Zinc Borohydride - A Reducing Agent with High Potential

Several new and novel applications of Zinc borohydride, a non-conventional hydride reducing agent, have been demonstrated for efficient chemo- and regioselective reductions of various important functionalities. These include : (a) chemoselective reduction of aldehydes over ketones; (b) chemoselective reduction of saturated ketones and conjugated aldehydes over conjugated enones; (c) chemoselective reduction of aliphatic ester over aromatic one; (d) chemoselective reduction of carboxylic acids; (e) chemoselective reduction of 2-nitrocycloalkanones to 2-nitrocycloalkanols; (f) highly selective reduction of monosubstituted conjugated nitroalkenes to the corresponding nitroalkanes and disubstituted ones to the corresponding oximes; (g) regio- and stereoselective reductive cleavage of unsymmetrical alkyl-substituted epoxide to the less-substituted alcohol; (h) regioselective 1,2-reduction of conjugated ketones and aldehydes; and (i) regioselective hydration of alkenes to the less-substituted alcohols. 1. Introduction 2. Chemoselective Reductions 2.1 Chemoselective Reduction of Aldehydes over Ketones 2.2 Chemoselective Reduction of Saturated Ketones and Conjugated Aldehydes over Conjugated Enones 2.3 Chemoselective Reduction of Aliphatic Ester over Aromatic one 2.4 Chemoselective Reduction of Carboxylic Acids 2.5 Chemoselective Reduction of 2-Nitrocycloalkanones to 2-Nitrocycloalkanols 2.6 Selective Reduction of Mono and Disubstituted Conjugated Nitroalkenes 3. Regioselective Reductions 3.1 Regio- and Stereoselective Reductive Cleavage of Epoxides 3.2 Regioselective 1,2-Reduction of Conjugated Ketones and Aldehydes 3.3 Regioselective Hydration of Alkenes 4. Concluding Remarks