A CONVERGENT SYNTHESIS OF GAMMA-UNSATURATED THIOALDEHYDE-S-OXIDES ANDTHIOKETONE-S-OXIDES

A general synthesis of the title compounds 4 is described, involving e ither treatment of vinylic or allenic sulfinates with allylic Grignard reagents, or allylic or allenic sulfinates with vinylic Grignard reag ents. Some alpha,beta-ethylenic thioaldehyde-S-oxides undergo a cycloa romatization to thiophenes 16, 19. Upon standing, the beta,beta-disubs tituted gamma-acetylenic thioaldehyde-S-oxides 21e-j dimerize to the s ubstituted 1,2-dithietane-1,l-dioxides 22a-f. Treatment of trans 22b-e with lithium cyanide in THF leads smoothly to the corresponding (Z)-a lkenes 28a-d.