Reductive Carbon-Carbon Bond Forming Reactions with Carbonyls Mediated by Rh-H Complexes

Carbon-carbon bond formation is a fundamental transformation of synthetic organic chemistry. This minireview focuses on our works related to reductive aldol reaction, reductive Mannich reaction, reductive alpha-acylation, and reductive alpha-carboxylation by using rhodium catalyst to achieve C-C bond formation. Rh-catalyzed reductive aldol reaction successfully gave beta-hydroxy carbonyl compounds from alpha,beta-unsaturated carbonyl compounds with aldehydes or ketones by treating with RhCl(PPh3)(3)and Et2Zn. This condition could apply to other electrophiles such as imines, acid chlorides, and acid anhydrides, and the corresponding beta-lactams, or beta-ketocarbonyl compounds were obtained in good yields, respectively. A key intermediate, Rh-H complex would play an important role to accomplish 1,4-reduction, which could easily be derived from RhCl(PPh3)(3)and Et2Zn. The synthesis of a cholesterol absorption inhibitor, ezetimibe, was also achieved by using Rh-catalyzed reductive Mannich reaction as an application. We expect that the reaction could be used in a wide range of fields by further development.