Mild and Highly Enantioselective Vinylogous Aldol Reaction of Brassard’s Diene with Aromatic Aldehydes by Combined Lewis Acid Catalyst

The combined Lewis acid catalytic system, generated from (R)-1,1′-bi-2-naphthol [(R)-BINOL], Ti(O-i-Pr)4, H2O, and lithium chloride, effectively catalyzed the enantioselective vinylogous aldol reaction of Brassard’s diene with aromatic aldehydes affording the (Z)-δ-hydroxyl-α,β-unsaturated esters exclusively in good yields with excellent enantioselectivities (90−99% ee) under mild conditions. A Lewis acid−Lewis acid bifunctional working model was proposed for the catalytic process based on some control experiments.