Application of DMSO as a methylthiolating reagent in organic synthesis

In the past decades, DMSO has been widely used not only as a common solvent but also as an environmentally benign oxidant in various organic transformations. Most strikingly, DMSO can be used as a sulfur source to construct methylthiolated building blocks of potential biologically active molecules, which is a remarkable achievement in the field of organic sulfur chemistry. The purpose of this review article is to summarize and discuss the main developments in the application of DMSO as a methylthiolating reagent to introduce the -SMe functionality in organic synthesis.

Robust, scalable construction of an electrophilic deuterated methylthiolating reagent: facile access to SCD3-containing scaffolds

We have established a practical and concise method for the straightforward access of a universal deuterated methylthiolating reagent through a one-pot gram-scale operation under mild conditions. This odourless electrophilic SCD₃ reagent was widely applied to react with numerous representative nucleophiles and approached various valuable SCD₃ analogues with excellent levels of deuterium content (>99% D). The divergent further transformations were smoothly carried out to obtain the significant derivatives with different oxidative states in high efficiency.

Recent Advance on Dimethyl Sulfoxide (DMSO) Used as a Multipurpose Reactant

Abstract:

Dimethyl sulfoxide (DMSO) is not only a common and cheap aprotic polar solvent with low toxicity, but also serves as an efficient and multipurpose reactant and has widely been used in organic synthesis. DMSO as an important precursor can effectively introducea broad range of functional fragments into organic molecules, such as -Me, -CH, -CH2, -SMe2, -CH2SMe, -CH2SOMe, -SMe, -SO2Me, -SOMe or as O substituents, and serves as a mild oxidant in organic transformations. Many significant achievements based on DMSO as a synthon in synthetic chemistry have rapidly made over the past several years. To help researchers further understand the recent advances in the field, the review summarizes the applications of DMSO as carbon, sulfur, and oxygen sources and is used as the dual synthon in synthetic transformations.

Electrosynthesis of S-thiocarbamates with disulfides as a sulfur source

An electrochemical oxidative synthesis of S-thiocarbamates by a carbamothioation reaction via a three-component coupling reaction (disulfide, water and isocyanide) is developed, which avoids the use of external oxidants and generates only hydrogen gas as the by-product. With NH₄I as the mediator and electrolyte, the desired S-thiocarbamates were obtained in good yields in an undivided cell at room temperature.

Broadening of horizons in the synthesis of CD3-labeled molecules

In the light of the recent potentials of deuterated molecules as pharmaceuticals or even in mechanistic understanding, efficient methods for their synthesis are continually desired. CD₃-containing molecules are prominent amongst these motifs due to the parallel of the "magic methyl effect": introducing a methyl group into pharmaceuticals could positively affect biological activities. The trideuteromethyl group is bound to molecules either by C, N, O, or S atom. For a long time, the preparation methods of such labeled compounds were underestimated and involved multi-step syntheses. More recently, specific approaches dealing with the direct incorporation of the CD₃ group have been developed. This Review gives an overview of the methods for the preparation of CD₃-labeled molecules from conventional functional group interconversion techniques to catalytic approaches and include radical strategy. Detailed reaction mechanisms are also discussed.

Directed Cobalt-Catalyzed C-H Activation to Form C-C and C-O Bonds in One Pot via Three-Component Coupling

Herein, we disclose an efficient cobalt-catalyzed three-component coupling of benzamides, diazo compounds, and tert-butyl hydroperoxide, which provides an efficient approach to construct C(sp²)-C(sp³) and C-O bonds in one-pot accompanied with C-H activation. This protocol features low catalyst loading (4 mol %), the avoidance of additives, and excellent functional group compatibility, providing three-component coupling adducts with high yields under mild conditions (up to 88%). Mechanism studies show that the reaction may involve a radical process.

Synthetic developments on the preparation of sulfides from thiol-free reagents

This critical review covers the main thiolating reagents with respect to their characteristics and reactivities. In fact, they are complementary to each other and bring different thiolation strategies, avoiding the hazardous thiol derivatives.

