Sodium borohydride in carboxylic acid media: a phenomenal reduction system
The union of sodium borohydride and carboxylic acids has yielded an amazingly versatile and efficient set of reducing reagents. These acyloxyborohydride species reduce and N-alkylate indoles, quinolines, isoquinolines, related heterocycles, imines, enamines, oximes, enamides, and similar functional groups. They reduce amides and nitriles, aryl alcohols and ketones, aldehydes in the presence of ketones, and β-hydroxyketones to 1,3-diols stereoselectively. This reagent is also extraordinarily useful for the N-alkylation of primary and secondary amines with aldehydes and ketones in a novel reductive amination process.