Synthesis and photoisomerization of azocalixarenes with dendritic structures

Article abstract of DOI:10.1002/ejoc.200901394

The synthesis of dendricalixarenes 1 and 2 containing azo groups at the upper rim of a calix[4]- or calix[6]arene and the corresponding model compounds 3-5 are described. Because the kinetics of the trans to cis isomerization were too fast for accurate determination of the rate constant, this parameter was obtained from the reverse cis to trans process, which was studied in two different solvents by either a photoinduced or a thermal process. On the basis of the UV/Vis absorption measurements, the global rate constants (k) for calixarenes 1b, 1c, and 2b, obtained for the two different mechanisms (photoinduced and thermal processes), are of the same order of magnitude as that for models 3b and 4b. Compound 5b with an expanded cavity recognizes N-methylpyridinium guests. The 1:1 stoichiometry for the complex of 4-(4-dimethylaminostyryl)-N-methylpyridinium iodide (DASPMI) with 5b was confirmed by Job plot analysis. Fluorescence spectroscopic titrations gave K_a = 3.76×105 M^-1. As expected, receptors 1b, 1c, and 2b (with the azo groups in the trans configuration) did not lead to complexation of any of the substrates. Similarly, conversion into the respective cis isomers caused structural changes that were too large to allow efficient complexation.

Full text of DOI:10.1002/ejoc.200901394

FULL PAPER
DOI: 10.1002/ejoc.200901394
Synthesis and Photoisomerization of Azocalixarenes with Dendritic Structures
Hitos Galán,[a] Gunther Hennrich,[a] Javier de Mendoza,[b] and Pilar Prados*[a]
Keywords: Calixarenes / Isomerization / Host–guest systems / Dendrimers / Diazo compounds
The synthesis of dendricalixarenes 1 and 2 containing azo
groups at the upper rim of a calix[4]- or calix[6]arene and the
corresponding model compounds 3–5 are described. Because
the kinetics of the trans to cis isomerization were too fast for
accurate determination of the rate constant, this parameter
was obtained from the reverse cis to trans process, which was
studied in two different solvents by either a photoinduced
or a thermal process. On the basis of the UV/Vis absorption
measurements, the global rate constants (k) for calixarenes
1b, 1c, and 2b, obtained for the two different mechanisms
(photoinduced and thermal processes), are of the same order
of magnitude as that for models 3b and 4b. Compound 5b
with an expanded cavity recognizes N-methylpyridinium
guests. The 1:1 stoichiometry for the complex of 4-(4-dimeth-
ylaminostyryl)-N-methylpyridinium iodide (DASPMI) with
5b was confirmed by Job plot analysis. Fluorescence spectro-
scopic titrations gave Ka = 3.76ϫ105
M
–1. As expected, recep-
tors 1b, 1c, and 2b (with the azo groups in the trans configu-
ration) did not lead to complexation of any of the substrates.
Similarly, conversion into the respective cis isomers caused
structural changes that were too large to allow efficient com-
plexation.
per-structures resulting from the connection of calixarene
units through flexible spacers are wide open and not rigid
enough to control the overall molecular shape.
Introduction
Dendrimers are macromolecules characterized by both
molecular uniformity and the presence of internal voids,
which render them ideal endo receptors. Due to the flexibil-
ity of the constituting dendrons, substrates can be accom-
modated inside the dendrimer, but permanent, rigid cavities
are absent.[1] In order to reduce the conformational flexibil-
ity of dendritic systems, different strategies have been em-
ployed such as metal coordination in the interior of the den-
drimer[2] or introduction of photoisomerizable groups to in-
duce structural and conformational changes in the macro-
molecule.[3] If these functionalities are part of the dendrimer
core, the directionality of the dendrons and hence the over-
all morphology of the macromolecule are changed.[4] On
the other hand, if the functional groups are located at the
periphery of the branches, the accessibility of the interior
could be controlled by photoisomerization.[5]
We recently reported the use of bulky, rigid subunits as
dendrons connected by short, rigid spacers, which allows
the conformational mobility of the dendrimer to be con-
trolled, thus generating defined voids from the first genera-
tion.[10] Herein we describe the preparation of photoiso-
merizable dendrimers 1 and 2 based on calix[6]arene den-
drons connected through azo groups to the upper rim of a
calix[4]- or calix[6]arene core. The trans/cis photoisomeriza-
Another strategy is based on the use of rigid scaffolds as
the central core in order to control the orientation of the
dendrons. For this purpose, calix[4]arenes have been used as
building blocks.[6] The first example of a calixarene-based
dendrimer was described by Lhotak and Shinkai,[7] and sev-
eral examples have been reported thereafter,[8] in some cases
reaching a second-generation dendrimer.[9] However, the su-
[a] Departamento de Química Orgánica (C-I), Facultad de Cien-
cias, Universidad Autónoma de Madrid,
Carretera de Colmenar Viejo Km 15.3, 28049 Madrid, Spain
Fax: +34-91-4973966
E-mail: pilar.prados@uam.es
[b] Institute of Chemical Research of Catalonia (ICIQ),
Avda. Paisos Catalans 16, 43007 Tarragona, Spain
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200901394.
Figure 1. Compounds 1–5.
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H. Galán, G. Hennrich, J. de Mendoza, P. Prados
FULL PAPER
tion of these linkers should control the opening and closure
of the surface. Model compounds 3 and 4 carrying a simple
azo function were also synthesized to assess the effect of
the calix[6]arene dendron on the photoisomerization pro-
cess. On the other hand, derivatives 5 are proposed as mod-
els of the expanded core (Figure 1).
Results and Discussion
Synthesis
The formation of a diazonium salt from a calixarene has
only one precedent,[11] and reaction conditions for the azo
coupling of lipophilic calixarenes had to be developed. Azo
compounds 1a and 2a were obtained upon coupling of the
diazonium salt of amino compound 6,[10a] with core calix-
arenes 7[12] and 8.[13] 2,6-Dimethylphenol was selected as a
model compound to optimize the reaction conditions.
Reaction of 6 with sodium nitrite in a minimum amount
of water, followed by coupling with 2,6-dimethylphenol
gave 3a in 80% yield, together with insignificant amounts
of 9[14] (Scheme 1).
Scheme 2. Synthesis of dendricalixarenes 1a–c.
Scheme 3. Synthesis of azocalixarenes 2a and 2b.
Compounds 1a and 2a were O-alkylated in order to al-
low photoisomerization of the corresponding dendricalixar-
enes, a process that does not occur in O-unsubstituted free
phenols due to tautomerism. Depending on the reaction
time, compounds 1b and 1c were obtained from 1a, sodium
hydride, and iodopropane in DMF (Scheme 2). Methylation
of 2a in DMF in the presence of NaH gave compound 2b
in 77% yield (Scheme 3).
Model compound 4b was synthesized in two steps by azo
coupling of 3,5-dimethylamine and 2,6-dimethylphenol, fol-
lowed by propylation, in 61% overall yield. Similarly, 3b
was obtained in 80% yield from 3a (Scheme 4). The reac-
Scheme 1. Synthesis of azocalixarene 3a.
When calixarene 7[12] was submitted to similar reaction
conditions, compounds 1a and 10 (containing three azo
moieties) were obtained in 3%, and 26% yields, respectively.
Optimization of the reaction conditions (time and tempera-
ture) produced 1a in a 26% yield (Scheme 2).
In the case of 25,27-dihydroxy-26,28-dipropoxycalix[4]-
arene,[15] the desired azo derivative could only be detected
in trace amounts by mass spectrometry. We attribute this to
the lower pKa of 7 with respect to the corresponding O-
alkyl analogues. After the initial azo coupling, the following
nucleophilic substitutions are self-accelerated as described
by Shinkai et al. for reactions of calix[4]arenes with diazo-
nium salts.[16] The reaction of calix[6]arene 8[13] and the di-
azonium salt of amine 6 gives a complex mixture of prod-
ucts from which only the di- and triazo compounds 11 and
2a could be isolated in 17 and 9% yield, respectively
(Scheme 3).
