Catalytic Enantioselective Cyanation: Recent Advances and Perspectives

Photocatalyzed Dicyanation of Alkenes Enabled by Phosphorus Radical Cation Addition

While notable progress has been made in alkene cyanation for the synthesis of alkyl nitriles, catalytic strategies enabling the direct dicyanation of simple alkenes remain relatively under-explored. In this study, we introduce a synergistic phosphine-photoredox catalytic system that facilitates the direct dicyanation of styrenes using TMSCN in the presence of oxidant. This approach utilizes a phosphorus radical cation to initiate an oxidative radical-polar crossover with alkenes, followed by sequential nucleophilic cyanation. This protocol allows for the efficient synthesis of alkyl 1,2-dinitriles from alkenes under mild conditions. Notably, the method exhibits broad substrate scope and commendable efficiency, serving as a valuable complement to existing cyanation methodologies. The synthetic utility of the dinitrile products is further demonstrated through diverse derivatization reactions, highlighting their applicability in constructing nitrogen-rich molecular architectures. Mechanistic studies provide further insight into the reaction pathway and underscore the potential of phosphorus radical cations in alkene functionalization.

Regioselective formal hydrocyanation of allenes: synthesis of β,γ-unsaturated nitriles with α-all-carbon quaternary centers

This study introduces a highly selective hydrocyanation method based on copper-catalyzed hydroalumination of allenes with diisobutylaluminum hydride, followed by the regio- and stereoselective allylation with p-toluenesulfonyl cyanide. The proposed methodology is efficient for accessing acyclic β,γ-unsaturated nitriles with α-all-carbon quaternary centers and achieves yields up to 99% and excellent regio- and E-selectivity. The reaction proceeds under mild conditions and shows broad applicability to di- and trisubstituted allenes. Its practicality is demonstrated through the gram-scale synthesis and functional group transformations of amines, amides, and lactams, emphasizing its versatility and synthetic significance.

Exploring the Chiral Match-Mismatch Effect in the Chiral Discrimination of Nitriles

This study tackles the challenge of enantiodifferentiation of nitrile compounds, which is typically difficult to resolve using nuclear magnetic resonance (NMR) due to the significant distance between the chiral center and the nitrogen atom involved in molecular interactions. We have developed novel chiral 19F-labeled probes, each featuring two chiral centers, to exploit the "match-mismatch" effect, thereby enhancing enantiodiscrimination. This strategy effectively differentiates chiral analytes with quaternary chiral carbon centers as well as those with similar substituents at the chiral center. Our approach not only provides a novel method for precise probe performance optimization but also offers a rapid and efficient technique for screening reaction conditions in asymmetric synthesis.

Enantioselective Synthesis of Axially Chiral Allylic Nitriles via Nickel-Catalyzed Desymmetric Cyanation of Biaryl Diallylic Alcohols

Axially chiral nitriles are common motifs in organic photoelectric materials, biological compounds, and agrochemicals. Unfortunately, the limited synthetic approaches to axially chiral nitriles have impeded their availability. Herein, we report the first nickel-catalyzed desymmetric allylic cyanation of biaryl allylic alcohols for the synthesis of axially chiral nitrile structures in high yields with excellent enantioselectivities (up to 90 % yield and >99 % ee). This process enables the synthesis of a diverse range of axially chiral allylic nitriles bearing β,γ-unsaturated alcohol moieties. Leveraging the allylic alcohol and cyano groups as versatile functionalization handles allow for further derivatization of these axially chiral frameworks. Density functional theory (DFT) calculations suggest that both steric and electronic interactions play crucial roles in determining the enantioselectivity of this transformation. Moreover, this mild and facile protocol is also applicable for gram-scale preparation of the chiral nitriles.

Asymmetric Hydrogenation of Exocyclic α,β-Unsaturated Nitriles: An Access to Chiral 2-Benzocyclic Acetonitriles and Ramelteon

A highly efficient and enantioselective hydrogenation of exocyclic α,β-unsaturated nitriles catalyzed by the Rh-JosiPhos complex for synthesis of the chiral 2-benzocyclic acetonitriles has been developed. Both (Z)- and (E)-isomers of exocyclic α,β-unsaturated nitriles with various benzocyclic structures, including heterocyclic (chroman and tetrahydroquinoline) scaffolds, were hydrogenated successfully, achieving excellent enantioselectivities (up to 97% ee) and high turnover numbers (TON up to 4000). Furthermore, this methodology provides an efficient, concise, and practical synthetic route to the sleep agent (S)-Ramelteon.

