Abstract: The invention provides antitumour compounds of formula (I), wherein R1 is an aromatic substituent; R2 is hydrogen or a substituent when the dotted line is absent, or R2 is absent when the dotted line represents a bond to give a double bond between the nitrogen which bears R2 and the carbon which bears R3; R3 is an oxo group =0 when the dotted line is absent or is a substituent when the dotted line represents a bond to give a double bond between the nitrogen bearing R2 and the carbon bearing R3; R4 is hydrogen or a substituent; and pharmaceutically acceptable salts thereof.