Microwave-assisted palladium-catalyzed C-C coupling versus nucleophilic aromatic substitution of hydrogen (SNH) in 5-bromopyrimidine by action of bithiophene and its analogues

Article abstract of DOI:10.1016/j.tet.2013.04.062

5-Bromopyrimidine reacts with 2,2′-bithiophene, [2,2′:5′, 2″]terthiophene and 2-phenylthiophene in the presence of a palladium catalyst to give 5-(het)aryl substituted pyrimidines due to the palladium-catalyzed aryl-aryl C-C coupling. However 5-bromo-4-(het)aryl- pyrimidines have been prepared from the same starting materials through the S_N^H-reaction catalyzed by a Lewis acid. Conditions for both types of reactions were optimized. All components of the reaction mixtures, including by-products, have been elucidated by gas-liquid chromatography/mass- spectrometry. Evidence for the structure of 4- and 5-bithiophenyl-substituted pyrimidines has first been obtained by means of X-ray crystallography analysis. Molecular orbital calculations (TDDFT), as well as the redox and optical measurements for all new compounds have also been performed.

Full text of DOI:10.1016/j.tet.2013.04.062

Tetrahedron xxx (2013) 1e9
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Microwave-assisted palladium-catalyzed CeC coupling versus
nucleophilic aromatic substitution of hydrogen (SHN) in
5-bromopyrimidine by action of bithiophene and its analogues
,
a
a
Egor V. Verbitskiy a , Ekaterina M. Cheprakova , Ekaterina F. Zhilina ,
*
Mikhail I. Kodess a, Marina A. Ezhikova a, Marina G. Pervova a, Pavel A. Slepukhin a,
,
,b
Julia O. Subbotina a b, Aleksandr V. Schepochkin a, Gennady L. Rusinov a
,
Oleg N. Chupakhin a b, Valery N. Charushin a
,
,b
a I. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, S. Kovalevskoy Str. 22, Ekaterinburg 620041, Russia
b Ural Federal University, Mira St. 19, Ekaterinburg 620002, Russia
a r t i c l e i n f o
a b s t r a c t
5-Bromopyrimidine reacts with 2,20-bithiophene, [2,20:50,200]terthiophene and 2-phenylthiophene in the
presence of a palladium catalyst to give 5-(het)aryl substituted pyrimidines due to the palladium-
catalyzed arylearyl CeC coupling. However 5-bromo-4-(het)aryl-pyrimidines have been prepared
from the same starting materials through the SHN-reaction catalyzed by a Lewis acid. Conditions for both
types of reactions were optimized. All components of the reaction mixtures, including by-products, have
been elucidated by gaseliquid chromatography/mass-spectrometry. Evidence for the structure of 4- and
5-bithiophenyl-substituted pyrimidines has first been obtained by means of X-ray crystallography
analysis. Molecular orbital calculations (TDDFT), as well as the redox and optical measurements for all
new compounds have also been performed.
Article history:
Received 5 February 2013
Received in revised form 26 March 2013
Accepted 15 April 2013
Available online xxx
Keywords:
CeH bond activations
Nucleophilic aromatic substitution of
hydrogen
Ó 2013 Elsevier Ltd. All rights reserved.
Pyrimidines
Palladium
Microwave-assisted synthesis
Cross-coupling reactions
1. Introduction
During the last decade, organic molecules bearing both electron-
donating and electron-withdrawing fragments, for instance pyr-
imidineethiophene conjugated monomers and polymers, have
received considerable attention due to their promising optical and
electronic properties.1 Therefore, a search for an access to novel
(hetero)arylated bithiophenes is an important task in organic and
organometallic chemistry.2
1
X
Het
R M
Het
S
+
S
+
or
1
R M
Het
Het
X
0
[Pd ], base
1
R M = B(OH) , SnR , ZnR, MgR;
2
3
Het = (hetero)aryl;
X is a halogen
The palladium-catalyzed Suzuki, Stille, and Negishi cross-
coupling reactions provide a valuable synthetic basis to prepare
such compounds.3 However, these reactions require a preliminary
preparation of organometallic intermediates (Scheme 1).
Het
Het
S
Scheme 1.
It is known that aryl halides can be coupled with a number of
electron
-excessive five-membered heteroaromatics,4 including
thiophenes5 in the presence of a palladium catalyst (Scheme 2).
p
* Corresponding author. Tel./fax: þ7 343 3693058; e-mail address: Verbitsky@
ios.uran.ru (E.V. Verbitskiy).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.04.062
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E.V. Verbitskiy et al. / Tetrahedron xxx (2013) 1e9
Fig. 1. Structures of by-products derived from the reactions of bithiophene and its
analogues with 5-bromopyrimidine, according to the GCeMS analysis.
Scheme 2.
Table 1
Indeed, the palladium-catalyzed arylation of heteroaromatics with
aryl halides has proved to be a very powerful method for the
synthesis of a wide range of aryl substituted heteroaromatics.
Aryl-aryl cross-coupling reactions with simple thiophenes have
been well elucidated,5 whereas the palladium-catalyzed arylations
of bi-, ter-, and polythiophenes have been scarcely studied.2 It
should be noted that only a few examples of the preparation of
monoarylated bithiophenyls by direct arylation reactions have
been reported.2,6
Another synthetic methodology to form the CeC and CeX (X is
a heteroatom) bonds is based on nucleophilic aromatic substitution
of hydrogen (SHN) (Scheme 2).7 The advantage of this approach is
that it does require the presence of a halogen atom in aromatic
substrate nor an expensive metal catalyst.
In this paper we wish to report new protocols for the direct
monoarylation of 2,20-bithiophene and its analogues by action of
5-bromopyrimidine. These reactions have been shown to proceed
in a regioselective manner to give the corresponding CeC coupling
products at C-5 of 2,20-bithiophene, although the outcome of these
reactions appears to depend on the nature of the activating agents
and reaction conditions.
