The Mizoroki-Heck reaction in organic and aqueous solvents promoted by a polymer-supported Kaiser oxime-derived palladacycle

A polystyrene-supported palladacycle derived from Kaiser oxime resin 3 is examined in organic and aqueous media used for the Mizoroki-Heck reactions. The couplings are efficiently performed in the presence of polymeric palladacycles in DMF, aqueous DMA, or water at relatively moderate temperature (110-130 degrees C) similarly to that in the presence of dimeric 4-hydroxyacetophenone 6 and 4-nitrobenzophenone oxime 2 palladacycles. Different acrylic, crotonic, and cinnamic acid derivatives as well as styrenes are arylated with aryl iodides, bromides, and chlorides with high efficiency. Enone precursors of 4-(p-hydroxyphenyl) and 4( p-methoxy)phenylbutan-2-one, which are natural odorous products extracted from Aloe wood with raspberry scent, have been prepared by arylation of methyl vinyl ketone. Methylated resveratrol and the anti-cancer agent DMU-212 [(E)-3,4,5,4'-tetramethoxystilbene] have been prepared in high yields. Related Mizoroki-Heck reactions of o-halobenzaldehydes and o-iodoaniline with tolane afforded indenone and indol derivatives, respectively. XPS analysis of the starting and recycled polymer indicated that contains exclusively Pd(II). In addition, poisoning studies with Hg(0) of the reaction mixture stop the process indicating that the palladacycle acts as source of Pd(0) species. Recycling experiments are performed in organic and aqueous solvents with relatively low palladium leaching from the polymer (0.4-5% in DMF and 2-2.7% in H2O). ICP-OES analyses also indicate very low levels of Pd in the isolated crude products (2.9-37.2 ppm).