Theoretical studies on formal hetero [3+3] cycloaddition reaction between vinylogous amide and α,β-unsaturated imine cation

Density functional theory (DFT) calculations at B3LYP/6-31G** level have been carried out to study the mechanism of title reaction. The whole picture for the possible mechanism has been explored and verified both in gas phase and C6H5CH3 solvent. The calculated results show that this reaction proceeds via the following several steps: (1) addition of two reactant molecules; (2) removing of and succedent elimination of from intermediates; (3) isomerization and final cyclization of intermediates, in which the elimination step of is the rate-controlling one in the whole reaction process. The final product has two competitive parallel paths, in which the 6π-electron electrocyclic ring closure is not reversible.