Straightforward asymmetric entry to highly functionalized medium-sized rings fused to β-lactams via chemo- and stereocontrolled divergent radical cyclization of Baylis-Hillman adducts derived from 4-oxoazetidine-2-carbaldehydes

DABCO promoted reactions of various activated vinyl systems with optically pure 4-oxoazetidine-2-carbaldehydes 1 gave rise to Baylis-Hillman adducts 3 With excellent syn stereoselectivities, without detectable racemization. Products 3 are used. for the asymmetric preparation of unusual 2-azetidinones fused to medium-sized rings via chemo- and Stereocontrolled divergent radical cyclization. The formation of bicyclic beta -lactams 4-6 could be rationalized through a tandem radical Michael addition/endo cyclization or a tandem radical addition/Michael addition, depending pn the electronic nature of the radical promoter.