STEREOSELECTIVE FORMATION OF ALLYLIC SULFIDES VIA 2 SEQUENTIAL [3,3]-SIGMATROPIC REARRANGEMENTS OF ALLYLIC XANTHATES AND ITS MECHANISTIC ASPECTS

O-(2-Alkenyl) S-alkyl dithiocarbonates (allylic xanthates) were pyrolyzed to give 2-alkenyl alkyl sulfides (allylic sulfides) via the corresponding allylically isomeric S-(2-alkenyl) S-alkyl dithiocarbonates. The reaction follows the firstorder rate law with relatively low sensitivity to the ionizing power of the medium and sizeably negative entropies of activation. When a mixture of two dithiol esters having different S-(2-alkenyl) groups and different S-alkyl groups was pyrolyzed, a “cross product” was not observed. The reaction was found to be facilitated by the presence of phenolic compounds or Lewis acids. Based on these findings together with modified neglect of diatomic overlap (MNDO) calculation data, the mechanism for the formation reaction of 2-alkenyl alkyl sulfides is discussed. © 1990, The Pharmaceutical Society of Japan. All rights reserved.