The demethylation of 3, 4-dioxygenated 6-methoxy-2-isopropoxyacetophenones was studied and it was found that 4-benzyloxy-6-hydroxy-3-methoxy-2-isopropoxyacetophenone was easily obtained from 4-benzyloxy-3, 6-dimethoxy-2-isopropoxyacetophenone by selective demethylation with anhydrous aluminum bromide-sodium iodide in acetonitrile. The acetophenone was converted into 7-benzyloxy-3-hydroxy-6-methoxy-5-isopropoxyflavones by cyclization followed by oxidation with dimethyldioxirane. The isopropoxy group in the flavones was selectively cleaved with anhydrous aluminum chloride via the corresponding tosylates to give 7-benzyloxy-3, 5-dihydroxy-6-methoxyflavones, which were converted into the desired 3, 5, 7-trihydroxy-6-methoxyflavones by hydrogenolysis. The process was suitable as a general method for synthesizing 3, 5, 7-trihydroxy-6-methoxyflavones and five flavones were synthesized. We also examined the ¹³C-NMR spectra of twelve kinds of 3, 5, 6, 7-tetraoxygenated 4'-methoxyflavones and revised the proposed structure of a natural flavone.