Supramolecular Columnar Liquid Crystals with Tapered-Shape Simple Pyrazoles Obtained by Efficient Henry/Michael Reactions

Article abstract of DOI:10.1002/chem.201504779

A straightforward synthesis of mesogenic pyrazoles starting from benzaldehydes by a combination of efficient Henry and Michael reactions led to novel supramolecular liquid crystals. The mesogens are fluorescent 3,5-dimethyl-4-(di or trialkoxyphenyl)pyrazoles and, in spite of the tapered shape of these molecules and their structural simplicity (only one phenyl ring), columnar liquid-crystal phases were formed that are stable at room temperature. The self-assembled structure was studied by XRD and the columnar cross section contains two molecules on average with an antiparallel arrangement of pyrazoles interacting through hydrogen bonds. In contrast, the single-crystal structure of a trimethoxy analog did not show hydrogen-bonded pyrazoles but chains of head-to-tail arranged molecules.

Full text of DOI:10.1002/chem.201504779

DOI: 10.1002/chem.201504779
Full Paper
&
Liquid Crystals
Supramolecular Columnar Liquid Crystals with Tapered-Shape
Simple Pyrazoles Obtained by Efficient Henry/Michael Reactions
Hugo Blanco,[a] Verónica Iguarbe,[a] Joaquín Barberµ,[a] JosØ Luis Serrano,[b]
Anabel Elduque,*[c] and Raquel GimØnez*[a]
Abstract: A straightforward synthesis of mesogenic pyra-
zoles starting from benzaldehydes by a combination of effi-
cient Henry and Michael reactions led to novel supramolec-
ular liquid crystals. The mesogens are fluorescent 3,5-di-
methyl-4-(di or trialkoxyphenyl)pyrazoles and, in spite of the
tapered shape of these molecules and their structural sim-
plicity (only one phenyl ring), columnar liquid-crystal phases
were formed that are stable at room temperature. The self-
assembled structure was studied by XRD and the columnar
cross section contains two molecules on average with an an-
tiparallel arrangement of pyrazoles interacting through hy-
drogen bonds. In contrast, the single-crystal structure of a tri-
methoxy analog did not show hydrogen-bonded pyrazoles
but chains of head-to-tail arranged molecules.
Introduction
lecular shapes, such as tapered-shape ones, to yield columnar
liquid crystals.[3] In particular, the 1H-pyrazole heterocycle is
able to form intermolecular NH···N interactions and this ability
has been successfully exploited to yield columnar mesophases
with luminescent properties with either disc-like supramolec-
ular dimeric entities[4] or aggregates formed by tapered mole-
cules.[5]
Supramolecular liquid crystals are fascinating examples of soft
matter in which the molecules give rise to ordered, yet fluid,
arrangements through non-covalent interactions.[1] There is in-
creasing interest in finding novel supramolecular columnar
liquid crystals, as they form architectures with control at the
nanoscale, and have the potential to respond to different ex-
ternal stimuli such as temperature, pressure, pH, light, etc.,
which are beneficial attributes for efficient responsive materi-
als.[2]
In terms of molecular structure, a common molecular design
for columnar liquid crystals is to have aromatic rings substitut-
ed with two or three long alkoxy tails (C6 or longer). To achieve
this goal, it is necessary to adapt previously described synthet-
ic routes for non-substituted analogs, or methoxy-substituted
analogs, and this task is not always straightforward.[6]
Among other possibilities, molecules with hydrogen-bond-
ing groups and appropriate shape anisotropy are able to form
columnar mesophases. They can interact by intermolecular hy-
drogen bonds forming disc-like entities, which then self-assem-
ble into columns or, in other cases, they provide dynamic hy-
drogen-bonded networks that self-assemble into columns
without any intermediate stage of disc-like supramolecules.
The latter approach allows a great variety of non-discoid mo-
The work described here concerns novel supramolecular col-
umnar liquid crystals made of structurally simple luminescent
molecules. Moreover, these novel functional molecules have
the desired property with a simple structural motif and are ob-
tained with atom-economy and efficient synthetic methodolo-
gies.[7] These compounds are 3,5-dimethyl-4-(di or trialkoxy-
phenyl)-1H-pyrazoles and were prepared by Henry and Michael
reactions (Scheme 1). This synthesis is compatible with both
methoxy-substituted compounds, and dialkoxy- or trialkoxy-
terminated (C10 and C14) molecules. In spite of the tapered
shape of these molecules and their structural simplicity (only
one phenyl ring), columnar liquid-crystal phases were formed
that are stable at room temperature.
