Base-Promoted Synthesis of Vinyl Sulfides from Sulfonium Triflates

O-Acylation triggered γ-umpolung functionalization of electron-poor alkenyl sulfoxides for the synthesis of 3-allyl indoles

Indole scaffolds, which are important structural motifs in organic chemistry, have garnered sustained interest due to their prevalence in pharmaceuticals, agrochemicals, and natural products. This study establishes a novel umpolung activation strategy for γ-position functionalization of electron-poor alkenyl sulfoxides, generating allylidenesulfonium intermediates that are subsequently trapped by indoles, achieving the synthesis of 3-functionalized indoles. Further transformations and plausible mechanism were investigated.

Recent Applications of Sulfonium Salts in Synthesis and Catalysis

The use of sulfonium salts in organic synthesis has experienced a dramatic increase during the last years that can arguably be attributed to three main factors; the development of more direct and efficient synthetic methods that make easily available sulfonium reagents of a wide structural variety, their intrinsic thermal stability, which facilitates their structural modification, handling and purification even on large scale, and the recognition that their reactivity resembles that of hypervalent iodine compounds and therefore, they can be used as replacement of such reagents for most of their uses. This renewed interest has led to the improvement of already existing reactions, as well as to the discovery of unprecedented transformations; in particular, by the implementation of photocatalytic protocols. This review aims to summarize the most recent advancements on the area focusing on the work published during and after 2020. The scope of the methods developed will be highlighted and their limitations critically evaluated.

Efficient accessibility of indole and pyrrole nuclei via late-stage aryl C-H activation of drug molecules promoted by thianthrenium salts

An efficient redox-neutral palladium-catalyzed system has been developed to introduce indole and pyrrole units to a wide range of bioactive molecules via late-stage aryl C-H activation, providing a robust tool for medicinal chemists to explore structure-activity relationships (SARs). Furthermore, the successful gram-scale reaction and subsequent synthetic investigations demonstrate the potential application of this established method in organic synthesis, materials science, and biochemistry.

Photoredox Ring Opening 1,2-Alkylarylation of Alkenes with Sulfonium Salts Toward Thioether-Substituted Oxindoles

A novel strategy for the difunctionalization of electron-deficient alkenes with aryl sulfonium salts to access remote sulfur-containing oxindole derivatives by using in situ-formed copper(I)-based complexes as a photoredox catalyst is presented. This method enables the generation of the C(sp3)-centered radicals through site selective cleavage of the C-S bond of aryl sulfonium salts under mild conditions. Moreover, the oxidation reactions of desired products provide a new strategy for the preparation of sulfoxide or sulfone-containing compounds. Importantly, this approach can be easily applied to late-stage modification of pharmaceuticals molecules.

Synthesis of alkynyl sulfides via base-promoted nucleophilic ring-opening of α-bromostyrene sulfonium salt

An efficient method for the synthesis of alkynyl sulfides via a C(sp3)-S bond cleavage of α-bromostyrene sulfonium salts has been developed. This base-promoted nucleophilic ring-opening pathway allows the preparation of diverse alkynyl sulfide compounds using tetramethylene sulfoxide as the sulfur source. The reaction proceeds with good functional group tolerance and could be applied to the late-stage functionalization of bioactive molecules and drugs. Furthermore, the synthetic utility of this method was demonstrated by a one-pot synthesis, scale-up reaction and further modification of various alkynyl sulfide products.

One-Pot, Three-Component Assembly of Sulfides Using a Sulfoxide Reagent as a Sulfur Dication Equivalent

We report a one-pot, three-component synthesis of sulfides by exploiting a sulfoxide reagent as a formal sulfur dication equivalent. Our protocol consists of three simple chemical operations involving two Grignard reagents and trimethylsilyl chloride (TMSCl) to sequentially form sulfenate anions, sulfenate esters, and sulfides. We demonstrate a wide range of Grignard reagents to be coupled, thereby allowing the modular, thiol-free synthesis of sulfides including dialkenyl and alkenyl-alkynyl sulfides.

1,4-Dithianes: attractive C2-building blocks for the synthesis of complex molecular architectures

This review covers the synthetic applications of 1,4-dithianes, as well as derivatives thereof at various oxidation states. The selected examples show how the specific heterocyclic reactivity can be harnessed for the controlled synthesis of carbon-carbon bonds. The reactivity is compared to and put into context with more common synthetic building blocks, such as 1,3-dithianes and (hetero)aromatic building blocks. 1,4-Dithianes have as yet not been investigated to the same extent as their well-known 1,3-dithiane counterparts, but they do offer attractive transformations that can find good use in the assembly of a wide array of complex molecular architectures, ranging from lipids and carbohydrates to various carbocyclic scaffolds. This versatility arises from the possibility to chemoselectively cleave or reduce the sulfur-heterocycle to reveal a versatile C2-synthon.