Luche Reduction

• General Characteristics

-While 1,4-reduction usually predominates in the reduction of α,β-unsaturated ketones with NaBH₄ alone, selective 1,2-reduction is possible using CeCl₃-7H₂O as an additive. Luche reduction can be used for a wide range of compounds and reaction times are also short (3-5 min). Simple procedure is another plus for this reaction. DIBAL is used for the same purpose but it requires lower temperature.

• General References

・ Luche, J. L. J. Am. Chem. Soc. 1978, 100, 2226. DOI: 10.1021/ja00475a040
・ Gemal, A. L.; Luche, J. L. J. Am. Chem. Soc. 1981, 103, 5454. DOI: 10.1021/ja00408a029

• Reaction Mechanism

Aside from acting as a hard Lewis acid, cerium is considered to promote ligand exchange on the boron atom leading to the formation of NaH_nB(OMe)_4-n, a harder reducing agent than NaBH₄.

• Examples

In the substrate containing both ketone and aldehyde groups, Ce(III)-catalyzed acetalization (or hemiacetalization or hydration) prevents the aldehyde from getting reduced, enabling selective reduction of the ketone.

An example in the synthesis of batracotoxinin.^[1]

• Experimetal Procedure

• Experimental Tips

• References

[1] Kurosu, M.; Marcin, L. R.; Grinsteiner, T. J.; Kishi, Y. J. Am. Chem. Soc. 1998, 120, 6627. doi: 10.1021/ja981258g

• Related Books

 

1, 2-Reduction, cerium, hard Lewis acid