The invention relates to compounds of formula (I) wherein R represents aryl or heteroaryl, X is a bond, a carbonyl group, a derivative of a carbonyl group, an ethylene group or an ethylenecarbonyl group, R1 is optionally substituted amino or hydroxy, and the substituents R2 to R6 have the meanings given in the specification, to methods of synthesis of such compounds, to pharmaceutical compositions containing compounds of formula (I), to intermediates, to the use of a compounds of formula (I) as a medicament and for the preparation of a pharmaceutical composition for the treatment of neoplastic and autoimmune diseases, and to methods of treatment of neoplastic and autoimmune diseases using such compounds of formula (I) or of pharmaceutical compositions containing same.