Benzoic acid 3-bromo-2-(4-nitro-phenyl)-4-oxo-cyclobut-1-enyl ester
Benzoic acid 3-chloro-2-(4-nitro-phenyl)-4-oxo-cyclobut-1-enyl ester
4-Methyl-benzoic acid 3-bromo-2-(4-nitro-phenyl)-4-oxo-cyclobut-1-enyl ester
3-Bromo-4-(4-nitro-phenyl)-cyclobut-3-ene-1,2-dione
1-(p-nitrophenyl)-2-hydroxycyclobutene-3,4-dione