[a] H. Blanco, V. Iguarbe, Prof. J. Barberµ, Dr. R. GimØnez
Instituto de Ciencia de Materiales de Aragón (ICMA)
Dpto de Química Orgµnica, Facultad de Ciencias
CSIC—Universidad de Zaragoza, 50009 Zaragoza (Spain)
E-mail: rgimenez@unizar.es
[b] Prof. J. L. Serrano
Dpto de Química Orgµnica, Facultad de Ciencias
Instituto de Nanociencia de Aragón (INA)
Universidad de Zaragoza 50018 Zaragoza (Spain)
Results and Discussion
[c] Dr. A. Elduque
Dpto de Química Inorgµnica
Synthesis
Instituto de Síntesis Química y Catµlisis HomogØnea (ISQCH)
Facultad de Ciencias, CSIC—Universidad de Zaragoza
50009 Zaragoza (Spain)
An efficient method frequently used in the synthesis of meso-
morphic pyrazoles is the condensation reaction of a 1,3-dike-
tone with hydrazine hydrate.[8] The synthesis of the target 3,5-
dimethyl-4-aryl-1H-pyrazoles by this straightforward method
E-mail: anaelduq@unizar.es
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201504779.
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(about 90%) by using DMF at 1208C and 8 h for dialkylation or
15 h for trialkylation. This first step was not necessary for com-
pound 4 f as the 3,4,5-trimethoxybenzaldehyde is commercially
available.
In the second and third steps, nitroethane was used both as
the reagent and solvent. In the second step, the aldol conden-
sation between nitroethane and polyalkoxybenzaldehyde[17]
(Henry reaction) gave the nitroalkene product in very high
yield. In the third step, the Michael addition of nitroethane to
the nitroalkene occurred at room temperature for the C10 and
at 508C for the C14 derivatives owing to the low solubility of
the latter in nitroethane. The 1,3-dinitroalkane product is not
unique but a mixture of four stereoisomers[18] owing to the for-
mation of two stereogenic centers (a dl pair and two meso
forms for 3a–d and 3 f, and four diastereoisomers for 3e),
which appear on a thin layer chromatography (TLC) plate as
three spots. These components could be isolated and charac-
Scheme 1. Synthesis of the 3,5-dimethyl-4-polyalkoxyphenyl-1H-pyrazoles.
1
terized by H NMR spectroscopy (Figure S1 in the Supporting
Information). As in the next step all of the stereoisomers give
the same pyrazole, the final isolated yield of this reaction is
70%.
would require the preparation of the 3-aryl-2,4-pentanediones.
For the synthesis of these substituted 1,3-diketone precursors,
arylation of activated methylene compounds mediated by
copper salts using iodoarenes is a well-established process[9]
and usually requires a stoichiometric[9,10] or catalytic[11] amount
of copper salt. This approach was used to prepare 3-(4-benzyl-
The final step is the limiting one and it involves the reaction
of the 1,3-dinitroalkanes with hydrazine hydrate to form the
pyrazole ring.[15] A side reaction related to that in which the 2-
aryl-1,3-dinitro compounds can be readily transformed under
basic conditions into 2-isoxazoline-2-oxides or isoxazoles has
been reported.[18,19] In our case, the formation of the 3,5-di-
methyl-4-arylisoxazole byproduct was also observed and this
was minimized by adding acetic acid. The best reaction condi-
tions provided the pyrazoles in 65% yield. In addition, the iso-
xazole byproduct could be isolated and transformed into the
desired pyrazole in a further step (Figure S2 in the Supporting
Information) by heating with hydrazine hydrate and Raney
nickel.[20] Pyrazoles were characterized by elemental analysis,
NMR spectroscopy, and mass spectrometry and the data are
consistent with the proposed chemical structures (see the Ex-
perimental Section).
