Tuning conformations of calix[4]tubes by weak intramolecular interactions

Article abstract of DOI:10.1039/c2nj40961e

The conformational distribution in distally functionalized adamantylated calix[4]tubes was analyzed with NMR and quantum-chemical calculations. Without any intramolecular interactions, ester-, acid-, amino-, alcohol-, isocyanate-, phthalimide- and urea-substituted calixtubes preferred less sterically hindered flattened cone conformers in solution. In contrast, in a non-polar medium (CDCl₃) for calixtubes bearing two 3-carboxymethyl-1-adamantyl or 3-(2-ureidoethyl)-1-adamantyl units, the less sterically preferable flattened cone conformation with bulky substituents connected by intramolecular hydrogen bonds was found to be more favorable. On the other hand, for a calixtube with two positively charged units, only the conformer with distanced substituents was exclusively detected. Thus, the conformational equilibrium in functionalized calix[4]tubes can be controlled by intramolecular hydrogen bonding between appropriately arranged carboxylic groups or urea moieties, or by electrostatic repulsion of positively charged substituents.

Full text of DOI:10.1039/c2nj40961e

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Tuning conformations of calix[4]tubes by weak
intramolecular interactions
Kirill Puchnin,a Dmitry Cheshkov,ab Pavel Zaikin,a Ivan Vatsouro*a and
Vladimir Kovalev*a
Received (in Montpellier, France) 22nd October 2012, Accepted 27th October 2012
DOI: 10.1039/c2nj40961e
The conformational distribution in distally functionalized adamantylated calix[4]tubes was
analyzed with NMR and quantum-chemical calculations. Without any intramolecular
interactions, ester-, acid-, amino-, alcohol-, isocyanate-, phthalimide- and urea-substituted
calixtubes preferred less sterically hindered flattened cone conformers in solution. In contrast,
in a non-polar medium (CDCl3) for calixtubes bearing two 3-carboxymethyl-1-adamantyl or
3-(2-ureidoethyl)-1-adamantyl units, the less sterically preferable flattened cone conformation with
bulky substituents connected by intramolecular hydrogen bonds was found to be more favorable.
On the other hand, for a calixtube with two positively charged units, only the conformer with
distanced substituents was exclusively detected. Thus, the conformational equilibrium in
functionalized calix[4]tubes can be controlled by intramolecular hydrogen bonding between
appropriately arranged carboxylic groups or urea moieties, or by electrostatic repulsion of
positively charged substituents.
characteristic signal doubling in 1H and 13C NMR spectra. Still,
Introduction
conformational interconversion is not blocked but is significantly
decelerated in calixtubes, and exchange rates can be easily derived
from EXSY experiments. For calixtubes 1–3, representing
different combinations of classical and thiacalixarenes,
conformational exchange rate constants in CDCl3 are 0.9 sꢀ1
(328 K),6b 9.3 sꢀ1 (273 K),7 and 2.5 sꢀ1 (328 K),8 respectively.
Removal or replacement of tert-butyl groups with different
alkyl residues or halogens may alter the rate constants but keep
The control of macrocycle conformations is one of the most
important parts in the design of calixarene-based receptors.1
Despite the well-studied ‘fixing’ of a calix[4]arene core in one
of four main conformations (cone, partial cone, 1,2-alternate,
or 1,3-alternate) by simple introduction of bulky groups to
the narrow rim, the internal conformational mobility of the
macroring is not completely suppressed in most cases. When
the cone conformation is mounted by four alkyl residues at the
narrow rim, residual interconversion between two C2v-symme-
trical flattened cone conformers is fast on the NMR time scale
and produces broadened spectra reflecting the time-averaged
C4v symmetry of the core.2 The conformational motions can
be more or less efficiently suppressed by intramolecular
bridging,3 guest (cation) complexation,4 or by the grafting of
several calixarene molecules into aggregates by covalent or
weak intramolecular interactions.5
In calix[4]tubes (Fig. 1), which are unique quadruple-bridged
bis-macrocycles first introduced by Beer and co-workers,6 the
calix[4]arene counterparts are greatly rigidified and possess C2v
symmetry not only in the solid state (that is common for most of
cone calix[4]arene tetra-ethers) but also in solution as follows from
a Department of Chemistry, M.V. Lomonosov Moscow State
University, Lenin’s Hills, Moscow, 119991, Russia.
E-mail: vatsouro@petrol.chem.msu.ru, kovalev@petrol.chem.msu.ru
b State Research Institute for Chemistry and Technology of
Organoelement Compounds, 38, Sh. Entuziastov, Moscow, 105118,
Russia
Fig. 1 Examples of classical (1), thia- (2), and hybrid (3) calix[4]tubes;
conformational interconversions in calix[4]tubes.
c
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them measurable by NMR at ambient or even elevated
temperatures.6b,c,7,8
Recently we have prepared a series of calixtubes bearing
substituted adamantanes at the wide rims, which have made
available bis-macrocycles with different functional groups
(esters, acids, amides, alcohols, amines and ureas).9 Among
them, a series of calixtubes with two distal functional units
have been obtained. Due to, at least, different sterical crowding
of the calixarene moieties, the disubstituted calixtubes have an
unequal distribution of flattened cone conformers (A and B,
Fig. 1), and for known selectively de-tert-butylated and
halogenated calixtubes, less sterically hindered conformers B
have been found dominant.6b,c
Herein we examined calixtubes 4–15 (Fig. 2) to assess
the influence of functional groups on the conformational
equilibrium, assuming that their possible interactions are
competing forces to the steric hindrance of bulky units.
Results and discussion
Calixtubes 4, 5, 11–15 were obtained earlier,9 and tubes 6–10
were prepared according to a scheme presented in Fig. 2, using
approaches developed earlier for tetra-functionalized
calixtubes.9
Fig. 3 (a) Parts of the 600 MHz 1H NMR spectrum (scaled non-
proportional) of diester 4 in CDCl3 at 298 K: major conformer – a–r,
green; minor conformer – a0–r0, red (from 2D EXSY); (b) NOEs in
major conformer of 4 (CDCl3, 223 K, tmix 0.3 s); (c) energy-minimized
structure of conformer 4B.
Despite the fact that for the previously known calixtubes
with two bulky substituents the less sterically hindered conformer
B was published to be the major one, the only conclusions made
from NOESY were presented with no details of the structure
analysis.6b,c To gain a tool for extracting conformer ratios of
disubstituted calixtubes from 1H NMR spectra, signals of the
main conformer of diester 4, as a representative example, in the
spectra were completely assigned. After splitting the spectral
derived by integration of the signals with the corresponding
diagonal peak intensity set to 100% (Table 1, Fig. 3b). Measure-
ment of the cross-peak volumes directly from the 2D spectrum
gave the same numerical values of NOEs for well-resolved signals,
but returned unreliable data for partly overlapped peaks.
