tetramethyl 2,5-dioxo-1,3,3a,4,6,6a-hexahydropentalene-1,3,4,6-tetracarboxylate

cis-bicyclo[3.3.0]octane-3,7-dione 3,7-bis(2',2'-dimethylpropylidene) acetal

monosodium mono((1R,3aS,4R,6aS)-1,3,4,6-tetrakis(methoxycarbonyl)-1,3a,4,6a-tetrahydropentalene-2,5-bis(olate))