Regioselective ipso-nitration of calix[4]arenes

Article abstract of DOI:10.1016/j.tet.2012.03.102

A novel protection/deprotection method leading to the regioselective ipso-substitution of calix[4]arenes is described. The introduction of nosyl (p-nitrobenzenesulfonyl) groups into the lower rim of partly alkylated tert-butylcalix[4]arenes leads subsequently to the exclusive ipso-nitration of the alkylated phenol rings, while the protecting groups can be easily removed in the next step. This method gives dialkoxy- or trialkoxy-substituted calix[4]arenes with nitro groups on the alkylated rings and tert-butyl groups on the remaining ones. The above substitution pattern is complementary to the isomers so far known in the chemistry of calix[4]arenes and could be used in the design of novel type of calixarene-based receptors.

Full text of DOI:10.1016/j.tet.2012.03.102

Tetrahedron 68 (2012) 4187e4193
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Regioselective ipso-nitration of calix[4]arenes
a
a
b
a,
*
ꢀ
Oldrich Hudecek , Jan Budka , Vaclav Eigner , Pavel Lhotak
a
ꢀ
Department of Organic Chemistry, Institute of Chemical Technology, Technicka 5, 16628 Prague 6, Czech Republic
Department of Solid State Chemistry, Institute of Chemical Technology, Technicka 5, 16628 Prague 6, Czech Republic
b
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel protection/deprotection method leading to the regioselective ipso-substitution of calix[4]arenes
is described. The introduction of nosyl (p-nitrobenzenesulfonyl) groups into the lower rim of partly al-
kylated tert-butylcalix[4]arenes leads subsequently to the exclusive ipso-nitration of the alkylated phenol
rings, while the protecting groups can be easily removed in the next step. This method gives dialkoxy- or
trialkoxy-substituted calix[4]arenes with nitro groups on the alkylated rings and tert-butyl groups on the
remaining ones. The above substitution pattern is complementary to the isomers so far known in the
chemistry of calix[4]arenes and could be used in the design of novel type of calixarene-based receptors.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 3 January 2012
Received in revised form 6 March 2012
Accepted 26 March 2012
Available online 30 March 2012
Keywords:
Calixarene
Electrophilic substitution
Nitration
Regioselectivity
Anion recognition
1. Introduction
well-established method, which can be carried out either directly,4
or via the ipso-substitution5 of tert-butyl groups. ipso-Substitution
Contemporary supramolecular chemistry mostly relies on sev-
eral families of macrocyclic compounds capable of preorganization.
Among them, calix[n]arenes1 are especially popular for their easy
preparation and almost limitless derivatization potential, which
makes them ideal candidates for various applications in supramo-
lecular chemistry.2 Because of their tuneable three-dimensional
shapes, calix[4]arenes became indispensable in the design of
sophisticated receptors and hosteguest systems. Over last three
decades a plethora of regioselective and/or stereoselective deriva-
tisation methods of the basic skeleton was described,1 thus en-
abling the application of calix[4]arene as a molecular scaffold. In
this context, a calixarene macrocycle is usually frozen in one of the
four common conformations (cone, partial cone, 1,2-alternate, or 1,3-
alternate), and selected structural fragments responsible for the
recognition are introduced into the molecule. These highly preor-
ganised systems, with precisely defined 3-D shapes and mutual
spatial arrangement of functional groups, can then be used as re-
ceptors for ions or neutral molecules.3
is usually used for tetranitration of peralkylated calix[4]arenes
where all four tert-butyl groups can be changed for nitro groups in
high yields.6 On the other hand, it can be also used for regiose-
lective substitution of the upper rim through the partial alkylation
of the lower rim. Thus, introduction of two alkyl groups into the
distal positions makes these two aromatic rings less reactive
compared with those bearing free hydroxyl groups. Consequently,
subsequent ipso-nitration proceeds selectively7 on the unsub-
stituted rings (Scheme 1, path a).
Nitro-substituted calix[4]arenes are frequently used as in-
termediates for the design and preparation of novel receptors or
calixarene-based building blocks (usually via reduction to amino
groups and subsequent derivatisation with suitable agent). There-
fore, the nitration of calix[4]arenes represents an important and
Scheme 1. Two different substitution patterns in dialkylated calix[4]arenes: (a)
common ipso-nitration, (b) ipso-nitration using nosyl protection/deprotection method.
During our ongoing research on calix[4]arene derivatization we
found that nosyl-substituted derivatives can be used for regiose-
lective introduction of various functional groups through direct
* Corresponding author. Tel.: þ420 220445055; fax: þ420 220444288; e-mail
ꢀ
addresses: lhotakp@vscht.cz, pavel.lhotak@vscht.cz (P. Lhotak).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.03.102

4188
O. Hudecek et al. / Tetrahedron 68 (2012) 4187e4193
electrophilic substitution of the free (de-tert-butylated) upper rim.8
In this paper we report a straightforward regioselective ipso-ni-
tration in the calix[4]arene series starting from nosyl-substituted
tert-butyl derivatives. The whole strategy, consisting of lower-rim
protection/ipso-nitration/deprotection steps, allows the in-
troduction of nitro groups to the alkylated phenolic units, thus
representing so far almost inaccessible substitution pattern
(Scheme 1, path b) in calix[4]arene chemistry complementary to
commonly used isomers.
lower field (9.50 ppm) because of the presence of the nitro group
on the same ring.
The final unambiguous structural evidence for compound 12
was obtained by X-ray crystallography. It proved that proximal
derivative adopts the cone conformation with NO2 groups being
introduced into the para positions of alkoxy-substituted rings
(Fig. 2a). The main motif of crystal packing is represented by self-
inclusion of one tert-butyl group into the cavity of the neighbour
macrocycle (Fig. 2b) leading to the formation of self-included
dimers.
2. Results and discussion
To show the usefulness of this novel synthetic approach in calix
[4]arene chemistry we attempted the transformation of nitro de-
rivative 11 into the corresponding anion receptor 15 and to com-
pare its complexation ability with a recently reported8 analogue 16
without tert-butyl groups on the upper rim. Thus, dinitro derivative
11 was reduced using Raney nickel11 in methanol under reflux
conditions to yield amino substituted compound 14 in 97% yield.
This compound was then reacted with phenyl isocyanate in DCM at
room temperature to give the target receptor 15 in 29% yield. The
low yield of receptor is probably a consequence of the repeated
chromatographic purifications, which were necessary to remove
the impurities formed by the quenching of phenyl isocyanate with
MeOH.
