Diels−Alder Active-Template Synthesis of Rotaxanes and Metal-Ion-Switchable Molecular Shuttles

摘要

Abstract: A synthesis of [2]rotaxanes in which Zn(II) or Cu(II) Lewis acids catalyze a Diels Alderncycloaddition to form the axle while simultaneously acting as the template for the assembly of the interlockednmolecules is described. Coordination of the Lewis acid to a multidentate endotopic 2,6-di(methyleneoxy-nmethyl)pyridyl- or bipyridine-containing macrocycle orients a chelated dienophile through the macrocyclencavity. Lewis acid activation of the double bond causes it to react with an incoming “stoppered” diene,naffording the [2]rotaxane in up to 91% yield. Unusually for an active-template synthesis, the metal bindingnsite “lives on” in these rotaxanes. This was exploited in the synthesis of a molecular shuttle containing twondifferent ligating sites in which the position of the macrocycle could be switched by complexation withnmetal ions [Zn(II) and Pd(II)] with different preferred coordination geometries.