Chemoselective Conjugate Reduction of α,β-Unsaturated Ketones Catalyzed by Rhodium Amido Complexes in Aqueous Media

Although a notable feature of Noyori’s Ru−TsDPEN complex is that the transfer hydrogenation reaction is highly chemoselective for the CO functional group and tolerant of alkenes, our early report indicated that the chemoselectivity could be switched from CO to CC bonds in the transfer hydrogenation of activated α,β-unsaturated ketones. Now we have found that a variety of α,β-unsaturated ketones, even without other electron-withdrawing functional groups, could be reduced on the alkenic double bonds with high selectivities employing amido-rhodium hydride complex in aqueous media, and up to 100% chemoselectivity has been achieved. It is notable that the chemoselectivity was improved significantly on going from organic solvent to water. Moreover, a 1,4-addition mechanism has been proposed on the basis of the corresponding experimental details and computational analysis.