'19 I 2 0 reduce ketones at room temperature in THF without the presence of a Lewis acid. The increased reactivity of the borane complexes may be explained in the same manner as proposed by Corey for reductions with chiral oxazaborolidine-BH, complexes. 2 Thus, the boron of the cyclic azaborane compound presumably complexes the carbonyl oxygen and activates it toward reduction. Freshly distilled liquid azaboracyclohexanes 9-13 exist ...