A mixture of 57 (1.23 g, 4.0 mmol), 2,4-thiazolidinedione (0.48 g, 4.0 mmol), benzoic acid (0.60 g, 4.8 mmol) and piperidine (0.61 mL, 6.0 mmol) in toluene (30 mL) was heated to a vigorous reflux until most of the solvent had evaporated. A yellow suspension was achieved by addition of acetic acid (25 mL) followed by sonication. Filtration of the suspension followed by washing with acetic acid (10 mL) yielded 58 (1.25 g, 75%) after filtration and oven drying. 1H NMR (400 MHz, DMSO-d6): δ 12.57 (br s, 1H), 7.78 (s, 1H), 7.63 (d, J=8.8 Hz, 2H), 7.62 (d, J=8.8 Hz, 2H), 7.49 (d, J=5.2 Hz, 2H), 7.36 (t, J=1.6 Hz, 1H), 7.16 (d, J=8.8 Hz, 2H), 7.03 (m, 1H), 7.01 (d, J=8.8 Hz, 2H), 3.7 (s, 3H).
