Tandem intermolecular–intramolecular carbolithiation: application to the synthesis of silacyclopentanes

Silacyclopentanes have been prepared from vinyl(homoallyl)silanes or vinyl(homopropargyl)silanes and organolithium reagents by a tandem intermolecular–intramolecular sequence involving a 5-exo cyclisation process. The unexpected stereochemical outcome of the sequence involving a 5-exo-dig cyclisation is rationalised.