7.1
Introduction
Design and synthesis of macrocyclic compounds are always one of the cutting-edge
research topics since the birth of supramolecular chemistry [1–5]. From Pedersen’s
groundbreaking discovery of crown ethers in the mid-1960s [6, 7], countless macrocyclic hosts have been impelling the development of host-guest and supramolecular chemistry [8–12]. Among them, macrocyclic arenes comprising of multiaromatic units have made a great contribution owing to their easy accessibility and
selective host-guest properties. The most representative case is definitely the calix[n]
arene family (calixarenes for short) [13, 14], being considered as the third generation
of star supramolecular host. Their structure and conformation properties, postmodification methods, host-guest properties, and supramolecular functions have
been intensively studied [15–19]. Besides that, pillar[n]arenes (pillararenes, or
pillarenes for short) [20], a relatively new family of synthetic macrocyclic arenes,
have also gained wide attention due to their unique and outstanding binding properties and ease of application development during the last decade [21–29], which
have also been regarded as the fifth generation of star supramolecular host after
cucurbit[n]urils [30].
However, in spite of many significant advances in calixarene and pillarene
families, the design and exploration of new synthetic macrocyclic receptors are
still an everlasting and challenging topic in supramolecular macrocyclic chemistry.
In the last few years, scientists have reported several new families of synthetic
macrocyclic arenes, inspired by the rapid development of calixarene and pillarene
chemistry. Therefore, we take this good opportunity to give a brief overview of these
newly designed macrocyclic receptors, especially with the focus on their syntheses,
structures, chemical functionalization, and host-guest properties. We believe that it
will be a timely and valuable reference for those who have been engaged in or are
interested in the design and development of macrocyclic compounds.
7.2
New Macrocyclic Arenes Related to Calixarenes
7.2.1 Calix[2]arene[2]triazines
Calix[2]arene[2]triazines (1–8) as a new class of heteroatomic calixarene derivatives
were first reported by Wang and coworkers in 2004 [31]. These macrocycles can be
easily obtained through a high yielding fragment coupling approach with cyanuric
chloride and resorcinol as the ring-forming monomers (Fig. 1a, b). The single crystal
structures of calix[2]arene[2]triazines (1–8) show a 1,3-alternate conformation with
two benzene rings almost perpendicular to the plane of the four bridging heteroatoms. And, the bridging heteroatoms are more inclined to form a conjugation
system with the triazine rings rather than the benzene rings as a result of the
intramolecular/intermolecular steric and electronic effects. In addition, the cavity
features of calix[2]arene[2]triazines, i.e., the distances and inclined angles between
182
D. Dai et al.
Introduction
Design and synthesis of macrocyclic compounds are always one of the cutting-edge
research topics since the birth of supramolecular chemistry [1–5]. From Pedersen’s
groundbreaking discovery of crown ethers in the mid-1960s [6, 7], countless macrocyclic hosts have been impelling the development of host-guest and supramolecular chemistry [8–12]. Among them, macrocyclic arenes comprising of multiaromatic units have made a great contribution owing to their easy accessibility and
selective host-guest properties. The most representative case is definitely the calix[n]
arene family (calixarenes for short) [13, 14], being considered as the third generation
of star supramolecular host. Their structure and conformation properties, postmodification methods, host-guest properties, and supramolecular functions have
been intensively studied [15–19]. Besides that, pillar[n]arenes (pillararenes, or
pillarenes for short) [20], a relatively new family of synthetic macrocyclic arenes,
have also gained wide attention due to their unique and outstanding binding properties and ease of application development during the last decade [21–29], which
have also been regarded as the fifth generation of star supramolecular host after
cucurbit[n]urils [30].
However, in spite of many significant advances in calixarene and pillarene
families, the design and exploration of new synthetic macrocyclic receptors are
still an everlasting and challenging topic in supramolecular macrocyclic chemistry.
In the last few years, scientists have reported several new families of synthetic
macrocyclic arenes, inspired by the rapid development of calixarene and pillarene
chemistry. Therefore, we take this good opportunity to give a brief overview of these
newly designed macrocyclic receptors, especially with the focus on their syntheses,
structures, chemical functionalization, and host-guest properties. We believe that it
will be a timely and valuable reference for those who have been engaged in or are
interested in the design and development of macrocyclic compounds.
7.2
New Macrocyclic Arenes Related to Calixarenes
7.2.1 Calix[2]arene[2]triazines
Calix[2]arene[2]triazines (1–8) as a new class of heteroatomic calixarene derivatives
were first reported by Wang and coworkers in 2004 [31]. These macrocycles can be
easily obtained through a high yielding fragment coupling approach with cyanuric
chloride and resorcinol as the ring-forming monomers (Fig. 1a, b). The single crystal
structures of calix[2]arene[2]triazines (1–8) show a 1,3-alternate conformation with
two benzene rings almost perpendicular to the plane of the four bridging heteroatoms. And, the bridging heteroatoms are more inclined to form a conjugation
system with the triazine rings rather than the benzene rings as a result of the
intramolecular/intermolecular steric and electronic effects. In addition, the cavity
features of calix[2]arene[2]triazines, i.e., the distances and inclined angles between
182
D. Dai et al.