N-Acyl-1,2,3-triazoles - key intermediates in denitrogenative transformations

Direct N-acylation of 1,2,3-NH-triazoles aimed at obtaining elusive N-acyl-1,2,3-triazoles was investigated. A preference for the formation of thermodynamically favoured N2 isomers was established and an influence of the hard/soft character of the electrophile on the regioselectivity of acylation was found. Although N-acylated 1,2,3-triazoles are hydrolytically unstable compounds, they were isolated and fully characterized, including crystal structure determination of examples of N1 and N2 acylated products by X-ray difraction. N1- and N2-acyltriazoles interconvert in the presence of Bronsted or Lewis acids, which explained the efficiency of triazole cleavage transformations proceeding via N1-acylated triazoles. Efficient synthesis of enamido triflates from NH-triazoles proceeding via the intermediacy of N2-acyl-1,2,3-triazoles was developed.