Dithienoquinazolines - A convenient synthesis by the oxidative photocyclization of 4,5-dithienyl-substituted pyrimidines and their photophysical properties

Article abstract of DOI:10.1002/ejoc.201403212

A convenient synthetic route to novel thienoacene systems bearing a fused pyrimidine ring has been advanced. The commercially available 5-bromopyrimidine was used as the starting material to obtain various dithienoquinazoline systems through nucleophilic aromatic substitution of hydrogen (the SN H reaction), Suzuki cross-coupling, and oxidative photocyclization. The redox and optical properties of some of the new compounds have been investigated. The data obtained show the potential of dithienoquinazoline systems in organic electronic applications.

Full text of DOI:10.1002/ejoc.201403212

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DOI: 10.1002/ejoc.201403212
Dithienoquinazolines – A Convenient Synthesis by the Oxidative
Photocyclization of 4,5-Dithienyl-Substituted Pyrimidines and Their
Photophysical Properties
Egor V. Verbitskiy,*[a,b] Pavel A. Slepukhin,[a,b] Marina S. Valova,[a]
Ekaterina M. Cheprakova,[a,b] Akesandr V. Schepochkin,[a] Gennady L. Rusinov,[a,b] and
Valery N. Charushin[a,b]
Keywords: Photocyclization / Nucleophilic substitution / UV/Vis spectroscopy / Luminescence / Nitrogen heterocycles /
Fused ring systems
A convenient synthetic route to novel thienoacene systems
bearing a fused pyrimidine ring has been advanced. The
commercially available 5-bromopyrimidine was used as the
starting material to obtain various dithienoquinazoline sys-
tems through nucleophilic aromatic substitution of hydrogen
(the SNH reaction), Suzuki cross-coupling, and oxidative pho-
tocyclization. The redox and optical properties of some of the
new compounds have been investigated. The data obtained
show the potential of dithienoquinazoline systems in organic
electronic applications.
type characteristics, including polymeric materials.[6,7]
Meanwhile, data concerning the effects of nitrogen incorpo-
ration into thienoacene systems are scarce in the literature.
Only a few examples have been reported that deal with
angular benzodithiophenes bearing a fused pyrazine ring,
for example, dithieno[3,2-f:2Ј,3Ј-h]quinoxalines (QDTs) and
quinoxalino[6,5-b:7,8-bЈ]bis([1]benzothiophene)s (DTNQs;
see Figure 1), to modulate effectively HOMO and LUMO
energies.[2,8] In addition, QDT derivatives have been used as
“weak donor” moieties for the fabrication of bulk hetero-
junction (BHJ) polymer solar cells,[8] whereas in the case of
DTNQ, a p-type field effect was observed.[2]
Introduction
Fused polycyclic aromatic compounds are considered to
be at the forefront of research into organic semiconductors
(OSC) due to their unique characteristics, including high
charge mobility. Indeed, organic semiconductors have
undergone significant developments during the past two
decades due to their potential applications in future-genera-
tion ultrathin, large-area and/or flexible devices, including
organic field-effect transistors (OFETs), organic light-emit-
ting diodes (OLEDs), and organic photovoltaics (OPVs).
Compounds of the thienoacene family[1–3] have emerged as
high-performance OSCs due to their high charge mobility
as compared with acenes such as pentacene[4] and rub-
rene.[5] A great number of thienoacenes with diverse molec-
ular structures have been synthesized and elucidated as
promising organic semiconductors. In particular, acenedi-
thiophenes, in which two thiophene rings are fused to a
benzene ring, for example, linear benzodithiophenes (BDT-
1 and -2) and their angular isomers (BDT-3–5; Figure 1),
proved to have many advantages over other classes of com-
pounds owing to their ease of functionalization at the α
positions of the thiophene subunits, thus providing access
to a wide range of organic semiconductors with p- to n-
[a] I. Postovsky Institute of Organic Synthesis, Ural Branch,
Russian Academy of Sciences,
S. Kovalevskoy Str. 20, Ekaterinburg 620990, Russia
E-mail: Verbitsky@ios.uran.ru
www.ios.uran.ru
[b] Ural Federal University named after the First President of
Russia, B. N. Eltsin,
Mira Str. 19, Ekaterinburg 620002, Russia
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201403212.
Figure 1. Chemical structures of benzodithiophenes (BDTs) and
their derivatives containing the fused pyrazine ring.
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In this paper we wish to report the synthesis and charac- Table 1. Yields of 4,5-dithiophenylpyrimidines 3a–d.
terization of four novel thienoacene systems (see Figure 2)
that incorporate
a fused pyrimidine ring: dithieno-
[2,3-f:3Ј,2Ј-h]quinazoline (DTQ-1), dithieno[3,2-f:3Ј,2Ј-h]-
quinazoline (DTQ-2), [1]benzothieno[2,3-f]thieno[3,2-h]-
quinazoline (BTTQ-1), and [1]benzothieno[3,2-f]thieno-
[3,2-h]quinazoline (BTTQ-2).
