2,3-Diaminopyridine → 2-[2-(Pyridin-2-yl)-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazol-3-yl]-1H-imidazo[4,5-b]pyridine

Participants

Reaction Steps

Add 2,3-diaminopyridine (Fluka; 120 mg, 1.09 mmol) and phosphorous oxychloride (4.4 mL) to 2-(pyridin-2-yl)-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazole-3-carboxylic acid (Preparation 3; 251 mg, 1.09 mmol) and heat the reaction at 106° C. for 3 h. Cool the reaction to 0° C. and add 1N aqueous hydrochloric acid (10 mL) slowly and stir for 10 min. Neutralize the mixture with saturated aqueous sodium bicarbonate and extract with chloroform. Wash the combined organic layers with brine, dry with sodium sulfate, concentrate in vacuo, purify by flash column chromatography, and triturate with hexanes to provide the title compound (159 mg, 48%) as a tan solid. Mp 170-172° C. MS ESI+ m/e 303 (M+1). 1H NMR (CDCl3) δ 8.80 (br, 1H), 8.34 (m, 2H), 7.88 (m, 2H), 7.36 (m, 1H), 7.11 (m, 1H), 4.29 (m, 2H), 3.54 (m, 2H), 2.71 (m, 2H). HPLC: 96.3%, Rt=13.59 min. TLC (SiO2): Rf0.3 (1:3 [80:18:2 chloroform/methanol/concentrated aqueous ammonium hydroxide]/dichloromethane).

Provenance & Evidence