Active Metal Template Synthesis of [2]Catenanes

The synthesis of [2]catenanes by single macrocyclization and double macrocyclization strategies using Cu(l) ions to catalyze covalent bond formation while simultaneously acting as the template for the mechanically interlocked structure is reported. These "active metal template" strategies employ appropriately functionalized pyridine ether or bipyridine ligands and either the CuAAC "click" reaction of azides with terminal alkynes or the Cul(l)-mediated Cadiot-Chodkiewicz heterocoupling of an alkyne halide with a terminal alkyne. Using one macrocyclic and one acyclic building block, heterocircuit (the rings are constitutionally different) [2]catenanes are produced via the single macrocyclization route in up to 53% yield by optimizing the reaction conditions and relative stoichiometry of the starting materials. Alternatively, with the active template CuAAC reaction, a single acyclic unit can be used to form a homocircuit (two identical rings) [2]catenane in 46% yield through a one-pot, double macrocyclization, procedure. Remarkably, <7% of the corresponding noninterlocked macrocycle is isolated from this reaction, indicating the efficacy of Cu(l) as both a template for the catenane and a catalyst for covalent bond formation in the reaction.