Stereoselectivity in the photoinduced electron transfer (PET) promoted intramolecular cyclisations of 1-alkenyl-2-silyl-piperidines and -pyrrolidines: rapid construction of 1-azabicyclo[m.n.0]alkanes and stereoselective synthesis of (±)-isoretronecanol and (±)-epilupinine

PET promoted cyclisations of 1-alkenyl-2-silyl-pyrrolidines and -piperidines 9a–d to 1-azabicyclo[m.n.0]alkanes have been found to be stereoselective. The five-membered ring formation gives predominantly cis products while six-membered rings are trans. Application of such cyclisations to the synthesis of (±)-isoretronecanol 22a, (±)-epilupinine 29 and related alkaloids has been demonstrated.