Enantioselective Reduction and Sulfenylation of Isoflavanone Derivatives via Bisguanidinium Hypervalent Silicate

In this work, we describe an enantioselective reduction and sulfenylation of isoflavanone derivatives by an ion pair strategy. The chiral cationic catalyst bisguanidinium (BG) is capable of chiral induction in catalytic systems. Silane hydride works as a reductant and helps to form an anionic hypervalent silicate complex and intermediates with substrates to pair with chiral catalyst. A series of umpolung sulfur reagents accomplish electrophilic attack in the presence of a silicate anion. Both chemoselectivity and enantioselectivity are good to excellent to afford a wide scope of 4-oxo-4H-chromene-3-carbonitrile and S-electrophilic reagents. Further transformations were completed to introduce more applications.

Stereoselective Electrophilic Sulfenylation of β,β-Disubstituted Enesulfinamides: Asymmetric Construction of Less Accessible Acyclic α,α-Disubstituted α-Sulfenylated Ketimines

Current methods for the asymmetric α-sulfenylation of carbonyls cannot be applied to acyclic carbonyls that have two similar substituents at the α-position. This research demonstrated that the electrophilic sulfenylation of geometry-defined acyclic β,β-disubstituted enesulfinamides using S-aryl or S-alkyl benzenethiosulfonates can be highly stereoselective. This process results in enantioenriched α,α-disubstituted α-sulfenylated ketone surrogates with sulfur-containing acyclic tetrasubstituted carbon stereocenters bearing two electronically and sterically similar substituents (e.g., methyl and ethyl). Furthermore, by employing the corresponding stereoisomers of enensulfinamides, any of the four stereoisomers of α-sulfenylated ketimines can be selectively accessed.

Enantioselective α-Trifluoromethylthiolation of Carbonyl Compounds with AgSCF3 and Trichloroisocyanuric Acid

We successfully developed an enantioselective trifluoromethylthiolation of structurally diverse carbonyl compounds. Trichloroisocyanuric acid and AgSCF3 were employed to generate active electrophilic trifluoromethylthio species in situ for asymmetric C-SCF3 bond formation. A broad variety of chiral SCF3-carbon nucleophiles (pyrazolones, β-keto esters, and β-keto amides) were obtained in excellent yields with high enantioselectivities (up to 92% ee) by Cinchona alkaloid derived squaramide catalysts. The reaction exhibits high efficiency, good enantioselectivity, and high functional group tolerance, which provided a novel and efficient way for asymmetric synthesis of trifluoromethylthiolated carbonyl compounds.

Copper-Catalyzed Enantioselective C(sp3 )-SCF3 Coupling of Carbon-Centered Benzyl Radicals with (Me4 N)SCF3

In contrast with the well-established C(sp2 )-SCF3 cross-coupling to forge the Ar-SCF3 bond, the corresponding enantioselective coupling of readily available alkyl electrophiles to forge chiral C(sp3 )-SCF3 bond has remained largely unexplored. We herein disclose a copper-catalyzed enantioselective radical C(sp3 )-SCF3 coupling of a range of secondary/tertiary benzyl radicals with the easily available (Me4 N)SCF3 reagent. The key to the success lies in the utilization of chiral phosphino-oxazoline-derived anionic N,N,P-ligands through tuning electronic and steric effects for the simultaneous control of the reaction initiation and enantioselectivity. This strategy can successfully realize two types of asymmetric radical reactions, including enantioconvergent C(sp3 )-SCF3 cross-coupling of racemic benzyl halides and three-component 1,2-carbotrifluoromethylthiolation of arylated alkenes under mild reaction conditions. It therefore provides a highly flexible platform for the rapid assembly of an array of enantioenriched SCF3 -containing molecules of interest in organic synthesis and medicinal chemistry.

Thiosuccinimide enabled S-N bond formation to access N-sulfenylated sulfonamide derivatives with synthetic diversity

A thiosuccinimide enabled S-N cross-coupling strategy has been established for the intermolecular N-sulfenylation of clinically approved sulfa drugs under additive-free conditions. This approach features simple operation, high chemoselectivity for sulfenylating the phenylamino group of sulfonamides, wide substrate scope, and easy scale production, affording N-sulfenylated products in moderate to excellent yields (up to 90%). In addition, we also found that this transformation can be realized in a one-pot manner by employing readily available thiols as starting materials, and the obtained sulfonamide derivatives are capable of various late-stage functionalizations, including oxidation, arylation, benzylation, and methylation.

