Regioselective catalytic transformations involving beta-silyl-substituted (eta(3)-allyl)palladium complexes: An efficient route to functionalized allylsilanes

Various alkyl derivatives of 1-(trimethylsilanyl)but-3-en-2-ol acetate (1a- e) undergo regioselective palladium-catalyzed nucleophilic substitution via beta-silyl-substituted (eta(3)-allyl)palladium intermediates. With externa l nucleophiles, such as malonates and enolates, the nucleophilic substituti on occurs with complete allylic rearrangement, providing functionalized all ylsilanes as building blocks of high synthetic potential. Internal nucleoph iles, such as disilanes and NaBPh4, afford bisallylic disilanes and (allyls ilyl)benzene derivatives with good regioselectivity. For both types of nucl eophiles, the double bond geometry of the resulting allylsilane is selectiv ely traits. The beta-silyl-substituted (eta(3)-allyl)palladium intermediate s of the reaction were also isolated. The H-1 NMR studies indicate selectiv e formation of the syn-isomer of the key (eta(3)-allyl)palladium intermedia tes, which explains the high trans-selectivity of the double bond formation in the allylsilane products. According to the C-13 NMR studies, the beta-s ilyl functionality exerts deshielding effects on the nearest allylic termin al carbon (C3), which can be ascribed to hyperconjugative interactions betw een the silyl functionality and the allylpalladium moiety. It was concluded that, together with the steric effects of the silyl group, these electroni c interactions are responsible for the high regioselectivity of the nucleop hilic attack in the catalytic process.