Influences of Electronic Effects and Anions on the Enantioselectivity in the Oxazaborolidine-Catalyzed Asymmetric Borane Reduction of Ketones.
- Resource Type
- Article
- Authors
- Jiaxi Xu; Tiezheng Wei; Qihan Zhang
- Source
- Journal of Organic Chemistry. 10/1/2004, Vol. 69 Issue 20, p6860-6866. 7p. 2 Diagrams, 2 Charts, 4 Graphs.
- Subject
- *KETONES
*ANIONS
*ORGANIC compounds
*CATALYSTS
*PYRROLIDINE
*AROMATIC compounds
*CHEMICAL inhibitors
- Language
- ISSN
- 0022-3263
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 parasubstituted acetophenones and propiophenones with a variety of functional groups and Bunsubstituted 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. [ABSTRACT FROM AUTHOR]