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

In the field of organosulfur chemistry, sulfenylating agents are an important key in C-S bond formation strategies. Among various organosulfur precursors, N-sulfenylsuccinimide/phthalimide derivatives have shown highly electrophilic reactivity for the asymmetric synthesis of many organic compounds. Hence, in this review article, we focus on the application of these alternative sulfenylating reagents in organic transformations.

Asymmetric organocatalytic sulfenylation for the construction of a diheteroatom-bearing tetrasubstituted carbon centre

Catalytic enantioselective sulfenylation to construct diheteroatom-bearing carbon centres was achieved by employing chiral guanidine organocatalysts. This protocol provided a facile route towards the synthesis of α-fluoro-α-sulfenyl-β-ketoamides, azlactone adducts and α-sulfur-substituted amino acid derivatives in high yields with good to excellent enantioselectivities. A possible working mode was proposed to elucidate the chiral control of the process.

Recent advances in thiolation via sulfur electrophiles

This review systematically summarizes the recent developments for constructing sulfur compounds from sulfur electrophiles, and the mechanism mainly involved thirranium ions, sulfur ylides, C–S cross coupling and electrophilic substitution.

Trifluoromethylthiolation of Hindered α-Bromoamides with Nucleophilic Trifluoromethylthiolating Reagents

General methods have not been previously developed for the synthesis of sterically hindered α-SCF₃-substituted carbonyl compounds using nucleophilic trifluoromethylthiolating reagents. Thus, we herein report sp³C-SCF₃ bond formation in hindered α-bromoamides containing 3-bromo-oxindoles and linear α-bromoamides using CuSCF₃ or AgSCF₃ under mild conditions to access sterically hindered α-SCF₃-substituted amides. This transformation is applicable to not only 3-SCF₃-substituted oxindoles but also primary and secondary amides and reveals a broad functional group tolerance. This method will benefit the fields of medicinal and agricultural chemistry.

Assessing Methodologies to Synthesize α-Sulfenylated Carbonyl Compounds by Green Chemistry Metrics

α-Sulfenylated carbonyl compounds are important both as active pharmaceutical ingredients and as intermediates in organic synthesis. Owing to their relevance in synthetic organic chemistry, this Minireview focuses on assessing the most relevant synthetic procedures based on green chemistry metrics. The Minireview starts with the traditional routes and then focuses on more recently developed methodologies. These routes include sulfenylating reagents using organocatalysis, cross-dehydrogenative couplings using in situ halogenations to prevent reactive intermediates in high concentrations, oxidative couplings using terminal oxidants such as DDQ or TEMPO, and redox-neutral couplings using transition metal catalysis. These methodologies have been evaluated on the basis of atom economy, E factor, and the safety and toxicity of the transformations and the solvents used. Besides using green metrics to evaluate these novel methodologies, the synthetic utility is also assessed with regard to the availability of starting materials and the generality of the reactions. This Minireview aims to inspire researchers to apply green assessments to other methodologies and also for them to take measures to increase the greenness of their developed transformations.

Recent Advances in Synthesis of Chiral Thioethers

Chiral thioethers is an important class of organosulfur molecules with extensive applications, especially in the field of medicine and organic synthesis. This review discusses the recent progress of synthesis of enantioenriched chiral thioethers and hopes to be helpful for related research in the future. It is summarized from organosulfur compounds-participating organic reaction types, including nucleophilic substitution, cross coupling, sulfa-Michael addition, sulfenylation, asymmetric allylic reaction, asymmetric Doyle-Kirmse reaction, Pummerer-type rearrangement, Smiles rearrangement,^[2,3] Stevens and Sommelet-Hauser rearrangement.

A nickel-catalyzed tandem reaction involving cyclic esterification/C-S bond formation for synthesizing 5-oxa-11-thia-benzofluoren-6-ones

A nickel-catalyzed tandem reaction involving cyclic esterification/C–S bond formation has been developed. Starting from samples containing 3-(2-hydroxy-phenyl)-acrylic acids with 2-halide-benzenethiols, versatile biologically active 5-oxa-11-thia-benzofluoren-6-one compounds were efficiently synthesized in good to high yields. This new methodology provides an economical approach toward C–S bond formation.

A nickel-catalyzed tandem reaction involving cyclic esterification/C–S bond formation has been developed.

Asymmetric trifluoromethylthiolation of azlactones under chiral phase transfer catalysis

The first enantioselective method for the installation of the SCF₃ group at the C-4 position of azlactones is described in the present communication under quinidinium phase transfer catalysis.

A Mild and Direct C(sp3)-S Cross-Coupling of Oxindoles with Thiols: Synthesis of Unsymmetrical 3-Thiooxindoles

Herein, an operationally simple and mild strategy to construct sulfenation of oxindoles with a series of thiols in the absence of transition metals was developed. This methodology provides an efficient way to directly form a C-S bond at the C-3 position of oxindoles under mild reaction conditions with a cheap and common solvent and base in moderate to good yields.

