General procedure for the synthesis of 2-bromo-5-nitro-3-methylpyridine from 3-methyl-5-nitropyridin-2(1H)-one:
Synthesis of common intermediates of Scheme 4 Step 1: Synthesis of 2-bromo-3-(bromomethyl)-5-nitropyridine (Scheme 4, compound 27)
A sample of 3-methyl-5-nitropyridin-2-ol (1.44 g, 9.34 mmol) was placed in a 35 mL pressure vessel and dissolved in a solvent mixture of toluene/DMF (10:1 v/v; 15 mL). The container was sealed with a septum, and after argon replacement, phosphorus tribromide (1.32 mL, 14.0 mmol) was added via syringe. The septum was replaced with a polytetrafluoroethylene cap and the mixture was stirred at 120°C for 20 minutes. Upon completion of the reaction, the mixture was cooled to room temperature, neutralized with 3M NaOH solution, and extracted with toluene (3 x 15 mL). The organic phases were combined, dried with anhydrous magnesium sulfate and concentrated in vacuum to give 2.00 g of the target product 2-bromo-3-methyl-5-nitropyridine as an orange solid in 99% yield.
1H NMR (400MHz, CDCl3) δ 9.04 (d, J = 2.7Hz, 1H), 8.29 (d, J = 2.5Hz, 1H), 2.54 (s, 3H).
13C NMR (126 MHz, CDCl3) δ 150.65, 142.47, 136.76, 132.75, 22.20.
