Transition-Metal-Catalyzed C−S, C−Se, and C−Te Bond Formation via Cross-Coupling and Atom-Economic Addition Reactions

Sulfur-containing molecules such as thioethers are commonly found in chemical biology, organic synthesis, and materials chemistry. While many reliable methods have been developed for preparing these compounds, harsh reaction conditions are usually required in the traditional methods. The transition metals have been applied in this field, and the palladium-catalyzed coupling of thiols with aryl halides and pseudo halides is one of the most important methods in the synthesis of thioethers. Other metals have also been used for the same purpose. Here, we summarize recent efforts in metal-catalyzed C-S bond cross-coupling reactions, focusing especially on the coupling of thiols with aryl- and vinyl halides based on different metals.

Transition-metal-catalyzed C-S bond coupling reaction.

Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

The presence of aryl sulfides in biologically active compounds has resulted in the development of new methods to form carbon-sulfur bonds. The synthesis of aryl sulfides via metal catalysis has significantly increased in recent years. Historically, thiolates and sulfides have been thought to plague catalyst activity in the presence of transition metals. Indeed, strong coordination of thiolates and thioethers to transition metals can often hinder catalytic activity; however, various catalysts are able to withstand catalyst deactivation and form aryl carbon-sulfur bonds in high-yielding transformations. This review discusses the metal-catalyzed arylation of thiols and the use of disulfides as metal-thiolate precursors for the formation of C-S bonds.

/pdf/transition-metal-catalyzed-synthesis-of-aryl-sulfides-3bkoo3wo5j.pdf

Transition metal catalyzed synthesis of aryl sulfides.

Transition-metal-catalyzed cross-coupling reactions have become indispensable tools for the synthetic chemist. 2] The construction of carbon–heteroatom bonds is of particular interest. Consequently, a large number of general and efficient systems for the catalytic amination and etherification of aryl and vinyl halides have been described. 4] In contrast, research in the field of carbon–sulfur coupling reactions has lagged behind, largely because of sulfur’s long-standing reputation as a catalyst poison. Despite this difficulty, coupling reactions of thiols with aryl halides under the catalysis of Pd, Cu, Ni, Co, Fe, and In have been reported. Reactions of vinyl halides are comparatively rare: only a handful of publications describe the vinylation of thiols, 15] and the palladium-catalyzed intramolecular coupling is unknown. We anticipated that the use of Pd could facilitate access to a number of tandem coupling reactions in which an Svinylation reaction could be combined with orthogonal carbon–carbon bond formation in a single synthetic operation. Tandem/domino reactions are an area of intense research, as they enable streamlined synthetic sequences and a consequent reduction of waste. Herein, we disclose a tandem catalytic reaction of a gem-dihalovinyl thiophenol system in which an intramolecular S-vinylation is paired with an intermolecular C C bond-forming reaction (a Suzuki– Miyaura, Heck, or Sonogashira reaction) to yield 2-substituted benzothiophenes (Scheme 1). These heterocycles form the core of a number of medicinally important molecules, such as raloxifene and zileuton. However, catalytic routes to these targets have only recently been developed. To the best of our knowledge, the reaction described herein is the first example of a tandem catalytic process that incorporates a C S coupling, as well as the first example of the palladium-catalyzed vinylation of a thiol. We and others have previously reported the synthesis of indoles substituted at the 2-position by tandem coupling reactions of gem-dihalovinyl anilines. In these systems, an intramolecular amination or amidation was combined with an interor intramolecular Suzuki–Miyaura, Heck, or Sonogashira coupling, amidation, direct arylation, or carbonylation. Similar transformations involving C S coupling would provide rapid access to benzothiophenes and expand the range of available tandem coupling reactions. Our initial attempts were aimed at combining the carbon– sulfur bond-forming process with a Suzuki–Miyaura coupling (Table 1). We found that the conditions developed previously for the aniline system were less effective for the thiophenol substrate 1a : the desired product was isolated in only 48% yield (Table 1, entry 1). The screening of various bases (Table 1, entries 1–4, 8), precatalysts (entries 5–7), and ligand/ catalyst ratios (entries 9 and 10) revealed that the best results were obtained when the reaction was carried out with PdCl2, SPhos, and anhydrous K3PO4/Et3N in dioxane at 110 8C. Under these conditions, 2 a was formed in 89 % yield (Table 1, entry 10). Lowering of the catalyst loading to 1 mol % led to enhanced turnover with minimal impact on the yield (Table 1, entry 12). With these optimized conditions in hand, we investigated the effect of varying the boronic acid on the tandem process (Table 2). The reaction was found to tolerate changes in the electronic nature of the boronic acid. Electron-poor boronic acids displayed similar reactivity to that of electron-rich 3,4dimethoxyphenylboronic acid: the boronic acid used for optimization of the reaction (Table 2, entries 1–4). The coupling proceeded equally well when a sterically congested boronic acid was used (Table 2, entry 5). The use of heteroaromatic boronic acids gave the best results: the corresponding heterocyclic products were obtained in up to 99% yield Scheme 1. Retrosynthetic strategy.

Efficient synthesis of benzothiophenes by an unusual palladium-catalyzed vinylic C-S coupling.

Successive copper(I)-catalyzed cross-couplings in one pot: A novel and efficient starting point for synthesis of carbapenems

Catalytic Asymmetric Intermolecular Bromoesterification of Unfunctionalized Olefins

This paper describes azidation of indoles with NaN3 and ceric ammonium nitrate (CAN), giving a variety of spirocyclic 2-azido indolines in good yields and moderate diastereoselectivities.

A facile approach to spirocyclic 2-azido indolines via azidation of indoles with ceric ammonium nitrate

An effective enantioselective 6-endo bromoaminocyclization of 2,4-dienyl N-tosylcarbamates catalyzed by a chiral phosphine oxide-Sc(OTf)3 complex is described. A wide variety of optically active 5-bromo-1,3-oxazinan-2-ones containing various functional groups can be obtained in 61–91% yields and 92–99% ees. An additive, such as NaCl, has been found to be crucial for the reaction process.

Enantioselective 6-endo bromoaminocyclization of 2,4-dienyl N-tosylcarbamates catalyzed by a chiral phosphine oxide-Sc(OTf)3 complex. A dramatic additive effect

Phosphine Oxide-Sc(OTf)3 Catalyzed Highly Regio- and Enantioselective Bromoaminocyclization of (E)-Cinnamyl Tosylcarbamates. An Approach to a Class of Synthetically Versatile Functionalized Molecules.

Hua Tian

Papers

Successive copper(I)-catalyzed cross-couplings in one pot: A novel and efficient starting point for synthesis of carbapenems

Catalytic Asymmetric Intermolecular Bromoesterification of Unfunctionalized Olefins

A facile approach to spirocyclic 2-azido indolines via azidation of indoles with ceric ammonium nitrate

Enantioselective 6-endo bromoaminocyclization of 2,4-dienyl N-tosylcarbamates catalyzed by a chiral phosphine oxide-Sc(OTf)3 complex. A dramatic additive effect

Phosphine Oxide-Sc(OTf)3 Catalyzed Highly Regio- and Enantioselective Bromoaminocyclization of (E)-Cinnamyl Tosylcarbamates. An Approach to a Class of Synthetically Versatile Functionalized Molecules.