The complexation ability of ligand 15 was studied by standard
1H NMR titration experiments using an increasing concentration of
appropriate anion to obtain different host/guest ratios (1e20:1). To
ensure the solubility of both ligand 15 and anion (tetrabutyl-
ammonium salts of benzoate, acetate, chloride) a mixed solvent
system (CDCl3/DMSO-d6¼4:1, v/v) was used. As the same solvent
system was recently used for the measuring of the complexation
properties of 16,8 it also allowed us a direct comparison with our
receptor.
To check the general applicability of regioselective ipso-nitration
three different partly alkylated isomers were prepared using
known procedures. Thus, the alkylation of starting tert-butylcalix
[4]arene (PrI/K2CO3/MeCN)9 gave a distal dipropoxy derivative 2 in
74% yield. Proximally disubstituted compound 3 was obtained in
53% yield using PrBr/NaOH in aqueous DMSO,10 while the trialky-
lated isomer 4 was isolated in 51% yield using PrI/BaO/Ba(OH)2
system in DMF.11 These partly alkylated calixarenes were reacted
with p-nitrobenzenesulfonyl chloride (nosyl chloride) in the pres-
ence of NaH as a base. Reaction was carried out either in DMF at 0 ꢀC
(for 2, 4) or in THF under reflux (for 3) and the isomers 5e7 were
obtained in acceptable yields (78, 75 and 69% yield, respectively).
The 1H NMR spectra of 5e7 confirmed the exclusive formation of
the cone conformation. Thus, the presence of two doublets at 3.91
and 2.76 ppm for eCH2e bridges with typical geminal coupling
constants (Jz13 Hz) clearly showed the cone conformation for
distal derivative 5. Analogously, the expected splitting pattern
(three doublets for equatorial protons of eCH2e bridging units at
3.10, 2.76 and 2.74 ppm in 1:2:1 integral ratio) is in perfect accord
with the lower symmetry of derivative 6.
The ipso-nitration of compounds 5e7 was carried out using
100% HNO3 in an AcOH/DCM mixture at room temperature. In all
cases, nitration proceeded almost quantitatively and the corre-
sponding nitro-substituted compounds 8e10 were obtained in 99,
98 and 99% yields, respectively. The 1H NMR spectrum of 8 clearly
proves the regioselective formation of distally p-nitro-substituted
product where both NO2 groups are on the alkylated rings. Thus,
compound 8 possesses one singlet of nitro-substituted phenyl rings
The addition of anions to 15 led to the remarkable down-field
shifts of ureido NH signals supporting the complexation phenom-
enon under fast exchange conditions. A typical titration curve
constructed from the complexation induced chemical shifts (CIS)
for compound 15/benzoate system is shown in Fig. 3a. The addition
of 20 equiv of BzOꢂ led to the CIS value higher than 3.3 ppm. This is
an unusually high value indicating very strong hydrogen-bonding
interactions between the ureido functions and benzoate. On the
other hand, data obtained could not be analysed as 1:1 complex,
which was recently observed for receptor 16.8 The Job plot analysis
(Fig. 3b) revealed the more complex behaviour corresponding to
a 2:1 stoichiometry (anion/calix). As the same stoichiometries were
observed also for other anions studied (acetate, chloride) we as-
sumed that this behaviour is general for receptor 15. The most
likely explanation of the difference between the operating of re-
ceptors 15 and 16 lies in the steric hindrance on the upper rim of
calixarene receptors. Derivative 16 can use both ureido functions
for cooperative binding of anions leading always to 1:1 stoichi-
ometry. On the other hand, the presence of tert-butyl groups in
receptor 15 does not allow efficient cooperation of the ureido units.
Consequently, both urea moieties behave independently and prefer
the separate binding of anions leading to the 2:1 complexes.
(d 7.94 ppm), and one singlet from tert-butyl substituted rings (d
6.52 ppm). The unequivocal structural evidence was obtained by
X-ray crystallography, which fully proved the expected structure
of compound 8 (see Supplementary data).
Nitro-substituted derivatives 8e10 were finally deprotected by
basic hydrolysis of nosyl groups with KOH in EtOH/dichloro-
methane mixture. The corresponding calixarenes 11e13 with partly
unsubstituted lower rims were obtained in essentially quantitative
yields (ꢁ96% after isolation). The 1H NMR spectrum of 11 in CDCl3
clearly shows the cone conformation (pair of doublets at 4.36 and
3.48 ppm, J¼13 Hz), with two nitro groups introduced into the
upper rim of calixarene (two singlets for aromatic protons at 7.87
and 7.13 ppm). Similarly, the isomers 12 and 13 also adopt the cone
conformation as ascertained by series of doublets for equatorial and
axial protons in eCH2e bridging units with typical geminal cou-
pling constants Jz13 Hz (Scheme 2).
The exact position of the nitro groups in derivative 11 was also
confirmed by direct comparison with the corresponding
regioisomer 17 having NO2 groups on the unsubstituted aromatic
rings. This compound can be prepared5a,7a by direct ipso-nitration
of dipropoxy derivative 2 and possesses the same type of splitting
pattern and signal multiplicity as compound 11 (Scheme 3). How-
ever, the chemical shifts of some signals are significantly different,
proving the different positions of nitro groups on calixarene skel-
eton (see Fig. 1). While the signal of free phenolic OH group in 11
can be found at 7.91 ppm, the same signal in 17 is shifted to much
3. Conclusions
In conclusion, we have demonstrated the usefulness of nosyl
groups in the selective ipso-nitration of calix[4]arenes. The in-
troduction of nosyl groups into the lower rim of calix[4]arene en-
ables
a highly regioselective ipso-nitration of the alkoxy-
substituted aromatic rings. The whole strategy, consisting of the
lower-rim protection/ipso-nitration/deprotection steps, leads to so
far almost inaccessible substitution pattern, which can be useful in
the design of novel calixarene-based receptors.

O. Hudecek et al. / Tetrahedron 68 (2012) 4187e4193
4189
Scheme 2. Regioselective nitration of partly alkylated calix[4]arenes: (i) PrI/K2CO3/MeCN (2,74%); (ii) PrBr/NaOH/DMSO/H2O (3, 53%); (iii) PrI/BaO/Ba(OH)2/DMF (4, 51%); (iv) nosyl
chloride/NaH/DMF, 0 ꢀC (5, 78%; 7, 69%); nosyl chloride/NaH/THF, reflux (6, 75%); (v) 100% HNO3/AcOH/DCM, 0 ꢀC (8, 99%, 9, 98%, 10, 99%); (vi) KOH/DCM/EtOH, rt (11, 96%, 12, 99%,
13, 98%).

