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 Asy

摘要

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.