Figure 2. Chemical structures of dithienoquinazolines (DTQs) and
[1]benzothienothienoquinazolines (BTTQs).
Results and Discussion
Synthesis
It has previously been shown that 5-bromo-2-(hetero)-
arylpyrimidines react with a variety of (hetero)aryl-substi-
tuted boronic acids under Pd-catalyzed microwave-assisted
conditions.[9,10] 4,5-Dithienyl-substituted pyrimidines 3a–d,
employed as the key synthetic intermediates in the prepara-
tion of dithienoquinazoline systems (DTQ and BTTQ),
were generated by using a sequence that is initiated by the
conversion of readily available[9] 5-bromo-4-(thien-2-yl)pyr-
imidine (2) into 5-(hetero)aryl-4-(thien-2-yl)pyrimidines 3a–
d in dioxane/H2O (3:4), which is similar to the above-men-
tioned microwave-assisted Suzuki cross-coupling reaction
(Scheme 1, Table 1). The structures of the 4,5-dithienyl-
pyrimidines 3a–d were established unequivocally by X-ray
crystallography analysis, performed for compound 3b (Fig-
ure 3).
Figure 3. Mercury[11] representation of the X-ray crystal structure
of 3b with thermal ellipsoids drawn at the 50% probability level.
Compounds 3a–d were subjected to oxidative photocycli-
zation by the action of iodine in toluene in the presence of
an excess of propylene oxide as the scavenger of hydrogen
iodide. The reaction mixtures were irradiated at room tem-
perature with a UV lamp to yield the dithienoquinazolines
DTQ and BTTQ in moderate yields (Scheme 2, Table 2).
Scheme 2.
Note that the yields of the [1]benzothienothienoquin- solubility in toluene of both the starting pyrimidines 3b,d
azolines (BTTQs) were lower than those of the dithieno- and the products 4b,d, as well as radical-mediated side-reac-
quinazolines (DTQs). This can be explained by the poor tions.[12]
Scheme 1.
2
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Dithienoquinazolines and Their Photophysical Properties
Table 2. Yields of dithienoquinazolines (DTQs) and [1]benzo-
thienothienoquinazolines (BTTQs).
Table 3. Composition of the reaction mixtures obtained from di-
thienoquinazolines (DTQs) and N-bromosuccinimide.
Entry
Dithieno- Product
quinazoline
Yield [%]
Reaction mixture Isolated yield
GC–MS
1
DTQ-1
DTQ-2
6-Br-DTQ-1
41.7
9.7
8.8
16.4
23.3
24.1
75.9
not isolated
8-Br-DTQ-1
9-Br-DTQ-1
6,9-diBr-DTQ-1
N,9-diBr-DTQ-1
DTQ-2
2
9-Br-DTQ-2
61
To prove the structure of the by-product 9-Br-DTQ-1,
the targeted synthesis of 9-bromodithieno[2,3-f:3Ј,2Ј-h]-
quinazoline (9-Br-DTQ-1) was carried out by photocycliza-
tion of 4-(5-bromothien-2-yl)-5-(thien-2-yl)pyrimidine[9]
(3e; Scheme 4). Moreover, the structure of 9-Br-DTQ-1 was
established unequivocally by an X-ray diffraction study (see
Figure 4).
To explore the reactivity of the novel dithienoquinazoline
systems and their further functionalization, we investigated
the reactions of dithienoquinazolines (DTQs) with an ex-
cess (5 equiv.) of N-bromosuccinimide (NBS) at room tem-
perature for 24 h in DMF. In the case of dithieno[2,3-
f:3Ј,2Ј-h]quinazoline (DTQ-1), the reaction resulted in a
mixture of mono- and dibromo-substituted compounds
(Scheme 3) that could not be separated. Under similar con-
ditions, only 9-bromodithieno[3,2-f:3Ј,2Ј-h]quinazoline (9-
Br-DTQ-2) was obtained in 61% yield from the reaction of
dithieno[3,2-f:3Ј,2Ј-h]quinazoline (DTQ-2) (Scheme 3). All
the reaction mixtures were analyzed by GC–MS and several
by-products were identified (Table 3).
Scheme 4.
Scheme 3.
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Scheme 5.
Figure 5. Mercury[11] representation of the X-ray crystal structure
of 3g with thermal ellipsoids drawn at the 50% probability level.
Figure 4. Mercury[11] representation of the X-ray crystal structure
of 9-Br-DTQ-1 with thermal ellipsoids drawn at the 50% prob-
ability level.
Unfortunately, the bromination of novel dithienoquin-
azolines has proved to be a nonselective process leading to
rather complicated mixtures of products, whereas mono-
and dibromo-substituted dithienoquinazolines can be ob-
tained simply by direct photocyclization of the correspond-
ing bromo-substituted 4,5-dithienylpyrimidines.
The structure of 9-Br-DTQ-2 was also determined une-
quivocally by the targeted synthesis of 9-Br-DTQ-2 by the
SNH reaction[9,10] of 5-(thien-3-yl)pyrimidine (4) followed by
oxidative photocyclization of the intermediate 4-(5-
bromothien-2-yl)-5-(thien-3-yl)pyrimidine (3f; Scheme 5).
