Rearrangement and elimination reactions in 1,2,4-triazole derivatives

Abstract

Four possible nucleophilic sites are available when 3-amino-1,2,4-triazole (4) reacts with isocyanates or alkylating agents. In the reaction with ethoxycarbonyl isothiocyanate at 22°, addition to a ring nitrogen took place yielding 5-amino-1-[ethoxycarbonylarnino(thiocarbonyl)]-1,2,4-triazole (1). The rearrangement of compound (1) to the amino-substituted isomer (2) in dimethylformamide was followed by n.m.r. spectroscopy and found to be complete in 34 min under ambient conditions. In pyridine solution compound (1) reacted differently, with HNCS elimination, to give 5-amino-1-ethoxycarbonyl-1,2,4-triazole (3). Two additional isomers of (3) were prepared, by the rearrangement of (3) and by the low temperature reaction of (4) with ethyl chloroformate. The carbonyl analogues of (1) and (2) were prepared by use of the analogous isocyanate. The ring-substituted carbonyl compound rearranged more slowly to the amino-substituted isomer than did compound (1), and elimination of HNCO was not observed. Both carbonyl analogues were cyclised to [1,2,4]triazolo[1,5-a][1,3,5]triazine-5,7-dione (5-azaxanthine). Two methylaminocarbonyl derivatives of (4) were also prepared, isolated, and characterized.