Synthesis of 4,4-diphenyl-3,4-dihydro-2H-1,4-thiasiline

4,4-Diphenyl-3,4-dihydro-2H-1,4-thiasiline (3) was synthesized starting from diphenyl(divinyl)silane by a sequence of reactions including free-radical thiylation with thioacetic acid, reduction of thioacetate to thiol, heterocyclization of the latter, oxidation and the Pummerer rearrangement of the cyclic sulfoxide to the unsaturated cyclic organosilicon sulfide. Although compound 3 is hydrolytically more stable than its Si-dimethylated analogue, both compounds are hydrolyzed to the corresponding siloxanes with the cleavage of the Si? C_sp2 rather than the Si? C_sp3 bond. A theoretical rationalization for this is given.