Example 56 Preparation of 3,4,5-trichlorobenzaldehyde (C96): first, a 500 mL round-bottomed flask was dried in an oven and flushed with nitrogen. The flask was equipped with a pressure-balanced addition funnel. 5-Bromo-1,2,3-trichlorobenzene (10.0 g, 38.4 mmol) was dissolved in tetrahydrofuran (100 mL), and the resulting solution was cooled in an ice bath under nitrogen protection. Isopropylmagnesium chloride (2M tetrahydrofuran solution, 21.1 mL, 42.3 mmol) was slowly added dropwise over a period of 15 minutes through the addition funnel with full stirring. After the dropwise addition, stirring was continued for 0.5 hours. Subsequently, N,N-dimethylformamide (3.72 mL, 48.0 mmol) was added to the dark solution under stirring. After 0.5 hours of reaction, 1N hydrochloric acid (100 mL) was added under stirring to terminate the reaction. The organic and aqueous layers were separated and the organic layer was washed with brine. The combined aqueous layers were extracted with ether and the combined organic phases were dried with anhydrous sodium sulfate, filtered and concentrated to give the title compound as a white solid (10:1 mixture of the title compound with 1,2,3-trichlorobenzene, 7.96 g, 99% yield). The product was confirmed by 1H NMR (CDCl3): δ 9.91 (s, 1H), 7.88 (s, 2H); EIMS m/z 209 ([M]+).
