Interplay of dual reactivity in the reaction of pentafulvenes with 1,2,4-triazoline-3,5-diones: experimental and theoretical investigations

Abstract

A detailed investigation on the reaction of pentafulvenes with N-substituted-1,2,4-triazoline-3,5-diones leading to the formation of five- and seven-membered azapolycycles is described. The observed reactivity is explained based on the electronic and frontier molecular orbital features of pentafulvene and triazoline dione, which suggested that the latter molecule can add to the former one via a [4 + 2] cycloaddition or it can undergo a nucleophilic reaction at the exo carbon atom of pentafulvene. These reactions would ultimately give the same product and the energetics of them suggested that both mechanisms are operative in the reaction conditions.