4.2.1. N-(3,5-dimethylphenyl)-2-(4-hydroxyphenyl)acetamide (12a)

To a stirring solution of 3,5-dimethylaniline 10a (2.7 g, 15.6 mmol) in toluene (25 mL) were add 2-(4-hydroxyphenyl)acetic acid 11a (2.0 g, 13 mmol) and boric acid (0.08 g, 0.13 mmol) at room temperature. The reaction mixture was refluxed at 140℃ with a water separator for 12 h. Upon completion, the mixture was cooled to room temperature and filtered, and the filter cake was washed with toluene (3 × 20 mL) and water (3 × 20 mL), respectively. Then, the filter cake was dried in a vacuum drying oven to give 12a as a white solid (3.0g, 90.5%). ¹H NMR (400 MHz, DMSO-d6) δ 9.88 (s, 1H), 9.25–9.23 (m, 1H), 7.18 (d, J = 0.6 Hz, 2H), 7.10–7.05 (m, 2H), 6.69–6.64 (m, 2H), 6.63 (dd, J = 4.2, 3.6 Hz, 1H), 3.42 (d, J = 5.6 Hz, 2H), 2.18 (d, J = 0.5 Hz, 6H). ESI-MS: m/z = 256.11 [M + H]⁺.