Amide Enolate Additions to Acylsilanes: In Situ Generation of Unusual and Stereoselective Homoenolate Equivalents

Photoredox/Copper-Catalyzed One-Pot Aminoalkylation/Cyclization of Alkenes with Primary Amines to Synthesize Polysubstituted γ-Lactams

Visible-light-driven chemical transformation has emerged as a powerful tool for the synthesis of γ-lactams. However, during this transformation, the α-bromoimides need to be pre-prepared. Herein, we report a photoreodox/copper-catalyzed one-pot three-component reaction of alkenes with primary amines for the construction of γ-lactams. In this transformation, the orthoquinones were generated via a photocatalytic pathway, followed by attack by Cu-amido complexes and intramolecular cyclization to give the γ-lactams. This method represents a simple synthetic route displaying broad functional group tolerance, including substrates bearing alcohols, ketones, heterocycles, esters, halides, alkynes, nitriles, ethers, etc.

Stereoselective Reductive Coupling Reactions Utilizing [1,2]-Phospha-Brook Rearrangement: A Powerful Umpolung Approach

[1,2]-Phospha-Brook rearrangement entails the generation of α-oxygenated carbanions via the umpolung process. Recently, these anionic species have been widely utilized for several C-C bond forming strategies, providing various useful frameworks that are difficult to access through conventional approaches. However, the application of this powerful methodology in the development of chiral strategies is still at the nascent stage due to challenges involved in controlling chemoselectivity and enantioselectivity. This synopsis provides a detailed summary of diastereo- and/or enantioselective chemical transformations using [1,2]-phospha-Brook rearrangement.

Asymmetric Hydrative Aldol Reaction (HAR) via Vinyl-Gold Promoted Intermolecular Ynamide Addition to Aldehydes

Herein, we reported an intermolecular asymmetric hydrative aldol reaction through vinyl-gold intermediate under ambient conditions. This tandem alkyne hydration and sequential nucleophilic addition afforded a "base-free" approach to β-hydroxy amides with high efficiency (up to 95 % yields, >50 examples). Vinyl gold intermediate was applied as reactive nucleophile and Fe(acac)3 was used as the critical co-catalyst to prevent undesired protodeauration, allowing this transformation to proceed under mild conditions with good functional group tolerance and excellent stereoselectivity (>20 : 1 d.r. and up to 99 % ee).

K2S2O8-Mediated Radical Cyclization of 1,6-Enyne for the Synthesis of Diiodonated γ-Lactams

A novel and convenient K₂S₂O₈-mediated diiodo cyclization of 1,6-enynes for the facile synthesis of functionalized γ-lactam derivatives has been developed. This reaction features mild and transition-metal-free conditions, which offer a green and efficient entry to synthetically important γ-lactam scaffolds. Mechanistic studies suggest that iodide radicals initiate the cascade cyclic transformation.

Coupling of α-bromoamides and unactivated alkenes to form γ-lactams through EDA and photocatalysis

γ-Lactams are prevalent in small-molecule pharmaceuticals and provide useful precursors to highly substituted pyrrolidines. Despite numerous methods for the synthesis of this valuable motif, previous redox approaches to γ-lactam synthesis from α-haloamides and olefins require additional electron withdrawing functionality as well as N-aryl substitution to promote electrophilicity of the intermediate radical and prevent competitive O-nucleophilicity about the amide. Using α-bromo imides and α-olefins, our strategy enables the synthesis of monosubstituted protected γ-lactams in a formal [3 + 2] fashion. These species are poised for further derivatization into more complex heterocyclic scaffolds, complementing existing methods. C-Br bond scission occurs through two complementary approaches, the formation of an electron donor-acceptor complex between the bromoimide and a nitrogenous base which undergoes photoinduced electron transfer, or triplet sensitization with photocatalyst, to furnish an electrophilic carbon-centered radical. The addition of Lewis acids allows for further increased electrophilicity of the intermediate carbon-centered radical, enabling tertiary substituted α-Br-imides to be used as coupling partners as well as internal olefins.

Cobalt-catalyzed direct α-hydroxymethylation of amides with methanol as a C1 source

Herein, we report a cobalt-catalyzed α-hydroxymethylation of amides with methanol under mild conditions. Using CoCl₂·6H₂O as an inexpensive and efficient catalyst, some important bioactive β-hydroxyamides were obtained in moderate to excellent yields. The developed method features a wide substrate scope and good functional group tolerance. In addition, anticholinergic tropicamide was easily synthesized in this way.

