The general procedure for the synthesis of 2,3-diaminobenzamide from 2-amino-3-nitrobenzamide is as follows:
1. 2-Amino-3-nitrobenzoic acid (3.00 g, 16.47 mmol) was dissolved in dimethoxyethane (15 ml), thionyl chloride (2.61 g, 21.91 mmol) was added, and the mixture was stirred at 50 °C for 12 hours. After completion of the reaction, the solvent was removed by concentration under reduced pressure and concentrated again by adding toluene. Subsequently, saturated aqueous ammonia solution (40 ml) was added to a round-bottom flask and cooled to 10 °C, and unpurified chloroyl chloride (3.30 g, 16.45 mmol) was slowly added dropwise, keeping the reaction temperature below 40 °C. After dropwise addition, the mixture was stirred at 50 °C for 1 h. The mixture was diluted with water and stirred at room temperature. The orange precipitate was collected by filtration, washed with water and dried to give 2-amino-3-nitrobenzamide (2.60 g, 87% yield).
2. A methanolic solution (80 ml) of 2-amino-3-nitrobenzamide (2.60 g, 14.35 mmol) with a palladium/carbon catalyst (aqueous wet, 10% Pd, 0.05 eq, 0.072 mmol) was placed in a metal vessel. Hydrogen was passed in a laboratory reactor and stirred for 5 h at room temperature and 2 bar pressure. After the reaction was complete, the catalyst was removed by diatomaceous earth filtration and the filtrate was washed with methanol. The filtrate was concentrated under reduced pressure and the residue was extracted with water and ethyl acetate. The organic phases were combined, dried over magnesium sulfate, filtered and concentrated to afford 2,3-diaminobenzamide (2.15 g, 98% yield) of >95% purity without further purification.
3. 2,3-Diaminobenzamide (200 mg, 1.32 mmol) was dissolved in chlorodifluoroacetic acid (3 ml) and refluxed for 3 hours with vigorous stirring. After cooling to room temperature, NaHCO3 solution was added and 2-[chloro(difluoromethyl)-1H-benzimidazole-4-carboxamide (190 mg, 58% yield) was precipitated as a colorless solid, pumped, washed with water and dried.
Product characterization data: 1H NMR (400 MHz, d6-DMSO δ, ppm) 14.40 (br.s, 1H, NH), 8.72 (br.s, 1H, NH), 8.02 (m, 1H, NH), 7.92 (m, 1H), 7.74 (m, 1H), 7.55 (m, 1H); 13C NMR (150MHz d6-DMSO δ, ppm) 165.5, 147.9, 139.1, 134.2, 124.9, 124.5, 123.9, 118.4-122.2 (t, CF2Cl), 116.6.
