Two Axles Threaded Using a Single Template Site: Active Metal Template Macrobicyclic [3]Rotaxanes

摘要

Template approaches to rotaxanes normally require at least n - 1 template sites to interlock nncomponents. Here we describe the one-pot synthesis of [3]rotaxanes in which a single metal template siteninduces formation of axles through each cavity of a bicyclic macrocycle. Central to the approach is that anportion of the bicyclic molecule acts as a ligand for a transition metal ion that mediates covalent bondnformation through one or other macrocyclic cavity, depending on the ligand’s orientation, making anmechanical bond. The ligand can then rotate so that the transition metal can catalyze the formation of ansecond axle through the other macrocycle. Using this strategy with the Cu(I)-catalyzed azide-alkynencycloaddition (the CuAAC reaction) generates a [3]rotaxane with two identical axles in up to 86% yield.n[3]Rotaxanes with two different axles threaded through the macrobicyclic rings can also be created usingna single template site, either by having copper(I) sequentially form both mechanical bonds (via the CuAACnreaction) using different sets of building blocks for each axle or by using two different reactions catalyzednby two different metal ions: a palladium(II)-mediated alkyne homocoupling to assemble the first threadnthrough one cavity, followed by a copper(I)-mediated CuAAC reaction to form the second axle through thenother ring.