Lanthanoids in Organic Synthesis. 6. The Reduction of α-Enones by Sodium Borohydride in the Presence of Lanthanoid Chlorides: Synthetic and Mechanistic Aspects

Article abstract of DOI:10.1021/ja00408a029

Lanthanoid chlorides (LnCl3) are efficient catalysts for the regioselective 1,2-reduction of α-enones by NaBH4 in methanol solution.Optimal conditions of this reaction have been determined.A mechanistic interpretation depicting the role of the Ln³⁺ ions is given.The major effect of Ln³⁺ is the catalysis of BH4^- decomposition by the hydroxylic solvent to afford alkoxyborohydrides, which may be responsible for the observed regioselectivity.The stereoselectivity of the process is also modified by the presence of the Ln³⁺ ions, in that axial attack of cyclohexanone systems is enhanced.