Palladium-catalyzed cyclization of allylsilanes with nucleophilic displacement of the silyl group

Allylsilanes containing hydroxy or tosylamide groups undergo palladium (ii) -catalyzed cyclization to afford derivatives of tetrahydrofuran, piperidine , and pyrrolidine. This catalytic reaction proceeds through an (eta (3)-all yl)palladium intermediate that is generated by allylic displacement of the silyl group of the allylsilane precursors. The internal nucleophilic attack on the (eta (3)-allyl)palladium intermediates proceeds with high chemo- an d regioselectivity. Benzoquinone and copper(H) chloride can be used for reg eneration of the palladium(ii) catalyst precursor. Mechanistic studies reve aled that the copper(ii) chloride reoxidant also activates the (eta (3)-all yl)palladium intermediate towards nucleophilic attack. Kinetic studies on t he formation of the (eta (3)-allyl)palladium intermediates showed that the reaction rate is highly dependent on the concentration of chloride ligand a nd the solvent. The structure and reactivity of the key intermediates of th e palladadesilylation process were studied by density functional theory (DF T) calculations, which showed that coordination of the electrophilic pallad ium(ii) catalyst precursor to allylsilanes leads to a relatively weak beta -silicon effect. The DFT studies also indicate that the cleavage of the car bon-silicon bond takes place by coordination of a chloride ion to the silic on atom.