, our theoretical findings suggest that, except for Tl(C6F5)3, the other four Lewis acid catalysts (B(C6F5)3, Al(C6F5)3, Ga((C6F5)3, and In((C6F5)3) demonstrate effectiveness in catalyzing the carbazolation reaction of alkyne alongside with N-carbazole. Additionally, it is anticipated that, among the five categories of G15-carbazole molecules studied, only N-carbazole can participate in the carbazolation reaction with alkyne catalyzed by B(C6F5)3, considering both kinetic and thermodynamic factors at room temperature. Our theoretical investigations, as outlined in this study, indicate that the carbazolation reaction of the alkyne, catalyzed by G13(C6F5)3 and G15-carbazole, follows Hammond's postulate. To put it more plainly, when the transition state of the chemical reaction occurs earlier, it results in a decrease in activation energy.

Asymmetric 1,2-Migration at Vicinal Tetrasubstituted Stereocenters Constructed from α-Keto Imines

A carbonyl-assisted asymmetric 1,2-migratory allylation through in situ generation of vicinal tetrasubstituted stereocenters is reported to access enantiopure α-amino ketones and amino alcohols with excellent yields and diastereoselectivities. In a remarkable divergence, despite higher steric hindrance, the allylation exclusively occurs on ketones over imines in the first step, followed by a face-selective 1,2-allyl transfer, thus highlighting an exciting interplay between two distinct electrophiles. The methodology distinguishes itself through its adaptability to gram-scale synthesis, showcasing broad functional-group tolerance and stereodivergence. Density functional theory (DFT) analysis led to a deeper understanding of its selectivity and mechanistic framework. Highlighting its transformative potential, the method was applied to the total synthesis of hapalindole alkaloids.

Recent Advances in Asymmetric Catalysis Using p-Block Elements

The development of new methods for enantioselective reactions that generate stereogenic centres within molecules are a cornerstone of organic synthesis. Typically, metal catalysts bearing chiral ligands as well as chiral organocatalysts have been employed for the enantioselective synthesis of organic compounds. In this review, we highlight the recent advances in main group catalysis for enantioselective reactions using the p-block elements (boron, aluminium, phosphorus, bismuth) as a complementary and sustainable approach to generate chiral molecules. Several of these catalysts benefit in terms of high abundance, low toxicity, high selectivity, and excellent reactivity. This minireview summarises the utilisation of chiral p-block element catalysts for asymmetric reactions to generate value-added compounds.

Enantioselective α-Amination of Amides by One-Pot Organo-/Iodine Sequential Catalysis

An one-pot organo- and iodine sequential catalysis strategy for reactions of amides with pyrazole-based primary amines was described to synthesize chiral α-amino amides with a quaternary stereocenter. This methodology exhibited strong asymmetric induction, resulting in a typical enantiomeric excess value exceeding 99% and diastereoselectivity up to >99:1 dr. Moreover, the reaction was conducted without the use of any metals or strong bases.

Asymmetric catalysis with FLPs

Chiral catalysts play a crucial role in the realm of asymmetric catalysis. Since their breakthrough discovery in 2006, chiral frustrated Lewis pairs (FLPs) have risen as a novel catalyst category for a broad range of metal-free asymmetric reactions. This review provides an overview of the remarkable progress made in this field over the past 15 years. The design and synthesis of chiral FLPs and their applications in hydrogenation, hydrosilylation, transfer hydrogenation, and various other reactions are summarized and highlighted.

Synthesis of Allenes by Hydroalkylation of 1,3-Enynes with Ketones Enabled by Cooperative Catalysis

A method for the synthesis of allenes by the addition of ketones to 1,3-enynes by cooperative Pd(0)Senphos/B(C6F5)3/NR3 catalysis is described. A wide range of aryl- and aliphatic ketones undergo addition to various 1,3-enynes in high yields at room temperature. Mechanistic investigations revealed a rate-determining outer-sphere proton transfer mechanism, which was corroborated by DFT calculations.

