Metal-assisted reactions. Part 8. Selectivity in the reaction of organic halides with tetrahydroborate and the reduction of acyl halides to aldehydes

Abstract

Addition of metal ions such as Cu⁺, Cu²⁺, Cd²⁺, and Zn²⁺ with dimethylformamide to sodium tetrahydroborate in acetonitrile affords a reducing medium in which acyl halides are converted to aldehydes but alkyl, aryl, and benzylic halides are unaffected. The inertness of these last, synthetically useful, functional groups along with the inertness of other potentially reducible groups, makes the reagent very selective for direct reduction of acyl halides to aldehydes. The reducing solution is stable, readily prepared from cheap materials, rapid in action, and easy to use, making the conversion of acids to aldehydes via acyl halides a routine synthetic procedure.