Straightforward asymmetric entry to highly functionalized medium-sized rings fused to beta-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 on the electronic nature of the radical promoter.
Departamento de Química Orgánica I, Facultad de Química, Universidad Complutense 28040-Madrid, Spain. alcaideb@eucmax.sim.ucm.es
B
B
Alcaide
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P
Almendros
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C
Aragoncillo