Microwave-assisted arylation of 2,20-bithiopene (2a), 2-phenylthiophene (2b), and
[2,20:50,200]terthiophene (2c) with 5-bromopyrimidine (1)a
Entry
Thiophene
Conditionsb
Time
(min)
Reaction
mixtures
GCeMS (%)
Product,
isolated
yield (%)
1
2a
A
60
10
2ad55.3
3ad32.2
4ad0.5
5d1.7
Cy3POd10.3
3ad52
2
2a
B
2ad29.1
3ad45.1
4ad0.7
5d3.3
3ad49
6d1.2
7d0.6
8d0.3
9d0.3
Cy3POd
Impuritiesd0.4
3
2a
C
10
2ad25.5
3ad34.6
4ad0.5
3ad30
5e9.2
6d1.1
2. Results and discussion
7d0.7
8d0.3
9d0.3
Ph3POd27.2
Impuritiesd0.6
It has previously been shown that 2,20-bithiophene reacts
with a number of bromo-substituted (hetero)aromatic compounds,
including 5-bromopyrimidine, in the presence of air-stable
[PdCl(C3H5)dppb] complex as catalyst at 150 ꢀC for 16 h to form
5-(het)aryl-2,20-bithiophenes.2
In order to determine the reactivity of 5-bromopyrimidine (1)
toward bithiophene (2a), 2-phenylthiophene (2b), and [2,20:50,200]
terthiophene (2c), a series of microwave-assisted palladium-cata-
lyzed CeC cross-coupling reactions have been performed under
various reaction conditions (see Scheme 3, Fig. 1, Table 1).
4
5
6
2b
2b
2c
B
D
A
10
10
60
2bd34.3
3bd39.9
4bd0.2
5d6.0
10d0.4
11d0.1
12d0.8
Cy3POd16.7
Impuritiesd1.6
3bd52
3bd44
3cd56
2bd32.0
3bd37.7
4bd0.2
5d6.0
10d0.3
11d0.1
12d0.8
Ph3POd21.5
Impuritiesd1.4
Scheme 3.
Initially we explored the activity of Pd(OAc)2 (taking into ac-
count that it is one of the best catalysts8 for direct arylations), in
combination with two phosphorus ligands, such as triphenyl-
phosphine or tricyclohexylphosphine. Also we have examined
some classical catalysts of organometallic chemistry, such as
Pd(PPh3)4 and Pd(dba)2.
2cd42.5
3cd34.3
4cd1.0
5d4.8
Cy3POd17.4
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E.V. Verbitskiy et al. / Tetrahedron xxx (2013) 1e9
3
Table 1 (continued )
It has been found that 5-bromopyrimidine (1) reacts with
bithiophene (2a) and 2-phenylthiophene (2b) in CF3COOH
(method G) or methanol in the presence of boron trifluoride diethyl
etherate (BF3$Et2O) (methods H and I) to afford the corresponding
Entry
Thiophene
Conditionsb
B
Time
(min)
Reaction
mixtures
GCeMS (%)
Product,
isolated
yield (%)
s
H-adductsd5-bromo-4-[5-(het)aryl-thiophen-2-yl]-3,4-dihydro-
7
2c
2c
2c
2c
10
60
60
60
2cd60.8
3cd31.5
4cd1.3
3cd50
3cd40
3cc
pyrimidin-1-ium salts 15a,b. After removal of the solvent these
salts 15a,b were oxidized with K3Fe(CN)6 in an aqueous solution of
KOH (Scheme 4, Table 2). The reaction mixtures were analyzed by
GCeMS. 5-Bromo-4-(het)aryl substituted pyrimidines 16a,b were
obtained in moderate yields due to side reactions (see Fig. 3).
The structure of 4-[2,20]-bithiophenyl-5-yl-5-bromopyrimidine
(16a) and 5-bromo-4-(5-phenylthiophen-2-yl)-pyrimidine (16b)
has been established unequivocally by X-ray crystallography
(Figs. 4 and 5). Unfortunately, the reaction of pyrimidine 1 with
thiophene 2c under the same conditions gave a mixture of tar
products, which could not been identified by GCeMS.
Cy3POd6.4
8
9
D
E
F
2cd61.3
3cd29.8
4cd0.9
Ph3POd17.4
2cd75.3
3cd4.9
5d4.5
Ph3POd15.3
10
2cd83.2
3cd13.0
5d2.9
3cc
dbad0.9
a
In DMF under argon unless noted otherwise.
Method A: [1]/[2]/[Pd(OAc)2]/[PCy3]/K2CO3¼1:3:0.1:0.2:5 (in mmol); method B:
b
[1]/[2]/[Pd(OAc)2]/[PCy3]/K2CO3¼1:2:0.1:0.2:3 (in mmol); method C: [1]/[2]/
[Pd(OAc)2]/[PPh3]/K2CO3¼1:1:0.1:0.2:3 (in mmol); Method D: [1]/[2]/[Pd(OAc)2]/
[PPh3]/K2CO3¼1:2:0.1:0.2:3 (in mmol); method E: [1]/[2]/[Pd(PPh3)4]/
K2CO3¼1:2:0.1:3 (in mmol); method F: [1]/[2]/[Pd(dba)2]/K2CO3¼1:2:0.1:3 (in
mmol); Cydcyclohexyl; dbaddibenzylideneacetone.
Scheme 4.
c
The product was not isolated.
It has also been shown that the formation of the diaryl derivatives
of 2,20-bithiophene (6e8) and its analogues (10, 11, 13) in these
reactions is possible. In order to minimize the formation of these
by-products, we used an excess of 2-(het)aryl substituted thio-
phenes 2aec. Since 2,20-bithiophene, 2-phenylthiophene, and
[2,20:50,200]terthiophene are relatively stable under the reaction
conditions, an excess of these reagents can easily be recovered after
the reaction.
We have established that the reaction of 5-bromopyrimidine
with 2 equiv of 2-(het)aryl-thiophenes 2aec in DMF under mi-
crowave irradiation at 180 ꢀC in the presence of mixture 10 mol % of
Pd(OAc)2 and 20 mol % PCy3 (catalyst) with 3 equiv K2CO3 (base)
provides the best yields of 5-[2,20]bithiopen-5-yl-pyrimidine (3a),
5-(5-phenylthiophen-2-yl)-pyrimidine (3b), and 5-[2,20;50,200]the-
thiophen-5-yl-pyrimidine (3c) (Table 1, entries 2, 4, and 7, method
B). All of these reaction mixtures have been analyzed by GCeMS
and several by-products were identified. Moreover, the crystal
structure of 5-[2,20]bithiopen-5-yl-pyrimidine (3a) was established
unequivocally by X-ray diffraction study (see Fig. 2).
Table 2
Composition of the reaction mixtures of 5-bromopyrimidine (1) with 2,20-bithio-
pene (2a) and 2-phenylthiophene (2b) and yields of 5-bromo-4-(het)aryl
substituted pyrimidines 16a,ba
Entry
1
Thiophene
Conditionsb
Reaction mixtures
GCeMS (%)
Product, isolated
yield (%)
2a
G
2ad25.1
16ad55.7
17ad19.2
16ad23
16ad64
2
2a
H
2ad9.4
16ad90.1
17ad0.5
3
4
2a
2b
I
16ad95.4
Impuritiesd4.6
16ad87
16bd76
G
2bd6.6
16bd82.0
17bd7.5
Impuritiesd3.9
Another approach for the direct (hetero)arylation of five-
5
2b
2b
H
I
2bd8.4
16bd89.1
17bd1.2
16bd84
16bd56
membered
p-electron-excessive heterocycles by action of 5-
bromopyrimidine is the SHN-reaction catalyzed by a Lewis acid.
