Synthesis of Derivatives of (1R*,10aR*)-1-Azido-10-benzylidene-4-(diethylphosphono)-1,2,10,10a-tetrahydro-2-oxo-4H-azeto[1,2-a]pyrido[1,2-d]pyrazin-9-ylium Bromide

The synthesis of some derivatives of the title compound VI is described. Bromination of diethyl (cis-3-azido-2-oxo-4-styrylazetidin-1-yl)(pyridin-2-yl)methylphosphonate ( 6 ) in MeOH gave tricyclic β-lactam 7 , while similar bromination of diethyl (cis-3-azido-2-oxo-4-vinylazetidin-1-yl)(pyridin-2-yl)methylphosphonate ( 9 ) afforded tri-cyclic β-lactam 10 . Mechanisms for these transformations are proposed (Schemes 1 and 2).