A compound of formula in which: - R 1 represents a hydrogen atom, a (C 1 -C 6)alkyl group, a (C 3 -C 7)cycloalkyl group, a (C 3 -C 7)cycloalkyl-(C 1 -C 6)alkyl- group, a Rb-O-Ra- group where Rb represents a (C 1 -C 6)alkyl group or a (C 3 -C 7)cycloalkyl group and Ra represents a (C 1 -C 6)alkyl group, or a Rd-O-C -O-Rc- group where Rd represents a (C 1 -C 6)alkyl group or a (C 3 -C 7)cycloalkyl group and Rc represents a (C 1 -C 6)alkyl group, or a Rf-C -ORe- where Re represents a (C 1 -C 6)alkyl group and Rf represents a (C 1 -C 6)alkyl group, - R 2 represents a halogen atom, -OH, -CN, a (C 1 -C 6)alkyl group, an -O-(C 1 -C 6)alkyl group, said alkyl groups being non-substituted or substituted by one or more halogen atoms, identical to or different from one another, or a Rg-O-Rh-O- where Rg represents a (C 1 -C 6)alkyl group and Rh represents a (C 1 -C 6)alkyl group, - R 2 ' represents a hydrogen atom or a (C 1 -C 6)alkyl group, - R 3 represents: - R 4 and R 5 represent, independently of one another, a (C 1 -C 6) alkyl group or a (C 3 -C 7)cycloalkyl group, - or R 4 and R 5 together form, with the nitrogen atom to which they are attached, a 3 to 7 membered heterocycloalkyl group comprising from 1 to 2 heteroatoms chosen from nitrogen, oxygen and sulphur, said heterocycloalkyl group being non-substituted or substituted by one or more groups, identical or different from one another, chosen from halogen atoms and (C 1 -C 6)alkyl groups, (C 1 -C 6)alkoxy groups, -CF 3, -OCF 3, - R 6 represents a halogen atom, a hydrogen atom, a (C 1 -C 6)alkyl group, a (C 1 -C 6)alkoxy group or -CN; as well as their enantiomers, diastereoisomers and their mixtures, and the pharmaceutically acceptable salts thereof. - R 1 represents a hydrogen atom, a (C 1 -C 6)alkyl group, a (C 3 -C 7)cycloalkyl group, a (C 3 -C 7)cycloalkyl-(C 1 -C 6)alkyl- group, a Rb-O-Ra- group where Rb represents a (C 1 -C 6)alkyl group or a (C 3 -C 7)cycloalkyl group and Ra represents a (C 1 -C 6)alkyl group, or a Rd-O-C -O-Rc- group where Rd represents a (C 1 -C 6)alkyl group or a (C 3 -C 7)cycloalkyl group and Rc represents a (C 1 -C 6)alkyl group, or a Rf-C -ORe- where Re represents a (C 1 -C 6)alkyl group and Rf represents a (C 1 -C 6)alkyl group, - R 2 represents a halogen atom, -OH, -CN, a (C 1 -C 6)alkyl group, an -O-(C 1 -C 6)alkyl group, said alkyl groups being non-substituted or substituted by one or more halogen atoms, identical to or different from one another, or a Rg-O-Rh-O- where Rg represents a (C 1 -C 6)alkyl group and Rh represents a (C 1 -C 6)alkyl group, - R 2 ' represents a hydrogen atom or a (C 1 -C 6)alkyl group, - R 3 represents: - R 4 and R 5 represent, independently of one another, a (C 1 -C 6) alkyl group or a (C 3 -C 7)cycloalkyl group, - or R 4 and R 5 together form, with the nitrogen atom to which they are attached, a 3 to 7 membered heterocycloalkyl group comprising from 1 to 2 heteroatoms chosen from nitrogen, oxygen and sulphur, said heterocycloalkyl group being non-substituted or substituted by one or more groups, identical or different from one another, chosen from halogen atoms and (C 1 -C 6)alkyl groups, (C 1 -C 6)alkoxy groups, -CF 3, -OCF 3, - R 6 represents a halogen atom, a hydrogen atom, a (C 1 -C 6)alkyl group, a (C 1 -C 6)alkoxy group or -CN;