Previously, we have used this SHN-protocol for coupling of rather
simple heterocycles, such as thiophene, pyrrole, and indole, with
5-substituted pyrimidines.9,10 In this paper we wish to report ap-
plication of the SHN-methodology to more complex 2-(het)aryl-
thiophenes 2aec.
Impuritiesd1.3
6
2bd5.4
16bd72.2
17bd14.9
Impuritiesd7.5
a
The reaction was carried out in the corresponding solvent on air at room tem-
perature, followed by oxidation with aqueous solution K3Fe(CN)6/KOH¼2:4 (in
mmol); oxidation time¼6 h.
b
Method G: [1]/[2]¼1:1.2 (in mmol) in CF3COOH, reaction time¼24 h; method H:
[1]/[2]/[BF3$Et2O]¼1:1.2:2.4 (in mmol) in MeOH, reaction time¼1 week; method I:
[1]/[2]/[BF3$Et2O]¼1:1.2:2.4 (in mmol) in MeOH, reaction time¼1 month.
It is worth noting that in the reactions of 5-bromopyrimidine (1)
with 2-(het)aryl-thiophenes 2a,b compounds 17a and 17b are
formed as by-products. 4-([2,20]-Bithiophenyl-5-yl)-pyrimidine
Fig. 2. X-ray structure of 3a.
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E.V. Verbitskiy et al. / Tetrahedron xxx (2013) 1e9
Fig. 3. By-products derived from the SHN-reactions of bithiophene and its analogues
with 5-bromopyrimidine, determined by GCeMS analysis.
Fig. 6. X-ray structure of 17b.
Scheme 6.
Fig. 4. X-ray structure of 16a.
Table 3
Composition of the reaction mixtures of 5-[2,20]-bithiophenyl-5-yl-pyrimidine (3)
with thiophene (2d) and 5-bromo-4-thiophen-2-yl-pyrimidine (23) with 2,20-bi-
thiopene (2a) and 2-phenylthiophene (2b)
Entry
Reaction
Conditions
Reaction
mixtures
GCeMS (%)
Retention time
tR for the
productsa (min)
1
3bþ2d
G
3bd3.1
3cd87.2
21ad5.5
22d4.2
3cd32.60
21ad29.54
22d29.62
Fig. 5. X-ray structure of 16b.
2
23þ2a
23þ2b
B
B
23d34.5
(17a) was prepared previously by other way12 and this compound
was identified by GCeMS data.
21ad27.4
24ad17.1
25d1.2
Cy3POd18.9
Impuritiesd0.9
21ad29.55
24ad29.94
25d28.34
In order to prove the structure of by-product 17b, the synthesis
of 17b was carried out by reacting unsubstituted pyrimidine (20)
with 2-phenylthiophene (2b) in CF3COOH under the same reaction
conditions (method G) (Scheme 5). 4-(5-Phenylthiophen-2-yl)-
pyrimidine (17b) was obtained as an off-white crystalline product
in rather good yield (69%). The retention time (in GCeMS) for
the obtained compound 17b proved to coincide with that for the
by-product derived from the reaction of 1 with 2b. The crystal
structure of 4-(5-phenylthiophen-2-yl)pyrimidine (17b) was also
confirmed by the X-ray diffraction analysis (see Fig. 6).
3
23d49.0
21bd10.2
24bd18.3
25d1.3
Cy3POd19.7
Impuritiesd1.5
21ad29.49
24ad29.85
25d28.34
a
Analyzed by GCeMS for reaction mixtures.
Attempts to cause (hetero)arylation of thiophenes 2a,b with
previously12 obtained 5-bromo-4-thiophen-2-yl-pyrimidine (23)
have also been unsuccessful. The reactions proved to be non-
selective and led to complex mixtures including arylated products
21a,b and 24a,b and by-product 25 (Scheme 7, Table 3, entries 2 and
3). Unfortunately, due to close retention times (in GCeMS) for
compounds 21 and 24 we were unable to isolate these products.
Scheme 5.
Unfortunately, all attempts to use a combination of the cross-
coupling and SHN-reactions for pyrimidines bearing the bithiophene
fragment have been unsuccessful. Indeed, 5-[2,20]bithiophenyl-5-yl-
pyrimidine (3b) proved to react with thiophene (2d) in CF3COOH
followed by oxidation with K3Fe(CN)6, affording a mixture with the
major component 3c, instead of 5-[2,20]bithio-phenyl-5-yl-4-
thiophen-2-yl-pyrimidine (21a) (Scheme 6, Table 3, entry 1). It
seems the production of side-products 3c and 22 arises from the
electrophilicaromatic substitution reactionsof thiophene2dwith3b.
3. Electrochemical and optical properties of (het)aryl
substituted pyrimidines
Cyclic voltammetry of each isolated thiophenyl-substituted py-
rimidine was done to determine their redox potentials (see Table 4).
Both the reduction and oxidation processes of compounds 3aec,
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E.V. Verbitskiy et al. / Tetrahedron xxx (2013) 1e9
5
comparison with 3aec probably due to the different positions of
the (het)aryl substituent in these pyrimidines: the C(4) position of
pyrimidine cycle seems to be more favorable. Meanwhile, the
presence of a bromine atom leads to a decrease of quantum yields.
4. Molecular orbital calculations
Oligothiophenes are well known as photoactive compounds due
to their ability to conduct electrons along the highly p-conjugated
system of thiophene rings.12 Our personal interest is focused on
using them as sensitizers of semiconducting surfaces in dyes
Scheme 7.
sensitized solar cells (DSSC), namely in classical ‘titanium
13
dioxideeIꢁ3 =Iꢁ redox couple’ photovoltaic Gratzel cell.
