FIELD: chemistry.
SUBSTANCE: invention relates to a method of producing (S)-7,8-difluoro-2,3-dihydro-3-methyl-4H-[1,4]benzoxazine of formula 
(S)-1. The method is realised by reacting racemic 7,8-difluoro-2,3-dihydro-3-methyl-4H-[1,4]benzoxazine of formula 
(I) with an acyl chloride of (S)-naproxen of formula 
(II) in toluene or dichloromethane at temperature ranging from 0 to -40°C and molar ratio of compound (I) to compound (II) equal to 1:0.5. The obtained mixture is treated with hexane and recrystallised from ethyl alcohol to obtain a compound of formula 
(III). Compound (III) undergoes acid hydrolysis in a mixture of acetic and hydrochloric acid at temperature 92-96°C for 8-10 hours to obtain a compound (S)-l.
EFFECT: improved method of obtaining a composition with high content of the basic substance and high enantiomeric excess.
1 cl, 3 dwg, 1 tbl, 3 ex
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