Organic heterocyclothiazenes. Part 1. The trithiadiazepine and trithiatriazepine ring systems

Abstract

Reaction of S₄N₄ with dimethyl acetylenedicarboxylate in boiling toluene has been found to give dimethyl 1,2,5-thiadiazole-3,4-dicarboxylate (3) as the major product, together with the rearranged dimethyl 1,2,4-thiadiazole-3,5-dicarboxylate (4), dimethyl 1,3λ⁴δ²,5,2,4-trithiadiazepine-6,7-dicarboxylate (7), and methyl 1,3λ⁴δ²,5,2,4,6-trithiatriazepìne-7-carboxylate (8). The two seven-membered rings are new stable planar delocalised 10π electron aromatic systems. Mechanisms involving cycloaddition, rearrangement, and ring cleavage are proposed for the formation of the products.