Synthesis and reactions of some azolecarboxylic acid derivatives

Reaction of several azoles with phosgene or triphosgene was studied. Besides benzotriazole (previously described reaction), only indazole, 5-nitroindazole and 5-methylbenzotriazole gave the corresponding 1-azolecarbonyl chlorides 1a-d. Azoles of weak acidity (imidazole, 1,2,3-triazole, 1,2,4-triazole, benzimidazole) could not give stable acyl chlorides, while strong acidic azoles like tetrazole and 4,5,6,7-tetrachlorobenzotriazole did not react at all. Chlorides 1b-d readily reacted with alcohols, amines, amino acids and their esters like the previously described 1-benzotriazolecarboxylic acid chloride (1a), giving 1-azolecarboxylic acid esters (2) or amides (3), N-(1-azolecarbonyl)amino acids (4, 5), their esters (8, 9) or amides (10, 11). However, a significant difference was observed in the reactivity of azole derivatives 2-11 with amines, alcohols and N-protected amino acids or in their stability in acidic and basic aqueous media. Benzotriazole and methylbenzotriazole derivatives were more reactive than indazole or nitroindazole derivatives. The higher reactivity was in correlation with the shift of the IR carbonyl absorption band to higher wave numbers.