Addition Compounds of Alkali Metal Hydrides. 32. A Comparison Study of Chiral Trialkylborohydrides and Chiral Dialkylmonoalkoxyborohydrides for the Asymmetric Reduction of Prochiral Ketones: The Effect of Comparable Chiral Alkyl and Alkoxy Groups on Asymmetric Industion$^\dag$

Several chiral potassium B-alkyl-9-boratabicyclo[3.3.1]nonanes $(K\; B-R^*-9-BBNH)$ and potassium B-alkoxy-9-boratabicyclo[3.3.1]nonanes $(K \;B-OR^*-9-BBNH)$ were synthesized by treatment of the corresponding trialkylboranes and dialkylmonoalkoxyboranes with a small excess of potassium hydride. The chiral B-alkoxy derivatives generally reduce representative ketones, such as acetophenone and 3-methyl-2-butanone, with greater optical induction than the corresponding B-alkyl derivatives, suggesting the involvement of the oxygen atom in the control process for asymmetric synthesis.