Formal 1,1-Hydrocyanation Reaction of Alkynyl Halides with Isocyanides Enabled by Dual Nickel/Base Catalysis Relay

We herein describe a formal 1,1-hydrocyanation reaction of alkynyl halides with isocyanides enabled by a dual nickel/base catalysis relay. tert-Butyl isocyanide serves as a "HCN" precursor that is introduced to the α-position of alkynyl halides, and the halogen atom is moved to the β-position. As a result, a series of (Z)-3-bromo/iodo acrylonitrile derivatives could be obtained in moderate yields. Mechanistic experiments were carried out, and the collective data could support our proposal of the mechanism details.

Geminal Aminocyanation Enabled by Ylide Mediated Rearrangement

Herein, we describe experimental and computational studies to understand the features of oxycyanopyridinium ylides generated in situ from oxy-cyanopyridines and rhodium carbene. This chemistry has enabled the concomitant formation of both C-N and C-C bonds, providing a complementary approach for cyanation reactions. Density functional theory calculations indicate the sequential metal-bound ylide formation, rhodium-associated five-membered transition state, and 1,4-cyano group relocation. Moreover, the enantioselective rearrangement has been realized by using chiral dirhodium complexes as the catalysts.

Enantioconvergent Cross-Nucleophile Coupling: Copper-Catalyzed Deborylative Cyanation

Organoboron compounds are widely utilized in organic synthesis for their diverse reactivity, modular preparation, and stability compared to other classes of organometallic reagents. While organoboron species are commonly employed as nucleophiles in cross-coupling reactions, their potential as racemic building blocks in enantioconvergent transformations remains largely untapped. Herein, we demonstrate the direct utilization of alkylboronic pinacol esters in intermolecular enantioconvergent transformations. Specifically, this work describes the development and mechanistic study of an enantioconvergent deborylative cyanation enabled by Cu catalysis. This method imparts a high degree of enantioselectivity and tolerates a wide range of common functional groups and heterocycles. The reaction is proposed to proceed through a radical-relay mechanism. Aniline-assisted homolysis of the carbon-boron bond results in prochiral alkyl radicals that are functionalized by in situ generated Cu(II)(CN)2 species in an enantioselective fashion. The Cu(II)(CN)2 intermediate was characterized by electron paramagnetic resonance (EPR) spectroscopy, and its electronic structure was probed using density functional theory (DFT) calculations. Computational studies were carried out to corroborate the proposed radical-relay mechanism.

Overcoming Copper Reduction Limitation in Asymmetric Substitution: Aryl-Radical-Enabled Enantioconvergent Cyanation of Alkyl Iodides

Cu-catalyzed enantioconvergent cross-coupling of alkyl halides has emerged as a powerful strategy for synthesizing enantioenriched molecules. However, this approach is intrinsically limited by the weak reducing power of copper(I) species, which restricts the scope of compatible nucleophiles and necessitates extensive ligand optimization or the use of complex chiral scaffolds. To overcome these challenges, we introduce an aryl-radical-enabled strategy that decouples the alkyl halide activation step from the chiral Cu center. We demonstrate that merging aryl-radical-enabled iodine abstraction with Cu-catalyzed asymmetric radical functionalization enables the conversion of racemic α-iodoamides to enantioenriched alkyl nitrile products with good yield and enantioselectivity. The rational design of chiral ligands identified a new class of carboxamide-containing BOX ligands. Mechanistic studies support an aryl-radical-enabled pathway and the unique hydrogen-bonding ability in the newly designed BOX ligands. This aryl-radical-enabled asymmetric substitution reaction has the potential to significantly expand the scope of Cu-catalyzed enantioconvergent cross-coupling reactions.

H-Bond Donor-Directed Switch of Diastereoselectivity in the Enantioselective Intramolecular Aza-Henry Reaction of Ketimines

We report an H-bond donor controlled diastereoselective switchable intramolecular aza-Henry reaction of ketimines derived from α-ketoesters and 2-(2-nitroethyl)anilines, allowing facile access to chiral tetrahydroquinolines bearing an aza-quaternary carbon stereocenter, which are privileged scaffold for medicinal researches. While newly developed cinchona alkaloid derived phosphoramide-bearing quaternary ammonium salt C2 selectively give cis-adducts in up to 20 : 1 dr and 99 % ee, the corresponding urea-bearing analogue C8 preferentially give trans-adducts in up to 20 : 1 dr and 99 % ee.

