“Super Armed” Glycosyl Donors: Conformational Arming of Thioglycosides by Silylation
作者:Christian Marcus Pedersen、Lars Ulrik Nordstrøm、Mikael Bols
DOI:10.1021/ja071955l
日期:2007.7.1
Glycosyl donors protected with bulky silyl protective groups (tert-butyldimethylsilyl, TBS), on the 2-, 3-, and 4-OH groups were found to have superior reactivity compared with benzylated thioglucosides. The enhanced reactivity is explained by the stereoelectronic effects associated with the conformational change induced by the silylation. A TBS silylated thioglucoside donor has axial OR groups, whereas a benzylated thioglucoside has equatorial OR groups, leading to much more favorable charge-dipole interactions in the transition state. This concept could be used to create "super armed" glucosyl, mannosyl, rhamnosyl, and galactosyl donors, which could cross-couple with the armed acceptors, phenyl 2,3,4-tri-O- benzyl-beta-D-thioglucoside or phenyl 2,3,6-tri-O-benzyl-beta-D-thioglucoside, to give the corresponding armed disaccharides in good to excellent yields.