Through Friedel-Crafts acylation, the synthesis of benzophenone
intermediate as precursors for cyclization to xanthones can be achieved
conveniently. In the case of Friedel-Crafts acylation of methoxybenzene
derivatives and substituted benzoyl chloride in ether, the acylation process
occurs adjacent to the methoxy group, and a selective demethylation in the
presence of aluminium trichloride occurs at the ortho position to the
carbonyl group. In fact, this o-monodemethylation of the substituted
benzophenone intermediate through cyclization by elimination of
methanol can occur by extending the reaction time to 30 hours (Figure
2.8).