4190
O. Hudecek et al. / Tetrahedron 68 (2012) 4187e4193
Scheme 3. Preparation of anion receptor: (i) Ni(R)/NH2NH2$H2O/MeOH, reflux (14, 97%); (ii) phenyl isocyanate/DCM, rt (15, 29%).
7.87 ppm
6.97 ppm
1.29 ppm
1.07ppm
t
t
But
NO2
NO2
Bu
But
NO2
O2N
Bu
H
H
8.04 ppm
7.13 ppm
H
H
O
O
Pr
17
OH
OH
OH
O
HO
O
Pr
Pr
Pr
7.91 ppm
9.50 ppm
11
Fig. 1. Differences in 1H NMR spectra of regioisomers 11 and 17 (CDCl3, 300 MHz,
298 K).
Fig. 3. (a) Binding isotherm of ligand 15 with benzoate anion; (b) Job plot for the same
system in CDCl3/DMSO-d6 4:1 v/v system (1H NMR titration, 300 MHz, 298 K).
4. Experimental
4.1. General
Melting points were determined on a Boetius block (Carl Zeiss
Jena, Germany) and are not corrected. The IR spectra were mea-
sured on an FT-IR spectrometer Nicolet 740 in CHCl3 and/or in KBr.
1H NMR spectra were recorded on a Varian Gemini 300 spec-
trometer. Dichloromethane used for the reaction was dried with
CaH2 and stored over molecular sieves. The purity of the substances
and the courses of reactions were monitored by TLC using TLC al-
uminium sheets with Silica gel 60 F254 (Merck). Preparative TLC
chromatography was carried out on 20ꢃ20 cm glass plates covered
by Silica gel 60 GF254 (Merck).
Fig. 2. (a) ORTEP drawing of proximal dinitro derivative 12, (b) self-inclusion motif in
crystal packing of 12 (hydrogens omitted for better clarity).

O. Hudecek et al. / Tetrahedron 68 (2012) 4187e4193
4191
Starting compounds 2e4 were prepared according to known
procedures.
(KBr)
n
cmꢂ1
:
2964, 1537, 1350, 1312, 1196; EA calcd for
C62H74N2O12S2: C, 67.49; H, 6.76; N, 2.54; S, 5.81%. Found: C, 67.45;
H, 6.71; N, 2.51; S, 5.79%.
4.2. Synthesis of 5,11,17,23-tetra-tert-butyl-25,27-bis(p-
nitrobenzenesulfonyloxy)-26,28-dipropoxycalix[4]arene
(cone) 5
4.4. Synthesis of 5,11,17,23-tetra-tert-butyl-25-(p-
nitrobenzenesulfonyloxy)-26,27,28-tripropoxycalix[4]arene
(cone) 7
A mixture of 5,11,17,23-tetra-tert-butyl-26,28-dipropoxycalix[4]
arene-25,27-diol 2 (5.00 g, 6.82 mmol) and sodium hydride (1.1 g,
27.50 mmol, 60% suspension in mineral oil) was stirred for 30 min
at 0 ꢀC in anhydrous DMF (300 ml). Then, p-nitrobenzenesulfonyl
chloride (7.80 g, 34.13 mmol, 97% purity) was added and the re-
action mixture was stirred at room temperature for 5 days. The
resulting mixture was acidified with 1 M HCl (aq) and extracted
with CH2Cl2 (3ꢃ100 ml). The combined organic layers were washed
with water (300 ml), brine (300 ml) and dried over MgSO4. Organic
solvent was removed under reduced pressure, and the oily residue
was dissolved in CH2Cl2 (15 ml) and precipitated by addition of
methanol (150 ml). The precipitate was filtered off, washed twice
with methanol and dried to give 5.92 g of title compound 5 as
a yellowish powder (78%), mp: 261e264 ꢀC. 1H NMR (300 MHz;
CDCl3, 298 K): dH 8.39e8.36 (m, 4H, ArHeNs), 7.98e7.96 (m, 4H,
ArHeNs), 7.02 (s, 4H, ArH), 6.48 (s, 4H, ArH), 3.91 (d, 4H, J¼12.9 Hz,
ArCH2Ar ax), 3.82 (t, 4H, J¼6.6 Hz, OCH2), 2.76 (d, 4H, J¼13.2 Hz,
ArCH2Ar eq), 2.15e2.02 (m, 4H, OCH2CH2), 1.28 (s, 18H, tBu), 0.99 (t,
6H, J¼7.5 Hz, CH3), 1.09 (s, 18H, tBu). 13C{1H} NMR (75 MHz, CDCl3,
A mixture of trialkyl derivative 4 (1.10 g, 1.42 mmol) and sodium
hydride (0.11 g, 4.58 mmol, 60% suspension in mineral oil) was
stirred for 30 min at 0 ꢀC in anhydrous DMF (50 ml). Then, p-
nitrobenzenesulfonyl chloride (0.63 g, 2.84 mmol, 97% purity) was
added and the reaction mixture was stirred at room temperature
for 5 days. The resulting mixture was acidified by 1 M aqueous HCl
and extracted with CH2Cl2 (3ꢃ60 ml). The combined organic layers
were washed with water (150 ml), brine (150 ml) and dried over
MgSO4. Organic solvent was removed under reduced pressure, and
the residue was dissolved in CH2Cl2 (5 ml) and reprecipitated by
addition of methanol (60 ml). The precipitate was filtered off,
washed twice with methanol and dried to give 0.94 g of product 7
as a white powder (69% yield), mp: 217e219 ꢀC. 1H NMR (300 MHz;
CDCl3, 298 K):
d 8.38e8.34 (m, 2H, ArHeNs), 7.99e7.94 (m, 2H,
ArHeNs), 7.09 (d, 2H, J¼2.6 Hz, ArH), 6.98 (d, 2H, J¼2.4 Hz, ArH),
6.53 (s, 2H, ArH), 6.40 (s, 2H, ArH), 4.38 (d, 2H, J¼12.9 Hz, ArCH2Ar
ax), 4.05 (td, 2H, J¼10.7, 5.1 Hz, OCH2), 3.96 (d, 2H, J¼12.9 Hz,
ArCH2Ar ax), 3.79 (td, 2H, J¼10.6, 5.4 Hz, OCH2), 3.65 (t, 2H,
J¼7.2 Hz, OCH2), 3.11 (d, 2H, J¼12.6 Hz, ArCH2Ar eq), 2.75 (d, 2H,
J¼12.9 Hz, ArCH2Ar eq), 2.23e2.11 (m, 2H, OCH2CH2), 2.08e1.98 (m,
2H, OCH2CH2),1.96e1.84 (m, 2H, OCH2CH2),1.29 (s,18H, tBu),1.06 (t,
298 K):
d 154.4, 151.1, 148.6, 145.9, 142.1, 141.7, 134.7, 133.2, 130.3,
126.0,125.7,124.4, 76.9, 34.3, 34.1, 32.0, 31.9, 31.1, 29.9, 23.4. TOF MS
(ESIþ): calcd for C62H74N2O12S2: 1103.42. Found: m/z (rel int. %)
1125.63 (100) [MþNa]þ. IR (KBr)
n
cmꢂ1: 2963, 1536, 1350, 1312,
1195; EA calcd for C62H74N2O12S2: C, 67.49; H, 6.76; N, 2.54; S, 5.81%.
