The invention relates to compounds of the formula ##STR1## wherein R.sup.1 is hydrogen, acyl, lower-alkyl or --CHO, --CH.sub.2 OR.sup.10, --COR.sup.7 or OR.sup.13 ; R.sup.2, R.sup.3 and R.sup.4 are, independently, hydrogen, lower-alkyl, lower-alkoxy or halogen; R.sup.5 and R.sup.6 are, independently, hydrogen or lower-alkyl; R.sup.7 is hydroxy, lower-alkoxy or NR.sup.8 R.sup.9 ; R.sup.8 and R.sup.9 are, independently, hydrogen or lower-alkyl; X and Y are, independently, >CR.sup.14 R.sup.15, --O--, --S--, >SO, >SO.sub.2 or >NR.sup.18 ; R.sup.10 and R.sup.18 are, independently, hydrogen, lower-alkyl or acyl; M is --C(R.sup.11).dbd.C(R.sup.12)--, --CONH-- or --NH--CO--; R.sup.11, R.sup.12, R.sup.14 and R.sup.15 are, independently, hydrogen or lower-alkyl, R.sup.13 is hydrogen, lower-alkoxycarbonyl or lower-alkyl, which can be substituted by amino, mono-alkylamino, di-alkylamino, morpholino, thiomorpholino or piperazino; and n is 1, 2, 3 or 4; with the proviso that at least one of X and Y comprises a hetero atom and that n is 1, 3 or 4 when X contains a hereto atom, Y is >C(CH.sub.3).sub.2 and R.sup.1 is lower-alkyl or --CH.sub.2 OR.sup.10 or --COR.sup.7, or a salt of a compound of formula I, when R.sup.1 is carboxy. The compounds of formula I are useful in the treatment and prophylaxis of neoplasms, dermatoses and ageing of the skin.