Pd-Catalyzed Directed Thiocyanation Reaction by C-H Bond Activation

The Pd-catalyzed directed thiocyanation reaction of arenes and heteroarenes by C-H bond activation was achieved. In the presence of an electrophilic SCN source, this original methodology offered an efficient tool to access a panel of functionalized thiocyanated compounds (21 examples, up to 78 % yield). Post-functionalization reactions further demonstrated the synthetic utility of the approach by converting the SCN-containing molecules into value-added scaffolds.

Synthesis of diaryl sulfides based on copper-doped OMS-2

We describe a practical protocol for efficiently preparing diaryl sulfide compounds using Cu–OMS-2 as the catalyst. Cu–OMS-2 originates from manganese oxide octahedral molecular sieves modified with copper ions and catalyzes the C–S coupling reaction of substituted thiophenols and aryl halides. This protocol has the advantages of environmental friendliness, simple operation, high yields, good tolerance of functional groups, and the Cu–OMS-2 catalytic material can be recycled several times.

N-Aminopyridinium Ylide-Directed, Copper-Promoted Chalcogenation of Arene C-H Bonds

N-Aminopyridinium ylide-directing group is employed for copper-promoted chalcogenation of sp² C-H bonds with aryl and alkyl disulfides as well as diphenyl diselenide. Reactions proceed in hexafluoroisopropanol (HFIP) solvent at elevated temperatures and are promoted by copper(II) acetate.

IrIII -Catalyzed Selective ortho-Monoiodination of Benzoic Acids with Unbiased C-H Bonds

An iridium-catalyzed selective ortho-monoiodination of benzoic acids with two equivalent C-H bonds is presented. A wide range of electron-rich and electron-poor substrates undergo the reaction under mild conditions, with >20:1 mono/di selectivity. Importantly, the C-H iodination occurs selectively ortho to the carboxylic acid moiety in substrates bearing competing coordinating directing groups. The reaction is performed at room temperature and no inert atmosphere or exclusion of moisture is required. Mechanistic investigations revealed a substrate-dependent reversible C-H activation/protodemetalation step, a substrate-dependent turnover-limiting step, and the crucial role of the AgI additive in the deactivation of the iodination product towards further reaction.

On the development of a nucleophilic methylthiolation methodology

Methylthiolation reactions are usually explored to access organosulfur compounds using methanethiol, an extremely flammable and toxic compound. Herein, methylthiomethyl esters were successfully applied as novel methylthiolation reagents in a low cost, transition-metal-free methodology. These reagents allowed the methylthiolation of a wide scope of chalcones, acyl ester derivatives and Morita-Baylis-Hillman acetates with good group tolerance, affording the methylthiolated products in moderate to excellent yields. The reaction mechanism was investigated through several control experiments, as well as by theoretical calculations employing Density Functional Theory. The results strongly support that a sulfurane and a sulfonium ylide appear as key intermediates and that a Pummerer type rearrangement is also crucial for the formation of this novel reagent. Furthermore, the methylthiolation mechanism is likely to proceed through the nucleophilic attack of the reagent, followed by an entropically favoured step involving the acetate attack to the positively charged species, then releasing the product.

Cobalt-Catalyzed Oxidative C-H Activation: Strategies and Concepts

Inexpensive cobalt-catalyzed oxidative C-H functionalization has emerged as a powerful tool for the construction of C-C and C-Het bonds, which offers unique potential for transformative applications to modern organic synthesis. In the early stage, these transformations typically required stoichiometric and toxic transition metals as sacrificial oxidants; thus, the formation of metal-containing waste was inevitable. In contrast, naturally abundant molecular O₂ has more recently been successfully employed as a green oxidant in cobalt catalysis, thus considerably improving the sustainability of such transformations. Recently, a significant momentum was gained by the use of electricity as a sustainable and environmentally benign redox reagent in cobalt-catalyzed C-H functionalization, thereby preventing the consumption of cost-intensive chemicals while at the same time addressing the considerable safety hazards related to the use of molecular oxygen in combination with flammable organic solvents. Considering the unparalleled potential of the aforementioned approaches for sustainable green synthesis, this Review summarizes the recent progress in cobalt-catalyzed oxidative C-H activation until early 2020.