Found: C, 67.35; H, 6.80; N, 2.53; S, 5.77%.
3H, J¼7.3 Hz, CH3), 0.95 (t, 6H, J¼7.5 Hz, CH3), 0.85 (s, 9H, tBu), 0.78
t
(s, 9H, Bu). 13C{1H} NMR (75 MHz, CDCl3, 298 K):
d 154.7, 152.8,
151.0, 148.5, 145.3, 144.2, 142.2, 141.8, 135.9, 134.5, 133.5, 132.0,
130.4, 126.5, 125.7, 125.1, 124.6, 124.3, 77.8, 34.3, 33.8, 32.1, 31.9,
31.4, 31.1, 23.8, 23.4, 11.0, 10.2. TOF MS (ESIþ): calcd for C59H77NO8S:
960.34. Found: m/z (rel intensity, %) 982.52 (100) [MþNa]þ. IR (KBr)
4.3. Synthesis of 5,11,17,23-tetra-tert-butyl-25,26-bis(p-
nitrobenzenesulfonyloxy)-27,28-dipropoxycalix[4]arene
(cone) 6
n
cmꢂ1: 2963, 1537, 1481, 1362, 1311, 1196. EA calcd for C59H77NO8S:
C, 73.79; H, 8.08; N, 1.46; S, 3.34%. Found: C, 73.68; H, 8.01; N, 1.42;
S, 3.37%.
Proximal derivative 3 (3.00 g, 4.09 mmol) was added into the
suspension of sodium hydride (0.98 g, 24.5 mmol, 60% suspension
in mineral oil, washed with hexane) in 200 ml of dried THF, and the
mixture was heated to reflux. Then, the solution of p-nitro-
benzenesulfonyl chloride (3.62 g, 16.36 mmol, 97% purity) in dry
THF (20 ml) was added dropwise during 30 min. The reaction
mixture was refluxed for 24 h and the solvent was removed under
reduced pressure. The solid residue was dissolved in CH2Cl2
(150 ml) and the resulting solution was carefully poured into the
water (1 l) while stirring. Water phase was separated and extracted
with CH2Cl2 (2ꢃ100 ml). Combined organic layers were washed
with water (300 ml), brine (300 ml) and dried over MgSO4. The
solvent was removed by evaporation and the oily residue was
dissolved in CH2Cl2 (5 ml) and precipitated by addition of methanol
(120 ml). The precipitate was filtered off, washed twice with
methanol and dried to give 3.40 g of title compound 6 (75% yield) as
a yellow powder, mp: 214e217 ꢀC. 1H NMR (300 MHz; CDCl3,
4.5. ipso-Nitration (general procedure)
The corresponding derivatives 5e7 were dissolved in the mix-
ture of CH2Cl2 (10 ml for 1 mmol) and glacial acetic acid (10 ml for
1 mmol). Nitric acid (100%, 80 equiv) was added dropwise to the
solution while cooling to 0 ꢀC in an ice bath. The reaction mixture
was then stirred until the colour changed from deep purple to light
yellow, poured into water and extracted with CH2Cl2. The combined
organic layers were washed with water, saturated aqueous
NaHCO3, then with brine and dried over MgSO4. Organic solvent
was removed under reduced pressure to give the corresponding
ipso-nitrated products 8e10.
4.5.1. Synthesis of 11,23-di-tert-butyl-5,17-dinitro-25,27-bis(p-nitro-
benzenesulfonyloxy)-26,28-dipropoxycalix[4]arene (cone) 8. General
procedure was applied to compound 5 (4.00 g, 3.63 mmol) and
product was isolated as an orange powder (3.9 g, 99% yield), mp:
280 ꢀC (dec). 1H NMR (300 MHz; CDCl3, 298 K): dH 8.43e8.40 (m,
4H, ArHeNs), 8.01e7.97 (m, 4H, ArHeNs), 7.94 (s, 4H, ArH), 6.52 (s,
4H, ArH), 4.02e3.95 (m, 8H, ArCH2Ar axþOCH2), 2.96 (d, 4H,
J¼13.5 Hz, ArCH2Ar eq), 2.11e1.98 (m, 4H, OCH2CH2), 1.02 (t, 6H,
J¼7.5 Hz, CH3), 0.83 (s, 18H, tBu). 13C{1H} NMR (75 MHz, CDCl3, rt):
298 K):
d 8.37e8.34 (m, 4H, ArHeNs), 8.04e8.01 (m, 4H, ArHeNs),
6.81 (d, 2H, J¼2.3 Hz, ArH), 6.76e6.74 (m, 4H, ArH), 6.65 (d, 2H,
J¼2.6 Hz, ArH), 4.39 (d, 1H, J¼12.6 Hz, ArCH2Ar ax), 4.09 (d, 2H,
J¼13.2 Hz, ArCH2Ar ax), 3.91 (td, 2H, J¼10.1, 5.8 Hz, OCH2),
3.82e3.71 (m, 3H, m, OCH2þArCH2Ar ax), 3.10 (d, 1H, J¼12.6 Hz,
ArCH2Ar eq), 2.76 (d, 2H, J¼13.2 Hz, ArCH2Ar eq), 2.74 (d, 1H,
J¼14.4 Hz, ArCH2Ar eq), 2.11e1.87 (m, 4H, OCH2CH2), 1.07 (s, 18H,
t
tBu), 1.03 (s, 18H, Bu), 0.99 (t, 6H, J¼7.5 Hz, CH3). 13C{1H} NMR
(75 MHz, CDCl3, 298 K):
d
153.4, 151.0, 149.6, 145.0, 142.2, 141.5,
d 162.3, 151.4, 150.2, 143.0, 142.0, 141.4, 136.7, 132.1, 130.3, 126.3,
135.8, 134.2, 133.8, 132.6, 131.0, 126.8, 126.1, 125.9, 124.6, 124.2, 77.3,
34.4, 34.1, 31.8, 31.6, 31.4. TOF MS (ESIþ): calcd for C62H74N2O12S2:
1103.42. Found: m/z (rel intensity, %) 1125.53 (100) [MþNa]þ. IR
124.6, 124.4, 31.8, 31.1, 23.4, 10.1. TOF MS (ESIþ): calcd for
C54H56N4O16S2: 1081.19. Found: m/z (rel intensity, %) 1103.50 (100)
[MþNa]þ. IR (KBr)
n
cmꢂ1: 2967, 1534, 1348, 1314, 1195. EA calcd for

4192
O. Hudecek et al. / Tetrahedron 68 (2012) 4187e4193
C54H56N4O16S2: C, 59.99; H, 5.22; N, 5.18; S, 5.93%. Found: C, 60.03;
H, 5.20; N, 5.12; S, 5.88%.
