Ethyl bromopyruvate → Ethyl 6-iodoimidazo[1,2-a]pyridine-2-carboxylate

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Reaction Steps

A mixture of sulfuric acid (0.5 mL), acetic acid (12 mL) and water (2 mL) was added to a reaction flask containing 2-aminopyridine (2.0 g, 21.26 mmol) and the solution was stirred for 5 minutes. NaIO4 (1.81 g, 8.5 mmol) followed by 12 (2.16 g, 8.5 mmol) was added into the reaction flask and stirred at 80° C. for 4 hrs. The reaction mixture was cooled to ambient temperature, diluted with cold water, basified with 20% aqueous KOH solution and extracted with DCM. The organic layer was washed with brine solution, dried over sodium sulfate and concentrated under reduced pressure to obtain the crude residue. Purification by column chromatography (using silica gel 60-120 and 8% EtOAc in hexane as eluent) and subsequent recrystallisation from ethanol afforded 53 g (58.6% Yield) of 5-iodo-pyridin-2-ylamine. Ethyl bromopyruvate (4.89 g, 25.11 mmol) was added to solution of 5-iodo-pyridin-2-ylamine (5.0 g, 22.83 mmol) in DMF (25 mL) and stirring was continued at 80° C. for 2 hrs. The reaction mixture was diluted with cold water and extracted with ethyl acetate. The organic layer was washed with brine solution, dried over sodium sulfate and concentrated under reduced pressure to obtain the crude residue. The residue obtained was purified by recrystallisation from methanol to afford 4.2 g (57.8% Yield) of 6-iodo-imidazo[1,2-a]pyridine-2-carboxylic acid ethyl ester. A mixture of imidazole (513 mg, 7.5 mmol), cuprous oxide (71 mg, 0.5 mmol), 6-iodo-imidazo[1,2-a]pyridine-2-carboxylic acid ethyl ester (1.6 g, 5.02 mmol), salox (137 mg, 1.0 mmol) and cesium carbonate (3.27 g, 10.05 mmol) in ACN (2 mL) in a seal tube were subjected to reaction in a microwave reactor (time: 15 min, temp: 85° C., power: zero, pressure: zero). The reaction mixture was filtered through celite and the filtrate collected was concentrated under reduced pressure. The residue was diluted with cold water, extracted with ethyl acetate, dried over sodium sulfate and concentrated under reduced pressure. The residue was purified by column chromatography (using neutral alumina and 0.2% MeOH in DCM as eluent) to afford 400 mg (31% Yield) of 6-pyrazol-1-yl-imidazo[1,2-a]pyridine-2-carboxylic acid ethyl ester. A mixture of 6-pyrazol-1-yl-imidazo[1,2-a]pyridine-2-carboxylic acid ethyl ester (250 mg, 0.97 mmol) in 8N aqueous HCl (3 mL) was stirred at 100° C. for 2 hrs. The reaction mixture was concentrated under reduced pressure to afford 130 mg (58.5% Yield) of 6-pyrazol-1-yl-imidazo[1,2-a]pyridine-2-carboxylic acid.

Provenance & Evidence