tert-Butyl 4-Hydroxy-2,6-dioxotetrahydro-2H-pyran-4-carboxylate is an intermediate in the synthesis of Oseltamivir Citric Acid Adduct (O701055), an impurity of Oseltamivir (O701005), an antiviral drug that is an orally active inhibitor of influenza virus neuraminidase; converted in vivo to the active acid metabolite.