Scheme 4. Synthesis of model compounds 4 and 5.
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Synthesis and Photoisomerization of Azocalixarenes with Dendritic Structures
tion of 3,5-dimethylphenyldiazonium chloride with 7[12]
gave 75% of 5a, which was subsequently converted into 5b
by reaction with iodopropane in the presence of K2CO3
(82%, Scheme 4).
Conformational Analysis of the Azocalixarenes
The new azocalixarenes were studied by 1H and 13C
NMR spectroscopy. At room temperature in CDCl3, the
(ArCH2Ar) methylene carbon signals of the core calixarene
appeared at δ = 31.9 ppm in 1a, indicative of a cone confor-
mation.[17] In variable-temperature NMR experiments
(403–183 K) the signal slightly shifted to 32.4 ppm at
263 K, whereas the methylene protons displayed an AX sys-
tem below 278 K. These results indicate that the cone con-
formation is stable below 263 K and the system is increas-
ingly flexible at higher temperatures (cone-cone inversion).
According to their symmetry, 1b and 1c displayed one and
two AX systems, respectively. This pattern was maintained
over the whole temperature range studied (403–188 K), sug-
gesting a rigid conformation of the core. The chemical shifts
for the methylene carbon atoms (1b: 32.3 ppm, 1c:
32.5 ppm) confirm a rigid pinched cone conformation. On
the other hand, azocalixarenes 2a and 2b, based on the
calix[6]arene core, displayed the expected cone-cone inver-
sion.[13] Furthermore, the aromatic proton signals ortho to
the azo groups were located around 8.00 and 7.40 ppm, typ-
ical for the trans isomers. However, HPLC analysis of 1b
revealed the presence of two peaks with the same molecular
mass as the major components, which could be assigned as
two different conformational isomers in a ratio of 1:4.
Figure 3. (a) UV/Vis spectra of 1b, 1c, 2b, 4b, and 3b in toluene;
Photoisomerization of the Azo Derivatives
(b) UV/Vis spectra of 1b, 1c, 2b, 4b, and 3b after irradiation at
350 nm.
Comparison of the UV/Vis spectra of 1–5 with analo-
gous nitro derivative 12[10a] revealed that the characteristic
azo bands (300–500 nm) do not interfere with the absorp-
tions corresponding to the calixarene cores or dendrons
(Figure 2, see Supporting Information).
Simultaneously, a decrease in the intensity of the aro-
matic protons ortho to the azo moiety was observed in the
1H NMR spectra, accompanied by the appearance of a new
set of signals around 6.8 ppm. The maximum percentage of
the cis isomer could be quantified by NMR spectroscopy.
In deuterated benzene, 84% of cis isomer of 3b was ob-
tained, although the initial isomer distribution (90% trans,
Table 1. Percentage of cis isomer after irradiation at 350 nm. 1H
NMR spectroscopic data.
Solvent
% cis
% trans Recovered
Figure 2. Compound 12.
Before
After
Stored in
darkness
Stored in
daylight
irradiation irradiation
The isomerization experiments were carried out in a pho-
toreactor by using toluene (1b, 1c, 2b) or a chloroform/tolu-
ene mixture (3b, 4b) as solvents for 15 min.[18] Upon irradia-
tion the hypo- and hypsochromic shifts of the π–π* transi-
tion, initially at 350 nm, were detected (Figure 3).
4b
3b
2b
C6D6
CDCl3
C6D6
CDCl3
C6D6
10
0
10
0–3
3
95
90
84
82
92
40
53
69
100
–
85
100
82
100
–
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H. Galán, G. Hennrich, J. de Mendoza, P. Prados
Table 2. Values of kv(cisǞtrans) for 4b and 3b calculated on the basis of UV/Vis and H NMR spectroscopic data.
FULL PAPER
1
Solvent
λ (nm)
Concentration ()
kv(cisǞtrans) (s–1)
R2
UV/Vis
daylight
darkness
4b
3b
4b
3b
4b
3b
toluene
CHCl3
toluene
CHCl3
toluene
CHCl3
toluene
CHCl3
C6D6
343
348
345
344
343
348
345
344
ArCH3
ArCH3
ArH
ArCH3
8.0ϫ10–5
1.0ϫ10–4
8.0ϫ10–5
1.0ϫ10–4
8.0ϫ10–5
1.0ϫ10–4
8.0ϫ10–5
1.0ϫ10–4
1.8ϫ10–2
1.9ϫ10–2
1.8ϫ10–2
1.8ϫ10–2
1.29ϫ10–3
1.25ϫ10–3
1.74ϫ10–3
1.65ϫ10–3
5.60ϫ10–5
–
0.997
0.997
0.998
0.992
0.996
–
0.992
0.992
0.999
0.999
0.999
0.999
4.20ϫ10–5
4.97ϫ10–5
1.56ϫ10–5
1.27ϫ10–5
2.10ϫ10–5
1.20ϫ10–4
NMR[a] darkness
CDCl3
C6D6
[b]
CDCl3
[a] 500 MHz, 298 K. [b] The only case where the equilibrium is completely recovered to the trans isomer in the dark.
10% cis) was not completely recovered after allowing the and 1c, owing to the nonisomerizable azo functions in the
sample to relax in the dark, but a final 7:3 ratio (69% trans, molecules. A global first-order process could be assumed
31% cis) was measured instead (Table 1).
for the cis Ǟ trans transformation.[3b] On the basis of the
Similar results were obtained for 4b in deuterated benz- UV/Vis absorption measurements, the global rate constants
ene, reaching a maximum of 60% of the cis isomer (40% k were calculated for the two different mechanisms, which
trans). Upon exposure of the solutions of 4b and 3b to day- were of the same order of magnitude as the values found
light, 85 and 82% of the trans isomer were regenerated, for 4b and 3b (Table 3).
respectively, and these values are lower than the initial ra-
tios. Isomerization took place to a minor extent when deu-
terated chloroform was used as solvent (Table 1).
Table 3. Values of kv(cisǞtrans) for 2b, 1b, and 1c [2ϫ10–5 –1] calcu-
lated on the basis of UV/Vis spectroscopic data (298 K, toluene).[23]
λ (nm)
kv(cisǞtrans) (s–1)
R2
In the cases of 1b and 1c, only partial disappearance of
the signals corresponding to the trans isomer was detected
as a consequence of the presence of the phenol units, which
do not isomerize. As a consequence, the resulting spectra
were even more complex and did not allow an accurate inte-
gration of the signals of the respective isomers. In deuter-
ated benzene, 3% of the cis isomer was present for com-
pound 2b before irradiation, which turned into 92% after
irradiation. For all three compounds, the progress of the
conformational changes over time was visualized by moni-
toring the symmetry changes in the core. In none of the
cases studied were the initial amounts of the trans isomer
fully recovered when the relaxation process was determined
by a thermal process.
Daylight
Darkness
1b
1c
2b
1b
1c
2b
340
338
346
340
338
346
1.25ϫ10–3
1.50ϫ10–3
1.35ϫ10–3
2.60ϫ10–5
3.28ϫ10–5
2.60ϫ10–5
0.992
0.992
0.997
0.992
0.998
0.997
To assess the efficiency of the opening and closing of the
cavity of these compounds, the photoisomerization of 2b
and 1b in chloroform was determined five times consecu-
tively, confirming that in all cases the initial state is reached
upon exposure to daylight.
Kinetics of the trans/cis isomerization were first order.