Direct Asymmetric Synthesis of α-Aminoimines from 1,2-Bis-N-Sulfinylimines by Using Allyl Boronic Acids

A unique direct asymmetric synthesis of α-aminoimines is realized, through rapid and exclusive mono-allylation of chiral bis-N-sulfinylimines using allylboronic acids. The highly selective allylation was possible as electrophilic imine functional group in the product α-aminoimines remained unreactive towards allyl boronic acid nucleophiles. Notably, by varying the geometry and chiral auxiliary, all four isomers of the α-aminoimines were accessed from readily available precursors. A range of allyl nucleophiles, which are tricky to generate by other means possessing highly reactive functional groups also took part in this reaction, expanding the scope further. The applicability of the products α-aminoimines were further demonstrated by accessing a range of structurally diverse chiral cyclic and acyclic 1,2-diamines bearing adjacent stereocenters through addition of a second nucleophile or Prins-type cyclization by exploiting the nucleophilicity of the tethered alkene moiety. Moreover, the leaving group aptitude of sulfinyl auxiliary attached to imine, was exploited to access valuable chiral α-aminonitriles under thermal conditions without employing any reagents. Detailed DFT calculation revealed a chair-like transition state, arising from corresponding allylboroxine species, likely operating for the allylboration reaction across imine.

Optical Enantiodifferentiation of Chiral Nitriles

Chiroptical sensing of nitriles is achieved with excellent functional group tolerance by hydrozirconation and subsequent transmetalation of the corresponding iminate to a chromophoric palladium complex. A one-pot workflow that uses the Schwartz reagent and [(η3-1-tert-butylindenyl)(μ-Cl)Pd]2 as sensor generates a palladium complex displaying red-shifted CD inductions and characteristic UV changes. These chiroptical responses are accurately correlated to the enantiomeric ratio and total concentration of the original nitrile.

Di-π-ethane Rearrangement of Cyano Groups via Energy-Transfer Catalysis

Molecular rearrangement occupies a pivotal position among fundamental transformations in synthetic chemistry. Radical translocation has emerged as a prevalent synthetic tool, efficiently facilitating the migration of diverse functional groups. In contrast, the development of di-π-methane rearrangement remains limited, particularly in terms of the translocation of cyano functional groups. This is primarily attributed to the energetically unfavorable three-membered-ring transition state. Herein, we introduce an unprecedented di-π-ethane rearrangement enabled by energy-transfer catalysis under visible light conditions. This innovative open-shell rearrangement boasts broad tolerance toward a range of functional groups, encompassing even complex drug and natural product derivatives. Overall, the reported di-π-ethane rearrangement represents a complementary strategy to the development of radical translocation enabled by energy-transfer catalysis.

Stereoselective Construction of Less-Accessible Acyclic α,α-Disubstituted β-Ketiminonitriles via Electrophilic Cyanation of β,β-Disubstituted Enesulfinamides

The metalloenamines, formed by NH-deprotonation of β,β-disubstituted enesulfinamides, can undergo reactions with commercially available electrophilic cyanating reagents such as tosyl cyanide (TsCN) or 3-oxo-1,2-benziodoxole-1(3H)-carbonitrile (CBX). Through the utilization of appropriate stereoisomers of enesulfinamides, this method enables the selective synthesis of any of the four stereoisomers of α,α-disubstituted β-sulfinylimino nitriles, which feature acyclic quaternary stereocenters and are typically more challenging to synthesize. These compounds can then undergo stereoselective nucleophilic addition, leading to the creation of valuable enantioenriched multisubstituted β-amino carbonyl surrogates with a high degree of structural diversity.

Enantioselective Synthesis of Axially and Centrally Chiral Styrenes via Nickel-Catalyzed Desymmetric Hydrocyanation of Biaryl Dienes

Herein, a highly regio-, enantio-, and diastereoselective nickel-catalyzed desymmetric hydrocyanation of biaryl dienes for the simultaneous construction of axial and central chiralities is presented, which offers a convenient approach to a variety of tirenes containing the union of an axially chiral biaryl and a centrally α-chiral nitrile under mild conditions using a commercially available catalyst. The synthetic utility is highlighted by the development of a novel axially chiral phosphine ligand and biphenyl-based chiral diene ligand and their potential applications in the field of asymmetric catalytic reactions.

