The selective 1,2-reduction of enones with sodium borohydride is achieved in combination with CeCl3.
Mechanism of the Luche Reduction
CeCl3 is a selective Lewis acid catalyst for the methanolysis of sodium borohydride. The resulting reagents, various sodium methoxyborohydrides, are harder reducing agents (according to HSAB principles) and therefore effect an 1,2-reduction with higher selectivity.
Furthermore, CeCl3 activates methanol.
Reduction of ketones to alcohols using a decaborane/pyrrolidine/cerium(III) chloride system in methanol
J. W. Bae, S. H. Lee, Y. J. Jung, C.-O. M. Yoon, C. M. Yoon, Tetrahedron Lett., 2001, 42, 2137-2139.