A very effective method for the preparation of the (S)-enantiomers of 2,3-dihydro-3-methyl- and 7,8-difluoro-2,3-dihydro-3-methyl-4H-1,4-benzoxazines (1a and 2a) was developed using (S)-(+)-naproxen acyl chloride as the chiral agent for kinetic resolution of racemates. This method enables one to obtain the (S)-enantiomers of benzoxazines 1a and 2a of high enantiomeric purity (99% ee) in nearly 50% yield, taking into account that the (R)-enantiomers are recycled after their racemisation.