161798-03-4

Ethyl 2-(3-formyl-4-isobutoxyphenyl)-4-methylthiazole-5-carboxylate is an impurity of Febuxostat (F229000), which is a xanthine oxidase/xanthine dehydrogenase inhibitor, used for treatment of hyperuricemia and chronic gout.

Preparation of Compound of formula III)[0094] A compound of formula II (10.0 gr, 34.33 mmol) was reacted with iso- butyl bromide (18.9 gr, 137.3 mmol) in the presence of potassium carbonate (19.0 gr, 137.3 mmol) and potassium iodide (2.3 gr, 13.7 mmol) in 60 ml dimethylformamide. The reaction was performed at about 70°C during 4 hours. The reaction mixture was extracted at 70°C using 300 ml ethyl acetate and 600 ml water. The separated aqueous phase was washed twice with 100 ml ethyl acetate. The combined organic phase was washed twice with 100 ml water and then concentrated to dryness. The resulting solid residue was re- crystallized from 70 ml ethyl acetate, filtered and dried under reduced pressure at about 40°C to provide a compound of formula III (8.9 gr, yield - 83percent). The Compound of formula III purity is 99.1percent (by HPLC).