Enantioselective Copper-Catalyzed Reductive Coupling of Alkenylazaarenes with Ketones

Phosphoric Acid-Catalyzed Alkene Difunctionalization of 2-Vinylpyridines via HOMO/LUMO Biactivated Diels-Alder Reaction

The difunctionalization of vinylpyridines based on the cyclization strategy remains rare and underdeveloped, in contrast to the well-developed hydrogen functionalization. Current exploration on [4 + 2] cyclization of vinylpyridines mainly relies on extremely high temperatures and the LUMO activation of vinylpyridines using boron trifluoride as a strong Lewis acid. Herein, we established a phosphoric acid-catalyzed [4 + 2] cyclization reaction of 3-vinyl-1H-indoles and 2-vinylpyridines by means of the LUMO/HOMO bifunctional activation model. This protocol features mild reaction conditions, high functional group tolerance, broad substrate compatibility, and high diastereoselectivity, enabling the efficient construction of various functionalized pyridine-substituted tetrahydrocarbazoles with prominent potential in drug discovery.

Chiral phosphoric acid-catalyzed asymmetric epoxidation of alkenyl aza-heteroarenes using hydrogen peroxide

The synthesis of chiral α-azaheteroaryl oxiranes via enantioselective catalysis is a formidable challenge due to the required complex stereoselectivity and diverse N-heterocyclic structures. These compounds play a crucial role in developing bioactive molecules, where precise chirality significantly influences biological activity. Here we show that using chiral phosphoric acid as a catalyst, our method efficiently addresses these challenges. This technique not only achieves high enantio- and diastereoselectivity but also demonstrates superior chemo- and stereocontrol during the epoxidation of alkenyl aza-heteroarenes. Our approach leverages a synergistic blend of electrostatic and hydrogen-bonding interactions, enabling the effective activation of both substrates and hydrogen peroxide. The resulting chiral oxiranes exhibit enhanced diversity and functionality, aiding the construction of complex chiral azaaryl compounds with contiguous stereocenters. Kinetic and density functional theory studies elucidate the mechanism, highlighting chiral phosphoric acid's pivotal role in this intricate enantioselective process.

Switchable supramolecular helices for asymmetric stereodivergent catalysis

Despite recent developments on the design of dynamic catalysts, none of them have been exploited for the in-situ control of multiple stereogenic centers in a single molecular scaffold. We report herein that it is possible to obtain in majority any amongst the four possible stereoisomers of an amino alcohol by means of a switchable asymmetric catalyst built on supramolecular helices. Hydrogen-bonded assemblies between a benzene-1,3,5-tricarboxamide (BTA) achiral phosphine ligand coordinated to copper and a chiral BTA comonomer are engaged in a copper-hydride catalyzed hydrosilylation and hydroamination cascade process. The nature of the product stereoisomer is related to the handedness of the helices and can thus be directed in a predictable way by changing the nature of the major enantiomer of the BTA comonomer present in the assemblies. The strategy allows all stereoisomers to be obtained one-pot with similar selectivities by conducting the cascade reaction in a concomitant manner, i.e. without inverting the handedness of the helices, or sequentially, i.e. by switching the handedness of the supramolecular helices between the hydrosilylation and hydroamination steps. Supramolecular helical catalysts appear as a unique and versatile platform to control the configuration of molecules or polymers embedding several stereogenic centers.

NiH-Catalyzed Regio- and Enantioselective Hydroalkylation for the Synthesis of β- or γ-Branched Chiral Aromatic N-Heterocycles

A nickel hydride-catalyzed regio- and enantioselective hydroalkylation reaction was developed to give access to a library of chiral β- or γ-branched aromatic N-heterocycles. This intriguing asymmetric transformation features excellent selectivities, step- and atom-economies, and generating two kinds of chiral products through one synthetic strategy. Furthermore, the possible reaction mechanism was extensively investigated using numerous control experiments and density functional theory calculations.

