Step E: Under nitrogen protection, the intermediate (11.6 g) obtained from Step D was dissolved in anhydrous dichloromethane (100 mL) and the reaction vessel was cooled to 0 °C in an ice bath. Oxalyl chloride (12.0 mL) was slowly added dropwise to the above solution, and after the dropwise addition was completed, the reaction was continued to be stirred at 0 °C for 3 hours. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure. The resulting dark residue was redissolved in anhydrous dichloromethane (300 mL), followed by the addition of aluminum trichloride (6.40 g). After the addition was complete, the reaction mixture was heated to reflux for 4 hours. At the end of the reaction, the mixture was carefully poured into ice water (500 mL) and extracted with dichloromethane (2 x 100 mL). The organic phases were combined, dried over anhydrous magnesium sulfate, filtered and concentrated to give the intermediate as a light brown solid (10.6 g; 98% yield). The product was characterized by 1H-NMR (CDCl3): δ= 2.40 (s, 9H), 2.70 (t, 2H), 3.05 (t, 2H), 7.50 (d, 1H), 7.65 (d, 1H).
