Further Studies and Synthesis of Five-membered Rings via 1,3-Dipolar Cycloaddition of 1-Aza-2-azoniaallene Cations to Isothiocyanates and Nitriles

Abstract

Cycloaddition of 1-aza-2-azoniaallene salts ( 2 , 9 and 17 ) with isothiocyanates gave different types of 1,2,4-triazolium salts ( 5 , 6 and 25-34 ), and 1,3,4-thiadiazolium salts ( 12 , 14 and 19 ). The obtained products depend on: a) the ability of a substituent of the heteroallene salts to undergo a [1,2] shift as a cationic charged migrant or to act as a cationic leaving groups (as a stable carbenium ion), b) Dimroth rearrangement of the initially formed thiadiazolium salts to triazolium salts. Accordingly, 1-aza-2-azoniaallenes ( 22 and 29 ) reacted with nitriles and dinitriles to give 1,2,4-triazolium salts ( 25 , 27 and 32-34 ).