Synthesis of Thioesters from Aldehydes via N-Heterocyclic Carbene (NHC) Catalyzed Radical Relay

We have developed an efficient N-heterocyclic carbene (NHC)-catalyzed thioesterification of aldehydes using N-thiosuccinimides as the thiolation reagent. This organocatalyzed transition involves the generation of sulfur radicals by single electron transfer of the Breslow enolate (generated from aldehyde and NHC catalyst) with N-thiosuccinimides. This method offers facile access to various highly functionalized thioesters and exhibits good chemical yields and functional group tolerance.

The journey of C–S bond formation from metal catalysis to electrocatalysis

This perspective describes the journey of C–S bond constructions starting from transition metal catalysis through oxidant catalysis, photocatalysis and very recently employed electrocatalysis by using various sulfur surrogates.

From methylarenes to Esters: Efficient oxidative Csp3-H activation promoted by CuO decorated magnetic reduced graphene oxide

Magnetic reduced graphene oxide supported CuO (rGO/Fe3O4-CuO) as the heterogeneous catalyst in cross dehydrogenative coupling (CDC) reactions has been demonstrated for the synthesis of esters using methyl aromatics, aldehydes/benzyl alcohols...

Manganese(III)-promoted thiocarbonylation of alkylborates with disulfides: synthesis of aliphatic thioesters

A Mn(III)-promoted thiocarbonylation procedure toward the synthesis of thioesters has been developed. By employing easily available disulfides and potassium alkyltrifluoroborates as the starting materials, and cheap and non-toxic Mn(OAc)₃·2H₂O as the promotor, a broad range of thioesters were synthesized in good to excellent yields via radical intermediates.

Photocatalytic Activation of Elemental Sulfur Enables a Chemoselective Three-Component Thioesterification

A mild and chemoselective three-component thioesterification using olefins, α-ketoacids, and elemental sulfur has been developed. The photocatalytic activation of elemental sulfur, a cheap and abundant sulfur source, enables the rapid installation of a sulfur atom into molecules, reactions that ordinarily would require the use of reactive and malodorous sulfur-containing compounds such as thiols and thioacids. This novel reaction is characterized by high yields and a broad substrate scope, which enables the introduction of thioester moieties into complex molecules including a steroid, a peptide, and a nonprotected glycoside. Mechanistic studies indicated that the success of this transformation depends on the multiple roles played by the elemental sulfur, including those of a sulfurizing agent, a terminal oxidant, and a HAT mediator.

The Rich Legacy and Bright Future of Transition-Metal Catalyzed Peroxide Based Radical Reactions

This personal account is mainly focused on the author's involvement in the field of transition metal-catalyzed peroxide based radical reactions. Over the past decades, radical chemistry has flourished and become crucial in contemporary synthetic organic chemistry. Owing to the presence of a single electron in one orbital, radicals are very unstable and react very fast. To carry out desired transformations and to control the side reactions the stabilizations of these radicals is essential. Fortunately, the implementation of a suitable transition metal and peroxide combination into the radical reactions have proved beneficial. Transition metals not only stabilizes the radicals but also protects them from being quenched by undesired homo-coupling or fragmentation. Transition metal-catalyzed radical-radical reactions provide an innovative way for the construction and derivatization of carbocycles and heterocycles. The objective of this review is to give an overview of the construction and derivatization of heterocycles through the lens of radical chemistry, mainly focusing on research work done by our group.

Cu-Catalyzed Oxidative Thioesterification of Aroylhydrazides with Disulfides

An alternative thioesterification reaction via copper-catalyzed oxidative coupling of readily available aroylhydrazides with disulfides is developed, in which oxidative expulsion of N₂ overcomes the activation barrier between the carboxylic acid derivatives and the products. The reaction produces various thioesters in good to excellent yields with good functional group tolerance. In the reaction, stable and easily available aroylhydrazides are used as acyl sources and the relatively odorless disulfides are used as S sources. Mechanistic investigations demonstrate that the reaction of copper salt and oxidant (NH₄)₂S₂O₈ allows for achievement of tandem processes, including deprotonation, free-radical-mediated denitrogenation, and C-S bond formation.

