The present invention provides .beta.-methyl carbapenem compounds and pharmaceutical compositions useful in the treatment of bacterial infections and methods for treating such infections using such compounds and/or compositions, wherein the compounds are generally of the Formulae ##STR00001## The invention includes administering an effective amount of a carbapenem compound or salt and/or prodrug thereof to a host in need of such a treatment. The present invention is also in the field of synthetic organic chemistry and is specifically provides an improved method of synthesis of -methyl carbapenems which are useful as antibacterial agents.