Abstract: Compounds of general formula (I) ##STR1## wherein R.sup.1 represents an optinally substituted carbocyclic or heterocyclic aryl group, or an optionally substituted alkyl, alkenyl, cycloalkyl or cycloalkenyl group; R.sup.2 represents an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group or an optionally substituted carbocyclic or heterocyclic aryl or aralkyl group; R.sup.3 represents a hydrogen atom or an alkyl group; and either X represents an oxygen or sulphur atom, a group --CH.sub.2 -- or a group NR.sup.4 where R.sup.4 represents a hydrogen atom or a C.sub.1-4 alkyl group; and Y represents a group --CH.sub.2 -- or --CH.sub.2 CH.sub.2 -- X-Y together represent the group --CH.dbd.CH--; and salts and physiologically functional derivatives thereof are useful in the treatment of tumours. Processes for preparing the compounds, intermediates useful in their preparation, pharmaceutical compositions containing them and their use in the treatment of tumours are also described.