Dimerization reactions, thiocarbonyl ylide

Over the past two decades, important contributions to the chemistry of thiocarbonyl ylides were made by Huisgen et al. (27). By carrying out the reaction of thiobenzophenone with diazomethane at low temperature, formation of 2,5-dihydro-l,3,4-thiadiazole (15) with subsequent elimination of N2 was established as the route to the reactive thiobenzophenone (S)-methylide (16) (17,28). In the absence of intercepting reagents, 16 undergoes electrocyclization to give 17 or head-to-head dimerization to yield 1,4-dithiane 18 (Scheme 5.3). 

Oxathietans, Oxathiets, and Dioxathietans.—Oxathietan intermediates have been considered in the reaction of thiocarbonyl ylides with diphenylketen and in the vapour-phase thermolysis of S-methoxymethyl thioacetates. The behaviour of solutions of monothiobenzil may indicate isomerization to an oxathiet. The photo-oxidation of tetramethyl-3-thiocyclobutane-l,3-dione by oxygen may proceed via a l,2-dioxa-3-thietan. The l,3-dioxa-2-thietan 2,2-dioxide (210) was obtained by treatment of 3,3,3-trifluoro-2-tri-fluoromethylpropanoic acid with sulphur trioxide. It is cleaved by various nucleophiles to bis-trifluoromethylketen, which dimerizes, and its reactions with fluoroethylenes have been determined. Thermolysis of (210) yields anhydride (211). ... 

---