Into a mL are placed -{[2-amino-4-(trifluoromethyl)phenyl]amino}benzonitrile (100 mg, 0.361 mmol), Et3N (0.15 mL, 1.08 mmol), tetrabromo-2-sulfobenzoic acid cyclic anhydride (270 mg, 0.541 mmol), and THF (5 mL). The mixture is heated with efficient shaking at 40° C. for 16 h. The solution is cooled and 1M HCl is added and the organic phase is extracted with EtOAc (3×). The organic fractions are combined, washed with brine, and concentrated. The crude product is dissolved in MeOH (20 mL) and then Dowex (10 eq) is added. The mixture is efficiently shaken at rt for 16 h. The resin is then filtered and the solution concentrated. The yield is 108 mg of 2,3,4,5-tetrabromo-6-({[2-[(4-cyanophenyl)amino]-5-(trifluoromethyl)phenyl]amino}carbonyl)benzenesulfonic acid, 46%. 1H NMR (400 MHz, DMSO-d6): □ 10.06 (s, 1 H), 8.89 (s, 1 H), 7.70-7.68 (m, 2 H), 7.65-7.61 (m, 2 H), 7.56-7.54 (m, 1 H), 7.32-7.30 (m, 2 H). ESI+ for C21H10Br4F3N3O4S m/z 778 (M+H)+.