oxyphenyl)-2,4-pentanodione,
a compound similar to our
target, in moderate yield (54%).[12] More recently, it has been
reported that acetylacetone can be arylated with iodoarenes
under milder conditions by treatment with a catalytic amount
of copper(I) iodide and l-proline as a promoter.[13] In this way,
and after optimizing the reaction temperature and time in
order to avoid the deacylation side reaction that leads to
benzyl methyl ketones,[14] the synthesis of 3-aryl-2,4-pentano-
diones with one electron-withdrawing group (NO2), or with
one electron-donating group (OH or OCH3) in the para-position
was achieved with yields of 74% and 44%, respectively in our
previous work.[5]
This route could be applied to the required 1,3-diketones by
using the commercially available 4-iodo-1,2-dimethoxybenzene
and 5-iodo-1,2,3-trimethoxybenzene. In subsequent steps, the
diketone would be demethylated and alkylated with the long
chains, that is, a deprotection step would be necessary. How-
ever, all attempts to obtain the diketones gave only very low
yields (less than 20%). This setback led us to explore other syn-
thetic routes that were more compatible with the presence of
two or three long alkoxy chains.
UV/Vis absorption and fluorescence properties
The UV/Vis absorption spectra of the pyrazoles in tetrahydro-
furan solution are different depending on the number of termi-
nal alkoxy chains (Table 1). Two bands at 249 nm and 287 nm
appear for the disubstituted compounds and only one band at
253 nm for the trisubstituted compounds, which is consistent
with a less conjugated or less planar ground state for the latter
A successful route was identified and this involved the prep-
aration of 3,5-dimethyl-4-aryl-1H-pyrazoles from 1,3-dinitroal-
kanes,[15] which can be obtained from readily accessible benzal-
dehydes by efficient Henry/Michael reactions. This synthetic
route, along with the chemical structures of the resulting pyra-
zoles 4a–f, is depicted in Scheme 1. The di- and trialkoxy-sub-
stituted compounds were obtained in high yields.
Table 1. UV/Vis and fluorescence data for the pyrazoles.
Compound
labs [nm]
e”10À4 [LmolÀ1 cmÀ1
]
lem [nm]
QY [%][a]
4a
4b
4c
4d
4 f
249, 287
249, 287
253
253
253
1.14, 0.43
1.36, 0.42
1.35
1.33
1.27
335
337
358
359
364
8.5
8.0
0.2
0.2
0.1
The first step involved alkylation with 1-bromodecane or 1-
bromotetradecane of the commercially available 3,4-dihydroxy-
or 3,4,5-trihydroxybenzaldehyde under Williamson condi-
tions.[16] The alkylated products were obtained in high yields
[a] Quantum yield (QY) relative to quinine sulfate.[22]
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(a non-planar structure is observed in the crystal structure of
4 f, see below).
All these compounds showed one emission band in the near
UV region. The emission wavelength is similar to that found
for 3,5-bis(alkoxyphenyl)-substituted pyrazoles.[4,21] The number
of terminal chains also influences the fluorescence spectra. The
trisubstituted compounds show a band at higher wavelengths
with much lower quantum yields than the disubstituted com-
pounds. This observation is consistent with these non-planar
compounds having more effective pathways for non-radiative
deactivation by torsional motions.
Liquid crystalline properties and self-organization model
Polarized optical microscopy (POM) and differential scanning
calorimetry (DSC) studies were performed on the final pyrazole
compounds 4a–e to determine their mesomorphic properties.
The thermal data are collected in Table 2. In addition, thermo-
Table 2. Thermal properties of the pyrazoles.
Compound
Phase transitions, T [8C] (DH [kJmolÀ1])[a]
4a
Cr 71 (38.7) Iso[b]
Iso 10 (18.0) Cr’
4b
4c
4d
4e
Cr 50[c] Cr’ 85[d] (56.6) Iso
Iso 47 (48.4) Cr’
Colr 79 (12.7) Iso
Iso 78 (13.1) Colr
Figure 1. Microphotographs under crossed polarizers of the liquid-crystal
textures observed on cooling from the isotropic liquid: a) 4c at 648C (10”
magnification), b) 4c at 788C (20” magnification), c) 4d at 458C (20” mag-
nification), d) 4e at 748C (10” magnification), e) sheared 4c at 788C (20”
magnification), f) sheared 4d at 458C (20” magnification).
