Remarkable High-pressure Enhancement of Enantiopure Nitrone Cycloadditions to Glycals: General Access to (1 → 2)-Linked Pseudo Aza-<i>C</i>-disaccharides
1,3-Dipolar cycloadditions of enantiopure hydroxylated nitrones to glycals are strongly accelerated under high pressure. Under 10 Kbar pressure the process gains generality and broad scope and allows a direct access, in good to excellent yields, to stereodifferentiated tricyclic isoxazolidines, key intermediates for the synthesis of a new class of (1 → 2) linked pseudo aza-C-disaccharides.
在高压条件下,对映体纯羟基腈与缩水甘油的 1,3-二极环加成反应被大大加速。在 10 Kbar 的压力下,该过程具有通用性和广泛性,可以直接获得立体异构的三环异噁唑烷,产量从好到优,是合成一类新的(1 → 2)连接假氮杂-C-二糖的关键中间体。
New Access to Aza-C-disaccharides by Cycloadditions of Pyrroline N-Oxides to Glycals
A novel, highly stereoselective intermolecular cycloaddition reaction of simple and enantiopure cyclic nitrones to glucose and galactose-derived 1,2-glycals offers a direct access to a new class of pseudoaza-C-disaccharides with isoxazolidine structure, potential glycosidase inhibitors. The synthesis of new (1-->2)-linked aza-disaccharides is accomplished by simple reductive ring-opening of the isoxazolidine. (C) 1997 Elsevier Science Ltd.