Abstract: The invention concerns compounds of formula (I), wherein: R1, R2, R3 and R4 represent a hydrogen atom, an alkyl radical comprising 1 to 4 carbon atoms, a phenyl radical optionally substituted by one or several groups selected among vinyl, hydroxy, nitro, amino, bromo, chloro, fluoro, iodo, benzyloxy radicals, alkyl or alkyloxy radicals comprising 1 to 4 carbon atoms optionally substituted by one or several bromo, chloro, fluoro or iodo groups; R5, R6, R7 and R8 represent a hydrogen atom or an alkyl radical comprising 1 to 4 carbon atoms; Ra, Rb, and Rc represent a hydrogen atom, a phenyl radical optionally substituted by one or several groups selected among the vinyl, hydroxy, nitro, amino, bromo, chloro, fluoro, iodo, benzyloxy radicals, alkyl or alkyloxy radicals comprising 1 to 4 carbon atoms, optionally substituted by one or several bromo, chloro, fluoro or iodo groups.