Cross-peaks between j, m, n, o, p allowed assignment of the
signals from the substituted adamantane units (confirmed by
HSQC and 13C NMR chemical shifts calculations by the
additive scheme). Intensive NOEs b–n and b–o identified
adamantylated aromatic units, and the far less intensive NOEs
between n, o, p and d reflected the proximity of the adaman-
tylated and unsubstituted calixarene aromatic moieties. From
the NOEs a–q and c–r, the pairs of tert-butyl groups and
calixarene aromatic rings were correlated. Intensive NOEs a–l
and c–l, and the less intensive a–h and c–h showed h and l to be
resonances from the axial and equatorial protons in the
ArCH2Ar linkers in the tert-butylated calix[4]arene macro-
cycle, respectively. Analogously, methylene protons in the
opposed calixarene macroring were identified from the NOEs
b–k, d–k, b–g, and d–g.
1
pattern in the H NMR spectrum of 4 into two sets by EXSY
(Fig. 3a), the NOESY spectrum was collected at a lowered
temperature (223 K) in CDCl3 to suppress conformational
motions and minimize contribution of the chemical exchange
into the NOESY cross-peaks, and also to shift the equilibrium
toward the more stable conformer (conformer ratio changed from
25/75 at 298 K to 10/90 at 223 K). The 2D NOESY spectrum was
cut into slices through diagonal peaks and the NOE values were
Thus, nearly all signals in the 1H NMR spectrum of the
major conformer of diester 4 were assigned, except for those
from the OCH2CH2O-linkers. As distances between the
protons of the ethylene groups and the calixarene aromatics
are too large, the assignments of trans- and gauche-OCH2-
CH2O could not be done by NOESY. Next, the 13C NMR
spectrum of 4 was collected and resonances from the major
conformer were fully assigned (see Experimental section) with
HSQC and HMBC correlations. In particular, cross-peaks in
Fig. 2 Disubstituted calixtubes studied (Pht = N-phthalimide, Tol
= 4-tolyl, Pyr = 1-pyrenyl). (i) nBu4NOH/THF then HCl; (ii)
LiAlH4/THF; (iii) SOCl2/benzene, then NaN3/acetone/H2O, then
benzene/heating; (iv) HCl/dioxane.
c
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Table 1 Significant NOEs in diester 4a
Hdiagonal
Hcross
NOE
Hdiagonal
Hcross
NOE
a
c
h
ꢁꢁꢁꢁꢁ
i
e
f
ꢁꢁꢁ
ꢁꢁꢁ
ꢁꢁꢁꢁ
ꢁꢁꢁꢁ
ꢁꢁꢁꢁ
ꢁ
l
g
q
d
g
ꢁꢁꢁꢁ
ꢁꢁꢁꢁ
h
k + l
b
j
d
o
a
b
c
k
ꢁ
n
o
p
a
ꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁꢁ
ꢁ
k + l
ꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁ
ꢁꢁꢁ
ꢁꢁꢁꢁ
ꢁꢁꢁꢁ
ꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁꢁ
ꢁꢁꢁ
ꢁꢁꢁ
ꢁ
c
ꢁꢁꢁꢁ
d
e
h
l
f
r
b
g
ꢁꢁꢁꢁ
ꢁꢁꢁ
i
Fig. 4 Parts of HMBC spectrum of
4
(CDCl3, 273 K) and
d
m
n
o
p
b
m
o
b
m
n
p
m
o
a
c
ArH–OCH2CH2O-connections found (red lines).
j
k
ꢁ
were obtained (Table 2). As calixtubes 4, 5, 11–15 have been
characterized only as potassium complexes,9 the 1H NMR
spectra of their conformers B are also presented in the
Experimental section.
e
g
h
ꢁꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁ
ꢁꢁ
o
i
k + l
g
ꢁꢁꢁ
ꢁꢁ
f
ꢁꢁ
In most cases, the less sterically hindered conformers B were
found to be dominant. Also, adamantane units themselves
seemed bulky enough to provide steric repulsions and stabilize
conformer B, regardless of the size of the functional
substituents: only small differences in the conformation
distributions were observed for the calixtubes with ester,
hydroxy, phthalimido and amino units.
h
p
ꢁꢁꢁ
ꢁꢁꢁꢁꢁ
ꢁꢁ
i
k + l
q
r
g + h
a
b
c
d
e
f
ꢁꢁ
ꢁꢁꢁ
ꢁꢁꢁ
ꢁꢁꢁ
ꢁꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁꢁ
ꢁꢁꢁꢁꢁꢁ
This was not the case for diacid 7 and bis-ureas 14, 15. As
1
follows from the H NMR spectrum, in neat CDCl3 (Fig. 5a)
i
a
All NOEs are negative (have the same sign as diagonal peaks) and
are shown as ‘‘ꢁ’’, ‘‘ꢁꢁ’’, ‘‘ꢁꢁꢁ’’, ‘‘ꢁꢁꢁꢁ’’, ‘‘ꢁꢁꢁꢁꢁ’’, ‘‘ꢁꢁꢁꢁꢁꢁ’’ for
absolute values of o2, 2–5, 5–10, 10–15, 15–20, and 420%,
respectively.
the major conformer of 7 was A with two bulky 3-carboxy-
methyl-1-adamantyl substituents located close to each other.
This unexpected conformational distribution was maintained
at different calixtube concentrations and was not drastically
affected by the cooling or heating of the sample.
When several drops of CF3CO2D were added to the
solution, the conformational distribution was reversed, and
conformer 7B became dominant (Fig. 5b, 7A/7B = 25/75).
The same effect was achieved by addition of DMSO-d6 to a
CDCl3-solution of 7. This behavior is consistent with the
formation of internal hydrogen bonds, providing stabilization
of the less sterically favorable conformer 7A in non-polar
medium.
the HMBC spectrum allowed indirect correlation between
pairs of aromatic and OCH2CH2O–protons (a–f, b–e, c–i,
and d–i, Fig. 4) through the calixarene narrow rim aromatic
quaternary carbons, thus completing the assignment of the
1H NMR spectrum of 4.
Molecular structures of A and B conformers of diester 4
were accessed by quantum-chemical calculations (DFT PBE/
L1).10 In both cases, distances between calixarene aromatic
protons and protons of adjacent ArCH2Ar-groups were
clearly distinguishable for aromatic moieties of different
inclination, and measured values of NOE a–l, c–l, a–h, c–h,
b–k, d–k, b–g, and d–g were well-correlated with
corresponding intramolecular distances only in conformer
4B (Fig. 3c). So, the main conformer of diester 4 in CDCl3
proved to be flattened cone B with 1H NMR resonances e
and f representing trans-OCH2CH2O-linkers, and resonance
i – gauche-OCH2CH2O-linkers.