Cr 19 (21.0) Cr’ 29 (15.7) Colr 56[d] (3.8) Iso
Iso 49 (3.9) Colr 25 (16.3) Cr’ 13 (19.6)[e] Cr
Colr 76 (10.7) Iso
Iso 74 (12.4) Colr
[a] DSC data at 108CminÀ1 of the first cooling and second heating cycle.
Onset temperatures given. Abbreviations: Cr, Cr’=crystal phases, Colr =
rectangular columnar mesophase, Iso=isotropic liquid. [b] First heating
cycle. [c] Includes a cold recrystallization. [d] Peak temperature. [e] Com-
bined enthalpy of several crystal-to-crystal transitions.
crossed needles appeared from the isotropic liquid (Figure 1a)
and this remained down to room temperature. A faster cooling
of the sample gave rise to a texture with some pseudo focal-
conic defects more commonly observed for columnar meso-
phases (Figure 1b). Similar behavior was observed for 4d,
albeit in a shorter temperature interval (Figure 1c), and 4e
(Figure 1d). Even though such needle-like growth is not con-
ventional for liquid-crystal phases, the textures show shear
flow, a typical property of a liquid-crystal phase (Figure 1e, f).
The columnar-to-isotropic liquid transition of the DSC heat-
ing cycle is quite broad and showed some thermal hysteresis
at a standard rate of 108CminÀ1 (6–128C considering the peak
temperature maxima, but only 1–28C considering onset tem-
peratures), which is a common behavior for viscous supra-
molecular liquid crystals. Moreover, by reducing the rate to
18CminÀ1, the thermal hysteresis between peak maxima was
reduced to 4–68C (see DSC thermograms in the Supporting In-
formation).
gravimetric analysis (see the Supporting Information) con-
firmed the stability of the compounds below 3008C, that is,
well above the melting and clearing points.
The melting temperatures decrease upon increasing the
number of alkoxy chains (4a vs. 4c and 4b vs. 4d) and in-
crease with the length of the alkoxy chain (4a vs. 4b and 4c
vs. 4d). The melting enthalpies are also higher for longer
chains as a consequence of the increase in the London disper-
sion forces.
Although pyrazoles 4a–f do not have the classical shape of
liquid crystals (i.e., rod-like or disc-like), the compounds with
three long alkoxy chains, 4c, 4d, and 4e, display columnar
liquid crystal phases (Figure 1).
The XRD studies confirmed unambiguously the liquid-crystal
phase. An XRD study at 208C of 4c gave a diffraction pattern
that is compatible with a columnar mesophase (Figure 2a). In
the high-angle region of the diffractogram a broad diffuse halo
Compound 4c is a viscous paste at room temperature and it
shows birefringence by POM and a transition to the isotropic
liquid at 798C. On slow cooling, a texture growing as long
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Table 3. XRD data for the liquid crystalline phases.
Comp-
ound
T
[8C]
dobs
[Š]
hk
dcalc
[Š]
Mesophase
and lattice
constants [Š]
4c
20
22.8
16.8
13.5
12.2
10.9[a]
9.3[a]
8.6
11
21
02
31
22, 40
32, 13
42
22.8
16.7
13.5
12.6
11.4, 10.6
9.8, 8.8
8.4
Colr
a=42.6
b=27.0
7.6
33
7.6
6.7
04
6.7
6.2
4.5 (br)[b]
62
–
6.3
–
4d
35
25.9
14.5
12.0
10.4
20
31
22
32
25.85
14.5
12.0
10.65
9.7
Colr
a=51.7
b=27.1
10.0
51
7.3
4.5 (br)[b]
43, 62
–
7.4, 7.3
–
4e
20
22.0
16.1
13.5
12.3
10.8
9.1[a]
8.2
11
21
02
31
22.2
16.1
13.3
12.0
Colr
Figure 2. a) X-ray diffractogram of 4c at 208C. b) Schematic drawing of a rec-
tangular columnar mesophase with p2gg symmetry, indicating the parame-
ters obtained for 4c.
a=40.3
b=26.6
22
11.1
32, 13
23, 42
33
9.5, 8.7
8.1, 8.0
7.4
that is characteristic of a liquid crystal was observed at a dis-
tance of 4.5 Š, which is typical of the conformational disorder
of the hydrocarbon chains in a fluid phase. In addition, the dif-
fractogram contained multiple diffraction maxima in the low-
angle region and these can be assigned to a columnar meso-
phase with rectangular symmetry. Compound 4d and 4e gave
similar diffractograms (see the Supporting Information).
