METHYLTHIOLATION OF UNSATURATED SULFIDES - THIOSULFONIUM IONS

The reactions of methanesulfenyl chloride and dimethyl(methylthio)sulfonium fluoroborate with 2-propenyl methyl sulfide, 3-butenyl methyl sulfide, and 4-pentenyl methyl sulfide are described. Addition to the double bond occurs in each case. 1-Chloro-2, 3-bis(methylthio)propane is the kinetic product of addition of CH3SCl to 2-propenyl methyl sulfide, and this product rearranges on heating at 100 °C for 2-3 days to an equilibrium 34: 66 mixture of 1-chloro-and 2-chlorobis(methylthio)propanes. The rate of the reaction was followed using the adducts of 2-pro-penyl methyl-d3 sulfide and CH3SCl, and the data provide support for the intervention of an unsymmetrical thiiranium intermediate. The adduct formed from 2-propenyl methyl sulfide and the sulfenyl salt (CH3)2+SSCH3 BFBF4- does not rearrange on heating. Methylthiolation of the higher homologues, 3-butenyl and 4-pentenyl methyl sulfides, produces adducts that do not rearrange and which do not show exchange or scrambling of alkylthio groups. The adduct of CH3SCl and 3-butenyl methyl sulfide was identified as l-chloro-2, 4-bis(methylthio)butane. In contrast, the salt (CH3)2 + SSCH3 BF4- forms a cyclic sulfonium salt with 3-butenyl methyl sulfide. In the case of 4-pen-tenyl methyl sulfide, only cyclic products were obtained on reaction with sulfenyl reagents. © 1979, American Chemical Society. All rights reserved.