Enantioselective Synthesis of 4H‑Pyran via Amine-Catalyzed Formal (3 + 3) Annulation of δ‑Acetoxy Allenoate
datasetposted on 27.03.2017 by Weiping Zhou, Chunjie Ni, Jiangfei Chen, Dong Wang, Xiaofeng Tong
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The formal (3 + 3) annulations of δ-acetoxy allenoates and 1C,3O-bisnucleophiles are reported with the use of 6′-deoxy-6′-perfluorobenzamido-quinine (4g) as a catalyst, which provide rapid access to 4H-pyrans with excellent enantioselectivity. 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 δ-position for nucleophilic 1,6-addition.