Asymmetric induction. Part 3. Asymmetric reduction of ketones with amine-boranes in the presence of acids

Abstract

Asymmetric reductions of a series of ketones with (+)-1-phenylethylamine–borane and boron trifluoride–diethyl ether are described; solvent and temperature effects have been studied, and the use of other acidic components has been explored. Asymmetric reductions have also been effected with α-amino-ester–boranes (14–23% optical yields) and with diastereoisomeric amine–boranes containing chiral nitrogen atams. 2-Aminoethanols were prepared in high yield by reaction of α-amino-ester–boranes with boron trifluoride.