Luche reduction

Luche reduction is the selective organic reduction of ketones to alcohols with lanthanoid chlorides such as cerium(III) chloride and sodium borohydride as enones or in presence of aldehydes [Strategic Applications of Named Reactions in Organic Synthesis (Paperback) by Laszlo Kurti, Barbara Czako ISBN 0-12-429785-4 ] ["Lanthanides in organic chemistry. 1. Selective 1,2 reductions of conjugated ketones" Jean Louis Luche J. Am. Chem. Soc.; 1978; 100(7); 2226-2227. DOI|10.1021/ja00475a040] ["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 DOI|10.1021/ja00408a029] An enone forms an allyl alcohol in a 1,2-addition. Competing conjugate 1,4-addition is suppressed. The solvent is an alcohol such as methanol or ethanol.

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The selectivity can be explained in terms of HSAB theory: carbonyl groups require hard nucleophiles for 1,2-addition. The hardness of the borohydride is increased by replacing hydride groups with alkoxide groups, a reaction catalyzed by the cerium salt. Another purpose for cerium is to increase the electrophilicity of the carbonyl group.

In one application a ketone is selectively reduced in presence of an aldehyde.

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