Iron-Catalyzed Cyanide-Free Synthesis of Alkyl Nitriles: Oxidative Deconstruction of Cycloalkanones with Ammonium Salts and Aerobic Oxidation

A sustainable, cyanide-free synthesis of alkyl nitriles via the aerobic oxidative deconstruction of unstrained cycloalkanones with ammonium salts has been developed. Using inexpensive and stable ammonium salts as the nitrogen source, a variety of alkyl nitriles containing a distal carbonyl group were obtained in good yields under visible-light-promoted iron catalysis. This protocol is characterized by mild conditions, abundant and environmentally benign materials, and high atom and step economy with minimal waste generation. The primary mechanism study revealed that 1O2 is likely to be involved in this reaction.

Enantio- and Diastereoselective Variations on α-Iminonitriles: Harnessing Chiral Cyclopropenimine-Thiourea Organocatalysts

Chiral 1-pyrrolines containing a nitrile motif serve as crucial structural scaffolds in biologically active molecules and exhibit diversity as building blocks owing to their valuable functional groups; however, the asymmetric synthesis of such compounds remains largely unexplored. Herein, we present an enantio- and diastereoselective method for the synthesis of α-chiral nitrile-containing 1-pyrroline derivatives bearing vicinal stereocenters through the design and introduction of chiral cyclopropenimine-based bifunctional catalysts featuring a thiourea moiety. This synthesis entails a highly stereoselective conjugate addition of α-iminonitriles to a wide array of enones, followed by cyclocondensation, thereby affording a series of cyanopyrroline derivatives, some of which contain all-carbon quaternary centers. Moreover, we demonstrate the synthetic utility of this strategy by performing a gram-scale reaction with 1% catalyst loading, along with a variety of chemoselective transformations of the product, including the synthesis of a vildagliptin analogue. Finally, we showcase the selective synthesis of all four stereoisomers of the cyanopyrroline products through trans-to-cis isomerization, highlighting the versatility of our approach.

Asymmetric Cyanation of α-Ketimino Ester Derivatives with Chiral Ru-Li Combined Catalysts

Asymmetric cyanation of α-ketimino esters catalyzed by combined systems of amino acid/BINAP derivative/Ru(II) complexes and lithium compounds was examined. The use of an appropriate combination of amino acid and BINAP ligands achieved high enantioselectivity for a variety of α-alkynyl (Val/XylBINAP/Ru), α-alkenyl (Val/TolBINAP/Ru), and α-aryl imino esters (Val/XylBINAP/Ru) as well as an isatin-derived cyclic imino amide (t-Leu/BINAP/Ru) to afford the α-cyano-α-amino esters and the amide with an α-nitrogen-substituted quaternary chiral center with up to 98% ee.

Multiple Hydrogen-Bonding Catalysts Enhance the Asymmetric Cyanation of Ketimines and Aldimines

A highly enantioselective cyanation of imines (up to >99 % ee) has been developed using well-designed C2 -symmetric hydrogen bonding catalysts. The catalytic strategy was characterized with low catalyst loading (0.1-1 mol %), easily accessible catalysts with diverse functional groups, and catalytic base additives. A wide range of imines, including the challenging N-Boc and N-Cbz protected ketimines and aldimines, as well as fluoroalkylated ketimines, were investigated under mild conditions to afford the products with good to excellent yields (up to 99 % yield) and high enantioselectivity (up to >99 % ee). Control experiments revealed that the multiple hydrogen bonding catalysts enhanced the reactivity and enantioselectivity of the Strecker reaction initiated by the base.

Photoelectrochemical Asymmetric Catalysis Enables Enantioselective Heteroarylcyanation of Alkenes via C-H Functionalization

The asymmetric difunctionalization of alkenes, a method transforming readily accessible alkenes into enantioenriched chiral structures of high value, has long been a focal point of organic synthesis. Despite tremendous efforts in this domain, it remains a considerable challenge to devise enantioselective oxidative dicarbofunctionalization of alkenes, even though these transformations can utilize stable and unfunctionalized functional group donors. In this context, we report herein a photoelectrocatalytic method for the enantioselective heteroarylcyanation of aryl alkenes, which employs unfunctionalized heteroarenes through C-H functionalization. The photoelectrochemical asymmetric catalysis (PEAC) method combines photoredox catalysis and asymmetric electrocatalysis to facilitate the formation of two C-C bonds operating via hydrogen (H2) evolution and obviating the need for external chemical oxidants.

