Y-Pyrone«2,6-dicarboxylic acid

Meconic acid (3-hydroxy-Y-pyrone-2,6-dicarboxylic acid) [497-59-6] M 200.1, m 100 (-H2O). Crystd from water and dried at 100° for 20min. 

The construction of a y-pyrone is essentially the construction of a 1,3,5-tricarbonyl compound since such compounds easily form cyclic hemiacetals then requiring only dehydration. Several methods are available for the assembly of such precursors the synthesis of chelidonic acid (4-pyrone-2,6-dicarboxylic acid) represents the obvious approach of bringing about two Claisen condensations, one on each side of a ketone carbonyl group. Chelidonic acid can be decarboxylated to produce y-pyrone itself. ... 

Fused 3-bromo-5-carbethoxy-4,6-dimethyl-2-pyrone added rapidly to boiling 7 M KOH, the flask inclined at an angle of 40° to prevent loss during a violent evolution of alcohol occurring ca. 1 min. after the addition, then boiling continued for 30 min. frans-l-methylenecyclopropane-2,3-dicarboxylic acid. Y ... 

Acoxy-2-pyrone ring. 7-Nitrofluorene-l,9-dicarboxylic acid refluxed with acetyl chloride until after ca. 3 days the startg. m. has disappeared crude 9-nitro-l-acetoxy-2-oxa-3-oxo-2,3-dihydrofluoranthene. Y 89%. R. Kuhn and U. Breyer, B. 95, 111 (1962). 

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