| abstract |
The invention relates to variants of a process for the preparation of a compound of the formula I, in which R is n-propyl, or its salts, including reacting a compound of formula I-1 in which X is bromine, chlorine or fluorine, with a compound of formula I-2 in which R salt of the compounds of formula I-2, and this reaction is carried out in the presence of a base in a polar aprotic organic solvent or polar mixture of aprotic organic solvents, and if X is bromine or chlorine, in the presence of tetra-n-butyl fluoride hydrate onium or cesium fluoride. In addition, the invention relates to the use of a compound of formula I-1 in a process for the preparation of a compound of formula I. |