Synthesis of novel regioisomeric phenanthro[a]phenazine derivatives through the SNAr strategy and their self-assembly into columnar phases

Article abstract of DOI:10.1039/d0nj05042c

The cyclocondensation reaction of triphenylene-1,2-diquinone with 1,2-diamino-4-nitrobenzene results in two regioisomers, and is succeeded by a nucleophilic substitution reaction with alkyl mercaptans. The synthesis of unsymmetrically substituted phenazin

Full text of DOI:10.1039/d0nj05042c

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Synthesis of novel regioisomeric
phenanthro[a]phenazine derivatives through the
SNAr strategy and their self-assembly into
columnar phases†
Cite this: New J. Chem., 2021,
45, 4185
a
ab
ab
Alakananda Patra, K. Swamynathan and Sandeep Kumar
*
The cyclocondensation reaction of triphenylene-1,2-diquinone with 1,2-diamino-4-nitrobenzene results
in two regioisomers, and is succeeded by a nucleophilic substitution reaction with alkyl mercaptans. The
synthesis of unsymmetrically substituted phenazines, separation and characterization of their
regioisomers are rare in discotic liquid crystal chemistry. Here, we report for the first time the synthesis
Received 14th October 2020,
Accepted 20th January 2021
N
of two regioisomers of phenanthro[a]phenazine via a simple S Ar substitution reaction. Separation of
these regioisomers was achieved successfully via column chromatography and they were well
characterized by spectroscopic analysis. Both the regioisomers were found to be mesomorphic. This
DOI: 10.1039/d0nj05042c
N
study throws a lot of light on the S Ar strategy for functionalizing diverse p-conjugated systems for
rsc.li/njc
various applications.
which are known for their excellent photophysical properties have
also been reported for their mesogenicity. Expansion of p-
1
. Introduction
5
The chemical structures of discotic liquid crystals (DLCs) are conjugation by extending the core or by incorporating heteroa-
composed of central p-conjugated cores functionalized with toms is observed to be effective for producing more stable
1
various flexible tails around the periphery. These one- materials with lower HOMO–LUMO gaps, higher temperature
6
dimensional columnar stacks of molecules have a stunning range mesophase and better charge carrier mobility.
ability to self-organize into several two-dimensional lattices.
These 2D macrostructures can either be self-assembled into reported in the literature,
least-ordered arrangements, thus forming a discotic nematic notable discotic liquid crystalline cores,
Out of the numerous carbocyclic and heterocyclic DLCs
7
–9
triphenylene is one of the most
1
0,11
thanks to its
phase, or in a typical columnar fashion, which can later arrange wonderful thermal stability, accessible chemistry and reasonable
into a hexagonal, rectangular, oblique or lamellar lattice. The charge carrier mobility. Over the years, triphenylene cores have
self-assembly of these DLCs is due to the interplay of two been heavily studied and diversified by fusing with different
attractive interactions, namely p–p attraction between the cores heteroatoms through numerous synthetic strategies leading to
1
2–14
which provides the rigidity to the system and hydrophobic novel p-extended discotic core structures.
It has been docu-
interaction between the tails which counterbalances the former mented that the introduction of nitrogen atoms into the aro-
from forming three-dimensional crystals in a certain temperature matic core is an effective strategy for increasing the electron-
2
range. The columnar structure exhibited by discogens has shown withdrawing character and endowing the discotic central core
1
5–18
great potential in various semiconducting applications such as with n-type characteristics.
photoconductors, organic light emitting diodes, solar cells, etc., heterocyclic moieties in the organic material literature for their
Phenazines are well known
1
9,20
because of their excellent property of one-dimensional charge numerous semiconducting and biological applications.
transport through the columnar stack due to the long-range synthesis of phenazines is often accomplished through the cyclo-
The
3,4
order.
The derivatives of heterocyclic p-conjugated systems condensation of 1,2-diketones with 1,2-diamines in the presence
of acid or base. Phenazine dyes have also shown excellent
a
21–27
Raman Research Institute, Soft Condensed Matter, C. V. Raman Avenue,
Bangalore 560080, India. E-mail: skumar@rri.res.in; Fax: +91 80 23610492;
Tel: +91 80 23610122
electronic properties.
There are many literature reports on
mesogens based on the phenazine skeleton; besides, they have
been shown to exhibit good hole-mobility and conducting
b
Department of Chemistry, Nitte Meenakshi Institute of Technology (NMIT),
Yelahanka, Bangalore 560064, India
2
8–37
behavior.