€
Table 4
Molecular orbital calculations, electrochemical and optical properties of 4- and 5-(het)aryl substituted pyrimidines
calcd
abs
exp
calcd
/
lem (nm) fb
em
exp
Compound Epa (V)
Epc (V)
HOMOa (eV) LUMOa (eV)
D
Eabs (eV)
l
/
labs (nm) fb
3
(l molꢁ1 cmꢁ1
)
D
Eemb (eV)
l
F
b
b
b
3a
3b
3c
16a
16b
17b
1.39; 1.65 ꢁ1.97
ꢁ7.29
ꢁ7.46
ꢁ6.94
ꢁ0.94
ꢁ0.84
ꢁ1.14
ꢁ1.38
ꢁ1.31
ꢁ1.19
3.87
4.09
3.45
3.57
3.78
3.86
320.6/346
303.1/330
359.8/386
347.1/378
328.1/358
321.4/348
0.857 23,183
0.864 22,630
1.204 29,698
0.883 26,400
0.898 28,859
0.925 35,259
2.83
3.01
2.45
2.78
2.98
3.25
438.6/420
412.3/394
505.2/472
445.4/450
416.5/421
411.6/409
0.920 0.06
0.975 0.09
1.311 0.11
0.954 0.88
0.997 0.82
0.995 1.00
1.65
1.19
ꢁ2.05
ꢁ1.90
1.49; 1.80 ꢁ1.53; ꢁ1.78 ꢁ7.35
1.69
1.68
ꢁ1.57, ꢁ1.79 ꢁ7.54
ꢁ1.82 ꢁ7.53
DEdvertical excitation energy.
F
dquantum yield of the photoluminescence.
a
Calculated at CAM-B3LYP/6-311þþG**
.
b
Calculated by TDDFT at CAM-B3LYP/6-311þþG** level.
16a,b, and 17b are not reversible, as seen in Figs. S1eS6 (see
Supplementary data). This is expected, since the radical ions, which
can be obtained in these processes, are highly reactive and able to
cross-couple to form their corresponding dimers11 as thin electro-
active films on the platinum electrode. Unfortunately, we had no
large-surface-area mesh electrode and could not obtain sufficient
quantities of dimers for characterization.
UVevis absorption and photoluminescent spectra of 3aec, 16a,b,
and 17b were carried out and the results were summarized in Table 4
and Fig. 7. The absorption maxima of 4- and 5-(het)arylated pyrim-
idine were bathochromically shifted in 3b, 3a, 17b, 16b, 16a, 3c se-
quence. The bathochromic shift suggests an introduction of
a bromine atom (17b compared with 16a and 16b). On the other
hand, the bathochromic shift implies an increased degree of conju-
gation resulting from the terthiophene unit relative to bithiophene
(3c compared with 3a) and conjugation with the nitrogen atom (17b
compared with 3b).
To evaluate their ability to transfer electrons to the conducting
band of TiO2 we have performed time-dependent density func-
tional theory (TDDFT) calculations at CAM-B3LYP/6-311þþG**
level. The choice of level of theory was based on the published
benchmark done for coumarin dyes.14 Authors have shown that the
best estimates for excitation energies in photoactive systems can be
achieved if long-corrected density functionals are used (LC-PBE,
CAM-B3LYP, etc.). Previously published 2,20-bithiophene case study
on the quality of standard sulfur basis sets has shown the impor-
tance of inclusion of polarized and diffusion functions in basis
set and recommended 6-311þþG** basis for oligo- and poly-
thiophenes.15 To improve the accuracy of calculated values,
polarizable continuum model (PCM) was implied, using dichloro-
methane as a solvent. Calculated energy gaps between HOMO/
LUMO levels and parameters of the most intensive electron tran-
sitions for absorption and excitation are listed in Table 4. Addi-
tionally cyclic voltammetry was performed to evaluate HOMO/
LUMO energy levels and to estimate the accuracy of calculations.
Oxidation and reduction potentials are listed in Table 4. Details of
measurement are explained in ‘Supplementary data’ section. In
general computations reproduced experimentally observed trends.
Errors in calculated wavelengths for absorption and emission peaks
were in range 1O30 nm. Oscillator strengths (f) for the strongest
transitions were in good agreement with experimentally observed
intensities for most compounds.
As one can see from this table, the energy gaps associated with
light absorption are relatively higher than is desired for sensitizing
agents for DSSC: w3e4 eV versus w2 eV. Indeed, the system is
photoactively responsible to the change of structure and thus it will
be possible to tune them up to the conducting level of TiO2 (ꢁ4.0 eV)
and Iꢁ3 =Iꢁ redox potential (ꢁ4.8 eV).16 For example, elongating the
structure with extra thiophene ring (from 3a to 3c) shifted the ab-
sorption band closer to NIR area: from 320.6 to 359.8 nm, as calcu-
lated. The effect of structural change was even more drastic for the
luminescent properties of compound 3a. The maximum of excitation
was moved to 505.2 nm and by w67 nm. The elongation of conju-
gation was also reflected in higher intensities of light absorption/
emission. Calculated oscillatory strength of associated transitions
rose from 0.857/0.920 to 1.204/1.311.
Fig. 7. UVevis absorption spectra of 3aec, 16a,b, 17b.
Concerning the photoluminescent spectra of 3aec,16a,b,17b, all
compounds emitted in the violet/blue electromagnetic wavelength
range (see Table 4). Quantum yields were high for 16a,b, 17b in
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E.V. Verbitskiy et al. / Tetrahedron xxx (2013) 1e9
Introduction of an electron-withdrawing substituent to the py-
5. Conclusion
rimidine ring (from 3a to 16a) created a subtle charge separation in
the entire molecule. This resulted in a decreased energy gap, by
0.13 eV, and led to the small shift of wavelengths for absorption and
emission, by around 17 and 7 nm, respectively.
The obtained energies of highest occupied molecular orbitals
are in direct correlation with the oxidation potentials obtained by
cyclic voltammetry. HOMO values were increasing and, conse-
quentially, Epa values were decreasing in the following order:
16b<17b<3b<16a<3a<3c.
Visual representation of boundary molecular orbitals reflecting
orbitals responsible for the absorption suggests that in order to
increase it, stronger donor and acceptor groups should be in-
troduced (Table 5). Otherwise the electron density will stay located
on the same atoms along the whole molecule and no absorp-
tiondenhanced charge separation will be introduced.
Microwave-assisted palladium-catalyzed CeH bond func-
tionalization and SHN-reactions have proved to be versatile tools
for the synthesis of regioisomeric 4- or 5-monothiophenyl-
substituted pyrimidines, some of which showed relatively high
fluorescent efficiency. The X-ray crystallography data for a num-
ber of new monothiophenyl-substituted pyrimidines have been
presented.
In summary, it is legitimate to say that the studied com-
pounds can be potentially used for DSSC application, but addi-
tional modifications are required in order to do so. Future
direction for the syntheses we are planning to follow is to
create pushepull systems with stronger donor and acceptor
groups attached to the opposite sides of the oligothiophene
motif.
