Abstract Reaction of 1, 3-diene 1, 4-epiperoxides with Pd (PPh 3) 4 catalyst forms the corresponding 4-hydroxy enones, syn diepoxides, and 1, 4-diols as the major products. The results are interpreted as being due to competing Pd (0)/Pd (II) and Pd (0)/Pd (I) exchange mechanisms.