Our group has reported novel phenanthro[a]
3
8
39
phenazine
and phenanthro[b]phenazine
DLCs in the
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
d0nj05042c
past by the condensation of triphenylene-o-quinones with
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o-phenylenediamine. Our recent work on the charge mobility reaction. Separation of these regioisomers was achieved success-
studies of these compounds suggests a similar hole mobility to fully by column chromatography and they were well characterized
3
3
that of hexakis(hexyloxy)triphenylene.
by spectroscopic analysis. The mercaptoalkyl substituted phena-
The aromatic nucleophilic substitution reactions (S Ar) zines as well as the pre-final i.e. nitro functionalized
N
have been the strategy to go for in the development of new phenanthro[a]phenazines self-assemble into the hexagonal
4
0,41
organic materials in recent times.
on the role of S Ar reactions in the synthetic design of macro-
cycles, polymers, molecular cages and crosslinked network
There are many reports columnar phase in a wide temperature range.
N
2
. Results and discussion
4
2–50
compounds. The scope of this reaction is underexplored.
The precursors needed for this synthetic strategy are both easily
2.1. Design and synthesis
available and synthetically feasible. The halo derivatives are one The commercial pyrocatechol was alkylated using the William-
of the mainly used precursors for the S Ar pathway. This may son synthetic conditions to form 1,2-bis(dodecyloxy)benzene
N
be due to their good leaving ability as well as electron- (2). The obtained 1,2-bis(dodecyloxy)benzene was oxidatively
1
5
withdrawing nature. Apart from halogens, there are few trimerized through the Scholl reaction using ferric chloride
5
1
52
reports on nitro and cyano groups being used in S
N
3
Ar (FeCl ) which led to the desired 3,6,7,10,11-pentakis(dodecyloxy)
reactions for making novel materials. In this report, we have triphenylene-2-ol as a by-product (3) along with 2,3,6,7,10,11-
0
adopted the nitro group for functionalizing phenanthro[a] hexakis(dodecyloxy)triphenylene (3 ). The 3, 6,7,10,11-pentakis
phenazines through the S Ar strategy with mercaptoalkyl (dodecyloxy)triphenylene-2-ol was separated from the reaction
chains mainly because of the cheaper cost of the precursor mixture using gravity column chromatography. Further oxida-
and easier purification.
tion of 3 in the presence of ceric ammonium nitrate gives rise
N
In this work, we have used the S Ar pathway to functionalize to 3,6,7,10,11-pentakis(dodecyloxy)triphenylene-1,2-dione, which
N
a nitro group containing phenanthro[a]phenazine with a upon cyclo-condensation with commercially obtained 1,2-
mercaptoalkyl moiety. The synthesis of unsymmetrically sub- diamino 4-nitrobenzene gives both 5(a) and 5(b) regioisomers.
stituted phenazines, and the separation and characterization of Both the regioisomers were successfully separated using gravity
their regioisomers are rare in discotic liquid crystal chemistry. column chromatography and taken for the final step involving
Here, we report for the first time the synthesis of two regioisomers substitution with mercaptans. The structures of the obtained
of phenanthro[a]phenazine via a simple S Ar substitution final products 6(a–c) and 6i(a–c) were assigned through NMR
N
Scheme 1 Synthetic pathway of novel phenathro[a]phenazine derivatives (i) alkyl halide, anhydrous K
room temperature, 1 h, (iii) ceric ammonium nitrate, THF–dioxane mixture, room temperature, 3 h, (iv) toluene, acetic acid, reflux, 12 h, (v) alkanethiol,
anhydrous K CO , dry DMF, reflux, 12 h.
2 3 3
CO , ethanol, reflux, 36 h, (ii) FeCl , dry DCM,
2
3
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techniques and elemental analysis. The synthetic procedure is between both, hence proving that the structure assigned is
shown in Scheme 1. correct.
