Disclosed are 2-aza-substituted 1-carbadethiapen-2-em-3-carboxylic acids. I, where the generic 2-aza group includes azido, acylamino, amino, alkylamino, dialkylamino, triazolyl, triazolinyl, aziridinyl, and their pharmaceutically acceptable salt, ester, anhydride and amide derivatives which are useful as antibiotics. Also disclosed are processes for the preparation of I from the known, appropriately substituted bicyclic keto ester II via the 2-azido central intermediate III: ##STR1## wherein R.sup.16 is H or CH.sub.3, preferably beta-methyl; R.sup.6, and R.sup.7 are independently hydrogen, linear, branched or cyclic C.sub.1 -C.sub.5 alkyl, which can be substituted with fluoro, hydroxy, protected hydroxy, sulfoxy, amino, protected amino, wherein R.sup.6 and R.sup.7 taken together can also be C.sub.2 -C.sub.4 alkylidene, similarly substituted; with the proviso that both R.sup.6 and R.sup.7 are not unsubstituted alkyl, R.sup.1 and R.sup.2 are, inter alia, hydrogen, alkyl, acyl, and can be joined to form a ring comprising 3 to 7 atoms; R.sup.a is hydrogen, a salt cation, a removable protecting group, or a pharmaceutically acceptable ester moiety.Also disclosed are processes for the preparation of such compounds; pharmaceutical compositions comprising such compounds; and methods of treatment comprising administering such compounds and compositions when an antibiotic effect is indicated.