The retention time (GC–MS) for compound 9-Br-DTQ-2
proved to coincide with that for the product derived from
the reaction of DTQ-2 with NBS.
Finally, we prepared 6,9-dibromodithieno[2,3-f:3Ј,2Ј-h]-
quinazoline (6,9-diBr-DTQ-1) in 55% yield by the bromina-
tion of 3a and subsequent UV irradiation of the resulting
4,5-bis(5-bromothien-2-yl)pyrimidine (3g) under similar
conditions (Scheme 6).
Photophysical and Electrochemical Properties
Cyclic voltammetry was performed on the four basic di-
thienoquinazolines (DTQs) and [1]benzothienothienoquin-
azolines (BTTQs) to determine their redox potentials. Un-
fortunately, in the accessible range[13] of potentials [0–2.5 V,
analogously[2] to quinoxalino[6,5-b:7,8-bЈ]bis[1]benzothio-
phene (DTNQ) in THF], no oxidation or reduction peaks
were determined for any of the compounds.
The UV/Vis absorption and photoluminescent spectra of
DTQ-1, DTQ-2, BTTQ-1, and BTTQ-2 were recorded, and
the results are summarized in Table 4 and Figures S1–S4
in the Supporting Information. All four compounds show
several maxima in the UV spectra resulting from vibronic
coupling of the π–π* transition. This behavior is common
for rigid thienoacenes, which have limited conformational
disorder as a result of their fused structures.[14] The optical
band gaps (Egopt) of DTQ-1, DTQ-2, BTTQ-1, and BTTQ-
2 have been estimated from the long-wavelength absorption
edge and are summarized in Table 4. Although the electro-
chemical studies have not enabled the HOMO and LUMO
levels to be determined, the optical band gap values of
3.16–3.36 eV for DTQ and BTTQ appear to be typical of
Scheme 6.
The structure of the intermediate 4,5-bis(5-bromothien- similar semiconducting thienoacenes (e.g., the optical band
2-yl)pyrimidine (3g) was established unequivocally by X-ray gap is 3.29 eV for DTNQ).[2] In addition, it has been found
diffraction (see Figure 5).
that the optical band gaps (Egopt) and quantum yields of
4
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Dithienoquinazolines and Their Photophysical Properties
Table 4. Photophysical properties of dithienoquinazolines (DTQs) and [1]benzothienothienoquinazolines (BTTQs).
opt[a]
Eg
Absorbance
λabs [nm]
Fluorescence
λem [nm]
exp
exp
exp
[eV]
ε [Lmol–1 cm–1]
λex [nm]
Stokes shift [cm–1]
Φ[b]
DTQ-1
DTQ-2
BTTQ-1
3.32
3.36
3.16
361.0
344.0
328.5
285.0
350.5
335.0
278.0
248.5
373.0
356.0
336.5
304.0
273.5
253.5
373.5
355.0
339.5
273.5
4143
4661
4640
48009
6540
7319
27157
34516
5058
5927
7763
38808
25474
26903
8303
8211
9700
363
346
285
388
395
417
1928
3174
2757
1.8
338
284
3.7
2.8
374
355
336
307
BTTQ-2
3.20
373
340
277
406
2107
4.1
43859
opt
[a] Eg is the energy gap estimated from the onset of the absorption spectra recorded in THF solution. [b] Φ is the quantum yield of
photoluminescence.
(thien-3-yl)pyrimidine (4) were prepared according to the earlier
reported method.[9,10] The solvents (1,4-dioxane and H2O) for the
microwave-assisted Suzuki cross-coupling reactions were deoxy-
genated by bubbling argon for 1 h.
photoluminescence for DTQ-1 and BTTQ-1 are less than
those for DTQ-2 and BTTQ-2 as a result of longer conjuga-
tion lengths in DTQ-1 and BTTQ-1 and higher intramolec-
ular charge transfer (ICT). On the other hand, the quantum
yields of photoluminescence proved to be lower for DTQ-1
and DTQ-2 than for BTTQ-1 and BTTQ-2, whereas the
1H and 13C NMR spectra were recorded with Bruker DRX-400
and AVANCE-500 spectrometer using Me4Si as an internal stan-
dard. Elemental analysis was carried with a Eurovector EA 3000
automated analyzer. Melting points were determined on Boetius
combined heating stages.
opt
values of Eg were higher due to the effect of benzannul-
ation. This finding suggests that an increase in conjugation
in structurally similar compounds could lead to smaller
band gaps and may be a useful strategy for the design of
semiconductors.