Fig. 2 shows the proton NMR and the corresponding ROESY
spectra of compound 6(b). On analysing the ROESY spectrum of
compound 6(b), proton H shows a correlation with H (peak
around d = 8 ppm, doublet with J = 1.5 Hz) which matches with
2
.2. Assignment of the structure of regioisomers through
a
b
NMR analysis
The structures of both the regioisomers were assigned by the structure 6(b).
combination of both 1D and 2D NMR techniques. Assignment
2
.2. Mesomorphic and thermal properties
of the protons arranged in an ABX fashion, namely H
d
, H
, is mainly done using the H NMR technique. In both the The primary indication of mesomorphism was realized from
isomers 6i(b) and 6(b), H and H undergo ortho coupling with the observation of distinct liquid crystalline textures under
a J of value around 9–9.5 Hz and H
smaller coupling constant (J around 1–1.5 Hz), giving rise to a points from differential scanning calorimetry (DSC).
c
and
1
H
b
c
d
5
3
b
d
interacts with H with a polarized optical microscopy (POM) and the double melting
5
4,55
The
doublet of doublets. The doublet for a single proton with J exact values of phase transition as well as the corresponding
around 9 Hz is H and J around 1.5 Hz is H . Other protons are enthalpy values were obtained from DSC measurements and
c
b
1
assigned to the peaks using H and COSY NMR spectra (Fig. S5– the phases were confirmed using X-ray diffraction studies.
S8, ESI†).
2.2.1. Polarized optical microscopy. The thermotropic beha-
The ROESY experiment was used to ascertain the structure vior of all the prefinal 5(a–b) and final 6i(a–c) and 6(a–c)
of regioisomers because a weak signal was expected between H
compounds was first examined by polarising optical microscopy
and H in 6i(b), and also between H and H in 6(b) due to their (POM) in both heating and cooling cycles by placing a small
a
c
a
b
proximity in space. Fig. 1 shows the proton NMR and the amount of compound between a normal glass slide and cover-
corresponding ROESY spectrum of 6i(b). The most deshielded slip. The prefinal compounds 5(a) and 5(b) showed dendritic
proton H shows a correlation with H (peak around d = 8 ppm, and mosaic textures respectively (Fig. 3), which suggests the
a
c
doublet with J = 9 Hz) which signifies the spatial proximity presence of the columnar mesophase. The POM textures of the
1
Fig. 1 H and ROESY NMR spectra of compound 6i(b).
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1
Fig. 2 H and ROESY NMR spectra of compound 6(b).
final compounds 6(a–c) and 6i(a–c) are found to be exhibiting
2.2.2. Differential scanning calorimetry. The DSC measure-
mosaic textures under crossed polarisers (Fig. 3 and Fig. S1, ments of all the mesomorphic samples on both heating and
ESI†). These mosaic textures with rectilinear defects suggest that cooling scans are recorded under an inert atmosphere. The
the final compounds show columnar mesophase as well.
phase transition temperatures are in good agreement with POM
observations. The thermal behavior of all the pre-final and final
compounds is summarized in Table 1. The peak temperatures
are given in 1C and the numbers in parentheses indicate the
ꢀ
1
phase transition enthalpy (DH) in kJ mol
.
DSC thermograms of all the compounds show two peaks
corresponding to melting and clearing transitions respectively.
In the heating cycle, the isomers 6i(a–c) transit to the liquid
Table 1 Phase transition temperature (peak temperature in 1C) and
ꢀ1
enthalpies (kJ mol , in brackets) of compounds 5a, 5b, 6i(a–c) and
(a–c) on heating and cooling cycles. Cr = crystalline phase; Col
hexagonal columnar phase; I = isotropic phase
6
h
=
Heating cycle
Cooling cycle
5
5
6
6
6
6
a
b
Cr 64.3 (42.4) Col
Cr 12.2 (29.7) Col
h
h
h
h
h
h
242.3 (4.4) I I 236.2 (3.5) Col
236.0 (2.9) I I 230.5 (3.7) Col
178.9 (6.5) I I 175.9 (6.2) Col
176.7 (3.9) I I 173.6 (4.4) Col
172.9 (6.5) I I 170.6 (6.9) Col
169.6 (4.7) I I 166.9 (4.5) Col
h
h
h
h
h
h
12.6 (36.8) Cr
5.6 (30.7) Cr
21.3 (71.8) Cr
21.6 (61.7) Cr
21.2 (69.6) Cr
49.7 (70.0) Cr
ia Cr 48.0 (69.4) Col
ib Cr 44.9 (51.3) Col
ic Cr 45.7 (58.6) Col
a
Cr 79.9 (65.6) Col
Fig. 3 Polarising optical microscopy textures: dendric textures of 5(a) and 6b Cr 79.2 (63.0) Colh 170.8 (6.4) I I 168.6 (6.4) Colh 45.7 (67.8) Cr
mosaic texture of 5(b), 6i(a), and 6(a).
