[Synthesis]
Step 5: Synthesis of 1-(2-chloro-4-nitrophenyl)ethanone (7)
Anhydrous magnesium chloride (47 g, 0.214 mol, 0.7 eq.) was suspended in toluene (300 mL) under dry conditions, followed by the addition of triethylamine (75.04 mL, 0.535 mol, 2.5 eq.) and diethyl malonate (41.09 g, 0.257 mol, 1.2 eq.). The reaction mixture was stirred at room temperature for 1.5 hours. 2-Chloro-4-nitrobenzoyl chloride (6) (47 g, 0.214 mol, 1 eq.) was slowly added dropwise, and an exothermic increase in temperature to 50 °C was observed during the dropwise addition. Flush with toluene (50 mL) to ensure complete transfer of 2-chloro-4-nitrobenzoyl chloride to the reaction system. The reaction mixture was continued to be stirred at room temperature for 18 h. The reaction progress was monitored by thin layer chromatography (TLC) and nuclear magnetic resonance (NMR). After complete consumption of the feedstock, 35% concentrated hydrochloric acid (300 mL) was added to separate the toluene layer. The toluene layer was concentrated under reduced pressure (temperature below 50 °C). Dimethyl sulfoxide (DMSO) (200 mL) and water (10 mL) were added to the residue and the mixture was heated at 160 °C for 12 h. The reaction progress was followed by TLC and NMR. After the reaction mixture was cooled to room temperature, water (40 mL) was added and extracted with ethyl acetate (EtOAc) (3 x 200 mL). The organic phases were combined, washed with saturated brine (3 × 300 mL) and dried over anhydrous sodium sulfate. The EtOAc layer was concentrated under reduced pressure to give a yellow liquid 1-(2-chloro-4-nitrophenyl)ethanone (7) (43 g, 84% yield), which was cooled and solidified.
1H NMR (400 MHz, CDCl3): δ (ppm): 8.29 (d, J = 2.2 Hz, 1H), 8.17 (dd, J = 8.5, 2.1 Hz, 1H), 7.65 (d, J = 8.4 Hz, 1H), 2.66 (s, 3H). |