Pyrrolidinones of formula I ##STR1## wherein R is hydrogen, C.sub.1 -C.sub.4 alkyl, or phenyl unsubstituted or substituted by halogen, C.sub.1 -C.sub.4 alkyl or by C.sub.1 -C.sub.4 haloalkyl, or is fluorine, chlorine or bromine;R.sub.0 is hydrogen or halogen;R.sub.1 and R.sub.2 independently of one another are hydrogen or C.sub.1 -C.sub.4 alkyl;X is hydrogen, flourine, chlorine, bromine, cyano, --COOR.sub.1, --CONR.sub.1 R.sub.2, --NH.sub.2 or --NHCOR.sub.3, wherein R.sub.1 and R.sub.2 are as defined, and R.sub.3 is C.sub.1 -C.sub.4 alkyl; andY is hydrogen, chlorine or bromine; andthe diastereoisomeric forms thereof, exhibit pre- and post-emergence herbicidal properties. The preparation of those compounds and their use as herbicidal active ingredients are described.