temperature is more than 100
C, which is much higher than those of the classic ptert-butylcalix[4]arene and p-tert-butylcalix[5]arene. This indicated that the significant contributor in determining the conformational mobility of 16a is not due to the
intramolecular hydrogen bonds and the bulky tert-butyl groups but mainly attributed
to the introduction of the triptycene moiety with rigid structure. For triptycenederived calix[5]arenes 16b–c, they also showed the similar spectral features to those
of 16a. The results showed that all of the triptycene-derived calix[5]arenes 16a–c
containing two dimethoxy groups had C s symmetric structures with a fixed cone
conformation in solution. Their demethylated compounds also have the similar
1 H
NMR spectra features and the same fixed cone conformations as those of their
precursors. Moreover, the variable-temperature
1 H NMR experiments of 16a–c in
DMSO-d 6 showed no obvious changes of the methylene proton signals with the
increase of the temperatures even up to 373 K. These observations not only confirmed their fixed conformations but also indicated that the conformational inversion
barriers of these compounds are very high. Similarly, 21, 22, and 24 with different
substituents at the upper rim also kept fixed cone conformation in solution due to the
rigid structure of triptycene and the intramolecular hydrogen bonding of the adjacent
phenol groups. But after 22 and 24 were all methyl etherified, products 23 and 25
showed 1,2-alternate conformations in the tested temperatures [22].
We also investigated the structures of triptycene-derived calix[6]resorcinarenelike hosts 32–33 [23] in solution by the
1 H NMR,
13 C NMR, and variable-temperature
1 H NMR experiments. The spectra features showed that these calix[6]
resorcinarene-like hosts 32–33 are all the cis isomers with fixed cone conformation
in solution. Similar to triptycene-derived calixarenes, triptycene-derived
oxacalixarenes 35a–d and 36a–d are also a pair of diastereomers with high symmetric structures and fixed conformation in solution, in which 35a–d are cis isomers
and 36a–d are trans isomers [24, 26]. For triptycene-derived homooxacalixarene
analogues, the
1 H NMR spectra of 39a–d [28] showed two singlets for the bridgehead protons with small Δδ value, which implied that they were cis isomer with a
high symmetric structure. Meanwhile, the
1 H NMR spectra of 40a–d showed the
relatively significant different chemical shifts for bridgehead protons, which
suggested that they were the trans isomers. It was noteworthy that the two sets of
doublet signals of trans isomer 40c for the methylene group were gradually changed
to one set of doublet signals above 370 K, which meant that at very high temperature,
the rigid conformation of 40c was no longer existed. However, for cis isomer 39c,
the methylene proton signals exhibited no obvious changes even up to 380 K. When
the two p-phenyl-substituted benzene rings were linked together by crown ether
chains, the conformations of macrocycles 41 and 42 could be fixation up to 380 K
without free rotation.
Triptycene-derived N(H)-bridged azacalixarenes 44a–47a and 44b–47b [29] are
also pairs of diastereomers. It was found that the
1 H NMR spectra of cis isomers
44a–47a showed the close chemical shifts of the aromatic protons and small
different shifts for the benzylic protons with the high symmetry boat conformation,
while the trans isomers 44b–46b showed four singlets with significant different
chemical shifts for bridgehead protons and two singlets for the protons of NÀH
6 Triptycene-Derived Macrocyclic Arenes
153
C, which is much higher than those of the classic ptert-butylcalix[4]arene and p-tert-butylcalix[5]arene. This indicated that the significant contributor in determining the conformational mobility of 16a is not due to the
intramolecular hydrogen bonds and the bulky tert-butyl groups but mainly attributed
to the introduction of the triptycene moiety with rigid structure. For triptycenederived calix[5]arenes 16b–c, they also showed the similar spectral features to those
of 16a. The results showed that all of the triptycene-derived calix[5]arenes 16a–c
containing two dimethoxy groups had C s symmetric structures with a fixed cone
conformation in solution. Their demethylated compounds also have the similar
1 H
NMR spectra features and the same fixed cone conformations as those of their
precursors. Moreover, the variable-temperature
1 H NMR experiments of 16a–c in
DMSO-d 6 showed no obvious changes of the methylene proton signals with the
increase of the temperatures even up to 373 K. These observations not only confirmed their fixed conformations but also indicated that the conformational inversion
barriers of these compounds are very high. Similarly, 21, 22, and 24 with different
substituents at the upper rim also kept fixed cone conformation in solution due to the
rigid structure of triptycene and the intramolecular hydrogen bonding of the adjacent
phenol groups. But after 22 and 24 were all methyl etherified, products 23 and 25
showed 1,2-alternate conformations in the tested temperatures [22].
We also investigated the structures of triptycene-derived calix[6]resorcinarenelike hosts 32–33 [23] in solution by the
1 H NMR,
13 C NMR, and variable-temperature
1 H NMR experiments. The spectra features showed that these calix[6]
resorcinarene-like hosts 32–33 are all the cis isomers with fixed cone conformation
in solution. Similar to triptycene-derived calixarenes, triptycene-derived
oxacalixarenes 35a–d and 36a–d are also a pair of diastereomers with high symmetric structures and fixed conformation in solution, in which 35a–d are cis isomers
and 36a–d are trans isomers [24, 26]. For triptycene-derived homooxacalixarene
analogues, the
1 H NMR spectra of 39a–d [28] showed two singlets for the bridgehead protons with small Δδ value, which implied that they were cis isomer with a
high symmetric structure. Meanwhile, the
1 H NMR spectra of 40a–d showed the
relatively significant different chemical shifts for bridgehead protons, which
suggested that they were the trans isomers. It was noteworthy that the two sets of
doublet signals of trans isomer 40c for the methylene group were gradually changed
to one set of doublet signals above 370 K, which meant that at very high temperature,
the rigid conformation of 40c was no longer existed. However, for cis isomer 39c,
the methylene proton signals exhibited no obvious changes even up to 380 K. When
the two p-phenyl-substituted benzene rings were linked together by crown ether
chains, the conformations of macrocycles 41 and 42 could be fixation up to 380 K
without free rotation.
Triptycene-derived N(H)-bridged azacalixarenes 44a–47a and 44b–47b [29] are
also pairs of diastereomers. It was found that the
1 H NMR spectra of cis isomers
44a–47a showed the close chemical shifts of the aromatic protons and small
different shifts for the benzylic protons with the high symmetry boat conformation,
while the trans isomers 44b–46b showed four singlets with significant different
chemical shifts for bridgehead protons and two singlets for the protons of NÀH
6 Triptycene-Derived Macrocyclic Arenes
153