The present invention relates to preparing derivatives of formula (1), wherein, in particular R1 and R2, identical or different, represent a hydrogen, fluorine or chlorine atom, a hydroxy group, an alkyl radical and an alkoxy radical, R3 is an alkyl radical, a hydroxy group or a methoxy radical, R4 is a hydrogen atom or a methyl radical and R5 and R6, identical or different, represent a hydrogen atom, analkyl radical, an alkoxy radical, an alkylthio radical and an alkylamino radical. The inventive method consists in reducing an amide of formula (9).