Rational synthesis of multicyclic bis[2]catenanes

Bis-loop tetraurea calix[4]arene 6 has been prepared by acylation of the wide-rim calix[4]arene tetraamine I with the activated bis(urethane) 8 under dilution conditions. Similarly the bis(Boc-protected) tetraamine 2 is converted into the mono-loop derivative 3 which after deprotection and acylation gives the bisalkenyl derivative 5. In apolar solvents this tetraurea calix[4]arene 5 forms regioselectively a single hydrogen-bonded homodimer, from which the bis[2]catenane 10a is formed in 49% by a metathesis reaction followed by hydrogenation. Bis-loop derivative 6 forms no homodimers for steric reasons, but a stoichiometric mixture with the open-chain tetra-alkenyl derivative 7a contains exclusively the heterodimer. Metathesis and subsequent hydrogenation now yields 65% of the pure bis[2]catenane 10a which could not be isolated from the complex reaction mixture obtained from the homodimer 7a(.)7a. The chirality of 10a (D-2 symmetry) has been verified by optical resolution using HPLC on a chiral stationary phase.