Potassium carbonate (23.11 g, 140 mmol) and 4-fluorobenzaldehyde (25.0 mL, 233 mmol) were added to a solution of tert-butoxycarbonylamino-(4-hydroxy-phenyl)-acetic acid (12.5 g, 46.7 mmol) in anhydrous DMF (40 mL). The resulting suspension was refluxed at 75±5° C. under an atmosphere of argon. After 72 hr, the reaction mixture was cooled to room temperature, diluted with water (200 mL) and extracted with EtOAc (2×150 mL). The aqueous layer was collected, acidified with 5.0 M HCl to pH ˜2.0 and extracted with EtOAc (3×150 mL). The resulting EtOAc layer was extracted with water (2×300 mL) and brine (1×300 mL), dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to yield the desired aldehyde 29 as a low melting solid (12.0 g, 69%). 1H NMR (400 MHz, DMSO-d6): 12.9 (br, 1H), 9.93 (s, 1H), 7.93 (d, J=8.8 Hz, 2H), 7.65 (d, J=8.8 Hz, 1H), 7.49 (d, J=8.8 Hz, 2H), 7.13 (overlapped d, J=8.8 Hz, 2H), 7.13 (overlapped d, J=8.8 Hz, 2H), 5.16 (d, J=8.0 Hz, 1H), 1.40 (s, 9H).
