1, 2-trans-Stereoselective 7-O-Glycosylation of Flavonoids with Unprotected Pyranoses by Mitsunobu Reaction

The glycosylation of protecting-group-free pyranoses with flavonoids to generate flavonoid O-glycosides under Mitsunobu conditions was reported. The methodology allows to prepare a wide range of natural 7-flavonoid O-glycosides and their derivatives from commercially available chemicals in good to excellent yields with exclusive 1,2-trans-stereoselectivity regardless the anomeric configuration of employed pyranoses. The highly regioselective glycosylation was also achieved among different types of hydroxyl groups on the glycosyl acceptors.