Synthesis and characterization of cholesterol-based nonsymmetric dimers terminated with ferrocenyl core

Article abstract of DOI:10.1016/j.tet.2009.07.042

The molecular design, synthesis, and thermal behavior of cholesterol-based nonsymmetric dimers, which can also be regarded as metallomesogens, consisting of either two- or three-ring aromatic cores terminated with ferrocenyl unit are reported. The spacer

Full text of DOI:10.1016/j.tet.2009.07.042

Tetrahedron 65 (2009) 7998–8006
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Synthesis and characterization of cholesterol-based nonsymmetric dimers
terminated with ferrocenyl core
*
K.C. Majumdar , Santanu Chakravorty, Nilashish Pal, Randhir K. Sinha
Department of Chemistry, University of Kalyani, Kalyani 741235, West Bengal, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 May 2009
Received in revised form 18 July 2009
Accepted 21 July 2009
Available online 24 July 2009
The molecular design, synthesis, and thermal behavior of cholesterol-based nonsymmetric dimers,
which can also be regarded as metallomesogens, consisting of either two- or three-ring aromatic cores
terminated with ferrocenyl unit are reported. The spacer length connecting the cholesterol and aromatic
cores is held constant while the length of the spacer connecting ferrocene and aromatic cores has been
varied. The occurrence of the enantiotropic mesomorphism in these compounds has been adjudged by
optical, calorimetric, and X-ray diffraction studies. In particular these systems exhibit liquid crystal
phases such as chiral nematic, twist grain boundary, and smectic A phases. Of these, the chiral nematic
phase commonly occurs in all the synthesized compounds.
Keywords:
Ferrocene
Cholesterol
TGB
Ó 2009 Elsevier Ltd. All rights reserved.
SmA
POM
XRD
1. Introduction
crystals15–18 while the unsymmetrical dimers exhibit smectic
phases.19–31 Moreover, chiral unsymmetrical dimers, in particular
Liquid crystalline compounds containing a metallic atom in their
structure combine properties of the metal with those of the meso-
gens, leading to processable material with interesting magnetic,
electronic, optical, and anisotropic properties. Ferrocene-based met-
allomesogens have emerged as important liquid crystalline materials
overlast10–20yearsduetotheirnovelthermal, optical,and magnetic
properties.1,2 Ferrocene, because of its aromatic character, facilitates
several substitutions whereby a range of low molecular mass
calamitic(rod-like)systemscanbepreparedbymono-substitution, or
1,1-,1,2-,1,3-, di-substitution or 1,1,3-tri-substitution of the ferrocene
nucleus.3–12 However, there are few reports on mono-substituted
ferrocene-based metallomesogen in recent years.13,14 This may be
compound possessing a cholesteryl ester unit as the chiral entity
joined to different aromatic mesogens through an alkyl spacer,
show interesting thermal properties. Recently we have synthe-
sized such unsymmetrical dimers exhibiting smectic A (SmA),
twist grain boundary (TGB), and cholesteric (N
) phase.14 Due to
*
wide spread applicability of both cholesterol-based liquid crys-
talline materials and ferrocene-based metallomesogens, we are
interested in the design of ferrocene-based metallomesogens with
interesting structure, in which the ferrocenyl unit is connected as
a terminal group onto a rod-like molecule composed of choles-
teryl unit.
partly attributed to their unfavorable molecular shape (L-shaped
2. Synthesis and characterization
geometry) and to the repulsive steric effects of the ferrocene unit
reducing the ability of the molecules to be arranged in layers thus
favoring mostly the formation of nematic phase.
Chiral liquid crystalline dimers composed of either identical
(symmetrical) or non-identical (unsymmetrical) mesogenic seg-
ments, connected through a flexible paraffinic central spacer, are
attracting a great deal of attention. This is because the symmetric
dimers are regarded as model compounds for polymeric liquid
The methodology for the synthesis of the required intermediate
for the preparation of the aforesaid ferrocene-based metal-
lomesogens is depicted in Scheme 1.
Ferrocene was first converted to either 6-bromohexyloyl fer-
rocene (2a) or 11-bromodecyloyl ferrocene (2b) by treatment
with respective acid chlorides in dry chloroform in the presence
of anhydrous aluminum chloride. Compound 2a or 2b on treat-
ment with zinc amalgam in the presence of concentrated
hydrochloric acid in benzene–water under refluxing conditions
afforded compound 3a or 3b. Compound 3a or 3b in turn was
alkylated with p-hydroxybenzaldehyde in refluxing acetone in
* Corresponding author. Tel.: þ91 33 2582 7521; fax: þ91 33 2582 8282.
E-mail address: kcm_ku@yahoo.co.in (K.C. Majumdar).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.07.042

K.C. Majumdar et al. / Tetrahedron 65 (2009) 7998–8006
7999
(
)
Br
n (iii)
n
Br
(ii)
O
CHO
(
)
(i)
(
)
n
Fe
Fe
Fe
O
Fe
4a. n = 6
4b, n = 11
3a. n = 6
3b, n = 11
1
2a. n = 5
2b. n = 10
(iv)
O
CO2H
O
CO2Et
(
)
n
(
)
n
(v)
Fe
Fe
6a. n = 6
6b. n = 11
5a. n = 6
5b. n = 11
(vii)
(vi)
R'
O
R
CHO
O
O
NO2
O
(
)
n
O
O
(
)
Fe
n
7a. n = 6, R = OH, R' = H
Fe
8. n = 6
7b. n = 6, R = H, R' = NO2
7c. n = 11, R = H, R' = H
(viii)
O
O
NH2
O
(
)
n
Fe
9. n = 6
(ix)
O
Br
OH
(
)
5
O
10
11
(x)
(xi)
O
(
O
NO2
O
)
5
O
O
CHO
13
(
)
5
O
(xii)
12
O
O
NH2
(
)
5
O
14
Scheme 1. Reagents and conditions: (i) 6-bromohexanoyl chloride/11-bromodecanoyl chloride, AlCl3, CHCl3, rt, 2h; (ii) Zn–Hg, concd HCl, benzene–water, reflux, 36–48 h;
(iii) p-hydroxybenzaldehyde, acetone, K2CO3, reflux, 12 h; (iv) p-hydroxyethylbenzoate, acetone, K2CO3, reflux, 12 h; (v) C2H5OH, KOH, reflux, 2 h; (vi) p-hydroxybenzaldehyde/
2,4-dihydroxybenzaldehyde/3-nitro-4-hydroxybenzaldehyde, DCC, DMAP, CHCl3, rt, 2 h; (vii) p-nitrophenol, DCC, DMAP, CHCl3, rt, 2 h; (viii) Pd–C, H2, ethyl acetate, rt, 4 h; (ix)
6-bromohexanoyl chloride, THF, pyridine, rt, 12 h; (x) p-hydroxybenzaldehyde, acetone, K2CO3, reflux, 12 h; (xi) p-nitrophenol, acetone, K2CO3, reflux, 12 h, (xii) Pd–C, H2, ethyl
acetate, rt, 8 h.
