Medium-sized cyclophanes. Part 46.1 The preparation and novel [3.3]- and [1.5]-sigmatropic rearrangements of [n.2]cyclophanes having a spiro skeleton†

Abstract

Oxidation of dihydroxy[n.2]metacyclophanes 4 with K₃[Fe(CN)₆] affords in good yield the intramolecular O–C coupling products 5 having a spiro skeleton. Variable temperature ¹H NMR measurements indicate that compounds 5 are interconvertible by thermal [3.3]sigmatropic rearrangement. The free energies for the [3.3]sigmatropic rearrangement increase with increasing length of the methylene bridge in compounds 5. The substituent effect on the [1.5]sigmatropic rearrangement of [2.2]cyclophanes 3 having a spiro skeleton is also discussed.