Visible-light induced cross-electrophile coupling of imines and anhydrides to synthesize α-amino ketones

α-Amino ketones are important motifs in synthetic and medicinal chemistry. Efficient methods to directly access these motifs from feasible precursors are, however, limited. Herein, a visible-light mediated reductive cross-electrophile coupling of readily available imines and anhydrides was developed. Under mild reaction conditions, the umpolung reactivity of diverse imines engaged with anhydrides gives a variety of α-amino ketones with good yields and a broad functional group compatibility. Primary mechanistic studies revealed that this transformation might proceed through a radical-radical cross coupling pathway dominantly.

Incorporation of Chiral Frustrated Lewis Pair into Metal-Organic Framework with Tailored Microenvironment for Heterogeneous Enantio- and Chemoselective Hydrogenation

The development of efficient heterogeneous catalysts with multiselectivity (e.g., enantio- and chemoselectivity) has long been sought after but with limited progress being made so far. To achieve enantio- and chemoselectivity in a heterogeneous system, as inspired by enzymes, we illustrate herein an approach of creating an enzyme-mimic region (EMR) within the nanospace of a metal-organic framework (MOF) as exemplified in the context of incorporating a chiral frustrated Lewis pair (CFLP) into a MOF with a tailored pore environment. Due to the high density of the EMR featuring the active site of CFLP and auxiliary sites of the hydroxyl group/open metal site within the vicinity of CFLP, the resultant EMR@MOF demonstrated excellent catalysis performance in heterogeneous hydrogenation of α,β-unsaturated imines to afford chiral β-unsaturated amines with high yields and high enantio- and chemoselectivity. The role of the hydroxyl group/open metal site in regulating chemoselectivity was proved by the observation of a catalyst-substrate interaction experimentally, which was also rationalized by computational results. This work not only contributes a MOF as a new platform for multiselective catalysis but also opens a promising avenue to develop heterogeneous catalysts with multiselectivity for challenging yet important transformations.

Nanosized Ti-Based Perovskite Oxides as Acid-Base Bifunctional Catalysts for Cyanosilylation of Carbonyl Compounds

The development of effective solid acid-base bifunctional catalysts remains a challenge because of the difficulty associated with designing and controlling their active sites. In the present study, highly pure perovskite oxide nanoparticles with d⁰-transition-metal cations such as Ti⁴⁺, Zr⁴⁺, and Nb⁵⁺ as B-site elements were successfully synthesized by a sol-gel method using dicarboxylic acids. Moreover, the specific surface area of SrTiO₃ was increased to 46 m² g^-1 by a simple procedure of changing the atmosphere from N₂ to air during calcination of an amorphous precursor. The resultant SrTiO₃ nanoparticles showed the highest catalytic activity for the cyanosilylation of acetophenone with trimethylsilyl cyanide (TMSCN) among the tested catalysts not subjected to a thermal pretreatment. Various aromatic and aliphatic carbonyl compounds were efficiently converted to the corresponding cyanohydrin silyl ethers in good-to-excellent yields. The present system was applicable to a larger-scale reaction of acetophenone with TMSCN (10 mmol scale), in which 2.06 g of the analytically pure corresponding product was isolated. In this case, the reaction rate was 8.4 mmol g^-1 min^-1, which is the highest rate among those reported for heterogeneous catalyst systems that do not involve a pretreatment. Mechanistic studies, including studies of the catalyst effect, Fourier transform infrared spectroscopy, and temperature-programmed desorption measurements using probe molecules such as pyridine, acetophenone, CO₂, and CHCl₃, and the poisoning effect of pyridine and acetic acid toward the cyanosilylation, revealed that moderate-strength acid and base sites present in moderate amounts on SrTiO₃ most likely enable SrTiO₃ to act as a bifunctional acid-base solid catalyst through cooperative activation of carbonyl compounds and TMSCN. This bifunctional catalysis through SrTiO₃ resulted in high catalytic performance even without a heat pretreatment, in sharp contrast to the performance of basic MgO and acidic TiO₂ catalysts.