(100) [MꢂH]ꢂ. IR (KBr)
n
cmꢂ1: 3359, 2963, 1522, 1487, 1344, 1212.
EA calcd for C42H50N2O8: C, 70.96; H, 7.09; N, 3.94%. Found: C,
70.91; H, 7.04; N, 3.93%.
4.5.2. Synthesis of 17,23-di-tert-butyl-5,11-dinitro-25,26-bis(p-ni-
trobenzenesulfonyloxy)-27,28-dipropoxycalix[4]arene
(cone)
4.6.2. Synthesis of 17,23-di-tert-butyl-5,11-dinitro-27,28-
dipropoxycalix[4]arene-25,26-diol (cone) 12. General procedure
was applied to calixarene 9 (0.8 g, 0.74 mmol), product was
obtained as a yellow powder (0.52 g, 99% yield), mp: 216e220 ꢀC.
1H NMR (300 MHz; CDCl3, 298 K): dH 8.65 (m, 2H, ArOH), 7.99 (d,
2H, J¼2.6 Hz, ArH), 7.95 (d, 2H, J¼2.9 Hz, ArH), 7.05 (d, 2H, J¼2.3 Hz,
ArH), 7.02 (d, 2H, J¼2.6 Hz, ArH), 4.69 (d,1H, J¼12.9 Hz, ArCH2Ar ax),
4.39 (d, 2H, J¼12.9 Hz, ArCH2Ar ax), 4.20 (d, 1H, J¼13.5 Hz, ArCH2Ar
ax), 4.15e3.98 (m, 2H, OCH2), 4.06e3.98 (m, 2H, OCH2), 3.60 (d, 1H,
J¼12.6 Hz, ArCH2Ar eq), 3.50 (d, 2H, J¼13.2 Hz, ArCH2Ar eq), 3.39 (d,
9. Calixarene 6 (1.00 g, 0.90 mmol) was ipso-nitrated according to
general procedure, product 9 was isolated as an orange powder
(0.96 g, 98% yield), mp: 137e141 ꢀC. 1H NMR (300 MHz; CDCl3,
298 K): dH 8.41e8.36 (m, 4H, ArHeNs), 8.02e7.98 (m, 4H, ArHeNs),
7.62e7.60 (m, 4H, ArH), 6.71e6.68 (m, 4H, ArH), 4.56 (d, 1H,
J¼13.8 Hz, ArCH2Ar ax), 4.19 (d, 2H, J¼13.5 Hz, ArCH2Ar ax), 4.11 (td,
2H, J¼10.1, 6.1 Hz, OCH2), 3.95 (td, 2H, J¼10.1, 5.8 Hz, OCH2), 3.68 (d,
1H, J¼14.1 Hz, ArCH2Ar ax), 3.36 (d, 1H, J¼13.8 Hz, ArCH2Ar eq), 2.93
(d, 2H, J¼14.1 Hz, ArCH2Ar eq), 2.74 (d, 1H, J¼14.1 Hz, ArCH2Ar eq),
t
2.03e1.83 (m, 4H, OCH2CH2), 1.08e0.93 (m, 24H, 2ꢃ CH3þ2ꢃ Bu).
1H, J¼13.5 Hz, ArCH2Ar eq), 2.18e2.06 (m, 4H, OCH2CH2), 1.25e1.16
13C{1H} NMR (75 MHz, CDCl3, 298 K):
d
161.8, 151.3, 150.9, 142.8,
(m, 24H, CH3þ Bu). 13C{1H} NMR (75 MHz, CDCl3, 298 K):
d 159.4,
t
142.5, 140.9, 135.7, 135.3, 134.1, 130.8, 126.9, 126.7, 124.4, 124.3, 78.2,
34.3, 31.8, 31.7, 31.5, 31.2, 29.9, 23.6, 10.3. TOF MS (ESIþ): calcd for
C54H56N4O16S2: 1081.19. Found: m/z (rel intensity, %) 1103.48 (100)
148.8, 144.4, 144.0, 136.5, 135.2, 128.2, 127.0, 126.6, 125.7, 125.3,
124.1, 79.3, 34.4, 32.9, 32.6, 31.8, 30.3, 30.0, 23.6, 10.5. TOF MS
(ESIþ): calcd for C42H50N2O8: 710.88. Found: m/z (rel intensity, %)
[MþNa]þ. IR (KBr)
n
cmꢂ1: 2965, 1535, 1347, 1313, 1195. EA calcd for
733.57 (100) [MþNa]þ. IR (KBr)
n
cmꢂ1: 3369, 2962, 1517, 1456,
C54H56N4O16S2: C, 59.99; H, 5.22; N, 5.18; S, 5.93%. Found: C, 59.83;
H, 5.19; N, 5.15; S, 5.90%.
1346, 1214. EA calcd for C42H50N2O8: C, 70.96; H, 7.09; N, 3.94%.
Found: C, 70.90; H, 7.05; N, 3.96%.
