Abstract As a consequence of our continuing interests in the cycloaddition reaction of the 2- pyrone derivatives, 1 we have required methyl esters of four 2-pyronecarboxylic acid isomers. Whereas 2-pyrone-3-, 5-, and 6-carboxylic acids or their esters2) had been already synthesized, only 2-pyrone-4-carboxylic acid (la) is still unknown, except its 6-methyl derivative. 3 In this communication we disclose the preparation of 1 by Wittig reaction ...