Table 5
Schematic representation of the frontier molecular orbitals of the HOMO and LUMO energy levels calculated at the CAM-B3LYP/6-311þþG** level of 3aec, 16a,b,
and 17b
Compound
HOMO
LUMO
3a
3b
3c
16a
16b
17b
Please cite this article in press as: Verbitskiy, E. V.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.04.062

E.V. Verbitskiy et al. / Tetrahedron xxx (2013) 1e9
7
6. Experimental section
6.1. General information
Bu4NClO4 (0.1 M) as a supporting electrolyte by the use of a plati-
num disk working electrode (2 mm diameter), a glassy carbon as a
counter electrode, and a Ag/AgCl electrode as a reference electrode
at a scan rate of 100 mV/s.
All reagents and solvents were obtained from commercial
sources and dried by standard procedures before use. Starting
materials, such as 5-bromopyrimidine (1), bithiophene (2a), 2-
phenylthiophene (2b), [2,20:50,200]terthiophene (2c), and pyrimi-
dine (20) were purchased from SigmaeAldrich and used without
additional purification. 5-Bromo-4-thiophen-2-yl-pyrimidine (23)
was prepared according to the earlier reported method.9 N,N-
Dimethylformamide (DMF) for the microwave-assisted cross-cou-
pling reaction were deoxygenated by bubbling with argon for 1 h.
1H and 13C NMR spectra were recorded on an AVANCE-500 in-
strument using Me4Si as an internal standard. All signals in the 1H
and 13C NMR spectra were assigned on the basis of 2D 1He1H COSY,
1He13C HSQC, and HMBC experiments. Elemental analysis was
carried on an Eurovector EA 3000 automated analyzer. Melting
points were determined on Boetius combined heating stages and
were not corrected.
The GCeMS analysis of all samples was carried out using an
Agilent GC 7890A MS 5975C Inert XL EI/CI GCeMS spectrometer
with a quadrupole mass-spectrometric detector with electron
ionization (70 eV) and scan over the total ionic current in the
range m/z 20O1000 and a quartz capillary column HP-5MS
(30 mꢂ0.25 mm, film thickness 0.25 mm). Helium served as a car-
rier gas, the split ratio of the flow was 1:50, and the consumption
through the column was 1.0 mL minꢁ1; the initial temperature of
the columꢁn1 was 40 ꢀC (storage 3 min), programming rate was
10 ꢀC min to 290 ꢀC (storage 20 min), the temperature of the
evaporator was 250 ꢀC, the temperature of the source was 230 ꢀC,
the temperature of the quadrupole was 150 ꢀC, and the tempera-
ture of the transition chamber was 280 ꢀC. Solutions of the samples
with a concentration of 3e4 mg mLꢁ1 were prepared in THF.
Samples of 1 mL of the obtained solutions were analyzed. Column
chromatography was carried out using Lancaster silica gel
0.040e0.063 mm (230e400 mesh), eluting with ethyl acetate/
hexane, 1:2. The progress of reactions and the purity of compounds
were checked by TLC on Sorbfil plates (Russia), in which the spots
UVevis spectra were recorded for a 1ꢂ10ꢁ5 M dichloromethane
solution with Shimadzu UV-2401PC spectrophotometer. Photo-
luminescent spectra were recorded for a 1ꢂ10ꢁ6 M dichloromethane
solution on a Varian Cary Eclipse fluorescence spectrophotometer.
Quantum yields (
F) were estimated with 1N H2SO4 solution of qui-
nine bisulfate (
F
¼0.55) as a reference.17
IR spectra of samples (solid powders) were recorded on
a Spectrum One Fourier transform IR spectrometer (Perkin Elmer)
equipped with a diffuse reflectance attachment (DRA) in the fre-
quency range 4000O400 cmꢁ1. Spectrum processing and band
intensity determination were carried out using the special software
supplied with the spectrometer.
6.3. Molecular orbital calculation
Quantum chemical calculations were performed by employing
the Gaussian 09 program.18 Compounds were fully optimized at
CAM-B3LYP/6-311þþG** level. The minima were confirmed by
frequency calculations. Then compounds were fully reoptimized at
the same level of theory, but within PCM framework. TDDFT was
done at CAM-B3LYP/6-311þþG** level. Solvent effects were simu-
lated by polarizable continuum model including SCRF¼(Sol-
vent¼Dichloromethane) keyword in the input file.
6.4. General procedure for the microwave-assisted palla-
dium-catalyzed CeC coupling reactions
5-Bromopyrimidine (1) (79 mg, 0.5 mmol), the corresponding 2-
(het)aryl substituted thiophene (2a, 2b or 2c) (1.0 mmol), Pd(OAc)2
(11 mg, 10 mol %), PCy3 (28 mg, 0.1 mmol), and K2CO3 (207 mg,
1.5 mmol) were dissolved in DMF (5 mL). The resulting reaction
mixture was deaerated by bubbling argon and irradiated in a mi-
crowave apparatus at 180 ꢀC (250 W) for 10 min. After that the
solvent was distilled off under reduced pressure, and the residue
was purified by flash column chromatography (hexane/ethyl
acetate, 1:2) to afford the desired product (3a, 3b or 3c). Yields
of reaction products are based on the molar amount of
5-bromopyrimidine used. The regioisomeric products 4a, 4b, and
4c were not isolated.
were visualized with UV light (l 254 or 365 nm).
Microwave experiments were carried out in a Discover unim-
odal microwave system (CEM, USA) with a working frequency of
2.45 GHz and the power of microwave radiation ranged from 0 to
300 W. The reactions were carried out in a 10 mL reaction tube with
the hermetic Teflon cork. The temperature of the reaction was
monitored using an inserted IR sensor by the external surface of the
reaction vessel.
