Chemoselectivity and Regioselectivity in the Hydrogenation of ???-unsaturated carbonyl compounds promoted by Cu/Al2O3

The hydrogenation of various ?, ?-unsaturated carbonyl compounds containing also an isolated olefinic bond (carvone, ?- and ?-ionone, etc.) has been studied under very mild conditions (1 atm H2, 90 °C) in the presence of a supported copper catalyst, Cu/Al2O3. This catalyst shows excellent chemoselectivity, as only the olefinic bond of the conjugated enone is reduced, leaving the isolated one unaffected even when the ?, ?-unsaturated moiety is sterically hindered. This kind of selectivity is unique for a heterogeneous catalyst, and the results obtained are comparable only with those reported for hydridic, homogeneous catalysts.