α-Amination of Carbonyl Compounds by Using Hypervalent Iodine-Based Aminating Reagents Containing a Transferable (Diarylmethylene)amino Group

Hypervalent iodine-based aminating reagents containing a transferable (diarylmethylene)amino group can be used for the α-amination of simple carbonyl compounds such as esters, amides, and ketones in the presence of a lithium base. The (diarylmethylene)amino groups of the products can be readily modified, thus providing access to primary amines and diarylmethylamines. The developed method features transition-metal-free conditions and a simple one-pot procedure without the need to prepare enolate equivalents separately, thus offering a general and practical approach to the synthesis of a wide variety of α-amino carbonyl compounds. Experimental mechanistic investigations indicate that this amination proceeds through a unique radical coupling of an α-carbonyl radical with an iminyl radical; they are generated through a single-electron transfer between a lithium enolate and the hypervalent iodine reagent.

Boron-Catalyzed α-Functionalizations of Carboxylic Acids

Catalytic, chemoselective, and asymmetric α-functionalizations of carboxylic acids promise up-grading simple feedstock materials to value-added functional molecules, as well as late-stage structural diversifications of multifunctional molecules, such as drugs and their leads. In this personal account, we describe boron-catalyzed α-functionalizations of carboxylic acids developed in our group (five reaction types). The reversible boron carboxylate formation is key to the acidification of the α-protons and enolization using mild organic bases, allowing for chemoselective and asymmetric bond formations of carboxylic acids. The ligand effects on reactivity and stereoselectivity, substrate scopes, and mechanistic insights are summarized.

Recent Advances in Asymmetric Catalysis Associated with B(C6F5)3

The prevalence and significance of asymmetric catalysis in the modern medicinal industry has been witnessed in recent years, which have already been used to manufacture the (S)-Naproxen and the (S)-Propranolol. With matched specificities such as the Lewis acidity and steric bulk, B(C₆F₅)₃ has gained accelerating attention on its application in asymmetric catalysis of Diels-Alder cycloaddition reactions, carbonyl-ene cyclization, and other various reactions, which have been demonstrated by the elegant examples from the most recent literature. Some significant progress in the reaction of indirect activation of substrates through in situ generation of numerous supramolecular catalysts from B(C₆F₅)₃ based on Lewis-acid-assisted Lewis acid (LLA) or Lewis acid assisted Brønsted acid (LBA) strategies or the reaction promoted by cooperative actions of chiral co-catalysts and B(C₆F₅)₃ which played a direct role on the activation of substrates have been demonstrated in this review.

New boro amino amide organocatalysts for asymmetric cross aldol reaction of ketones with carbonyl compounds

Distinct types of new boron fused primary amino amide organocatalysts were designed and synthesized from commercially available amino acids. Their catalytic activities were investigated in asymmetric crossed aldol reaction of ketones with aromatic aldehydes to afford the corresponding chiral anti-aldol adducts with good chemical yields, moderate diastereoselectivity and good to excellent enantioselectivities (up to 94% yields, up to 90 : 10 dr, up to 94% ee).

Asymmetric Reductive Amination with Pinacolborane Catalyzed by Chiral SPINOL Borophosphates

The catalytic asymmetric reductive amination of ketones with pinacolborane employing chiral SPINOL-derived borophosphates as catalysts has been realized. A series of chiral amine derivatives bearing multiple functional groups were obtained in good to excellent yields and enantioselectivities (up to 97% yield, 98% ee) under mild reaction conditions. Moreover, the synthetic applicability of the established method has been demonstrated by the asymmetric synthesis of (R)-Fendiline.

Reactions of Diethylazo-Dicarboxylate with Frustrated Lewis Pairs

Reactions of PAr3 /B(C6 F5 )3 (Ar=o-Tol, Mes, Ph) FLPs with diethyl azodicarboxylate (DEAD) afford the corresponding FLP addition products 1-3 in which P-N and B-O linkages are formed. In contrast, the reaction of BPh3 , PPh3 and DEAD gave product 4 where P-N and N-B linkages were confirmed. In all cases, other binding modes were computed to be both higher in energy and readily distinguishable by 31 P and 11 B NMR parameters. These data illustrate the influence of steric demands and electronic structures on the nature of the products of FLP reactions with DEAD.

