(DFT) calculations. The multi-conformational feature of calix[n]triazoles endows
this group of calixarene derivatives with great potential in anion binding and
molecular recognition.
7.2.8 Calix[n]tetrolarenes
Calix[n]tetrolarenes, a new family of macrocyclic arenes, were firstly reported by
Cohen and Zafrani in 2017 [47]. Calix[4,5]tetrolarenes (27, 28) were facilely
prepared by reaction of the partially methylated 1,2,3,5-benzenetetrol and paraformaldehyde catalyzed by trifluoroacetic acid (TFA) with a total separation yield of
73% (Fig. 4c). Solvents, reaction time, temperatures, and monomeric hydroxyl
groups all strongly affect the reaction rate and the distribution of products. It is
noteworthy that cyclic pentamers could be facilely produced during the macrocyclization of calix[n]tetrolarenes, which has been proven to be very difficult in
the synthesis of traditional calixarenes as a result of its poor thermodynamic favor.
Overall, taking both advantages of the synthetic ease and fancy structures of calix[n]
tetrolarenes, a wide scope of applications will be unearthed in the near future.
7.2.9 Coumarin[4]arene
In 2018, Venkatakrishnan and coworkers introduced a bicyclic heteroaromatic
macrocyclic receptor, namely, coumarin[4]arene (29) [48]. This new macrocyclic
arene, closely related to both calix[4]arene and resorcin[4]arene, meanwhile, possesses a specific fluorescence emissive property. 29 could be obtained through a twostep synthetic strategy by using easily available raw materials, giving the desirable
compound in a satisfied yield of 84%. Interestingly, compared with an averaged
crown conformation of 29 in solution, a stable boat conformation in the solid state
was further demonstrated by X-ray single crystal diffraction (Fig. 4d). The flexibility
of the structure and connatural fluorescence feature endow 29 with great potentials in
molecular recognition and fluorescence sensing. For instance, the idea of
constructing fluorescent capsules based on this macrocyclic arene is probable to be
realized via complementary multipoint interactions in the near future.
7.3
New Macrocyclic Arenes Related to Pillarenes
7.3.1 Asararenes
In 2013, Stoddart and coworkers reported a new class of macrocyclic arenes with
6–12 aromatic units, namely, asar[n]arenes [49]. Similar to pillarenes, asar[6–15]
arenes (30–35) could be obtained through a one-step method by reaction of the
monomers (1,2,4,5-tetramethoxybenzenes) with paraformaldehyde, using BF 3 ÁOEt 2
as the catalyst. Besides that, asar[6]arene (30) was demonstrated to be the smallest
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D. Dai et al.
this group of calixarene derivatives with great potential in anion binding and
molecular recognition.
7.2.8 Calix[n]tetrolarenes
Calix[n]tetrolarenes, a new family of macrocyclic arenes, were firstly reported by
Cohen and Zafrani in 2017 [47]. Calix[4,5]tetrolarenes (27, 28) were facilely
prepared by reaction of the partially methylated 1,2,3,5-benzenetetrol and paraformaldehyde catalyzed by trifluoroacetic acid (TFA) with a total separation yield of
73% (Fig. 4c). Solvents, reaction time, temperatures, and monomeric hydroxyl
groups all strongly affect the reaction rate and the distribution of products. It is
noteworthy that cyclic pentamers could be facilely produced during the macrocyclization of calix[n]tetrolarenes, which has been proven to be very difficult in
the synthesis of traditional calixarenes as a result of its poor thermodynamic favor.
Overall, taking both advantages of the synthetic ease and fancy structures of calix[n]
tetrolarenes, a wide scope of applications will be unearthed in the near future.
7.2.9 Coumarin[4]arene
In 2018, Venkatakrishnan and coworkers introduced a bicyclic heteroaromatic
macrocyclic receptor, namely, coumarin[4]arene (29) [48]. This new macrocyclic
arene, closely related to both calix[4]arene and resorcin[4]arene, meanwhile, possesses a specific fluorescence emissive property. 29 could be obtained through a twostep synthetic strategy by using easily available raw materials, giving the desirable
compound in a satisfied yield of 84%. Interestingly, compared with an averaged
crown conformation of 29 in solution, a stable boat conformation in the solid state
was further demonstrated by X-ray single crystal diffraction (Fig. 4d). The flexibility
of the structure and connatural fluorescence feature endow 29 with great potentials in
molecular recognition and fluorescence sensing. For instance, the idea of
constructing fluorescent capsules based on this macrocyclic arene is probable to be
realized via complementary multipoint interactions in the near future.
7.3
New Macrocyclic Arenes Related to Pillarenes
7.3.1 Asararenes
In 2013, Stoddart and coworkers reported a new class of macrocyclic arenes with
6–12 aromatic units, namely, asar[n]arenes [49]. Similar to pillarenes, asar[6–15]
arenes (30–35) could be obtained through a one-step method by reaction of the
monomers (1,2,4,5-tetramethoxybenzenes) with paraformaldehyde, using BF 3 ÁOEt 2
as the catalyst. Besides that, asar[6]arene (30) was demonstrated to be the smallest
188
D. Dai et al.