Direct synthesis and applications of solid silylzinc reagents

The increased synthetic utility of organosilanes has motivated researchers to develop milder and more practical synthetic methods. Silylzinc reagents, which are typically the most functional group tolerant, are notoriously difficult to synthesize because they are obtained by a pyrophoric reaction of silyllithium, particularly Me3SiLi which is itself prepared by the reaction of MeLi and disilane. Furthermore, the dissolved LiCl in silylzinc may have a detrimental effect. A synthetic method that can avoid silyllithium and involves a direct synthesis of silylzinc reagents from silyl halides is arguably the simplest and most economical strategy. We describe, for the first time, the direct synthesis of PhMe2SiZnI and Me3SiZnI reagents by employing a coordinating TMEDA ligand, as well as single crystal XRD structures. Importantly, they can be obtained as solids and stored for longer periods at 4 °C. We also demonstrate their significance in cross-coupling of various free alkyl/aryl/alkenyl carboxylic acids with broader functional group tolerance and API derivatives. The general applicability and efficiency of solid Me3SiZnI are shown in a wide variety of reactions including alkylation, arylation, allylation, 1,4-addition, acylation and more.

Ruthenium-catalyzed C-H amination of aroylsilanes

Acylsilane represents a valuable synthon in synthetic chemistry. We report on ruthenium(ii)-catalyzed ortho-C-H amination of aroylsilanes to provide facile access to synthetically useful imidobenzoylsilanes and tosyl-amidobenzoylsilanes. The protocols, with broad substrate scope and excellent functional group tolerance, are enabled with the weak chelation-assistance of acylsilane via C-H cyclometallation.

Radical coupling of β-ketoesters and amides promoted by Brønsted/Lewis acids

Recent advances in photocatalysis have enabled radical methods with complementary chemoselectivity to established two electron bond forming approaches. While this radical strategy has previously been limited to substrates with favorable redox potentials, Brønsted/Lewis acid activation has emerged as a means of facilitating otherwise difficult reductions. We report herein our investigations into the Lewis acid-promoted redox activation of β-ketocarbonyls in a model photocatalytic radical alkylation reaction. Rapid evaluation of substrates and reactions conditions was achieved by high throughput experimentation using 96-well plate photoreactors.

A Sequential Umpolung/Enzymatic Dynamic Kinetic Resolution Strategy for the Synthesis of γ-Lactones

Combining biological and small-molecule catalysts under a chemoenzymatic manifold presents a series of significant advantages to the synthetic community. We report herein the successful development of a two-step/single flask synthesis of γ-lactones through the merger of Umpolung catalysis with a ketoreductase-catalyzed dynamic kinetic resolution, reduction, and cyclization. This combined approach delivers highly enantio- and diastereoenriched heterocycles and demonstrates the feasibility of integrating NHC catalysis with enzymatic processes.

Aqueous ZnCl2 Complex Catalyzed Prins Reaction of Silyl Glyoxylates: Access to Functionalized Tertiary α-Silyl Alcohols

An efficient Prins reaction of silyl glyoxylates in the presence of an aqueous ZnCl₂ complex as a catalyst was developed, providing functionalized tertiary α-silyl alcohols in high yields under mild conditions. A preliminary investigation indicated that the aqueous ZnCl₂ complex acted as a dual functional catalyst of Brønsted and Lewis acid to activate the carbonyl groups of silyl glyoxylates via a dual-activation model.

Base-catalyzed C-alkylation of potassium enolates with styrenes via a metal-ene reaction: a mechanistic study

Base-catalyzed, C-alkylation of potassium (K) enolates with styrenes (CAKES) has recently emerged as a highly practical and convenient method for elaboration or synthesis of pharmaceutically-relevant cores. K enolate-type precursors such as alkyl-substituted heterocycles (pyridines, pyrazines and thiophenes), ketones, imines, nitriles and amides undergo C-alkylation reactions with styrene in the presence of KOtBu or KHMDS. Surprisingly, no studies have probed the reaction mechanism beyond the likely initial formation of a K enolate. Herein, a synergistic approach of computational (DFT), kinetic and deuterium labelling studies rationalizes various experimental observations and supports a metal-ene-type reaction for amide CAKES. Moreover, our approach explains experimental observations in other reported C-alkylation reactions of other enolate-type precursors, thus implicating a general mechanism for CAKES.

Cu-Catalyzed Carbonylative Silylation of Alkyl Halides: Efficient Access to Acylsilanes

A Cu-catalyzed carbonylative silylation of unactivated alkyl halides has been developed, enabling efficient synthesis of alkyl-substituted acylsilanes in high yield. A variety of functional groups are tolerated under the mild reaction conditions, and primary, secondary, and tertiary alkyl halides are all applicable. The practical utility of this method has been demonstrated in the synthesis of acylsilanes bearing different silyl groups as well as in situ reduction of a product to the corresponding α-hydroxylsilane in one pot. Mechanistic experiments indicate that a silylcopper intermediate activates alkyl halides by single electron transfer to form alkyl radical intermediates and that carbon-halogen bond cleavage is not involved in the rate-determining step.

BF3·OEt2-Catalyzed Vinyl Azide Addition to in Situ Generated N-Acyl Iminium Salts: Synthesis of 3-Oxoisoindoline-1-acetamides

BF₃·OEt₂-catalyzed nucleophilic addition of vinyl azides to in situ generated N-acyl iminium salts obtained from 3-hydroxyisoindolinones is described in this article. The procedure is operationally simple, mild, additive, and metal-free. The reaction proceeds smoothly at ambient temperature with a wide range of 3-hydroxyisoindol-1-ones and vinyl azides to afford 3-oxoisoindoline-1-acetamides (32 examples) in high yields (up to 97%). Furthermore, the synthetic utility of this methodology is depicted by exploiting the reactivity of an amide functionality in the products.

