FIELD: chemistry.
SUBSTANCE: invention relates to an improved process for the preparation of compounds of formula 
. The process involves the conversion of the compound of formula 
into a compound of formula (I) in the presence of at least one base and in the presence of at least one polymerisation inhibitor, selected from 2,2,6,6-tetramethylpiperidine-N-oxyl, sulphur, p-benzoquinone, 4-tert-butylpyrocatechol, phenothiazine, di-tert-butylhydroxytoluene or mixtures of these polymerisation inhibitors. In the compounds of formulas (I) and (II) R1 and R2 are identical or different and, independently of one another, represent hydrogen, C1-C15-alkyl, C6-C24-aryl,or C1-C15-alkoxy, R3 is C1-C15-alkoxy, and X in formula (II) represents Cl, Br, I or pseudohalogen.
EFFECT: invention provides the process for the production of compounds with good yields and high purities.
14 cl, 4 ex