Although the trans Ǟ cis process was too fast for a rate
constant to be measured, this parameter can be obtained in
Complexation Studies of 1b, 1c, 2b, and 5b
Complexation studies were evaluated by UV/Vis, fluores-
the reverse process. This was studied in two different sol- cence, and 1H NMR spectroscopy. As substrates, 4-
vents by either a photoinduced (daylight, UV/Vis spec- (4-dimethylaminostyryl)-N-methylpyridinium
iodide
troscopy) or a thermal process (dark, UV/Vis and 1H NMR (DASPMI), with a rod-like geometry, and some roughly
spectroscopy).[19] In the case of model compounds 4b and spherical N-methylpyridinium halides of different sizes to
3b, similar rate constants k were measured in both solvents; fill the voids remote from the core were selected. Also, p-
the value of k was approximately two orders of magnitude fluorotoluene was used to determine whether or not a posi-
lower for the thermal process than for the photoinduced tive charge is necessary in the guest molecule. Additionally,
process. The values obtained by 1H NMR spectroscopy 19F NMR spectroscopy can be employed in this case, avoid-
(dark, [D6]benzene,[20] CDCl3) were comparable to those ing the overlap of signals of the receptor and the substrate
obtained by UV/Vis (Table 2).
(Figure 4).
The same experiments as those for the model compounds
Using model compound 5b (UV/Vis and NMR spec-
were performed on azodendrimers 1b, 1c, and 2b.[21] Irradi- troscopy, CD2Cl2) proved that the ammonium cation is
ation of 2b in toluene resulted in hypo- and hypsochromic complexed in the cavity of the calix[4]arene substituted by
shifts (48 nm) of the π–π* transition band as for analogue electron-withdrawing groups. From the blueshift and hyp-
3b (45 nm), indicating the isomerization of the three N=N sochromism observed in the absorption spectra we conclude
bonds.[22] Minor effects (27 and 36 nm) were found for 1b that complexation is occurring, even though the overlap of
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Synthesis and Photoisomerization of Azocalixarenes with Dendritic Structures
basis of the results obtained for 5b, a dendricalixarene re-
ceptor with only one photoisomerizable group might be a
promising candidate for photocontrolled complexation.
Experimental Section
General Procedure for the Synthesis of Azo Derivatives: A solution
of amine 6[10a] or 3,5-dimethylaniline in THF (25.0 m) and 35%
HCl (3 drops for each 0.021 mmol of amine) was stirred for 30 min
at room temperature. Next, the mixture was cooled to 2 °C and
then it was added to a solution of aqueous sodium nitrite
(2.3 equiv., 0.7 ). The mixture was stirred for 30–40 min at 2–5 °C
to give the corresponding diazonium salt, which was maintained at
2 °C and used immediately without purification. A suspension of
the corresponding phenol or calixarene and NaOAc in DMF/
MeOH was stirred for some time at room temperature. The mixture
was cooled to 2 °C and a suspension of diazonium salt of amine 6
was added slowly. This mixture was stirred for some time under the
same conditions, and finally at room temperature; 25% HCl was
added until acidic pH, and then the mixture was heated. The re-
Figure 4. Guests chosen for recognition.
the substrate and receptor (Ͼ3 equiv.) bands hampers cal-
culation of a reliable association constant (Ka). From fluo-
rescence spectroscopic measurements, Ka was determined as
3.76ϫ105 –1, and a 1:1 stoichiometry was confirmed by
Job plot analysis.
The 1H NMR spectrum of complex 5b-DASPMI in
CD2Cl2 clearly shows a high-field shift of the methyl pro-
tons of the pyridinium guest (∆δ = 0.10 ppm) as well as the sulting red solid was filtered and purified.
aromatic protons of the calix[4]arene scaffold ortho to the
Compound 1a: Prepared by the general procedure described above
from calix[4]arene 7[12] (24.6 mg, 0.058 mmol) and NaOAc
(900.0 mg, 11.0 mmol) in DMF/MeOH (3:2, 5.1 mL). The mixture
was stirred for 30 min. A first portion of the diazonium salt of
amine 6 (150.0 mg) was added, and the mixture was stirred for 2 h;
a second portion of the diazonium salt of amine 6 (150.0 mg) re-
cently synthesized was added, and the mixture was stirred for
5.50 h. Finally, the last portion was added, and the mixture was
stirred for 14 h until it reached 17 °C, and then it was stirred at
room temperature for 30 min. HCl (3 ) was added, and the solu-
tion was heated at 60 °C for 1 h. Purification: precipitation in
MeOH/H2O, four consecutive size-exclusion columns (GPC, used
Bio-Beads SX-1, toluene), and finally trituration in methanol to
give 1a as an orange solid (78.5 mg, 26%) and byproduct 10
(21.1 mg, 9%). Data for 1a: M.p. Ͼ200 °C (decomp). 1H NMR
(500 MHz, CD2Cl2, 263 K, ROESY): δ = 10.48 (s, 4 H, ArOH),
7.84 (s, 8 H, ArHazo), 7.69 (s, 8 H, ArHazo), 7.30 (s, 16 H, ArH),
6.81 (s, 16 H, ArH), 6.76 (s, 16 H, ArH), 5.30 (s, 4 H, ArHxylylenyl),
4.42 [d, 2J(H,H) = 14.5 Hz, 4 H, ArCH2Arcalix[4]arene], 4.35 [d,
2J(H,H) = 15.4 Hz, 16 H, ArCH2Arcalix[6]arene], 4.23–4.12 (m, 24 H,
ArOCH2 and ArCH2Arcalix[6]arene), 3.90 [d, 2J(H,H) = 14.8 Hz, 4
H, ArCH2Arcalix[4]arene], 3.48–3.38 (m, 32 H, OCH2CH3), 3.32 [d,
azo moiety of 5b, which confirms the inclusion of the guest
(i.e., the pyridinium-CH3 function) in the calixarene cavity.
To evaluate how the photoisomerization of the azo substit-
uents affects the formation of the complex formed, the lat-
ter was irradiated and subsequently left at daylight.[24] UV/
1
Vis and H NMR spectroscopy revealed the changes ex-
pected for the isomerization of the azocalixarene host.
Minor changes in the absorption spectrum of the substrate
were insignificant, and only a slight upfield shift of the N-
methyl protons of the pyridinium guest was found in the
1H NMR spectrum, accompanied with general signal
broadening. Upon initial irradiation of 5b, followed by ad-
dition of the substrate to the azocalixarene host (cis isomer)
1
in the dark, formation of the complex was observed by H
NMR spectroscopy (∆δMe = 0.07 ppm), although no band
broadening occurred under these conditions.
The same effects were observed by 1H NMR spec-
troscopy for the rest of the N-methylpyridinium substrates.
However, no evidence for the complexation of 4-fluorotolu-
ene could be found by 19F NMR spectroscopy, verifying the
importance of the positive charge for the substrate to be
complexed.
2
2J(H,H) = 15.8 Hz, 16 H, ArCH2Arcalix[6]arene], 3.10 [d, J(H,H) =
14.2 Hz, 8 H, ArCH2Arcalix[6]arene], 1.36 [s, 72 H, C(CH3)3], 0.92–
0.80 [m, 192 H, ArOCH2CH3 and C(CH3)3] ppm. 13C NMR
(125 MHz, CD2Cl2, 263 K, DEPT, HSQC): δ = 152.6, 152.5, 152.0,
151.7, 148.2, 146.1, 145.2, 139.6, 133.5, 133.2, 132.9 (Ar), 128.6,
128.4, 125.3, 124.9, 124.3, 117.7 (ArH), 71.5 (ArOCH2), 69.1
(ArOCH2CH3), 34.5, 34.2 [C(CH3)3], 32.4 (ArCH2Arcalix[4]arene),
31.8, 31.2 [C(CH3)3], 30.1, 28.7 (ArCH2Arcalix[6]arene), 15.7
(ArOCH2CH3) ppm. UV/Vis (ArN=NAr, CH2Cl2, 10–5 ): λ (ε,
mol–1 dm3 cm–1) 340 (62589), 430 (4258) nm. MS (MALDI-TOF,
As expected, the use of receptors 1b, 1c, and 2b as hosts
(with the azo groups in the trans configuration) did not lead
to complexation of any of the substrates. Also, complex-
ation was not observed upon conversion into the respective
cis forms by photoisomerization.
dithranol
+ NaI): m/z (%) = 5301.4 (100) [M +
Na]+.
