Antibacterial activity is exhibited by .beta.-lactams having a 3-acylamino substituent and having in the 1-position an activating group of the formula ##STR1## wherein R is
Antibacterial activity is exhibited by 2-azetidinones having an acylamino substituent in the 3-position and having an activating group in the 1-position of the formula ##STR1##
Antibacterial activity is exhibited by β-lactams having a 3-acylamino substituent and having in the 1-position an activating group of the formula
wherein R is