Access to S-Stereogenic Free Sulfoximines via Bifunctional Phosphonium Salt-Catalyzed Desymmetrization of Bisphenols

Chiral Brønsted Acid-Catalyzed Kinetic Resolution of Sulfoximines for the Synthesis of Benzothiadiazine-1-Oxides

Benzothiadiazine-1-oxide scaffolds with S-stereogenic centers are prevalent in bioactive and pharmaceutical molecules. Reported works mainly focused on the metal-catalyzed asymmetric C-H amination/cyclization reaction for the synthesis of benzothiadiazine-1-oxides. Here, we reported a chiral phosphoric acid-catalyzed kinetic resolution of sulfoximines, providing chiral benzothiadiazine-1-oxides and recovered chiral sulfoximines with moderate to good enantioselectivities (s factors up to 36.6).

Electrooxidative Rhodium(III)/Chiral Carboxylic Acid-Catalyzed Enantioselective C-H Annulation of Sulfoximines with Alkynes

The combination of achiral Cp*Rh(III) with chiral carboxylic acids (CCAs) represents an efficient catalytic system in transition metal-catalyzed enantioselective C-H activation. However, this hybrid catalysis is limited to redox-neutral C-H activation reactions and the adopt to oxidative enantioselective C-H activation remains elusive and pose a significant challenge. Herein, we describe the development of an electrochemical Cp*Rh(III)-catalyzed enantioselective C-H annulation of sulfoximines with alkynes enabled by chiral carboxylic acid (CCA) in an operationally friendly undivided cell at room temperature. A broad range of enantioenriched 1,2-benzothiazines are obtained in high yields with excellent enantioselectivities (up to 99 % yield and 98 : 2 er). The practicality of this method is demonstrated by scale-up reaction in a batch reactor with external circulation. A crucial chiral Cp*Rh(III) intermediate is isolated, characterized, and transformed, providing rational support for a Rh(III)/Rh(I) electrocatalytic cycle.

Kinetic Resolution of Sulfoximines via Asymmetric Organocatalyzed Formation of Benzothiadiazine-1-oxides

A catalytic kinetic resolution of sulfoximines has been developed through chiral phosphoric acid-catalyzed intramolecular dehydrative cyclizations. A variety of racemic sulfoximines bearing an ortho-amidophenyl moiety underwent asymmetric dehydrative cyclizations using this method, yielding both the recovered sulfoximines and benzothiadiazine-1-oxide products with good to high enantioselectivities (with s-factor up to 61). The diverse derivatizations of the chiral products into a wide range of S-stereogenic center-containing S,N-heterocycles have demonstrated the value of this method.

Nickel-Catalyzed Enantioselective Synthesis of Dienyl Sulfoxide

Sulfoxides are widely used in the pharmaceutical industry and as ligands in asymmetric catalysis. However, the efficient asymmetric synthesis of this structural motif remains limited. In this study, we disclosed a Ni-catalyzed enantioconvergent reaction that utilizes both racemic allenyl carbonates and β-sulfinyl esters. Our method employs cheap and more sustainable Ni(II) as a precatalyst and successfully overcomes the challenging poisoning effect and instability of sulfenate generated in situ. This enables the synthesis of a series of dienyl sulfoxides with enantioselectivity of up to 98 % ee. The product exhibits tremendous potential in various applications, including diastereoselective Diels-Alder reactions, coordination with transition metals, and incorporation into medicinal compounds, among others. Using a combination of experimental and computational methods, we have uncovered an interesting associated outersphere mechanism that contrasts with conventional mechanisms commonly observed in asymmetric transition metal catalysis.

Design and Application of Peptide-Mimic Phosphonium Salt Catalysts in Asymmetric Synthesis

Chiral phosphonium salt catalysis, traditionally classified as a type of phase transfer catalysis, has proven to be a powerful strategy for the stereoselective preparation of diverse optically active molecules. However, there still remain numerous forbidding issues of reactivity and selectivity in such well-known organocatalysis system. Accordingly, the development of new and high-performance phosphonium salt catalysts with unique chiral backbones is highly desirable, yet challenging. This Minireview describes the prominent endeavours in the development of a new family of chiral peptide-mimic phosphonium salt catalysts with multiple hydrogen-bonding donors and their applications in a plethora of enantioselective synthesis during the past few years. Hopefully, this minireview will pave a way for further developing much more efficient and privileged chiral ligands/catalysts featuring exclusively catalytic ability in asymmetric synthesis.

Synthesis of Sulfoximines by Copper-Catalyzed Oxidative Coupling of Sulfinamides and Aryl Boronic Acids

A novel copper-catalyzed cross-coupling reaction of sulfinamides and aryl boronic acids is developed. The reaction is highly chemoselective and stereospecific, which allows mild synthesis of optically pure sulfoximines with broad scope and functional group tolerance. The utility of this method is demonstrated by the asymmetric synthesis of pharmaceutical intermediates.

