Potassium Triphenylborohydride. A New Reducting Agent for the Reduction of Carbonyl Compounds with an Exceptional Stereo- and Chemoselectivity

Article abstract of DOI:10.1021/jo00352a018

Potassium triphenylborohydride (KTPBH), a highly hindered potassium triarylborohydride prepared from triphenylborane and potassium hydride, exhibits remarkable stereo- and chemoselectivity for the reduction of carbonyl compounds.KTPBH reduces 2-methylcyclohexanone to give cis-2-methylcyclohexanol with an excellent stereospecificity (98.5:1.5), approaching that of lithium tri-sec-butylborohydride.KTPBH also shows a remarkable chemoselectivity.It shows 97:3 selectivity between cyclohexanone and cyclopentanone and 99.4:0.6 selectivity between cyclohexanone and 4-heptanone.This chemoselectivity is comparable to those achieved by lithium di-n-butyl-9-BBN and tert-butylamine-borane, the best two reagents reported for such purposes.KTPBH is stable over 2 months at room temperature, and this reagent possesses a practical advantage in the isolation of the alcohol product without oxidation and distillation.