Conclusions
C356H440N8O28·CH2Cl2 (5364.27): calcd. C 79.93, H 8.31, N 2.09;
found C 79.63, H 8.37, N 2.23. Data for 10: M.p. 218 °C (decomp).
1H NMR (500 MHz, CDCl3, 298 K): δ = 10.46 (br. s, 4 H, ArOH),
7.91 (s, 2 H, ArHazo), 7.87 [d, 3J(H,H) = 2.0 Hz, 2 H, ArHazo], 7.83
Despite the increased accessibility of the inner spaces of
the dendrimers (1b, 1c, and 2b), the structural changes
caused by photoisomerization are too large, which thus pre-
vents efficient complexation, or in any case, makes it diffi-
cult. Nevertheless, model compound 5b gives a stable com-
3
(br. s, 2 H, ArHazo), 7.81 [d, J(H,H) = 1.9 Hz, 2 H, ArHazo], 7.79
(br. s, 4 H, ArHazo), 7.37 (br. s, 13 H, ArH), 7.28 [d, 3J(H,H) =
7.9 Hz, 2 H, ArH], 6.91–6.76 (m, 24 H, ArH), 5.50 (s, 1 H,
plex with DASPMI with a large binding constant. On the ArHxylylenyl), 5.46 (s, 2 H, ArHxylylenyl), 4.56–4.37 (m, 16 H, Ar-
Eur. J. Org. Chem. 2010, 1249–1257
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H. Galán, G. Hennrich, J. de Mendoza, P. Prados
CH2Ar), 4.38–4.22 (m, 18 H, ArOCH2, and ArCH2Arcalix[6]arene), 125.9, 125.8, 125.6, 125.1, 124.8, 124.6, 124.1, 117.4, 117.2 (ArH),
FULL PAPER
3.91 (br. s, 2 H, ArCH2Arcalix[4]arene), 3.75 (br. s, 2 H, ArCH2Ar),
3.68–3.54 (m, 24 H, ArOCH2CH3), 3.44 (m, 12 H, ArCH2Ar),
71.4 (ArOCH2), 68.8 (ArOCH2CH3), 61.9, 61.5 (OCH3), 34.9,
34.34, 34.26, 34.0 [C(CH3)3], 31.7, 31.34, 31.27 [C(CH3)3], 31.9,
3.28–3.14 (m, 6 H, ArCH2Ar), 1.47 [s, 54 H, C(CH3)3], 1.04–0.96 31.2, 30.9, 30.6, 30.2, 29.7, 29.4, 28.7 (ArCH2Ar), 15.6, 14.1, 13.8
[m, 144 H, ArOCH2CH3 and C(CH3)3] ppm. 13C NMR (125 MHz, (ArOCH2CH3) ppm. MS (MALDI-TOF, dithranol + NaI): m/z
CDCl3, 298 K, DEPT): δ = 152.5, 152.3, 151.8, 145.9, 144.9, 139.4,
133.4, 132.9, 132.8 (Ar), 129.6, 128.0, 125.0, 124.1, 117.4 (ArH),
71.3 (ArOCH2), 68.7 (ArOCH2CH3), 34.3, 34.0 [C(CH3)3], 31.8,
31.7, 31.28, 31.26 [C(CH3)3], 30.2, 29.7, 29.4, 28.7 (ArCH2Ar), 15.6
(ArOCH2CH3) ppm. MS (MADI-TOF, dithranol + NaI): m/z (%)
(%) = 3297.0 (90) [M +Na]+, 3341.9 (50) [M + 3Na – 2 H]+,
3275.0 (20) [M
221H274N4O18·0.5CHCl3 (3334.25): calcd. C 79.79, H 8.30, N 1.68;
found C 79.76, H 8.60, N 1.77.
+ –
H]+, 2074.3 (100) [M C82H105NO6]+.
C
5,11,17,23,29,35-Hexa-tert-butyl-37,38,40,41-tetraethyloxy-39,42-
{5-[(4-hydroxy-3,5-dimethyl)phenylazo]-1,3-phenylenbis(methyl-
enoxy)}calix[6]arene (3a): Prepared by the general procedure de-
scribed above from 2,6-dimethylphenol (3.0 mg, 0.025 mmol) and
NaOAc (404.4 mg, 4.930 mmol) in DMF/MeOH (8:5, 1.3 mL). The
mixture was stirred for 10 min. The diazonium salt of amine 6
(25.0 mg, 0.021 mmol) was added. Coupling: 40 min at 0–5 °C and
30 min at room temperature; after HCl (3 ) addition, reflux for
1 h. Purification: recrystallization in EtOH/CHCl3 (22.4 mg, 80%).
M.p. Ͼ240 °C (decomp.). 1H NMR (500 MHz, CDCl3, 298 K): δ
= 7.78 (s, 2 H, ArHazo), 7.65 (s, 2 H, ArHazo), 7.37 (s, 4 H,
ArHcalix[6]arene), 6.89 (s, 4 H, ArHcalix[6]arene), 6.84 (s, 4 H,
ArHcalix[6]arene), 5.44 (s, 1 H, ArHxylylenyl), 4.93 (s, 1 H, ArOH), 4.50
[d, 2J(H,H) = 15.5 Hz, 4 H, ArCH2Ar], 4.34 [d, 2J(H,H) = 14.3 Hz,
2 H, ArCH2Ar], 4.28 (s, 4 H, ArOCH2), 3.64–3.57 (m, 8 H, Ar-
OCH2), 3.45 [d, 2J(H,H) = 15.5 Hz, 4 H, ArCH2Ar], 3.24 [d,
2J(H,H) = 14.3 Hz, 2 H, ArCH2Ar], 2.35 (s, 6 H, ArCH3), 1.46 [s,
18 H, C(CH3)3], 1.04 [t, 3J(H,H) = 6.9 Hz, 12 H, ArOCH2CH3],
0.92 [s, 36 H, C(CH3)3] ppm. 13C NMR (125 MHz, CDCl3, 298 K,
DEPT): δ = 152.3, 145.9, 145.0, 138.2, 133.4, 132.9, 132.8 (Ar),
128.1, 125.0, 124.1, 123.5, 122.4, 117.4 (ArH), 71.7 (ArOCH2Ar),
68.7 (ArOCH2CH3), 34.3, 34.0 [C(CH3)3], 31.7, 31.3 [C(CH3)3],
30.9, 29.7 (ArCH2Ar), 16.0 (ArCH3), 15.5 (ArOCH2CH3) ppm.
UV/Vis (ArN=NAr, CH2Cl2, 10–5 ): λ (ε, mol–1 dm3 cm–1) = 353
(17715), 437 (1151) nm. MS (MALDI-TOF, dithranol + NaI): m/z
=
C
4088.7 (25) [M
+
Na]+. HRMS (MALDI): calcd. for
274H336N6O22Na [M + Na]+ 4088.536; found 4088.536.