the presence of anhydrous potassium carbonate to give the
product 4a or 4b. On the other hand, compound 3a or 3b upon
reaction with p-hydroxyethylbenzoate and anhyd potassium
carbonate in refluxing acetone and subsequent hydrolysis of the
resulting ester with ethanolic potassium hydroxide afforded the
acid derivatives 6a or 6b. The acid derivatives on esterification
with either p-nitrophenol or different hydroxybenzaldehydes
give corresponding nitro derivative 8 or aldehyde derivatives
7a–c. The nitro derivatives on reduction with hydrogen in the
presence of palladised charcoal in ethyl acetate afforded corre-
sponding amine derivative 9. Reaction between cholesterol and
6-bromohexanoyl chloride in THF at room temperature gave the
corresponding ester derivative 11. The ester derivatives were
then subjected to alkylation with p-hydroxybenzaldehyde and
p-nitrophenol, respectively, in refluxing dry acetone in the
presence of anhyd K2CO3 to afford the corresponding aldehyde 12
and nitro derivative 13 (Scheme 1). The nitro derivative on hy-
drogenation gave the corresponding amine derivative 14. The
aldehyde 12 and amine 14 derivatives on condensation with
different amines and aldehydes afforded a series of compounds
15a,b and 16a–d (Scheme 2).
3. Results and discussion
All the intermediate compounds containing ferrocenyl moiety
are non-mesomorphic in nature (2–9). Intermediate 11 is also non-
mesomorphic. Compound 13 exhibits only the N
termediate compounds 12 and 14 on slow cooling from the isotropic
phase exhibit characteristic textures on N phase, on further cooling
*
phase. The in-
*
homeotropic textures appears and it exists till room temperature for
both the compounds. But on standing both the compounds solidify.
The transition temperatures and associated enthalpy of all the final
compounds obtained from their DSC thermogram (Figs.1 and 2) are
summarized in Table 1. Compound 15a with two aromatic ring and
a hexa-methylene spacer between phenyl ring and ferrocenyl unit
exhibits two transitions in heating cycles and only one transition in
cooling cycles in DSC experiment. On cooling the isotropic phase of
compound 15a, elliptical shape droplet is found to appear, which
coalesces to form fan-like texture of cholesteric phase (in accor-
dance with the reported texture for cholesteric phase). On very slow
cooling of the sample it solidifies at about 75 ꢀC in POM study.
Compound 15a on heating also exhibited typical oily-streak texture
of N phase. When hexa-methylene spacer of 15a was replaced by
*

8000
K.C. Majumdar et al. / Tetrahedron 65 (2009) 7998–8006
O
(
)
5
O
CHO
H2N
O
(
)
n
O
14
Fe
4a. n = 6
4b, n = 11
(i)
O
(
)
5
N
O
O
O
)
n
(
15a. n = 6
15b. n = 11
Fe
9 + 12
(i)
O
(
)
5
O
O
O
O
N
6 O
(
)
16a
Fe
R'
R
O
(
)
5
O
O
CHO
H2N
O
+
O
14
O
(
)
n
Fe
7a. n = 6, R = OH, R' = H
7b. n = 6, R = H, R' = NO2
7c. n = 11, R = H, R = H
(i)
O
R'
O
R
(
)
5
Y
X
O
O
n O
)
(
O
Fe
16b. n = 11, X = C, Y = N, R = H, R' = H
16c. n = 6, X = C, Y = N, R = OH, R' = H
16d. n = 6, X = C, Y = N, R = H, R' = NO2
Scheme 2. Reagents and conditions: (i) C2H5OH, Cat. AcOH, reflux.
undeca-methylene spacer we observed another two transitions in
heating as well as in cooling cycle. The first transition corresponds to
crystal–crystal transition. On slow heating of compound 15b, the
filament texture of the TGB phase shown in Figure 3, grows slowly in
the homeotropic regions of the SmA phase and ends up into a cho-
lesteric phase with a fan-shaped texture (Fig. 4). Oily streaks are
seen upon subjecting the preparation to mechanical stress. Com-
attention to alternate the structure of 16a by lateral introduction of
groups like hydroxyl (16c) and nitro (16d) groups. Seemingly the
salicyalaldimines and Schiff’s base compounds virtually possess
same transitional behavior with obvious exception that transition
temperatures are higher for the former case due to the presence of
intramolecular H-bonding compared to the latter. On the other
hand introduction of nitro group to the lateral position decreases
the melting and clearing temperatures dramatically compared to
16a, and also reduces the thermal stability of the compound.
Compound 16d decomposes above the isotropic temperature. Both
pound 15b when placed in thin cell with a cell gap of d¼5ꢁ0.2
mm
with homogenous planar boundary condition, texture for the cho-
lesteric, TGB, and smectic phase (typical focal conic texture of SmA
phase, Fig. 5) were observed.
16c and 16d possess only the N phase over a wide temperature
*
The influence of orientation of the ester linkage, which diverts
the electron delocalization and the coplanarity of the two aromatic
rings of benzylideneaniline probably enhances the polarizability of
the rigid core due to extended conjugation. This in turn enhances
the preponderance of smectic phases and creates favorable packing
condition. Furthermore, the presence of a long flexible spacer be-
tween phenyl ring and ferrocenyl unit in 15b is primarily re-
sponsible for the formation of ordered phase, in the absence of
ranges (Figs. 6 and 7). However, introduction of an additional aro-
matic ring in structure 15b suppresses the appearance of TGB phase
but increases the stability of N phase over a wide range of tem-
*
perature. It also shows the textures of SmA phase underneath of N
*
phase (Fig. 8).
The diffraction diagram exhibits a sharp peak in the small angle
region with 2
¼2.42 (d¼36.38 Å) and a broad diffuse peak in the
wide angle region centered at d-spacing of 5.19 Å. We also observed
a diffuse peak in the low angle region in between 2
q
a long flexible spacer only N
*
phase was observed. Introduction of
q¼5–7.5 due to
another aromatic ring to the structure 15a increases not only the
melting and clearing temperatures but also increases the stability
fluctuation of the holder, which was confirmed by taking the X-ray at
same temperature in the absence of any samples. The sharp Bragg’s
reflection in the small angle region is due to one-dimensional
of N phase over a wider temperature ranges. We then turn our
*

K.C. Majumdar et al. / Tetrahedron 65 (2009) 7998–8006
8001
Figure 2. DSC thermogram in cooling cycles.