Isothiourea-Catalyzed Acylative Desymmetrization of Silicon-Centered Bisphenols

The preparation of optically pure organosilicon compounds bearing a stereogenic center at the silicon atom is an attractive but challenging enterprise. Herein we disclose an isothiourea (ITU)-catalyzed monoacylation reaction of silicon-centered bisphenols with 2,2-diphenylacetic pivalic anhydride, delivering tetrasubstituted organosilanes in moderate to excellent yields (36-91%) with moderate to excellent enantiomeric ratios (68:32-97.5:2.5). This organocatalytic desymmetrization approach can be performed on gram scale, and the products can be converted to other valuable compounds.

Asymmetric Synthesis of S(IV) and S(VI) Stereogenic Centers

Sulfur can form diverse S(IV) and S(VI) stereogenic centers, of which some have gained significant attention recently due to their increasing use as pharmacophores in drug discovery programs. The preparation of these sulfur stereogenic centers in their enantiopure form has been challenging, and progress made will be discussed in this Perspective. This Perspective summarizes different strategies, with selected works, for asymmetric synthesis of these moieties, including diastereoselective transformations using chiral auxiliaries, enantiospecific transformations of enantiopure sulfur compounds, and catalytic enantioselective synthesis. We will discuss the advantages and limitations of these strategies and will provide our views on how this field will develop.

One-Pot Tandem Oxidative Bromination and Amination of Sulfenamide for the Synthesis of Sulfinamidines

The sulfinamidines as aza analogues of sulfinamides received limited attention from both organic chemists and pharmaceutical chemists. Herein, we present a tandem oxidative/nucleophilic substitution approach for the synthesis of sulfinamidines in high yield (up to 98%). This cascade reaction method is enabled by N-bromosuccinimide (NBS) as an oxidant and diverse readily available amines as nucleophiles without any additives or catalysts. Notably, this method is highly time-economical, safe to operate, and easy to scale up and has excellent functional group compatibility.

Synthesis of Chiral Sulfonimidoyl Chloride via Desymmetrizing Enantioselective Hydrolysis

Direct construction of chiral S(VI) from prochiral S(II) is a formidable challenge due to the inevitable formation of stable chiral S(IV). Previous synthetic strategies rely on the conversion of chiral S(IV) or enantioselective desymmetrization of preformed symmetrical S(VI) substrates. Here, we report desymmetrizing enantioselective hydrolysis of in situ-generated symmetric aza-dichlorosulfonium from sulfenamides for the preparation of chiral sulfonimidoyl chlorides, which could be used as a general stable synthon for obtaining a series of chiral S(VI) derivatives.

Organocatalytic asymmetric deoxygenation of sulfones to access chiral sulfinyl compounds

Over the past decades, many efficient methodologies have been developed that allow for the enantioselective synthesis of chiral sulfinyl compounds. However, the enantioselective deoxygenation of hexavalent sulfones for the formation of chiral sulfinyl compounds still remains one of the major challenges in the fields of asymmetric synthesis and organosulfur chemistry. Here we have demonstrated that a synergistic combination of organocatalysis and the incorporation of a cyano group into the sulfone generates a chiral sulfinic species as an active intermediate. A wide range of chiral sulfinates with high enantioselectivities could then be acquired using alcohols as nucleophiles, and the subsequent transformations allowed the collective preparation of a variety of chiral sulfinyl compounds. Density functional theory calculations revealed that the catalytic cycle involves a quinuclidine-assisted stepwise 1,2-cyano group transfer, base-assisted intermolecular substitution with alcohol and regeneration of the active catalyst. The enantioselectivity was determined by the cyano migration step.

Enantioselective Synthesis of Atropisomeric Biaryl Phosphorus Compounds by Chiral-Phosphonium-Salt-Enabled Cascade Arene Formation

Axially chiral biaryl monophosphorus molecules, exemplified by atropisomeric 1,1'-biaryl aminophosphines, are significant motifs in numerous chiral ligands/catalysts. Developing efficient methods for preparing phosphorus compounds with these privileged motifs is an important endeavor in synthetic chemistry. Herein, we develop an effective, modular method by a chiral-phosphonium-salt-catalyzed novel cascade between phosphorus-containing nitroolefins and α,α-dicyanoolefins, leading to a great diversity of atropisomeric biaryls bearing phosphorus groups in high yields with excellent stereoselectivities. The reaction features include a Thorpe-type cycloaddition/oxidative hydroxylation/aromatization cascade pathway with a central-to-axial chirality transfer process. Insight gained from our studies is expected to advance general efforts towards the catalytic synthesis of atropisomeric biaryl phosphorus compounds, offering a platform for developing new efficient chiral ligands and catalysts.

Practical Asymmetric Synthesis of Chiral Sulfoximines via Sulfur-Selective Alkylation

Chiral sulfoximines have recently been considered as promising bioisosteres in medicinal chemistry. However, methods for preparing chiral sulfoximines in a stereoselective manner are underdeveloped. Herein, we demonstrate an asymmetric synthesis of chiral sulfoximines through a stereospecific S-alkylation of readily accessible chiral sulfinamides under practical conditions. A key to establishing the practical conditions was the identification of the intermediate structure in our previously reported S-alkylation by X-ray crystallographic analysis.