Functional-group translocation of cyano groups by reversible C-H sampling

Chemical transformations that introduce, remove or manipulate functional groups are ubiquitous in synthetic chemistry1. Unlike conventional functional-group interconversion reactions that swap one functionality for another, transformations that alter solely the location of functional groups are far less explored. Here, by photocatalytic, reversible C-H sampling, we report a functional-group translocation reaction of cyano (CN) groups in common nitriles, allowing for the direct positional exchange between a CN group and an unactivated C-H bond. The reaction shows high fidelity for 1,4-CN translocation, frequently contrary to inherent site selectivity in conventional C-H functionalizations. We also report the direct transannular CN translocation of cyclic systems, providing access to valuable structures that are non-trivial to obtain by other methods. Making use of the synthetic versatility of CN and a key CN translocation step, we showcase concise syntheses of building blocks of bioactive molecules. Furthermore, the combination of C-H cyanation and CN translocation allows access to unconventional C-H derivatives. Overall, the reported reaction represents a way to achieve site-selective C-H transformation reactions without requiring a site-selective C-H cleavage step.

Chiral Discrimination of Nitrile Compounds Using a 19F-Labeled Palladium Probe

This study presents a ¹⁹F-labeled cyclopalladium probe for the rapid discrimination of chiral nitriles in pharmaceuticals, natural products, and agrochemicals. The probe binds reversibly to chiral nitriles, generating distinct ¹⁹F nuclear magnetic resonance signals for each enantiomer and enabling quick determination of enantiocomposition. The method allows for simultaneous detection of seven pairs of enantiomeric nitriles and application in assessing the enantiomeric excess of an asymmetric C-H cyanation reaction.

Copper-Catalyzed Enantioselective Decarboxylative Cyanation of Benzylic Acids Promoted by Hypervalent Iodine(III) Reagents

Copper-catalyzed asymmetric radical cyanation reactions have emerged as a powerful strategy for rapid construction of α-chiral nitriles. However, the directly decarboxylative cyanation reactions of common alkyl carboxylic acids remain largely elusive. Herein, we report a protocol for copper-catalyzed direct and enantioselective decarboxylative cyanation of benzylic acids. The in situ activation of acid substrates by a commercially inexpensive hypervalent iodine(III) reagent promoted the yield of the alkyl radicals under mild reaction conditions without prefunctionalization. The structurally diverse chiral alkyl nitriles were produced in good yields with high enantioselectivities. In addition, the chiral products can be readily converted to other useful chiral compounds via further transformations.

Synthesis of β-Ketonitriles via N-Heterocyclic-Carbene-Catalyzed Radical Coupling of Aldehydes and Azobis(isobutyronitrile)

Herein, an NHC (N-heterocyclic carbene)-catalyzed radical coupling reaction between aldehydes and azobis(isobutyronitrile) (AIBN) has been developed. This method provides an efficient and convenient approach for the synthesis of β-ketonitriles containing a quaternary carbon center (31 examples, up to >99% yield) utilizing commercially available substrates. This protocol features broad substrate scope, good functional group tolerance, and high efficiency under metal-free and mild reaction conditions.

Construction of defected MOF-74 with preserved crystallinity for efficient catalytic cyanosilylation of benzaldehyde

Numerous open metal sites and well-developed micropores are the two most significant characteristics that should be imparted to design metal-organic frameworks (MOFs) as effective catalysts. However, the construction of the best MOF catalyst with both these characteristics is challenging because the creation of numerous open metal sites generally triggers some structural collapse of the MOF. Herein, we report the construction of well-structured but defected MOFs through the growth of defected MOFs, where some of the original organic linkers were replaced with analog organic linkers, on the surface of a crystalline MOF template (MOF-on-MOF growth). Additional open metal sites within the MOF-74 structure were generated by replacing some of the 2,5-dihydroxy-1,4-bezenedicarboxylic acid presenting in MOF-74 with 1,4-benzenedicarboxylic acid due to the missing hydroxyl groups. And the resulting additional open metal sites within the MOF-74 structure resulted in enhanced catalytic activity for the cyanosilylation of aldehydes. However, the collapse of some of the well-developed MOF-74 structure was also followed by structural defects. Whereas, the growth of defected MOF-74 (D-MOF-74) on the well-crystallized MOF-74 template led to the production of relatively well-crystallized D-MOF-74. Core-shell type MOF-74@D-MOF-74 having abundant open metal sites with a preserved crystallinity exhibited the efficient catalytic cyanosilylation of several aldehydes. Additionally, MOF-74@D-MOF-74 displayed excellent recyclability during the consecutive catalytic cycles.

