p-Toluenesulfonic acid → diethyl 4-oxo-4H-pyrano[2,3-b]pyridine-6,7-dicarboxylate

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Reaction Steps

Diethyl 5-[3-(dimethylamino)acryloyl]-1,6-dihydro-6-oxo-2,3-pyridinedicarboxylate (6 g, 0.0178 mol), and p-toluenesulfonic acid (4.5 g, 0.021 mol) in acetic acid (60 mL) are heated to reflux for three hours. The mixture is then evaporated to dryness, neutralized with a saturated NaHCO3 solution and extracted with methylene chloride. The organic solution is dried over Na2SO4, and concentrated to a thick oil, which solidifies after trituration with hexane-ether (4 g, 77%). The product is recrystallized from isopropanol to give a melting point 71°-72° C.

Provenance & Evidence