Compounds of the formula ##STR1## wherein R.sup.1 and R.sup.1' are independently alkyl, aryl, alkenyl or alkynyl; R.sup.2 and R.sup.2' are independently hydrogen, alkyl, aralkyl, alkoxyalkyl, hydroxyalkyl, haloalkyl, aminoalkyl, monoalkylaminoalkyl, dialkylaminoalkyl, acylaminoalkyl, alkylsulphonylaminoalkyl, arylsulphonyl-aminoalkyl, mercaptoalkyl, alkylthioalkyl, carboxyalkyl, alkoxycarbonylalkyl, aminocarbonylalkyl, alkylthio or alkylsulphinyl; R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.4', R.sup.5', R.sup.6', and R.sup.7' each independently are hydrogen, ##STR2## CO.sub.2 R.sup.9, CH.sub.2 OR.sup.10, CHO, CH.sub.2 NR.sup.11 R.sup.12, CON(R.sup.13).sub.2, halogen, cyano, aryl, alkyl, hydroxy, alkoxy, aryloxy, haloalkyl, nitro, amino, aralkyloxy, acylamino, monoalkylamino, dialkylamino, thio, alkyl, alkylsulphinyl, alkylsulphonyl, arylsulphinyl, azide, phosphate or phosphonate provided that at least one of R.sup.4, R.sup.5, R.sup.6 and R.sup.7 and at least one of R.sup.4', R.sup.5', R.sup.6', and R.sup.7' are other than hydrogen, with the proviso that when R.sup.6 is methoxy, R.sup.5 or R.sup.5 ' are not methoxy; R.sup.8 is alkyl or aryl; R.sup.9 is alkyl or aryl; R.sup.10 is hydrogen, alkyl or aryl; R.sup.11 and R.sup.12 are independently hydrogen, alkyl, aryl, aralkyl or acyl; R.sup.13 is hydrogen, alkyl, aryl or aralkyl; and one of X and Y signifies O and the other signifies O, S, (H,OH) or (H,H); as well as pharmaceutically acceptable prodrugs or pharmaceutically acceptable salts of acidic compounds of formula I with bases and or basic compounds of formula I with acids are antiproliferative agents useful in the treatment of cancer.