A subject-matter of the invention is the compounds of general formula (I) in which X represents a hydrogen or halogen atom; R1 represents a hydrogen atom or a (C1-C4)alkyl group; R2 and R3 each represent, independently of one another, a hydrogen atom or a (C1-C4)alkyl group or else R2 and R3 form, with the nitrogen atom which carries them, a pyrrolidinyl, piperidinyl, morpholinyl or 4-alkylpiperazinyl group; and Het represents a heteroaromatic group of pyridinyl, 1-oxidopyridinyl, quinolinyl, isoquinolinyl, pyrimidinyl, pyrazinyl or pyridazinyl type, it being possible for the heteroaromatic group to carry one or more halogen atoms and/or one or more (C1-C4) alkyl or (C1-C4) alkoxy groups; in the form of bases, of addition salts with acids, of solvates or of hydrates, the pharmaceutical compositions comprising them, processes for their preparation and synthetic intermediates.