1,3-dipolar cycloadditions, 117 Reactions of thiobenzophenone S-methylide with thiocarbonyl compounds

2,5-Dihydro-2,2-diphenyl-1,3,4-thiadiazole (4) eliminates N-2 at -45 degree s C and generates thiobenzophenone S-methylide (5), which is intercepted by dipolarophiles. The 1,3-cycloadditions of 5 with thiones (aromatic and ali phatic thioketones, dithioesters, trithiocarbonate) furnish 1,3-dithiolanes 7, in which the substituents, even voluminous ones, appear in the proximal 4- and 5-positions. The reaction of 5 with adamant-anethione furnishes 7h and 4,4,5,5-tetraphenyl-1,3-dithiolane (7a) in a ratio of 4:1; a methylene transfer is involved, and the mechanistic pathways are discussed. The cyclo adduct 7f originating from 5 and diphenyl trithiocarbonate undergoes an iso merization which consists of ionization and ring-opening leading to a keten e dithioacetal structure.