Electrophotochemical Metal-Catalyzed Enantioselective Decarboxylative Cyanation

In contrast to the rapid growth of electrophotocatalysis in recent years, enantioselective catalytic reactions powered by this unique methodology remain rare. In this work, we report an electrophotochemical metal-catalyzed protocol for direct asymmetric decarboxylative cyanation of aliphatic carboxylic acids. The synergistic merging of electrophotochemical cerium catalysis and asymmetric electrochemical copper catalysis permits mild reaction conditions for the formation and utilization of the key carbon centered radicals by combining the power of light and electrical energy. Electrophotochemical cerium catalysis enables radical decarboxylation to produce alkyl radicals, which could be effectively intercepted by asymmetric electrochemical copper catalysis for the construction of C-CN bonds in a highly stereoselective fashion. This environmentally benign method smoothly converts a diverse array of arylacetic acids into the corresponding alkyl nitriles in good yields and enantioselectivities without using chemical oxidants or pre-functionalization of the acid substrates and can be readily scaled up.

Mutability-Landscape-Guided Engineering of l-Threonine Aldolase Revealing the Prelog Rule in Mediating Diastereoselectivity of C-C Bond Formation

l-threonine aldolase (LTA) catalyzes C-C bond synthesis with moderate diastereoselectivity. In this study, with LTA from Cellulosilyticum sp (CpLTA) as an object, a mutability landscape was first constructed by performing saturation mutagenesis at substrate access tunnel amino acids. The combinatorial active-site saturation test/iterative saturation mutation (CAST/ISM) strategy was then used to tune diastereoselectivity. As a result, the diastereoselectivity of mutant H305L/Y8H/V143R was improved from 37.2 %_syn to 99.4 %_syn . Furthermore, the diastereoselectivity of mutant H305Y/Y8I/W307E was inverted to 97.2 %_anti . Based on insight provided by molecular dynamics simulations and coevolution analysis, the Prelog rule was employed to illustrate the diastereoselectivity regulation mechanism of LTA, holding that the asymmetric formation of the C-C bond was caused by electrons attacking the carbonyl carbon atom of the substrate aldehyde from the re or si face. The study would be useful to expand LTA applications and guide engineering of other C-C bond-forming enzymes.

Catalytic Cyanation of C-N Bonds with CO2/NH3

Cyanation of benzylic C-N bonds is useful in the preparation of important α-aryl nitriles. The first general catalytic cyanation of α-(hetero)aryl amines, analogous to the Sandmeyer reaction of anilines, was developed using reductive cyanation with CO₂/NH₃. A broad array of α-aryl nitriles was obtained in high yields and regioselectivity by C-N cleavage of intermediates as ammonium salts. Good tolerance of functional groups such as ethers, CF₃, F, Cl, esters, indoles, and benzothiophenes was achieved. Using ¹³CO₂, a ¹³C-labeled tryptamine homologue (five steps, 31% yield) and Cysmethynil (six steps, 37% yield) were synthesized. Both electronic and steric effects of ligands influence the reactivity of alkyl nickel species with electrophilic silyl isocyanates and thus determine the reactivity and selectivity of the cyanation reaction. This work contributes to the understanding of the controllable activation of CO₂/NH₃ and provides the promising potential of the amine cyanation reaction in the synthesis of bio-relevant molecules.

Paired Electrolysis for Decarboxylative Cyanation: 4-CN-Pyridine, a Versatile Nitrile Source

A decarboxylative cyanation of amino acids under paired electrochemical reaction conditions has been developed. 4-CN-pyridine was found to be a new and effective cyanation reagent under catalyst-free conditions. Mechanistic studies support a nucleophilic reaction pathway, and the cyanation protocol can be applied to diverse substrates including N,N-dialkyl aniline and indole derivatives.

