Synthesis of macrocycles and an unusually asymmetric [2]catenane via templated acetylenic couplings

An unusually asymmetric [2]catenane has been prepared by interlocking a hyb rid crown macrocycle (containing one polyether and one butadiyne linker) wi th a diimide-derived macrocycle itself constructed with a pair of rigid but adiyne links. This system of complementary building blocks and connectors h as proved a versatile vehicle for demonstration of a number of templating e ffects. Synthesis of the hybrid crown monomer by intramolecular cyclisation is promoted by the presence of a benzene diimide, acting as a positive tem plate, but a sufficiently different effect is exerted by a naphthalene diim ide derivative that intermolecular dimerisation becomes significant. Templa ting the hybrid crown synthesis with an 'active' benzene diimide, itself be aring acetylene functions, allows the first tandem synthesis of a catenane comprising two different rings: the diimide first acts as a template for th e formation of the hybrid crown, which itself in turn acts as a template fo r cyclodimerisation of the acetylenic diimide. Remarkably, the yield of cat enane is essentially independent of the initial cyclisation state of the cr own component. No significant production of covalently linked donor-accepto r species is observed from these reactions, supporting the presence of an i ntermediate complex pre-organised to catenane formation. In contrast, oxida tive coupling of an alkyl solubilised diimide gave no interlocked products and yielded only small amounts of cyclic poly-imide macrocyles.