C (SmC
*
) phase domain, a TGBA phase in between SmA and N
*
, and
a blue phase just before the clearing point, in spite of a bulky
pendant ferrocene unit on the other side and a relatively small
terminal group appended to the chiral center on the other side.
Recently32 they synthesized several mono-mesogens of ferrocene
derivatives bearing N-benozyl-N0-arylthiourea (BATU) bidentate
ligand, and a nonsymmetric dimesogen in which two structurally
different mesogenic groups, namely the BATU and cholesteryl
moieties, interlinked by a flexible spacer. The achiral mono-meso-
gens exhibit enantiotropic smectic C and nematic phases, while the
chiral mono-mesogens show a cholesteric phase. The dimesogen,
on the other hand, exhibits an enantiotropic cholesteric phase with
selective reflection in the visible region with iridescent colors. We
have also synthesized14 cholesterol-based chiral dimer with mono-
substituted ferrocene unit but unfortunately we did not observe
any mesophase behavior. In conclusion we have synthesized a se-
ries of Schiff’s base dimer with either varying the number of aro-
matic rings, the spacer between phenyl ring and ferrocenyl unit,
introducing lateral substitution. Most of the dimers exhibit only an
Figure 1. DSC thermogram in heating cycles.
layering in the condensed SmA phase and a diffuse peak in the wide
angle region is due to liquid-like correlation of the molecules. The
calculated molecular length from molecular modeling is about
53.3 Å. Therefore, we expect a intercalated SmA phase. A schematic
diagram of packing of molecules in smectic phase deduced from
X-ray diffraction study is presented in Figure 9.
N
*
phase over a wide temperature ranges. One of the dimers shows
interesting phase sequence of N -TGB-SmA. Introduction of one
*
Compound 16b however causes a severe damage to the holder
after taking the X-ray at different temperatures; this may be due to
the partial decomposition of the sample. So, it is not possible for us
to know the layer arrangement of the SmA phase of the compound
15b. Imrie and Loubser6 synthesized a series of mono-substituted
ferrocene derivatives with ester linkages. They observed that the
size and shape of the aromatic core of the substituent on ferrocene
play an important role in determining the thermal properties of
these compounds. According to them minimum of three rings in
the substituent core are necessary for stabilizing the nematic phase,
but that four rings vastly enhance the nematic behavior. Seshadri
and Haupt8 reported a mono-substituted ferrocene-based metal-
lomesogen with a chiral Schiff’s base with long chiral smectic
aromatic ring to that dimer suppresses the formation of TGB phase.
Appearance of TGB phase in the Schiff’s base dimer with two aro-
matic rings is interesting. To the best of our knowledge there is no
report for the appearances of such phase in mono-substituted fer-
rocene containing materials with two aromatic rings.
4. Experimental
4.1. General
All the chemicals were procured from either Sigma Aldrich
Chemicals Pvt. Ltd or Spectrochem, India. Silica gel (60–120 mesh)

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K.C. Majumdar et al. / Tetrahedron 65 (2009) 7998–8006
Table 1
Transition temperature (ꢀC) and associated enthalpy (kJ/mol) calculated from DSC thermogram
15a* :
113.6
(36.8)
156.1
(3.3)
157.5
(3.0)
Cr
N*
N*
I
15b :
153.1
(1.61)
153.8
(4.0)
154.6
(3.7)
73.2
(7.9)
110.4
152.2
Cr
SmA
N*
I
Cr1
TGB
N*
(....)
(54.3)
(....)
152.6
53.0
152.2
(1.4)
Cr'
SmA
TGB
(22.8)
16a :
122.3
(26.7)
227.7
(2.4)
223.4
(1.0)
73.7
(6.4)
Cr
Cr
N*
N*
I
Cr'
16b :
188.8
216.8
218.5
(2.7)
124.2
(30.4)
130.6
(35.9)
SmA
N*
I
Cr1
N*
(2.7)
(0.68)
186.3 (0.5)
124.2
(13.6)
79.1
Cr'
Cr1
SmA
(18.7)
16c* :
229.8
(2.5)
131.9
(39.7)
240.2
(2.9)
Cr
N*
N*
N*
I
16d** :
Cr
90.2
191.9
(2.5)
I
(18.9)
*For both the compounds we did not observe N
*
–Cr transitions in the cooling cycles of DSC experiments.
**Compound 16d decomposes after isotropization both in POM and DSC, so we did not observe any transition in cooling cycles of DSC experiment.
was used for chromatographic separation. Silica gel G [E-Merck
(India)] was used for TLC. Petroleum ether refers to the fraction
boiling between 60 ꢀC and 80 ꢀC. IR spectra were recorded on
a Perkin–Elmer L 120-000A spectrometer (nmax in cmꢂ1) on KBr
disks. 1H NMR (400 MHz) spectra were recorded on a Bruker DPX-
400 spectrometer or DPX-300 spectrometer in CDCl3 (chemical
were established by thermal microscopy (Nikon polarizing micro-
scope LV100POL attached with Instec hot and cold stage HCS302,
with STC200 temperature controller configured for HCS302 and the
phase transitions were confirmed by differential scanning calo-
rimetry (Perkin–Elmer Diamond DSC Pyris1 system)).
Powder X-ray diffraction was carried out on a Philips powder
diffractometer, equipped with a temperature controller permitting
shift in d) with TMS as internal standard. CHN was recorded on
2400 series II CHN analyzer Perkin Elmer from the Chemistry De-
partment of Kalyani University. The liquid crystalline properties
low as well as high temperature operation as needed (with Cu Ka
radiation of
l¼1.5418 nm).
Figure 3. TGB phase of 15b at 152.5 ꢀC observed in thin cell with a cell gap of d¼5ꢁ0.2.
Figure 4. POM textures of 15b at 152.2 ꢀC.

K.C. Majumdar et al. / Tetrahedron 65 (2009) 7998–8006
8003
Figure 5. SmA of 15b at 150.4 ꢀC observe in thin cell with a cell gap of d¼5ꢁ0.2.
Figure 8. POM texture of 16b at 175 ꢀC.
subjected to column chromatography over silica gel using petro-
leum ether/ethyl acetate (99:1) as eluent to afford the product 2a.
The procedure for the preparation of compound 2b was already
reported.32
Figure 6. Oily-streak texture of 16c at 225.2 ꢀC.
