Unveiling the zwitterionic and stepwise mechanism for the domino reactions of amidine with 1,2,4,5‐ and 1,2,3,5‐tetrazines

Abstract

AbstractThe mechanisms of the domino reactions between 4,6‐diphenyl‐1,2,3,5‐tetrazine (TTZ 1) and 3,6‐diphenyl‐1,2,4,5‐tetrazine (TTZ 2) with amidine 3, have been studied at the M06‐2X/6‐311G(d,p) level of theory. The domino reactions of TTZ1 with amidine comprise three consecutive reactions, an aza Diels‐Alder (ADA) reaction with a stepwise mechanism, a retro Diels‐Alder (rDA) reaction, and an amine elimination process, which leads to the resulting aromatic triazine ring. However, the most favorable pathway for domino reaction of the amidine with TTZ2 consists of nucleophilic addition, N2 elimination, and cyclization steps which is deal with the formation of a neutral intermediate. The N2 loss step in both mechanisms is spontaneously, with extremely exergonic formation of the corresponding intermediates. Finally, NH3 is removed through an irreversible intramolecular elimination. The global electron density transfer (GEDT) calculations unleash the polar natures of the first step of the reactions.