Enantioselective Synthesis of 4H-Pyrans Through Organocatalytic Asymmetric Formal [3+3] Cycloadditions of 2-(1-Alkynyl)-2-alken-1-ones with β-Keto Esters

4H-Pyran units are frequently present in molecules with significant biological and pharmaceutical activities. Herein, we present the first enantioselective formal [3+3] cycloaddition between 2-(1-alkynyl)-2-alken-1-ones and β-keto esters catalyzed by a cyclohexyldiamine-based thiourea-tertiary amine bifunctional catalyst. Under the mild and eco-friendly conditions, a wide range of polysubstituted 4H-pyrans were obtained in moderate yields with good enantioselectivities. (Figure presented.).