5-[(5S,5aS,8aS,9S)-9-hydroxy-6-oxo-5,5a,6,8,8a,9-hexahydrofuro[3',4':6,7]naphtho[2,3-d][1,3]dioxol-5-yl]-3-methoxycyclohexa-3,5-diene-1,2-dione