Aerobic Oxidations of Conjugated Dienes Using a Catalytic Palladium(II)−Quinone−Heteropolyacid System for Electron Transfer from Organic Substrates to Molecular Oxygen

The heteropolyacid H 5 PMo 10 V 2 O 40 ·34H 2 O was found to be an efficient oxygen activating agent in palladium-catalyzed reactions. Aerobic 1,4-oxidations of conjugated dienes were carried out by employing a triple catalytic system consisting of palladium−quinone−heteropolyacid. With this system a mild electron transfer from the organic substrate to molecular oxygen occurs. 1,4-Diacyloxylations and 1,4-dialkoxylations were studied using this mild reoxidation system. 1,4-Diacetoxylation of 1,3-cyclohexadiene was studied in some detail. Some advantages of the heteropolyacid over previously employed metal macrocycles are high stability, easy access to an active catalyst, and simpler workup procedures.