Antibacterially active penem compounds and salts of the formula ##STR1## wherein R is hydrogen or an esterifying group, R.sup.2 is hydrogen, hydroxy, or protected hydroxy, and R.sup.1 is phenyl, naphthyl, thienyl, pyridyl, quinolyl, or isoquinolyl, or such a group which is mono-, di-, or tri-substituted; methods for making such compounds or salts; and antibacterial pharmaceutical preparations containing the compounds or salts.