Total synthesis of three naturally occurring 6,8-di-C-glycosylflavonoids: phloretin, naringenin, and apigenin bis-C-beta-D-glucosides.

Three naturally occurring di-C-glycosylflavonoids, phloretin (dihydrochalcone), naringenin (flavanone), and apigenin (flavone) bis-6,8-C-beta-D-glucopyranosides (4, 5, and 6), were synthesized in total yields of 52.3%, 53.5%, and 36.4%, respectively, starting from the key compound, di-C-beta-D-glucopyranosylphloroacetophenone (1). Benzyl protection of the phenolic hydroxyls in 1 and a subsequent aldol condensation with benzyloxybenzaldehyde led to the production of chalcone 3, which, after hydrogenolysis or acid hydrolysis and deprotection, gave 4 and 5, respectively. The acetylation of 5, followed by DDQ oxidation and deprotection, gave 6.