AN UNORTHODOX PATHWAY TO THE 1,2-DITHIIN SYSTEM

Tetracyanoethylene combines with two molecules of thiobenzophenone in refluxing benzene to give the tetrasubstituted 1,2-dithiin 8(21-29%) b esides the corresponding thiophene derivative 9 (40-52%). The X-ray an alysis of the ruby-red 8 reveals a half-chair conformation with a tors ion angle of 58.9 degrees at the disulfide bond. The thermal desulfuri zation 8-->9 (benzonithrile, 100 degrees C) proceeds with t(1/2) = 26. 7 h, whereas the sulfur loss induced by triethyl phosphite is a billio n times faster. The mechanisms of the formation of 8 and its sulfur ex trusion are discussed in the light of recent literature.