Rearrangements and fragmentations of phenyl styryl sulfides: 2—labelling studies

Metastable molecular ions of phenyl styryl sulfides may decompose by loss of CH₃^˙, SH^˙, CHS^˙, C₆H₅^˙, C₆H₆ or C₇H₇^˙. Labelling with carbon-13 and deuterium gave information about the mechanisms of these reactions. It appears that extensive rearrangements occur prior to most of these fragmentations. In the case of phenyl β-styryl sulfide both phenyl groups and both vinyl carbon atoms are found in the C₇H₇ fragment in comparable amounts. For phenyl α-styryl sulfide this fragmentation leads more specifically to the loss of the S-phenyl group and the β-vinyl carbon atom. It was concluded that rearrangements occur, partly via symmetric diphenyl ethene sulfide structures, to benzyl phenyl thione ions, from which the fragmentation occurs. For the loss of CHS^˙ an earlier proposed mechanism was confirmed. From both compounds the S-phenyl ring can be lost as C₆H₅^˙ or C₆H₆ as well as the C-phenyl ring. Fragmentation occurs from one of the initial structures as well as from benzyl phenyl thione. Loss of CH₃^˙ is thought to occur after ring closure with formation of dihydrobenzob]thiophenes followed by ring opening by rupture of a C? S bond. While phenyl β-styryl sulfide shows a strong tendency towards isomerization to a symmetric structure like 1,2-diphenylethene sulfide, phenyl α-styryl sulfide easily rearranges in an electrocyclic reaction with formation of benzyl phenyl thione.