Synthesis of a conformationally restricted polyoxygenated crownophane

A new polyoxygenated crownophane has been synthesized from syringaldehyde and diethyleneglycol by means of McMurry pinacol reaction, whereas ring closing metathesis with Grubbs’ catalyst failed in producing the macrocyclization to the corresponding stilbenophane. The NMR data of the crownophane show a restricted conformational space accessible to the phenyl rings.     

Synthesis, crystal structure and complexation with dibenzylammonium ion of a novel class of crownophanes containing bridged fragments of fluorenone and stilbene

Two representatives of a novel class of crownophanes containing fragments of fluorenone and stilbene bridged by units of diethylene glycol and triethylene glycol, respectively, have been synthesized. The crystal structure and complexation behavior of these crownophanes were studied. They form much stronger complexes with dibenzylammonium hexafluorophosphate (logK_a value in CH₃CN is equal to 3.92 ± 0.06 and 4.40 ± 0.05, respectively) than benzocrown ethers. This makes them an attractive alternative for benzocrown ethers as components in supramolecular synthesis.     

Wurster''s crownophanes: an alternate topology for para-phenylenediamine-based macrocycles

Six redox-active cyclophane/crown hybrid molecules (crownophanes) were prepared via cyclization reactions involving N,N′-dimethyl-p-phenylenediamine and tosylated oligoethylene glycols of varying length. These new host molecules differ from other phenylenediamine-containing crown ethers in that the electron-rich π face is designed to be part of the ligating group. Their electrochemical properties were determined by cyclic voltammetry with a correlation found between macrocyclic architecture and ease of oxidation. The affinity of the smaller crownophanes for cations was studied by cyclic voltammetry with the result that these hosts show no electrochemical response to alkali metal cations, but, dependent on macrocycle size, modest selectivity for alkaline earth metal cations. This stands in contrast to previously reported phenylenediamine-containing crown ethers in which the redox centers are linked to guest ions through a macrocyclic amino group.     

Modular synthesis of triaroylbenzene-derived crownophanes

An isomeric series of homologous crownophanes (i.e., macrocycles possessing structural features of crown ethers and cyclophanes) has been prepared via a concise and modular synthetic route. Macrocyclization is achieved in reasonable yield during the course of an enaminone-triggered benzannulation with bis(aryl ethynyl ketone) reaction partners. The crownophanes examined were active alkali cation binding agents in the gas phase, but failed to exhibit ionophoric properties in solution. On the basis of X-ray crystallographic analysis, it is concluded that the cyclophane framework of these macrocycles is too large and rigid to allow efficient interaction with the cations examined.