Dynamic kinetic asymmetric arylation and alkenylation of ketones

Despite the importance of enantioenriched alcohols in medicinal chemistry, total synthesis, and materials science, the efficient and selective construction of enantioenriched tertiary alcohols bearing two contiguous stereocenters has remained a substantial challenge. We report a platform for their preparation through the enantioconvergent, nickel-catalyzed addition of organoboronates to racemic, nonactivated ketones. We prepared several important classes of α,β-chiral tertiary alcohols in a single step with high levels of diastereo- and enantioselectivity through a dynamic kinetic asymmetric addition of aryl and alkenyl nucleophiles. We applied this protocol to modify several profen drugs and to rapidly synthesize biologically relevant molecules. We expect this nickel-catalyzed, base-free ketone racemization process to be a widely applicable strategy for the development of dynamic kinetic processes.

Selective Reductive Coupling of Vinyl Azaarenes and Alkynes via Photoredox Cobalt Dual Catalysis

A visible light-induced Co-catalyzed highly regio- and stereoselective reductive coupling of vinyl azaarenes and alkynes has been developed. Notably, Hünig's base together with simple ethanol has been successfully applied as the hydrogen sources instead of commonly used Hantzsch esters in this catalytic photoredox reaction. This approach has considerable advantages for the straightforward synthesis of stereodefined multiple substituted alkenes bearing an azaarene motif, such as excellent regioselectivity (>20 : 1 for >30 examples) and stereoselectivity (>20 : 1 E/Z), broad substrate scope and good functional group compatibility under mild reaction conditions, which has been utilized in the concise synthesis of natural product monomorine I. A reasonable catalytic reaction pathway involving protolysis of the cobaltacyclopentene intermediate has been proposed based on the mechanistic studies.

Dual-Catalytic Enantioselective Allylation of N-(Heteroaromatic-methyl)imine Derivatives

We report the dual-catalytic enantioselective allylic alkylation of 2-(pyridylmethyl)amine-derived ketimines with allylic carbonates. The reaction proceeds under mild reaction conditions to generate α-amino heteroaryl benzylamine stereocenters in good yield and enantioselectivity. Enantioselectivity is achieved through the use of a copper catalyst modified with chiral bisphosphine ligand (2S,4S)-bis(diphenylphosphino)pentane.

Enantioselective Conjugate Addition of Alkenyl Trifluoroborates to Alkenyl-Substituted Benzimidazoles Catalyzed by Chiral Binaphthols

The enantioselective organocatalytic conjugate alkenylation of β-substituted alkenyl benzimidazoles afforded β-stereogenic 2-alkyl benzimidazole derivatives in excellent enantioselectivities. Chiral binaphthols were effective catalysts for promoting the nucleophilic addition of bench-stable alkenyl trifluoroborate salts under mild conditions, expanding their applications by utilizing C=N-containing azaarenes as activating groups. The synthetic utility of this strategy is demonstrated by conversions into several useful enantiomerically enriched benzimidazole building blocks.

Confronting the Challenging Asymmetric Carbonyl 1,2-Addition Using Vinyl Heteroarene Pronucleophiles: Ligand-Controlled Regiodivergent Processes through a Dearomatized Allyl-Cu Species

The selective reductive coupling of vinyl heteroarenes with aldehydes and ketones represents a versatile approach for the rapid construction of enantiomerically enriched secondary and tertiary alcohols, respectively. Herein, we demonstrate a CuH-catalyzed regiodivergent coupling of vinyl heteroarenes with carbonyl-containing electrophiles, in which the selectivity is controlled by the ancillary ligand. This approach leverages an in situ generated benzyl- or dearomatized allyl-Cu intermediate, yielding either the dearomatized or exocyclic addition products, respectively. The method exhibits excellent regio-, diastereo-, and enantioselectivity and tolerates a range of common functional groups and heterocycles. The dearomative pathway allows direct access to a variety of functionalized saturated heterocyclic structures. The reaction mechanism was probed using a combination of experimental and computational approach. Density functional theory studies suggest that the ligand-controlled regioselectivity results from the C-H/π interaction and steric repulsion in transition states, leading to the major and minor regioisomers, respectively. Hydrocupration of vinyl heteroarene pronucleophile is the enantiodetermining step, whereas the diastereoselectivity is enforced by steric interactions between the benzylic or allyl-Cu intermediate and carbonyl-containing substrates in a six-membered cyclic transition state.