4.2. Procedure for the preparation of intermediates 2a and 2b
To a mixture of 6-bromohexanoyl chloride (5.0 g, 23.41 mmol)
and AlCl3 (3.1 g, 23.41 mmol) in 50 ml CHCl3 a solution of ferrocene
(4.3 g, 23.41 mmol) in 50 ml CHCl3 was added dropwise. After
stirring for 2 h at room temperature, the reaction mixture was
quenched with ice water (50 ml). The organic layer was separated,
washed with dilute aqueous NaHCO3 solution (2ꢃ25 ml), and dried
over Na2SO4. The residue obtained after removing the solvent was
Figure 9. A schematic diagram of packing of molecules in smectic phase deduced from
X-ray diffraction study.
Figure 7. N
*
phase of 16d at 152 ꢀC.

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K.C. Majumdar et al. / Tetrahedron 65 (2009) 7998–8006
4.2.1. Compound 2a. Deep red liquid, yield 75%, Rf¼0.7 (1% EtOAc/
pet. ether), IR (KBr) nmax: 3096, 2936, 1667, 1454 cmꢂ1 1H NMR
reflux for 12 h. After removal of the solvent 25 ml water was added
to the residue and the mixture was extracted with chloroform. The
organic phase was washed with water (2ꢃ15 ml) and dried over
Na2SO4. The residue obtained after removing the solvent was
subjected to column chromatography over silica gel using petro-
leum ether/ethyl acetate (19:1) as eluent to afford the product 5a.
The procedure for the preparation of compound 5b was already
reported.32
;
(CDCl3, 300 MHz) 4.78 (2H, s, Ferrocenyl H), 4.50 (2H, s, Ferrocenyl
H), 4.19 (5H, s, Ferrocenyl H), 3.44 (2H, t, J 7.1 Hz, CH2Br), 2.72 (2H, t,
J 7.8 Hz, CH2), 1.92 (2H, quin, J 7.2 Hz, –CH2–CH2–CH2), 1.50–1.73
(4H, m, aliphatic H); Anal. Calcd for C16H19BrFeO: C, 52.93; H, 5.27.
Found: C, 53.20; H, 5.37%.
4.2.2. Compound 2b. Ref. 32.
4.5.1. Compound 5a. Deep red liquid, yield 90%, Rf¼0.7 (5% EtOAc/
4.3. Procedure for preparation of intermediates 3a and 3b
pet. ether), IR (KBr) nmax: 3090, 2933, 1710, 1606, 1510 cmꢂ1 1H
;
NMR (CDCl3, 400 MHz) 7.96 (2H, d, J 8.6 Hz, ArH), 6.87 (2H, d,
J 8.6 Hz, ArH), 4.30 (q, 2H, J 7.1 Hz, –CH2CH3), 4.08 (5H, S, Ferrocenyl
H), 3.97–4.03 (6H, m, Ferrocenyl Hþ–OCH2), 2.30 (2H, t, J 7.8 Hz,
–CH2), 1.77–1.81 (2H, quin, J 7.4 Hz, –CH2–CH2–CH2), 1.35–1.57 (9H,
m, aliphatic Hþ–CH3); Anal. Calcd for C25H30FeO3: C, 69.13; H, 6.96.
Found: C, 69.09; H, 7.06%.
A mixture of Zn (10.3 g, 16.51 mmol), HgCl2 (0.8 g, 2.9 mmol),
acetyl derivative 2a (4 g, 11.01 mmol), and concentrated HCl (15 ml)
in benzene/water mixture (20 ml each) was heated under reflux for
48 h. Then the mixture was filtered through filter paper and the
filtrate was washed with water (2ꢃ10 ml). The residue obtained
after removing the solvent was subjected to column chromato-
graphy over silica gel using petroleum ether/ethyl acetate (99:1) as
eluent to afford the product 3a. The procedure for the preparation
of compound 3b was already reported.32
4.5.2. Compound 5b. Ref. 32.
4.6. Procedure for preparation of intermediates 6a and 6b
4.3.1. Compound 3a. Deep red liquid, yield 80%, Rf¼0.75 (1% EtOAc/
In a mixture of 5a (0.9 g, 2.07 mmol) in 50 ml of alcohol, KOH
(1 g) in 2 ml of water was added and the mixture was heated under
reflux for 2 h. Dilute HCl was added gradually to the mixture in cold
condition. The product 6a is precipitated as yellow solid, which was
filtered out from the mixture. The pure product was obtained after
recrystallization from ethanol. The procedure for the preparation of
compound 6b was already reported.32
pet. ether), IR (KBr) nmax: 3092, 2929, 2854, 1460 cmꢂ1 1H NMR
;
(CDCl3, 400 MHz) 4.07 (5H, S, Ferrocenyl H), 4.02 (4H, S, Ferrocenyl
H), 3.76 (2H, t, J 7.0 Hz, CH2Br), 2.29 (2H, t, J 7.9 Hz, CH2), 1.79–1.83
(2H, quin, J 7.2 Hz, –CH2–CH2–CH2), 1.32–1.53 (6H, m, aliphatic H);
Anal. Calcd for C16H21BrFe: C, 55.05; H, 6.06. Found: C, 55.20; H,
6.17%.
4.3.2. Compound 3b. Ref. 32.
4.6.1. Compound 6a. Yellow solid, mp 146–148 ꢀC, yield 86%, IR
(KBr) nmax: 3075, 2942, 1680, 1605, 1577 cmꢂ1 1H NMR (CDCl3,
;
4.4. Procedure for preparation of intermediates 4a and 4b
400 MHz) 8.02 (2H, d, J 8.5 Hz, ArH), 6.90 (2H, d, 8.5 Hz, ArH), 4.07
(5H, S, Ferrocenyl H), 3.99–4.03 (6H, m, Ferrocenyl Hþ–OCH2), 2.31
(2H, t, J 7.8 Hz, –CH2), 1.76–1.83 (2H, quin, J 6.7 Hz, –CH2–CH2–CH2),
1.38–1.56 (6H, m, aliphatic H); Anal. Calcd for C23H26FeO3: C, 67.99;
H, 6.45. Found: C, 68.19; H, 6.60%.
A mixture of 3a (1 g, 2.9 mmol), 4-hydroxybenzaldehyde (0.4 g,
3.3 mmol), K2CO3 (3.0 g) in 50 ml acetone was heated under reflux
for 12 h. After removal of the solvent 25 ml water was added to the
residue and the mixture was extracted with chloroform. The or-
ganic phase was washed with water (2ꢃ15 ml) and dried over
Na2SO4. The residue obtained after removing the solvent was
subjected to column chromatography over silica gel using petro-
leum ether/ethyl acetate (19:1) as eluent to afford the product 4a.
The other intermediate 4b also prepared similarly.
