Synthesis of 1,2,3-thiadiazole-5-carbaldehydes and their conversion into 6aδ4-Thia-1,2,5,6-tetraazapentalenes

A convenient method for the synthesis of the virtually unknown 1,2,3-thiadiazole-5-carbaldehydes consists in monobromination of the 5-methyl derivatives, followed by treatment with sodium azide and decomposition in concentrated sulfuric acid ( 6 → 7 → 9 → 10 ). These compounds can be transformed via methylation of the corresponding hydrazones 12 into 6aδ⁴-thia-1,2,5,6-tetraazapentalenes 13 .