Cycloadditions of 1-aza-2-azoniaallene cations to isothiocyanates

Isothiocyanates react as S-nucleophiles with 1-aza-2-azoniaallene salts 1 to give different types of 1,3,4-thiadiazolium salts (9, 11, 12) and 1,2,4-triazolium salts (10). Which product is formed, depends on the one hand on the ability of a substituent of the heteroallene salt 1 to undergo a [1,2] shift as a positively charged migrant (generalized Wagner–Meerwein rearrangement) or to act as a cationic leaving group, and on the other hand on Dimroth rearrangement of the initially formed thiadiazolium salt 8 to triazolium salts. The structures of the thiadiazolium salt 9c and the triazolium salt 10d were confirmed by X-ray structural analyses.