Hydrochloric Acid → Di-tert-butyl 5-methylisophthalate

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1,1′-Carbonyldiimidazole (6.67 g, 0.0411 mol) was added to a solution of toluene-3,5-dicarboxylic acid (2) (3.364 g, 0.0187 mol) in DMF (30 mL) and the resulting mixture stirred at 40° C. under N2. After 1.5 h DBU (6.15 mL, 0.041 mol) and t-BuOH (7.7 mL, 0.0822 mol) were added. After 24 h the solution was cooled, ether (150 mL) added and the mixture acidified (HCl (aq.), 1.5 M). The ethereal layer was separated and the aqueous layer further extracted (ether, 150 mL). The organic fractions were combined, washed with water and 10% K2CO3 (aq.), dried (MgSO4), filtered and the solvent removed. The residue was purified by flash chromatography (EtOAc:hexane, 1:50) to afford a colorless oil which solidified upon standing to give di-tert-butyl toluene-3,5-dicarboxylate (4.58 g, 84%) as a white solid; mp 86.5-87.5° C. (hexane); IR (film) 1712 cm−1 (C═O), 1606, 1476 cm−1 (Ar C═C); 1H NMR (CDCl3) δ1.60 (s, 18H, C(CH3)3), 2.43 (s, 3H, CH3), 7.95 (br s, 2H, H-2, H-6), 8.38 (br s, 1H, H-4); 13C NMR (CDCl3) δ21.4 (CH3), 28.2 (C(CH3)3), 81.4 (C(CH3)3), 127.7, 132.1, 133.7, 138.1 (Ar), 165.2 (COO).

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