Enantiomers of 2-methyl- and 2,4-dimethyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid: Preparation by resolution,determination of absolute configuration,and Curtius rearrangement

Both enantiomers of 2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid 2 and 2,4-dimethyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid 3 were prepared via resolution of the corresponding racemic carboxylic acids with (R)- and (S)-1-phenylethylamine, respectively. Absolute configuration of (−)-(R)-2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid was determined by X-ray crystallography. Curtius rearrangement of acyl azides prepared from enantiomers of these heterocyclic carboxylic acids carried out in benzyl alcohol afforded enantiomers of the corresponding benzyl carbamates, which upon hydrogenolysis gave racemic 2-amino-2-methyl-3,4-dihydro-2H-1,4-benzoxazin-3-one 4 and 2-amino-2,4-dimethyl-3,4-dihydro-2H-1,4h-benzoxazin-3-one 5. Chirality 10:791–799, 1998. © 1998 Wiley-Liss, Inc.