GC–MS analysis was carried out by using an Agilent GC 7890A
MS 5975C Inert XL EI/CI GC–MS spectrometer with a quadru-
pole mass-spectrometric detector with electron ionization (70 eV)
and scan over the total ionic current in the range m/z = 20–1000
and a quartz capillary column HP-5MS (30 mϫ0.25 mm, film
thickness 0.25 mm). Helium served as the carrier gas, the split ratio
of the flow was 1:50, and the consumption through the column
was 1.0 mLmin–1; the initial temperature of the column was 40 °C
(storage 3 min), the heating rate was 10 °Cmin–1 to 290 °C (storage
20 min), the temperature of the evaporator was 250 °C, the tem-
perature of the source was 230 °C, the temperature of the quadru-
pole was 150 °C, and the temperature of the transition chamber
was 280 °C. Solutions of the samples at a concentration of 3–
4 mgmL–1 were prepared in THF and 1 mL of the solutions was
analyzed.
Conclusions
A convenient synthetic route to novel thienoacene sys-
tems with a fused pyrimidine ring has been advanced. A
commercially available 5-bromopyrimidine was used to syn-
thesize various dithienoquinazoline systems through a se-
quence of reactions involving nucleophilic aromatic substi-
tution of hydrogen (the SNH reaction), Suzuki coupling, and
oxidative photocyclization. The X-ray diffraction data have
been obtained for a number of new dithienoquinazolines
and intermediate pyrimidines.
It is legitimate to say that the compounds studied herein
have potential as organic semiconductors, but additional
modifications are required to achieve this. Future research
will be directed at creating push–pull systems with stronger
donor and acceptor groups attached to the opposite ends
of the oligothiophene motif.
Flash column chromatography was carried out by using Lancaster
silica gel 0.040–0.063 mm (230–400 mesh), eluting with ethyl acet-
ate/hexane. The progress of the reactions and the purity of com-
pounds were checked by TLC on Sorbfil plates (Russia); the spots
were visualized with UV light (λ = 254 or 365 nm).
Microwave experiments were carried out in a Discover unimodal
microwave system (CEM, USA) with a working frequency of
2.45 GHz and the power of the microwave radiation ranged from
0 to 300 W. The reactions were carried out in a 10 mL reaction
tube fitted with hermetic Teflon cork. The temperature of the reac-
tion was monitored by using an IR sensor at the external surface
of the reaction vessel.
Experimental Section
General: All reagents and solvents were obtained from commercial
sources and dried by using standard procedures before use. 5-
Bromo-4-(thien-2-yl)pyrimidine (2), 4,5-di(thien-2-yl)pyrimidine
(3a), 4-(5-bromothien-2-yl)-5-(thien-2-yl)pyrimidine (3e) and 5-
The light source used for the photochemical reactions was a Hano-
via medium-pressure mercury lamp (PC 451050/805221).
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A suitable crystal of 3g was selected and X-ray analysis was per-
formed with an Xcalibur E diffractometer by following a standard
procedure (Mo-Kα graphite-monochromated irradiation, ω scan-
ning with steps of 1 ). The crystal was kept at 120.00(10) K during
data collection and empirical absorption correction was applied.
By using Olex2,[15] the structure was solved by using the Su-
perflip[16] structure solution program using Charge Flipping and
refined with the SHELX[17] refinement package by using the full-
matrix least-squares on F2 method with anisotropic approximation
for non-hydrogen atoms. X-ray analyses of crystals of 3b and 9-Br-
DTQ-1 were performed with an Xcalibur S diffractometer follow-
ing a standard procedure (Mo-Kα graphite-monochromated irradi-
ation, ω scanning with steps of 1°). The crystals were kept at
295(2) K during data collection. For compound 9-Br-DTQ-1, em-
pirical absorption correction was applied. By using the SHELX
program package,[17] the structures were solved by direct methods
and refined by the full-matrix least-squares on F2 method with an-
isotropic approximation for non-hydrogen atoms. Crystal data and
data collection parameters are summarized in Table S5 in the Sup-
porting Information.
5-Benzo[b]thien-2-yl-4-(thien-2-yl)pyrimidine (3b): Yield 78%, pale-
yellow solid; m.p. 156–158 °C. 1H NMR (500 MHz, [D6]DMSO):
δ = 7.03 (dd, J = 5.0, 3.9 Hz, 1 H, 4Ј-H), 7.14 (dd, J = 3.9, 1.0 Hz,
1 H, 4Ј-H), 7.43–7.50 (m, 2 H, benzo[b]thienyl), 7.68 (s, 1 H, 3ЈЈ-
H), 7.79 (dd, J = 5.0, 1.0 Hz, 1 H, 5Ј-H), 7.95 (dd, J = 6.6, 2.2 Hz,
1 H, benzo[b]thienyl), 8.05–8.08 (m, 1 H, benzo[b]thienyl), 8.85 (s,
1 H, 6-H), 9.20 (s, 1 H, 2-H) ppm. 13C NMR (126 MHz, [D6]-
DMSO): δ = 122.16, 123.23, 124.12, 124.85, 124.96, 127.86, 128.32,
130.11, 131.00, 131.66, 137.44, 139.54, 140.79, 156.30, 157.76,
159.45 ppm. GC: tR = 27.58 min. MS: m/z (%) = 294 (100) [M]+.
C16H10N2S2 (294.40): calcd. C 65.28, H 3.42, N 9.52; found C
64.94, H 3.58, N 9.45.
