Diastereoselective preparation of silylated pyrrolidones through palladium-catalysed cyclisations

A new palladium-catalysed allylic alkylation affording silylated 3-vinylpyrrolidones has been developed. The method relies upon the interaction between a stabilized acetamide enolate anion and a silicon-containing, nitrogen-tethered η3- allylpalladium moiety. Two variants have been studied, involving the location of the silicon atom on either olefinic carbon atom of the cyclisation precursor. In both cases 5-exo ring closure was the only cyclisation process observed. The stereoselectivity of these processes is discussed. These results contrast with related β-oxo ester cyclisations, in which competitive 7-endo mode is observed.