Diverse synthesis of α-tertiary amines and tertiary alcohols via desymmetric reduction of malonic esters

Amines and alcohols with a fully substituted α-carbon are structures of great value in organic synthesis and drug discovery. While conventional methods towards these motifs often rely on enantioselective carbon-carbon or carbon-heteroatom bond formation reactions, a desymmetric method is developed here by selectively hydrosilylating one of the esters of easily accessible α-substituted α-amino- and -oxymalonic esters. The desymmetrization is enabled by a suite of dinuclear zinc catalysts with pipecolinol-derived tetradentate ligands and can accommodate a diverse panel of heteroatom substituents, including secondary amides, tertiary amines, and ethers of different sizes. The polyfunctionalized reduction products, in return, have provided expeditious approaches to enantioenriched nitrogen- and oxygen-containing molecules, including dipeptides, vitamin analogs, and natural metabolites.

Chiral α-tertiary amines and tertiary alcohols are prevalent in bioactive molecules yet challenging targets to access. Here, the authors provide a dinuclear zinc-catalyzed desymmetric approach based on readily available malonic esters.

Organocatalytic stereoselective cyanosilylation of small ketones

Enzymatic stereoselectivity has typically been unrivalled by most chemical catalysts, especially in the conversion of small substrates. According to the ‘lock-and-key theory’^1,2, enzymes have confined active sites to accommodate their specific reacting substrates, a feature that is typically absent from chemical catalysts. An interesting case in this context is the formation of cyanohydrins from ketones and HCN, as this reaction can be catalysed by various classes of catalysts, including biological, inorganic and organic ones^3–7. We now report the development of broadly applicable confined organocatalysts for the highly enantioselective cyanosilylation of aromatic and aliphatic ketones, including the challenging 2-butanone. The selectivity (98:2 enantiomeric ratio (e.r.)) obtained towards its pharmaceutically relevant product is unmatched by any other catalyst class, including engineered biocatalysts. Our results indicate that confined chemical catalysts can be designed that are as selective as enzymes in converting small, unbiased substrates, while still providing a broad scope.

The development of confined organocatalysts for the enantioselective cyanosilylation of small, unbiased substrates, including 2-butanone, is shown to lead to catalysts that are as selective as enzymes, with excellent levels of control.

Palladium-catalyzed synthesis of nitriles from N-phthaloyl hydrazones

The Pd-catalyzed transformation of N-phthaloyl hydrazones into nitriles involving the cleavage of an N-N bond is reported. The use of N-heterocyclic carbene as a ligand is essential for the success of the reaction. N-Phthaloyl hydrazones prepared from aromatic aldehydes or cyclobutanones are applicable to this transformation, which gives aryl or alkenyl nitriles, respectively.

Making Chiral Salen Complexes Work with Organocatalysts

Bisimine derivatives of salicylaldehyde with chiral diamines (salens) are privileged ligands in asymmetric organometallic catalysis, which can be used in cooperation with organocatalysts as additives. The latter can be a modifier of the metal reactivity by liganding or a true co-catalyst working in tandem or in a dual system. All scenarios encountered in the literature are reviewed and classified according to the organocatalyst. In each case, mechanistic and physical-organic chemistry considerations are discussed to better understand the gears of these complex catalytic settings.

Asymmetric Cyanosilylation of Aldehydes by a Lewis Acid/Base Synergistic Catalyst of Chiral Metal Clusters

Metal clusters with well-defined crystal structures are extremely useful for studying the synergistic catalytic effects and associated catalytic mechanisms. In this study, two pairs of chiral lanthanide-transition metal clusters (R)/(S)-Co₃Ln₂ (Ln = Tb or Dy) were synthesized using Schiff-base ligands [(R)- or (S)-H₃L] with multiple Lewis base sites (O sites). The as-prepared (R)/(S)-Co₃Ln₂ chiral metal clusters exhibited good catalytic functionality in the asymmetric synthesis of chiral cyanohydrins, with high conversions of up to 99% and medium-to-high enantiomeric excess values of up to 78%. The catalysis process followed a mechanism in which the bifunctional metal clusters of (R)/(S)-Co₃Ln₂, containing Lewis acid sites and Lewis base sites, simultaneously activated the aldehydes and trimethylsilyl cyanide, respectively. Consequently, synergistic catalysis was realized. The enantioselectivity of the different aldehydes and stereochemical configuration of the resulting products are attributed to the formation of a steric chiral pocket via the external chiral ligands on the clusters. In addition, heterogeneous asymmetric cyanosilylation using (R)/(S)-Co₃Ln₂ chiral metal clusters achieved high chemoselectivity and regioselectivity under mild conditions.