CCDC-1018352 (for 3b), -1018351 (for 3g), and -1018350 (for 9-
Br-DTQ-1) 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.ac.uk/
data_request/cif.
Cyclic voltammetry was carried out with a Metrohm Autolab
PGSTAT128N potentiostat with a standard three-electrode config-
uration. Typically, a three-electrode cell equipped with a glass car-
bon (and platinum) working electrode, an Ag/AgNO3 reference
electrode, and a glass carbon rod counter electrode was employed.
The measurements were performed in anhydrous THF solution
containing the compound (2 mm) and tetrabutylammonium hexa-
fluorophosphate (0.1 m) as the supporting electrolyte under argon
at a scan rate of 100 mVs–1. The potential of the Ag/AgNO3 refer-
ence electrode was calibrated by using the ferrocene/ferrocenium
redox couple (Fc/Fc+), which has a known oxidation potential of
+4.8 eV.
5-(Thien-3-yl)-4-(thien-2-yl)pyrimidine (3c): Yield 72%, off-white
solid; m.p. 95–97 °C. 1H NMR (500 MHz, [D6]DMSO): δ = 6.89
(d, J = 3.7 Hz, 1 H, thienyl), 7.03 (dd, J = 4.7, 4.1 Hz, 1 H, thienyl),
7.16 (dd, J = 4.7, 1.5 Hz, 1 H, thienyl), 7.76–7.78 (m, 3 H, thienyl),
8.66 (s, 1 H, 6-H), 9.11 (s, 1 H, 2-H) ppm. 13C NMR (126 MHz,
[D6]DMSO): δ = 125.53, 125.93, 127.70, 128.31, 128.33, 130.10,
131.39, 135.74, 141.24, 156.61, 157.14, 158.45 ppm. GC: tR
=
22.99 min. MS: m/z (%) = 244 (100) [M]+. C12H8N2S2 (244.34):
calcd. C 58.99, H 3.30, N 11.46; found C 58.65, H 3.49, N 11.30.
UV/Vis spectra were recorded for 1ϫ 10–5 m dichloromethane solu-
tions with a Shimadzu UV-2401PC spectrophotometer. Photolumi-
nescent spectra were recorded as 1ϫ 10–6 m THF solutions with a
Varian Cary Eclipse fluorescence spectrophotometer. Quantum
yields (Φ) were estimated by using a 1 n H2SO4 solution of quinine
bisulfate (Φ = 0.55) as a reference.[18]
IR spectra of samples (solid powders) were recorded with a Spec-
trum One Fourier transform IR spectrometer (Perkin–Elmer)
equipped with a diffuse reflectance attachment (DRA) in the fre-
quency range 3500–450 cm–1. Spectrum processing and band inten-
sity determination were carried out by using the special software
supplied with the spectrometer.
5-(Benzo[b]thien-3-yl)-4-(thien-2-yl)pyrimidine (3d): Yield 77%,
pale-yellow solid; m.p. 99–101 °C. 1H NMR (500 MHz, [D6]
DMSO): δ = 6.78 (dd, J = 4.1, 0.6 Hz, 1 H, 3Ј-H), 6.88 (dd, J =
4.8, 4.1 Hz, 1 H, 4Ј-H), 7.23–7.33 (m, 1 H, benzo[b]thienyl), 7.39–
7.45 (m, 1 H, benzo[b]thienyl), 7.68 (dd, J = 4.8, 0.6 Hz, 1 H, 5Ј-
H), 8.05 (s, 1 H, 2ЈЈ-H, benzo[b]thienyl), 8.13 (s, J = 8.2 Hz, 1 H,
7ЈЈ-H), 8.75 (s, 1 H, 6-H), 9.24 (s, 1 H, 2-H) ppm. 13C NMR
(126 MHz, [D6]DMSO): δ = 122.14, 123.21, 124.10, 124.81, 124.91,
General Procedure for the Microwave-Assisted Suzuki Cross-Cou-
pling Reactions: A solution of K2CO3 (346 mg, 2.5 mmol) in H2O
(4 mL) was added to a mixture of 5-bromo-4-(thien-2-yl)pyrimidine
(2; 0.5 mmol), (benzo[b]thien-2-yl)boronic acid [or 3-thienylboronic
acid or (benzo[b]thien-3-yl)boronic acid] (107 mg, 0.6 mmol) and
[Pd(PPh3)4] (29 mg, 5 mol-%) in THF (3 mL). The resulting mix-
ture was irradiated in a microwave oven at 150 °C (250 W) for 127.75, 128.32, 130.08, 130.99, 131.66, 137.44, 139.54, 140.79,
25 min. Then the solvent was distilled off in vacuo and the residue
purified by flash column chromatography (hexane/ethyl acetate,
1:3) to afford the desired cross-coupling products (3b–3d).
156.30, 157.76, 159.40 ppm. GC: tR = 27.04 min. MS: m/z (%) =
294 (100) [M]+. C16H10N2S2 (294.40): calcd. C 65.28, H 3.42, N
9.52; found C 65.01, H 3.50, N 9.43.
