Methanesulfenic acid

Methylsulfinyl enolates are more recently developed d -reagents. They are readily prepared from carboxylic esters and dimsyl anion. Methanesulfenic acid can be eliminated thermally after the condensation has taken place. An example is found in Bartlett s Brefeldin synthesis (P.A. Bartlett. 1978). 

The formation of dimethyl sulfide, dimethyl sulfone, and methane (by H-abstraction) observed in these photolyses is thus accounted for. Hydrogen abstraction by the methylsulfinyl radical affords methanesulfenic acid, CH3SOH, a very reactive molecule, which rapidly undergoes a series of secondary reactions to produce the methanesulfonic acid, methyl methanethiolsulfonate (CH3S02SCH3), and dimethyl disulfide which were also observed during these photolyses. 

Furthermore, as described by Mori and coworkers, the domino aldol/cyclization reaction of the 3-keto sulfoxide 2-422 with succindialdehyde (2-423) in the presence of piperidine at r.t. afforded the chromone 2-424 which, on heating to 140 °C, underwent a thermal syn-elimination of methanesulfenic acid to provide 2-426 in 22 % overall yield (Scheme 2.100) [227]. This approach was then used for the synthesis of the natural products coniochaetones A (2-425) and B (2-427) [228]. 

For DMS and DMTS, S-mothyl-L-cysteine sulfoxide is a precursor action of a C-S lyase enzyme yields methanesulfenic acid, CH3-S-OH, and hence methyl methanethiosulfinate, CH3-SO-S-CH3. Disproportionation reactions yield polysulfides such as DMS.56... 

Sulfoxonium ylides also undergo 3,2-sigmatropic rearrangements. A useful preparation of conjugated dienes is based on a 3,2-rearrangement followed by spontaneous elimination of methanesulfenic acid (Scheme 59, equation a). In some cases, the reaction proceeds without isolation of the intermediate ylide (Scheme 59, equation b). 

Methyl Methanethiosulfinate. Methanethiol-related compounds are secondary products of the primary C-S lyase action on S-methyl-L-cysteine sulfoxide (19). The primary product, presumably methanesulfenic acid, is very unstable and facilely convert to methyl methanethiosulfinate which has been found in macerated Brussels sprouts (20). Methyl methanethiosulfinate has also been reported to be present in a model system composed of S-methyl-L-cysteine sulfoxide and partially purified cabbage C-S lyase (20). 

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