Stereocontrolled chemical glycosylation remains a major challenge despite vast efforts reported over many decades and so far still mainly relies on trial and error. Now it is shown that the relative reactivity value (RRV) of thioglycosides is an indicator for revealing stereoselectivities according to four types of acceptors. Mechanistic studies show that the reaction is dominated by two distinct intermediates:
Halogen-bond-assisted radical activation of glycosyl donors enables mild and stereoconvergent 1,2-cis-glycosylation
作者:Chen Zhang、Hao Zuo、Ga Young Lee、Yike Zou、Qiu-Di Dang、K. N. Houk、Dawen Niu
DOI:10.1038/s41557-022-00918-z
日期:2022.6
2-cis-glycosylation without using metals, strong (Lewis) acids, elaborate catalysts or labile substrates. Our method operates by a unique mechanism: it activates glycosyl donors through a radical cascade rather than the conventional acid-promoted, ionic process. As elucidated by computational and experimental studies, the allyl glycosyl sulfones (as donors) form halogen bond complexes with perfluoroalkyl iodides, which—merely
Highly Stereoselective Glycosyl-Chloride-Mediated Synthesis of 2-Deoxyglucosides
作者:Ved Prakash Verma、Cheng-Chung Wang
DOI:10.1002/chem.201203418
日期:2013.1.14
Cl intermediates: The glycosylation of per-O-benzylated 2-deoxy- and 2,6-dideoxythioglycosides, promoted by the combination of para-toluenesulfenyl chloride (p-TolSCl) and silver triflate (AgOTf), furnished the products in high yields and high stereoselectivity. The glycosyl chloride was the intermediate (see scheme).