6c Cr 79.5 (44.8) Col 169.7 (5.6) I I 166.7 (5.5) Col 52.4 (54.7) Cr
h
h
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Fig. 5 XRD diffractograms of 5(a) at 120 1C and 5(b) at 130 1C (intensity in
arbitrary unit and d spacing in Å).
peaks are observed, of which one is associated with the fluid
nature of the alkyl chains and the other is due to the interaction
between the cores. The representative X-ray diffraction patterns
of all the mesogens are shown in Fig. 5, 6 and Fig. S4 (ESI†) and
data are summarized in Table 2.
The diffractograms of the prefinal (5a, 5b) and the final (6ia–c,
a–c) compounds show small-angle peaks in the ratio corres-
Fig. 4 DSC thermogram of compounds 5(a), 5(b), 6i(a), and 6(a) at the
6
ꢀ1
scan rate of 10 1C min
.
ponding to that of a hexagonal lattice, which confirms the
columnar hexagonal arrangements of all the novel materials.
From the diffraction results, we have shown the number of
molecules occupying one slice of a column to be around 1. Based
on this we propose the following model for the arrangement of
these compounds in their mesophase (Fig. 7).
crystal phase around 45 1C to 50 1C and completely melt around
70 1C to 180 1C. The second isomers 6(a–c) melt around 79 1C
1
to the liquid crystal phase, and they go to the isotropic phase
around 170 1C. Further, in the cooling cycle, they crystallize at
around 43 1C to 50 1C. Upon comparing with the previous
reports from our group (compounds containing two thio-alkyl
chains) these compounds show a higher clearing point which is
2.3. Photophysical properties
The optical properties of all the final compounds were studied
using UV-vis and fluorescence spectrometry (Fig. 8). The absorption
spectra of compounds 6i(a–c) exhibited four absorption peaks
at 288 nm, 307 nm, 394 nm and 462 nm whereas the absorption
spectra of compounds 6(a–c) exhibited six absorption peaks at
3
3
because of a fewer number of flexible tails. The details of the
transition temperature and the associated enthalpy of all the
prefinal and final compounds are listed in Table 1. DSC
thermograms are shown in Fig. 4 and Fig. S3 (ESI†). The crystal
to liquid crystal transition temperature of 5a is 64 1C and its
isotropic temperature is 242 1C, whereas 5b shows the first
transition at 12 1C and clearing temperature at 236 1C. This
indicates that they are thermodynamically more stable among
all our novel materials, because they possess the electron
withdrawing nitro moiety, thereby decreasing the repulsion
between the electron clouds originally expected in higher
2
64 nm, 285 nm, 307 nm, 348 nm, 411 nm and 450 nm. The
emission spectra displayed a single peak for the isomer set
i(a–c) at 615 nm, 616 nm and 617 nm for 6ia, 6ib, and 6ic
6
respectively and for isomer set 6(a–c) at 616 nm for all the
compounds.
The absorptions (lmax) of 6i(a–c) isomers at 394 nm and
462 nm correspond to the n–p* and p–p* transitions and the
peaks at 288 nm and 307 nm are possibly because of p–p*
transitions of aromatic rings of the phenazine extended
triphenylene core.
In the case of the second set of isomers 6(a–c), the absorption
at 411 nm and 449 nm correspond to n–p* and p–p* transitions
and the less intense peaks at 264 nm, 285 nm, 307 nm and
5
6
conjugated systems.
.2.3. Thermogravimetric analysis. The thermal stability of
2
two compounds from each series of new materials was
measured using thermogravimetric analysis (TGA) with a heat
ꢀ
1
scan rate of 10 1C min
under an inert atmosphere. The
compounds were found to be stable up to around 370 1C. The
decomposition temperature was found to be around 480–
500 1C which is much higher than the isotropic temperature
indicating that the compounds possess good thermal stability,
which in fact is the evidence of the suitability of our molecules
for numerous application purposes. The representative TGA
thermogram of the compounds is shown in Fig. S2 (ESI†).
2.2.4. X-Ray diffraction study. The columnar structure was
further validated through X-ray diffraction. The diffractograms
of the final compounds show the spacings of the low angle
peaks in the ratio of 1 : 1/O3 : 1/2 and can be indexed to a
Fig. 6 XRD diffractograms of compounds 6i(a) at 125 1C and 6(a) at 90 1C
hexagonal lattice. Also, in the wide-angle region, two broad (intensity in arbitrary unit and d spacing in Å).
