A compound of formula (I) ##STR1## in which X represents a hydrogen atom, a halogen atom, a trifluoromethyl group, a C.sub.1 -C.sub.3 alkyl group or a C.sub.1 -C.sub.3 alkoxy group in which case two such alkoxy groups X can be present,Y represents a hydrogen atom, a halogen atom, a C.sub.1 -C.sub.3 alkyl group or a C.sub.1 -C.sub.3 alkoxy group,R.sub.1 represents C.sub.1 -C.sub.4 alkyl group, andR represents a hydroxyl group, a methoxy group, an ethoxy group or a group of formula NR.sub.2 R.sub.3 in which R.sub.2 and R.sub.3 each independently represents a hydrogen atom or a C.sub.1 -C.sub.4 alkyl group, or a pharmaceutically acceptable addition salt thereof, processes for their preparation and their therapeutic application.