tructures B1 to B6: in which R10 represents a C1-C4 alkyl radical, R11 and R12, which are identical or different, represent a hydrogen atom or a C1-C4 alkyl radical; c) the compounds of the following formulae (III) and (III???): in which: R13 represents a hydrogen atom, a C1-C4 alkoxy radical, a halogen atom such as bromine, chlorine, iodine or fluorine or an amino radical, R14 represents a hydrog