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Table 2 X-ray diffraction data for all mesomorphic compounds (a =
2
lattice parameter = O(4/3) ꢁ d10; lattice area A = S
h
= a sin 601; lattice
2
volume V
h
= a sin 601 ꢁ h
c a c
(h if h is not observed); no. of molecules
2
per slice of column (Z) = (O3 ꢁ N
a
ꢁ r ꢁ a ꢁ h)/2M; N
a
= Avogadro
ꢀ3
number; r = density in kg m ; a = lattice parameter; h = core core peak
c
ꢀ3
(
1
h
a
if core–core is not observed); M = molecular weight in kg m , r =
ꢀ
3
000 kg m )
Spacing (Å)
Phase
d
obs
d
cal
Index
Lattice parameters
5
a
Col
Col
Col
Col
Col
Col
Col
Col
h
h
h
h
h
h
h
h
(120 1C)
(130 1C)
(125 1C)
(120 1C)
(125 1C)
(90 1C)
23.55
23.55
13.59
11.78
10
11
20
a = 27.19 Å
A = 640.324 Å
V = 2273.1519 Å
Z = 1.05
2
1
1
3.63
1.85
3
4
3
.58
.55
5
6
6
6
6
6
6
b
23.79
23.79
13.73
11.89
10
11
20
a = 27.47 Å
A = 653.503 Å
V = 2306.8675 Å
Z = 1.07
2
1
1
3.63
1.97
3
Fig. 8 (a) Absorbance spectra of 6i(a–c), (b) absorbance spectra of 6(a–
c), (c) emission spectra of 6i(a–c) excited at 460 nm, and (d) emission
spectra of 6(a–c) excited at 450 nm. All the compounds were dissolved in
chloroform to obtain 7 mM concentration for recording the spectra.
4
3
.66
.53
ia
ib
ic
a
24.70
24.70
14.26
12.35
10
11
20
a = 28.52 Å
A = 704.3960 Å
V = 2521.7379 Å
Z = 1.08
2
1
1
4.37
2.37
3
4
3
.63
.58
348 nm are mostly because of the p–p* transitions of the
aromatic core as the previous set of compounds.
The amount of light absorbed and the intensity of the peaks
in the absorption spectrum generally depend on the extent of
conjugation present in the discotic cores. On comparing with
hexa-alkoxy triphenylene (lmax = 300–400 nm), these systems
show that a bathochromic shift of around 150 nm has occurred
for both absorption and emission. This occurs due to the
extension of conjugation in the central phenazine cores by
three aromatic rings.
24.70
24.70
14.26
12.35
10
11
20
a = 28.52 Å
A = 704.3960 Å
V = 2486.5179 Å
Z = 1.05
2
1
1
4.37
2.44
3
4
3
.60
.53
25.25
25.25
14.58
8.42
10
11
20
a = 29.15 Å
A = 735.859 Å
V = 2634.3776 Å
Z = 1.09
2
1
1
4.60
2.61
3
4
3
.61
.58
The Stokes shifts (the difference between the lmax of absorp-
tion and emission) are 153 nm, 154 nm, and 155 nm for 6ia,
6ib, and 6ic respectively and 167 nm for all the compounds of
the 6(a–c) series. lonset was determined by the intersection
between the extrapolated tangent of the longest wavelength
24.20
24.20
13.97
12.10
10
11
20
a = 27.94 Å
A = 676.057189 Å
V = 2420.28474 Å
Z = 1.04
2
1
1
4.01
2.17
3
4
3
.56
.58
absorption peak and the x-axis and the optical energy gap (E
g
)
b
(75 1C)
24.57
24.57
14.19
12.29
10
11
20
a = 28.37 Å
A = 697.026522 Å
V = 2453.53336 Å
Z = 1.03
2
in eV was calculated according to the equation E = 1240/lonset.
g
1
1
4.14
2.37
3
This along with the molar extinction coefficient data are
summarized in Table 3. The absorbance and emission spectra
of all the final compounds are shown in Fig. 8.