Compound 2a: Prepared by the general procedure described above
from calix[6]arene 8[13] (22.0 mg, 0.026 mmol) and NaOAc (300 mg,
3.7 mmol) in DMF/MeOH (8:5, 2.6 mL). The mixture was stirred
for 30 min. A first portion of the diazonium salt of amine 6
(100.0 mg) was added, and the mixture was stirred for 22 h; a sec-
ond portion of the diazonium salt of amine 6 (50.0 mg) recently
synthesized was added, and the mixture was stirred for 24 h until
it reached 17 °C. HCl (3 ) was added, and the mixture was heated
at 60 °C for 40 min. Purification: precipitation in MeOH/H2O, 3–
4 consecutive size-exclusion columns (GPC, Bio-Beads SX-1, tolu-
ene), preparative TLC (silica gel; hexane/THF, 4:1Ǟ3:1), and fi-
nally trituration in methanol to give 2a as a yellow solid (10.0 mg,
9%) and 11 (14.6 mg, 17%). Data for 2a: M.p. Ͼ220 °C (decomp.).
1H NMR (500 MHz, CDCl3, 298 K, ROESY): δ = 7.79 (s, 6 H,
ArHazocore), 7.77 (s, 6 H, ArHazodendron), 7.75 (s, 3 H, ArOH), 7.36
(s, 12 H, ArHdendron), 7.10 (s, 6 H, ArHcore), 6.89 (s, 12 H,
ArHdendron), 6.84 (s, 12 H, ArHdendron), 5.46 (s, 3 H, ArHxylylenyl),
2
2
4.50 [d, J(H,H) = 15.4 Hz, 12 H, ArCH2Ar], 4.35 [d, J(H,H) =
13.8 Hz, 6 H, ArCH2Ar], 4.28 (s, 12 H, ArOCH2), 4.02 (br. s, 12
H, ArCH2Arcore), 3.65 (s, 9 H, OCH3), 3.64–3.57 (m, 24 H,
2
ArOCH2CH3), 3.45 [d, J(H,H) = 15.5 Hz, 12 H, ArCH2Ar], 3.24
[d, 2J(H,H) = 14.1 Hz, 6 H, ArCH2Ar], 1.46 [s, 54 H, C(CH3)3],
1.15 [s, 27 H, C(CH3)3core], 1.04 [t, 3J(H,H) = 6.9 Hz, 36 H, Ar-
OCH2CH3], 0.92 [s, 108 H, C(CH3)3] ppm. 13C NMR (125 MHz,
CDCl3, 298 K, DEPT, HSQC): δ = 155.5, 152.6, 152.3, 152.0,
147.8, 146.3, 146.0, 145.0, 139.3, 133.5, 132.9, 132.8, 132.0 (Ar),
128.1 (ArH), 127.5 (Ar), 126.0, 125.1, 124.5, 124.3, 124.1, 117.4
(ArH), 71.5 (ArOCH2), 68.8 (ArOCH2CH3), 61.6 (ArOCH3), 34.4,
34.3, 34.0 [C(CH3)3], 31.7, 31.4, 31.3 [C(CH3)3], 31.1 (ArCH2Ar-
core), 30.2, 28.7 (ArCH2Ar), 15.6 (ArOCH2CH3) ppm. UV/Vis
(ArN=NAr, CH2Cl2, 10–5 ): λ (ε, mol–1 dm3 cm–1) = 360 (58539),
445 (3493) nm. MS (MALDI-TOF, dithranol + NaI): m/z (%) =
4510.8 (96) [M + Na]+, 4488.9 (15) [M + H]+, 3288.1 (62) [M –
(%) = 1358. 9 (100) [M + Na]+ , 1335. 9 (34) [M + H]+
.
C90H114N2O7·0.5(EtOH·CHCl3) (1418.85): calcd. C 77.47, H 8.35,
N 1.97; found C 77.27, H 8.85, N 1.78.
4-Hydroxy-3,3Ј,5,5Ј-tetramethyl Azobenzene (4a): Prepared by the
general procedure described above from 2,6-dimethyphenol
(252.0 mg, 2.063 mmol) and NaOAc (700.0 mg, 8.533 mmol) in
DMF/MeOH (8:5, 5.1 mL). The mixture was stirred for 10 min.
The diazonium salt of 3,5-dimethylaniline (300.0 mg, 2.475 mmol)
in DMF (3 mL) was added. Coupling: 5.50 h at 2–5 °C and 30 min
at room temperature; after HCl (3 ) addition, reflux for 1 h. Puri-
fication: trituration in hexane to give 4a as an orange solid
(342.1 mg, 70%). M.p. 136–139 °C. 1H NMR (300 MHz, CDCl3,
298 K): δ = 7.60 (s, 2 H, ArH), 7.49 (s, 2 H, ArH), 7.08 (s, 1 H,
ArH), 4.97 (s, 1 H, ArOH), 2.41 (s, 6 H, ArCH3), 2.34 (s, 6 H,
ArCH3) ppm. 13C NMR (75 MHz, CDCl3, 298 K, DEPT): δ =
154.9, 153.0, 146.4, 138.7 (Ar), 132.0, 123.6 (ArH), 123.5 (Ar),
120.3 (ArH), 21.3, 16.0 (CH3) ppm. UV/Vis (ArN=NAr, CH2Cl2,
10–5 ): λ (ε, mol–1 dm3 cm–1) = 352 (21281), 445 (797) nm. MS
C82H105NO6+H]+, 1225.8 (62) [C82H105NO6
+ 2H +
Na]+.
C303H378N6O24·CHCl3·2hexane (4780.00): calcd. C 79.40, H 8.58,
N 1.76; found C 79.28, H 8.97, N 1.68. Data for 11: M.p. Ͼ180 °C
1
(decomp.). H NMR (500 MHz, CDCl3, 298 K): δ = 8.93 (s, 1 H,
ArOH), 8.13 (s, 2 H, ArOH), 7.88–7.80 (m, 8 H, ArH), 7.44–7.36
(m, 10 H, ArHdendron and ArHcore), 7.13–7.00 (m, 7 H, ArHcore),
6.94 (s, 8 H, ArHdendron), 6.89 (s, 8 H, ArHdendron), 5.50 (s, 2 H,
ArHxylylenyl), 4.55 [d, 2J(H,H) = 15.4 Hz, 8 H, ArCH2Ardendron],
4.43–4.27 (m, 12 H, ArCH2Ardendron and ArOCH2), 4.08 (br. s, 6
H, ArCH2Arcore), 3.99–3.98 (m, 6 H, ArCH2Arcore), 3.83 (s, 3 H,
ArOCH3), 3.72–3.46 (m, 30 H, ArOCH3, ArCH2Ardendron and Ar-
OCH2CH3), 3.29 [d, 2J(H,H) = 14.2 Hz, 4 H, ArCH2Ardendron],
( FA + , m - N B A ) : m / z ( % ) = 2 5 5 . 2 ( 1 0 0 ) [ M + H ] +
.
C16H18N2O·0.25H2O (258.83): calcd. C 74.25, H 7.20, N 10.82;
found C 74.23, H 7.11, N 10.69.
