Enantioselective Synthesis of 4H-Pyran via Amine-Catalyzed Formal (3+3) Annulation of δ-Acetoxy Allenoate

The formal (3 + 3) annillations of delta-acetoxy allenoates and 1C,30-bisnucleophiles are reported with the We of 6'-deoxy-6'-perfluorobenzamido-quinine (4g) as a catalyst, which provide rapid access to 4H-pyrans with excellent enantioselectiyity. The reaction features a wide reaction scope, and mild reaction conditions. The crucial roles of amide NH of 4g as a H-bond donor have also been elucidated, which not only activates allenoate to facilitate formation of cationic intermediate A but also enhances the electrophilicity of its delta-position for nucleophilic 1,6-addition.