It can be observed from the diffractograms for 4c, 4d, and
4e that, for some reflections, the sum of the Miller indexes
(h+k) is an odd number (Table 3). This suggests that the sym-
metry of the 2D packing of columns is p2gg and implies that
in the mesophase the cross section of the columns is elliptical
and the direction of the main axes of the ellipses is alternating
(Figure 2b). The p2gg symmetry is consistent with the pres-
ence of two columns per unit cell in the rectangular columnar
phase.
7.2
6.1
24, 62
–
6.3, 6.0
–
4.5 (br)[b]
[a] This peak probably corresponds to two overlapped reflections.
[b] br=broad halo.
ecules that interact by hydrogen bonds (Figure 3). The three
alkoxy chains surround an inner polar region formed by hydro-
gen-bonded pyrazoles in a column, which is tilted in the rec-
tangular columnar mesophase (Figure 2b).
Compounds 4d and 4e show the same features by POM
and XRD, and the same model is applicable to these two com-
pounds. The chiral terminal tails of compound 4e do not
impart any observable chiral features to the XRD diffracto-
grams,[4] although an increase in the lattice constant is ob-
served for 4d, as one would expect given the longer chains.
On the other hand, 4e has similar lattice constants (only slight-
ly smaller) to 4c. Although the chains are shorter for 4e com-
pared with 4c, this is not relevant for the dimensions of the
unit cell. Indeed, as a result of the high conformational disor-
der of the hydrocarbon chains in the columnar mesophase, for
the same core, the lattice constants depend mainly on the
total number of carbon atoms in the hydrocarbon chain (ten
in both cases) and not on its length.
These data allow us to propose a model for the self-organi-
zation of the molecules of 4c in the mesophase. Although the
molecular geometry of the molecule is tapered, it is known
that molecules that do not have a discoid geometry can as-
semble through supramolecular interactions to give rise to
a columnar organization.[3]
An estimation of the number of molecules in the unit cell
gives a value of four (see the Supporting Information). Taking
into account that the proposed geometry of the rectangular
cell includes two discs per cell unit, then each disc should be
formed by two molecules on average. In addition, the IR spec-
trum of the mesophase indicates that the pyrazoles are associ-
ated by hydrogen bonding (3174 cmÀ1 for the NÀH stretching
band). A model for the columnar mesophase can be proposed
in which the columnar cross section is formed by a pair of mol-
The driving force for the formation of the columnar meso-
phase is the nanosegregation between long alkoxy terminal
chains (lipophilic part) and hydrogen-bonded pyrazoles (polar
part). The change of the alkyl chain volume by decreasing the
number of alkoxy tails from three to two resulted in the loss of
mesomorphism. This behavior is different from that reported
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Figure 4. ORTEP drawing of the molecular structure of 4 f.
rings are not co-planar but are twisted by 46.78. This structure
is consistent with reported single-crystal structures of 4-aryl-
3,5-dimethylpyrazoles.[5,27] The methyl groups of the methoxy
substituent in the meta-position lie close to the plane of the
phenyl ring (9.48 and 48), whereas that in the para-position is
almost perpendicular to the phenyl ring (78.48).
As far as the packing structure is concerned, the molecules
are arranged in antiparallel chains along the c axis, with each
chain formed by a head-to-tail arrangement of molecules that
interact by NH···OCH3 hydrogen bonds between the NH of one
pyrazole and the oxygen atoms of the next molecule (Figure 5,
dashed lines). These distances (N1–O1’ and N1–O2’) are 2.94 Š
and 3.29 Š, respectively, which are longer than typical hydro-
gen bonds. In addition, antiparallel chains establish N···H–CO
short contacts in the ac plane, that is, between the pyridinic ni-
trogen of the pyrazole and the methoxy groups of adjacent
chains (Figure 5, dashed lines).
