Thiourea-catalyzed asymmetric formal [3+2] cycloaddition of azomethine ylides with nitroolefins |
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Authors: | Jianwu Xie |
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Institution: | Graduate School of Pharmaceutical Sciences, Kyoto University, Shimoadachi-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan |
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Abstract: | A chiral thiourea catalyst possessing an amine function catalyzes an asymmetric 3+2] cycloaddition of azomethine ylides to nitroolefins to provide highly functionalized pyrrolidines with high diastereo- and enantioselectivities (up to 98:1:1 dr, 92% ee). The reaction proceeds in a stepwise manner consisting of Michael addition and subsequent intramolecular aza-Henry reaction. Both reactions are promoted by the thiourea catalyst, and the reaction rate of the latter step is efficiently enhanced by the addition of 2,2,2-trifluoroethanol. |
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Keywords: | Organocatalyst [3+2] Cycloaddition Asymmetric catalyst Pyrrolidines |
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