6
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Dithienoquinazolines and Their Photophysical Properties
EtOAc/hexane (from 1:3 to 1:1) as eluent to afford the desired di-
thienoquinazoline system.
Synthesis of 4-[5-Bromo(thien-2-yl)]-5-(thien-3-yl)pyrimidine (3f): 2-
Bromothiophene (5; 387 μL, 4 mmol) was added to a solution of
5-(thien-3-yl)pyrimidine (4; 324 mg, 2 mmol) in CF3COOH (5 mL).
The reaction mixture was stirred at room temperature for 24 h and
the solvents evaporated. A solution of KOH (449 mg, 8.0 mmol,
4 equiv.) and K3[Fe(CN)6] (1.317 g, 4.0 mmol, 2 equiv.) in water
(15 mL) was added to the residue. The resulting mixture was stirred
for 6 h at room temperature, and the precipitate formed was fil-
tered, 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-bromo(thien-2-yl)]-5-(thien-3-yl)pyrimidine (3f),
yield 381 mg, 59%, off-white crystalline powder; m.p. 168–170 °C.
1H NMR (500 MHz, [D6]DMSO): δ = 6.67 (d, J = 4.1 Hz, 1 H,
3Ј-H), 7.17 (d, J = 4.1 Hz, 1 H, 4Ј-H), 7.19 (dd, J = 4.5, 1.7 Hz, 1
H, 3ЈЈ-H), 7.78–7.81 (m, 2 H, thienyl), 8.68 (s, 1 H, 6-H), 9.11 (s,
1 H, 2-H) ppm. 13C NMR (126 MHz, [D6]DMSO): δ = 117.80,
125.78, 125.88, 128.02, 128.26, 130.76, 131.80, 135.12, 143.00,
154.47, 157.16, 158.72 ppm. GC: tR = 25.35 min. MS: m/z (%) =
322 (100) [M]+ for 79Br, 324 (100) [M]+ for 81Br. C12H7BrN2S2
(323.23): calcd. C 44.59, H 2.18, N 8.67; found C 44.65, H 2.29, N
8.73.
Dithieno[2,3-f:3Ј,2Ј-h]quinazoline (DTQ-1): Yield 64%, pale-brown
solid; m.p. 224–226 °C. 1H NMR (500 MHz, [D6]DMSO): δ =
8.14–8.18 (m, 3 H, 6-H, 7-H, 9-H), 8.29 (d, J = 5.2 Hz, 1 H, 8-H),
9.37 (s, 1 H, 4-H), 9.87 (s, 1 H, 2-H) ppm. 13C NMR (126 MHz,
[D6]DMSO): δ = 118.32, 123.23, 123.92, 129.51, 131.74, 132.86,
133.36, 134.73, 138.80, 145.46, 155.00, 155.14 ppm. IR (DRA): ν
˜
= 513, 577, 628, 643, 691, 726, 738, 764, 801, 851, 908, 963, 1010,
1098, 1115, 1149, 1201, 1218, 1229, 1250, 1271, 1327, 1357, 1385,
1413, 1440, 1478, 1487, 1556, 1576, 1658, 3008, 3061, 3077,
3098 cm–1. GC: tR = 25.87 min. MS: m/z (%) = 242 (100) [M]+.
C12H6N2S2 (242.32): calcd. C 59.48, H 2.50, N 11.56; found C
59.22, H 2.31, N 11.57.
Dithieno[3,2-f:3Ј,2Ј-h]quinazoline (DTQ-2): Yield 47%, pale-brown
solid; m.p. 238–240 °C. 1H NMR (500 MHz, [D6]DMSO): δ = 7.93
(d, J = 5.3 Hz, 1 H), 8.10 (d, J = 5.3 Hz, 1 H), 8.32 (d, J = 5.3 Hz,
1 H), 8.45 (d, J = 5.3 Hz, 1 H), 9.38 (s, 1 H, 4-H), 10.15 (s, 1 H,
2-H) ppm. 13C NMR (126 MHz, [D6]DMSO): δ = 118.11, 122.62,
123.06, 127.83, 132.36, 132.54, 133.69, 133.71, 137.41, 145.90,
154.89, 156.16 ppm. IR (DRA): ν = 478, 568, 630, 657, 687, 731,
˜
756, 803, 862, 895, 920, 1012, 1064, 1101, 1129, 1205, 1333, 1366,
1416, 1425, 1440, 1470, 1494, 1555, 1583, 3058, 3078 cm–1. GC: tR
= 25.89 min. MS: m/z (%) = 242 (100) [M]+. C12H6N2S2 (242.32):
calcd. C 59.48, H 2.50, N 11.56; found C 59.63, H 2.47, N 11.34.
