Neighboring-Group Participation in Nitrile-Forming Beckmann Fragmentation Reactions: Synthesis of Enantiopure (E)-2,3-Di-O-substituted-5-methoxy- pent-4-enenitriles and Their Conversion into Pyranosylamines
作者:Pietro Passacantilli、Clara Centore、Elena Ciliberti、Giovanni Piancatelli、Francesca Leonelli
DOI:10.1002/ejoc.200400498
日期:2004.12
C1−C2 heterolytic fragmentation was completely controlled and directed by the adjacent C1 ether oxygen, which generates a carbonium-oxonium ion as an active electrofugal group. Unexpectedly, the C3 heteroatom did not assist the cleavage reaction and products derived from C2−C3 fragmentation were never detected. The excellent regio- and stereospecificity of the fragmentation reaction, based on the stereochemical
多功能酮肟的选择性贝克曼碎裂已被证明可以有效地进行,以产生相应的腈。手性 (E)-1,3,4-三-O-取代-6-甲氧基-hex-5-en-2-one 肟衍生物,可从糖基和糖基糖基中获得,得到对映体纯 (E)-2,3 -二-O-取代的-5-甲氧基戊-4-烯腈通过用甲磺酰氯和三乙胺处理。C1-C2 异裂裂解完全由相邻的 C1 醚氧控制和引导,产生碳正离子作为活性电离基团。出乎意料的是,C3 杂原子并没有帮助裂解反应,并且从未检测到来自 C2-C3 碎片的产物。讨论了基于立体化学结果的断裂反应的出色区域和立体特异性。还描述了一些吡喃糖胺的简单合成方法。(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)