Compounds of formula (I):
wherein:

either one of R 1 and R 2 is hydrogen and the other is selected from the class of C 1-6 alkylcarbonyl, C 1-6 alkoxycarbonyl, C 1-6 alkylcarbonyloxy, C 1-6 alkylhydroxymethyl, nitro, cyano, chloro, trifluoromethyl, C 1-6 alkylsulphinyl, C 1-6 alkylsulphonyl, C 1-6 alkoxysulphinyl, C 1-6 alkoxysulphonyl, C 1 - 6 alkylcarbonylamino, C 1-6 alkoxycarbonylamino, C 1-6 alkyl-thiocarbonyl, C 1-6 alkoxy-thiocarbonyl, C 1-6 alkyl-thiocarbonyloxy, C 1-6 alkyl-thiomethyl, formyl or aminosulphinyl, aminosulphonyl or aminocarbonyl, the amino moiety being optionally substituted by one or two C 1-6 alkyl groups, or C 1-6 alkylsulphinylamino, C 1-6 alkylsulphonylamino, C 1-6 alkoxysulphinylamino or C 1-6 alkoxysulphonylamino or ethylenyl terminally substituted by C l - 6 alkylcarbonyl, nitro or cyano, or one of R 1 and R 2 is nitro, cyano or C 1-3 alkylcarbonyl and the other is methoxy or amino optionally substituted by one or two C 1-6 alkyl groups or by C 2 - 7 alkanoyl; one of R 3 and R 4 is hydrogen or C l - 4 alkyl and the other is C l - 4 alkyl or R 3 and R 4 together are C 2 - 5 polymethylene; either R 5 is hydrogen, hydroxy, C 1-6 alkoxy or C 1-7 acyloxy and R 6 is hydrogen or R 5 and R 6 together are a bond; R 7 is selected from the class consisting of C 1 - 6 alkyl substituted by amino optionally substituted by one or two C 1-6 alkyl groups which may be the same or different; amino optionally substituted by a C 1-6 alkyl or C 1-6 alkenyl group or a C 5-8 cycloalkyl group or by a phenyl group optionally substituted by C 1-6 alkyl, C l - 6 alkoxy or halogen; or C 1-6 alkoxy, or phenoxy optionally substituted by C 1-6 alkyl, C 1-6 alkoxy or halogen; or, when X is oxygen, R 7 is selected from the class of carboxy, C 1-6 alkoxycarbonyl, or aminocarbonyl optionally substituted by one or two C 1-6 alkyl groups which may be the same or different;
R 8 is hydrogen or C 1-6 alkyl; and
X is oxygen or sulphur;
The R 8 -N-CX-R 7 group being trans to the R 5 group when R 5 and R 6 together are not a bond;

or when the compound of formula (I) contains a salifiable group, pharmaceutically acceptable salts thereof, having pharmacological activity, a process for preparing them, pharmaceutical compositions containing them, and their use in the treatment of mammals.