Abstract
The enantioselective reduction of prochiral ketones with NaBH4/Me2SO4/(S)-Me-CBS is described. Borane is generated in situ via the reaction of NaBH4 with Me2SO4 in tetrahydrofuran, which is as efficient as the commercial one. Such in situ–generated borane reagent was applied to reduce prochiral ketones in the presence of chiral oxazaborolidine catalyst directly. The corresponding chiral secondary alcohols were obtained with excellent enantiomeric excesses (93–99% ee) and good to excellent yield (80–99%).
GRAPHICAL ABSTRACT
Notes
a Reaction conditions: NaBH4/Me2SO4/ketone = 0.7/0.7/1.
b Isolated yield.
c Determined by HPLC with a chiral column (Daicel OD).
d NaBH4/Me2SO4/ketone = 0.6/0.6/1.