Directing effect by remote electron-withdrawing protecting groups at O-3 or O-4 position of donors in glucosylations and galactosylations
Directing effect by remote electron-withdrawing protecting groups at O-3 or O-4 position of donors in glucosylations and galactosylations
复制标题
DOI：
10.1016/j.tet.2015.06.014
复制
发表时间：
2015-08-19
期刊：
影响因子：
2.1
通讯作者：
Kim, Kwan Soo
中科院分区：
文献类型：
--
作者：
Baek, Ju Yuel;Kwon, Hea-Won;Kim, Kwan Soo
葡萄糖基化和半乳糖基化的各种受体与具有吸电子苄基磺酰基，苯甲酰基，或乙酰基基团在O-3或O-4位置的供体进行。观察到葡萄糖基供体的O-3处的苄基磺酰基和葡萄糖基供体的O-4处的苄基磺酰基和酰基的β-定向作用。相比之下，葡萄糖基供体的O-3处的酰基和半乳糖基供体的O-3和O-4处的酰基表现出α-导向效应。α-导向效应部分被认为是酰基的远程参与，而β-导向效应在某种程度上归因于受体与糖基三氟甲磺酸酯或接触离子对的S（N）2样反应，其通过远程吸电子基团稳定。通过低温NMR研究确定了α-糖基三氟甲磺酸酯稳定性的进一步证据。(C)2015爱思唯尔有限公司版权所有。
Glucosylations and galactosylations of various acceptors with donors possessing an electronwithdrawing benzylsulfonyl, benzoyl, or acetyl group at the O-3 or O-4 position were performed. A beta-directing effect by the benzylsulfonyl group at O-3 of the glucosyl donors and by the benzylsulfonyl and acyl groups at O-4 of the glucosyl donors was observed. In contrast, acyl groups at O-3 of the glucosyl donors and acyl groups at O-3 and O-4 of the galactosyl donors exhibited an alpha-directing effect. The alpha-directing effect is partly considered to remote participation of the acyl groups, whereas the beta-directing effect is somewhat attributed to the S(N)2-like reaction of the acceptor with the glycosyl triflate or the contact ion pair, which is stabilized by remote electron-withdrawing groups. Further evidence for the stability of the alpha-glycosyl triflates was determined by a low-temperature NMR study. (C) 2015 Elsevier Ltd. All rights reserved.