Heterocyclic compounds of the formula ##STR1## wherein R.sub.1 denotes hydrogen or C.sub.1 -C.sub.4 -alkyl or the two R.sub.1 s together denote CO,R.sub.2 denotes a substituent andn denotes 0, 1, 2, 3 or 4,processes for their preparation, azo pigments prepared therefrom by a coupling reaction with a diazo component of an aromatic or hetero-aromatic amine free from sulphonic acid groups, and the use of these azo pigments for pigmenting organic macromolecular materials and especially in the spin dyeing of polyacrylonitrile.