C[O:2][C:3]([C:5]1[CH:6]=[C:7]([C:11]2[CH:16]=[CH:15][C:14]([O:17][CH3:18])=[C:13]([O:19][CH3:20])[C:12]=2[O:21][CH3:22])[CH:8]=[CH:9][CH:10]=1)=[O:4].[Li+].[OH-].Cl>CC#N>[CH3:22][O:21][C:12]1[C:13]([O:19][CH3:20])=[C:14]([O:17][CH3:18])[CH:15]=[CH:16][C:11]=1[C:7]1[CH:8]=[CH:9][CH:10]=[C:5]([C:3]([OH:4])=[O:2])[CH:6]=1Dissolve 2′,3′,4′-Trimethoxy-biphenyl-3-carboxylic acid methyl ester (43) (566 mg, 1.87 mmol) in MeCN (19.0 mL) at rt and add 1M aqu LiOH (9.36 mL, 9.36 mmol). Stir reaction mixture overnight at rt. Quench reaction mixture (cooling bath) with 1M aqu. HCl (to get pH ca. 3). Extract the mixture with EtOAc (3×), wash the combined organic layer with brine and dry with Na2SO4. Recrystallize crude product from EtOAc/CyH 1+3 to obtain 2′,3′,4′-Trimethoxy-biphenyl-3-carboxylic acid (44) as a white solid (392 mg, to 72%). 1H NMR (400 MHz, CD3OD: 3.68 (s, 3H); 3.93 (br.s, 6H); 6.92 (d, 1H, J=8.6 Hz); 7.11 (d, 1H, J=8.6 Hz); 7.54 (t, 1H, J=7.7 Hz); 7.75 (d, 1H, J=7.6 Hz); 8.01 (d, 1H, J=7.8 Hz); 8.18 (br.s 1H).
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