6.4.1. 5-[2,20]Bithiophenyl-5-yl-pyrimidine (3a).2
3'
3"
4'
4"
2"
6
X-ray intensity data were collected with an Xcalibur S diffrac-
2'
5
1
5'
5"
S
1'
S
1"
ꢀ
N
tometer on standard procedure (Mo K
a
(l¼0.71069 A) radiation,
T¼295(2) K
u
-scanning with step 1ꢀ). Crystal data and data col-
4
2
N
3
lection parameters are summarized in Table 6 (see Supplementary
data). Unit cell parameters were refined using all collected spots
after the integration process. The details of the refinement and the
final R indices are presented in Table 6. Deposition numbers CCDC
921369 for 3a, CCDC 921368 for 16a, CCDC 921367 for 16b, and
CCDC 921370 for 17 b contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
the Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
3a
Yield (see Table 1, entry 2), yellow powder; mp 97e99 ꢀC (lit.2 mp
not available). dH (500 MHz, CDCl3) 7.05 (dd, 1H, H-400, J¼5.0, 3.7 Hz),
7.21 (d, 1H, H-30, J¼3.8 Hz), 7.25 (d, 1H, H-300, J¼3.7 Hz), 7.28 (d, 1H,
H-500, J¼5.0 Hz), 7.33 (d, 1H, H-40, J¼3.8 Hz), 8.94 (s, 2H, H-4,6), 9.11
(s, 1H, H-2); dC (126 MHz, CDCl3) 124.52 (C-300), 124.82 (C-30), 125.32
(C-500), 125.93 (C-40), 128.02 (C-400), 128.41 (C-5), 134.54 (C-50),136.38
(C-200), 139.43 (C-20),153.03 (C-4,6), 157.14 (C-2); GC tR 24.47 min; MS
m/z (rel intensity) 244 (Mþ, 100). Anal. Calcd for C12H8N2S2 (244.34):
6.2. Redox and optical properties
C, 58.99; H, 3.30; N, 11.46. Found: C, 59.02; H, 3.08; N, 11.39. n (DRA)
Cyclic voltammetry (CV) was performed with a potentiostat/
galvanostat Autolab PGSTAT128N at ambient temperature. The
measurements were performed in anhydrous and deaerated
dichloromethane solution containing the compound (2 mM) and
405, 458, 495, 550, 577, 591, 631, 700, 716, 735, 744, 805, 838, 886,
906, 956, 977, 1045, 1062, 1083, 1121, 1185, 1205, 1226, 1270, 1320,
1351, 1409, 1421, 1462, 1509, 1545, 1578, 1614, 1770, 1796, 1878, 1951,
2351, 3017, 3051, 3071, 3086, 3808, 3911.
Please cite this article in press as: Verbitskiy, E. V.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.04.062

8
E.V. Verbitskiy et al. / Tetrahedron xxx (2013) 1e9
6.4.2. 5-(5-Phenylthiophen-2-yl)-pyrimidine (3b).
time (see Table 2) and evaporated. A solution of KOH (112 mg,
2.0 mmol, 4 equiv) and K3Fe(CN)6 (329 mg, 1.0 mmol, 2 equiv) in
water (5 mL) was added to residue. The resulting mixture was stirred
for the appropriate time (see Table 2) at room temperature, the
precipitate or semisolid formed was filtered off, washed with H2O,
and air-dried. The residue was purified by flash column chromatog-
raphy (hexane/ethyl acetate, 1:2) to afford the desired SHN-products.
3"
4'
2"
3'
1"
6
4"
5'
5
1
2'
S
1'
N
6"
5"
2
4
N
3
6.5.1. 4-[2,20]Bithiophenyl-5-yl-5-bromopyrimidine (16a).
3b
6
Yield (see Table 1, entry 4), pale yellow powder; mp 130e131 ꢀC.
dH (500 MHz, CDCl3) 7.34 (tt, 1H, Hp, J¼7.3, 1.1 Hz), 7.36 (d, 1H, H-40,
J¼3.8 Hz), 7.41 (d, 1H, H-30, J¼3.8 Hz), 7.42 (dd, 2H, Hm, J¼8.1,
7.3 Hz), 7.65 (dd, 2H, Ho, J¼8.3, 1.1 Hz), 8.97 (s, 2H, H-4,6), 9.12 (s,
1H, H-2); dC (126 MHz, CDCl3) 124.38 (C-40), 125.88 (Co), 126.19 (C-
30), 128.27 (Cp), 128.65 (C-5), 129.08 (Cm), 133.49 (Ci), 135.13 (C-20),
146.49 (C-50), 153.11 (C-4,6), 157.13 (C-2); GC tR 24.52 min; MS m/z
(rel intensity) 238 (Mþ, 100); Anal. Calcd for C14H10N2S (238.31): C,
Br
1
N
5
1"
5"
S
1'
5'
2
S
4
N
3
4"
2"
2'
3"
4'
3'
16a
Yield (see Table 2, entries 1e3), yellow crystal powder; mp
138e140 ꢀC. dH (500 MHz, CDCl3) 7.05 (dd, 1H, H-400, J¼5.1, 3.6 Hz),
7.22 (d, 1H, H-30, J¼4.1 Hz), 7.30 (d, 1H, H-500, J¼5.1, 1.1 Hz), 7.33 (dd,
1H, H-300, J¼3.6,1.1 Hz), 8.33 (d, 1H, H-40, J¼4.1 Hz), 8.80 (s, 1H, H-6),
8.98 (s, 1H, H-2); dC (126 MHz, CDCl3) 115.00 (C-5), 124.51 (C-30),
125.17 (C-300), 126.00 (C-500), 128.15 (C-400), 132.96 (C-40), 136.49
(C-200), 138.90 (C-50), 143.55 (C-20), 155.72 (C-4), 156.13 (C-2), 160.69
(C-6); GC tR 26.93 min; MS m/z (rel intensity) 322 (Mþ, 100) for 79Br,
324 (Mþ, 100) for 81Br; Anal. Calcd for C12H7BrN2S2 (323.23): C,
70.56; H, 4.23; N, 11.75. Found: C, 70.34; H, 4.04; N, 11.64.
n (DRA)
425, 417, 462, 494, 567, 590, 633, 690, 717, 735, 761, 808, 885, 902,
940, 968, 982, 999, 1028, 1045, 1076, 1100, 1163, 1184, 1211, 1237,
1287, 1308, 1338, 1354, 1413, 1427, 1447, 1461, 1498, 1537, 1551, 1574,
1596, 1678, 1769, 1878, 1905, 1956, 2368, 3030, 3078, 3822.
6.4.3. 5-[2,20:50,200]Terthiophenyl-5-yl-pyrimidine (3c).
44.59; H, 2.18; N, 8.67. Found: C, 44.75; H, 2.26; N, 8.65. n (DRA) 418,
3'
3"
4'
4"
457, 475, 512, 586, 598, 611, 623, 639, 655, 675, 711, 733, 742, 759,
808, 835, 889, 923, 980, 1028, 1048, 1073, 1140, 1161, 1183, 1201,
1219, 1231, 1246, 1270, 1279, 1322, 1345, 1384, 1425, 1447, 1514,
1550, 1634, 1740, 1776, 1827, 1903, 1963, 2143, 2321, 2426, 2494,
2716, 2889, 2960, 3078, 3102, 3810, 3913.
