4,7-Etheno-1,3,3a,4,4',5,5',6,7,7a-decahydro-4'-methylenespiro[isobenzofuran-5,2'(3'H)-furan]-1,3,6-trione

4',5'-Dihydro-4'-methylene-3-oxospiro[bicyclo[2.2.2]octane-2,2'(3'H)-furan]-7-ene-5,6-dicarboxylic anhydride