25,26,27,28-Tetrahydroxy-5,11,17,23-tetra-(3,5-dimethylphenylazo)-
1.51 {s, 36 H, [C(CH3)3]}, 1.20, 1.13 [s, 27 H, C(CH3)3], 1.09 [t, calix[4]arene (5a): Prepared by the general procedure described
3J(H,H) = 6.9 Hz, 24 H, ArOCH2CH3], 0.97 [s, 72 H, C(CH3)3] above from calix[4]arene 7[12] (233.5 mg, 0.550 mmol) and NaOAc
ppm. 13C NMR (125 MHz, CDCl3, 298 K, DEPT): δ = 155.3,
152.6, 152.3, 152.1, 151.9, 148.2, 148.0, 146.4, 146.0, 145.0, 140.4,
(900.0 mg, 11.0 mmol) in DMF/MeOH (8:5, 45.6 mL). The mixture
was stirred for 20 min. The diazonium salt of 3,5-dimetylaniline
139.4, 135.8, 133.4, 132.9, 132.7, 132.3, 131.7, 130.94, 128.3, (one portion of 300.0 mg, 2.5 mmol) was added. Coupling: 3.50 h
128.15, 128.08, 127.4, 127.1 (Ar), 130.90, 128.9, 128.1, 126.9, 126.6, at 2–5 °C and 30 min at room temperature; after HCl addition,
1254
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 1249–1257

Synthesis and Photoisomerization of Azocalixarenes with Dendritic Structures
reflux for 1 h. Purification: extraction in CH2Cl2, recrystallization
in CHCl3 to give 5a (392 mg, 75%). M.p. Ͼ322 °C (decomp.). H
COSY): δ = 7.85 (s, 2 H, ArHazocalix[4]arene), 7.83 (s, 2 H,
1
ArHazocalix[4]arene), 7.73 (s, 2 H, ArHazocalix[6]arene), 7.71 (s, 2 H,
ArHazocalix[6]arene), 7.54 (s, 4 H, ArHazocalix[6]arene), 7.45 (s, 2 H, Ar-
Hazocalix[4]arene), 7.41 (s, 2 H, ArHazocalix[4]arene), 7.25–7.16 (m, 16 H,
ArHcalix[6]arene), 6.85–6.63 (m, 32 H, ArHcalix[6]arene), 5.42 (s, 1 H,
ArHxylylenyl), 5.40 (s, 1 H, ArHxylylenyl), 5.36 (s, 2 H, ArHxylylenyl),
4.58 [d, 2J(H,H) = 12.9 Hz, 2 H, ArCH2Arcalix[4]arene], 4.46–4.05
(m, 44 H, ArCH2Ar, ArOCH2 and ArOCH2CH2CH3), 3.94–3.78
(m, 4 H, ArOCH2CH2CH3), 3.63 [d, 2J(H,H) = 12.2 Hz, 2 H,
ArCH2Arcalix[4]arene], 3.59–2.98 (m, 60 H, ArOCH2CH3 and
ArCH2Ar), 2.30–2.20 (m, 2 H, ArOCH2CH2CH3), 2.06–1.88 (m, 4
H, ArOCH2CH2CH3), 1.40 [s, 18 H, C(CH3)3], 1.38 [s, 18 H,
C(CH3)3], 1.32 [s, 18 H, C(CH3)3], 1.16–0.98 (m, 9 H, Ar-
OCH2CH2CH3), 0.94–0.80 [m, 192 H, ArOCH2CH3 and C(CH3)3]
ppm. 13C NMR (125 MHz, C2D2Cl4, 298 K, DEPT, 321 K HSQC):
δ = 152.3, 152.1, 145.7, 144.8, 144.7, 139.2, 133.4, 132.7 (Ar), 128.0,
125.0, 124.8, 124.3, 124.1, 123.0, 117.3 (ArH), 78.5, 77.5 (Ar-
OCH2CH2CH3), 71.2 (ArOCH2), 68.7 (ArOCH2CH3), 34.2, 34.1,
33.93, 33.89 [C(CH3)3], 32.0, 32.5 (ArCH2Arcalix[4]arene), 31.8, 31.7,
31.3 [C(CH3)3], 30.2, 28.7 (ArCH2Arcalix[6]arene), 23.5, 22.8
(ArOCH2CH2CH3), 15.66, 15.62, 15.60 (ArOCH2CH3), 10.8, 9.8
(ArOCH2CH2CH3) ppm. UV/Vis (ArN=NAr, CH2Cl2, 10–5 ): λ
(ε, mol–1 dm3 cm–1) = 343 (57348), 436 (4116) nm. MS (MALDI-
TOF, dithranol + NaI): m/z (%) = 5428.5 (100) [M + Na]+, 5406.5
(25) [M + H]+, 4206.7 (25) [M – C82H105NO6 + 2H]+, 1225.7 (40)
[C82H105NO6 + 2H + Na]+. C365H458N8O28·2CHCl3 (5644.33):
calcd. C 78.09, H 8.21, N 1.99; found C 77.98, H 8.65, N 1.96.
NMR (500 MHz, CDCl3, 298 K): δ = 10.29 (s, 4 H, ArOH), 7.80
(s, 8 H, ArH), 7.47 (s, 8 H, ArH), 7.06 (s, 4 H, ArH), 4.39 (br. s, 4
H, ArCH2Ar), 3.86 (br. s, 4 H, ArCH2Ar), 2.38 (s, 24 H, ArCH3)
ppm. 13C NMR (125 MHz, CDCl3, 298 K, DEPT): δ = 153.0,
151.2, 147.9, 138.7, 128.3 (Ar), 132.3, 124.4, 120.4 (ArH), 31.9
(ArCH2Ar), 21.2 (ArCH3) ppm. MS (MALDI-TOF, dithranol +
NaI): m/z (%) = 975.5 (65) [M + Na]+, 953.5 (100) [M + H]+.
C60H56N8O4·0.5CHCl3 (1012.83): calcd. C 71.74, H 5.62, N 11.06;
found C 72.16, H 5.69, N 11.03.
General Procedure for O-Alkylation of Compound 1a: A mixture of
1a (1 equiv.) and NaH (oil mineral suspension 60%, 4 equiv.) in
DMF dry was stirred under an argon atmosphere for 10 min. Next,
propyl iodide (3–4 equiv.) was added, and the mixture was stirred
at room temperature for some time, monitoring the reaction by
TLC (hexane/THF, 4:1). H2O and HCl (1 ) were added, and the
mixture was stirred for 30 min. The precipitate was filtered and
triturated in methanol. The obtained solid, which contained dif-
ferent proportions of 1b and 1c in function of the time and tem-
perature used, was purified by chromatography using a TLC plate
(silica gel; hexane/THF, 7:1Ǟ7:4).
Compound 1b: Prepared by the general procedure described above
from 1a (20.0 mg, 3.788 µmol), NaH (0.6 mg, 0.015 mmol), and
propyl iodide (1.8 µL, 0.018 mmol) in dry DMF (2.5 mL). Time:
5 h (until apparition of 1c by TLC). After purification by using a
TLC plate (silica gel; hexane/THF, 7:1Ǟ7:4), the solid was tritu-
rated in methanol to give 1b (9.5 mg, 47%). M.p. Ͼ174 °C (de-
Compound 2b: A suspension of 2a (20.5 mg, 4.567 µmol) and NaH
(oil mineral suspension 60%, 1.2 mg, 0.027 mmol) in DMF dry
(2.0 µL) in a sealed tube was stirred for 30 min at room temperature
under an argon atmosphere. Next, methyl iodide (1.7 µL,
0.027 mmol) was added, and the mixture was stirred for 24 h at
room temperature. H2O and HCl (1 ) were added, and the precipi-
tate was filtered and purified by trituration in CH2Cl2/MeOH to
give 2b as a yellow solid (16.0 mg, 77%). M.p. Ͼ242 °C (decomp.).
