From sulfonium compounds

At present, the method of choice for preparing poly(arylenevinylene)s is the precursor method starting from sulfonium compounds (Fig. 9b). The resulting pol-... 

Synthesis of epoxides from carbonyl compounds and sulfonium salts... 

Sulfonium compounds occur in a wide range of unicellular algae as well as red algae. They have been shown to be the major source of atmospheric sulfur compounds such as dimethyl sulfide and from methanethiol from the ocean, which has a central role ir he global sulfur cycle [143]. 

Cullen et al. (1994) have proposed a possible mechanism of arsenic methylation after the study in which arsenite, arsenate, monomethyl-arsonate or dimethylarsinic acid were added to the growth medium in the presence of the unicellular alga Polyphsa peniculus. Evidence of arsenic biomethylation by the micro-organism Apiotrichum humicola in the presence of L-methionine-methyl-d3 has come from the same laboratory (Cullen et al., 1995). Their findings point to the role of S-adenosylmethionine, or a related sulfonium compound as possible methyl donors. Arsenic biomethylation and biotransformation has also been demonstrated in a freshwater environment (Kuroiwa et al., 1994). 

The simplest sulfur ylids are formed from sulfonium salts 69 by deprotonation in base. These ylids react with carbonyl compounds to give epoxides.18 Nucleophilic attack on the carbonyl group 70 is followed by elimination 71 of dimethylsulfide 72 and formation of the epoxide 73. You should compare diagram 71 with diagram 23 in chapter 15. The phosphonium ylid reacted by formation of a P-0 bond and an alkene in the Wittig reaction. The sulfonium compound reacts by formation of a C-O bond 71 as the S-O bond is much weaker than the P-0 bond. The sulfonium salt 69 can be reformed by reaction of 72 with Mel. 

Rouillon, A., Surdin-Keijan, Y., Thomas, D. (1999). Transport of sulfonium compounds. Characterization of the S adenosylmethionine and S-methylmethionine permeases from the yeast Saccharomyces cerevisiae. J. Biol Chem., 274, 28096-28105. 

An elegant and efficient way for preparation of sulfonium ylides under mild conditions is the so-called Doyle-Kirmse reaction [25,26], which involves transition metal catalyzed decomposition of diazo compounds (usually a-diazocarbonyls) in the presence of sulfides. For the catalytic generation of matallocarbenes from diazo compounds, copper catalysts have traditionally been employed. More recently, rhodium and ruthenium compoimds were reported to be efficient catalysts, especially for the generation of sulfoniiun ylides [27-29]. 

Oxiranes can be prepared in excellent yield from carbonyl compounds by alkylidene transfer with sulfonium ylides. The reaction is generally carried out with dimethylsulfonium methylide 77, dimethylsulfoxonium methylide 78, or related compounds such as anionoid species originating from sulfylimines 79 and sulfox-imines 80 that can undergo addition to the electrophilic carbonyl carbon. 

Methionine is utilized primarily in protein synthesis, providing sulfur for cysteine synthesis, and is the body s principal methyl donor. In methylation reactions, S-adenosylmethionine (SAM) is the methyl group donor. SAM is a sulfonium compound whose adenosyl moiety is derived from ATP as follows ... 

Methionine in plants can be converted to the sulfonium compound S-methyl-L-methionine, also called vitamin U. It has strong osmoprotectant activity and accumulates in many marine algae and some flowering plants.Other organisms, including mammals, can use S-methylmethionine to methylate homocysteine, converting both reactants back to methionine enabling animals to meet some of their methionine need from this source. 

Absorption of quaternary ammonium and sulfonium compounds from the GI tract is incomplete and unpredictable, due to the limited ability of these ionized substances to penetrate cell membranes and depression of propulsive movements of the small intestine and gastric emptying. 

DesilyltUive reactions. A new version of the Peterson olefination employs a combination of ethyl trimethylsilylacetate, an aldehyde, and CsF. Similarly, epoxide synthesis from carbonyl compounds avoids strongly basic conditions by using [Ph SCHjSiMej]" TfO as a source of the sulfonium methylide. ... 

Reported S -substituents are restricted to oxygen or alkyl groups. Both have the expected reactivity patterns of sulfones or sulfonium compounds. The presence of a ring formed from two substituents on the sulfur atom does not confer any special reactivity to A-substituents. 

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