Mechanistic investigations on C–H activated dealkylating cyclo-amination reactions of substituted triazenes, formamidines and amidines

Abstract

Abstract Catalytic dealkylating cycloamination reactions of N 1-methylated-N 1,N 3-diarylated triazenes proceed via two subsequent oxidative addition reactions, regioselectivity producing benzotriazoles by C–H and C–Br activation steps. Whereas palladium-based catalysis in the presence of dealkylating reagents and directing phosphane ligands leads to high yields, the homologous metals nickel and platinum as well as other 3d transition metals show only poor catalytic activity in similar procedures. Starting compounds have been widely varied to introduce potentially competing reaction sites and to investigate the reaction mechanism of the catalytic cyclization reactions. Yields of the benzotriazole synthesis strongly depend on the electronic and steric properties of the directing phosphane ligands, the nature of the dealkylating bases and the substitution pattern in 2- and 4-position of the aryl groups of the starting triazenes. In order to clarify the role of the catalyst, palladium-based intermediates were identified. Finally, formamidines and bulky amidines were tested in related C–H activated dealkylating cycloamination reactions.