[CH3:1][CH:2]1[C:6]2[CH:7]=[CH:8][C:9]([C:11]([O:13]C)=[O:12])=[CH:10][C:5]=2[O:4][CH2:3]1.C(N(CC)CC)C.C1(P(C2C=CC=CC=2)CCCP(C2C=CC=CC=2)C2C=CC=CC=2)C=CC=CC=1>CO.C([O-])(=O)C.[Pd+2].C([O-])(=O)C>[CH3:1][CH:2]1[C:6]2[CH:7]=[CH:8][C:9]([C:11]([OH:13])=[O:12])=[CH:10][C:5]=2[O:4][CH2:3]1To a reversible vial was added methyl 3-methyl-2,3-dihydrobenzofuran-6-carboxylate (384 mg, 2 mmol) in methanol (16 mL) was added triethylamine (900 mg, 9 mmol), palladium acetate (116 mg, 0.5 mmol) and 1,3-bis(diphenylphosphino) propane (480 mg, 1 mmol). Then the reaction mixture was charged with carbonate monoxide under 15 atm at 110° C. for 12 hours. The suspension was concentrated in vacuum and quenched with aqueous 1N hydrochloric acid (5 mL). The residue was taken up with water (50 mL) and extracted with dichloromethane (50 mL). The combined extract was dried over sodium sulphate, evaporated and purified by column chromatography (silica gel, dichloromethane/methanol=20:1) to give the product 3-methyl-2,3-dihydrobenzofuran-6-carboxylic acid (0.28 g, 78%) as colorless oil.
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