4.6.2. Compound 6b. Ref. 32.
4.7. Procedure for preparation of intermediates 8 and 7a–c
A mixture of acid 6a (0.4 g, 0.9 mmol), 4-nitrophenol (0.16 g,
1.18 mmol) or 2,4-dihydroxybenzaldehyde (0.2 g, 1.47 mmol) or
3-nitro-4-hydroxybenzaldehyde (0.197 g, 1.17 mmol), DCC (0.3,
1.47 mmol) and catalytic amount of DMAP in 50 ml dry DCM was
stirred at room temperature for 2 h. The residue left after removal
of the solvent was subjected to column chromatography over silica
gel using petroleum ether/ethyl acetate (9:1) as eluent to afford
either the product 8 or 7a or 7b. The procedure for the preparation
of compound 7c was already reported.32
4.4.1. Compound 4a. Yellow solid, mp 80–82 ꢀC; Rf¼0.65 (5%
EtOAc/pet. ether), 1H NMR (CDCl3, 300 MHz) 9.87 (1H, s, CHO), 7.80
(2H, d, J 8.4 Hz, ArH), 6.97 (2H, d, J 8.4 Hz, ArH), 4.08 (5H, s, Fer-
rocenyl H), 4.01–4.03 (6H, m, Ferrocenyl Hþ–OCH2), 2.31 (2H, t,
J 7.8 Hz, –CH2), 1.76–1.83 (2H, quint, J 6.3 Hz, –CH2–CH2–CH2), 1.39–
1.63 (6H, m, aliphatic H); Anal. Calcd for C23H26FeO2: C, 70.78; H,
6.71. Found: C, 70.90; H, 6.51%.
4.4.2. Compound 4b. Yellow solid, mp 54–56 ꢀC, Rf¼0.7 (5% EtOAc/
4.7.1. Compound 8. Yellow solid, mp 94–96 ꢀC, yield 84%, Rf¼0.55
(10% EtOAc/pet. ether), IR (KBr) nmax: 3083, 2936, 1739, 1605, 1589,
pet. ether), IR (KBr) nmax: 3094, 2919, 2849, 1685, 1603 cmꢂ1 1H
;
NMR (CDCl3, 300 MHz) 9.87 (1H, s, CHO), 7.81 (2H, d, J 7.5 Hz, ArH),
6.97 (2H, d, J 7.5 Hz, ArH), 4.08 (5H, s, Ferrocenyl H), 4.01–4.03 (6H,
m, Ferrocenyl Hþ–OCH2), 2.30 (2H, t, J 7.8 Hz, –CH2), 1.29–1.81
(18H, m, aliphatic H); 13C NMR (CDCl3, 100 MHz) 190.8, 164.3, 132.0,
129.7, 114.7, 68.6, 68.4, 68.2, 68.1, 31.1, 29.7, 29.6, 29.5, 29.3, 29.0,
25.9; Anal. Calcd for C28H36FeO2: C, 73.04; H, 7.88. Found: C, 73.24;
H, 7.96%.
1489, 1343 cmꢂ1 1H NMR (CDCl3, 400 MHz) 8.29 (2H, d, J 8.9 Hz,
;
ArH), 8.11 (2H, d, J 8.6 Hz, ArH), 7.38 (2H, d, J 8.9 Hz, ArH), 6.96 (2H,
d, 8.6 Hz, ArH), 4.08 (5H, S, Ferrocenyl H), 4.03–4.06 (6H, m, Fer-
rocenyl Hþ–OCH2), 2.31 (2H, t, J 7.8 Hz, –CH2), 1.80–1.84 (2H, quin,
J 7.3 Hz, –CH2–CH2–CH2), 1.39–1.55 (6H, m, aliphatic H); 13C NMR
(CDCl3, 100 MHz) 164.0, 163.9, 155.9, 145.2, 132.5, 125.2, 122.7,
120.4, 114.5, 69.3, 68.7, 68.4, 67.7, 31.0, 29.5, 29.3, 29.0, 25.9; Anal.
Calcd for C29H29FeNO5: C, 66.04; H, 5.54; N, 2.66. Found: C, 66.29;
H, 5.60; N, 2.49%.
4.5. Procedure for preparation of intermediates 5a and 5b
A mixture of 3a (1 g, 2.9 mmol), ethyl 4-hydroxyethylbenzoate
(0.5 g, 3.2 mmol), K2CO3 (3.0 g) in 50 ml acetone was heated under
4.7.2. Compound 7a. Yellow solid, mp 88–90 ꢀC, Rf¼0.65 (10%
EtOAc/pet. ether), IR (KBr) nmax: 3327, 2927, 2851, 1738, 1658,

K.C. Majumdar et al. / Tetrahedron 65 (2009) 7998–8006
8005
1604 cmꢂ1; 1H NMR (CDCl3, 300 MHz) 9.88 (1H, s, CHO), 8.10 (2H,
d, J 8.1 Hz, ArH), 7.59 (1H, d, J 8.1 Hz, ArH), 6.87–6.98 (5H, m,
ArHþOH), 4.09 (5H, s, Ferrocenyl H), 4.01–4.04 (6H, m, Ferrocenyl
Hþ–OCH2), 2.32 (2H, t, J 7.2 Hz, –CH2), 1.17–1.94 (8H, m, aliphatic
H); yield 80%, 13C NMR (CDCl3, 100 MHz) 195.5, 163.9, 163.2,
157.9, 134.9, 132.5, 120.7, 118.6, 114.4, 114.2, 110.9, 68.6, 68.4, 68.3,
69.0, 67.8, 67.7, 67.0, 33.9, 31.2, 31.0, 29.5, 29.3, 29.0, 25.9, 25.6,
24.9; Anal. Calcd for C30H30FeO5: C, 68.45; H, 5.74. Found: C,
68.13; H, 5.84%.
73.8, 68.6, 68.2, 68.1, 67.9, 67.1, 56.7, 56.1, 50.0, 42.3, 39.74, 39.5, 38.1,
37.0, 36.6, 36.2, 35.8, 34.6, 31.9, 31.8, 31.0, 29.5, 29.3, 29.1, 29.0, 28.2,
28.0, 27.8, 25.9, 25.6, 24.8, 24.3, 23.8, 22.8, 22.6, 21.0, 19.3, 18.7, 11.9;
Anal. Calcd for C62H85FeNO4: C, 77.23; H, 8.89; N, 1.45. Found: C,
77.50; H, 8.99; N, 1.30%.
4.10.2. Compound 15b. A mixture of 4b (0.10 g, 0.22 mmol) and 14
(0.13 g, 0.22 mmol) was refluxed in absolute ethanol (10 ml) in the
presence of a catalytic amount of glacial acetic acid for 3 h. The
Schiff’s base 15b was precipitated out from reaction mixture. It was
collected, washed repeatedly with hot ethanol, and dried in
vacuum.
