Luche reduction

What is Luche reduction?

The Luche reduction is a reaction that was first reported by Luche in 1978. It involves the reduction of a carbonyl group into an alcohol using a combination of sodium borohydride (NaBH4) and cerium chloride (CeCl3) in methanol MeOH as the reducing agent. This reaction is known as the Luche reduction and the combination of NaBH4 and CeCl3 is referred to as the Luche reagent.

Luche reduction - general reaction scheme
Luche reduction

R, R’ = H, alkyl, aryl

The Luche reduction occurs under mild conditions and can tolerate a wide range of functional groups, including azido, peroxide, ester, α-halocarbonyl, cyano, epoxide, lactone, cyclopropanyl, vinyl ester, t-butoxycarbamido, phenoxycarbamido, acetal, ketal, and carbonate.

One of the significant features of the Luche reduction is its ability to give 1,2-addition products when the carbonyl group is conjugated to an alkenyl, aryl, or alkynyl group. Furthermore, the reaction shows chemoselectivity between ketone and aldehyde groups, and often the ketone is reduced in the presence of an aldehyde group. The reduction also demonstrates stereoselectivity and diastereoselectivity, with the selectivity being higher at lower temperatures. Additionally, the reduction provides a certain level of stereoselectivity and diastereoselectivity.

Other lanthanides besides cerium chloride are also suitable for this reduction, and the stereoselectivity is in a bell-shaped correlation with the size of the lanthanides, in the order of TbCl3 > EuCl3HoCl3 > CeCl3ErCl3 > LaCl3.