Ring Expansion of Epoxides under Brønsted Base Catalysis: Formal [3+2] Cycloaddition of β,γ‐Epoxy Esters with Imines Providing 2,4,5‐Trisubstituted 1,3‐Oxazolidines |
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| Authors: | Dr Azusa Kondoh Kenta Odaira Prof Dr Masahiro Terada |
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| Affiliation: | 1. Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Aramaki, Aoba‐ku, Sendai 980‐8578 (Japan);2. Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba‐ku, Sendai 980‐8578 (Japan) |
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| Abstract: | A novel ring‐expansion reaction of epoxides under Brønsted base catalysis was developed. The formal 3+2] cycloaddition reaction of β,γ‐epoxy esters with imines proceeds in the presence of triazabicyclodecene (TBD) as a superior Brønsted base catalyst to afford 2,4,5‐trisubstituted 1,3‐oxazolidines in a highly diastereoselective manner. This reaction involves the ring opening of the epoxides with the aid of the Brønsted base catalyst to generate α,β‐unsaturated esters having an alkoxide at the allylic position, which would formally serve as a synthetic equivalent of the 1,3‐dipole, followed by a cycloaddition reaction with imines in a stepwise fashion. This methodology enables the facile synthesis of enantioenriched 1,3‐oxazolidines from easily accessible enantioenriched epoxides. |
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| Keywords: | asymmetric synthesis brø nsted base cycloaddition organocatalyst ring expansion |
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