Iodine-Mediated Thiolation of Substituted Naphthols/Naphthylamines and Arylsulfonyl Hydrazides via C(sp2)–H Bond Functionalization

I2-Induced Umpolung: Synthesis of a 1,6-Dihydrofuro[3,2-b]pyrazolo[3,4-e][1,4]thiazine Skeleton via an Unconventional 1,4-Dithiane-2,5-diol Reaction Mode

In this paper, novel sulfur-containing 1,6-dihydrofuro[3,2-b]pyrazolo[3,4-e][1,4]thiazine skeletons were constructed from the simple and readily available materials enaminone, 5-aminopyrazole, and 1,4-dithiane-2,5-diol. Furthermore, a novel 1,4-dithiane-2,5-diol reaction mode has been developed through a double-dipole-reversal process induced by iodine that results in the formation of six new bonds and two new rings in a one-pot reaction. This method shows good substrate compatibility, and the products can be further modified with a variety of pharmaceuticals. Additionally, this novel skeleton exhibits good fluorescence properties in solution, enabling bright and stable green fluorescence imaging in HeLa cells.

Iodine-catalyzed regioselective direct sulfenylation of uracil with sulfonyl hydrazide as sulfur source under solvent free conditions

A facile method was developed for the selective thioetherification of uracils using sulfonyl hydrazide as the thioetherification reagent. This method offers advantages such as avoiding the use of additives and expensive metal catalysts, and providing good to excellent yields of various uracil thioethers. Experimental studies have demonstrated that the reaction follows a free radical pathway. Notably, the reaction can be carried out without solvent.

Recent advances in selective mono-/dichalcogenation and exclusive dichalcogenation of C(sp2)-H and C(sp3)-H bonds

Organochalcogen compounds are prevalent in numerous natural products, pharmaceuticals, agrochemicals, polymers, biological molecules and synthetic intermediates. Direct chalcogenation of C-H bonds has evolved as a step- and atom-economical method for the synthesis of chalcogen-bearing compounds. Nevertheless, direct C-H chalcogenation severely lags behind C-C, C-N and C-O bond formations. Moreover, compared with the C-H monochalcogenation, reports of selective mono-/dichalcogenation and exclusive dichalcogenation of C-H bonds are relatively scarce. The past decade has witnessed significant advancements in selective mono-/dichalcogenation and exclusive dichalcogenation of various C(sp2)-H and C(sp3)-H bonds via transition-metal-catalyzed/mediated, photocatalytic, electrochemical or metal-free approaches. In light of the significance of both mono- and dichalcogen-containing compounds in various fields of chemical science and the critical issue of chemoselectivity in organic synthesis, the present review systematically summarizes the advances in these research fields, with a special focus on elucidating scopes and mechanistic aspects. Moreover, the synthetic limitations, applications of some of these processes, the current challenges and our own perspectives on these highly active research fields are also discussed. Based on the substrate types and C-H bonds being chalcogenated, the present review is organized into four sections: (1) transition-metal-catalyzed/mediated chelation-assisted selective C-H mono-/dichalcogenation or exclusive dichalcogenation of (hetero)arenes; (2) directing group-free selective C-H mono-/dichalcogenation or exclusive dichalcogenation of electron-rich (hetero)arenes; (3) C(sp3)-H dichalcogenation; (4) dichalcogenation of both C(sp2)-H and C(sp3)-H bonds. We believe the present review will serve as an invaluable resource for future innovations and drug discovery.

Direct C-H Thiolation for Selective Cross-Coupling of Arenes with Thiophenols via Aerobic Visible-Light Catalysis

An aerobic metal-free, visible-light-induced regioselective thiolation of phenols with thiophenols is reported. The cross-coupling protocol exhibits great functional group tolerance and high regioselectivity. Mechanistic studies reveal that the disulfide radical cation plays a crucial role in the visible-light catalysis of aerobic thiolation. Simply controlling the equivalent ratio of substrates enables the selective formation of sulfide or sulfoxide products with high activity in a one-pot reaction.

Transition-Metal-Free Synthesis of Aryl Trifluoromethyl Thioethers through Indirect Trifluoromethylthiolation of Sodium Arylsulfinate with TMSCF3

Herein, we report an indirect trifluoromethylthiolation of sodium arylsulfinates. This transition-metal-free reaction significantly provides an environmentally friendly and practical synthetic method for aryl trifluoromethyl thioethers using commercial Ruppert-Prakash reagent TMSCF₃. This approach is also a potential alternative to the current industrial production method owing to facile substrates, excellent functional group compatibility, and operational simplicity.