Highly Enantioselective Iridium-Catalyzed Hydrogenation of o-Amidophenyl Ketones Enabled by 1,2-Diphenylethylenediamine-Derived P,N,N-Ligands with Tertiary Amine Terminus

A readily available and highly modular class of chiral P,N,N-ligands based on a structurally flexible nonchiral phosphine-amine framework with an optically active 1,2-diphenylethylenediamine unit bearing a tertiary amine terminus as the chiral source have been developed and successfully applied in the Ir-catalyzed asymmetric hydrogenation of o-amidophenyl ketones. These tridentate P,N,N-ligands exhibited excellent activity, enantioselectivity, and substrate tolerance, thus furnishing various optically active o-amidobenzhydrols in up to 99% yields and with >99% ee. The utility of this protocol has been proven by synthetically diverse product transformation and highly enantioselective production of a rice plant growth regulator, (S)-inabenfide.

Catalytic hydroaminations of alkynes: A facile protocol to vinyl- carbazole derivatives via a frustrated Lewis pair mechanism

N-vinylcarbazoles are important skeletons for photoluminescent materials. Herein, a metal-free, B(C6F5)3 mediated carbazolation reaction of alkynes is reported. This provides 24 variants of N-vinylcarbazole derivatives. These N-vinylcarbazole products were obtained...

Recent advances in the synthesis and applications of phosphoramides

Phosphoramide, as an important framework of many biologically active molecules, has attracted widespread attention in recent decades. It is not only widely used in pharmaceuticals because of its excellent biological activities, but it also shows good performance in organic dyes, flame retardants and extractors. Thus, it is of great significance to develop effective and convenient methods for the synthesis of phosphoramides. In this review, the recent advancements made in the synthesis routes and applications of phosphoramides are discussed. The synthetic strategies of phosphoramides can be separated into five categories: phosphorus halides as the substrate, phosphates as the substrate, phosphorus hydrogen as the substrate, azides as the substrate and other methods. The latest examples of these methods are provided and some representative mechanisms are also described.

Relay Catalysis by Achiral Borane and Chiral Phosphoric Acid in the Metal-Free Asymmetric Hydrogenation of Chromones

A strategy of relay catalysis by achiral borane and chiral phosphoric acid was successfully developed for the asymmetric hydrogenation of chromones, giving the desired products in high yields with up to 95% ee. Achiral borane and chiral phosphoric acid are highly compatible in this reaction. The achiral borane acts as a Lewis acid for the first-step hydrogenation, and the chiral phosphoric acid acts as an effective chiral proton shuttle to control the enantioselectivity.

Asymmetric Halocyclizations of 2-Vinylbenzyl Alcohols with Chiral FLPs

By the use of a chiral frustrated Lewis pair (FLP) consisting of a chiral-diene-derived borane and ^tBu₃P as the catalyst, an asymmetric halocyclization of 2-vinylbenzyl alcohols with NBS or NIS was successfully realized. A variety of optically active 1,3-dihydroisobenofuran derivatives were obtained in high yields with up to 87% ee and could be conveniently converted to other useful chiral compounds.

Synergistic Catalysis by Brønsted Acid/Carbodicarbene Mimicking Frustrated Lewis Pair-Like Reactivity

Carbodicarbene (CDC), unique carbenic entities bearing two lone pairs of electrons are well-known for their strong Lewis basicity. We demonstrate herein, upon introducing a weak Brønsted acid benzyl alcohol (BnOH) as a co-modulator, CDC is remolded into a Frustrated Lewis Pair (FLP)-like reactivity. DFT calculation and experimental evidence show BnOH loosely interacting with the binding pocket of CDC via H-bonding and π-π stacking. Four distinct reactions in nature were deployed to demonstrate the viability of proof-of-concept as synergistic FLP/Modulator (CDC/BnOH), demonstrating enhanced catalytic reactivity in cyclotrimerization of isocyanate, polymerization process for L-lactide (LA), methyl methacrylate (MMA) and dehydrosilylation of alcohols. Importantly, the catalytic reactivity of carbodicarbene is uniquely distinct from conventional NHC which relies on only single chemical feature of nucleophilicity. This finding also provides a new spin in diversifying FLP reactivity with co-modulator or co-catalyst.