4.5.3. Synthesis
benzenesulfonyloxy)-26,27,28-tripropoxycalix[4]arene
10. General procedure was applied to calixarene
of
23-tert-butyl-5,11,17-trinitro-25-(p-nitro-
4.6.3. Synthesis of 23-tert-butyl-5,11,17-trinitro-26,27,28-
tripropoxycalix[4]arene-25-ol (cone) 13. General procedure was
applied to calixarene 10 (1.24 g, 1.34 mmol), product was isolated
(cone)
7
(1.4 g,
1.46 mmol), product 10 was isolated as an orange powder (1.34 g,
99% yield), mp: 166e168 ꢀC. 1H NMR (300 MHz; CDCl3, 298 K): dH
8.44e8.41 (m, 2H, ArHeNs), 8.03e8.00 (m, 2H, ArHeNs), 7.93 (d,
2H, J¼2.6 Hz, ArH), 7.86 (d, 2H, J¼2.9 Hz, ArH), 7.34 (s, 2H, ArH), 6.45
(s, 2H, ArH), 4.52 (d, 2H, J¼13.5 Hz, ArCH2Ar ax), 4.17e4.08 (m, 4H,
ArCH2ArþOCH2), 3.95 (td, 2H, J¼10.4, 5.8 Hz, OCH2), 3.86 (t, 2H,
J¼7.2 Hz, OCH2), 3.39 (d, 2H, J¼13.8 Hz, ArCH2Ar eq), 3.00 (d, 2H,
J¼14.1 Hz, ArCH2Ar eq), 1.99e1.83 (m, 6H, OCH2CH2), 1.09 (t, 3H,
J¼7.5 Hz, CH3), 0.97 (t, 6H, J¼7.3 Hz, CH3), 0.80 (s, 9H, tBu). 13C{1H}
as a slightly yellowish powder (0.97 g, 98% yield), mp:
116e117 ꢀC. 1H NMR (300 MHz; CDCl3, 298 K): dH 8.21 (s, 2H,
ArH), 7.34 (d, 2H, J¼2.4 Hz, ArH), 7.23 (d, 2H, J¼2.6 Hz, ArH), 7.17
(s, 2H, ArH), 4.68 (s, 1H, ArOH), 4.51 (d, 2H, J¼13.5 Hz, ArCH2Ar
ax), 4.34 (d, 2H, J¼14.1 Hz, ArCH2Ar ax), 3.99e3.93 (m, 2H, OCH2),
3.82 (td, 4H, J¼6.6, 2.2 Hz, OCH2), 3.44 (d, 2H, J¼13.8 Hz, ArCH2Ar
eq), 3.40 (d, 2H, J¼13.8 Hz, ArCH2Ar eq), 2.20e2.12 (m, 2H,
OCH2CH2), 1.99e1.86 (m, 4H, OCH2CH2), 1.38 (s, 9H, C(CH3)3), 1.13
(t, 6H, J¼7.5 Hz, CH3), 0.95 (t, 3H, J¼7.5 Hz, CH3). 13C{1H} NMR
NMR (75 MHz, CDCl3, 298 K):
d
162.4,161.1,151.3,150.6,143.2,143.0,
(75 MHz, CDCl3, 298 K): d 162.4, 159.8, 150.5, 143.8, 143.6, 143.4,
142.5, 141.5, 136.7, 136.1, 134.4, 132.8, 130.3, 126.5, 124.7, 124.6,
123.9, 78.5, 77.7, 32.0, 31.3, 30.9, 23.6, 23.4, 10.7, 10.1; TOF MS
(ESIþ): calcd for C47H50N4O14S: 927.00. Found: m/z (rel intensity, %)
137.4, 135.3, 133.8, 128.0, 126.4, 125.4, 124.3, 123.2, 78.6, 34.4, 31.9,
31.5, 31.1, 30.0, 23.6, 22.8, 10.9, 9.7. TOF MS (ESIþ): calcd for
C41H47N3O10: 741.85. Found: m/z (rel intensity, %) 764.31 (100)
949.29 (100) [MþNa]þ. IR (KBr)
n
cmꢂ1: 2966, 1523, 1460, 1346,
[MþNa]þ. IR (KBr)
n
cmꢂ1: 3557, 2965, 1524, 1344, 1216. EA calcd
1313, 1196. EA calcd for C54H56N4O16S2: C, 60.90; H, 5.44; N, 6.04; S,
3.46%. Found: C, 60.81; H, 5.44; N, 6.02; S, 3.44%.
for C41H47N3O10: C, 66.38; H, 6.39; N, 5.66. Found: C, 66.33; H,
6.35; N, 5.62%.
4.6. Deprotection of nosyl group (general procedure)
4.7. Synthesis of 5,17-diamino-11,23-di-tert-butyl-26,28-
dipropoxycalix[4]arene-25,27-diol (cone) 14
The corresponding calixarenes 8e10 were dissolved in a mix-
ture of dichloromethane and ethanol (1:1, v/v, 150 ml for 1 g) and
50 equiv of powdered potassium hydroxide was added. The re-
action mixture was stirred at room temperature for 24 h, then
acidified with 1 M hydrochloric acid and extracted with CH2Cl2. The
combined organic layers were washed with water and brine, and
dried over MgSO4. Organic solvent was then removed under re-
duced pressure to give the corresponding products 11e13 bearing
free hydroxyl groups.
A catalytic amount of Raney nickel (10 mg) was added to the
solution of nitro-substituted calix[4]arene 11 (200 mg, 0.28 mmol)
and hydrazine monohydrate (0.7 ml) in methanol (50 ml), and the
mixture was heated to reflux. After 1 h the same amount of hy-
drazine monohydrate (0.7 ml) was added and mixture was refluxed
for further 4 h. After cooling to room temperature, the resulting
suspension was filtered through a short column of Celite, the col-
umn was washed by additional MeOH. The evaporation of solvent
gave product as a slightly brown powder (178 mg, 0.27 mmol, 97%),
mp: 293e298 ꢀC. 1H NMR (300 MHz; CDCl3, 298 K): dH 8.29 (s, 2H,
ArOH), 6.99 (s, 4H, ArH), 6.25 (s, 4H, ArH), 4.24 (d, 4H, J¼12.9 Hz,
ArCH2Ar ax), 3.90 (t, 4H, J¼6.2 Hz, OCH2), 3.24e3.20 (m, 8H,
ArCH2Ar eqþNH2), 2.05e1.94 (m, 4H, OCH2CH2), 1.30e1.25 (m, 24H,
4.6.1. Synthesis of 11,23-di-tert-butyl-5,17-dinitro-26,28-
dipropoxycalix[4]arene-25,27-diol (cone) 11. General procedure
was applied to calixarene 8 (3.5 g, 3.24 mmol), product 11 was
isolated as a yellow powder (2.23 g, 96% yield), mp: >250 ꢀC (dec).
