A compound of formula (i) according to claim 3 in which R4 is hydrogen or methyl, X is a direct bond and R is a group --NR1 R2 in which R1 is hydrogen or a methyl group and R2 is a non-aromatic C3 -C15 carbocyclic radical or a saturated 5- to 8-membered heterocyclic radical selected from 1-pyrrolidinyl, 1-piperidinyl, 1-hexahydroazepinyl, 4-morpholinyl and 4-thiomorpholinyl, or one of its salts. 7