α,α,α-Trifluoroacetophenone (2), which is susceptible to noncatalytic reduction by BH3, could be reduced to chiral alcohol up to 90% ee by using electronically tuned-CBS catalyst (1) with BH3. The enantioselectivities highly correlated with the differential orbital energies between 1–BH3 adduct and 2, which were calculated by DFT method.
Novel oxazaborolidines B-C6F5 were synthesized by modified protocol from C6F5B(OMe)(2) (in place of usual C6F5B(OH)(2)) and the corresponding amino alcohols, aiming to know the pi-pi stacking and electron-withdrawing effects of C6F5 group in asymmetric reduction of ketones. Although the results were not simply explained by the expected effects, significant difference was observed in the enantioselectivity between the catalysts with B-C6H5 and B-C6F5. (C) 2007 Elsevier B.V. All rights reserved.