4
3
.60
.52
c
(135 1C)
25.25
25.25
14.58
12.62
10
11
20
a = 29.16 Å
A = 735.859 Å
V = 2634.3776 Å
2
1
1
4.60
2.61
3
2. GAUSSIAN studies
4
3
.61
.58
Z = 1.09
Density functional theory (DFT) studies were carried out using
the GAUSSIAN-09 program at Becke’s three-parameter
Table 3 Molar extinction coefficient and the optical band gap of the
compounds 6i(a–c) and 6(a–c)
Molar extinction
coefficient (emax) (M cm
Optical bandgap
(1240/lonset) (eV)
ꢀ1
ꢀ1
Compound
)
4
6
6
6
6
ia
ib
ic
a
e
e
e
e
462 = 1.85 ꢁ 10
462 = 1.87 ꢁ 10
462 = 1.89 ꢁ 10
450 = 1.77 ꢁ 10
2.31
2.34
2.35
2.35
2.36
2.38
4
4
4
4
4
Fig. 7 Proposed arrangement of molecules of compounds 5a, 5b, 6(a–c) 6b
e450 = 1.69 ꢁ 10
&
6i(a–c); in the figure, the compound shown is 6ib.
6c
e
450 = 1.60 ꢁ 10
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Fig. 9 Energy minimized structures, and HOMOs and LUMOs of 5a, 5b, 6, and 6i.
functional and the Lee, Yang and Parr correlation functional
3
. Conclusion
3
8
(DFT-B3LYP) by using the 6-31G(d) basis set. The energy
minimized structure of prefinal and final isomers and the In our presented work, we have prepared two regioisomeric
HOMOs and LUMOs are given in Fig. 9. The energy gap was series of phenazine fused triphenylene-based compounds
found to be 2.47 eV for the minimized structure of 5a and 2.44 eV through the S
for the minimized structure of 5b, 2.84 eV for the compounds of gravity column chromatography, thoroughly characterized and
structure 6i and 2.83 eV for compounds of structure 6.
confirmed using both 1D and 2D NMR and theoretical calcula-
N
Ar strategy which are successfully separated via
From the GAUSSIAN data, it was noticed that theoretically tions. The synthesized compounds and their precursors were
the net dipole moments of the structures assigned to molecule found to be assembling in columns in their mesophase regime.
6
i (3.6949 D) and 5a (8.7233 D) are less than those of 6 (4.0655 The mesomorphic behaviour was analysed through the POM,
D) and 5b (12.1927 D) sequentially. This inference agrees with DSC and XRD techniques. This S Ar strategy can be one of the
N
our observations that R
values of 6 and 5b respectively.
f
values of 6i and 5a are larger than R
f
better alternatives in the expedition of the synthesis of novel
organic materials. Furthermore, we are looking forward to
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studying the charge transport and efficiency of these as semi- 149.41, 148.84, 148.16, 143.83, 141.72, 140.68, 139.61, 137.43,
conducting materials for practical applications. 130.92, 129.88, 128.87, 126.64, 124.98, 124.62, 123.17, 122.83,
18.44, 112.65, 108.20, 106.63, 105.97, 105.31, 69.95, 69.80, 69.54,
9.31, 68.87, 32.32, 31.95, 29.77, 29.74, 29.71, 29.69, 29.68, 29.65,
29.62, 29.60, 29.56, 29.52, 29.49, 29.41, 29.39, 29.23, 29.11, 28.94,
8.51, 26.37, 26.26, 26.23, 22.71, 14.13. Elemental analysis
S): C 79.39%, H 10.97%, N 1.93%, S 2.21% (expected);
1
6
4
. Experimental section
2
The comprehensive synthetic procedure, and the spectral and
elemental analysis data of all the intermediates can be found in
the ESI.†
96 158 2 5
(C H N O
C 79.35%, H 11.41%, N 1.70%, S 1.99% (observed).
Compound 6(a). Orange solid, yield 60%, m.p. in Table 1,
1
H NMR: 10.756 (s, 1H), 8.283 (d, 1H, J = 9.5 Hz), 7.062–7.952
Synthesis of compounds 6i(a–c) & 6(a–c)
(m, 5H), 7.701–7.679 (dd, 1H, J = 9.5, 1.5 Hz), 4.528 (t, 2H, J =
A mixture of compound 5(a) or 5(b) (1 eq.), potassium carbo- 6 Hz), 4.477 (t, 2H, J = 6.5 Hz), 4.322–4.270 (m, 6H), 3.173 (t, 2H,
nate (4 eq.), and alkyl mercaptan (1.2 eq.) in dry DMF (10 ml per J = 7.5 Hz), 2.211–1.272 (112H), 0.890–0.863 (m, 18H, J = 6 Hz).
