Kiwamu Tokuhisa

Medium-sized cyclophanes. Part 18. 5-tert-Butyl-8-substituted [2.2]metaparacyclophanes: preparation, X-Ray diffraction studies, and their treatment with Lewis acids in benzene

The preparation of various 8-substituted 5-tert-butyl[2.2]metaparacyclophanes 8 using the sulfur method, and X-ray diffraction studies of dithia[3.3]metaparacyclophanes 6 and 8-methyl[2.2]metaparacyclophane 1b, are described. AlCl3–MeNO2-catalysed trans-tert-butylation of 8-alkyl- and 8-hydroxy-5-tert-butyl[2.2]metaparacyclophanes 8 in benzene gave the desired 8-alkyl- and 8-hydroxy[2.2]metaparacyclophanes 1 in good yield. However, 5-tert-butyl-8-methoxy[2.2]metaparacyclophane 8c was isomerized to the strainless 5-tert-butyl-8-methoxy[2.2]metacyclophane 13 and this was converted into the tetrahydropyrenes 11 and 12. The mechanism of this reaction is also discussed.

The preparation and novel [3.3] sigmatropic rearrangement of cyclophanes having a spiro skeleton

Oxidation of dihydroxy[n.2]metacyclophanes 1 with K3[Fe(CN)6] afforded the intramolecular O–C coupling product 2, which has a spiro skeleton in good yield; variable temperature 1H NMR measurements indicated that compounds 2 are interconvertible by a thermal [3.3] sigmatropic rearrangement, and the activation free energies for the [3.3] sigmatropic rearrangement increased with increasing length of the methylene bridge in compounds 2.