High-Atom Economic Approach To Prepare Chiral α-Sulfenylated Ketones

Chiral α-sulfenylated ketones are versatile building blocks, although there are still several limitations with their preparation. Here we report a new two-step procedure, consisting of Pd-catalyzed hydrothiolation of propargylic alcohols followed by an enantioselective Rh isomerization of allylic alcohols. The isomerization reaction is the key step for obtaining the ketones in their enantioenriched form. The new methodology has a high atom economy and induces good to high levels of enantioselectivity; no waste is produced. A mechanism involving a Rh-hydride-enone intermediate is proposed for the isomerization reaction.

Nickel(ii)-catalyzed C(sp2)-H sulfuration/annulation with elemental sulfur: selective access to benzoisothiazolones

The first nickel(ii)-catalyzed direct sulfuration/annulation of C(sp²)-H bonds with elemental sulfur has been achieved by using 2-amino alkylbenzimidazole (MBIP-amine) as a N,N-bidentate directing group. This strategy tolerates a wide range of functional groups, furnishing structurally diverse benzoisothiazolone derivatives with benzimidazole skeletons in moderate to excellent yields in a simple and efficient way.

Diastereoselective α-Sulfenylation of N- tert-Butanesulfinyl Imidates

A diastereoselective α-sulfenylation of chiral α-aryl/alkyl N- tert-butanesulfinyl imidates has been developed. Suitable sulfur electrophiles can be used as sulfenylating reagents to intercept aza-enolates generated from imidate deprotonation, giving α-thiofunctionalized imidates in good yields with high diastereocontrol. This protocol for C-S bond formation can efficiently synthesize enantioenriched 1,2-sulfanyl amine derivatives such as sulconazole.

TfNHNHBoc as a SCF3 source for the sulfenylation of indoles

An unprecedented use of TfNHNHBoc as an effective SCF₃ source has been established in the copper-catalyzed oxidative sulfenylation of indoles.

Catalytic enantioselective α-sulfenylation of β-ketocarbonyls by chiral primary amines

A simple chiral primary amine catalyst was identified to enable effective catalysis in direct α-sulfenylation of acyclic and cyclic β-ketocarbonyls with good yields and excellent enantioselectivities.

Copper-catalyzed C–S direct cross-coupling of thiols with 5-arylpenta-2,4-dienoic acid ethyl ester

A selective copper (Cu)-catalyzed C–S bond direct cross-coupling of thiols with 5-arylpenta-2,4-dienoic acid ethyl ester was developed. Notably, various biologically active 5-phenyl-3-phenylsulfanylpenta-2,4-dienoic acid ethyl ester derivatives were efficiently synthesized under moderate conditions. Finally, a plausible Cu(i)/Cu(iii) reaction mechanism was proposed.

A selective copper (Cu)-catalyzed C–S bond direct cross-coupling of thiols with 5-arylpenta-2,4-dienoic acid ethyl ester was developed.

Catalytic asymmetric synthesis of hetero-substituted oxindoles

The construction of chiral disubstituted oxindoles is an intriguing challenge for organic chemists.

N-Trifluoromethylthio-dibenzenesulfonimide: A Shelf-Stable, Broadly Applicable Electrophilic Trifluoromethylthiolating Reagent

The super electrophilicity of a shelf-stable, easily prepared trifluoromethylthiolating reagent N-trifluoromethylthio-dibenzenesulfonimide 7 was demonstrated. Consistent with the theoretical prediction, 7 exhibits reactivity remarkably higher than that of other known electrophilic trifluoromethylthiolating reagents. In the absence of any additive, 7 reacted with a wide range of electron-rich arenes and activated heteroarenes under mild conditions. Likewise, reactions of 7 with styrene derivatives can be fine-tuned by simply changing the reaction solvents to generate trifluoromethylthiolated styrenes or oxo-trifluoromethylthio or amino-trifluoromethylthio difunctionalized compounds in high yields.

Quantitative Scale for the Trifluoromethylthio Cation-Donating Ability of Electrophilic Trifluoromethylthiolating Reagents

A new parameter, trifluoromethylthio cation-donating ability (Tt(+)DA), is introduced as a quantitative descriptor for the propensity of electrophilic trifluoromethylthiolating reagents to transfer a CF3S moiety in organic synthesis. The first Tt(+)DA scale of popular reagents has been established through DFT calculations. Excellent correlation has been identified between the Tt(+)DAs of N-SCF3-type reagents and the pKa of the corresponding acids, offering a powerful avenue for the rational design of novel reagents.