Cathodic Regioselective Coupling of Unactivated Aliphatic Ketones with Alkenes

A regioselective coupling of aliphatic ketones with alkenes has been realized by cathodic reduction. This reaction enables the formation of ketyl radicals and the activation of challenging alkenes under mild electrolysis conditions, providing an effective protocol for accessing diverse tertiary alcohols with substrate-dependent regioselectivity. The practicability of this reaction is demonstrated by scale-up experiments. The hydrogen source for the products, the migration isomerization of allylarenes, and the applicability of internal alkenes are demonstrated by control experiments.

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

We present here a review of the photochemical and electrochemical applications of multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis. MS-PCETs are redox mechanisms in which both an electron and a proton are exchanged together, often in a concerted elementary step. As such, MS-PCET can function as a non-classical mechanism for homolytic bond activation, providing opportunities to generate synthetically useful free radical intermediates directly from a wide variety of common organic functional groups. We present an introduction to MS-PCET and a practitioner's guide to reaction design, with an emphasis on the unique energetic and selectivity features that are characteristic of this reaction class. We then present chapters on oxidative N-H, O-H, S-H, and C-H bond homolysis methods, for the generation of the corresponding neutral radical species. Then, chapters for reductive PCET activations involving carbonyl, imine, other X═Y π-systems, and heteroarenes, where neutral ketyl, α-amino, and heteroarene-derived radicals can be generated. Finally, we present chapters on the applications of MS-PCET in asymmetric catalysis and in materials and device applications. Within each chapter, we subdivide by the functional group undergoing homolysis, and thereafter by the type of transformation being promoted. Methods published prior to the end of December 2020 are presented.

Copper-Catalyzed Enantioselective Reductive Aldol Reaction of α,β-Unsaturated Carboxylic Acids to Ketones: Silanes as Activator and Transient Protecting Group

We have developed the first enantioselective reductive aldol reaction of unprotected α,β-unsaturated carboxylic acids by employing a copper/bisphosphine catalyst. The reaction features in situ protection and activation of an α,β-unsaturated carboxylic acid by a hydrosilane. The copper enolate formed in situ reacts with a ketone to afford the β-hydroxy carboxylic acid with excellent enantioselectivity (up to 99% ee). The corresponding gram-scale reaction with a low catalyst loading and the derivatization of the β-hydroxy carboxylic acids highlight the practicality of this transformation.

Copper(I)-Catalyzed Asymmetric Synthesis of Unnatural α-Amino Acid Derivatives and Related Peptides Containing γ-(aza)Aryls

Chiral α-amino acids are indispensable compounds in organic chemistry, biochemistry, and medicinal chemistry. Herein, by means of copper(I)-catalyzed asymmetric conjugate addition of derivatives of glycine, serine, cysteine, and β-amino-alanine to electron-deficient vinyl(aza)arenes, an array of novel unnatural chiral α-amino acid derivatives bearing a γ-(aza)aryl is prepared in moderate to high yields with high enantioselectivity. Various azaarenes, such as pyrimidine, 1,3,5-triazine, pyridine, pyridine-N-oxide, quinoline, quinoxaline, purine, benzo[d]imidazole, benzothiazole, and 1,2,4-oxadiazole, are well tolerated. Moreover, the electrophiles are nicely extended to (Z)/(E) mixtures of electron-deficient butadienylpyridine and benzene, which are transformed to the corresponding chiral α-amino acid derivatives in high (E)/(Z) ratio and high enantioselectivity. More importantly, the present methodology is successfully applied in the catalytic asymmetric functionalization of Schiff bases derived from peptides, which finally afforded a new chiral tripeptide bearing two electron-deficient azaaryls and one electron-deficient aryl in high total yield with high diastereo- and excellent enantioselectivities.

