Benzotriazoles and Triazoloquinones: Rearrangements to Carbazoles, Benzazirines, Azepinediones, and Fulvenimines.

The denitrogenative rearrangements of several types of benzotriazoles were investigated by DFT (B3LYP/6-311G(d,p)) and CASPT2(10,10)sp/6-311G(d,p) calculations. The Graebe-Ullmann synthesis of carbazoles by pyrolysis or photolysis of 1-arylbenzotriazoles proceeds without the involvement of benzazirines and without Wolff-type ring contraction to fulvenimines. However, 1-aryltetrahydrobenzotriazoles undergo both cyclization to tetrahydrocarbazole and ring contraction. Triazoloquinones like undergo predominant ring contraction to aminofulvenediones like and also ring expansion to azepinediones like and cyclization to -arylbenzaziridinediones , whereas carbazolediones are not formed. Denitrogenation of 1-methylbenzotriazole results in a facile 1,2-H shift with formation of -phenylmethanimine . 1-Cyanobenzotriazole undergoes destructive pyrolysis with charring, and the calculations predict the occurrence of several low-activation energy reaction pathways.