TBHP promoted demethylation of α-amino carbonyl compounds: a concise approach to substituted γ-lactams

A novel tert-butyl hydroperoxide (TBHP) promoted CH₂-extrusion reaction of α-amino carbonyl compounds has been developed, which is driven by a demethylenation process to give various ring contraction products γ-lactams under radical conditions.

Divergent synthesis of polysubstituted cyclopropanes and β-silyoxy imidates via switchable additions of N-tert-butanesulfinylimidates to acylsilanes

A switchable addition of N-tert-butanesulfinylimidates to acylsilanes leads to divergent synthesis of polysubstituted cyclopropanes and β-silyloxy imidates.

Intramolecular nitration–aminocarbonylation of unactivated olefins: metal-free synthesis of γ-lactams

A novel, metal-free synthesis of valuable γ-lactams through the radical-mediated nitration–aminocarbonylation of unactivated olefins is reported.

Three-component reaction to synthesize E-vinyl silyl anti-1,2-diols via sequential [1,4]-O-to-O/[1,4]-C-to-O silyl migrations

A three-component reaction of geminal bis(silyl) allyl silyl ether, aldehyde and electrophile has been developed to synthesize trisubstituted E-vinyl silyl anti-1,2-diols. The approach features a sequential [1,4]-O-to-O/[1,4]-C-to-O silyl migrations process.

A catalyst-controlled switchable reaction of β-keto acids to silyl glyoxylates

A catalyst-controlled switchable reaction of β-keto acids to silyl glyoxylates was developed and the decarboxylative-addition products were generated by using a thiourea catalyst.

Visible light-induced aerobic oxidative cross-coupling of glycine esters with α-angelicalactone: a facile pathway to γ-lactams

A rapid synthesis of substituted γ-lactams is achieved via metal-free photocatalyzed aerobic oxidative dehydrogenative formal [2 + 3] cyclization of glycine esters with α-angelicalactone.

C-Alkylation of N-alkylamides with styrenes in air and scale-up using a microwave flow reactor

C-Alkylation of N-alkylamides with styrenes is reported, proceeding in ambient air/moisture to give arylbutanamides and other pharmaceutically-relevant scaffolds in excellent mass balance.

3-Hydroxy-2-(trialkylsilyl)phenyl Triflate: A Benzyne Precursor Triggered via 1,3-C-sp2-to-O Silyl Migration

3-Hydroxy-2-(trialkylsilyl)phenyl triflates are presented as new versatile hydroxyaryne precursors. These are base-activated aryne precursors induced via a C-sp²-to-O 1,3-Brook rearrangement. The reaction of various arynophiles and 3-trialkylsiloxybenzyne generated from 3-hydroxy-2-(trialkylsilyl)phenyl triflate efficiently afforded highly regioselective phenol derivatives. Furthermore, through crossover experiments, the intramolecular mechanism of silyl migration was demonstrated.

Enantioselective synthesis of chiral acylsilanes by copper/HZNU-Phos-catalyzed asymmetric conjugate addition of diethyzinc to α,β-unsaturated acylsilanes

The catalytic asymmetric copper-catalyzed conjugate addition of diethylzinc reagent to α,β-unsaturated acylsilanes was found to proceed smoothly in moderate to good yields and enantioselectivities (up to 85% ee) in the presence of the multifunctional HZNU-Phos.

Organobase-catalyzed [1,2]-Brook rearrangement of silyl glyoxylates

A highly efficient [1,2]-Brook rearrangement of silyl glyoxylates has been developed using DBU as the organo-base catalyst.

Silyllithium-Initiated Coupling of α-Ketoamides with tert-Butanesulfinylimines for Stereoselective Synthesis of Enantioenriched α-(Silyloxy)-β-amino Amides

A silyllithium-initiated coupling of α-ketoamides with tert-butanesulfinylimines was developed for the efficient, stereoselective synthesis of enantioenriched α-(silyloxy)-β-amino amides. Nucleophilic addition of silyllithium to α-ketoamides, followed by 1,2-Brook rearrangement, generates nucleophilic enolates, which are then intercepted by chiral imines to provide three-component coupling products. Use of α-ketoamides is critical for achieving high yields and diastereoselectivities in the resulting α-hydroxy-β-amino acid derivatives.

Carbamoyl anion-initiated cascade reaction for stereoselective synthesis of substituted α-hydroxy-β-amino amides

A carbamoyl anion-initiated cascade reaction with acylsilanes and imines allows rapid construction of substituted α-hydroxy-β-amino amides in high yields with excellent diastereoselectivities.

Direct transformation of amides: a one-pot reductive Ugi-type three-component reaction of secondary amides

An efficient reductive Ugi-type reaction employing common secondary amides as starting materials has been established. The reaction exhibited a broad substrate scope, good chemoselectivity and functional group tolerance.