C-Glycosylflavonoids. III. The Synthesis of 5,7,4'-Tri-O-methylvitexin (8-C-β-D-Glucopyranosyl-5,7,4'-trimethoxyflavone)

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Abstract
The reaction between 1,3,5-trimethoxybenzene and tetraacetyl-α-D-glucosyl bromide in the presence of zinc oxide gave β-D-glucopyranosyl-2,4,6-trimethoxybenzene tetraacetate (12). The tetraacetate (12) was converted by acetic anhydride and anhydrous aluminium chloride into 3-β-D- glucopyranosyl-2-hydroxy-4,6-dimethoxyacetophenone tetraacetate (15). Condensation of the acetophenone tetraacetate (15) with 4-methoxybenzaldehyde in the presence of sodium hydroxide gave 3'-β-D-glucopyranosyl-2'-hydroxy-4,4',6'-trimethoxychacone (6). Reaction of the chalcone (6) with selenium dioxide gave 8-C-β-D-glucopyranosyl-5,7,4'-trimethoxyflavone (5,7,4'-tri-O- methylvitexin)(10). The chemical shifts of the olefinic protons of chalcones are discussed.