3a′-[4-(2-Methyl-2-propanyl)phenyl]dihydrodispiro[cyclopentane-1,3′-furo[3,2-b]furan-6′,1″-cyclopentane]-2′,5′-dione

3a′-[4-(2-Methyl-2-propanyl)phenyl]dihydrodispiro[cyclopentane-1,3′-furo[3,2-b]furan-6′,1″-cyclopentane]-2′,5′-dione

Dispiro[cyclopentane-1,3′(2′H)-furo[3,2-b]furan-6′(5′H),1″-cyclopentane]-2′,5′-dione, 3′a-[4-(1,1-dimethylethyl)phenyl]dihydro-

3a′-(4-tert-butylphenyl)dihydrodispiro[cyclopentane-1,3′-furo[3,2-b]furan-6′,1″-cyclopentane]-2′,5′-dione

6a-[4-(tert-butyl)phenyl]dispiro[cyclopentane-1,3′-1′,3,4′,6′,3a′,6a′-hexahydro-1′,4′-dioxapentalene-6′,1″-cyclopentane]-7,10-dione