The structures of the conformers of 7 were accessed
by quantum-chemical calculations. First, the structure of
conformer 7B was optimized at the DFT PBE/L1 level,10 then
the structure of conformer 7A was obtained from the
calculated structure of conformer 7B by a scanning procedure
with gradual changing of the geometry of the calixtube core
Table 2 Conformers A/B ratios for 4–15 in CDCl3 at 298 Ka
Tube
A/B ratio
Tube
A/B ratio
Tube
A/B ratio
As follows from the data analysis, the A/B ratio in the
disubstituted calixtubes can be easily derived from the relative
intensities of the aromatic d/d0 (AB2/AX2 spin systems) or/and
b/b0 (singlets) protons and verified, if resolved, from other
signals in spectra (e.g., from methoxy j/j0 and tert-butyl
resonances q/q0, r/r0 in the case of 4). Following this simple
measurements, the conformer ratios for the calixtubes 4–15
4
5
6
7
25/75
25/75
35/65
75/25
8
9
10
11
35/65
25/75b
25/75
35/65
12
13
14
15
30/70
35/65
50/50
50/50
a
b
Accuracy ꢂ5%. Measured in CD3OD due to insolubility of the salt
in CDCl3.
c
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hydrogen bonds in the first case because of similar acidities of
acetic acid and 1-adamantylacetic acid units in 7.
In calixtubes 14 and 15, with urea groups located in
adamantane units, the A/B populations are nearly equal in
CDCl3 (Fig. 7a). Addition of CF3CO2D turned the con-
formational composition to A/B = 10/90 for both compounds
(Fig. 7b), thus proving hydrogen bonding between the urea
groups in non-competing medium; the titration experiment
with acetic acid returned a plot similar to that presented in
Fig. 5e for diacid 7, with the final 14A/14B value of 35/65.
The 50/50 conformer ratio maintained at 273, 303 and 328 K
(within the accuracy of measurements) in CDCl3 resembled
that of the tetra-substituted calixtubes, so it was supposed
that in 14 and 15 the flexibly attached urea moieties
may remain hydrogen bonded through all the conformational
exchange processes between the energetically equal
conformers.
As direct evidence of the hydrogen bonds maintenance was
not available from the 1H NMR spectra and NOESY correlations,
quantum-chemical calculations were applied to judge if the
mechanism of the conformational exchange includes hydrogen
bonds breaking or not. Molecular structures of conformers
14A, 14B, and 14B0 sealed with hydrogen bonds (Fig. 7)
were optimized first at the DFT PBE/L1 level,10 and
then by B3LYP/6-31G, and subjected to single point
energy calculations at the B3LYP/Def2-TZVP level with
the environment (CHCl3) modelled by COSMO.11 The results
showed conformer 14A to be more favorable than 14B
and 14B0, and among the latter 14B was more stable.
Fig. 5 Parts of the 600 MHz 1H NMR spectra of
7 (scaled
non-proportional) in neat CDCl3 at 298 K (a) and after addition of
CF3CO2D (b); signals used for A/B determination are colored red (7A)
and green (7B); calculated structures of 7A (c) and 7B (d); 7A/7B ratio
at different concentrations of acetic acid in CDCl3 (e).
from flattened cone B to flattened cone A, and finally the
structures were optimized at the DFT B3LYP/6-31G level.11
The results (Fig. 5c and d) showed that in conformer 7A two
co-facial carboxylic groups can form two hydrogen bonds,
stabilizing the conformer and making it more favorable than
conformer 7B.12 The same calculations were made for the
homologous diacid 6 (Fig. 6), which showed that in conformer
6A only one hydrogen bond can be formed between the
non-coplanar carboxylic groups, thus allowing the steric
repulsion to prevail over the bridging interactions. Still, the
conformational equilibrium in 6/CDCl3 (as well as in cases of
8, 11 and 13) is a little bit shifted toward flattened cone A, if
compared to the more sterically hindered calixtubes 4 and 5
having no interacting functional groups (see Table 2).
The stability of the hydrogen bonds in 7 was probed by
NMR-titration with acetic acid, which was used instead of
CF3CO2H as its concentration can be controlled more accurately
and monitored by NMR. Upon increase of the solvent polarity,
the 7A/7B ratio dropped down smoothly with no intermittent
changes, showing the gradual destabilization of conformer 7A
(Fig. 5e). The final 7A/7B ratio reached in the CDCl3/CH3CO2H
system was somewhat higher than that in CDCl3/CF3CO2D
solution, which could be due to the uncomplete disruption of
Fig. 7 Parts of the 600 MHz 1H NMR spectra of 14 (scaled
non-proportional) in neat CDCl3 at 298 K (a) and after addition of
CF3CO2D (b); signals used for A/B determination are colored red
(14A) and green (14B). Calculated structures of conformers 14A (c),
14B (d), and 14B0 (e) with hydrogen bonds maintained.
Fig. 6 Calculated structures of 6A (a) and 6B (b).
c
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Thus, the exchange 14A 2 14B seems to take place rather
than 14A 2 14B0. Though all the integration approximations
were switched off at the single point calculation step to
minimize numerical errors, the energy differences between
14A and 14B (1.2 kcal molꢀ1), and between 14A and 14B0
(4.4 kcal molꢀ1) are rather small, and one can say that they are
below the trusted value for the method, so the presence of 14B0
in the mixture must not be completely excluded.
The outstandingly high (and equal) contents of conformers
14B and 15B (90%) in the CDCl3/CF3CO2D medium, and
also the significant decrease of 14B population when
CF3CO2D was replaced with weaker acetic acid or DMSO,
made it reasonable to suppose that the Coulomb repulsion
of the protonated urea groups may contribute to the stability
of conformers 14B and 15B. Such an effect was occasionally
found in a pure form for calixtube 20 prepared from
imidazophenanthrene-enriched calix[4]arene 18 and tetratosylate
19 (Scheme 1).
Fig. 8 Energy-minimized structure of protonated calixtube 20 (DFT
PBE/L1) and a part of its 600 MHz 1H NMR spectrum in CDCl3 at
298 K with signal attribution.
Table 3 Exchange rate constants for calixtubes at 328 Ka
As pure 20 had an extremely broadened 1H NMR spectrum
in CDCl3, it was converted into the protonated form by
treatment with CF3CO2H. Surprisingly, the 1H NMR
spectrum of 20ꢃ2H+ was not only well-resolved, but it
also contained signals from exclusively one conformer
(Fig. 8). The conformer B structure of 20ꢃ2H+ was concluded
from full assignment of the 1H NMR spectrum with NOESY,
which showed a trans-configuration of the OCH2CH2O
units connected to imidazol-substituted calixarene moieties.
