Chemoselective reduction of aldehydes and ketones to alcohols using boron tri-isopropoxide, B(O-i-Pr)3 and boron tri-secondary butoxide, B(O-s-Bu)3 as catalysts

Abstract

The reduction of some aldehydes and ketones in the presence of boron tri-iso-propoxide, B(O-i-Pr)3 (BIP) and boron tri-secondary butoxide B(O-sec-Bu)3 (BSB) has been studied. The Meerwein-Pondorf-Verley (MPV) reaction is used for reduction of various aldehydes and ketones. BIP and BSB were prepared in situ from corresponding alcohols and borane (BH 3.THF) under nitrogen atmosphere at room temperature. The reductions were completed within 6 hours by refluxing in THF. The alcohols that are the reduction product were analyzed by GC-FID and then confirmed by GC-MS. It was found that BIP and BSB catalyze the reduction of aliphatic aldehydes and ketones to alcohols at room temperature. On the other hand, aromatic aldehydes and ketones were not reduced under the same conditions. Moreover, yield of the alcohols were found to be higher with BIP than with BSB. The mechanism proposed involves a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same boron centre of a boron alkoxide catalyst. ©ARKAT USA, Inc.