4.7.3. Compound 7b. Gummy mass, yield 75%, Rf¼0.7 (10% EtOAc/
pet. ether), IR (KBr) nmax: 3083, 2929, 1744, 1704, 1605 cmꢂ1
;
1H NMR (CDCl3, 400 MHz) 10.54 (1H, S, –CHO), 8.57 (1H, S, ArH),
8.11–8.19 (3H, m, ArH), 7.57 (1H, d, J 7.8 Hz, ArH), 6.97 (2H, d, J
7.8 Hz, ArH), 4.08 (5H, S, Ferrocenyl H), 4.03–4.04 (6H, m, Ferrocenyl
Hþ–OCH2), 1.08–2.34 (10H, m, aliphatic H); Anal. Calcd for
C30H29FeNO6: C, 64.88; H, 5.26; N, 2.52. Found: C, 64.99; H, 5.29; N,
2.57%.
Yellow solids, yield 90%, [aD
in CHCl3 at 26.8 ꢀC, IR (KBr) nmax: 2921, 2853, 1729, 1620,
1608 cmꢂ1 1H NMR (CDCl3, 400 MHz): 8.39 (1H, s, CH]N), 7.80
]
¼ꢂ4.86 at C¼1% solution
l
¼589nm
;
(2H, d, J 8.7 Hz, ArH), 7.17 (2H, d, J 8.8 Hz, ArH), 6.94 (2H, d,
J 8.7 Hz, ArH), 6.88 (2H, d, J 8.8 Hz, ArH), 5.36 (1H, d, J 4.7 Hz,
]CH), 4.58–4.65 (1H, m, OCH), 4.08 (3H, s, Ferrocenyl H), 3.99–
4.04 (6H, m, Ferrocenyl H), 3.96 (2H, t, J 6.4 Hz, OCH2), 0.67–2.33
(73H, m, aliphatic and cholesteric protons are overlapped); 13C
NMR (CDCl3, 100 MHz) 173.0, 161.6, 157.8, 157.4, 145.0, 139.7,
130.3, 129.2, 122.6, 122.0, 114.9, 114.6, 73.8, 68.6, 68.2, 68.1, 67.9,
67.1, 56.7, 56.1, 50.0, 42.3, 39.7, 39.5, 38.1, 37.0, 36.6, 36.2, 35.8,
34.6, 31.9, 31.8, 31.1, 29.7, 29.6, 29.4, 29.2, 29.0, 28.2, 28.0, 27.8,
26.0, 25.6, 24.8, 24.3, 23.8, 22.8, 22.6, 21.0, 19.3, 18.7, 11.9; Anal.
Calcd for C67H95FeNO4: C, 77.80; H, 9.26; N, 1.35. Found: C, 77.98;
H, 9.50; N, 1.45%.
4.7.4. Compound 7c. Ref. 32.
4.8. Procedure for preparation of intermediate 9
The nitro derivative 8 (0.3 g, 0.6 mmol) was dissolved in 25 ml
ethyl acetate and 15 mg of 10% Pd/C was added and stirred under
hydrogen atmosphere for 4 h and filtered through Celite to
remove the catalyst. The residue left after removal of the solvent
was subjected to column chromatography over silica gel using
petroleum ether/ethyl acetate (5:1) as eluent to afford either the
product 9.
4.10.3. Compound 16a. A mixture of 9 (0.10 g, 0.26 mmol) and 12
(0.16 g, 0.26 mmol) was refluxed in absolute ethanol (10 ml) in the
presence of a catalytic amount of glacial acetic acid for 3 h. The
Schiff’s base 16a was precipitated out from reaction mixture. It was
collected, washed repeatedly with hot ethanol, and dried in
vacuum.
4.8.1. Compound 9. Yellow solids, mp 96–98 ꢀC, yield 95%, Rf¼0.5
(20% EtOAc/pet. ether), IR (KBr) nmax: 3380, 3309, 2921, 1717,
1605 cmꢂ1 1H NMR (CDCl3, 400 MHz) 8.09 (2H, d, J 8.7 Hz, ArH),
;
l
¼589nm
6.95 (2H, d, J 8.6 Hz, ArH), 6.93 (2H, d, J 8.7 Hz, ArH), 6.68 (2H, d,
8.6 Hz, ArH), 4.08 (5H, S, Ferrocenyl H), 4.00–4.04 (6H, m, Ferro-
cenyl Hþ–OCH2), 3.63 (2H, broad s, NH2) 2.31 (2H, t, J 7.8 Hz, –CH2),
1.79–1.82 (2H, quin, J 7.3 Hz, –CH2–CH2–CH2), 1.39–1.55 (6H, m,
aliphatic H); 13C NMR (CDCl3, 100 MHz) 165.6, 163.3, 144.2, 143.2,
132.2, 122.4, 121.9, 115.7, 114.3, 68.5, 68.2, 68.1, 67.0, 31.1, 29.6, 29.3,
29.1, 25.9; Anal. Calcd for C29H31FeNO3: C, 70.03; H, 6.28; N, 2.82.
Found: C, 70.23; H, 6.24; N, 2.90%.
Yellow solids yield 92%, [aD
]
¼ꢂ10.14 at C¼1% solution in
CHCl3 at 26.6 ꢀC, IR (KBr) nmax: 2933, 2865, 1727, 1620, 1605 cmꢂ1
;
1H NMR (CDCl3, 400 MHz) 8.48 (1H, s, CH]N), 8.12 (2H, d, J 8.8 Hz,
ArH), 7.92 (2H, d, J 8.6 Hz, ArH), 7.29 (2H, d, J 8.6 Hz, ArH), 7.20 (2H,
d, J 8.8 Hz, ArH), 6.95 (2H, d, J 8.9 Hz, ArH), 6.89 (2H, d, J 8.8 Hz,
ArH), 5.35 (1H, d, J 3.8 Hz, ]CH), 4.61–4.62 (1H, m, OCH), 4.02–4.07
(9H, m, Ferrocenyl H), 3.95 (2H, t, J 6.4 Hz, OCH2), 0.66–2.33 (63H,
m, aliphatic and cholesteric protons are overlapped); 13C NMR
(CDCl3, 100 MHz) 173.0, 165.0, 163.5, 159.9, 148.9, 139.6, 132.3, 132.1,
132.0, 130.7, 122.6, 122.4, 121.8, 121.5, 114.7, 114.3, 114.2, 78.8, 69.5,
68.9, 68.3, 68.0, 67.9, 56.7, 56.1, 50.0, 42.3, 39.7, 39.5, 38.1, 37.0, 36.6,
36.2, 35.8, 34.5, 31.9, 31.8, 31.0, 29.5, 29.3, 29.0, 28.9, 28.7, 28.2, 28.0,
27.8, 25.9, 25.6, 24.7, 23.8, 22.8, 22.5, 21.0,19.3,18.7,11.9; Anal. Calcd
for C69H89FeNO6: C, 76.43; H, 8.27; N, 1.29. Found: C, 76.70; H, 8.48;
N, 1.40%.
