New heterocyclization reactions for the preparation of fused [1,2,4]triazoles: synthesis of 1,2,4-triazolo[4,3-b][1,2,4]triazole derivatives from 4-amino-1,2,4-triazoles and carbodi-imides or via iminophosphoranes and disubstituted thioureas

Abstract

A number of 1,2,4-triazolo[4,3-b][1,2,4]triazole derivatives have been prepared. 4-Amino-2-methyl-5-methylthio-2H-1,2,4-triazol-3(4H)-one (1) reacts with diarylcarbodi-imides to yield the corresponding 4-(N,N′-diaryl)guanidino-2-methyl-5-methylthio-2H-1,2,4-triazol-3(4H)-ones (3)—(6). Reaction of the 2-methyl-5-methylthio-4-triphenylphosphoranylideneamino-2H-1,2,4-triazole-3(4H)-thione (2) with N,N′-diaryl thioureas leads to the corresponding 4-(N,N′-diaryl)guanidino-2-methyl-5-methylthio-2H-1,2,4-triazole-3(4H)-thiones (7)–(10). Compounds (3)—(10) undergo base-catalysed cyclization to give the 1,2,4-triazolo[4,3-b][1,2,4]triazoles (11)—(18). Sequential treatment of triazolo-triazoles (15)—(18) with methyl trifluoromethanesulphonate and triethylamine leads to the conjugated mesomeric betaines (23)—(26); on the other hand; sequential treatment of triazoles (7) and (10) with methyl trifluoromethanesulphonate and triethylamine leads to the mesomeric betaines (29) and (30).