Synthesis
Step a: Synthesis of 4-bromopyridine nitrogen oxides
4-Bromopyridine hydrochloride (25 g, 128 mmol) was dissolved in dichloromethane (250 mL) and potassium carbonate (21.25 g, 153 mmol) was added. The reaction mixture was stirred for 2 hours and then m-chloroperbenzoic acid (44 g, 256 mmol) was added. Stirring was continued at room temperature for 16 h. Solid precipitated during the reaction. The solid was collected by filtration and washed with ethyl acetate (2 x 200 mL). The filtrate was concentrated to obtain the solid product, which was further washed with a solvent mixture of ether and hexane (3 x 30 mL, 1:1 v/v). The final 4-bromopyridine nitride (20 g, 90% yield) was obtained and used directly in the next reaction without further purification.
References
[1] Patent: WO2012/160464, 2012, A1. Location in patent: Page/Page column 126-127
[2] Patent: US2014/155398, 2014, A1. Location in patent: Paragraph 0767
[3] Organic Letters, 2016, vol. 18, # 14, p. 3386 - 3389
[4] Patent: US2009/239876, 2009, A1. Location in patent: Page/Page column 24