1H NMR (300 MHz; CDCl3, 298 K): dH 7.91 (s, 2H, ArOH), 7.87 (s, 4H,
ArH), 7.13 (s, 4H, ArH), 4.36 (d, 4H J¼12.9 Hz, ArCH2Ar ax), 4.04 (t,
4H, J¼6.2 Hz, OCH3), 3.48 (d, 4H, J¼13.2 Hz, ArCH2Ar eq), 2.17e2.05
tBuþCH3). 13C{1H} NMR (75 MHz, CDCl3, rt):
d 151.4, 145.2, 142.8,
141.3, 134.5, 127.5, 125.4, 116.3, 78.5, 32.2, 32.0, 29.9, 23.7, 11.2; TOF
(m, 4H, OCH2CH2), 1.33 (t, 6H, J¼7.3 Hz, CH3), 1.29 (s, 18H, s, tBu). 13
C
MS (ESIþ): calcd for C42H54N2O4: 650.91. Found: m/z (rel intensity,
{1H} NMR (75 MHz, CDCl3, 298 K):
d
157.5, 150.9, 145.0, 143.2, 135.7,
%) 651.416 (100) [MþH]þ.
n
(KBr, cmꢂ1): 3366, 2959, 1636, 1485,
1225; Anal. Calcd for C42H54N2O4: C, 77.50; H, 8.36; N, 4.30. Found:
C, 77.45; H, 8.33; N, 4.30.
126.4, 126.2, 124.9, 79.4, 34.3, 32.1, 31.9, 23.8, 11.2. TOF MS (ESIꢂ):
calcd for C42H50N2O8: 710.88. Found: m/z (rel intensity, %) 709.34

O. Hudecek et al. / Tetrahedron 68 (2012) 4187e4193
4193
4.8. Synthesis of 11,23-di-tert-butyl-5,17-bis(N0-phenyl-
ureido)-26,28-dipropoxycalix[4]arene-25,27-diol (cone) 15
to carbon atoms were placed in calculated positions. The hydrogen
atoms attached to oxygen atoms were found from differential
electron density map and refined with soft restraints to regularize
their geometry after which the positions were refined with riding
constraints. The structure was deposited into Cambridge Structural
Database under number CCDC 846881.
Phenyl isocyanate (93 mg, 0.78 mmol) was added to a solution of
calix[4]arene 14 (100 mg, 0.15 mmol) in 30 ml of dry CH2Cl2 under
nitrogen atmosphere. The resulting solution was stirred for 2 days
at room temperature. Then, 5 ml of MeOH was added to quench the
reaction and the mixture was stirred for further 1 h. Solvents were
removed under reduced pressure and the residue was purified by
column chromatography (Al2O3, eluent CH2Cl2/MeOH¼100:1) and
then using preparative TLC (SiO2, eluent CH2Cl2/MeOH¼50:1) to
give a product as a slightly brown powder (40 mg, 0.045 mmol,
29%), mp: 315e317 ꢀC. 1H NMR (300 MHz; DMSO-d6, rt): dH 8.54 (s,
2H, NH), 8.42 (s, 2H, ArOH), 8.14 (s, 2H, NH), 7.36 (d, 4H, J¼8.8 Hz,
ArH), 7.21 (t, 4H, J¼7.5 Hz, ArH), 7.10 (s, 8H, ArH), 6.90 (d, 2H,
J¼7.3 Hz, ArH), 4.16 (d, 4H J¼12.3 Hz, ArCH2Ar ax), 3.91 (t, 4H,
J¼5.4 Hz, OCH2), 3.39 (d, 4H, J¼12.6 Hz, ArCH2Ar eq), 2.00e1.94 (m,
4H, OCH2CH2), 1.31 (t, 6H, J¼7.3 Hz, CH3), 1.23 (s, 18H, tBu). 13C{1H}
Acknowledgements
This research was partly supported by the Czech Science
Foundation (203/09/0691) and the Grant Agency of the Academy of
Sciences of the CR (IAAX08240901). Grants MSM6046137301 and
MSM6046137302 from Ministry of Education, Youth and Sports of
the CR are also highly acknowledged.
Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.tet.2012.03.102.
NMR (75 MHz, CDCl3, rt):
d 153.9, 151.1, 148.5, 141.9, 138.7, 134.8,
134.3, 129.0, 127.2, 125.6, 123.0, 121.6, 119.5, 78.5, 34.0, 32.0, 31.7,
23.6, 11.0; TOF MS (ESIþ): calcd for C56H64N4O6: 889.16. Found: m/z
(rel intensity, %) 911.472 (80) [MþNa]þ.
n
(KBr, cmꢂ1): 3365, 2958,
1650, 1465, 1364, 1216; Anal. Calcd for C56H64N4O6: C, 75.65; H,
7.26; N, 6.30. Found: C, 75.62; H, 7.24; N, 6.28.
References and notes
1. For books on calixarenes see: (a) Gutsche, C. D. In Calixarenes an Introduction:
Monographs in Supramolecular Chemistry; Stoddart, J. F., Ed.; The Royal Society
€
of Chemistry: Cambridge, 2008; (b) Calixarenes 2001; Asfari, Z., Bohmer, V.,
Harrowfield, J., Vicens, J., Eds.; Kluwer Academic: Dordrecht, 2001; (c) Man-
dolini, L.; Ungaro, R. Calixarenes in Action; Imperial College: London, 2000; (d)
Gutsche, C. D. In Calixarenes Revisited: Monographs in Supramolecular Chem-
istry; Stoddart, J. F., Ed.; The Royal Society of Chemistry: Cambridge, 1998;
Vol. 6.
4.9. Crystallographic measurements
4.9.1. Crystallographic data for C54H56N4O16S2$2(C3H6O) (8$2
acetone). M¼1197.35, monoclinic system, space group C2/c,
2. Calixarenes in the Nanoworld; Vicens, J., Harrowfield, J., Baklouti, L., Eds.;
Springer: Dordrecht, 2007.
