Furo[3',4':6,7]naphtho[2,3-d]-1,3-dioxole-6,9-dione,5,5a,8,8a-tetrahydro-5-(5-methoxy-3,4-dioxo-1,5-cyclohexadien-1-yl)-, [5R-(5a,5ab,8aa)]- (9CI)