A computational study and valence bond approach to the intramolecular electrophilic aromatic substitution mechanism of ortho-allyl-N-benzylanilines

Ab initio computational studies were performed for the intramolecular Friedel–Crafts alkylation of ortho-allyl-N-benzylanilines catalyzed by sulfuric acid, which results in the formation of both dihydrodibenz[b,e]azepine and tetrahydrodibenz[b,f]azocine isomers. This intramolecular reaction occurs through the rearrangement of the cationic species generated from the allyl moiety and falls into the type of electrophilic aromatic substitution rearrangements. Due to this fact, we discuss the reactivity trends of the intermediate species participated in this competitive 7-exo-trig versus 8-exo-trig cyclization process. The valence bond configuration mixing is used for this purpose and with this model the reduced potential energy surface and the reaction profile are constructed. The expected patterns such as single step or stepwise mechanism, and the trends in the reaction barriers for the electrophilic attack effects of the aryl substituents are discussed.