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.

C-H Diselenation and Monoselenation of Electron-Deficient Alkenes via Radical Coupling at Room Temperature

A new, simple, and metal-free route for the diselenation of maleimides has been first developed employing (bis(trifluoroacetoxy)iodo)benzene (PIFA) at room temperature. The present method is compatible with different functional groups, and various diselenyl maleimides were obtained in moderate to excellent yields. Moreover, this protocol further highlights the unique practical application for the functionalization of biologically relevant molecules and amino acid derivatives. Preliminary mechanism studies suggest that radicals may be involved in this novel transformation. Additionally, this protocol is also applicable for the monoselenation of maleimides by switching the reaction conditions and selenation of other electron-deficient alkenes.

A review on the role of transition metals in selenylation reactions

Organoselenium chemistry has emerged as a distinctive area of research with tremendous utility in the synthesis of biologically and pharmaceutically active molecules. Significant synthetic approaches have been made for the construction of C-Se bonds which find use in other organic transformations. This review focuses on the versatility of transition metal-mediated selenylation reactions, providing insights into various synthetic pathways and mechanistic details. Further, this review aims to offer a broad perspective for designing efficient and novel catalysts to incorporate organoselenium moiety into the inert C-H bonds.

NaI/TBHP-promoted reaction of indole-2-thiones with arylsulfonyl hydrazides: construction of achiral axial 3,3′-biindole-2,2′-dibenzenesulfonothioate derivatives

A new method for the synthesis of achiral axial 3,3′-biindole-2,2′-dibenzenesulfonothioate derivatives from indole-2-thiones with arylsulfonyl hydrazides promoted by NaI/TBHP is disclosed.

Transition metal catalysed direct selanylation of arenes and heteroarenes

Transition metal catalysed C-H functionalization has reached an exciting level of sophistication, and, today, it represents a paradigm shift from the standard logic of synthetic chemistry. The direct conversion of C-H bonds into C-heteroatoms remains, however, a critical challenge. Nowadays, there is a great demand in general synthetic chemistry in, for example, the materials science for the development of straightforward C-Se bond formation, in order to fulfil the practical requirements. In this sense, this review summarizes recent outstanding advances in the C-Se bond formation through transition metal-catalysed direct selanylation, providing new insights into their mechanistic aspects and disclosing effective synthetic routes with high atom economy. In addition, this review intends to show the growing opportunities to construct complex chemical scaffolds containing selenium atoms.

Oxidative dual C–H selenation of imidazoheterocycles with ethers or alkanes using selenium powder via a radical pathway

A DCP-mediated oxidative dual C–H selenation radical reaction of imidazoheterocycles with ethers or alkanes using selenium powder was developed.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Metal-free C-H thioarylation of arenes using sulfoxides: a direct, general diaryl sulfide synthesis

Metal-free C-H thioarylation of arenes and heteroarenes using methyl sulfoxides constitutes a general protocol for the synthesis of high value diaryl sulfides. The coupling of arenes and heteroarenes with in situ activated sulfoxides is regioselective, uses readily available starting materials, is operationally simple, and tolerates a wide range of functional groups.

Synthesis of symmetrical and unsymmetrical tellurides via silver catalysis

The cross-coupling reaction of diaryl ditellurides with aryl boronic acids is described using AgNO₃ as a catalyst.

Triphenyltin recognition by primary structures of effector proteins and the protein network of Bacillus thuringiensis during the triphenyltin degradation process

Herein, triphenyltin (TPT) biodegradation efficiency and its transformation pathway have been elucidated. To better understand the molecular mechanism of TPT degradation, the interactions between amino acids, primary structures, and quaternary conformations of effector proteins and TPT were studied. The results verified that TPT recognition and binding depended on amino acid sequences but not on secondary, tertiary or quaternary protein structure. During this process, TPT could change the molecular weight and isoelectric point of effector proteins, induce their methylation or demethylation, and alter their conformation. The effector proteins, alkyl hydroperoxide reductase and acetyl-CoA acetyltransferase, recognizing TPT were crucial to TPT degradation. Electron transfer flavoprotein subunit alpha, phosphoenolpyruvate carboxykinase, aconitate hydratase, branched-chain alpha-keto acid dehydrogenase E1 component, biotin carboxylase and superoxide dismutase were related to energy and carbon metabolism, which was consistent with the results in vivo. The current findings develop a new approach for investigating the interactions between proteins and target compounds.

Recent Advances in Radical C-H Activation/Radical Cross-Coupling

Research and industrial interest in radical C-H activation/radical cross-coupling chemistry has continuously grown over the past few decades. These reactions offer fascinating and unconventional approaches toward connecting molecular fragments with high atom- and step-economy that are often complementary to traditional methods. Success in this area of research was made possible through the development of photocatalysis and first-row transition metal catalysis along with the use of peroxides as radical initiators. This Review provides a brief and concise overview of the current status and latest methodologies using radicals or radical cations as key intermediates produced via radical C-H activation. This Review includes radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling of radicals with M-R groups, and coupling of radical cations with nucleophiles (Nu).

A conjugate Lewis base-Brønsted acid catalyst for the sulfenylation of nitrogen containing heterocycles under mild conditions

A new Lewis base/Brønsted acid approach allows for the sulfenylation of N-heterocycles under exceedingly mild conditions.

Generation of thioethers via direct C–H functionalization with sodium benzenesulfinate as a sulfur source

A novel ammonium iodide-induced sulfenylation method of flavones, indole and arylimidazo[1,2-a]pyridines using stable and odorless sodium benzenesulfinates as sulfur sources was developed, generating regioselective derivatives in good yields.

Aerobic copper-catalyzed decarboxylative thiolation

A copper-catalyzed decarboxylative thiolation reaction to furnish aryl sulfides using molecular oxygen as the sole oxidant is described.

Copper-mediated thiolation of carbazole derivatives and related N-heterocycle compounds

Cu-mediated direct thiolation of carbazole derivatives with disulfides via C–H bond cleavage to give diaryl and alkyl aryl sulfides which easily extends to the synthesis of thioethers with a benzo[h]quinolone, 2-phenylquinoline or indole moiety in satisfactory yields.

Nickel-catalyzed synthesis of diarylsulfides and sulfones via C–H bond functionalization of arylamides

The sulfenylation and sulfonylation of (sp²)C–H bonds of benzamides were achieved with the aid of a bidentate directing group.

Nickel-catalyzed and benzoic acid-promoted direct sulfenylation of unactivated arenes

A nickel-catalyzed direct sulfenylation of unactivated arenes using removable 2-(pyridine-2-yl)-isopropylamine as a directing group has been developed.