1
3
1
g of compound 5) was heated to 120 1C. The reaction was
C NMR: 151.84, 150.89, 149.38, 148.83, 148.09, 144.83, 142.09,
monitored using TLC. A saturated solution of sodium bicarbo- 141.47, 138.76, 136.54, 130.62, 130.10, 129.73, 126.77, 125.08,
nate (20 vol%) was added to the reaction mixture after comple- 124.55, 122.81, 118.19, 112.55, 108.27, 106.72, 105.91, 104.56,
tion of the reaction. The mixture was extracted using 69.95, 69.84, 69.52, 69.29, 68.69, 32.38, 31.95, 31.84, 29.77,
dichloromethane and washed with brine. The organic layer 29.72, 29.61, 29.57, 29.51, 29.41, 29.39, 29.26, 29.24, 29.15,
was dried using anhydrous Na SO and the solvent was 28.49, 26.52, 26.24, 22.71, 14.13. Elemental analysis
2
4
removed under reduced pressure. The crude product was (C H N O S): C 79.14%, H 10.83%, N 2.01%, S 2.30%
9
2
150 2 5
purified by column chromatography over silica gel using (expected); C 78.88%, H 11.19%, N 1.38%, S 1.86% (observed).
petroleum ether : ethyl acetate as the eluent (95 : 5). The isolated
compounds were reprecipitated twice using DCM/MeOH to
obtain a reddish-orange solid (60%).
Compound 6(b). Orange solid, yield 63%, m.p. in Table 1,
H NMR: 10.756 (s, 1H), 8.283 (d, 1H, J = 9.5 Hz), 7.964–7.939
(m, 5H), 7.692 (dd, 1H, J = 9.5, 1.5 Hz), 4.528 (t, 2H, J = 6 Hz),
1
Compound 6i(a). Orange solid, yield 60%, m.p. in Table 1, 4.477 (t, 2H, J = 6.5 Hz), 4.314–4.255 (m, 6H), 3.173 (t, 2H, J = 7.5 Hz),
H NMR: 10.733 (s, 1H), 8.116–8.101 (m, 2H), 8.039 (s, 1H), 2.196–1.272 (116H), 0.877 (t, 18H, J = 6 Hz). C NMR: 151.82,
1
13
7
4
6
.962 (s, 2H), 7.936 (s, 1H), 7.706–7.685 (dd, 1H, J = 9, 2 Hz), 150.88, 149.38, 148.82, 148.08, 144.83, 142.07, 141.45, 138.74,
.529 (t, 2H, J = 7 Hz), 4.446 (t, 2H, J = 7 Hz), 4.316–4.262 (m, 136.52, 130.61, 130.08, 129.71, 126.76, 125.09, 124.53, 122.81,
H), 3.181 (t, 2H, J = 7.5 Hz), 2.184–1.272 (112H), 0.896–0.864 118.18, 112.56, 108.26, 106.71, 105.90, 104.54, 69.94, 69.84,
1
3
(m, 18H). C NMR: 151.57, 150.76, 149.37, 148.80, 148.11, 69.50, 69.29, 68.69, 32.39, 31.96, 31.91, 29.81, 29.77, 29.72,
1
1
1
2
2
43.81, 41.68, 140.62, 139.56, 137.37, 130.86, 129.85, 128.86, 29.65, 29.61, 29.52, 29.41, 29.39, 29.35, 29.31, 29.15, 29.01,
26.61, 124.58, 123.14, 122.81, 118.39, 112.64, 108.15, 106.58, 28.50, 26.53, 22.71, 22.69, 14.13, 14.11. Elemental analysis
05.92, 105.25, 69.92, 69.78, 69.29, 68.85, 32.33, 31.96, 31.83, (C94
154 2 5
H N O S): C 79.27%, H 10.90%, N 1.97%, S 2.25%
9.77, 29.72, 29.62, 29.41, 29.22, 29.20, 29.12, 28.96, 28.51, (expected); C 79.02%, H 11.15%, N 1.78%, S 1.92% (observed).
