Skeletal Editing of Mechanically Interlocked Molecules: Nitrogen Atom Deletion from Crown Ether-Dibenzylammonium Rotaxanes

Abstract

Removing the nitrogen atom from secondary amines while simultaneously linking the remaining fragments is a powerful form of late-stage skeletal editing. Here, we report its use for the deletion of the nitrogen atom of the dibenzylammonium template used to assemble crown ether rotaxanes. The reaction uses an anomeric amide that activates secondary amines to generate a carbon–carbon bond that replaces the amine nitrogen. Despite the potential for dethreading of the intermediate diradical pair, the nitrogen atom was successfully deleted from a series of rotaxane axles as long as the macrocycle could access coconformations that did not inhibit the reaction of the amine group. The skeletally edited interlocked molecules were obtained directly from the parent crown ether-dibenzylammonium rotaxanes in modest yields (23–36%) and characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. One skeletally edited rotaxane shows a network of weak CH···O hydrogen bonds between the crown ether and benzylic methylene groups of the axle in the solid state, in place of the crown ether-ammonium binding motif used to assemble the parent, unedited, rotaxane.