3-Cyano-6-ethyl-2-pyridone (I) was chlorinated using phosphorus oxychloride to afford the chloropyridine (II). Subsequent addition of the Grignard reagent prepared from 3-bromochlorobenzene (III) to the cyano group of (II) produced ketone (IV). This was treated with ethylamine to give the aminopyridine derivative (V). Finally, the reaction of (V) with chlorosulfonyl isocyanate produced the target pyridopyrimidinone.