1H NMR (500 MHz, CDCl3, 298 K, ROESY): δ = 7.80 (s, 6 H,
ArHazodendron), 7.73 (s, 6 H, ArHazocore), 7.36 (s, 12 H, ArHdendron),
6.96 (s, 6 H, ArHcore), 6.89 (s, 12 H, ArHdendron), 6.84 (s, 12 H,
1
comp.). H NMR (500 MHz, C2D2Cl4, 340 K, COSY, ROESY): δ
= 8.85 (s, 2 H, ArOH), 7.87 (s, 2 H, ArHazocalix[4]arene), 7.73 (s, 2
H, ArHazocalix[6]arene), 7.62 (s, 2 H, ArHazocalix[4]arene), 7.60 (s, 2 H,
ArHazocalix[6]arene), 7.26 (s, 8 H, ArHcalix[6]arene), 7.19 (s, 8 H,
ArHcalix[6]arene), 6.83 (s,
8 H,ArHcalix[6]arene), 6.78 (s, 8 H,
ArHcalix[6]arene), 6.74 (s, 8 H, ArHcalix[6]arene), 6.70 (4s, 8 H,
ArHcalix[6]arene), 5.46 (s, 2 H, ArHxylylenyl), 5.42 (s, 2 H, ArHxylylenyl),
4.45–4.07 (m, 48 H, ArCH2Ar, ArOCH2 and ArOCH2CH2CH3),
3.71 [d, 2J(H,H) = 13.1 Hz, 4 H, ArCH2Arcalix[4]arene], 3.54–3.44
(m, 32 H, ArOCH2CH3), 3.43–3.27 (m, 16 H, ArCH2Arcalix[6]arene),
3.23–3.08 (m, 8 H, ArCH2Arcalix[6]arene), 2.11–2.00 (m, 6 H,
ArOCH2CH2CH3), 1.39 [s, 36 H, C(CH3)3], 1.33–1.32 (m, 6 H,
ArOCH2CH2CH3), 1.32 [s, 36 H, C(CH3)3], 0.99 [t, 3J(H,H) =
6.9 Hz, 24 H, ArOCH2CH3], 0.91–0.84 [m, 192 H, ArOCH2CH3
and C(CH3)3] ppm. 13C NMR (125 MHz, C2D2Cl4, 340 K, DEPT,
HMQC): δ = 156.6, 154.3, 152.7, 152.5, 152.3, 152.2, 145.9, 145.8,
144.82, 144.78, 139.34, 139.28, 133.7, 133.5, 133.4, 132.7 (Ar),
128.0 (ArH), 127.7 (Ar), 125.0, 124.1, 124.0, 117.4 (ArH), 78.8
(ArOCH2CH2CH3), 71.6, 71.3 (ArOCH2), 68.7 (ArOCH2CH3),
34.1, 33.93, 33.90 [C(CH3)3], 32.3 (ArCH2Arcalix[4]arene), 31.8, 31.7,
31.33, 31.30 [C(CH3)3], 30.4, 30.3, 28.9 (ArCH2Arcalix[6]arene), 23.6
(ArOCH2CH2CH3), 15.6, 15.5 (ArOCH2CH3), 11.0 (ArOCH2-
2
ArHdendron), 5.48 (s, 3 H, ArHxylylenyl), 4.95 [d, J(H,H) = 15.4 Hz,
12 H, ArCH2Ar], 4.33 [d, 2J(H,H) = 14.5 Hz, 6 H, ArCH2Ar], 4.28
(s, 12 H, ArOCH2), 4.04 (br. s, 12 H, ArCH2Arcore), 3.64–3.56 (m,
24 H, ArOCH2CH3), 3.46–3.43 (m, 21 H, ArCH2Ar and ArOCH3),
3.24 [d, 2J(H,H) = 13.5 Hz, 6 H, ArCH2Ar], 3.01 (br. s, 9 H,
ArOCH3), 1.45 [s, 54 H, C(CH3)3], 1.07 [s, 27 H, C(CH3)3core], 1.04
[t, 3J(H,H) = 6.9 Hz, 36 H, ArOCH2CH3], 0.92 [s, 108 H,
C(CH3)3] ppm. 13C NMR (125 MHz, CDCl3, 298 K, DEPT,
HSQC): δ = 152.6, 152.3, 151.9, 148.6, 146.0, 145.0, 139.4, 135.3,
133.4, 132.9, 132.8 (Ar), 128.1, 125.4, 125.0, 124.1, 117.6 (ArH),
71.4 (ArOCH2), 68.8 (ArOCH2CH3), 60.3, 60.2 (ArOCH3), 34.3,
34.2, 34.0 [C(CH3)3], 31.9 (ArCH2Arcore), 31.7, 31.4, 31.3
[C(CH3)3], 30.8 (ArCH2Arcore), 30.2, 28.7 (ArCH2Ar), 15.6 (Ar-
OCH2CH3) ppm. UV/Vis (ArN=NAr, CH2Cl2, 10–5 ): λ (ε,
mol–1 dm3 cm–1) = 347 (67932), 436 (3631) nm. MS (MALDI-TOF,
dithranol + NaI): m/z (%) = 4552.9 (100) [M + Na]+, 4529.9 (15)
[M + H]+. C306H384N6O24·CH2Cl2 (4615.28): calcd. C 79.89, H
8.43, N 1.82; found C 79.90, H 8.83, N 1.70.
CH2CH3) ppm. UV/Vis (ArN=NAr, CH2Cl2, 10–5 ):
λ (ε,
mol–1 dm3 cm–1) = 341 (56718), 438 (5182) nm. MS (MADI-TOF,
dithranol + NaI): m/z (%) = 5386.5 (100) [M + Na]+, 1224.9 (75)
[M – C82H105NO6 + 2H + Na]+. HRMS (MALDI): calcd. for
C362H452N8O28Na [M +Na]+ 5385.430; found 5385.426. HPLC:
94.6%.
General Procedure for O-Alkylation of Compounds 3a and 4a: A
Compound 1c: Prepared by the general procedure described above
solution of the corresponding azo derivative and K2CO3 in the ap-
from 1a (42.0 mg, 7.956 µmol), NaH (1.3 mg, 0.032 mmol), and propriate solvent was heated at 70 °C for 30 min under an argon
propyl iodide (3 µL, 0.0318 µmol) in dry DMF (1.4 mL). Time: 7 d.
After the purification by using a TLC plate (silica gel; hexane/THF,
10:1Ǟ7:4), the solid was triturated in methanol to give 1c (25.0 mg,
atmosphere. Next, propyl iodide was added, and the mixture was
heated at 60 °C for 48 h. H2O and HCl (3 ) were added, and the
mixture was stirred at room temperature for 30 min. The aqueous
58%). M.p. 250–255 °C. 1H NMR (500 MHz, C2D2Cl4, 321 K, solution was extracted with CH2Cl2 (2ϫ20 mL), and the organic
Eur. J. Org. Chem. 2010, 1249–1257
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1255

H. Galán, G. Hennrich, J. de Mendoza, P. Prados
FULL PAPER
phase was washed with H2O and dried (Na2SO4). The solvent was
removed under reduced pressure, and the obtained residue was trit-
urated in methanol.
4.38 [d, 2J(H,H) = 14.0 Hz, 2 H, ArCH2Ar], 4.23 [t, 3J(H,H) =
6.7 Hz, 2 H, ArOCH2CH2CH3], 3.77 [d, J(H,H) = 14.0 Hz, 2 H,
2
ArCH2Ar], 3.75 [d, 2J(H,H) = 13.0 Hz, 2 H, ArCH2Ar], 2.39 (s, 12
H, ArCH3), 2.35 (s, 6 H, ArCH3), 2.33 (s, 6 H, ArCH3), 2.26 [sext.,
3J(H,H) = 7.1 Hz, 2 H, ArOCH2CH2CH3], 1.36 [t, 3J(H,H) =
7.4 Hz, 3 H, ArOCH2CH2CH3] ppm. 13C NMR (125 MHz, CDCl3,
298 K, DEPT): δ = 154.0, 153.6, 153.1, 153.0, 152.9, 151.4, 150.3,
147.8, 147.0, 138.67, 138.66, 138.60, 134.3 (Ar), 132.6, 132.1, 132.0
(ArH), 128.7, 128.3, 128.1 (Ar), 124.41, 124.38, 124.3, 123.9, 120.5,
120.3 (ArH), 79.5 (OCH2CH2CH3), 32.1, 31.8 (ArCH2Ar),
23.4 (OCH2CH2CH3), 21.3, 21.21, 21.18 (ArCH3), 10.8
(OCH2CH2CH3) ppm. UV/Vis (ArN=NAr, CH2Cl2, 10–5 ): λ (ε,
mol–1 dm3 cm–1) = 338 (76812), 433 (4314) nm. MS (MALDI-TOF,
dithranol + NaI): m/z (%) = 1017.5 (45) [M + Na]+, 995.5 (100)
[M + H]+. C63H62N8O4·0.5H2O (1004.23): calcd. C 75.35, H 6.32,
N 11.16; found C 75.41, H 6.52, N 10.93.
