ALPHA-THIOXOTHIOAMIDES - [4-CYCLOADDIT ION REACTIONS WITH DIMETHYL ACETYLENEDICARBOXYLATE AND METHYL PROPIOLATE(2])

The title compounds are prepared from methyl ketones through a three-s tep reaction: chloration with thionyl chloride; amination of the resul ting alpha-chloro-beta-oxosulfenyl chlorides; and thionation of alpha- oxothioamides with Lawesson's reagent. Two competitive hetero-Diels-Al der processes were observed in the presence of acetylenic dienophiles according to the involved system, 1,4-dithiabutadiene or possible 1-th iabutadiene arrangement. Cycloaddition on dithiabutadiene gives unstab le 1,4-dithiines which contract to thiophenes via sulfur extrusion. Cy cloaddition on thiabutadiene yields the corresponding fused thiopyrans . The regiochemical preferences in these [4 + 2] cycloaddition and rin g contraction reactions have been demonstrated.