Acid-Controlled Access to β-Sulfenyl Ketones and α,β-Disulfonyl Ketones by Pummerer Reaction of β-Keto Sulfones and Sulfoxides

A convenient acid-mediated reaction of β-keto sulfones with sulfoxides under metal-free conditions has been developed, thereby delivering the acid-controlled synthesis of β-sulfenyl ketones and α,β-disulfonyl ketones in good to excellent yields. The mechanism of the transformations has been studied carefully, which suggested the involvement of a radical process in the formation of α,β-disulfonyl ketones.

Chelation-assisted transition metal-catalysed C–H chalcogenylations

This review summarizes recent advances in C–S and C–Se formationsviatransition metal-catalyzed C–H functionalization utilizing directing groups to control the site-selectivity.

Synthesis of Benzofulvenes via Cp*Co(III)-Catalyzed C-H Activation and Carbocyclization of Aromatic Ketones with Internal Alkynes

A highly efficient and practical synthesis of benzofulvenes was developed via ketone-directed Cp*Co(III)-catalyzed sequential C-H activation, addition, cyclization, and dehydration cascade processes between simple aromatic ketones and alkynes. The reaction tolerates a variety of functional groups, and various benzofulvenes were efficiently synthesized in 42-92% yields.

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.

Synthesis of 1-naphthols via Cp*Co(iii)-catalyzed C–H activation and cyclization of sulfoxonium ylides with alkynes

A highly practical synthesis of 1-naphthols was developed via Cp*Co(iii)-catalyzed C–H activation and cyclization between sulfoxonium ylides and alkynes.

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.

Cobalt-Catalyzed Direct C-H Thiolation of Aromatic Amides with Disulfides: Application to the Synthesis of Quetiapine

A direct C(sp²)-H thiolation of aromatic amides with disulfides was developed. The coupling reaction proceeds between the thioether radical and cobaltacycle intermediate. This method exhibits a relatively broad substrate scope and high functional group compatibility. A mechanistic study indicates that the cobalt(IV) intermediate is probably formed during the course of the reaction. The thiolation product can be transformed to Quetiapine, which is an atypical antipsychotic agent approved for the treatment of schizophrenia and bipolar disorder.

Metal-free Chlorothiolation of Alkenes using HCl and Sulfoxides

We report a novel method for the chlorothiolation of alkenes using HCl and sulfoxides to achieve the 1,2-difunctionalization of unactivated alkenes. The combination of our new HCl reagent (HCl/DMPU) with sulfoxides forms a unique chlorothiolation system. Both terminal and internal alkenes are suitable substrates. This method works at gram scale and is applicable in further synthetic elaborations.

Selective Synthesis of Aryl Nitriles and 3-Imino-1-oxoisoindolines via Nickel-Promoted C(sp2)-H Cyanations

An efficient nickel-promoted selective monocyanation of benzamides with TMSCN via 8-aminoquinoline directed ortho C-H activation has been developed. Varieties of functionalized ortho-cyanated (hetero)aryl nitriles can be selectively synthesized in moderate to good yields. These cyanation products can be easily transformed into various 3-imino-1-oxoisoindolines in a one-pot procedure. The mild reaction conditions, use of cheap and commercially available reagents, wide functional group tolerance, and operational convenience make this protocol practical to the synthetic community.

Nickel-catalyzed direct C–H bond sulfenylation of acylhydrazines

An efficient Ni-catalyzed direct C–H bond sulfenylation of acylhydrazines for the synthesis of diverse diaryl sulfides.