[CH3:1][O:2][C:3]1[CH:13]=[CH:12][CH:11]=[C:5]2[C:6]([O:8][C:9](=[O:10])[C:4]=12)=[O:7].[Cl-].[Al+3].[Cl-].[Cl-].[CH3:18][O:19][C:20]1[CH:25]=[CH:24][C:23]([O:26][CH3:27])=[CH:22][CH:21]=1.Cl>C(Cl)Cl.C(O)C>[CH3:18][O:19][C:20]1[CH:25]=[CH:24][C:23]([O:26][CH3:27])=[CH:22][C:21]=1[C:6]([C:5]1[CH:11]=[CH:12][CH:13]=[C:3]([O:2][CH3:1])[C:4]=1[C:9]([OH:8])=[O:10])=[O:7]
3-Methoxyphthalic anhydride (17.8 g, 0.1 mole) was suspended in 100 ml. dry methylene chloride (previously distilled over anhydrous potassium carbonate). To the suspension was added anhydrous aluminum chloride (30.5 g, 0.23 mole) in one portion. The suspension quickly became bright yellow and was stirred at room temperature for 2 hours. A solution of p-dimethoxybenzene (27.6 g, 0.2 mole) in methylene chloride (100 ml) was added slowly to the vigorously stirred solution. The reaction mixture was stirred overnight at 25° and poured onto ice (300 g) and concentrated hydrochloric acid (50 ml). The slurry was stirred for 30 minutes and extracted with chloroform (4 × 150 ml). A white precipitate suspended in the aqueous layer is collected by filtration. The organic extract was washed once with water (200 ml) and washed with saturated sodium bicarbonate (4 × 150 ml). The aqueous bicarbonate extract was washed once with chloroform (150 ml) and acidified with concentrated hydrochloric acid, the mixture cooled on an ice bath and filtered. The residue was washed well with water and dried under reduced pressure and combined with the white precipitate to yield 2-(2',5'-dimethoxybenzoyl)-6-methoxybenzoic acid (I) as a pale yellow solid (13 g, 41% yield), m.p. 180°-182° C. (from ethanol); IR (KBr) 2.95, 5.72μ; NMR (CDCl3) δ, 7.60-6.80 (m, 6H), 6.10 (s, 1H), 3.75 (s, 3H), 3.70 (s, 3H), 3.49 (s, 3H).
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