Studies of the Selective O-Alkylation and Dealkylation of Flavonoids. VIII. : Synthesis of Pedaliin

3', 4'-Bis(benzyloxy)-6-hydroxy-5, 7-dimethoxyflavone (15) was obtained from 6-hydroxy-2, 4-dimethoxy-3-(methoxymethoxy)acetophenone (13) via 6'-hydroxy-2', 4'-dimethoxy-3'-methoxy-methoxy-2-[3, 4-bis(benzyloxy)benzoyl]acetophenone (14). The 5-methoxyl group of the acetate (16) of the flavone (15) was selectively split with about 5% (w/v) anhydrous aluminum chloride in acetonitrile to give 6-acetoxy-3', 4'-bix(benzyloxy)-5-hydroxy-7-methoxyflavone (17). The 5-hydroxyflavone (17) was converted into 3', 4', 5-tris(benzyloxy)-6-hydroxy-8-methoxyflavone (20) by benzylation and hydrolysis. Condensation of the 6-hydroxyflavone (20) with 2, 3, 4, 6-tetra-O-acetyl-α-D-glucosyl bromide, folowed by hydrolysis of the resultant compound afforded the corresponding 6-O-β-D-glucoside (22), which was converted into 3', 4', 5, 6-tetrahydroxy-7-methoxyflavone 6-O-β-D-glucoside (pedaliin) (1) by hydrogenolysis. The process should be useful as a general method for synthesizing 6-O-glucosides of 5, 6-dihydroxy-7-methoxyflavones.