Tube Solvent
k1, sꢀ1 (A - B)
k
ꢀ1, sꢀ1 (B - A)
4
CDCl3
1.6
0.6
0.4
1.5
0.8
1.0
0.3b
CDCl3 + CF3CO2D 1.4
CDCl3 0.5
CDCl3 + CF3CO2D 1.7
CDCl3 1.1
CDCl3 + CF3CO2D 1.0b
7
14
a
Measured from paired 2D EXSY correlations (tmix 0 s, and tmix 1 s).
Raw values due to significant cross-peaks overlap.
b
Thus, 20ꢃ2H+ represents the first calixtube system ‘fixed’
in a C2v-symmetrical flattened cone conformation, and electro-
static repulsions were shown to be the force which, along with
hydrogen bonding, can drastically affect the conformational
equilibrium of the bis-macrocycles.
Finally, for calixtubes with functional groups capable
of bonding interactions (7, 14) and diester 4 (as a reference)
the exchange rate constants were measured at 328 K (Table 3).
As follows from the data, in neat CDCl3 all the compounds
possessed exchange rates that were quite similar to
those known for classical calixtubes (at equal total con-
centrations of calixtubes), and neither bonding interactions
nor addition of CF3CO2D altered the rates significantly.
Conclusions
A series of calixtubes with different functional groups located
in distal positions of the upper rim was analyzed by NMR to
assess the conformational behavior of the bis-macrocycles.
It was found that the conformational distribution in calixtubes
can be controlled or, at least, influenced by weak
intramolecular interactions, such as hydrogen bonding or
Coulomb repulsions, if appropriate substituents are
introduced into the molecules. Still, these interactions did
not alter the kinetics of the intramolecular exchange process.
We hope, that these results will extend the applicability of
calixtubes for the design of novel switchable supramolecular
systems utilizing the unique ion-channel-like structure of the
calixtube core.
Scheme 1 Synthesis of imidazophenanthrene-containing calixtube
20. (i) HMTA/TFA; (ii) 9,10-phenanthrenequinone/CH3CO2NH3/
CH3CO2H; (iii) K2CO3/o-xylene.
c
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4.56 (d, 4H, J = 12.6 Hz, ArCH2Ar), 4.44 (br s, 8H, OCH2),
3.67 (s, 6H, OCH3), 3.29 (d, 4H, J = 13.1 Hz, ArCH2Ar), 3.27
(d, 4H, J = 12.6 Hz, ArCH2Ar), 2.20 (br s, 8H, CH2CO +
CHAd), 1.94–1.46 (m, 24H, CH2 Ad), 1.33 (s, 18H, C(CH3)3),
0.82 (s, 18H, C(CH3)3) ppm.
Experimental
General methods and materials
NMR spectra were acquired on Bruker Avance 400 and
Bruker Avance 600 instruments, and chemical shifts are
reported as ppm referenced to solvent signals. In the 13C
NMR spectra, signal attribution was assisted with APT and
DEPT135 experiments. MALDI-TOF mass spectra were run
by using a Bruker AutoFlex II apparatus, and ESI mass
spectra were obtained from an Agilent 1100 LC/MS system.
Chemicals received from commercial sources were used with-
out further purification. Solvents were purified and dried
according to standard procedures. Calixtubes 4, 5, 11–15,
tetratosylate 199 and calix[4]arene 1613 were synthesized
according to published procedures. NMR spectra for the main
conformers of known calixtubes are also presented, as they
were characterized previously as potassium complexes only.
Diacid 6. A mixture of diester 4 (0.65 g, 0.42 mmol), THF
(45 mL) and aqueous nBu4NOH (40%, 1 mL, 1.6 mmol) was
stirred at reflux for 6 h. After cooling, the solvents were
removed under reduced pressure, and the residue was treated
with 5 M HCl. The solid formed was collected, washed
repeatedly with water, and dried to afford pure 6 as a white
solid (0.59 g, 92%). M.p. 4300 1C; 1H NMR [400 MHz,
CDCl3, 303 K, main conformer (B)]: d = 7.11 (s, 4H, ArH),
7.04 (s, 4H, ArH), 6.50 (s, 4H, ArH), 6.36 (br s, 6H, ArH), 5.18
(m, 4H, OCH2), 5.03 (m, 4H, OCH2), 4.58 (d, 4H, J = 13.1 Hz,
ArCH2Ar), 4.55 (d, 4H, J = 12.6 Hz, ArCH2Ar), 4.42 (br s, 8H,
OCH2), 3.26 (br d, 8H, J = 12.1 Hz, ArCH2Ar), 2.26 (br s, 4H,
CHAd), 2.17–1.65 (m, 24H, CH2 Ad), 1.31 (s, 18H, C(CH3)3),
0.81 (s, 18H, C(CH3)3) ppm; ESI-MS: m/z: 1572.4 [M + K]+
for C102H116KO12 (1572.8).
Synthesis and characterization
Diester 4. 1H NMR [CDCl3, 600 MHz, 303 K, main
conformer (B)]: d = 7.11 (s, 4H, ArH20), 7.06 (s, 4H,
ArH11), 6.51 (s, 4H, ArH32), 6.41–6.34 (m, 6H, ArH24,25),
5.19 (m, 4H, OCH215), 5.04 (m, 4H, OCH216), 4.60 (d, 4H,
J = 13.0 Hz, ArCH2Ar14,ax), 4.55 (d, 4H, J = 12.7 Hz,
ArCH2Ar17,ax), 4.43 (m, 8H, OCH228,29), 3.69 (s, 6H,
Diacid 7. A mixture of diester 5 (0.079 g, 0.05 mmol), THF
(6 mL) and aqueous nBu4NOH (20%, 0.26 mL, 0.20 mmol)
was stirred at reflux for 6 h. After cooling, the solvents were
removed under reduced pressure, and the residue was treated
with 5 M HCl. The solid formed was collected, washed
repeatedly with water, and dried to afford pure 7 as a white
1
OCH3 ), 3.29 (d, 4H, J = 13.0 Hz, ArCH2Ar14,eq), 3.27 (d,
4H, J = 12.7 Hz, ArCH2Ar17,eq), 2.24 (m, 4H, CHAd5), 2.07
(br s, 4H, CH2 Ad8), 1.93 (m, 16H, CH2 Ad4,7), 1.75 (m, 4H,
1
solid (0.073 g, 94%). M.p. 4 300 1C; H NMR [400 MHz,
CH2 Ad6), 1.32 (s, 18H, C(CH3)323), 0.82 (s, 18H, C(CH3)3
)
35
CDCl3 + CF3CO2D, 298 K, main conformer (B)]: d = 7.14 (s,
4H, ArH), 7.09 (s, 4H, ArH), 6.54 (s, 4H, ArH), 6.51 (br m,
6H, ArH), 5.31 (m, 4H, OCH2), 5.06 (m, 4H, OCH2), 4.67 (d,
4H, J = 13.0 Hz, ArCH2Ar), 4.56 (d, 4H, J = 12.7 Hz,
ArCH2Ar), 4.43 (br s, 8H, OCH2), 3.37 (d, 4H, J = 13.0 Hz,
ArCH2Ar), 3.29 (d, 4H, J = 12.7 Hz, ArCH2Ar), 2.29 (s, 4H,
CH2CO), 2.22 (br s, 4H, CHAd), 1.89 (m, 8H, CH2 Ad), 1.78 (br
s, 4H, CH2 Ad), 1.70 (m, 12H, CH2 Ad), 1.32 (s, 18H, C(CH3)3),
0.83 (s, 18H, C(CH3)3) ppm; ESI-MS: m/z: 1579.5
[M + H2O]+ for C104H120O12ꢃH2O (1579.9).
