Diisopropylethylamine → 2-(1,3-Thiazol-4-yl)-1H-benzimidazol-6-amine

Participants

Reaction Steps

A solution of (4-Amino-3-nitro-phenyl)-carbamic acid tert-butyl ester (1-3, 0.409 g, 1.832 mmol), thiazole 4-carboxylic acid (0.226 g, 1.832 mmol) and diisopropylethylamine (0.81 mL, 4.03 mmol) in N,N-dimethylformamide (10 mL) was reacted at the ambient temperature with benzotriazol-1-yloxytripyrrolidinophosphonium hexafluorophosphate (PyBop, 1.05 g, 2.02 mmmol). After 3 h stirring at the same temperature, the reaction mixture was concentrated under the reduced pressure and the residue was partitioned between ethyl acetate (100 mL) and aqueous 0.5N-NaOH solution (70 mL). The organic layer was washed with brine, separated, dried (MgSO4) and concentrated in vacuo. The resulting crude product was triturated with ethyl acetate (5 mL), collected by filtration, and dried under the reduced pressure. The mixture of the intermediate products (1-4a and 1-4b) was dissolved in aqueous 20%(v/v)-acetic acid (50 mL) and heated at reflux for 2 h. The reaction mixture was cooled to the ambient temperature and concentrated in vacuo. The resulting crude thick oil was partitioned between ethyl acetate (100 mL) and saturated aqueous sodium bicarbonate solution (70 mL). The organic layer was washed with brine, separated, dried (MgSO4) and concentrated in vacuo. The crude product was triturated with ethyl acetate (15 mL) and hexanes (2 mL). The resulting solid, 2-thiazol-4-yl-3H-benzoimidazol-5-ylamine (1-5), was collected by filtration and dried under the reduced pressure; 1H NMR (500 MHz, DMSO-d6) δ 12.34 (s, 1H), 9.27 (s, 1H), 8.24 (s, 1H), 7.27 (bs, 1H), 6.66 (s, 1H), 6.54 (d, 1H, J=7.5 Hz), 4.96 (bs, 2H).

Provenance & Evidence