2"
6
5"
3"'
2'
5
1
S
1'
5'
S
1"
N
2"'
4"'
2
4
S
1"'
N
3
5"'
3c
6.5.2. 5-Bromo-4-(5-phenyl-thiophen-2-yl)-pyrimidine (16b).
Yield (see Table 1, entry 7), dark yellow powder; mp 170e172 ꢀC.
dH (500 MHz, CDCl3) 7.04 (dd, 1H, H-4000, J¼5.1, 3.6 Hz), 7.12 (d, 1H, H-
400, J¼3.8 Hz), 7.16 (d, 1H, H-300, J¼3.8 Hz), 7.20 (dd, 1H, H-3000, J¼3.6,
1.1 Hz), 7.21 (d, 1H, H-30, J¼3.8 Hz), 7.25 (dd, 1H, H-5000, J¼5.1, 1.1 Hz),
7.35 (d, 1H, H-40, J¼3.8 Hz), 8.94 (s, 2H, H-4,6), 9.12 (s, 1H, H-2); dC
(126 MHz, CDCl3) 124.05 (C-3000), 124.45 (C-400), 124.72 (C-30), 124.90
(C-5000), 125.13 (C-300), 126.05 (C-40), 127.97 (C-4000), 128.40 (C-5),
134.57 (C-50), 135.02 (C-500), 136.75 (C-2000), 137.29 (C-200), 139.15 (C-
20), 153.05 (C-4,6), 157.17 (C-2); GC tR 32.55 min; MS m/z (rel in-
tensity) 326 (Mþ, 100). Anal. Calcd for C16H10N2S3 (326.46): C, 59.87;
6
Br
5
1
N
3"
2"
1'
4"
2'
2
S
4
N
3
1"
5'
5"
6"
3'
4'
16b
Yield (see Table 2, entries 4e6), yellow crystal powder; mp
141e142 ꢀC. dH (500 MHz, CDCl3) 7.34 (t,1H, Hp, J¼7.3, Hz), 7.37 (d,1H,
H-40, J¼4.1 Hz), 7.41 (t, 2H, Hm, J¼7.6 Hz), 7.68 (dd, 2H, Ho, J¼8.3,
1.1 Hz), 8.39(d,1H, H-30, J¼4.1 Hz), 8.81(s,1H, H-6), 9.00 (s,1H, H-2);dC
(126 MHz, CDCl3) 115.10 (C-5), 124.20 (C-40), 126.10 (Co), 128.66 (Cp),
129.03 (Cm), 133.14 (C-30), 133.43 (Ci), 139.53 (C-20), 150.43 (C-50),
155.94 (C-4), 156.17 (C-2), 160.72 (C-6); GC tR 26.94 min; MS m/z (rel
intensity) 316 (Mþ,100) for 79Br, 318 (Mþ,100) for 81Br. Anal. Calcd for
C14H9BrN2S(317.21):C,53.01;H, 2.86;N, 8.83.Found:C, 53.03;H, 2.70;
H, 3.09; N, 8.58. Found: C, 59.64; H, 2.90; N, 8.31.
n (DRA) 404, 444,
470, 482, 524, 554, 574, 588, 607, 631, 707, 719, 741, 796, 834, 866,
876, 906, 956, 982,1047,1067,1118,1180,1201,1213,1223,1232,1242,
1272, 1306, 1338, 1355, 1409, 1425, 1451, 1468, 1551, 1603, 1655, 1755,
1790, 1884, 1946, 2342, 2853, 2924, 3030, 3063, 3077, 3115, 3802.
N, 8.70. n (DRA) 412, 453, 478, 514, 582, 598, 620, 663, 688, 699, 758,
6.5. General procedure for the synthesis of SHN-productsd5-
bromo-4-(het)aryl-pyrimidines
809, 844, 913, 922, 951, 985, 998, 1025, 1072, 1086, 1098, 1139, 1156,
1183, 1248, 1288, 1308, 1333, 1350, 1384, 1427, 1440, 1453, 1509, 1549,
1594, 1619, 1748, 1784, 1879, 1905, 1969, 2321, 2995, 3055, 3092, 3115.
Pathway A: 2-(Het)aryl-thiophene (2a, 2b or 2c) (1.2 mmol) was
added to a solution of 5-bromopyrimidine (1) (159 mg,1.0 mmol) in
CF3COOH (5 mL). The reaction mixture was stirred at room tem-
perature for 24 h and evaporated. The solution of KOH (224 mg,
4.0 mmol, 4 equiv) and K3Fe(CN)6 (658 mg, 2.0 mmol, 2 equiv) in
5 mL water was added to residue. The resulting mixture was stirred
for appropriate time (see Table 2) at room temperature, the pre-
cipitate or semisolid formed was filtered off, washed with H2O, and
air-dried. The residue was purified by flash column chromatogra-
phy (hexane/ethyl acetate, 1:2) to afford the desired SHN-product.
Pathway B: To a stirred mixture of 5-bromopyrimidine (1) (79 mg,
0.5 mmol) and corresponding 2-(het)aryl-thiophene (2a, 2b or 2c)
(0.6 mmol) in MeOH (3 mL) was added BF3$Et2O (1.1 mmol). The
reaction mixture was stirred at room temperature for appropriate
6.6. 4-(5-Phenylthiophen-2-yl)-pyrimidine (17b)
6
1
5
N
3"
2"
1'
4"
2'
2
S
4
N
3
1"
5'
5"
6"
3'
4'
17b
2-Phenylthiophene (2c) (288 mg, 1.8 mmol) was added to
a solution of pyrimidine (20) (120 mg, 1.5 mmol) in CF3COOH
(3 mL). The reaction mixture was stirred at room temperature for
Please cite this article in press as: Verbitskiy, E. V.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.04.062

E.V. Verbitskiy et al. / Tetrahedron xxx (2013) 1e9
9
583; (c) Wong, K.-T.; Hung, T.-S.; Lin, Y.; Wu, C.-C.; Lee, G.-H.; Peng, S.-M.; Chou,
C. H.; Su, Y. O. Org. Lett. 2002, 4, 513; (d) Kojima, T.; Nishida, J.; Tokito, S.; Ya-
mashita, Y. Chem. Lett. 2009, 38, 428; (e) Bolduc, A.; Dufresne, S.; Hanan, G. S.;
Skene, W. G. Can. J. Chem. 2010, 88, 236.
2. Larbi, K. S.; Djebbar, S.; Doucet, H. Eur. J. Inorg. Chem. 2011, 3493 and references
cited therein.
3. Li, J. J.; Gribble, G. W. Palladium in Heterocyclic Chemistry; Pergamon: Am-
sterdam, The Netherlands, 2000.
