Compounds of the formula ##SPC1## Wherein R.sub.1 represents a phenyl, phenoxy, phenylthio or cyclohexyl radical which is optionally substituted by halogen, nitro, alkyl and/or alkoxy, or a phenyl or cyclohexyl radical which is bonded via an alkylene, alkyleneoxy or alkylenethio bridge member, R.sub.2 represents cyano, carbamoyl, an alkoxycarbonyl, alkenyloxycarbonyl, alkinyloxycarbonyl, alkylcarbamoyl or dialkylcarbamoyl radical and R.sub.3 represents hydrogen or alkyl, their manufacture and ag...