Three isomeric bis(methoxycarbonyl)[2.2]paracyclophanes

The title isomers 4,16‐ (pseudo‐ortho), 4,15‐ (pseudo‐gem) and 4,12‐bis­(methoxy­carbonyl)2.2]­para­cyclo­phane (pseudo‐para), C₂₀H₂₀O₄, all show the typical structural features of 2.2]­para­cyclo­phanes (flattened boat conformation of the rings, lengthened single bonds in the bridges and narrow ring angles at the bridgehead atoms). The 4,12‐isomer displays crystallographic inversion symmetry. The carbonyl groups adopt a conformation in which they are directed away from the ring systems towards the nearest bridge; the corresponding angle at the ring substituent atom is widened. Crystal packing involves C—H?π interactions for the 4,15‐isomer and weak C—H?O hydrogen bonds for the other two isomers.