Iridium-Catalyzed Transfer Hydrogenation of α,β-Unsaturated and Saturated Carbonyl Compounds with 2-Propanol

The selective transfer hydrogenation of alpha,beta-unsaturated carbonyl compounds to saturated ones was achieved by the use of 2-propanol as a hydrogen donor under the influence of catalytic amounts of Ir(cod)Cl(2), 1,3-bis(diphenylphosphino)propane (dppp), and Cs(2)CO(3). Thus, a variety of conjugated enones were allowed to react with 2-propanol in the presence of the Ir(cod)Cl(2)/dppp/Cs(2)CO(3) system to give the corresponding saturated carbonyl compounds in good to excellent yields without formation of allylic alcohols. Both dppp and Cs(2)CO(3) were essential components to achieve the reduction satisfactorily. Additionally, the reduction of carbonyl compounds to alcohols was also promoted by the same catalytic system. When the reaction of a 1:1 mixture of a conjugated ketone and a saturated ketone with 2-propanol was carried out in the presence of Ir(cod)Cl(2) combined with dppp and Cs(2)CO(3), the reduction of the alpha,beta-unsaturated ketone was found to take place in preference to that of the saturated ketone.