Synthesis of ethyl cis 2-[(diethoxyphosphoryl)methyl]-7-oxo-3-phenyl-6-phthalimido-1-azabicyclo[3.2.0]hept-3-ene-2-carboxylate and methyl cis-2-bromo-3-methyl-8-oxo-7-phthalimido-4-oxa-1-azabicyclo[4.2.0]octane-2-carboxylate

The synthesis of a Δt-carbapenem and two β-lactams possessing a Br-atom at the N-substituting center not involved in the lactam ring and bearing the carboxyl group is described. The β-lactams having this kind of Br-substitution are more susceptible to nucleophilic attack than those having a conjugated double bond with the N-atom of the β-lactam ring. DBU is found to be an excellent reagent for the elimination of the silyloxy function. Moreover, a simple method for the addition of diethyl phosphite to an α,β-unsaturated double bond using a catalytic amount of NaH is described.