FIELD: organic synthesis. SUBSTANCE: new method for preparation of compound of 6 involves preparing solution of compound 2 by consecutively adding compound 1 to aprotic solvent A (4-30 mg/g) and aprotic diluent (0.0001-0.25 mg/g) at stirring under inert gas atmosphere, after which activation agent is added in amount 0.95-2.0 mole per 1 mole of compound 1. Preparation of compound 4: compound 3 and base in amount 1.9-3.0 mole/mole are consecutively added to mixture of aprotic solvent B and protonic solvent (respectively, 1.9-3.0 mg and 3-30 ml per 1 g compound 3) at temperature from minus 20 C to dephlegmation temperature of indicated mixture and maintaining pH of the mixture within a range of 8-13. Preparation of compound 5: said solution is added to said mixture under inert gas atmosphere at indicated temperature, resulting mixture is allowed to stand to achieve room temperature, organic solvent is added in amount 3-30 ml/g. Compound 6 is extracted form the mixture into indicated organic solvent by separating aqueous layer A and organic layer A and treating organic layer A with aqueous acid solution. Formulas of compounds 1-6 are connected: 
. In formula of compound 5 M+ denotes tetra-C1-C6-alkylammonium cation. EFFECT: reduced number of synthesis stages. 26 cl, 3 ex
