2016-99-1

99-11-6

2016-99-1

General procedure for the synthesis of 2,6-dibromopyridine-4-carboxylic acid from citrazinic acid: Citrazinic acid (2.33 g, 0.015 mol) was mixed with phosphorus tribromide and heated to 180 °C under nitrogen protection for 3 hours. After completion of the reaction, the reaction mixture was cooled and quenched carefully with ice water. The reaction mixture was filtered and the aqueous phase was extracted with dichloromethane (4 x 40 ml). The solid fraction was continuously extracted in a Soxhlet extractor using dichloromethane for 12 hours. The directly extracted organic phase was dried with anhydrous sodium sulfate, filtered and concentrated to give 2.2 g of slightly red solid. The organic phase of Soxhlet extraction was similarly dried with anhydrous sodium sulfate, filtered and concentrated to give 0.5 g of a slightly red solid. The two fractions of 2,6-dibromoisonicotinic acid (64% total yield) were combined after confirmation of structural identity by NMR hydrogen spectroscopy (CDCl3, δ 8.04, 2H, s).