1st. A compound of formula (I) or a pharmaceutically acceptable salt thereof: in which: R1 is halogen or cyano； R2 is hydrogen or methyl； R3 and R4 are independently -OR6, C1-C6 alkyl or C3-C6 cycloalkyl, the last two groups being optionally substituted with one or more halogen atoms； R5 is hydrogen or halogen； R6 is C1-C6 alkyl or C3-C6 cycloalkyl, any of which is optionally substituted with one or more halogen atoms； X is -CH2 -, -S-, or -O-； one of the groups Y and Y1 is hydrogen and the other is OR6, -C (= O) R7, NR8SO2R6 or a heterocyclic group selected from furan, thiophene, pyrrole, oxazole, thiazole, imidazole, pyrazole, isoxazole, isothiazole, 1, 2, 3-oxadiazol, 1, 2, 4-oxadiazol, 1, 3, 4ºxadiazol, furazano, 1, 2, 3-triazol, 1, 2, 4-triazol, 1, 2, 3-thiadiazole, 1, 2, 5-thiadiazole, 1, 3, 4-thiadiazole, tetrazol, pyridine, pyridazine, pyrimidine, pyrazine, 1, 2, 4-triazine and 1, 3, 5-triazine, any of which may be optionally substituted with one or more substituents chosen from halogen； cyano； C1-C6 alkyl optionally substituted with one or more halogen atoms； C3-C6 cycloalkyl optionally substituted with one or more halogen atoms； hydroxy； C1-C6 alkoxy optionally substituted with one or more halogen atoms； C1-C6 alkyl -O-CH2-, C1-C6-O-CH (RX) alkyl -and C1-C6 -OC alkyl (RX RY) -in which the C1-C6 alkyl part is optionally substituted with one or more halogen atoms； NH2 C (= O) -； RXNHC (= O) -； RX RY NC (= O) -； RX RY NS (= O) 2-； RX NHS (= O) 2-； NH2 S (= O) 2-； NH2-； RX NH-； RX RY N-； RX S (= O) 2-； RX C (= O) -； RX S (= O) 2 NH-； RX S (= O) 2 N RY -； RX C (= O) NH-y RX C (= O) N (RY) -； wherein RX and RY are independently C1-C4 alkyl or C3-C6 cycloalkyl, any of which is optionally substituted with one or more halogen atoms； or RX and RY, when attached to the same nitrogen atom, form a cyclic amino ring； R7 is C1-C6 alkyl or C3-C6 cycloalkyl being any of which optionally substituted with one or more halogen atoms； or phenyl or monocyclic heteroaryl having 5
