Enantioselective [4 + 1] Annulation Reactions of α‑Substituted Ammonium Ylides To Construct Spirocyclic Oxindoles
journal contributionposted on 29.07.2015, 00:00 by Peng-Fei Zheng, Qin Ouyang, Sheng-Li Niu, Li Shuai, Yi Yuan, Kun Jiang, Tian-Yu Liu, Ying-Chun Chen
Ammonium ylides have a long history in organic synthesis, but their application in asymmetric catalysis is still underdeveloped in regard to both substrate scope and reaction pathways compared with phosphorus and sulfur ylides. Here a previously unreported asymmetric [4 + 1] annulation reaction of 3-bromooxindoles and electron-deficient 1-azadienes has been developed through ammonium ylide catalysis of a newly designed 2′-methyl α-isocupreine (α-MeIC), efficiently delivering spirocyclic oxindole compounds incorporating a dihydropyrrole motif in excellent enantioselectivity (up to 99% ee). To the best of our knowledge, this work represents the first example of asymmetric catalysis of ammonium ylides bearing α-substitutions, and the catalytic [4 + 1] annulation pathway of ammonium ylides is also unprecedented. Moreover, 1H NMR, mass spectroscopy, and computational calculation studies were conducted, and the catalytic cycle and a tentative explanation of the enantioselective mechanism have been successfully elucidated.