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Part 2: Preparation of tert-butyl 4-(4-formyl-3-hydroxyphenyl)piperazine-1-carboxylate 4-Fluoro-2-hydroxybenzaldehyde (10 g, 71.4 mmol) was mixed with N-BOC-piperazine (15.3 g, 82.2 mmol) in DMSO (100 mL) and the reaction was heated at 100 °C for 27 hours. After completion of the reaction, the reaction mixture was diluted in aqueous K2CO3 and extracted with EtOAc. The organic layer was washed sequentially with water and brine, dried over MgSO4, filtered and concentrated under reduced pressure. The residue was ground with hexane/ether (1:1) mixed solvent to afford the target compound tert-butyl 4-(4-formyl-3-hydroxyphenyl)piperazine-1-carboxylate (18.8 g, 86% yield) as a yellow solid.MS m/z 307.2 [M + H]+; 1H NMR (500 MHz, CDCl3): δ 11.50 (1H, s), 9.60 ( 1H, s), 7.36 (1H, d, J = 9Hz), 6.27 (1H, d, J = 2Hz), 6.45 (1H, dd, J = 9Hz, 2Hz), 3.58 (4H, m), 3.42 (4H, m), 1.49 (9H, s).