ppm; 13C NMR [CDCl3, 151 MHz, 273 K, main conformer
(B)]: d = 178.25 (2), 156.35 (13), 156.04 (18), 154.83 (27),
152.52 (30), 144.58 (21), 144.18 (33), 143.39 (10), 135.12 (12),
135.03 (19), 133.15 (26), 131.73 (31), 127.93 (25), 125.40 (20),
125.09 (11), 124.73 (32), 122.37 (24), 72.91 (15), 72.78 (16),
72.18 (28,29), 51.80 (1), 44.37 (8), 42.25 (7), 41.81 (3), 38.04 (4),
35.79 (9), 35.55 (6), 34.05 (22), 33.47 (34), 32.41 (14), 32.06
(17), 31.66 (23), 30.92 (35), 28.62 (5) ppm.
Diisocyanate 8. A mixture of diacid 6 (0.31 g, 0.20 mmol),
SOCl2 (7.0 mL), dry benzene (7 mL) and pyridine (0.016 mL,
0.20 mmol) was carefully refluxed for 2 h. Excess SOCl2 was
removed by repeated re-evaporation with dry benzene under
reduced pressure, and the residue was dissolved in dry acetone
and cooled (ice). A solution of NaN3 (0.26 g, 4.0 mmol) in
water (1.0 mL) was added dropwise and the resultant mixture
was stirred at cooling for 1 h and then kept in the fridge
overnight. Water was added and the products were repeatedly
extracted with CH2Cl2. Combined organic layers were washed
with water, dried with MgSO4, and evaporated under reduced
pressure. The residue was dissolved in dry benzene (16 mL)
and the solution was refluxed for 1.5 h. The solvent was
removed to give pure 8 as a white solid (0.27 g, 87%).
1H NMR [400 MHz, CDCl3, 298 K, main conformer (B)]:
d = 7.11 (s, 4H, ArH), 7.02 (s, 4H, ArH), 6.51 (s, 4H, ArH),
6.38 (br s, 6H, ArH), 5.19 (m, 4H, OCH2), 5.04 (m, 4H, OCH2),
4.61 (d, 4H, J = 12.4 Hz, ArCH2Ar), 4.55 (d, 4H, J = 12.7 Hz,
ArCH2Ar), 4.43 (br s, 8H, OCH2), 3.28 (d, 4H, J = 12.7 Hz,
ArCH2Ar), 3.27 (d, 4H, J = 12.4 Hz, ArCH2Ar), 2.30 (br s, 4H,
Diester 5. 1H NMR [CDCl3, 400 MHz, 303 K, main
conformer (B)]: d = 7.12 (s, 4H, ArH), 7.05 (s, 4H, ArH),
6.51 (s, 4H, ArH), 6.39 (br s, 6H, ArH), 5.19 (m, 4H, OCH2),
5.05 (m, 4H, OCH2), 4.60 (d, 4H, J = 13.1 Hz, ArCH2Ar),
c
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CHAd), 2.11–1.45 (m, 24H, CH2 Ad), 1.32 (s, 18H, C(CH3)3),
0.81 (s, 18H, C(CH3)3) ppm.
(m, 4H, OCH2), 4.59 (d, 4H, J = 13.1 Hz, ArCH2Ar), 4.55 (d,
4H, J = 12.6 Hz, ArCH2Ar), 4.43 (br s, 8H, OCH2), 3.28 (d,
4H, J = 13.1 Hz, ArCH2Ar), 3.26 (d, 4H, J = 12.6 Hz,
ArCH2Ar), 2.76 (m, 4H, NCH2), 2.16 (br s, 4H, CHAd),
Diamine dihydrochloride 9. A mixture of diisocyanate 8
(0.27 g, 0.18 mmol), 1,4-dioxane (5 mL) and 2 M HCl
(5 mL) was stirred at reflux for 8 h. After cooling the solid
formed was collected, washed with dry ether and dried to give
pure 9 as a white solid (0.26 g, 95%). M.p. 4300 1C; 1H NMR
[400 MHz, CD3OD, 298 K, main conformer (B)]: d = 7.19 (s,
4H, ArH), 7.17 (s, 4H, ArH), 6.65–6.32 (m, 10H, ArH), 5.30
(m, 4H, OCH2), 4.94 (m, 4H, OCH2), 4.71 (d, 4H, J = 12.3 Hz,
ArCH2Ar), 4.59 (d, 4H, J = 12.5 Hz, ArCH2Ar), 4.42 (br s, 8H,
OCH2), 3.37 (d, 4H, J = 12.5 Hz, ArCH2Ar), 3.28 (d, 4H,
J = 12.3 Hz, ArCH2Ar), 2.40 (br s, 4H, CHAd), 2.10–1.64 (m,
24H, CH2 Ad), 1.34 (s, 18H, C(CH3)3), 0.85 (s, 18H, C(CH3)3)
ppm; MALDI-MS: m/z: 1497.9 [M + Na]+ for C100H118Na-
N2O8 (1497.9).
1.93–1.16 (m, 28H, CH2CH2N + CH2 Ad), 1.31 (s, 18H,
ꢀ
C(CH3)3), 0.81 (s, 18H, C(CH3)3) ppm.