4.9. Procedure for preparation of intermediates 11–14
Procedure for preparation of all the compounds and respective
data were already reported.14
4.10. General procedure for the Schiff’s base formation
15a,b and 16a–d
4.10.4. Compound 16b. A mixture of 7c (0.10 g, 0.17 mmol) and 14
(0.1 g, 0.17 mmol) was refluxed in absolute ethanol (10 ml) in the
presence of a catalytic amount of glacial acetic acid for 3 h. The
Schiff’s base 16b was precipitated out from reaction mixture. It was
collected, washed repeatedly with hot ethanol, and dried in
vacuum.
4.10.1. Compound 15a. A mixture of 4a (0.10 g, 0.25 mmol) and 14
(0.15 g, 0.25 mmol) was refluxed in absolute ethanol (10 ml) in the
presence of a catalytic amount of glacial acetic acid for 3 h. The
Schiff’s base 15a was precipitated out from reaction mixture. It was
collected, washed repeatedly with hot ethanol, and dried in
vacuum.
l
¼589nm
Pale yellow solids yield 92%, [aD
lution in CHCl3 at 26.6 ꢀC, IR (KBr) nmax: 2934, 2863, 1728, 1622,
1604 cmꢂ1 1H NMR (CDCl3, 400 MHz): 8.48 (1H, s, CH]N), 8.13
]
¼ꢂ10.60 at C¼1% so-
l¼589nm
Yellow solids, yield 96%, [aD
]
¼ꢂ4.90 at C¼1% solution in
CHCl3 at 26.8 ꢀC, IR (KBr) nmax: 2923, 2851, 1730, 1621, 1609 cmꢂ1
;
;
1H NMR (CDCl3, 400 MHz) 8.38 (1H, s, CH]N), 7.79 (2H, d, J 8.7 Hz,
ArH), 7.16 (2H, d, J 8.8 Hz, ArH), 6.93 (2H, d, J 8.7 Hz, ArH), 6.87 (2H,
d, J 8.8 Hz, ArH), 5.36 (1H, d, J 4.0 Hz, ]CH), 4.59–4.62 (1H, m,
OCH), 4.11 (3H, s, Ferrocenyl H), 3.98–4.08 (6H, m, Ferrocenyl H),
3.94 (2H, t, J 6.4 Hz, OCH2), 0.66–2.34 (63H, m, aliphatic and cho-
lesteric protons are overlapped); 13C NMR (CDCl3, 100 MHz) 173.0,
161.6, 157.8, 157.4, 145.0, 139.7, 130.3, 129.1, 122.6, 122.0, 114.9, 114.7,
(2H, d, J 8.9 Hz, ArH), 7.94 (2H, d, J 8.6 Hz, ArH), 7.30 (2H, d, J 8.6 Hz,
ArH), 7.21 (2H, d, J 8.8 Hz, ArH), 6.96 (2H, d, J 8.9 Hz, ArH), 6.90 (2H,
d, J 8.8 Hz, ArH), 5.36 (1H, d, J 4.7 Hz, ]CH), 4.59–4.63 (1H, m,
OCH), 4.08 (3H, s, Ferrocenyl H), 4.02–4.06 (6H, m, Ferrocenyl H),
3.97 (2H, t, J 6.4 Hz, OCH2), 0.67–2.33 (73H, m, aliphatic and cho-
lesteric protons are overlapped); 13C NMR (CDCl3, 100 MHz) 173.3,
164.3, 163.7, 157.9, 157.0, 153.2, 144.5, 139.7, 134.0, 132.3, 129.7,

8006
K.C. Majumdar et al. / Tetrahedron 65 (2009) 7998–8006
122.60, 122.2, 121.2, 115.0, 114.3, 73.7, 68.5, 68.3, 68.2, 68.1, 67.0,
56.7, 56.1, 50.0, 42.3, 39.7, 39.5, 38.1, 37.0, 36.6, 36.2, 35.8, 34.7, 31.9,
31.8, 31.1, 29.7, 29.6, 29.5, 29.4, 29.3, 29.2, 29.1, 28.2, 28.0, 27.8, 26.0,
25.9, 25.0, 24.3, 23.8, 22.8, 22.6, 21.0, 19.3, 18.7, 11.9; Anal. Calcd for
C74H99FeNO6: C, 76.99; H, 8.64; N, 1.21. Found: C, 77.22; H, 8.48; N,
1.43%.
28.0, 27.8, 25.9, 25.6, 24.8, 24.3, 23.8, 22.8, 22.5, 21.0, 19.3, 18.7, 11.8;
Anal. Calcd for C69H88FeN2O8: C, 73.39; H, 7.85; N, 2.48. Found: C,
73.63; H, 8.03; N, 2.63%.
Acknowledgements
We thank the DST (New Delhi) for financial assistance. Three of
us (S.C., N.P. and R.K.S) are grateful to the CSIR (New Delhi) for
Fellowships. We are also thankful to the Material Chemistry
Department of CMRI, Bhavnagar for providing XRD facility.
4.10.5. Compound 16c. A mixture of 7a (0.10 g, 0.19 mmol) and 14
(0.11 g, 0.19 mmol) was refluxed in absolute ethanol (10 ml) in the
presence of a catalytic amount of glacial acetic acid for 3 h. The
Schiff’s base 16c was precipitated out from reaction mixture. It was
collected, washed repeatedly with hot ethanol, and dried in
vacuum.
References and notes
l
¼589nm
1. Deschenaux, R.; Goodby, J. W. In Ferrocenes; Togni, A., Hayashi, Eds.; VCH:
Weinheim, 1995; Chapter 9.
Yellow solids yield 92%, [aD
]
¼ꢂ7.12 at C¼1% solution in
CHCl3 at 26.0 ꢀC, IR (KBr) nmax: 2936, 2862, 1729, 1622, 1607 cmꢂ1
;
2. Serrano, L. Metallomesogens; VCH: Weinheim, 1996; Bruce, D. W. In Inorganic
Materials, 2nd ed.; Bruce, D. W., Hare, D. O., Eds.; Wiley: Chichester, 1996.
