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The discrimination of enantiomeric cyclic hemiacetals and methyl acetals derived from hydroxamic acids and lactams with the 2H-1,4-benzoxazin-3(4H)-one and 2H-1,4-benzothiazin-3(4H)sne skeleton was investigated using Conditions for the enantiomeric discrimination of six configurationally stable methyl acetals are reported. 2,4-Dihydroxy-2H-1,4-benzoxazin-3(4~-one and its 7-methoxy derivative, bioactive aglucones from Gramineae species, are the first cyclic hemiacetals that could be differentiated into enantiomem by means of 'H NMR, despite their oxo-cyclo tautomerization that prevented enantioseparation by chromatography or capillary electrophoresis. However, 2-hydroxy-2H-1,4-benzothiazin-3(4~-ones (thiohemiacetals) could not be differentiated by the use of these CSA. The influence of the structure of the enantiomers, CSA, temperature and concentration on the size of the chemical shift anisochrony is discussed.

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