Allenes and Dienes as Chiral Allylmetal Pronucleophiles in Catalytic Enantioselective C=X Addition: Historical Perspective and State-of-The-Art Survey

The use of allenes and 1,3-dienes as chiral allylmetal pronucleophiles in intermolecular catalytic enantioselective reductive additions to aldehydes, ketones, imines, carbon dioxide and other C=X electrophiles is exhaustively catalogued together with redox-neutral hydrogen auto-transfer processes. Coverage is limited to processes that result in both C-H and C-C bond formation. The use of alkynes as latent allylmetal pronucleophiles and multicomponent C=X allylations involving allenes and dienes is not covered. As illustrated in this review, the ability of allenes and 1,3-dienes to serve as tractable non-metallic pronucleophiles has evoked many useful transformations that have no counterpart in traditional allylmetal chemistry.

CuH-Catalyzed Regio- and Enantioselective Hydrocarboxylation of Allenes: Toward Carboxylic Acids with Acyclic Quaternary Centers

We report a method to prepare α-chiral carboxylic acid derivatives, including those bearing all-carbon quaternary centers, through an enantioselective CuH-catalyzed hydrocarboxylation of allenes with a commercially available fluoroformate. A broad range of heterocycles and functional groups on the allenes were tolerated in this protocol, giving enantioenriched α-quaternary and tertiary carboxylic acid derivatives in good yields with exclusive branched regioselectivity. The synthetic utility of this approach was further demonstrated by derivatization of the products to afford biologically important compounds, including the antiplatelet drug indobufen.

Asymmetric Conjugate Addition of Chiral Secondary Borylalkyl Copper Species

We report the diastereo- and enantioselective conjugate addition of chiral secondary borylalkyl copper species derived from borylalkenes in situ to α,β-unsaturated diesters. In the presence of a chiral bisphosphine-ligated CuH catalyst, the conjugate addition provides a direct access to enantioenriched alkylboron compounds containing two contiguous carbon stereogenic centers in good yield with high diastereo- and enantioselectivity (up to >98:2 dr, >99:1 er) by assembling readily available starting alkenyl reagents in a single operation without using preformed organometallic reagents or chiral auxiliaries. The resulting products were used in various organic transformations. The utility of the synthetic approach was highlighted by the synthesis of (-)-phaseolinic acid.

Palladium-Catalyzed Allyl-Allyl Reductive Coupling of Allylamines or Allylic Alcohols with H2 as Sole Reductant

Catalytic carbon-carbon bond formation building on reductive coupling is a powerful method for the preparation of organic compounds. The identification of environmentally benign reductants is key for establishing an efficient reductive coupling reaction. Herein an efficient strategy enabling H₂ as the sole reductant for the palladium-catalyzed allyl-allyl reductive coupling reaction is described. A wide range of allylamines and allylic alcohols as well as allylic ethers proceed smoothly to deliver the C-C coupling products under 1 atm of H₂. Kinetic studies suggested that the dinuclear palladium species was involved in the catalytic cycle.

Ruthenium catalyzed β-selective alkylation of vinylpyridines with aldehydes/ketones via N2H4 mediated deoxygenative couplings

Umpolung (polarity reversal) tactics of aldehydes/ketones have greatly broadened carbonyl chemistry by enabling transformations with electrophilic reagents and deoxygenative functionalizations. Herein, we report the first ruthenium-catalyzed β-selective alkylation of vinylpyridines with both naturally abundant aromatic and aliphatic aldehyde/ketones via N₂H₄ mediated deoxygenative couplings. Compared with one-electron umpolung of carbonyls to alcohols, this two-electron umpolung strategy realized reductive deoxygenation targets, which were not only applicable to the regioselective alkylation of a broad range of 2/4-alkene substituted pyridines, but also amenable to challenging 3-vinyl and steric-embedded internal pyridines as well as their analogous heterocyclic structures.