Interestingly, the NH stretching band appears at 3353 cmÀ1
in the IR spectrum of compound 4 f and this is a higher wave-
number than that for the NH···N associated pyrazoles found in
4a–d and other pyrazoles (less than 3200 cmÀ1). This finding is
consistent with the absence of NH···N interactions in the
single-crystal structure of 4 f but the presence of NH···OCH3 in-
teractions.
Figure 3. Proposed molecular organization in a column cross section with
a pair of molecules interacting by hydrogen bonds.
for similar tapered amphiphiles such as 3,5-dihydroxycyclohex-
yl 3,4,5-trialkoxyphenylbenzoates[23] or polyol-substituted 3,4,5-
trialkoxybenzamides,[24] which usually display cubic or smectic
phases on changing the lipophilic volume. In addition, the
alkoxy substituents on the phenyl ring play a fundamental role
in the formation of the NH···N hydrogen bonds between the
pyrazoles as evident from the fact that in the single-crystal
structure of the trimethoxy analog 4 f, the hydrogen-bonded
dimers do not form in the absence of long alkoxy chains (see
next section).
The unexpected assembly capability found here is similar to
analogous structures with hydrogen-bonding ability such as
3,4,5-trialkoxybenzamides.[25] In contrast, 3,4,5-trialkoxybenzoic
acids are not liquid crystals.[26]
The supramolecular chemistry shown by these 3,5-dimethyl-
4-(3,4,5-trialkoxyphenyl)pyrazoles can be used as a model or
“generation-one”[1c] of larger generation dendrons with a pyra-
zole at the apex. This possibility is currently being studied in
our research group.
Crystal structure of the trimethoxy analog 4 f
Conclusion
The molecular structure of 4 f was solved by XRD crystallogra-
phy on a suitable single crystal (Figure 4). The results show
that the molecule is not flat and the pyrazole and the phenyl
A combination of Henry and Michael reactions on polyalkoxy-
benzaldehydes provides novel fluorescent supramolecular
Figure 5. Detail of the packing of 4 f in chains along the c axis, with intrachain and interchain contacts (dashed lines).
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69.4, 32.0, 31.9, 30.3, 29.74, 29.68, 29.64, 29.59, 29.4, 29.35, 26.1,
22.7, 14.2, 14.1 ppm; IR (KBr): n=3068, 2954, 2919, 2870, 2847,
1649, 1577, 1516, 1495, 1385, 1361, 1252, 1171, 1120 cmÀ1; elemen-
tal analysis calcd (%) for C39H69NO5: C 74.12, H 11.00, N 2.22; found:
C 74.26, H 10.77, N 2.52.
liquid crystals in an efficient way. The mesophases are stable at
room temperature.
In the columnar liquid-crystal phase, the columns consist of
the stacking of pairs of molecules on average formed by an
outer region with a peripheral spread of the terminal chains
and an inner region containing the rigid aromatic ring and the
polar pyrazole rings. The comparison of the long-chained com-
pounds with the trimethoxy parent compound shows that the
substituents at the phenyl ring, which are the lipophilic part
and determine the tapered shape, are an important driving
force for the supramolecular organization. Moreover, hydrogen
bonding and the tapered shape together, acting cooperatively,
give rise to formation of the columnar aggregates.
General procedure for the synthesis of the dinitroalkanes
3a–f
A mixture of the nitroalkene (10 mmol), nitroethane (50–100 mL),
and anhydrous K2CO3 (8 mmol) was stirred at room temperature
(at 508C for tetradecyloxy chains) for 10 h. The reaction mixture
was filtered, evaporated to dryness, and purified by column chro-
matography on silica gel or by recrystallization.
