Compounds of formula Ia or Ib ##STR00001## wherein A is an (n+1)-valent aliphatic, cycloaliphatic, araliphatic or aromatic radical and n is an integer from 0 to 5, E is an (m+1)-valent aliphatic, cycloaliphatic, araliphatic or aromatic radical and m is an integer from 0 to 3, X is --O--, --C(.dbd.O)O or --CHR.sub.4--, with R.sub.4 and R.sub.3 together forming an ethylene group, R.sub.1 and R.sub.2 are, each independently of the other, hydrogen or methyl, R.sub.3 is hydrogen, or R.sub.3 and R.sub.4 together form an ethylene group, and R.sub.5 is a monovalent aliphatic, cycloaliphatic, araliphatic or aromatic radical, are highly reactive curing agents for epoxy resins and yield cured products having improved resistance to chemicals.