5,11,17,23,29,35-Hexa-tert-butyl-37,38,40,41-tetraethyloxy-39,42-
{5-[(3,5-dimethyl-4-propyloxy)phenylazo]-1,3-phenylenbis(methylen-
oxy)}calix[6]arene (3b): Prepared by the general procedure de-
scribed above from 3a (87.5 mg, 0.066 mmol) and K2CO3 (18.1 mg,
0.130 mmol) in CH3CN/DMF (4:2, 6.0 mL). Propyl iodide (9.6 µL,
0.098 mmol) to give 3b as an orange solid (72 mg, 80%). M.p. 178–
1
181 °C. H NMR (500 MHz, CDCl3, 298 K): δ = 7.80 (s, 2 H, Ar-
H
azo), 7.64 (s, 2 H, ArHazo), 7.37 (s, 4 H, ArH), 6.90 (s, 4 H, ArH),
2
6.85 (s, 4 H, ArH), 5.46 (s, 1 H, ArHm-xylylenyl), 4.51 [d, J(H,H) =
15.4 Hz, 4 H, ArCH2Ar], 4.34 [d, 2J(H,H) = 14.2 Hz, 2 H, Ar-
CH2Ar], 4.29 (s, 4 H, ArOCH2), 3.80 [t, 3J(H,H) = 6.6 Hz, 2 H,
ArOCH2CH2CH3], 3.66–3.56 (m, 8 H, ArOCH2CH3), 3.46 [d,
2J(H,H) = 15.4 Hz, 4 H, ArCH2Ar], 3.25 [d, J(H,H) = 14.2 Hz, 2
2
H, ArCH2Ar], 2.38 (s, 6 H, ArCH3), 1.87 [sext., 3J(H,H) = 7.1 Hz,
Supporting Information (see footnote on the first page of this arti-
cle): Spectral characterization data; VT 1H NMR spectra (403–
193 K); photoisomerization, kinetics, and complexation studies.
3
2 H, ArOCH2CH2CH3], 1.46 [s, 18 H, C(CH3)3], 1.12 [t, J(H,H)
= 7.4 Hz, 2 H, ArOCH2CH2CH3], 1.04 [t, 3J(H,H) = 7.0 Hz, 12 H,
ArOCH2CH3], 0.93 [s, 36 H, C(CH3)3] ppm. 13C NMR (CDCl3,
125 MHz, 298 K, DEPT): δ = 158.4, 152.6, 152.3, 152.0, 148.8,
146.0, 145.0, 139.5, 133.5, 132.9, 132.8, 131.7 (Ar), 128.1, 125.1,
124.9, 124.1, 123.3, 117.5 (ArH), 74.1 (ArOCH2), 71.4 (Ar-
OCH2CH2CH3), 68.8 (ArOCH2CH3), 34.3, 34.0 [C(CH3)3], 31.7,
31.3 [C(CH3)3], 30.2, 29.7 (ArCH2Ar), 23.7 (ArOCH2CH2CH3),
16.5 (ArCH3), 15.5 (ArOCH2CH3), 10.7 (ArOCH2CH2CH3) ppm.
UV/Vis (ArN=NAr, CH2Cl2, 10–5 ): λ (ε, mol–1 dm3 cm–1) = 342
(23227), 432 (1275) nm. MS (MALDI-TOF, dithranol + NaI): m/z
Acknowledgments
Ministerio de Educación y Ciencia (Spain) (Project CTQ2005-
08948-C02-02) is kindly acknowledged for financial support. H.G.
acknowledges the Ministerio de Educación y Ciencia, Spain for a
predoctoral fellowship. We kindly acknowledge E. Cequier of ICIQ
for HPLC separation of the cis/trans isomers.
(%) = 1400.9 (100) [M + Na]+ , 1379.0 (70) [M + H]+
.
C93H120N2O7·0.5CHCl3 (1435.87): calcd. C 78.11, H 8.45, N 1.95;
found C 78.30, H 8.78, N 1.96.
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3,3Ј,5,5Ј-Tetramethyl-4-propyloxy Azobenzene (4b): Prepared by the
general procedure described above from 4a (100.0 mg, 0.393 mmol)
and K2CO3 (108.7 mg, 0.786 mmol) in CH3CN (5.0 mL). Propyl
iodide (57 µL, 0.589 mmol) to give 4b as an orange solid (116.5 mg,
90%). M.p. 63–65 °C. 1H NMR (300 MHz, CDCl3, 298 K): δ =
7.60 (s, 2 H, ArHazo), 7.50 (s, 2 H, ArHazo), 7.10 (s, 1 H, ArH),
3.79 [t, 3J(H,H) = 6.6 Hz, 2 H, ArOCH2CH2CH3], 2.41 (s, 6 H,
ArCH3 ), 2.37 (s, 6 H, ArCH3 ), 1.90–1.83 (m, 2 H, Ar-
OCH2CH2CH3) 1.10 [t, 3J(H,H) = 7.4 Hz, 3 H, ArOCH2CH2CH3]
ppm. 13C NMR (75 MHz, CDCl3, 298 K, DEPT): δ = 158.6, 153.0,
148.6, 138.7 (Ar), 132.2 (ArH), 131.8 (Ar), 123.3, 120.4 (ArH), 74.0
(ArOCH2CH2CH3), 23.7 (ArOCH2CH2CH3), 21.2, 16.5 (ArCH3),
10.6 (ArOCH2CH2CH3) ppm. UV/Vis (ArN=NAr, CH2Cl2,
10–5 ): λ (ε, mol–1 dm3 cm–1) = 344 (26829), 435 (1425) nm. MS
(70 eV): m/z (%) = 296.2 (80) [M]+, 163.1 (100) [M – C8H9N2]+.
C19H24N2O (296.41): calcd. C 76.99, H 8.16, N 9.45; found C
76.90, H 8.14, N 9.14.
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26,27,28-Tetrahydroxy-5,11,17,23-tetra-(3,5-dimethylphenylazo)-25-
propyloxycalix[4]arene (5b): To a suspension of 5a (76.3 mg,
0.080 mmol) and K2CO3 (22.1 mg, 0.168 mmol) in dry DMF
(3.0 mL) under an argon atmosphere was added propyl iodide
(16.3 µL, 0.168 mmol), and the mixture was heated at 80 °C for
6 h. H2O and HCl (1 ) were added, and the mixture was stirred
for 30 min. The precipitate was filtered, and the solid was purified
by trituration in MeOH to give 5b (65.2 mg, 82%) as an orange
solid. M.p. Ͼ310 °C (decomp.). 1H NMR (500 MHz, CDCl3,
298 K, ROESY): δ = 9.61 (s, 3 H, ArOH), 7.84 [d, 3J(H,H) =
2.5 Hz, 2 H, ArHazo], 7.81 [d, 3J(H,H) = 2.2 Hz, 2 H, ArHazo], 7.73
(s, 2 H, ArHazo), 7.72 (s, 2 H, ArHazo), 7.48 (s, 4 H, ArHazo), 7.41
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3
7.01 (m, 2 H, ArH), 4.48 [d, J(H,H) = 13.1 Hz, 2 H, ArCH2Ar],
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 1249–1257

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Received: December 1, 2009
Published Online: January 14, 2010
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