ꢁ
3
ꢁ
ꢂ3
, m
ꢁ
a¼28.894(5) A, b¼11.6449(8) A, c¼24.271(4) A,
b
¼131.44(3)ꢀ, Z¼4,
V¼6122(3) A , Dc¼1.299 g cm
(Cu Ka
)¼1.41 mmꢂ1, crystal di-
ꢁ
3. For review on cationic receptors see e.g.: (a) Siddiqui, S.; Cragg, P. J. Mini-Rev.
Org. Chem. 2009, 6, 283e299; (b) Leray, I.; Valeur, B. Eur. J. Inorg. Chem. 2009, 24,
3525e3535; For review on calixarene-based anion receptors see e.g.: (c)
Matthews, S. E.; Beer, P. D. In Calixarenes; 2001; pp 421e439 (see Ref. 1b); (d)
mensions of 0.32ꢃ0.43ꢃ0.54 mm. Data were collected at 150(2) K
on
a Xcalbur OnyxCCD diffractometer with graphite mono-
chromated Cu K
a
radiation. The structure was solved by direct
ꢀ
Lhotak, P. Top. Curr. Chem. 2005, 255, 65e96; (e) Matthews, S. E.; Beer, P. D.
methods12 using the CRYSTALS suite of programs13 and aniso-
tropically refined by full matrix least squares on F value to final
R¼0.0644 and Rw¼0.0760 using 5614 independent reflections
Supramol. Chem. 2005, 17, 411e435; For neutral molecules see e.g.: (f) Coquiere,
D.; Le Gac, S.; Darbost, U.; Seneque, O.; Jabin, I.; Reinaud, O. Org. Biomol. Chem.
2009, 7, 2485e2500; (g) Lhotak, P.; Kundrat, O. In Artificial Receptors for
Chemical Sensors; Mirsky, V., Yatsimirsky, A., Eds.; Wiley-VCH: Weinheim, 2011;
pp 249e272.
4. Kelderman, E.; Derhaeg, L.; Heesink, G. J. T.; Verboom, W.; Engbersen, J. F. J.;
Hulst, N. F.; Persoons, A.; Reinhoudt, D. N. Angew. Chem., Int. Ed. Engl. 1992, 31,
1075e1077.
(
Qmax¼77.9ꢀ), 406 parameters and 48 restrains. The positions of
disordered tert-butyl group were found from the electron density
maps. All distances between neighbouring atoms and angles were
fixed. Site occupancies were assigned resulting in similar thermal
parameters for both group positions. The hydrogen atoms were
placed in calculated positions. The structure was deposited into
Cambridge Structural Database under number CCDC 826041.
5. (a) Verboom, W.; Durie, A.; Egberink, R. J. M.; Egberink, J. M.; Asfari, Z.; Rein-
€
houdt, D. N. J. Org. Chem. 1992, 57, 1313e1316; (b) Jakobi, R. A.; Bohmer, V.;
€
Gruttner, C.; Kraft, D.; Vogt, W. New J. Chem. 1996, 20, 493e501.
6. (a) Mogck, O.; Pons, M.; Boehmer, V.; Vogt, W. J. Am. Chem. Soc. 1997, 119,
5706e5712; (b) Vatsouro, I.; Alt, E.; Vysotsky, M.; Boehmer, V. Org. Biomol.
Chem. 2008, 6, 998e1003; (c) Kenis, P. J. A.; Noordman, O. F. J.; Schoenherr, H.;
Kerver, E. G.; Snellink-Rueel, B. H. M.; van Hummel, G. J.; Harkema, S.; van der
Vorst, C. P. J. M.; Hare, J.; Picken, S. J.; Engbersen, J. F. J.; van Hulst, N. F.; Vancso,
G. J.; Reinhoudt, D. N. Chem.dEur. J. 1998, 4, 1225e1234.
4.9.2. Crystallographic data for C42H50N2O8: (12). M¼710.87,
ꢁ
monoclinic system, space group P21/n, a¼11.6699(8) A,
b¼30.6312(12) A, c¼21.9350(11) A,
b
¼103.653(6)ꢀ, Z¼8,
ꢁ
ꢁ
7. (a) Mogck, O.; Boehmer, V.; Ferguson, G.; Vogt, W. J. Chem. Soc., Perkin Trans. 1
1996, 14, 1711e1716; (b) Creaven, B. S.; Gernon, T. L.; McGinley, J.; Moore, A.-M.;
Toftlund, H. Tetrahedron 2006, 62, 9066e9071; (c) Bitter, I.; Gruen, A.; Toth, G.;
Szoellosy, A.; Horvath, G.; Agai, B.; Toke, L. Tetrahedron 1996, 52, 639e646; (d)
Rashidi-Ranjbar, P.; Taghvaei-Ganjali, S.; Shaabani, B.; Akbari, K. Molecules
2000, 5, 941e944.
3
ꢂ3
, m
V¼7619.4(7) A , Dc¼1.239 g cm
(Cu Ka
)¼0.69 mmꢂ1, crystal
ꢁ
dimensions of 0.24ꢃ0.37ꢃ0.49 mm. Data were collected at 170(2) K
on
a Xcalbur OnyxCCD diffractometer with graphite mono-
chromated Cu K
a
radiation. The structure was solved by direct
ꢀ
ꢀ
8. Hudecek, O.; Curinova, P.; Budka, J.; Lhotak, P. Tetrahedron 2011, 67, 5213e5218.
9. Iwamoto, K.; Araki, K.; Shinkai, S. J. Org. Chem. 1991, 56, 4955e4962.
10. (a) Boyko, V. I.; Podoprigorina, A. A.; Yakovenko, A. V.; Pirozhenko, V. V.; Kal-
chenko, V. I. J. Inclusion Phenom. Macrocyclic Chem. 2004, 50, 193e197; (b)
methods12 using the CRYSTALS suite of programs13 and aniso-
tropically refined by full matrix least squares on F2 value to final
R¼0.051 and Rw¼0.097 using 15,627 independent reflections
ꢀ
ꢀ
ꢀ
Lhotak, P.; Bíla, A.; Budka, J.; Pojarova, M.; Stibor, I. Chem. Commun. 2008,
1662e1664.
(
Qmax¼76.4ꢀ), 991 parameters and 62 restrains. The positions of
11. Iwamoto, K.; Araki, K.; Shinkai, S. Tetrahedron 1991, 47, 4325e4342.
12. Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla, M. C.; Polidori,
G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435e436.
disordered propoxy groups were found from the electron density
maps. All distances between neighbouring atoms and angles were
fixed. Site occupancies were assigned resulting in similar thermal
parameters for both group positions. The hydrogen atoms attached
13. Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.; Watkin, D. J. J. Appl.
Crystallogr. 2003, 36, 1487.