Sodium Tetraalkoxyborates: Intermediates for the Quantitative Reduction of Aldehydes and Ketones to Alcohols through Ball Milling with NaBH4

Abstract

AbstractStoichiometric molecular solid‐state vibrational ball milling, solvent‐free kneading ball milling, and mechanochemical ball milling of varied aldehydes and ketones with unmodified sodium borohydride under temperature control uses all hydrogen atoms of the reducing agent in fast reactions. It provides quantitative yields of thermally stable sodium tetraalkoxyborates. The easily isolated solids are extremely sensitive towards hydrolysis, leading to quantitative yields of the corresponding alcohols. The rapid syntheses are regiospecific and stereoselective. Varied substituents are not attacked, including the bromine of α‐bromo ketones. Conjugated aldehydes and ketones provide quantitative yields of the allylic alcohols free of contamination by saturated alcohols that would occur by reaction in solution. Depending on the stoichiometric ratio, benzil is quantitatively reduced to benzoin (4:1 ratio) or dihydrobenzoin (2:1 ratio). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)