Multiple catenanes based on tetraloop derivatives of calix[4]arenes

Abstract

Four novel tetraarylurea calix[4]arenes ( 4a– d) have been synthesized, substituted by ω-alkenyloxy residues in 3,5-positions of the arylurea residues. The eight alkenyl groups were pairwise connected by olefin metathesis and subsequent hydrogenation. The ring-closure reaction was carried out with heterodimers exclusively formed by 4 with a tetratosylurea calix[4]arene 1, which serves as a template in this reaction step. The potential trans-cavity bridging is entirely suppressed in this way. Bis- and tetraloop calix[4]arenes cannot form dimers due to overlapping loops. However, they readily form heterodimers with open-chain tetraureas, as long as their urea residues can pass through the loops. Thus, five heterodimeric capsules 8a– e with bis[3]catenane structure were synthesized using again the olefin metathesis followed by hydrogenation. Two different strategies were compared for this reaction sequence, starting with heterodimers formed either by tetraloop derivatives 5 with tetraalkenyl tetraureas 6 (pathway A) or by bisloop derivatives 7 with octaalkenyl tetraureas 4 (pathway B). A distinct advantage of one of these pathways was not observed; the bis[3]catenanes were obtained with yields of 20–60%. Heterodimers formed by tetraloop derivatives 5b– d and octaalkenyl ureas 4b– d were converted analogous to three novel cyclic [8]catenanes 9a– c in 30–42% yield. The structure of the novel catenanes was unambiguously proved by 1H NMR and ESI MS, and for 8a and 9a additionally by single crystal X-ray analysis.