Ruthenium-catalyzed β-selective alkylation of vinylpyridines with carbonyls (both aromatic and aliphatic ketones/aldehydes) via N₂H₄ mediated deoxygenative couplings was achieved.

Electroreductive Olefin-Ketone Coupling

A user-friendly approach is presented to sidestep the venerable Grignard addition to unactivated ketones to access tertiary alcohols by reversing the polarity of the disconnection. In this work a ketone instead acts as a nucleophile when adding to simple unactivated olefins to accomplish the same overall transformation. The scope of this coupling is broad as enabled using an electrochemical approach, and the reaction is scalable, chemoselective, and requires no precaution to exclude air or water. Multiple applications demonstrate the simplifying nature of the reaction on multistep synthesis, and mechanistic studies point to an intuitive mechanism reminiscent of other chemical reductants such as SmI₂ (which cannot accomplish the same reaction).

Asymmetric Synthesis of 1,2-Dihydronaphthalene-1-ols via Copper-Catalyzed Intramolecular Reductive Cyclization

We describe a copper-catalyzed intramolecular reductive cyclization of easily accessible benz-tethered 1,3-dienes containing a ketone moiety. This process provided biologically active 1,2-dihydronaphthalene-1-ol derivatives in good yields with excellent enantio- and diastereoselectivity. Mechanistic investigations using density functional theory revealed that (Z)- and (E)-allylcopper intermediates formed in situ from the diene and copper catalyst undergo isomerization and selective intramolecular allylation of the (E)-allylcopper form of the major product through a six-membered boatlike transition state. The resulting products were further transformed to fully saturated naphthalene-1-ols by reactions of the olefin moiety.

Enantioselective [4 + 2] Cycloaddition Reaction of Vinylquinolines with Dienals Enabled by Synergistic Organocatalysis

An unprecedented organocatalytic enantioselective [4 + 2] cycloaddition reaction of vinyl quinolines with dienals is achieved with the synergistic activation of CH₃SO₃H and a chiral aminocatalyst. The power of the process is demonstrated by its high efficiency of the production of new synthetically and biologically valued chiral quinoline architectures in high yields and with excellent enantioselectivities.

CuH-Catalyzed Olefin Functionalization: From Hydroamination to Carbonyl Addition

In organic synthesis, ligand-modified copper(I) hydride (CuH) complexes have become well-known reagents and catalysts for selective reduction, particularly toward Michael acceptors and carbonyl compounds. Recently, our group and others have found that these hydride complexes undergo migratory insertion (hydrocupration) with relatively unactivated and electronically unpolarized olefins, producing alkylcopper intermediates that can be leveraged to forge a variety of useful bonds. The resulting formal hydrofunctionalization reactions have formed the basis for a resurgence of research in CuH catalysis. This Account chronicles the development of this concept in our research group, highlighting its origin in the context of asymmetric hydroamination, evolution to more general C-X bond-forming reactions, and applications in the addition of olefin-derived nucleophiles to carbonyl derivatives.Hydroamination, the formal insertion of an olefin into the N-H bond of an amine, is a process of significant academic and industrial interest, due to its potential to transform widely available alkenes and alkynes into valuable complex amines. We developed a polarity-reversed strategy for catalytic enantioselective hydroamination relying on the reaction of olefins with CuH to generate chiral organocopper intermediates, which are intercepted by electrophilic amine reagents. By engineering the auxiliary ligand, amine electrophile, and reaction conditions, the scope of this method has since been extended to include many types of olefins, including challenging internal olefins. Further, the scope of amine reagents has been expanded to enable the synthesis of primary, secondary, and tertiary amines as well as amides, N-alkylated heterocycles, and anilines. All of these reactions exhibit high regio- and stereoselectivity and, due to the mild conditions required, excellent tolerance for heterocycles and polar functional groups.Though the generation of alkylcopper species from olefins was originally devised as a means to solve the hydroamination problem, we soon found that these intermediates could react efficiently with an unexpectedly broad range of electrophiles, including alkyl halides, silicon reagents, arylpalladium species, heterocycles, and carbonyl derivatives. The general ability of olefins to function as precursors for nucleophilic intermediates has proved particularly advantageous in carbonyl addition reactions because it overcomes many of the disadvantages associated with traditional organometallic reagents. By removing the need for pregeneration of the nucleophile in a separate operation, CuH-catalyzed addition reactions of olefin-derived nucleophiles feature improved step economy, enhanced functional group tolerance, and the potential for catalyst control over regio- and stereoselectivity. Following this paradigm, feedstock olefins such as allene, butadiene, and styrene have been employed as reagents for asymmetric alkylation of ketones, imines, and aldehydes.

