Synthesis of C-Glycosides via Ramberg-Backlund Reaction

A novel methodology has been described, employing the Ramberg-Backlund rearrangement to synthesize C-glycosides. The Ramberg-Backlund sequence to provide C-glycosides includes three intermediates: thioglycoside, sulfonyl glycoside, and exo-glycal. Thio-glycosides can be easily made using different methods. Sulfone formation was routine with MMPP. The one-pot Ramberg-Backlund reaction of sulfone was done using C2Br2F4, t-BuOH and KOH/Al2O3 under reflux to afford an exo-glycal intermediate. The belta-C-glycosides can be made by hydrogenolysis of exo-glycals using H2 and Pd/C. The alpha-C-glycosides can be made stereoselectively from exo-glycals via intramolecular ionic hydrogenation as the key step. Some of the C- glycerolipids that have been prepared exhibit strikingly similar in vitro antiproliferative effects to those of O-glycoside analogs.