Bisurea 14. 1H NMR [600 MHz, CDCl3 + CF3CO2D, 303 K,
main conformer (B)]: d = 7.25 (d, 4H, J = 8.3 Hz, ArHTol), 7.15
(s, 4H, ArH), 7.12 (d, 4H, J = 8.3 Hz, ArHTol), 7.06 (s, 4H, ArH),
6.55 (s, 4H, ArH), 6.52 (d, 4H, J = 7.5 Hz, ArH), 6.42 (t, 2H,
J = 7.5 Hz, ArH), 5.23 (m, 4H, OCH2), 5.06 (m, 4H, OCH2), 4.66
(d, 4H, J = 13.1 Hz, ArCH2Ar), 4.57 (d, 4H, J = 12.6 Hz,
ArCH2Ar), 4.43 (br s, 8H, OCH2), 3.38 (m, 4H, NCH2), 3.34 (d,
4H, J = 13.1 Hz, ArCH2Ar), 3.29 (d, 4H, J = 12.6 Hz,
ArCH2Ar), 2.37 (s, 6H, CH3), 2.19 (br s, 4H, CHAd), 1.88 (m,
8H, CH2 Ad), 1.71 (m, 4H, CH2 Ad), 1.61 (br s, 4H, CH2 Ad), 1.53
(m, 8H, CH2 Ad), 1.41 (m, 4H, CH2CH2N), 1.34 (s, 18H, C(CH3)3),
ꢀ
Diol 10. To the stirred suspension of LiAlH4 (0.076 g,
2.0 mmol) in dry THF (10 mL) a solution of diester 4
(0.31 g, 0.20 mmol) in THF (10 mL) was added. The mixture
was stirred at reflux for 3 h, cooled, and then water (0.08 mL),
3 M NaOH (0.08 mL) and water (0.24 mL) were added
consecutively with stirring. The solid formed was filtered off,
washed with THF, and the filtrate evaporated. The residue
was washed with methanol to give pure 10 as a white solid
0.84 (s, 18H, C(CH3)3) ppm.
Bisurea 15. 1H NMR [600 MHz, CDCl3 + CF3CO2D, 303 K,
main conformer (B)]: d = 8.35–7.90 (m, 18H, ArHPyr), 7.13 (s,
4H, ArH), 7.00 (s, 4H, ArH), 6.54 (s, 4H, ArH), 6.48 (d, 4H,
J = 7.5 Hz, ArH), 6.37 (t, 2H, J = 7.5 Hz, ArH), 5.26 (m, 4H,
OCH2), 5.02 (m, 4H, OCH2), 4.62 (d, 4H, J = 12.8 Hz,
ArCH2Ar), 4.54 (d, 4H, J = 12.5 Hz, ArCH2Ar), 4.40 (br s,
8H, OCH2), 3.37 (m, 4H, NCH2), 3.30 (d, 4H, J = 12.8 Hz,
ArCH2Ar), 3.28 (d, 4H, J = 12.5 Hz, ArCH2Ar), 2.09 (br s, 4H,
CHAd), 1.79 (m, 8H, CH2 Ad), 1.62 (m, 4H, CH2 Ad), 1.52 (br s,
4H, CH2 Ad), 1.42 (m, 8H, CH2 Ad), 1.32 (s, 18H, C(CH3)3), 1.29
1
(0.25 g, 84%). M.p. 4300 1C; H NMR [400 MHz, CDCl3,
303 K, main conformer (B)]: d = 7.12 (s, 4H, ArH), 7.07 (s,
4H, ArH), 6.51 (s, 4H, ArH), 6.39 (m, 6H, ArH), 5.18 (m, 4H,
OCH2), 5.04 (m, 4H, OCH2), 4.60 (d, 4H, J = 12.9 Hz,
ArCH2Ar), 4.56 (d, 4H, J = 12.9 Hz, ArCH2Ar), 4.44 (br s,
(m, 4H, CH2CH2N), 0.83 (s, 18H, C(CH3)3) ppm.
ꢀ
8H, OCH2), 3.34 (s, 4H, CH2OH), 3.29 (d, 4H, J = 12.9 Hz,
ꢀ
ArCH2Ar), 3.27 (d, 4H, J = 12.9 Hz, ArCH2Ar), 2.23 (br s,
4H, CHAd), 1.96–1.26 (m, 24H, CH2 Ad), 1.32 (s, 18H,
C(CH3)3), 0.82 (s, 18H, C(CH3)3); ESI-MS: m/z: 1523.4
[M + H2O]+ for C102H120O10ꢃH2O (1523.9) ppm.
Dialdehyde 17. A mixture of calixarene 16 (0.81 g, 1.0 mmol),
HMTA (2.10 g, 15.0 mmol), and CF3CO2H (40 mL) was stirred
at reflux (oil bath at 85 1C) for 24 h. After cooling, 2 M HCl
(25 mL) was added and the products were extracted with CH2Cl2.
Combined organic layers were washed with water, dried with
MgSO4 and evaporated to dryness. The residue was re-precipi-
tated from CH2Cl2/hexane to give pure 17 as white solid (0.78 g,
Diol 11. 1H NMR [400 MHz, CDCl3, 303 K, main con-
former (B)]: d = 7.11 (s, 4H, ArH), 7.04 (s, 4H, ArH), 6.50 (s,
4H, ArH), 6.38 (m, 6H, ArH), 5.19 (m, 4H, OCH2), 5.03 (m,
4H, OCH2), 4.60 (d, 4H, J = 13.1 Hz, ArCH2Ar), 4.55 (d, 4H,
J = 12.6 Hz, ArCH2Ar), 4.43 (br s, 8H, OCH2), 3.78 (t, 4H,
1
90%). M.p. 4200 1C (decomp); H NMR (400 MHz, CDCl3,
298 K): d = 9.78 (s, 2H, CHO), 9.38 (d, 4H, J = 2.0 Hz, ArHBzl),
9.26 (t, 2H, J = 2.0 Hz, ArHBzl), 7.67 (s, 4H, ArH), 7.00 (br s,
6H, ArH), 5.86 (s, 2H, OH), 3.98 (d, 4H, J = 14.7 Hz,
ArCH2Ar), 3.74 (d, 4H, J = 14.7 Hz, ArCH2Ar) ppm; MAL-
DI-MS: m/z: 892.9 [M + Na]+ for C44H28NaN4O16 (892.1).
J = 7.5 Hz, CH2OH), 3.28 (d, 4H, J = 13.1 Hz, ArCH2Ar),
ꢀ
3.26 (d, 4H, J = 12.6 Hz, ArCH2Ar), 2.17 (br s, 4H, CHAd),
1.94–1.22 (m, 28H, CH2CH2OH + CH2 Ad), 1.32 (s, 18H,
ꢀ
C(CH3)3), 0.81 (s, 18H, C(CH3)3) ppm.
