NEW MATERIAL: The compd. of formula I (Ar is (substd.) aryl or heteroaryl) and its isomers.

EXAMPLE: β-[3-2-Methylphenyl)-pyrrol-4-yl]-acrylonitrile.

USE: A pest control agent and plant protecting agent.

PROCESS: The compd. of the formula I is obtd. by bringing the compd. of formula II into reaction with the triphenyl phosphonium salts of formula III (X- is a suitable counter ion) or the phosphonate of formula IV (R is alkyl) at 0 to 80°C in the presence of a base (e.g.: NaH, n-butyllithium) and diluent (e.g.: benzene).