Compounds corresponding to the general formula ##STR1## wherein: R and R1, that may be different, represent a hydrogen atom, a halogen, an alkyl group, an alkoxy radical in which the alkyl group contains one to four carbon atoms, a nitro group, a cyano group, an amino group, an acetamino group, a sulfamidic or N-substituted sulfamidic group; R2 represents a hydrogen atom, a halogen, an alkoxy radical, an alkyl group, a phenyl group, a phenylalkyl group, a phenylalkylene or phenylalkenyl group in which the alkylene or alkenyl radical contains two to four carbon atoms, a nitro group, a cyano group, an amino group, an acetamino group, an N-substituted suylfamidic group; and R3 represents a hydrogen atom, an alkyl group, preferably containing one to three carbon atoms or a cyano group.