Synthesis of Pyrroles through the CuH-Catalyzed Coupling of Enynes and Nitriles

Herein, we describe an efficient method to prepare polysubstituted pyrroles via a copper hydride (CuH)-catalyzed enyne-nitrile coupling reaction. This protocol accommodates both aromatic and aliphatic substituents and a broad range of functional groups, providing a variety of N-H pyrroles in good yields and with high regioselectivity. We propose that the Cu-based catalyst promotes both the initial reductive coupling and subsequent cyclization steps. Density functional theory (DFT) calculations were performed to elucidate the reaction mechanism.

Nickel(II)-Catalyzed Addition of Aryl-, Alkenyl-, and Alkylboronic Acids to Alkenylazaarenes

A nickel(II)-catalyzed addition of aryl-, alkenyl-, and alkylboronic acids to alkenylazaarenes was presented. This reaction exhibited high efficiency (up to 93% yield), a broad substrate scope (seven types of heterocycles), and good functional group compatibility. The resulting products can be further transformed to many useful building blocks. Finally, the preliminary studies suggested that the adjacent N atom of the heterocycles was essential for the high reactivity.

Catalytic Reductive Aldol and Mannich Reactions of Enone, Acrylate, and Vinyl Heteroaromatic Pronucleophiles

Catalytic reductive coupling of enone, acrylate, or vinyl heteroaromatic pronucleophiles with carbonyl or imine partners offers an alternative to base-mediated enolization in aldol- and Mannich-type reactions. In this review, direct catalytic reductive aldol and Mannich reactions are exhaustively catalogued on the basis of metal or organocatalyst. Stepwise processes involving enone conjugate reduction to form discrete enol or (metallo)enolate derivatives followed by introduction of carbonyl or imine electrophiles and aldol reactions initiated via enone conjugate addition are not covered.

Direct Stereoconvergent Allylation of Chiral Alkylcopper Nucleophiles with Racemic Allylic Phosphates

Copper-catalyzed stereoconvergent allylation of chiral sp³ -hybridized carbon nucleophiles with a racemic mixture of acyclic secondary allylic phosphates is reported. In the presence of a copper-catalyst complexed with chiral BenzP* ligand, tandem coupling reaction of vinyl arenes, bis(pinacolato)diboron, and racemic allylic phosphates provided β-chiral alkylboronates possessing (E)-alkenyl moiety through a direct stereoconvergent allylic coupling with concomitant generation of a C(sp³ )-stereogenic center. A range of vinyl (hetero)arenes and secondary allylic phosphates bearing 1°, 2°, 3° alkyl and phenyl α-substituents were suitable for the reaction, forming products with high enantioselectivities up to 95 % ee. Density functional theory calculations were conducted in detail to elucidate the origin of the observed regioselectivity of borylcupration and stereoconvergent (E)-olefin formation from racemic allylic phosphates.

Reductive Hydroxymethylation of 4-Heteroarylpyridines

The activation of pyridinium salts with electron-withdrawing heterocycles enables an iridium-catalyzed reductive hydroxymethylation reaction to proceed smoothly, facilitating the preparation of useful 3D heteroaryl-substituted functionalized piperidines. The methodology is used to prepare 3-hydroxymethylated analogues of pharmaceutical agents. Mechanistically, formaldehyde acts as both a hydride donor and the electrophile, leading to the formation of two new carbon-hydrogen bonds and one new carbon-carbon bond under relatively mild conditions.

