[CH:1]([C:3]1[CH:11]=[CH:10][C:6]([C:7]([OH:9])=[O:8])=[C:5]([CH3:12])[CH:4]=1)=O.Br[C:14]1C=CC(C(O)=O)=C(C)[CH:15]=1.[Li][CH2:25]CCC.CN(C=O)C>C1COCC1>[CH3:12][C:5]1[CH:4]=[C:3]([CH:1]=[CH2:25])[CH:11]=[CH:10][C:6]=1[C:7]([O:9][CH2:14][CH3:15])=[O:8]
4-Formyl-2-methylbenzoic acid (AI15). To a stirred solution of 4-bromo-2-methylbenzoic acid (10 g, 46.4 mmol) in dry THF (360 mL) at −78° C. was added n-BuLi (1.6 M solution in hexanes; 58.17 mL, 93.0 mmol) and DMF (8 mL). The reaction mixture was stirred at −78° C. for 1 h then was warmed to 25° C. and stirred for 1 h. The reaction mixture was quenched with 1 N HCl solution and extracted with EtOAc. The combined EtOAc extracts were washed with brine and dried over Na2SO4 and concentrated under reduced pressure. The residue was washed with n-hexane to afford the title compound as a solid (3.0 g, 40%): mp 196-198° C.; 1H NMR (400 MHz, DMSO-d6) δ 13.32 (br s, 1H), 10.05 (s, 1H), 7.98 (m, 1H), 7.84 (m, 2H), 2.61 (s, 3H); ESIMS m/z 163.00 ([M−H]−).
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