3. Nakamura, N.; Hanasaki, T.; Onoi, H. Mol. Cryst. Liq. Cryst. 1993, 225, 269.
4. Nakamura, N.; Onoi, H.; Oida, T.; Hanasaki, T. Mol. Cryst. Liq. Cryst. 1994, 257, 43.
5. Imrie, C.; Loubser, C. J. Chem. Soc., Chem. Commun. 1994, 2159.
6. Loubser, C.; Imrie, C. J. Chem. Soc., Perkin Trans. 2 1997, 399.
7. Deschenaux, R.; Schweissguth, M.; Levelut, A.-M. Chem. Commun. 1996, 1275.
8. Seshadri, T.; Haupt, H.-J. Chem. Commun. 1998, 735.
9. Deschenaux, R.; Santiago, J.; Guillon, D.; Heinrich, B. J. Mater. Chem. 1994, 4, 679.
10. Deschenaux, R.; Santiago, J. Tetrahedron Lett. 1994, 35, 2169.
11. Nakamura, N.; Hanasaki, T.; Onoi, H.; Oida, T. Chem. Express 1993, 8, 467.
12. Nakamura, N.; Setodoi, S. Mol. Cryst. Liq. Cryst. 1999, 333, 151.
13. Carlescu, I.; Scutaru, A. M.; Apreutese, D.; Alupei, V.; Scutaru, D. Liq. Cryst. 2007,
34, 775.
14. Majumdar, K. C.; Chakravorty, S.; Pal, N.; Rao, N. V. S. Tetrahedron 2009, 65, 152.
15. For a recent review on dimers see: Imrie, C. T.; Luckhurst, G. R. In Hand book of
Liquid Crystal; Demus, D., Goodby, J., gray, G. W., Spiess, H. W., Vill, V., Eds.;
Wiley-VCH: Weinheim, 1998; Vol. 2B, p 801.
16. Emsley, J. W.; Luckhurst, G. R.; Shilstone, G. N.; Sage, I. Mol. Cryst. Liq. Cryst.
1984, 102, 223.
1H NMR (CDCl3, 400 MHz): 13.80 (1H, s, OH), 8.60 (1H, s, CH]N),
8.11 (2H, d, J 7.0 Hz, ArH), 7.38 (1H, d, J 8.5 Hz, ArH), 7.24 (1H, d,
J 8.7 Hz, ArH), 6.91–6.97 (5H, m, ArH), 6.85 (1H, d, J 2.2 Hz, ArH),
6.78 (1H, dd, J 8.5, 2.2 Hz, ArH), 5.36 (1H, d, J 4.7 Hz, ]CH), 4.59–
4.63 (1H, m, OCH), 4.07 (3H, s, Ferrocenyl H), 4.02–4.05 (6H, m,
Ferrocenyl H), 3.96 (2H, t, J 6.4 Hz, OCH2), 0.66–2.35 (63H, m, ali-
phatic and cholesteric protons are overlapped); 13C NMR (CDCl3,
100 MHz) 173.0, 164.4, 163.6, 159.4, 158.4, 153.7, 145.8, 143.3, 140.8,
139.6, 132.8, 132.4, 125.7, 122.6, 122.3, 121.3, 115.2, 114.3, 113.0, 73.8,
69.6, 68.3, 67.9, 56.7, 56.1, 50.0, 42.3, 39.7, 39.5, 38.1, 37.0, 36.6, 36.2,
35.8, 34.6, 31.9, 31.8, 30.9, 29.5, 29.3, 29.0, 28.9, 28.2, 28.0, 27.8,
25.9, 26.6, 24.8, 24.3, 23.8, 22.5, 21.0, 19.3, 18.7, 11.8; Anal. Calcd for
C69H89FeNO7: C, 75.32; H, 8.15; N, 1.27. Found: C, 75.62; H, 8.40; N,
1.42%.
17. Jin, J.-I.; Kwon, Y.-W.; Yun, Y.-K.; Zin, W.-C.; Kang, Y.-S. Mol. Cryst. Liq. Cryst.
1998, 309, 117.
18. Blatch, A. E.; Fletcher, I. D.; Luckhurst, G. R. J. Mater. Chem. 1997, 7, 9.
19. Yelamaggad, C. V.; Nagamani, S. A.; Hiremath, U. S.; Nair, G. G. Liq. Cryst. 2001,
28, 1009.
20. Yelamaggad, C. V.; Achalkumar, A. S.; Rao, D. S. S.; Prasad, S. K. Org. Lett. 2007, 9,
2641.
21. Yelamaggad, C. V.; Nagamani, S. A.; Hiremath, U. S.; Rao, D. S. S.; Prasad, S. K.
Mol. Cryst. Liq. Cryst. 2002, 29, 231.
22. Marcelis, A. T. M.; Koudijis, A.; Sudholter, E. J. R. Liq. Cryst. 2000, 27, 1515.
23. Marcelis, A. T. M.; Koudijis, A.; Klop, E. A.; Sudholter, E. J. R. Liq. Cryst. 2001, 28, 881.
24. Rao, D. S. S.; Prasad, S. K.; Raja, V. N.; Yelamaggad, C. V.; Nagamani, S. A. Phys.
Rev. Lett. 2001, 87, 085504.
4.10.6. Compound 16d. A mixture of 7b (0.10 g, 0.23 mmol) and 14
(0.13 g, 0.23 mmol) was refluxed in absolute ethanol (10 ml) in the
presence of a catalytic amount of glacial acetic acid for 3 h. The
Schiff’s base 16d was precipitated out from reaction mixture. It was
collected, washed repeatedly with hot ethanol, and dried in
vacuum.
l
¼589nm
Brown solids, yield 94%, [aD
in CHCl3 at 26.7 ꢀC, IR (KBr) nmax: 2936, 2864, 1725, 1625,
1604 cmꢂ1 1H NMR (CDCl3, 400 MHz): 8.59 (1H, d, J 2.0 Hz), 8.52
]
¼ꢂ7.82 at C¼1% solution
;
(1H s), 8.11 (1H, dd, J 8.5, 2.0 Hz), 8.12 (2H, d, J 8.8 Hz), 7.46 (1H, d, J
8.4 Hz), 7.26 (1H, d, J 8.9 Hz), 6.96 (2H, d, J 8.8 Hz), 6.91 (2H, d, J
8.9 Hz), 5.35 (1H, d, J 4.5 Hz), 4.57–4.65 (1H, m), 4.07 (3H, s), 4.03–
4.06 (6H, m), 3.97 (2H, t, J 6.4 Hz), 0.66–2.36 (63H, m); 13C NMR
(CDCl3, 100 MHz) 173.0, 164.1, 163.8, 158.5, 153.7, 145.9, 143.4,
142.42, 139.7, 135.2, 133.4, 132.8, 125.8, 125.5, 122.65, 122.5, 120.1,
115.0, 114.6, 73.8, 68.3, 67.9, 56.7, 56.1, 50.0, 42.3, 39.7, 39.5, 38.1,
37.0, 36.6, 36.2, 35.8, 34.6, 31.9, 31.8, 31.0, 29.5, 29.2, 29.0, 28.9, 28.2,
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