3c: Eluent for purification (hexane/ethyl acetate 9:1). Yield: 73%,
white solid. Rf: 0.83 (meso 1); 0.72 (dl pair); 0.55 (meso 2) (hexane/
1
ethyl acetate 8:2); m.p.: 338C (mixture of stereoisomers); H NMR
Experimental Section
(400 MHz, CDCl3, 208C, TMS): d=meso 1 (2R,3S,4S): 6.21 (s, 2H),
4.77 (q, J=6.5 Hz, 2H), 3.99 (t, J=7.7 Hz, 1H), 3.95–3.86 (m, 6H),
1.81–1.69 (m, 6H), 1.46 (d, J=6.5 Hz, 6H), 1.48–1.42 (m, 6H), 1.38–
1.18 (m, 36H), 0.87 (t, J=6.9 Hz, 9H); dl pair (2R,4R)+(2S,4S): 6.19
(s, 2H), 5.21 (dq, J=6.7, 10.2 Hz, 1H), 4.77 (dq, J=4.8, 6.6 Hz, 1H),
3.95–3.86 (m, 6H), 3.48 (dd, J=10.2, 4.8 Hz, 1H), 1.81–1.69 (m, 6H),
1.48–1.42 (m, 6H), 1.46 (d, J=6.6 Hz, 3H), 1.37 (d, J=6.7 Hz, 3H),
1.38–1.18 (m, 36H), 0.87 (t, J=6.9 Hz, 9H); meso 2 (2R,3R,4S): 6.19
(s, 2H), 5.12 (q, J=6.4 Hz, 2H), 3.95–3.86 (m, 6H), 3.39 (t, J=6.8 Hz,
1H), 1.81–1.69 (m, 6H), 1.65 (d, J=6.4 Hz, 6H), 1.48–1.42 (m, 6H),
1.38–1.18 (m, 36H), 0.87 ppm (t, J=6.9 Hz, 9H); 13C NMR (100 MHz,
CDCl3, 208C, TMS): (mixture of stereoisomers) d=153.5, 153.1,
138.83, 138.76, 127.1, 126.9, 126.5, 107.8, 107.32, 107.27, 83.53,
83.47, 83.0, 82.2, 73.34, 73.32, 73.2, 69.4, 69.3, 69.2, 53.9, 53.7, 52.6,
31.88, 31.86, 30.3, 29.7, 29.61, 29.57, 29.5, 29.4, 29.34, 29.32, 29.30,
26.0, 22.64, 22.63, 19.3, 17.6, 17.0, 16.1, 14.0 ppm; IR (KBr): n=
1589, 1557, 1389, 1356, 1338, 1244, 1167, 1114 cmÀ1; elemental
analysis calcd (%) for C41H74N2O7: C 69.65, H 10.55, N 3.96; found: C
70.05, H 10.23, N 4.01.
General synthetic procedures and characterization data for 4c and
precursors are reported as an example. Full data for all products
are collected in the Supporting Information.
General procedure for the synthesis of the aldehydes 1a–e
A solution of 3,4-dihydroxybenzaldehyde or 3,4,5-trihydroxybenzal-
dehyde (10 mmol) in DMF (100 mL) was mixed with anhydrous
K2CO3 (70 or 100 mmol, respectively). 1-Bromodecane or 1-bromo-
tetradecane (22 mmol for dialkylation or 32 mmol for trialkylation)
was added dropwise. The reaction mixture was heated at 1208C
and stirred for 8 h (dialkylation) or 15 h (trialkylation). The mixture
was cooled to room temperature and poured into distilled water
(150 mL). The product was extracted with hexanes/ethyl acetate
(9:1, 3”50 mL). The combined organic layers were dried (MgSO4)
and evaporated to dryness. The product was purified by flash
column chromatography on silica gel.
1c:[16b] Eluent for purification (hexane/CH2Cl2 3:2). Yield: 85%,
white solid. Rf: 0.71 (hexane/CH2Cl2 1:9); m.p: 358C; 1H NMR
(400 MHz, CDCl3, 208C, TMS): d=9.83 (s, 1H), 7.08 (s, 2H), 4.07–
4.02 (m, 6H), 1.86–1.71 (m, 6H), 1.51–1.44 (m, 6H), 1.40–1.20 (m,
36H), 0.88 ppm (t, J=6.9 Hz, 9H); 13C NMR (100 MHz, CDCl3, 208C,
TMS): d=191.3, 153.5, 143.9, 131.4, 107.9, 73.6, 69.2, 31.94, 31.92,
30.3, 29.73, 29.67, 29.63, 29.59, 29.55, 29.38, 29.35, 29.3, 26.1, 26.0,
22.7, 14.1 ppm; IR (KBr): n=2955, 2918, 2871, 2849, 1699, 1693,
1587,1501, 1256, 1239, 1226, 1145, 1118 cmÀ1; elemental analysis
calcd (%) for C37H66O4: C 77.30, H 11.57; found: C 77.23, H 11.01.
