Chiral N-acyloxazolidines: synthesis, structure, and mechanistic insights.
A series of chiral imines derived from 1-amino-1-deoxyalditols such as d-glucamine, a rather unexplored raw 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 supported by 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 rotation around the N-acetyl bond. The barriers to rotation have been determined by variable-temperature experiments. 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 experimental facts.
Avalos
Martín
M
Departamento de Química OrgAnica e InorgAnica, QUOREX Research Group, Universidad de Extremadura, E-06071 Badajoz, Spain.
Babiano
Reyes
R
Cintas
Pedro
P
Jiménez
José L
JL
Light
Mark E
ME
Palacios
Juan C
JC
Pérez
Esther M S
EM
D018360:Crystallography, X-Ray; D007097:Imines / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D015394:Molecular Structure; D010080:Oxazoles / Q000138:chemical synthesis* / Q000737:chemistry*; D012399:Rotation; D012545:Schiff Bases / Q000737:chemistry; D013237:Stereoisomerism
D007097:Imines; D010080:Oxazoles; D012545:Schiff Bases; C064210:oxazolidine