Reductive aldol coupling of divinyl ketones via rhodium-catalyzed hydrogenation: syn-diastereoselective construction of beta-hydroxyenones.

Catalytic hydrogenation of divinyl ketones 1a and 1e in the presence of diverse aldehydes 2a-e at ambient temperature and pressure using cationic rhodium catalysts ligated by tri-2-furyl phosphine enables formation of aldol products 3a-e and 5a-e, respectively, with high levels of syn diastereoselection. Through an assay of counterions (Rh(COD)2X), Rh(COD)2SbF6 is identified as the optimum precatalyst for reductive aldol couplings of this type. For para-substituted styryl vinyl ketones 1b-e, a progressive increase in isolated yield is observed for electron-releasing para substituents. [reaction: see text].