Synthesis and X‐Ray Diffraction Analysis of Bis(phenylsulphonyl)semibullvalenes. Lifting of the Degeneracy of Semibullvalenes in the Crystal Lattice[1]

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The bicyclo[3.3.0]octanediones 4 and 9a, b and the [n.3.3]‐propellanediones 9c, d, f, h react with thiophenol in the presence of titanium(IV) chloride and triethylamine to afford high yields of the vinyl sulphides 5 and mixtures of the vinyl sulphides 10/11. Sodium perborate oxidizes the vinyl sulphides 5 and 10/11 to the corresponding vinyl sulphones 6 and 12/13. N‐Bromosuccinimide converts 6 into the dibromodisulfones 7. The exo,exo configuration of 7b is established by X‐ray crystallography. The mixtures of disulphones 12/13 are brominated by N‐bromosuccinimide to yield complex mixtures of uncharacterized dibromodisulphones 14. Debromination of the dibromodisulphones 7, and the mixtures of 14 as well, by the zinc‐copper couple results in the formation of crystalline semibullvalenes 8 and 15 in moderate to high yields. – X‐ray diffraction analyses of 8a, b and 15a–d reveal large variations of the apparent atomic distances in the cyclopropane rings (C2–C8) and at the open ends of the molecules (C4…C6). This result is interpreted in terms of equilibrating, non‐degenerate valence tautomers resulting in averaged atomic distances. The equilibrium constants are calculated from the atomic distances on the basis of a limiting value of 157.8 pm for the C2–C8 bonds of the non‐rearranging valence tautomers. The results are compared to those obtained from X‐ray diffraction analyses of other substituted semibullvalenes. The lifting of the degeneracy of semibullvalenes in the solid state is attributed to subtle intermolecular interactions.