Bis-imidazophenanthrene calix[4]arene 18. A mixture of
calixarene 17 (0.87 g, 1.0 mmol), 9,10-phenanthrenequinone
(0.50 g, 2.4 mmol), ammonium acetate (3.85 g, 50 mmol), and
glacial acetic acid (50 mL) was heated with stirring at 120 1C
for 6 h. After cooling, the solid formed was collected, washed
with acetic acid, methanol, THF and dried to give pure 18 as a
light purple solid (0.32 g, 37%). M.p. 4 300 1C; 1H NMR
(400 MHz, DMSO[D6], 298 K): d = 8.91 (d, 4H, J = 8.8 Hz,
ArHPhen), 8.61 (d, 4H, J = 8.1 Hz, ArHPhen), 8.00 (s, 4H,
ArH), 7.81 (m, 4H, ArHPhen), 7.72 (m, 4H, ArHPhen), 7.17 (d,
4H, J = 7.6 Hz, ArH), 6.64 (t, 2H, J = 7.6 Hz, ArH), 4.17
(br s, 8H, ArCH2Ar) ppm; 13C NMR (100 MHz, DMSO[D6],
298 K): d = 159.67 br s, 153.12, 148.83, 131.23, 129.79 (CAr),
128.34 (CHAr), 127.87 (CAr), 127.48, 127.20, 126.34, 124.10,
Diphthalimide 12. 1H NMR [400 MHz, CDCl3, 303 K, main
conformer (B)]: d = 7.82 (m, 4H, ArHPht), 7.68 (m, 4H,
ArHPht), 7.10 (s, 4H, ArH), 7.04 (s, 4H, ArH), 6.50 (s, 4H,
ArH), 6.39 (m, 6H, ArH), 5.19 (m, 4H, OCH2), 5.04 (m, 4H,
OCH2), 4.60 (d, 4H, J = 13.1 Hz, ArCH2Ar), 4.56 (d, 4H, J =
12.5 Hz, ArCH2Ar), 4.43 (br s, 8H, OCH2), 3.76 (m, 4H,
NCH2), 3.28 (d, 4H, J = 13.1 Hz, ArCH2Ar), 3.26 (d, 4H, J =
12.5 Hz, ArCH2Ar), 2.20 (br s, 4H, CHAd), 1.97–1.35 (m, 28H,
CH2CH2N + CH2 Ad), 1.31 (s, 18H, C(CH3)3), 0.81 (s, 18H,
ꢀ
C(CH3)3) ppm.
Diamine 13. 1H NMR [400 MHz, CDCl3, 303 K, main
conformer (B)]: d = 7.11 (s, 4H, ArH), 7.04 (s, 4H, ArH), 6.50
(s, 4H, ArH), 6.39 (m, 6H, ArH), 5.18 (m, 4H, OCH2), 5.03
c
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122.12, 119.36 (CHAr), 114.51 (CAr), 32.31 (ArCH2Ar) ppm;
MALDI-MS: m/z: 856.9 [M]+ for C58H40N4O4 (856.3).
aggregation abilities of the calixarene derivatives by bringing the
core to nearly perfect C4v symmetry: (a) A. Arduini, A. Casnati,
L. Dodi, A. Pochini and R. Ungaro, Chem. Commun., 1990,
1597–1598; (b) A. Arduini, M. Fabbi, M. Mantovani, L. Mirone,
A. Pochini, A. Secchi and R. Ungaro, J. Org. Chem., 1995, 60,
Calixtube 20.
A mixture of calixarene 18 (0.057 g,
0.066 mmol), calixarene 19 (0.138 g, 0.070 mmol), anhydrous
K2CO3 (0.046 g, 0.333 mmol), and dry o-xylene (6.0 mL) was
stirred at reflux for 60 h. After cooling, the reaction mixture
was filtered, the solid was washed with CH2Cl2, and the
combined organic solutions were evaporated to dryness. The
residue was re-dissolved in CH2Cl2, washed with 10% aqueous
acetic acid, water, brine, and then concentrated. Purification
with column chromatography (SiO2, gradient from CH2Cl2 to
CH2Cl2/ethanol, 100 : 2) gave 20 as a gray solid (0.036 g, 25%).
1454–1457; (c) A. Arduini, V. Bohmer, L. Delmau, J.-F. Desreux,
¨
J.-F. Dozol, M. A. G. Carrera, B. Lambert, C. Musigmann,
A. Pochini, A. Shivanyuk and F. Ugozzoli, Chem.–Eur. J., 2000,
6, 2135–2144; (d) A. Arduini, E. Brindani, G. Giorgi, A. Pochini and
A. Secchi, J. Org. Chem., 2002, 67, 6188–6194; (e) G. Arena,
A. Contino, E. Longo, G. Spoto, A. Arduini, A. Pochini,
A. Secchi, C. Massera and F. Ugozzoli, New J. Chem., 2004, 28,
56–61; (f) M. O. Vysotsky, O. Mogck, Y. Rudzevich, A. Shivanyuk,
V. Bohmer, M. S. Brody, Y. L. Cho, D. M. Rudkevich and J. Rebek
¨
Jr., J. Org. Chem., 2004, 69, 6115–6120; (g) I. Vatsouro,
V. Rudzevich and V. Bohmer, Org. Lett., 2007, 9, 1375–1377.
¨
1
4 Calix[4]arene rigidification at cation complexation was first estab-
lished for calixarene tetraamides and tetraesters: (a) A. Arduini,
E. Ghidini, A. Pochini, R. Ungaro, G. Andreetti, G. Calestani and
F. Ugozzoli, J. Inclusion Phenom., 1988, 6, 119–134; (b) P. Guilbaud,
A. Varnek and G. Wipff, J. Am. Chem. Soc., 1993, 115, 8298–8312;
(c) A. Yamada, T. Murase, K. Kikukawa, T. Arimura and
S. Shinkai, J. Chem. Soc., Perkin Trans. 2, 1991, 793–797;
M.p. 4 300 1C; H NMR (600 MHz, CDCl3 + CF3CO2D,
303 K): d = 8.02 (d, 4H, J = 7.7 Hz, ArHPhen), 7.79 (d, 4H,
J = 7.7 Hz, ArHPhen), 7.41 (d, 4H, J = 7.7 Hz, ArHCalix H),
7.33 (s, 4H, ArHCalix Phen), 7.22 (t, 4H, J = 7.7 Hz, ArHPhen),
7.21 (t, 2H, J = 7.7 Hz, ArHCalix H), 7.14 (s, 4H, ArHCalix Ad),
7.10 (t, 4H, J = 7.7 Hz, ArHPhen), 6.55 (s, 4H, ArHCalix Ad),
5.27 (m, 4H, ArOCH2 Phen trans), 4.90 (m, 4H, ArOCH2 Ad trans),
4.74 (d, 4H, J = 14.0 Hz, ArCH2ArPhen ax), 4.67 (m, 4H,
ArOCH2 Phen gauche), 4.51 (d, 4H, J = 12.7 Hz, ArCH2ArAd ax),
4.47 (m, 4H, ArOCH2 Phen gauche), 3.67 (s, 6H, OCH3), 3.61 (s,
6H, OCH3), 3.52 (d, 4H, J = 14.0 Hz, ArCH2ArPhen eq), 3.34
(d, 4H, J = 12.7 Hz, ArCH2ArAd eq), 2.24 (s, 4H, CHAd), 2.06
(s, 4H, CHAd), 2.00–1.22 (m, 48H, CH2 Ad) ppm; 13C NMR
(100 MHz, CDCl3 + CF3CO2D, 298 K): d = 181.49, 181.28
(C = O), 160.10, 158.33, 156.12, 152.72, 144.14, 143.13 (CAr),
136.99, 136.17 (CAr Phen), 135.43, 131.93 (CAr), 129.84 (CHAr),
128.29 (CAr Phen), 127.59 (CHAr), 127.35, 127.12 (CHAr Phen),
125.28 (CHAr), 125.10 (CAr Phen), 124.66 (CHAr), 123.52,
123.16 (CHAr Phen), 120.26 (CHAr), 73.24, 72.57, 72.18, 72.13
(OCH2), 52.95, 52.85 (OCH3), 41.26, 43.79, 42.80, 42.41, 42.13
(CH2 Ad), 41.73 (CAd), 37.91, 37.74, 36.04 (CH2 Ad), 35.50,
35.45, 35.34 (CAd), 32.19 (ArCH2ArPhen), 31.91 (ArCH2ArAd),
28.72, 28.48 (CHAd) ppm; MALDI-MS: m/z: 2153.0 [M]+ for
(d) G. Horvat, V. Stilinovic, T. Hrenar, B. Kaitner, L. Frkanec
´
and V. Tomisic, Inorg. Chem., 2012, 51, 6264–6278. See also ref. 6–9.
