Aerobic Palladium(II)/Copper(II)-Catalyzed Oxidation of Olefins under Chloride-Free Nonacidic Conditions

A chloride-free Pd(OAc)2/Cu(OAc)2 system catalyzes the oxidation of organic substrates by molecular oxygen in nonacidic methanol solutions. Terminal olefins, i.e., 1-hexene, 1-octene, styrene, and 2-vinylnaphthalene, give the corresponding methyl ketones without a significant double-bond isomerization of long-chain substrates. The catalyst also promotes an unusual allylic oxidation of sterically encumbered trisubstituted internal double bonds in acyclic polyenes able to form η2−η2-chelates with palladium. Linalool and nerolidol, mono- and sesquiterpenic allylic alcohols, give corresponding allylic ethers arising from the exclusive oxidation of the internal double bonds. Monosubstituted terminal double bonds in both substrates remain intact due to the deactivating effect of the allylic hydroxyl group. Dihydromyrcene, a nonfunctionalized monoterpenic diene, gives allylic ether and methyl ketone arising from the oxidation of both trisubstituted and terminal double bonds, respectively. On the other hand, inte...