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

Abstract

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 18 by pyrolysis or photolysis of 1-arylbenzotriazoles 14 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 34 undergo predominant ring contraction to aminofulvenediones like 38 and also ring expansion to azepinediones like 40 and cyclization to N-arylbenzaziridinediones 39, whereas carbazolediones are not formed. Denitrogenation of 1-methylbenzotriazole 64 results in a facile 1,2-H shift with formation of N-phenylmethanimine 67. 1-Cyanobenzotriazole 71 undergoes destructive pyrolysis with charring, and the calculations predict the occurrence of several low-activation energy reaction pathways.

Preparation of Carbazoles Involving 6π‐Electrocyclization, Photoredox‐, Electrochemical‐, and Thermal Cyclization Reactions: Mechanistic Insights

“…Wentrup and colleagues conducted a thorough computational study on the mechanism of photolysis and pyrolysis of 1arylbenzotriazoles. [79] Pyrolytic processes [80,81] and photolytic reactions [82][83][84] applied to 1-arylbenzotriazoles A were known to yield carbazoles B in significant yields, as outlined in Scheme 45. Intermediate diazo compounds E,Z-XXIII were detected in matrix photolysis reactions.…”

Thermochemistry, Tautomerism, and Thermal Stability of 5,7-Dinitrobenzotriazoles

“…These values are the only available information on the thermal behavior of DBT and ADBT . At the same time, benzotriazoles with various non-explosophoric moieties have been extensively studied, and their pyrolysis and photolysis were proposed to occur via N 2 elimination [ 17 , 18 , 19 , 20 ]. In order to obtain a deeper insight into the possible decomposition mechanisms of dinitrobenzotriazoles, we also considered the structurally similar dinitrotriazolopyridines 3 and 4 , and simpler species with the dinitrobenzotriazoles skeleton, viz., 1,3-nitrobenzene ( 5 ) and 1,2,3-triazole ( 6 , Figure 1 ).…”

Visible-light-photocatalysis driven denitrogenative/radical 1,3-shift of benzotriazole: access to 3-aryl-aminoquinoxalin-2(1H)-one scaffolds

“…Due to their unique structural motif, considerable progress has been made in the utilization of this fascinating chemistry including unexpected cyclization and cross-coupling reactions, leading to the construction of various pharmacologically relevant nitrogen-containing compounds (Scheme 1c). 13 Considering their inherent reactivity, we wondered if they could be photo-initiated under light irradiation to release N 2 , delivering the ortho -amino aryl radical and subsequently undergoing a radical 1,3-shift to produce a new amino radical ( N -radical) that can serve as a novel aromatic amine source. With our long-standing interest in visible-light-induced photoredox organic chemical transformation and green synthesis, 14 herein we describe a visible-light-photocatalysis driven denitrogenative/radical 1,3-shift of benzotriazole to generate an unusual aromatic amine radical which then undergoes direct amination with quinoxalin-2(1 H )-ones, leading to 3-aryl-aminoquinoxalin-2(1 H )-ones (Scheme 1d).…”