An umpolung-enabled copper-catalysed regioselective hydroamination approach to α-amino acids

A copper-catalysed regio- and stereoselective hydroamination of acrylates with hydrosilanes and hydroxylamines has been developed to afford the corresponding α-amino acids in good yields. The key to regioselectivity control is the use of hydroxylamine as an umpolung, electrophilic amination reagent. Additionally, a judicious choice of conditions involving the CsOPiv base and DTBM-dppbz ligand of remote steric hindrance enables the otherwise challenging C-N bond formation at the α position to the carbonyl. The point chirality at the β-position is successfully controlled by the Xyl-BINAP or DTBM-SEGPHOS chiral ligand with similarly remote steric bulkiness. The combination with the chiral auxiliary, (-)-8-phenylmenthol, also induces stereoselectivity at the α-position to form the optically active unnatural α-amino acids with two adjacent stereocentres.

Development of Catalytic Reactions for Precise Control of Chemoselectivity

Catalytic chemoselective reactions of innately less reactive functionalities over more reactive functionalities are described. A cooperative catalyst comprising a soft Lewis acid/hard Brønsted base enabled chemoselective activation of a hydroxyl group over an amino group, allowing for nucleophilic addition to electron-deficient olefins. The reaction could be applicable for a variety of amino alcohols, including pharmaceuticals, without requiring a tedious protection-deprotection process. Chemoselective enolization and subsequent α-functionalization of carboxylic acid derivatives were also achieved by a redox active catalyst through the radical process, providing unnatural α-amino/hydroxy acid derivatives bearing a complex carbon framework and a diverse set of functionalities. The present chemoselective catalysis described herein offers new opportunities to expand the chemical space for innovative drug discovery research.

Propargylic Amination Enabled the Access to Enantioenriched Acyclic α-Quaternary α-Amino Ketones

A propargylic amination approach toward chiral acyclic α-quaternary α-amino ketones is described. This Cu-catalyzed procedure could be performed open to air using commercially available amines as nucleophiles. The key to success is the use of rationally designed propargylic cyclic carbonates as substrates, which can generate a Cu-bonded enolate zwitterionic intermediate upon decarboxylation. This protocol features wide functional group tolerance and high asymmetric induction, with typical ee value higher than 93%, and thus advances a great step forward in the challenging synthesis of acyclic chiral α-quaternary α-amino ketones.

Catalytic Asymmetric Disulfuration by a Chiral Bulky Three-Component Lewis Acid-Base

A three-component Lewis acid-base (Lewis trio) involving a bulky chiral primary amine, B(C₆ F₅ )₃ and a bulky tertiary amine has been developed as an effective enamine catalyst for enantioselective disulfuration reactions. The bulky tertiary amine was found to activate a bulky primary-tertiary diamine-borane Lewis pair for enamine catalysis via frustrated interaction. The resulted chiral bulky Lewis trio (BLT) allows for the construction of chiral disulfides via direct disulfuration with β-ketocarbonyls or α-branched aldehydes in a practical and highly stereocontrolled manner.

Electron-deficient boron-based catalysts for C-H bond functionalisation

In contrast to transition metal-catalysed C-H functionalisation, highly efficient construction of C-C and C-X (X = N, O, S, B, Si, etc.) bonds through metal-free catalytic C-H functionalisation remains one of the most challenging tasks for synthetic chemists. In recent years, electron-deficient boron-based catalyst systems have exhibited great potential for C-H bond transformations. Such emerging systems may greatly enrich the chemistry of C-H functionalisation and main-group element catalysis, and will also provide enormous opportunities in synthetic chemistry, materials chemistry, and chemical biology. This article aims to give a timely comprehensive overview to recognise the current status of electron-deficient boron-based catalysis in C-H functionalisation and stimulate the development of more efficient catalytic systems.

Recent advances in the synthesis of α-amino ketones

Due to the importance of the amino ketone motif in synthetic and medicinal chemistry, the number of protocols developed in recent years has considerably increased. This review serves to collate and critically evaluate novel methodologies published since 2011 towards this high value synthon. The chapters are divided by the requisite functionality in the starting material, and an emphasis is placed on discussing functional group compatibility and resultant product substitution patterns. Throughout, applications to medicinal targets are highlighted and mechanistic details are presented, and we further provide a short outlook for future development and emerging potential within this area.

