Palladium complex catalyzed acylation of allylic esters with acylsilanes

Acylation of allylic esters (2) with acylsilanes (1) in the presence of a catalytic amount (5 mol %) of a palladium complex is reported. The reaction proceeds selectively to afford beta,gamma -unsaturated ketones (3) in high yields. [Pd(eta (3)-C6H5CH=CHCH2) (CF3COO)](2) (4a) showed the best catalytic activity. After the reaction, formation of CF3COOSiMe3 (5a) was confirmed by Si-29 NMR measurement of the resulting reaction mixture, indicating the trimethylsilyl moiety effectively traps the CF3COO leaving group from 2. The leaving group of the allylic esters affects the reaction considerably: allylic trifluoroacetate gave the best result, while the corresponding acetates and trichloroacetates did not afford any acylation products at all. Stoichiometric reaction of 4a with 1 gave acylation product 3 with a formation of 5a and Pd(0), whereas no acylation reaction took place with the corresponding acetate complex [Pd(eta (3) -C6H5CH=CHCH2)(CH3COO)](2) (4b). A DFT calculation suggests that interaction of high-lying HOMO of 1 and low-lying LUMO of eta (3)-allylpalladium trifluoroacetate intermediate 4 would be indispensable in the catalytic cycle.