we describe here a suitable approach for the synthesis of n-unsubstituted monocyclic b-lactams under mild reaction conditions by the annelation of imines with substituted acetylchlorides. in this method the reaily available phtalimidoacetyl chloride were allowed to react with - dibenzylideneiminotoluene (hydrobenzamide) in the presence of an equimolar amount of triethylamine in refluxing toluene, which after the usual work up including a dilute acid (10 hcl) , afforded the corresponding phathalimido- n- unsubstituted b-lactams in good yield. the 5.4 hz coupling constant between the c3-h and c4-h indicated the cis stereochemistry for the product. the general applicability of this reaction was further demonstrated by other derivatives of phtalimidocetyl chloride and variation of the reaction condition for the preparation of cis and trans- b - lactams.