Computational Studies on the Intramolecular Cyclization on 1-Aza-2-azoniaallene Salts: C–N Bond Formation via the Nitrogen Rebound Mechanism

The cyclization reaction of 1-aza-2-azoniaallene salts plays a significant role in the synthesis of nitrogen-containing heterocyclic compounds. Starting from α-chloroazo compounds and halophilic Lewis acids, the detailed mechanisms of intramolecular cyclization for two different 1-aza-2-azoniaallene salts were investigated by using density functional theory (DFT). The results indicate that the dechlorination step proceeds readily in both reactions, and the resulting anions derived from the halophilic Lewis acids exert minimal influence on subsequent transformation steps. The formation of the carbon-nitrogen bond─the key step in both cyclization processes, occurs via the nitrogen rebound mechanism through an asynchronous concerted transition state, as demonstrated by intrinsic reaction coordinate (IRC) analysis and the bonding evolution theory (BET).