ALKYLTHIOLATION OF ALLYLIC SULFIDES - [2,3] SIGMATROPIC REARRANGEMENT OF THIOSULFONIUM IONS

The reactions of sulfenyl compounds RʹSX (X = Cl or +S(CH3)2) with various alkyl allyl sulfides RSCH2CH=CH2 (R = CH3, C2H5, i-C3H7, i-C4H9, C6H5, and C6H5CHCH3) in nitromethane or chloroform solution have been investigated. The results show that sulfenyl reagents add to the allylic double bond by an involved sequence in which an alkylthio group is transferred initially to the sulfur atom of the allylic sulfide. The resulting thiosulfonium ions CH2=CHCH2+S(SRʹ)R X- are formed reversibly when X = +S(CH3)2 and irreversibly when X = Cl. They undergo allylic rearrangement and alkyl migration depending on R and Rʹ. The observed adducts are derived in part from thiosulfonium intermediates by intramolecular transfer of RS or RʹS from positive sulfur to the double-bond carbons, and in part by direct addition of RʹSX to the double bond of the sulfide. Rearrangementof thiosulfonium ions leads to scrambling of RS and RʹS groups in the adducts and to alkylthio exchange in the starting sulfides. The extent of rearrangement decreases with increasing size of the alkylthio group. Negligible rearrangement occurs in the methylthiolation of phenyl allyl sulfide. © 1979, American Chemical Society. All rights reserved.