The Luche reduction converts selectively α,β-unsaturated ketones to allylic alcohols using a mixture of lanthanide chlorides and sodium borohydride.
The Lewis acidic cesium chloride activates methanol that replaces some of the hydrides of sodium borohydrides making it harder and more prone for a 1,2-attack on the carbonyl compounds.
The cesium chloride also acts as an Lewis catalyst to increase the electrophilicity of the carbonyl compound.
Lanthanides in organic chemistry. 1. Selective 1,2 reductions of conjugated ketones. Luche, J. L. J. Am. Chem. Soc. 1978, 100, 2226-2227.
Lanthanoids in organic synthesis. 6. Reduction of .alpha.-enones by sodium borohydride in the presence of lanthanoid chlorides: synthetic and mechanistic aspects. Andre L. Gemal, Jean Louis Luche J. Am. Chem. Soc., 1981, 103 (18), 5454–5459.
Stereochemically Controlled Asymmetric 1,2-Reduction of Enones Mediated by a Chiral Sulfoxide Moiety and a Lanthanum(III) Ion. Shigeyasu Motohashi, Kouichi Nagase, Toshinori Nakakita, Takeshi Matsuo, Yoshikazu Yoshida, Takashi Kawakubo, Motofumi Miura*, Masaharu Toriyama, and Mikhail V. Barybin J. Org. Chem., 2011, 76 (10), 3922–3936.