A compound of formula: wherein R1 is NR5R6 wherein R5 and R6 are each independently hydrogen, a group selected from straight or branched C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl; or R5 and R6 together with the nitrogen atom to which they are bound, form a 5 to 7 membered heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; R2 is aryl, arylalkyl, heterocyclyl or heterocyclylalkyl; R3 and R4 are each independently hydrogen, halogen, cyano, or a group selected from straight or branched C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl; or a pharmaceutically acceptable salt thereof, provided that when R3 and R4 are hydrogen, R5 is a group of formula wherein R7 is a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl and cycloalkyl-alkyl; and Y is N-R' or CH-NR'R", wherein R' and R" are each independently hydrogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, heterocyclyl and heterocyclylalkyl; wherein with "heterocyclyl" it is intended a 3- to 7-membered, saturated or partially unsaturated carbocyclic ring where one or more carbon atoms are replaced by heteroatoms such as nitrogen, oxygen and sulfur; wherein with "aryl" it is intended a carbocyclic or heterocyclic hydrocarbon with from 1 to 2 ring moieties, either fused or linked to each other by single bonds, wherein at least one of the rings is aromatic; wherein any of the above R2, R3, R4, R5, R6, R7, R' and R" group may be optionally substituted, in any of their free positions, by 1 to 6 groups independently selected from: halogen atom, nitro, oxo groups (=O), cyano, C 1 -C 6 alkyl, polyfluorinated alkyl, polyfluorinated alkoxy, alkenyl, alkynyl, hydroxyalkyl, aryl, arylalkyl, heterocyclyl, C 3 -C 7 cycloalkyl, hydroxy, alkoxy, aryloxy, heterocyclyloxy, methylenedioxy, alkylcarbonyloxy, arylcarbonyloxy, cycloalkenyloxy, heterocyclylcarbonyloxy, alkylideneaminooxy, carboxy, alkoxycarbonyl, aryloxycarbonyl, cycloalkyloxycarbonyl, heterocyclyloxycarbonyl, amino, ureido, alkylamino, dialkylamino, arylamino, diarylamino, heterocyclylamino, formylamino, alkylcarbonylamino, arylcarbonylamino, heterocyclylcarbonylamino, aminocarbonyl, alkylaminocarbonyl, dialkylaminocarbonyl, arylaminocarbonyl, heterocyclylaminocarbonyl, alkoxycarbonylamino, hydroxyaminocarbonyl alkoxyimino, alkylsulfonylamino, arylsulfonylamino, heterocyclylsulfonylamino, formyl, alkylcarbonyl, arylcarbonyl, cycloalkylcarbonyl, heterocyclylcarbonyl, alkylsulfonyl, arylsulfonyl, aminosulfonyl, alkylaminosulfonyl, dialkylaminosulfonyl, arylaminosulfonyl, heterocyclylaminosulfonyl, arylthio, alkylthio, phosphonate and alkylphosphonate. R1 is NR5R6 wherein R5 and R6 are each independently hydrogen, a group selected from straight or branched C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl; or R5 and R6 together with the nitrogen atom to which they are bound, form a 5 to 7 membered heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; R2 is aryl, arylalkyl, heterocyclyl or heterocyclylalkyl; R3 and R4 are each independently hydrogen, halogen, cyano, or a group selected from straight or branched C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl;