Synthesis of 1-methyl-3-oxo-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxylic acid methyl ester

A simple and efficient method for the preparation of 1-methyl-3-oxo-7- oxabicyclo2.2.1]hept-5-en-2-carboxylic acid methyl ester (1) is described. The first step is a highly regioselective Diels-Alder reaction between 2-methylfuran and methyl-3-bromo- propiolate. A remarkably difficult ketal hydrolysis reaction was effected by treatment with HCl, a simple reagent that was shown to be more efficient, in this case, than commonly used more elaborate methods.