Ten-membered Rings or Larger with One or More Oxygen Atoms

Abstract

Among heterocyclic compounds – consisting of 10-membered rings or larger, bearing only oxygen atoms – crown ethers have been, and still are, by far the most intensively studied. In keeping with this overwhelming interest in crown ethers, this chapter focuses almost exclusively on the chemistry of these compounds, with some space toward the end being made for two new emerging classes of oxygen-containing macrocycles (i.e., calixtubes and oxacalixarenes). From their initial discovery in the mid-1960s, crown ethers have played a leading role in the development of host–guest and supramolecular chemistry. Over the years, these heteromacrocycles have evolved from primordial molecular receptors for cations to viable building blocks for the construction of new materials/devices. Research in the crown ether field has shifted in the recent past (and will presumably continue to do so in the near future) beyond discrete host–guest complexes towards ‘smart’ supramolecular architectures, which are being designed to perform specific tasks following on from initial recognition processes between components. Considering the vast number of crown ether-based compounds and the enormous diversity of their structures, as well as their very different fields of application, this chapter has been divided by topics rather than by structures, in an attempt to provide a more reader-friendly survey. The chemistry of this class of heterocyclic compounds is considered under the following four main headings: (1) crown ethers as molecular receptors; (2) crown ether-based sensors; (3) crown ether supramolecular assemblies; and (4) crown-related macrocycles.