Rational synthesis of multicyclic bis[2]catenanes

Bis-loop tetraurea calix4]arene 6 has been prepared by acylation of the wide-rim calix4]arene tetraamine 1 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 calix4]arene 5 forms regioselectively a single hydrogen-bonded homodimer, from which the bis2]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 tetraalkenyl derivative 7a contains exclusively the heterodimer. Metathesis and subsequent hydrogenation now yields 65 % of the pure bis2]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.