[OH:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[CH:4][CH:3]=1.N1C=CC=CC=1.[C:17](Cl)(=[O:22])[C:18]([CH3:21])([CH3:20])[CH3:19].Cl>ClCCl>[C:17]([O:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[CH:4][CH:3]=1)(=[O:22])[C:18]([CH3:21])([CH3:20])[CH3:19]A solution of 4-hydroxybenzoic acid (6.91 g) and pyridine (12.1 ml) in dichloromethane (100 ml) was cooled to an ice-water temperature, and hereto was added dropwise pivaloyl chloride (13.26 g). The mixture was stirred at same temperature for 1.5 hours, and thereto was added a 10% aqueous hydrochloric acid solution (50 ml). The organic layer was washed with H2O (100 ml) and brine, and dried over magnesium sulfate. The insoluble materials were filtered off, and the filtrate was evaporated under reduced pressure. The residue was dissolved in tetrahydrofuran (100 ml)-H2O (15 ml), and the mixture was stirred at 50° C. for 17.5 hours. After being cooled to an ice-water temperature, the mixture was basified with a saturated aqueous sodium hydrogen carbonate solution (about 100 ml). After being stirred at room temperature for 4 hours, the mixture was acidified with a 36% aqueous hydrochloric acid solution at an ice-water temperature. The resultant mixture was extracted with ethyl acetate (100 ml), and the organic layer was dried over magnesium sulfate. The insoluble materials were filtered off, and the filtrate was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (chloroform:methanol=50:1-9:1) and triturated with diisopropyl ether to give 4-pivaloyloxybenzoic acid (7.10 g) as a colorless solid. ESI-Mass m/Z 221 (M−H). 1H-NMR (DMSO-d6) δ 1.31 (s, 9H), 7.23 (d, J=8.5 Hz, 2H), 7.99 (d, J=8.7 Hz, 2H), 10.03 (brs, 1H).
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