Abstract: The invention relates to new compounds of formula I ##SPC1##and salts thereof with pharmaceutically acceptable acids, in which formula all the substituents may be hydrogen, while R.sub.1 and R.sub.2 may furthermore be a methyl group, R.sub.3 an alkyl group, an alkoxy-alkylene group, an alkylthioalkylene group, an alkylsulphoxyalkylene group or an alkylsulphonalkylene group having up to 8 carbon atoms or a benzyl group, and R.sub.4, R.sub.5 and R.sub.6 a halogen atom, an alkyl group, an alkoxy group or an alkylthio group having up to 6 carbon atoms, a benzyloxy group, --OH, --NH.sub.2, a mono- or dialkylamino group, in which the alkyl group(s) contain(s) 1 or 2 carbon atoms, --CN or --CF.sub.3, and two of the substituents R.sub.4, R.sub.5 and R.sub.