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2005
Oxazine derivatives
R 0595
Stereodivergent Syntheses of Highly Substituted Enantiopure 4-Alkoxy-3,6-dihyby Addition of Lithiated Alkoxyallenes to Carbohydrate-De31- 151 dro-2H-1,2-oxazines
rived Aldonitrones. — Addition of lithiated alkoxyallenes (II) towards carbohydrate-based nitrones [cf. (I)] directly provides access to the [3 + 3] cycloadducts without isolation of the intermediate hydroxylamines. The reaction proceeds with moderate
to excellent syn-selectivity depending on the nature of auxiliary carbohydrate. The selectivity can, however, be altered in favor of the anti-diastereomer when the nitrone is
precomplexed with a Lewis acid like Et2AlCl [cf. (IV)]. — (HELMS, M.; SCHADE,
W.; PULZ, R.; WATANABE, T.; AL-HARRASI, A.; FISERA, L.; HLOBILOVA, I.;
ZAHN, G.; REISSIG*, H.-U.; Eur. J. Org. Chem. 2005, 6, 1003-1019; Inst. Chem.,
FU Berlin, D-14195 Berlin, Germany; Eng.) — Mischke
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