Cerium chloride, Luche reduction

The Luche reduction involves a selective 1,2-reduction of a,p-unsaturated aldehydes and ketones using sodium borohydride in combination with cerium(III) chloride, resulting in the formation of allylic alcohols.1... 

Trost coined the term chemoselective to describe the process where one of two similar functional groups is made to react, while the other is not affected or affected to a lesser extent [1]. This discrimination usually results from nuanced changes to a reagent s behavior, e.g., by addition of a salt. A typical example is the modification of sodium borohydride reduction by addition of cerium chloride in the Luche process, whereby the double bond of an ot-enone is not saturated during the reaction [85]. Similarly, a new approach to chemoselective reaction of n-pentenyl donors was soon to emerge. 

Selective reduction of ketones. Luche and Gemal have reported selective reduction of ketones in the presence of aliphatic aldehydes using sodium boro-hydride in combination with cerium(III) chloride. This reagent also effects selective reduction of conjugated aldehydes in the presence of saturated ones. 

Cerium(III) chloride as well as some other lanthanide salts invert the stereoselectivity of the reduction of bicyclo[3.1.0]hexane-2,4-diones and bicyclo[3.1.0]hexane-2-ones compared to sodium borohydride in methanol alone. This reversal leads to the more favored attack of the hydride from the most hindered, concave face of these molecules to give exo-4-hydrobicyclo[3.1.0]hexan-2-ones and exo-bicyclo[3.1.0]hexan-1 -ols, respectively, in excellent yields37 If Luche conditions are used on 30 at low temperatures, complete stereoselectivity is induced in the production of 31. 

This method was also applied to the reduction of natural products, using cerium(lll) chloride with sodium borohydride to minimize the formation of saturated alcohols and give good yields of allylic alcohols with good stereoselectivity (Luche et al., 1978). 

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