6.38, 26.27, 26.24, 22.71, 14.13. Elemental analysis
Compound 6(c). Orange solid, yield 63%, m.p. in Table 1,
H NMR: 10.740 (s, 1H), 8.269 (d, 1H, J = 9 Hz), 8.030–7.954 (m,
1
(C H N O S): C 79.14%, H 10.83%, N 2.01%, S 2.30%
92 150 2 5
(
expected); C 78.97%, H 11.16%, N 1.81%, S 1.91% (observed). 5H), 7.691 (dd, 1H, J = 9, 1.5 Hz), 4.528 (t, 2H, J = 7 Hz), 4.477 (t,
Compound 6i(b). Orange solid, yield 63%, m.p. in Table 1, 2H, J = 6.5 Hz), 4.296 (m, 6H), 3.173 (t, 2H, J = 7 Hz), 2.196–1.272
H NMR: 10.749 (s, 1H), 8.141 (d, 1H, J = 9 Hz), 8.11 (d, 1H, J = (120H), 0.877 (t, 18H, J = 6 Hz). C NMR: 151.77, 150.85,
1
13
1
7
6
Hz), 8.075 (s,1H), 7.989–7.982 (m, 2H), 7.958 (s, 1H), 7.718– 149.34, 148.78, 148.04, 144.80, 142.04, 141.42, 138.68, 136.46,
.698 (dd, 1H, J = 9, 1 Hz), 4.548 (t, 2H, J = 7 Hz) 4.459 (t, 2H, J = 130.58, 130.06, 129.65, 126.73, 125.07, 124.50, 122.77, 118.13,
.5 Hz), 4.321–4.272 (m, 6H), 3.186 (t, 2H, J = 7 Hz), 2.205–1.271 112.53, 108.20, 106.65, 105.85, 104.47, 69.91, 69.81, 69.46,
1
3
(m, 116H), 0.876 (t, 18H, J = 7 Hz). C NMR: 151.63, 150.81, 69.27, 68.67, 32.37, 31.96, 31.93, 31.60, 29.82, 29.77, 29.74,
1
1
1
6
2
49.42, 148.85, 148.17, 143.83, 141.75, 140.68, 139.63, 137.43, 29.72, 29.67, 29.62, 29.60, 29.59, 29.52, 29.43, 29.42, 29.40,
29.89, 128.88, 126.65, 124.97, 124.63, 123.16, 122.84, 118.46, 29.38, 29.33, 29.16, 29.01, 28.48, 26.54, 26.25, 22.72, 22.67,
12.65, 108.22, 106.63, 105.98, 105.32, 69.97, 69.80, 69.55, 69.32, 14.13. Elemental analysis (C96H N O S) S: C 79.39%, H
158 2 5
8.88, 32.32, 31.95, 29.73, 29.71, 29.59, 29.41, 29.38, 29.33, 29.22, 10.97%, N 1.93%, S 2.21% (expected); C 79.11%, H 11.19%, N
9.10, 28.94, 28.51, 26.36, 26.25, 26.22, 22.71, 14.13. Elemental 1.71%, S 1.93% (observed).
1
analysis (C94
154 2 5
H N O S): C 79.27%, H 10.90%, N 1.97%, S 2.25%
All synthesised compounds were characterised by H and
C NMR and elemental analysis. Detailed spectra are also
1
3
(expected); C 78.76%, H 10.63%, N 1.75%, S 2.55% (observed).
Compound 6i(c). Orange solid, yield 65%, m.p. in Table 1, given in the ESI.†
H NMR: 10.74 (s, 1H), 8.127 (d, 1H, J = 9.5 Hz), 8.109 (d, 1H, J =
1
1.5 Hz), 8.055 (s, 1H), 7.972 (s, 2H), 7.946 (s,1H), 7.711–7.690
(
6
1
dd, 1H, J = 9.5, 1.5 Hz), 4.537 (t, 2H, J = 7 Hz), 4.452 (t, 2H, J =
Conflicts of interest
.5 Hz), 4.317–4.266 (m, 6H), 3.183 (t, 2H, J = 7.5 Hz), 2.202–
1
3
.271 (120H), 0.877 (t, 18H, J = 6 Hz). C NMR: 151.62, 150.80, There is no conflict of interest.
4192 | New J. Chem., 2021, 45, 4185ꢀ4194
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Acknowledgements
21 N. Sato, Six-Membered Hetarenes with Two Identical Heteroa-
toms, Georg Thieme Verlag KG, 2004, p. 1.
The authors thank K. N. Vasudha for UV, DSC, XRD and
elemental analysis; Dr H. T. Srinivasa for NMR and TGA
measurements; Irla Sivakumar for valuable suggestions;
Marichandran Vadivel, Vanishree Bhat and Ashwath N Gowda
for their support and co-operation; Nancy Verma for help in PL
studies and David Joseph for discussion regarding NMR analy-
sis. We thank Prof. Victor Belyaev and Prof. Denis Chausov for
helpful discussion. Department of Science and Technology,
Government of India, Grant INT/RUS/RFBR/376 and Russian
Foundation for Basic Projects, grant No. 19-57-45011_Ind_a are
gratefully acknowledged.
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