(1S,5R,6S)-5-Isopropoxy-7-oxabicyclo[4.1.0]hept-3-ene-3-carboxylic Acid Ethyl Ester is an analog of (1R,5S,6S)-rel-5-(1-Ethylpropoxy)-7-oxabicyclo[4.1.0]hept-3-ene-3-carboxylic Acid Methyl Ester (E925665) which is an intermediate in the synthesis of neuraminidase inhibitors. Impurity of Oseltamivir.