Syntheses and Transformations of Sulfinamides

Sulfinamides, especially enantiopure sulfinamides, are widely used in organic and medicinal synthesis. Syntheses and transformations of racemic and enantioenriched sulfinamides have achieved great progress. Especially sulfinamides demonstrate interesting and valuable reactivity, which deserves to be pertinent. This review summarizes the latest development in the synthesis and transformation of sulfinamides and will be helpful for future related research.

1 Introduction

2 Synthesis of Sulfinamides

2.1 Synthesis of Racemic Sulfinamides

2.2 Synthesis of Enantiomerically Pure Sulfinamides

2.3 Synthesis of Other Sulfinamides

3 Transformations of Sulfinamides

3.1 Condensation with Aldehydes and Ketones

3.2 Reaction with Alkynes

3.3 Reaction with Alkenes

3.4 Reaction with Aryl and Alkyl Halides

3.5 Reaction with Alcohols, Dibenzyl Ether, and Benzyl Mercaptan

3.6 Synthesis of tert-Butyldisulfanyl-Substituted Hetarenes

3.7 Synthesis of Asymmetric Sulfides

3.8 Synthesis of N-Phosphino-sulfinamide Ligands

3.9 Asymmetric Synthesis of γ-Amino Acids

3.10 Sulfonylation of Heterocyclic Compounds

4 Summary and Outlook

Aerobic Cross-Dehydrogenative Coupling Reactions for Selective Mono- and Dithiolation of Phenols

A highly efficient strategy for the direct thiolation of phenols under transition metal-free and solvent-free conditions has been developed. These reactions are operationally simple with employing air (molecular oxygen) as an ideal oxidant and can selectively provide mono- and dithiolation products in good to excellent yields under basic conditions. The reaction tolerates a broad range of aryl thiols and arenes and is especially applicable for large-scale synthesis.

An iodine-mediated new avenue to sulfonylation employing N-hydroxy aryl sulfonamide as a sulfonylating agent

A novel and highly efficient I2/K2CO3 mediated regioselective sulfonylation of thiophenols, aryl acetylenic acid and aromatic alkynes with N-hydroxy sulfonamide has been developed. N-hydroxy sulfonamide has been used for the first time for the synthesis of these sulfones. The scope and versatility of the reaction has been demonstrated by the regio- and stereoselective synthesis of different analogs of sulfones with various structural features.

Recent Advances in Iodine-Promoted C-S/N-S Bonds Formation

Sulfur-containing scaffold, as a ubiquitous structural motif, has been frequently used in natural products, bioactive chemicals and pharmaceuticals, particularly C-S/N-S bonds are indispensable in many biological important compounds and pharmaceuticals. Development of mild and general methods for C-S/N-S bonds formation has great significance in modern research. Iodine and its derivatives have been recognized as inexpensive, environmentally benign and easy-handled catalysts or reagents to promote the construction of C-S/N-S bonds under mild reaction conditions, with good regioselectivities and broad substrate scope. Especially based on this, several new strategies, such as oxidation relay strategy, have been greatly developed and accelerated the advancement of this field. This review focuses on recent advances in iodine and its derivatives promoted hybridized C-S/N-S bonds formation. The features and mechanisms of corresponding reactions are summarized and the results of some cases are compared with those of previous reports. In addition, the future of this domain is discussed.

Sulfenylation of Arenes with Ethyl Arylsulfinates in Water

A tetrabutylammonium iodide-mediated direct sulfenylation of arenes with ethyl arylsulfinates in water was developed. Various electron-rich arenes and ethyl arylsulfinates were investigated in the reaction, and a series of aryl sulfides were obtained in excellent yields. The advantages of this green protocol were simple reaction conditions (metal-free, water as the solvent, and under air), odorless and easily available sulfur reagent, broad substrate scope, and gram-scale synthesis. Moreover, the potential application of aryl sulfides was exemplified by further transformations.

Metal-free C–S coupling of thiols and disulfides

A literature overview on C–S coupling reactions using thiols or disulfides as sulfur surrogates under metal-free conditions is presented. Reagents for the transformations include polyvalent iodines, peroxides, tert-butyl nitrite (TBN), DDQ, and aerial oxygen, among others.

KIO3-catalyzed cross dehydrogenative coupling reaction: sulfenylation of phenol and arylamine derivatives in water at room temperature

A metal-free direct sulfenylation of phenol and arylamine derivatives with various heterocyclic thiols and thiones using a cross dehydrogenative coupling protocol in water at room temperature has been developed.

