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
and 4-hydroxy-1-phenylpyridin-2(1
H)-ones
5" rel="references:#jhet2619-eo-0025">. Compounds
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
in excellent yields. Compounds
and
5" rel="references:#jhet2619-eo-0025"> 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
and 4-hydroxy-3-iodo-1-phenylpyridin-2(1
H)-ones
, respectively, in good yields. The structures were confirmed using infrared,
nuclear magnetic resonance , and elemental analysis.
