Luche reduction

The Luche reduction is a chemical reaction that is used for the selective reduction of ketones in addition to aldehydes. Its principle is based on the activation of the keto group Lewis acids. It is named after its developer Jean -Louis Luche.

Lying in a molecule of aldehyde and ketone functions coexist, thus reducing hard nucleophiles preferably the aldehyde. The reason is that the aldehydic carbon in comparison to the carbonyl carbon atom of the ketone carries a stronger positive charge and is thus preferred for attacking hard nucleophiles. Luche reduction in the hardness of the ketonic carbon is increased by complexing the oxygen by cerium ( III) chloride, thus activating this position for the reduction.

Mechanism

In the first step coordinated cerium ( III) chloride to the ketonic oxygen. The sodium borohydride used as a reducing agent now hydrogenated preferred this position. The resulting alcohol is released recently by aqueous workup.

The preferred reducing the keto function is reinforced by a second effect. Most simple alcohols are used as solvents which react with sodium borohydride and various Alkoxyborhydriden. This increases the hardness of the reducing agent and the selectivity is further shifted in favor of reduction of the activated ketone.

Further reactions

The Luche conditions are α also for reduction, β - unsaturated ketones. In these cases, due to the conjugation with the carbon-carbon double bond of the ketonic carbon is not hard enough to be attacked by hard nucleophiles. By activation with cerium (III ) chloride is, in turn, increases the hardness and allows the reduction.

Under Luche conditions also hard nucleophiles such as Grignard reagents or organolithium compounds can be used. These react with the activated keto function without enolization occurs.