Palladium(0) Catalyzes Reactions of 1,4-Epiperoxides

The Pd(PPh3)4 catalyzed reaction of 2,3-saturated and 2,3-unsaturated 1,4-epiperonides proceeds by courses markedly different from those of the previously reported transition metai catalyses.The Pd(0l-promoted reaction of 2 3 saturated epiperoxides gives the corresponding 4-hydroxy ketones and 1,Cdiois as the major products.From 2,3-dedihydroepiperoxides are formed the corresponding 4-hydraxy enones, E-1,2;3,4-dleponides, and i,4-diois.The results are interpreted in terms of competing Pd(OllPd(li) and Pd(O)/Pd(i) exchange mechanisms.Exposure of prostaglandin (PGI H2 methyl ester t o Pd(PPh314 produces a mixture of methyi e s t e r s of PGD2, PGE2, PGF2, , and (5~,BE,10~,12~)-i2-hydroxy-5,8,iOheotadecatrienoic acid.1,4-Epiperoxides (endoperoxides) serve as key substances in a variety of chemical' and b i ~l o g i c a i ~~~ transformations.The 0-0 bond undergoes either homoiytic or heterolytic cleavage depending on the reaction conditions.'Transition metai catalysis has been studied extensively oniy with metals such as ~u ( i ) , ~~ Cu(ll),3f ~e ( i i ) , ~~, g , ~~, ~, ~ or ~o l i l l , ~~~~ which have the ability to induce the reaction via a one-electron redax m e ~h a n i s m .~ The catalysis of epiperonides with Ru(iil-phosphine complexes, which exhibit unique reactivity,7 also belongs to the same category.The study of catalysis with metals which cause t h e reaction to occur by a two-electron exchange mechanism is quite ~i m i t e d .~ We have been intrigued by the catalytic decomposition of epiperonides with a zero-valent Pd c o m p i e ~, ~ which has a tendency to recycle the metai through a two-equivalent change mechanism.i0Behavior o f prostaglandin (PC) endoperoxides in the presence of such a metai campiex has also been examined.'' Results and DiscussionPalladium Catalyzed Reaction of 1.4-Epiperoxides.Both 2,3-saturated and 2,3-unsaturated 1.4epiperonides are stable in dichiaromethane or benzene without catalyst.