A chiral bimetallic Lewis acid as a reaction template. Asymmetric reduction of unsymmetric ketones with LiBH4

A new series of chiral bimetallic Lewis acids, 5,5'-bis[(R)-2-aryl-1,3,2-di oxaborolan-4-one], have been prepared from L-(+)-tartaric acid and arylboro nic acids. In the presence of these Lewis acids, unsymmetric ketones were r educed quantitatively by LiBH4, in moderate to good ee's (up to 99% ee). Th e counter cation of BH4- significantly affects the ee's of the products. Th e reaction is applicable to aryl alkyl ketones, dialkyl ketones, and diaryl ketones.