Enantioselective Copper-Catalyzed Intermolecular Cyanobenzoyldifluoromethylation of Alkenes: Access to Chiral β-Difluoroacyl Nitriles

A novel asymmetric copper-catalyzed intermolecular cyanobenzoyldifluoromethylation of alkenes with iododifluoromethyl ketones and TMSCN has been reported, which provides a particularly valuable route to access chiral β-difluoroacyl nitriles with excellent enantioselectivities. The method permits the efficient cyanation of varied β-difluoroacyl-benzylic radicals in mild conditions with high functional group tolerance. The reaction proceeds through a radical pathway. In order to get insight into the stereochemical outcome, computational mechanistic studies were conducted.

Ni-Catalyzed enantioselective reductive arylcyanation/cyclization of N-(2-iodo-aryl) acrylamide

A Ni/(S,S)-BDPP-catalyzed intramolecular Heck cyclization of N-(2-iodo-aryl) acrylamide with 2-methyl-2-phenylmalononitrile was developed to give oxindoles with good enantioselectivities. We found that utilizing such an electrophilic cyanation reagent could tackle the deleterious effect of the coordinative cyanide ion in the asymmetric alkene arylcyanation.

Me2(CH2CH)SiCN: a bifunctional ethylene equivalent for Diels–Alder reaction based controllable tandem synthesis

A bifunctional silyl reagent Me₂(CH₂CH)SiCN has been developed as a novel ethylene equivalent for the Diels–Alder (DA) reaction. The use of this reagent enables the controllable synthesis of value-added cyclohexenyl ketones or 2-acyl cyclohexancarbonitrile derivatives through a five- or six-step tandem sequence based on a Wittig/cyanosilylation/DA reaction/retro-cyanosilylation/isomerization sequence that involves a temporary silicon-tethered intramolecular DA reaction.

We report an unprecedented tandem Wittig/cyanosilylation/DA reaction/retro-cyanosilylation/isomerization sequence by using our designed bifunctional ethylene equivalent Me₂(CH₂CH)SiCN.

Enantioselective Synthesis of Cα-Tetrasubstituted N-Hydroxyl-α-amino Nitriles via Cyanation of Ketonitrones Using Me2(CH2Cl)SiCN

Here, we report an unprecedented catalytic enantioselective cyanation of ketonitrones enabled by the bifunctional cyanating reagent Me₂(CH₂Cl)SiCN. This approach allows facile access to optically active N-hydroxyl-α-amino nitriles that are of high synthetic value but difficult to acquire by other methods. The use of bifunctional cyanating reagent Me₂(CH₂Cl)SiCN not only achieves an enantioselectivity higher than that with TMSCN but also enables various diversification reactions of the resulting silylated adducts. This represents the first enantioselective catalytic nucleophilic addition reaction of unactivated ketone-derived nitrones, exhibiting the potential of such tetrasubstituted C═N bonds for asymmetric synthesis of N-hydroxy α-amino acids and other N-hydroxy tertiary amines.

Metal-to-Ligand Ratio-Dependent Chemodivergent Asymmetric Synthesis

Chemodivergent asymmetric synthesis was achieved by tuning the metal-to-ligand ratio in an organometallic catalytic system. Using N-(aroyloxy)phthalimide as the precursor of either an oxygen-centered aroyloxy radical or a nitrogen-centered phthalimidyl radical, enantioselective oxocyanation or aminocyanation of alkenes was achieved separately through a dual photoredox and copper catalysis. The metal-to-ligand ratio can exert chemoselective control while retaining the high enantiopurity of divergent products. Both reactions proceed efficiently with catalyst loading as low as 0.2 mol % and can be performed on a gram scale without loss of chemoselectivity or enantioselectivity. Chemodivergent asymmetric 1,5-aminocyanation or 1,5-oxocyanation of vinylcyclopropane can also be realized by this protocol. Mechanistic investigations involving electron paramagnetic resonance (EPR) experiments were performed to shed light on the stereochemical and chemodivergent results.