Abstract: The invention relates to new 2-oxoazetidines having the formulas ##STR1## where R.sub.1 stands for a lower fluoroalkyl or an optionally protected lower hydroxyalkyl group; R.sub.2 for chlorine, bromine, iodine, fluorine, an ##STR2## group in which n is 0, 1 or 2 and R.sub.5 is a lower alkyl, lower alkenyl, an optionally substituted benzyl group, optionally substituted phenyl group, a --CH.sub.2 COX group in which X means a lower alkyl, lower alkoxy or the amino group, or a ##STR3## group in which Y and Z are the same or different and in each case stand for oxygen, nitrogen or sulphur and R.sub.6 stands for a lower alkyl, lower alkoxy, lower alkylthio, lower dialkylamino, an aryl, aryloxy or arylthio group, or for a group having the formula ##STR4## where W stands for --CH.sub.2 CH.sub.2 --, --CH.dbd.CH-- or C.sub.6 H.sub.4 ; R.sub.3 stands for bromine, chlorine, iodine, SeC.sub.6 H.sub.5 or SC.sub.6 H.sub.5 ; and R.sub.4 stands for hydrogen, a group having the formula ##STR5## in which R.sub.