General procedure for the synthesis of the pyrazoles 4a–f
A
solution of hydrazine hydrate (20 mmol) and acetic acid
(20 mmol) in ethanol (10 mL) was added to a solution of dinitroal-
kane (10 mmol) in ethanol (100 mL) at 508C. The mixture was
heated at reflux for 10 h. The solvent was evaporated and the resi-
due was extracted with ethyl acetate (3”75 mL). The combined or-
ganic layers were dried (MgSO4) and evaporated to dryness. The
product was purified by column chromatography on silica gel or
by recrystallization.
General procedure for the synthesis of the nitroalkenes
2a–f
4c: Eluent for purification (hexane/ethyl acetate 8:2). Yield: 65%,
ivory solid. Rf: 0.17 (hexane/ethyl acetate 7:3); m.p.: see Table 2;
1H NMR (400 MHz, CD2Cl2, 208C, TMS): d=6.43 (s, 2H), 4.01–3.91
(m, 6H), 2.26 (s, 6H), 1.84–1.69 (m, 6H), 1.52–1.42 (m, 6H), 1.42–
1.20 (m, 36H), 0.88 ppm (t, J=6.9 Hz, 9H); 13C NMR (100 MHz,
CDCl3, 208C, TMS): d=153.0, 141.8, 137.1, 128.7, 118.8, 108.3, 73.5,
69.3, 31.96, 31.92, 30.4, 29.8, 29.7, 29.66, 29.60, 29.5, 29.41, 29.36,
29.3, 26.2, 26.1, 22.7, 14.1, 11.6 ppm; IR (KBr): n=3168, 3127, 3069,
A mixture of the appropriate benzaldehyde (10 mmol), NH4OAc
(10 mmol), and nitroethane (20–70 mL) was heated at reflux for
10 h. The mixture was cooled to room temperature and poured
into distilled water (100 mL). The product was extracted with
hexane/ethyl acetate (9:1, 3”50 mL). The combined organic layers
were dried (MgSO4) and evaporated to dryness. The product was
purified by flash column chromatography on silica gel or by recrys-
tallization.
2955, 2924, 2854, 1601, 1585, 1526, 1504, 1242, 1210, 1118 cmÀ1
;
elemental analysis calcd (%) for C41H72N2O3: C 76.82, H 11.32, N
4.37; found: C 77.15, H 10.98, N 4.54; MS (MALDI+, dithranol): m/z:
641.6 [M+H]+.
2c: Eluent for purification (hexane/CH2Cl2 4:1). Yield: 95%, yellow
solid. Rf: 0.85 (hexane/CH2Cl2 1:9); m.p.: 348C; 1H NMR (400 MHz,
CDCl3, 208C, TMS): d=8.01 (s, 1H), 6.63 (s, 2H), 4.03–3.96 (m, 6H),
2.47 (d, J=0.9 Hz, 3H), 1.85–1.71 (m, 6H), 1.53–1.42 (m, 6H), 1.40–
1.19 (m, 36H), 0.88 ppm (t, J=6.9 Hz, 9H); 13C NMR (100 MHz,
CDCl3, 208C, TMS): d=153.3, 146.6, 140.2, 134.2, 127.2, 109.1, 73.7,
Crystal data for 4 f
Colorless crystals suitable for crystallographic analysis were ob-
tained by slow diffusion of hexane into a solution of the com-
Chem. Eur. J. 2016, 22, 4924 – 4930
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4929
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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Acknowledgments
The authors thank the Spanish Ministerio de Economia y Com-
petitividad (MINECO) and Fondo Europeo para el Desarrollo
Regional (FEDER) (project numbers CTQ2012-35692, CTQ2011-
22516, CTQ2014-53033-P, and MAT2012-38538-CO3-01), the
Gobierno de Aragón and Fondo Social Europeo (FSE) (research
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also due to the Nuclear Magnetic Resonance, Mass Spectra
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Keywords: columnar
assembly · X-ray diffraction
· liquid crystals · pyrazoles · self-
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Published online on February 18, 2016
Chem. Eur. J. 2016, 22, 4924 – 4930
www.chemeurj.org
4930
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim