Tetraethyl 3′-oxo-2′,3′,5′,7′-tetrahydro-3H,6′H-spiro[cyclobutane-1,1′-[s]indacene]-3,3,6′,6′-tetracarboxylate

Spiro[cyclobutane-1,1′(6′H)-[s]indacene]-3,3,6′,6′-tetracarboxylic acid, 2′,3′,5′,7′-tetrahydro-3′-oxo-, tetraethyl ester

Tetraethyl 3′-oxo-2′,3′,5′,7′-tetrahydro-3H,6′H-spiro[cyclobutane-1,1′-[s]indacene]-3,3,6′,6′-tetracarboxylate