Changing Reaction Pathways of the Dimerization of 2‑Formylcinnamates by N‑Heterocyclic Carbene/Lewis Acid Cooperative Catalysis: An Unusual Cleavage of the Carbon–Carbon Bond

Catalyzed by a triazole carbene, the dimerization of 2-formylcinnamates underwent benzoin condensation followed by intramolecular oxa-Michael addition to afford isochromeno­[4,3-c]­isochromene products. Under the catalysis of a combination of triazole carbene and Ti­(OPr-i)4 catalysts, the dimerization reaction of 2-formylcinnamates proceeded through a completely different route to furnish the formation of isochromenone derivatives with the elimination of an acetate moiety.