Process for the manufacture of styrene compounds of the formula ##STR1## wherein A denotes one of the ring systems ##STR2## and wherein R.sub.1 denotes hydrogen, alkyl with 1 to 8 carbon atoms, cyclohexyl, phenylalkyl with 1 to 3 carbon atoms in the alkyl part, phenyl, alkoxy with 1 to 4 carbon atoms, or chlorine, or, conjointly with R.sub.2, denotes alkylene with 3 or 4 carbon atoms, R.sub.2 denotes hydrogen or alkyl with 1 to 4 carbon atoms or, conjointly with R.sub.1, denotes alkylene with 3 or 4 carbon atoms, R.sub.3 denotes hydrogen or methyl, R.sub.4 denotes hydrogen, m-methyl, alkyl with 2 to 8 carbon atoms, phenyl, alkoxy with 1 to 4 carbon atoms, or chlorine, or, conjointly with R.sub.5, denotes a fused benzene ring, R.sub.5 denotes hydrogen or chlorine or, conjointly with R.sub.4, denotes a fused benzene ring, X.sub.1 denotes hydrogen, alkyl with 2 to 4 carbon atoms, alkoxy with 1 to 4 carbon atoms or chlorine, X.sub.2 denotes hydrogen or chlorine, Y denotes hydrogen, chlorine, alkyl with 1 to 4 carbon atoms or phenyl and Z denotes hydrogen or chlorine, which is characterized in that a methyl compound of the formula ##STR3## is reacted with a Schiff's base of the formula ##STR4## wherein Ar denotes an aromatic radical, in dimethylformamide in the presence of a strongly basic alkali metal compound, the reaction mixture being irradiated, at least initially, with UV light.