4. Yu, J.-Q.; Shi, Z. CeH Activation in Topics in Current Chemistry; Springer: Berlin,
Heidelberg, Germany, 2010; Vol. 292
24 h and evaporated. The solution of KOH (337 mg, 6.0 mmol,
4 equiv) and K3Fe(CN)6 (988 mg, 3.0 mmol, 2 equiv) in water
(10 mL) was added to residue. The resulting mixture was stirred
for 6 h at room temperature; the precipitate formed was filtered
off, washed with H2O, and air-dried. The residue was purified by
flash column chromatography (hexane/ethyl acetate, 1:1) to afford
the desired 4-(5-phenylthiophen-2-yl)-pyrimidine (17b). Yield
(246 mg, 69%), off-white crystalline powder; mp 145e147 ꢀC. dH
(500 MHz, CDCl3) 7.34 (tt, 1H, Hp, J¼7.3, 1.1 Hz), 7.35 (d, 1H, H-40,
J¼3.9 Hz), 7.41 (dd, 2H, Hm, J¼8.1, 7.3 Hz), 7.53 (dd, 1H, H-5, J¼5.3,
1.4 Hz), 7.66 (dd, 2H, Ho, J¼8.1, 1.1 Hz), 7.72 (d, 1H, H-30 J¼3.9 Hz),
8.65 (d, 1H, H-6, J¼5.3 Hz), 9.13 (d, 1H, H-2, J¼1.4 Hz); dC
(126 MHz, CDCl3) 114.81 (C-5), 124.31 (C-40), 125.92 (Co), 128.47
(Cp), 128.62 (C-30), 129.02 (Cm), 133.56 (Ci), 140.58 (C-20), 149.23
(C-50), 156.98 (C-6), 158.62 (C-4), 159.02 (C-2); GC tR 24.88 min;
MS m/z (rel intensity) 238 (Mþ, 100). Anal. Calcd for C14H10N2S
(238.31): C, 70.56; H, 4.23; N, 11.75. Found: C, 70.54; H, 4.15; N,
5. For recent examples of direct arylations of thiophenes: (a) Battace, A.; Lem-
hadri, M.; Zair, T.; Doucet, H.; Santelli, M. Adv. Synth. Catal. 2007, 349, 2507; (b)
ꢁ
Dong, J. J.; Doucet, H. Eur. J. Org. Chem. 2010, 611; (c) Roger, J.; Pozgan, F.;
Doucet, H. Adv. Synth. Catal. 2010, 352, 696; (d) Laidaoui, N.; Roger, J.; Miloudi,
A.; El Abed, D.; Doucet, H. Eur. J. Org. Chem. 2011, 4373; (e) Larbi, K. S.; Fu, H. Y.;
Laidaoui, N.; Beydoun, K.; Miloudi, A.; El Abed, D.; Djabbar, S.; Doucet, H.
ChemCatChem 2012, 4, 815; (f) Bensaid, S.; Doucet, H. ChemSusChem 2012, 5,
1559; (g) Bensaid, S.; Doucet, H. Tetrahedron 2012, 68, 7655 and references cited
therein.
6. For recent examples for direct arylations of bithiophenes: (a) Yokooji, A.;
Satoh, T.; Miura, M.; Nomura, M. Tetrahedron 2004, 60, 6757; (b) Kobayashi,
K.; Sugie, A.; Takahsi, M.; Masui, K.; Mori, A. Org. Lett. 2005, 7, 5083; (c)
Amaladass, P.; Arul Clement, J.; Mohanakrishnan, A. K. Tetrahedron 2007, 63,
10363; (d) Abdo, N. I.; El-Shehawy, A. A.; El-Barbary, A. A.; Lee, J.-S. Eur. J.
Org. Chem. 2012, 5540.
7. For selected reviews on nucleophilic aromatic substitution of hydrogen: (a)
Chupakhin, O. N.; Charushin, V. N.; van der Plas, H. C. Nucleophilic Aromatic
Substitution of Hydrogen; Academic: San Diego, NY, 1994; (b) Charushin, V. N.;
Chupakhin, O. N. Pure Appl. Chem. 2004, 76, 1621; (c) Charushin, V. N.; Chu-
pakhin, O. N. Mendeleev Commun. 2007, 17, 249; (d) Makosza, M.; Wojcie-
chowski, K. Chem. Rev. 2004, 104, 2631; (e) Makosza, M. Chem. Soc. Rev. 2010, 39,
2855.
11.68. n (DRA) 450, 510, 575, 622, 661, 689, 727, 756, 773, 808, 847,
909, 949, 983, 995, 1031, 1069, 1088, 1101, 1168, 1213, 1244, 1287,
1307, 1332, 1390, 1447, 1466, 1501, 1532, 1574, 1594, 1671, 1696,
1746, 1802, 1875, 1892, 1948, 1967, 2032, 2236, 2555, 2751, 2911,
3021, 3076, 3823.
Acknowledgements
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This work was supported by the Ural Branch of the Russian
ꢀ
Academy of Sciences (Grants N 12-P-3-1014, 12-P-3-1030, 12-T-3-
1025, and 12-T-3-1031), the State Program for Supporting of
Leading Scientific Schools of the Russian Federation (grant
NSh 5505.2012.3) and the Russian Foundation for Basic Research
(research projects No. 12-03-31574-mol_a, 13-03-96049-r_ural_a,
and 13-03-90606-Arm_a), the Ministry of Education and Science of
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Mori, H.; Takimiya, K.; Harima, Y. Bull. Chem. Soc. Jpn. 2011, 84, 459.
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Russian Federation (projects N 8430 and 8634). J.O.S. thanks
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Compute CanadadCalcul Canada and West Grid for computing
recourses. J.O.S. also thanks Prof. Arvi Rauk (University of Calgary,
Canada) for his personal assistance and helpful advice.
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Supplementary data
18. The molecular orbital calculation was carried out using the Frisch, M. J.; Trucks,
G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.;
Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.;
Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda,
Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.;
Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi,
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Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakr-
zewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
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Revision C.01; Gaussian: Wallingford, CT, 2009.
Crystallographic and cyclic voltammetry data summary, copies
of the photoluminescent, IR, 1H and 13C NMR spectra of the new
compounds. Supplementary data associated with this article can
be found in the online version, at http://dx.doi.org/10.1016/
j.tet.2013.04.062. These data include MOL files and InChiKeys of the
most important compounds described in this article.
References and notes
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Kushida, T.; Saito, N.; Kuwajima, I.; Kubota, K.; Yamamoto, T. Chem. Lett. 1992,
Please cite this article in press as: Verbitskiy, E. V.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.04.062