3-Bromo-4-formyl-benzonitrile (20.5 g, 97.7 mmol), benzenesulfinic acid sodium salt (16.03 g, 97.6 mmol) and tert-butylcarbamate (11.4 g, 97.7 mmol) are suspended in water (312 mL) and THF (78 mL). Formic acid (28.8 g, 625 mmol) is added and the solution is stirred at room temperature for 6 days. Water (300 mL) is added and the precipitate is filtered off, washed with water and dried. The crude product is further purified by precipitation from tert-butylmethylether. Yield: 26.8 g; ESI mass spectrum: [M+Na]+=473 (bromine isotope pattern).