Synthesis of 4,5-Bis[5-bromo(thien-2-yl)]pyrimidine (3g): NBS
(219 mg, 1.23 mmol) was added to a solution of 4,5-di(thien-2-yl)
pyrimidine (3a; 100 mg, 0.41 mmol) in DMF (5 mL) at room tem-
perature. Then the mixture was stirred for 24 h at room tempera-
ture. The reaction mixture was diluted with H2O and the precipitate
formed was filtered, washed with H2O, and air-dried. The residue
was purified by flash column chromatography (hexane/ethyl acet-
ate, 1:1). The product 3g was isolated as a dark-yellow powder
(125 mg, 76%), m.p. 168–170 °C. 1H NMR (500 MHz, [D6]-
DMSO): δ = 6.90 (d, J = 4.1 Hz, 1 H, 3ЈЈ-H), 7.20 (d, J = 3.7 Hz,
1 H, 3Ј-H), 7.25 (d, J = 4.1 Hz, 1 H, 4ЈЈ-H), 7.40 (d, J = 3.7 Hz, 1
H, 4Ј-H), 8.76 (s, 1 H, 6-H), 9.15 (s, 1 H, 2-H) ppm. 13C NMR
(126 MHz, [D6]DMSO): δ = 113.74, 118.39, 122.60, 130.44, 131.36,
131.44, 132.08, 136.92, 142.15, 155.20, 158.02, 159.59 ppm. GC:
tR = 27.11 min. MS: m/z = 401 [M]+ for 79Br, 403 [M]+ for 81Br.
C12H6Br2N2S2 (402.13): calcd. C 35.84, H 1.50, N 6.97; found C
35.68, H 1.44, N 6.84.
[1]Benzothieno[2,3-f]thieno[3Ј,2Ј-h]quinazoline (BTTQ-1): Yield
38%, pale-brown solid; m.p. 281–284 °C. 1H NMR (500 MHz,
[D6]DMSO): δ = 7.69–7.77 (m, 2 H, 7-H, 8-H), 8.33 (d, J = 7.7 Hz,
1 H, 9-H), 8.48 (d, J = 5.6 Hz, 1 H, 10-H), 8.71 (d, J = 5.6 Hz, 1
H, 11-H), 8.90 (d, J = 7.7 Hz, 1 H, 6-H), 9.47 (s, 1 H, 4-H), 9.94
General Procedure for the Oxidative Photocyclization Reactions:
Iodine (0.037 g, 0.14 mmol) and excess propylene oxide (ca. 5 mL)
was added to a solution of 5-(het)aryl-4-(thien-2-yl)pyrimidine 3a–
3g (1 mmol) in toluene (150 mL). The reaction mixture was irradi-
ated at room temp. with a UV lamp. After 20 h of irradiation, the
toluene layer was washed with aqueous Na2S2O3, water, and brine,
dried with anhydrous MgSO4, and the solvents evaporated. The
residue was purified by flash column chromatography using
(s, 1 H, 2-H) ppm. IR (DRA): ν = 638, 691, 707, 722, 762, 800,
˜
869, 910, 963, 1013, 1022, 1103, 1119, 1147, 1163, 1207, 1265, 1307,
1342, 1380, 1408, 1433, 1448, 1483, 1546, 1579, 1661, 3046,
3109 cm–1. GC: tR = 31.52 min. MS: m/z (%) = 292 (100) [M]+.
C16H8N2S2 (292.38): calcd. C 65.73, H 2.76, N 9.58; found C 65.52,
H 2.61, N 9.39. The 13C NMR spectra of BTTQ-1 could not be
obtained due to the poor solubility of this compound in deuteriated
solvents.
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E. V. Verbitskiy et al.
FULL PAPER
6,9-Dibromodithieno[2,3-f:3Ј,2Ј-h]-quinazoline
(6,9-diBr-DTQ-1):
[1]Benzothieno[3,2-f]thieno[3Ј,2Ј-h]quinazoline (BTTQ-2): Yield
22%, pale-brown solid; m.p. 280–283 °C. 1H NMR (500 MHz,
[D6]DMSO): δ = 7.64–7.72 (m, 2 H, 6-H, 7-H), 8.00 (d, J = 5.2 Hz,
1 H, 10-H), 8.31 (dd, J = 8.0, 0.8 Hz, 1 H, 5-H), 8.39 (d, J = 5.2 Hz,
1 H, 11-H), 9.09 (d, J = 8.0 Hz, 1 H, 8-H), 9.45 (s, 1 H, 4-H), 10.65
(s, 1 H, 2-H) ppm. 13C NMR (126 MHz, [D6]DMSO): δ = 119.36,
123.46, 123.87, 124.89, 125.89, 126.00, 126.32, 134.22, 134.82,
135.11, 135.17, 137.33, 138.33, 146.18, 154.19, 154.85 ppm. IR
Yield 55%, beige solid; m.p. 264–266 °C. 1H NMR (500 MHz,
[D6]DMSO): δ = 8.33 (s, 1 H, 7-H), 8.35 (s, 1 H, 8-H), 9.37 (s, 1 H,
4-H), 9.83 (s, 1 H, 2-H) ppm. 13C NMR (126 MHz, [D6]DMSO): δ
= 116.35, 117.48, 120.18, 126.48, 127.39, 133.34, 133.56, 134.74,
137.58, 143.99, 155.34, 155.66 ppm. IR (DRA): ν = 470, 511, 561,
˜
572, 642, 659, 692, 709, 791, 818, 828, 916, 962, 971, 999, 1019,
1114, 1196, 1215, 1238, 1297, 1315, 1342, 1409, 1444, 1477, 1552,
1582, 1669, 3016, 3043, 3080 cm–1. GC: tR = 30.11 min. MS: m/z
(DRA): ν = 425, 482, 513, 567, 636, 688, 728, 742, 758, 802, 867,
˜
(%)
=
399 (100) [M]+ for 79Br, 401 (100) [M]+ for 81Br.
