Highly beta-selective and direct formation of 2-O-glycosylated glucosides by ring restriction into twist-boat
Yasunori Okada1, Osamu Nagata, Miyoko Taira
1School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan.
Abstract:
Three disaccharide donors, ethyl 2-O-(2,3,4-tris-O-tert-butyldimethylsilyl-beta-D-xylopyranosyl)-3,4,6-tris-O-tert-butyldimethylsilyl-1-thio-beta-D-glucopyranoside, ethyl 2-O-(2,3,4-tris-O-tert-butyldimethylsilyl-alpha-L-rhamnopyranosyl)-3,4,6-tris-O-tert-butyldimethylsilyl-1-thio-beta-D-glucopyranoside, and ethyl 2-O-(2,3,4,6-tetrakis-O-tert-butyldimethylsilyl-beta-D-glucopyranosyl)-3,4,6-tris-O-tert-butyldimethylsilyl-1-thio-beta-D-glucopyranoside, produced a highly beta-selective glycosidation up to alpha/beta = 2/98 using MeOTf as the activator and 2,6-lutidine as an additive. The ring conformations of the glucose part in these disaccharide donors were all restricted to 3S1, and the conformation would lead to the stereoselectivity.
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