کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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5214677 | 1383205 | 2015 | 6 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: 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](/preview/png/5214677.png)
Glucosylations and galactosylations of various acceptors with donors possessing an electron-withdrawing benzylsulfonyl, benzoyl, or acetyl group at the O-3 or O-4 position were performed. A β-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 α-directing effect. The α-directing effect is partly considered to remote participation of the acyl groups, whereas the β-directing effect is somewhat attributed to the SN2-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 α-glycosyl triflates was determined by a low-temperature NMR study.
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Journal: Tetrahedron - Volume 71, Issue 33, 19 August 2015, Pages 5315-5320