Phosphorus oxychloride → 5-(2-Fluoro-4-methylsulfanyl-phenylamino)-imidazo[1,5-a]pyridine-6-carboxylic acid methyl ester

To a suspension of 2-(2-fluoro-4-methylsulfanyl-phenylamino)-6-formylaminomethyl-nicotinic acid methyl ester (309 mg, 0.89 mmol) in toluene (15.6 mL) was added phosphorous oxychloride (91 μl, 0.98 mmol) and the reaction mixture heated to 95° C. and stirred for 1 hour. The cooled reaction mixture was quenched by the addition of water (ca. 2 mL) then concentrated in vacuo. The resultant residue was taken up in ethyl acetate and washed with water followed by a saturated aqueous solution of sodium bicarbonate and brine. The organic phase was isolated, dried (Na2SO4), filtered, concentrated in vacuo, and the residue subjected to flash chromatography (Si-PPC, gradient 0% to 40%, ethyl acetate in hexane) to afford the title compound as a yellow solid (150 mg, 51%). LCMS (method B): RT=3.44 min, [M+H]+=332.