De novo asymmetric syntheses of SL0101 and its analogues via a palladium-catalyzed glycosylation

The enantioselective syntheses of naturally occurring kaempferol glycoside SL0101 (1a) and its analogues 1b-e, as well as their enantiomers, have been achieved in 7-10 steps. The routes rely upon a diastereoselective palladium-catalyzed glycosylation, ketone reduction, and dihydroxylation to introduce the rhamno-stereochemistry. The asymmetry of the sugar moiety of these kaempferol glycosides was derived from Noyori reduction of an acylfuran. An acetyl group shift from an axial (C-2) to equatorial position (C-3) under basic conditions was also described.