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A series of chiral imines derived from 1-amino-1-deoxyalditols such as
D-glucamine, a rather unexploredraw material from the chiral pool, have been serendipitiously transformed into a novel family of
N-acetyl-1,3-oxazolidines by means of an unexpected acetylation. The structure of these substances is supportedby spectroscopic
and crystallographic data. The acetylates also trigger a complex dynamic transformation,in which an initially configured trans oxazolidine converts into a more stable cis-configured derivative.Both isomers can also exist as rotational conformers (
E,
Z) as a consequence of the restricted rotationaround the
N-acetyl bond. The barriers to rotation have been determined by variable-temperatureexperiments. Overall, this transformation most likely involves the intermediacy of a chiral iminium ion,which has been documented in the synthesis of nitrogen heterocycles, thus explaining the experimentalfacts.