The effect of ring size on catenane synthesis

The synthesis of a [2]catenane with 87-membered rings was improved and extended to [2]catenanes with 63- and 147-membered rings. One of the key features is the carbonate linkage between phenols with tolane substituents in the 2-and 6-positions, which serves as a covalent template for the geometrical arrangement of a macrocycle and a ring precursor. Subsequent cyclization of the threaded ring precursor gives the precatenane as the main product, and this is converted into the catenane by carbonate hydrolysis. As well as the precatenane, its dumbbell shaped isomer is formed in the cyclization step. From the known conformation of the templating carbonate moiety and the strong dependence of the ratio of precatenane and dumbbell on the ring size, the dumbbell's origin is attributed to the conformational flexibility of the large rings and not to geometrical ambiguity of the carbonate moiety. (C) Wiley-VCH Verlag GmbH Co.