Bifunctional Iminophosphorane Superbase Catalysis: Applications in Organic Synthesis

To improve the field of catalysis, there is a substantial and growing need for novel high-performance catalysts providing new reactivity. To date, however, the set of reactions that can be reliably performed to prepare chiral compounds in largely one enantiomeric form using chiral catalysts still represents a small fraction of the toolkit of known transformations. In this context, chiral Brønsted bases have played an expanding role in catalyzing enantioselective reactions between various carbon- and heteroatom-centered acids and a host of electrophilic reagents. This Account describes our recent efforts developing and applying a new family of chiral Brønsted bases incorporating an H-bond donor moiety and a strongly basic iminophosphorane, which we have named BIMPs (Bifunctional IMinoPhosphoranes), as efficient catalysts for reactions currently out of reach of more widespread tertiary amine centered bifunctional catalysts. The iminophosphorane Brønsted base is easily generated by the Staudinger reaction of a chiral organoazide and commercially available phosphine, which allows easy modification of the catalyst structure and fine-tuning of the iminophosphorane pK_BH+. We have demonstrated that BIMP catalysts can efficiently promote the enantioselective addition of nitromethane to low reactivity N-diphenylphosphinoyl (DPP)-protected imines of ketones (ketimines) to access valuable chiral diamine and α-quaternary amino acid building blocks, and later extended this methodology to phosphite nucleophiles. Subsequently, the reaction scope was expanded to include the Michael addition of high pK_a alkyl thiols to α-substituted acrylate esters, β-substituted α,β-unsaturated esters, and alkenyl benzimidazoles as well as the challenging direct aldol addition of aryl ketones to α-fluorinated ketones. Finally, BIMP catalysts were shown to be used in key steps in the synthesis of complex alkaloid natural products (-)-nakadomarin A and (-)-himalensine A, as well as in polymer synthesis. In most cases, the predictable nature of the BIMP promoted reactions was demonstrated by multigram scale-up while employing low catalyst loadings (down to 0.05 mol%). Furthermore, it was shown that BIMP catalysts can be easily immobilized onto a solid support in one-step for increased catalyst recycling and flow chemistry applications. Alongside our own work, this Account also includes elegant work by Johnson and co-workers utilizing the BIMP catalyst system, when alternative catalysts proved suboptimal.

Sequential Conia-ene-type cyclization and Negishi coupling by cooperative functions of B(C6F5)3, ZnI2, Pd(PPh3)4 and an amine

We disclose a method for sequential Conia-ene-type cyclization/Negishi coupling for the union of alkynyl ketones and aryl iodides. This process is promoted through cooperative actions of Lewis acidic B(C6F5)3, ZnI2, Pd-based complex, and a Brønsted basic amine. The three Lewis acid catalysts with potential overlapping functions play their independent roles as activators of carbonyl group, alkyne moiety, and alkenyl zinc intermediate, respectively. A variety of 1,2,3-substituted cyclopentenes can be synthesized with high efficiency.

Asymmetric Hydrogenation of Ketones and Enones with Chiral Lewis Base Derived Frustrated Lewis Pairs

The concept of frustrated Lewis pairs (FLPs) has been widely applied in various research areas, and metal-free hydrogenation undoubtedly belongs to the most significant and successful ones. In the past decade, great efforts have been devoted to the synthesis of chiral boron Lewis acids. In a sharp contrast, chiral Lewis base derived FLPs have rarely been disclosed for the asymmetric hydrogenation. In this work, a novel type of chiral FLP was developed by simple combination of chiral oxazoline Lewis bases with achiral boron Lewis acids, thus providing a promising new direction for the development of chiral FLPs in the future. These chiral FLPs proved to be highly effective for the asymmetric hydrogenation of ketones, enones, and chromones, giving the corresponding products in high yields with up to 95 % ee. Mechanistic studies suggest that the hydrogen transfer to simple ketones likely proceeds in a concerted manner.