Compounds of formula ##SPC1##Wherein R.sub.1 and R.sub.2 independently of one another denote optionally substituted alkyl radicals with 1-3 C atoms and R.sub.3 represents hydrogen or an optionally substituted alkyl radical with 1-5 C atoms, as well as compounds of the formula ##SPC2##Wherein R.sub.4 represents an alkyl group which is optionally substituted by hydroxyl or alkoxy groups, and R.sub.5 and R.sub.6 represent hydrogen or an amino group which is monosubstituted or disubstituted by a straight-chain alkyl group or a cycloalkyl group, with the proviso that R.sub.5 and R.sub.6 do not simultaneously represent hydrogen, and processes for their production.