Influences of electronic effects and anions on the enantioselectivity in the oxazaborolidine-catalyzed asymmetric borane reduction of ketones

The Journal of Organic Chemistry
Jiaxi XuQihan Zhang

Abstract

The influence of electronic effects on the enantioselectivity of the oxazaborolidine-catalyzed asymmetric borane reduction of ketones has been observed and investigated with use of para-substituted acetophenones and propiophenones with a variety of functional groups and B-unsubstituted and B-methoxyoxazaborolidines derived from (S)-2-(diphenylhydroxymethyl)pyrrolidine with borane and trimethyl borate as catalysts in toluene and THF. The results indicate that Hammett linear free energy electronic effects on the enantioselectivity in the asymmetric reduction were observed and rationalized. Tuning electronic effects of the catalyst can improve the enantioselectivity in the reduction. Another interesting finding to be noted is that anions heavily affect the enantioselectivity, especially for the B-methoxy catalyst, because of their coordination with the boron atom in the catalysts.

References

Apr 27, 2002·The Journal of Organic Chemistry·Shawn M NettlesJoseph A Corella

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Citations

Oct 14, 2010·Chemical Communications : Chem Comm·Toshinobu KorenagaTakashi Sakai
Jun 10, 2006·Organic & Biomolecular Chemistry·Nicolas Blanchard, Pierre van de Weghe
Mar 25, 2005·Organic Letters·Nicole HolubSiegfried Blechert

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