Autocatalytic Synthesis of Thioesters via Thiocarbonylation of gem-Difluoroalkenes

Herein, we report a new method for the synthesis of acyethanethioates via thiocarbonylation of gem-difluoroalkenes with thiols. This reaction provides a new pathway to prepare thioesters under mild conditions without the use of any additives. Mechanistic studies revealed that in situ generated HF facilitated the C-F bond cleavage in an autocatalytic manner.

Synthesis of S-aryl thioesters via palladium-catalyzed thiocarbonylation of aryl iodides and aryl sulfonyl hydrazides

Aryl sulfonyl hydrazide reacted with aryl iodide in the presence of CO to give the corresponding S-aryl thioesters.

Palladium-catalyzed carbonylative transformation of aryl iodides and sulfonyl chlorides: convenient access to thioesters

A palladium-catalyzed carbonylative transformation of aryl iodides and sulfonyl chlorides to thioesters has been studied.

Na2CO3-promoted thioesterification via N–C bond cleavage of amides to construct thioester derivatives

A mild, efficient, and transition-metal-free catalytic strategy is developed to construct thioesters via selective N–C bond cleavage of Boc2-activated primary amides. This strategy is successfully carried out with stoichiometric Na2CO3 as the base and provides the corresponding products in moderate to excellent yields.

Metal-free oxidative acylation/cyclization of N-methacryloyl-2-phenylbenzoimidazole with aryl aldehydes: an easy access to benzimidazo[2,1-a]isoquinolin-6(5H)-ones

A metal-free radical cyclization strategy has been developed for the synthesis of fused benzimidazo[2,1-a]isoquinolin-6(5H)-one derivatives using 70% tert-butylhydroperoxide in water (TBHP).

Metal-free thioesterification of amides generating acyl thioesters

A base-initiated thioesterification of amides with various thiols is reported. This reaction can take place efficiently under metal-free and air-atmospheric conditions, and provides a facile and practically useful approach to the synthesis of valuable acyl thioesters.

T3P® mediated domino C(sp2)–H sulfenylation/annulation of enaminones and methylsulfinyls for the synthesis of chromone thioether derivatives

Regio-selective preparation of 3-sulfenylated chromone using T3P® has been described for the first time.

Engineered C-S Bond Construction

Due to the versatile applications of thioethers and thioesters in organic synthesis, medicinal chemistry, the pharmaceutical industry, and materials science, recently the construction of C-S bonds has emerged as the forefront in the field of cross-coupling reactions. Enough progress has been made in this direction by using both metal catalysis and other alternative processes. A brief review of the recent developments in the area of C-S coupling reaction is described.

One-pot synthesis of thioesters with sodium thiosulfate as a sulfur surrogate under transition metal-free conditions

In this paper, we report an efficient synthetic method for thioester formation from sodium thiosulfate pentahydrate, organic halides, and aryl anhydrides. In the one-pot two-step reactions developed in this study, sodium thiosulfate was used as the sulfur surrogate for acylation with anhydrides, followed by substitution with organic halides through the in situ generation of thioaroylate. Furthermore, two important organic compounds could be successfully synthesized using our developed method. The advantages of the one-pot two-step reactions are operational simplicity, structurally diverse products with 42%-90% yields, use of relatively low toxic and odourless reagents, and easy applicability to large-scale operation.

Palladium-catalyzed carbonylation of thioacetates and aryl iodides for the synthesis of S-aryl thioesters

Palladium-catalyzed carbonylation of thioacetates and aryl iodides provided thioesters in good yields.

Microwave-Assisted Direct Thioesterification of Carboxylic Acids

A one-pot synthesis of thioesters directly from carboxylic acids, N,N'-diphenylthiourea, triethylamine, and primary alkyl halides is described. Microwave-assisted heating and a catalytic amount of 4-(dimethylamino)pyridine (DMAP) further improved the yields. Both aromatic and aliphatic carboxylic acids were converted to the corresponding thioesters, and many functional groups were compatible with this reaction. Several possible reaction intermediates were investigated, and the quaternary ammonium salts, derived from alkyl halides and tertiary amines, were the intermediates to yield thioesters. A new reaction mechanism for this thioesterification is proposed.

