A. 4-Bromopyridine 1-oxide at room temperature. To a suspension of 4-bromopyridine hydrochloride (5.0 g, 25.9 mmol) in dichloromethane (50 mL) was added triethylamine (2.62 g, 25.9 mmol). After stirring for 0.5 h, 3-chloroperoxybenzoic acid (4.46 g, 25.9 mmol) was added in batches, and the reaction mixture was stirred at room temperature for 5 h. The solution was washed with saturated aqueous sodium thiosulfate (30 mL), saturated aqueous sodium carbonate (30 mL), and brine (30 mL), and dried over sodium sulfate. The solvent was removed under reduced pressure to give the crude product, which was purified on silica gel chromatography (eluting with 50-100% ethyl acetate in methanol) to give 4-bromopyridine 1-oxide, solid (2.1 g, 44.8% yield).
B.4-Bromopyridine-2-carbonitrile. A mixture of 4-bromopyridine 1-oxide (2.0 g, 11.56 mmol), trimethylmethylsilyl cyanide (3.43 g, 34.68 mmol) and triethylamine (2.34 g, 23.12 mmol) in acetonitrile (10 mL) was stirred under nitrogen at 110 C for 3 h. The reaction mixture was concentrated under reduced pressure and the residue was purified on a silica gel column (with petroleum ether eluting with 20% ethyl acetate in petroleum ether) to afford 4-bromopyridine-2-carbonitrile (1.52 g, 72.4% yield).
