Synthesis of highly strained para-cyclophanes via ring-expansion [5,5]-sigmatropic rearrangement reaction

Abstract

para-Cyclophane scaffolds, characterized by their 1,4-disubstituted benzene frameworks, represent a structurally unique and biologically important class of compounds. Despite their extensive presence in natural products and bioactive molecules, the synthesis of highly strained para-cyclophanes remains challenging through conventional ring-closing strategies and alternative approaches. Here we report a facile preparation of para-cyclophanes containing bent 1,4-disubstituted benzene subunits via a N-arylation–ring-expansion [5,5]-sigmatropic rearrangement between cyclic tertiary amines and aryne intermediates. These scaffolds occupy a distinctive chemical space, with structural analyses revealing a remarkably high degree of angular distortion on the 1,4-disubstituted benzene rings. Notably, the rearrangement step not only exhibits diverse reaction modes in response to the location of the substituents but also demonstrates an intriguing point-to-planar chirality transfer. Density functional theory calculations provide mechanistic insights into both the diastereoselective control and the point-to-planar chirality transfer process.