Double C–S bond formation via C–H bond functionalization: synthesis of benzothiazoles and naphtho[2,1-d]thiazoles from N-substituted arylamines and elemental sulfur

An atom economic and environmentally friendly method for the synthesis of benzothiazoles and naphtho[2,1-d]thiazoles has been developed under metal-free conditions.

Cu(ii)-Mediated keto C(sp3)–H bond α-acyloxylation of N,N-dialkylamides with aromatic carboxylic acids

The first example of Cu(ii)-mediated oxidative coupling of aromatic carboxylic acids with the C(sp³)–H bond adjacent to the keto group of N,N-dialkylamides has been developed.

Synthesis of β-Hydroxysulfides from Thiophenols and Disulfides with tert-Butyl Hydroperoxide as the Oxidant and Reactant

In this Communication, we developed a new procedure for the synthesis of β‐hydroxysulfides from thiophenols or diaryl disulfides with TBHP as the oxidant. In the presence of zinc iodide or potassium iodide, with TBHP as the oxidant and pre‐reactant, thiophenols and diaryl disulfides reacted with the methyl group of tBuOH smoothly and selectivity to give the corresponding 2‐methyl‐1‐(arylthio)propan‐2‐ols as the terminal products in moderate to good yields.

Synthesis of esters via sp3 C–H functionalisation

This review describes various methods for the synthesis of eleven classes of esters involving sp³ C–H functionalisation.

Formation of C(sp2)–S bonds through decarboxylation of α-oxocarboxylic acids with disulfides or thiophenols

Copper-catalyzed decarboxylative coupling between α-oxocarboxylic acids and diphenyl disulfides or thiophenols is presented, which provided an effective and direct approach for the preparation of useful thioesters through C(sp²)–S bond formation.

Direct oxidative coupling of thiols and benzylic ethers via C(sp3)–H activation and C–O cleavage to lead thioesters

An unprecedented protocol for the synthesis of thioesters via C–H thioesterification and C–O cleavage was developed. This CDC protocol was found convenient and easy-to-handle involving the use of DTBP as the only green oxidant.

Direct construction of 2-alkylbenzo-1,3-azoles via C–H activation of alkanes for C–C and C–X (X = O, S) bond formation

2-Alkylated benzo(oxa)thiazoles were prepared directly from simple alkanes and aryl isocyanates/isothiocyanates in a one-pot procedure.

n-Bu4NI-catalyzed direct amination of ethers with aryl tetrazoles and triazoles via cross-dehydrogenative coupling reaction

An efficient, metal-free protocol for direct amination of ethers with aryl tetrazoles and triazoles has been developed using the TBAI/TBHP system.

Utilization of methylarenes as versatile building blocks in organic synthesis

This review attempts to describe the latest developments in the utilisation of methylarenes adopting C–H functionalization strategies and covers all the developments until March 2015.

Generation of ArS-substituted flavone derivatives using aryl thiols as sulfenylating agents

The regioselective and metal-free sulfenylation of flavones was achieved under aerobic conditions with ammonium iodide as an inducer.

I2-catalyzed oxidative C(sp3)–H/S–H coupling: utilizing alkanes and mercaptans as the nucleophiles

C(sp³)–S bond formation was achieved utilizing C(sp³)–H and S–H as the nucleophile. Methyl arenes, cycloalkanes and aliphatic ketones exhibited reactivity for this transformation. Mechanistic studies revealed that the C(sp³) radical and disulfide were the intermediates in the reaction.

Selective approach to thioesters and thioethers via sp3 C–H activation of methylarenes

Novel CDC approaches for the synthesis of thioesters and thioethers was developed via sp³ C–H activation of methylarenes and subsequent functionalization.