The present invention is concerned with compounds of formula ##STR00001## the N-oxides, the pharmaceutically acceptable addition salts and the stereochemically isomeric forms thereof, wherein X represents O, S or NR.sup.3; R.sup.1 represents hydrogen, hydroxy, C.sub.1-6alkyl or aryl; R.sup.2 represents hydrogen; optionally substituted C.sub.1-12alkyl; C.sub.3-7cycloalkyl; C.sub.2-8alkenyl; aryl; Het.sup.1; or R.sup.1 and R.sup.2 taken together may form a bivalent radical of formula --(CH.sub.2).sub.n-- wherein n is 2, 3, 4, 5 or 6; R.sup.3 represents hydrogen, optionally substituted C.sub.1-6alkyl, aryl, Het.sup.1; R.sup.4 represents hydrogen; hydroxy; mercapto; C.sub.1-6alkyloxy; C.sub.1-6alkylthio; aryloxy; arylthio; Het.sup.1-oxy; Het.sup.1-thio; optionally substituted C.sub.1-12alkyl; optionally substituted C.sub.2-8alkenyl; optionally substituted C.sub.2-8alkynyl; optionally substituted C.sub.3-7cycloalkyl; optionally substituted C.sub.5-7cycloalkenyl; aryl; Het.sup.1; or -Alk-NR.sup.3R.sup.5 (i) or --NR.sup.3R.sup.5 (ii) wherein Alk represents C.sub.1-6alkanediyl; and R.sup.5 represents hydrogen, C.sub.1-6alkyl, aryl, Het.sup.1, (aryl or Het.sup.1)C.sub.1-6alkyl, (aryl or Het.sup.1)carbonyl or (aryl or Het.sup.1)C.sub.1-6alkyloxycarbonyl; aryl represents optionally substituted indanyl, indenyl, naphtyl, 5,6,7,8-tetrahydro-2-naphtalenyl or phenyl; Het represents an optionally substituted unsaturated heterocycle; and Het.sup.1 represents an optionally substituted monocyclic or bicyclic heterocycle; having retinoic mimetic activity; their preparation, compositions containing them and their use as a medicine.