A one-pot metal-free protocol for the synthesis of chalcogenated furans from 1,4-enediones and thiols

Transition-metal-free synthesis of chalcogenated furans through the sequential thiol-Michael/Paal–Knorr reaction of 1,4-enediones in the presence of a catalytic amount of p-toluene sulfonic acid has been developed.

Biocatalytic synthesis of diaryl disulphides and their bio-evaluation as potent inhibitors of drug-resistant Staphylococcus aureus

Staphylococcus aureus is a WHO Priority II pathogen for its capability to cause acute to chronic infections and to resist antibiotics, thus severely impacting healthcare systems worldwide. In this context, it is urgently desired to discover novel molecules to thwart the continuing emergence of antimicrobial resistance. Disulphide containing small molecules has gained prominence as antibacterials. As their conventional synthesis requires tedious synthetic procedure and sometimes toxic reagents, a green and environmentally benign protocol for their synthesis has been developed through which a series of molecules were obtained and evaluated for antibacterial activity against ESKAPE pathogen panel. The hit compound was tested for cytotoxicity against Vero cells to determine its selectivity index and time-kill kinetics was determined. The activity of hit was determined against a panel of S. aureus multi-drug resistant clinical isolates. Also, its ability to synergize with FDA approved drugs was tested as was its ability to reduce biofilm. We identified bis(2-bromophenyl) disulphide (2t) as possessing equipotent antimicrobial activity against S. aureus including MRSA and VRSA strains. Further, 2t exhibited a selectivity index of 25 with concentration-dependent bactericidal activity, synergized with all drugs tested and significantly reduced preformed biofilm. Taken together, 2t exhibits all properties to be positioned as novel scaffold for anti-staphylococcal therapy.

Metal-Free Vinyl C-H Sulfenylation/Alkyl Thiolation of Ketene Dithioacetals for the Synthesis of Polythiolated Alkenes

The sulfenylation of the vinyl C-H bond in ketene dithioacetals leading to the synthesis of polythiolated alkenes is achieved via the promotion of molecular iodine. In addition, alkyl thiols also exhibit tolerance to the C-H bond elaboration reaction for the synthesis of corresponding alkylthiolated ketene dithioacetals.

Selective S-arylation of 2-oxazolidinethiones and selective N-arylation of 2-benzoxazolinones/2-benzimidazolinones

There exist three possible patterns for the reaction of cyclic 2-oxazolidinethione and 2-benzoxazolidinethione with arynes, namely (a) S-arylation, (b) N-arylation, and (c) aryne insertion into the thiocarbonyl group (C[double bond, length as m-dash]S). Our studies demonstrate that S-arylation wins out affording S-aryl dihydrooxazoles. In contrast, for related reactions of cyclic 2-benzoxazolinone and 2-benzimidazolinone with arynes, it is found that N-arylation outcompetes O-arylation and aryne insertion into the C[double bond, length as m-dash]O group to give N-aryl 2-benzoxazolinones and N-aryl 2-benzimidazolinones.

N-Hydroxy sulfonamides as new sulfenylating agents for the functionalization of aromatic compounds

An unprecedented use of N-hydroxy sulfonamides as sulfenylating agents has been established. In the presence of catalytic amounts of iodine and N-hydroxysuccinimide, N-hydroxy sulfonamides participated in sulfenylation with indoles, 7-azaindole, N-methyl pyrrole, and 2-naphthol to afford structurally diverse thioethers in moderate to excellent yields with very high regioselectivity.

Cooperative catalysis by bovine serum albumin-iodine towards cascade oxidative coupling-C(sp(2))-H sulfenylation of indoles/hydroxyaryls with thiophenols on water

Cooperative cascade catalysis by bovine serum albumin (BSA)-iodine allows for the first time the performance of C(sp(2))-H sulfenylation of indole from readily available thiophenol (-SH bond) via in situ generation/cleavage of disulfide (S-S bond) in air under aqueous conditions, whereas BSA or I2 individually do not permit this two step sequence to occur in the same pot towards C-S bond formation. This green cooperative protocol is extendable to sulfenylation of hydroxyaryls (i.e. 2-naphthol or 4-hydroxycoumarin) with diverse thiols (aryl/heteroaryl) without using any toxic metal catalysts, bases or oxidants, thus rendering the process environmentally and economically reliable. Further, the gram scale synthesis of a COX-2 inhibitor (3-(pyridin-2-ylthio)-1H-indole), regioselectivity and recyclability (up to four cycles) are the additional merits of this cooperative cascade bio-chemocatalytic (BSA-I2) protocol. Moreover, HPLC and ESI-MS provide powerful insights into the mechanistic aspects of the above cascade sulfenylation reaction.