5 For selected recent data on bis-calixarenes (except for calixtubes)
and calix(resorcin)arene dimers/oligomers see: (a) H. Dube and
J. Rebek Jr., Angew. Chem., Int. Ed., 2012, 51, 3207–3210;
(b) W. Hu, C. Blecking, M. Kralj, L. Suman, I. Piantanida and
T. Schrader, Chem.–Eur. J., 2012, 18, 3589–3597; (c) S. Slovak and
Y. Cohen, Chem.–Eur. J., 2012, 18, 8515–8520; (d) H. Gan and
B. C. Gibb, Chem. Commun., 2012, 48, 1656–1658; (e) H. Tang,
C. Santos de Oliveira, G. Sonntag, C. L. D. Gibb, B. C. Gibb and
C. Bohne, J. Am. Chem. Soc., 2012, 134, 5544–5547;
´
(f) S. Pasquale, S. Sattin, E. Escudero-Ada
Belmonte and J. de Mendoza, Nat. Commun., 2012, 3, 785;
(g) A. Lledo, S. Kamioka, A. C. Sather and J. Rebek Jr., Angew.
n, M. Martınez-
´ ´
´
Chem., Int. Ed., 2011, 50, 1299–1301; (h) Z. Lin, T. J. Emge and
R. Warmuth, Chem.–Eur. J., 2011, 17, 9395–9405; (i) L. Avram,
Y. Cohen and J. Rebek Jr., Chem. Commun., 2011, 47, 5368–5375;
(j) V. Rudzevich, O. Kasyan, A. Drapailo, M. Bolte,
D. Schollmeyer and V. Bohmer, Chem.–Asian J., 2010, 5,
¨
1347–1355; (k) Y. Rudzevich, V. Rudzevich and V. Bohmer,
¨
Chem.–Eur. J., 2010, 16, 4541–4549.
6 (a) P. Schmitt, P. D. Beer, M. G. B. Drew and P. D. Sheen, Angew.
Chem., Int. Ed. Engl., 1997, 36, 1840–1842; (b) S. E. Matthews,
P. Schmitt, V. Felix, M. G. B. Drew and P. D. Beer, J. Am. Chem.
Soc., 2002, 124, 1341–1353; (c) S. E. Matthews, V. Felix, M. G.
B. Drew and P. D. Beer, Org. Biomol. Chem., 2003, 1, 1232–1239.
7 S. E. Matthews, V. Felix, M. G. B. Drew and P. D. Beer, New J.
Chem., 2001, 25, 1355–1358.
C
142H136N4O16 (2153.0).
Acknowledgements
This work was supported by Russian Foundation for Basic
Research (projects 09-03-00971, 11-03-92006-HHC).
8 E. Khomich, M. Kashapov, I. Vatsouro, E. Shokova and
V. Kovalev, Org. Biomol. Chem., 2006, 4, 1555–1560.
9 K. Puchnin, P. Zaikin, D. Cheshkov, I. Vatsouro and V. Kovalev,
Chem.–Eur. J., 2012, 18, 10954–10968.
10 (a) D. N. Laikov, Chem. Phys. Lett., 1997, 281, 151–156;
(b) D. N. Laikov and Y. A. Ustynyuk, Russ. Chem. Bull., 2005,
54, 820–826 (Quantum-chemical program PRIRODA);
(c) J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.,
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11 (a) ORCA program package, release 2.9.0; (b) W. J. Hehre,
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References
1 For comprehensive reviews on calixarene synthesis, properties and
applications see: (a) V. Bohmer, Calixarenes, in The Chemistry of
Phenols, ed. Z. Rappoport, John Wiley & Sons, Ltd, Chichester,
2003, pp. 1369–1454; (b) C. D. Gutsche, Calixarenes, An Introduc-
tion, Royal Society of Chemistry, Cambridge, UK, 2008;
¨
(c) Calixarenes 2001, ed. Z. Asfari, V. Bohmer, J. M. Harrowfield
¨
and J. Vicens, Kluwer Academic Publishers, Dordrecht, 2001;
(d) Calixarenes in the Nanoworld, ed. J. Vicens, J. Harrowfield and
L. Backlouti, Springer, Dordrecht, 2007.
2 In the case of calix[4]arenes ‘flattened cone’ is equal to ‘pinched
cone’. For experimental evidences and the interconversion barrier
for the simplest case see: (a) A. Soi, W. Bauer, H. Mauser, C. Moll,
F. Hampel and A. Hirsch, J. Chem. Soc., Perkin Trans. 2, 1998,
1471–1478; (b) A. Ikeda and S. Shinkai, Chem. Rev., 1997, 97,
1713–1734, and references therein.
12 The calculated energy difference of 6 kcal molꢀ1 was at the level of
the accuracy of the method, and more precise calculations may be
performed, if needed, to ascribe the equilibrium quantitatively and
get the energy barrier of 7A 2 7B exchange.
13 K. A. See, F. R. Fronczek, W. H. Watson, R. P. Kashyap and
C. D. Gutsche, J. Org. Chem., 1991, 56, 7256–7268.
3 Probably, the most efficient rigidification of the calix[4]arene core
was achieved by the introduction of two short diethylene glycol
bridges onto a narrow rim, that affected drastically the binding and
c
New J. Chem.
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