>The synthesis of a new series of 1β‐methylcarbapenems having a substituted heterocyclic carbamoyl pyrrolidine moiety is described. Their in vitro antibacterialactivity against both gram‐positive and gram‐negative bacteria was tested, and the effect of heterocyclic substituents on the pyrrolidine was investigated. One particular compound (IIId) having a substituted oxadiazole moiety showed the most