Ytterbium acetate promoted asymmetric reductive amination: significantly enhanced stereoselectivity |
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Authors: | Nugent Thomas C El-Shazly Mohamed Wakchaure Vijay N |
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Institution: | Department of Chemistry, School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany. t.nugent@jacobs-university.de |
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Abstract: | Reductive amination of prochiral unhindered 2-alkanones 1 with (R)- or (S)-alpha-MBA in the presence of Yb(OAc)3 (50-110 mol %), Raney-Ni, and hydrogen (120 psi) results in increased diastereoselectivity for the amine products 2 (80-89% de) with good yield (80-87%). The increased de is based on comparison with the best previously reported de's when using (R)- or (S)-alpha-MBA, regardless of the strategy employed stepwise (isolation of ketimines) or one-pot (reductive amination)], reducing agent examined, or achiral Lewis acid or Br?nsted acid examined. An in situ cis- to trans-ketimine isomerization mechanism, promoted by Yb(OAc)3, has been proposed to account for the observed increase in diastereoselectivity and suggests a new entry into the control of ketimine geometry. |
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