Synthesis of Acetyl and Iodo Derivatives of 4‐Hydroxy‐6‐phenyl‐ 6H ‐pyrano[3,2‐ c ]pyridine‐2,5‐diones and 4‐Hydroxy‐1‐phenylpyridin‐2(1 H )‐ones

A simple and efficient method has been described for the synthesis of acetyl and iodo derivatives of 4‐hydroxy‐6‐phenyl‐ 6H ‐pyrano[3,2‐ c ]pyridine‐2,5‐diones 1 and 4‐hydroxy‐1‐phenylpyridin‐2(1 H )‐ones 5 . Compounds 1 with phenyl and alkyl substituent at C(7) and C(8), respectively, can be easily acetylated by refluxing in a mixture of acetic acid and polyphosphoric acid to give 3‐acetyl‐4‐hydroxy‐6‐phenyl‐6 H ‐pyrano[3,2‐ c ]pyridine‐2,5‐diones 2 in excellent yields. Compounds 1 and 5 can be iodinated with iodine and anhydrous sodium carbonate in boiling dioxane to give 4‐hydroxy‐3‐iodo‐6‐phenyl‐ 6H ‐pyrano[3,2‐ c ]pyridine‐2,5‐diones 3 and 4‐hydroxy‐3‐iodo‐1‐phenylpyridin‐2(1 H )‐ones 6 , respectively, in good yields. The structures were confirmed using infrared, nuclear magnetic resonance , and elemental analysis.