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PyBidine–Cu(OTf)2‐Catalyzed Asymmetric [3+2] Cycloaddition with Imino Esters: Harmony of Cu–Lewis Acid and Imidazolidine‐NH Hydrogen Bonding in Concerto Catalysis |
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| Authors: | Prof. Dr. Takayoshi Arai Hiroki Ogawa Dr. Atsuko Awata Dr. Makoto Sato Megumi Watabe Prof. Dr. Masahiro Yamanaka |
| Affiliation: | 1. Department of Chemistry, Graduate School of Science, Chiba University, 1‐33 Yayoi, Inage‐ku, Chiba 263‐8522 (Japan) http://synthesis.chem.chiba‐u.jp/index.html;2. Department of Chemistry, Rikkyo University, 3‐34‐1 Nishi‐Ikebukuro, Toshima‐ku, Tokyo 171‐8501 (Japan) |
| Abstract: | A bis(imidazolidine)pyridine (PyBidine)–Cu(OTf)2 complex catalyzing the endo‐selective [3+2] cycloaddition of nitroalkenes with imino esters was applied to the reaction of methyleneindolinones with imino esters to afford spiro[pyrrolidin‐3,3′‐oxindole]s in up to 98 % ee. X‐ray crystallographic analysis of the PyBidine–Cu(OTf)2 complex and DFT calculations suggested that an intermediate Cu enolate of the imino ester reacts with nitroalkenes or methyleneindolinones, which are activated by NH‐hydrogen bonding with the PyBidine–Cu(OTf)2 catalyst. |
| Keywords: | asymmetric catalysis asymmetric synthesis cycloaddition heterocycles indoles |