Cooperative photoredox and chiral hydrogen-bonding catalysis

Chiral hydrogen-bonding catalysis is a classic strategy in asymmetric organocatalysis. Recently, it has been used to cooperate with photoredox catalysis, becoming a powerful tool to access optical pure compounds via radical-based transformations.

Copper-catalyzed asymmetric silyl addition to alkenyl-substituted N-heteroarenes

Asymmetric conjugate addition of PhMe₂SiBPin to a wide range of N-heteroaryl alkenes proceeded in the presence of a copper catalyst coordinated with a chiral phosphoramidite ligand to afford useful β-silyl N-heteroarenes in high yields and ees.

Engaging Aldehydes in CuH-Catalyzed Reductive Coupling Reactions: Stereoselective Allylation with Unactivated 1,3-Diene Pronucleophiles

Recently, CuH-catalyzed reductive coupling processes involving carbonyl compounds and imines have become attractive alternatives to traditional methods for stereoselective addition because of their ability to use readily accessible and stable olefins as surrogates for organometallic nucleophiles. However, the inability to use aldehydes, which usually reduce too rapidly in the presence of copper hydride complexes to be viable substrates, has been a major limitation. Shown here is that by exploiting relative concentration effects through kinetic control, this intrinsic reactivity can be inverted and the reductive coupling of 1,3-dienes with aldehydes achieved. Using this method, both aromatic and aliphatic aldehydes can be transformed into synthetically valuable homoallylic alcohols with high levels of diastereo- and enantioselectivities, and in the presence of many useful functional groups. Furthermore, using a combination of theoretical (DFT) and experimental methods, important mechanistic features of this reaction related to stereo- and chemoselectivities were uncovered.

Enantioselective Alkylation of 2-Alkylpyridines Controlled by Organolithium Aggregation

Direct enantioselective α-alkylation of 2-alkylpyridines provides access to chiral pyridines via an operationally simple protocol that obviates the need for prefunctionalization or preactivation of the substrate. The alkylation is accomplished using chiral lithium amides as noncovalent stereodirecting auxiliaries. Crystallographic and solution NMR studies provide insight into the structure of well-defined chiral aggregates in which a lithium amide reagent directs asymmetric alkylation.

2-Azadienes as Enamine Umpolung Synthons for the Preparation of Chiral Amines

The development of new strategies for the preparation of chiral amines is an important objective in organic synthesis. In this Synpacts, we summarize our approach for catalytically accessing nucleophilic aminoalkyl metal species from 2-azadienes, and its application in generating a number of important but elusive chiral amine scaffolds. Reductive couplings with ketones and imines afford 1,2-amino tertiary alcohols and 1,2-diamines, respectively, whereas fluoroarylations of gem-difluoro-2-azadienes deliver α-trifluoromethylated benzylic amines.

CuH-Catalyzed Enantioselective Ketone Allylation with 1,3-Dienes: Scope, Mechanism, and Applications

Chiral tertiary alcohols are important building blocks for the synthesis of pharmaceutical agents and biologically active natural products. The addition of carbon nucleophiles to ketones is the most common approach to tertiary alcohol synthesis but traditionally relies on stoichiometric organometallic reagents that are difficult to prepare, sensitive, and uneconomical. We describe a mild and efficient method for the copper-catalyzed allylation of ketones using widely available 1,3-dienes as allylmetal surrogates. Homoallylic alcohols bearing a wide range of functional groups are obtained in high yield and with good regio-, diastereo-, and enantioselectivity. Mechanistic investigations using density functional theory (DFT) implicate the in situ formation of a rapidly equilibrating mixture of isomeric copper(I) allyl complexes, from which Curtin-Hammett kinetics determine the major isomer of the product. A stereochemical model is provided to explain the high diastereo- and enantioselectivity of this process. Finally, this method was applied to the preparation of an important drug, ( R)-procyclidine, and a key intermediate in the synthesis of several pharmaceuticals.