918, 933, 1011, 1029, 1094, 1122, 1165, 1177, 1204, 1252, 1295,
1311, 1336, 1353, 1377, 1412, 1446, 1466, 1484, 1545, 1574, 3033,
3060, 3097 cm–1. GC: tR = 31.56 min. MS: m/z (%) = 292 (100)
[M]+. C16H8N2S2 (292.38): calcd. C 65.73, H 2.76, N 9.58; found
C 65.59, H 2.68, N 9.45.
C12H4Br2N2S2 (400.21): calcd. C 36.02, H 1.01, N 7.00; found C
36.29, H 0.82, N 6.81.
Supporting Information (see footnote on the first page of this arti-
cle): UV/Vis and 1H and 13C NMR spectra of the new compounds,
crystal structural data for compounds 3b, 3g, and 9-Br-DTQ-1.
Acknowledgments
This work was supported by the Ural Branch of the Russian Acad-
emy of Sciences (grant numbers 12-P-3-1014, 12-P-3-1030, 12-T-3-
1025, and 12-T-3-1031), the Russian Foundation for Basic Re-
search (research project numbers 13-03-96049-r_ural_a, 13-03-
12434-ofi_m2, 13-03-90606-Arm_a, 14-03-01017-A, 14-03-00479-
A, and 14-03-31040-mol_a), and the Council of Grants of the Pres-
ident of the Russian Federation (Program of State Support for
Leading Scientific Schools of the Russian Federation and Young
Scientists, grant number MK-3939.2014.3). The authors thank Dr.
Marina G. Pervova for performing GC–MS analyses.
9-Bromodithieno[2,3-f:3Ј,2Ј-h]quinazoline (9-Br-DTQ-1): Yield
46%, beige solid; m.p. 224–226 °C. 1H NMR (500 MHz,
[D6]DMSO): δ = 8.08 (d, J = 5.3 Hz, 1 H, 7-H), 8.16 (d, J = 5.3 Hz,
1 H, 6-H), 8.36 (s, 1 H, 8-H), 9.34 (s, 1 H, 4-H), 9.83 (s, 1 H, 2-
H) ppm. 13C NMR (126 MHz, [D6]DMSO): δ = 118.23, 119.91,
123.13, 127.45, 129.84, 132.39, 133.68, 134.11, 138.61, 144.22,
155.10, 155.38 ppm. IR (DRA): ν = 466, 513, 542, 572, 626, 691,
˜
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9-Bromodithieno[3,2-f:3Ј,2Ј-h]quinazoline (9-Br-DTQ-2): Yield
61%, dark-yellow solid; m.p. 243–244 °C. 1H NMR (500 MHz,
[D6]DMSO): δ = 7.92 (d, J = 5.3 Hz, 1 H, 8-H), 8.33 (d, J = 5.3 Hz,
1 H, 9-H), 8.68 (s, 1 H, 5-H), 9.39 (s, 1 H, 4-H), 10.11 (s, 1 H, 2-
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155.23, 156.48 ppm. GC: tR = 27.97 min. MS: m/z (%) = 320 (100)
[M]+ for 79Br, 322 (100) [M]+ for 81Br. C12H5BrN2S2 (321.22): calcd.
C 44.87, H 1.57, N 8.72; found C 44.83, H 1.70, N 8.67.
8
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Dithienoquinazolines and Their Photophysical Properties
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Received: September 16, 2014
Published Online: ᭿
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Pages: 10
E. V. Verbitskiy et al.
FULL PAPER
Thieno-aza-acenes
A convenient route to a new class of
thienoacene systems bearing a fused pyrim-
idine ring is presented along with their op-
toelectronic properties. The photophysical
and electrochemical properties of these
newly developed thieno-aza-acenes have
been investigated by UV/Vis absorption
and photoluminescence spectrophotometry
and cyclic voltammetry, and some crystal
structures have also been determined.
E. V. Verbitskiy,* P. A. Slepukhin,
M. S. Valova, E. M. Cheprakova,
A. V. Schepochkin, G. L. Rusinov,
V. N. Charushin ............................... 1–10
Dithienoquinazolines – A Convenient Syn-
thesis by the Oxidative Photocyclization of
4,5-Dithienyl-Substituted Pyrimidines and
Their Photophysical Properties
Keywords: Photocyclization / Nucleophilic
substitution / UV/Vis spectroscopy / Lumi-
nescence / Nitrogen heterocycles / Fused
ring systems
10
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