Photochemical Synthesis of 4 H -Thieno[3,2- c ]chromene and Their Optical Properties

Article abstract of DOI:10.1055/a-1392-2209

4-{[(2-Iodoaryl)oxy]methyl}thiophene-2-carbaldehydes and 5-iodo-4-(aryloxymethyl)thiophene-2-carbaldehydes were obtained by the reaction of phenols with 4-(chloromethyl)thiophene-2-carbaldehyde or its 5-iodo analogue, respectively. These products underwent ring closure upon irradiation with UV light (254 nm) to form the corresponding 4 H -thieno[3,2- c ]chromene-2-carbaldehydes in high yield. The formation of intermediate radical species was detected by EPR spectroscopy. Comparative analysis of ring-closure methods showed that photochemical cyclization of 5-iodo-4-(aryloxymethyl)thiophene-2-carbaldehyde is superior to Pd-catalyzed intramolecular arylation. A series of substituted 4 H -thieno[3,2- c ]chromene-2-carbaldehydes were synthesized by the photochemical cyclization of the corresponding precursors, and the photophysical properties of the products were studied. The 4 H -thieno[3,2- c ]chromene-2-carbaldehydes can be used as covert marking pigments.

Full text of DOI:10.1055/a-1392-2209

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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart
2021, 32, 790–794
letter
790
en
E. B. Ulyankin et al.
Letter
Synlett
Photochemical Synthesis of 4H-Thieno[3,2-c]chromene and Their
Optical Properties
Evgeny B. Ulyankina
Yulia P. Bogzab
Anastasia S. Kostyuchenkoa,b
Sergey A. Chernenkoa
Anna L. Samsonenkob
Anton L. Shatsauskasb
Vyacheslav L. Yurpalovc
Alexander S. Fisyuk*a
a Laboratory of New Organic Materials, Omsk State Technical
University, 11 Mira Ave, 644050, Omsk, Russian Federation
fisyuk@chemomsu.ru
b Department of Organic Chemistry, Omsk F.M. Dostoevsky
State University, 55a Mira Ave, 644077, Omsk,
Russian Federation
c Center of New Chemical Technologies BIC,
54 Neftezavodskaya St., 644040 Omsk, Russian Federation
Corresponding Author
Received: 16.01.2021
Accepted after revision: 16.02.2021
Published online: 16.02.2021
pling reactions catalyzed by transition metals are most of-
ten used to form the C–C bond between the benzene and
thiophene rings. Despite its effectiveness, this approach has
disadvantages associated with the toxicity and high cost of
the catalyst, the use of ligands, and the laborious purifica-
tion of the reaction products. Therefore, the development of
an ecofriendly photochemical method for the preparation
of 4H-thieno[3,2-c]chromenes is an urgent task.
Previously, we have developed two methods for the syn-
thesis of 4H-thieno[3,2-c]chromenes based on palladium-
catalyzed intramolecular arylation of compounds 5a (Meth-
od B)11 or compounds 6a–o (Method D),12 differing in the
position of iodine in the molecule (Table 1); the yields of
compounds 7a–i obtained by these methods were in the
ranges 20–69% and 44–85%, respectively.
The starting compounds 5a–c were synthesized by
treating14 o-iodophenols 3a–c with 4-(chloromethyl)thio-
phene-2-carbaldehyde (1), prepared by chloromethylation
of thiophene-2-carbaldehyde.15 Compounds 6a–o were
synthesized by the reaction of the appropriate phenol 4a–o
with 5-iodo-4-(chloromethyl)thiophene-2-carbaldehyde
(2), obtained by iodination of aldehyde 1.12 Note that the
latter approach is preferable because of the ready availabili-
ty of phenols 4a–o.
UV light-initiated arylation of 2-iodothiophenes has
been known for a long time;16 however, this approach has
not been used to obtain 4H-thieno[3,2-c]chromenes. There-
fore, it was of interest to study the possibility of intramolec-
ular photocyclization of model compounds 5a (Method A)
and 6a (Method C). To select the optimal irradiation wave-
length, the absorption spectra of solutions of compounds
5а and 6а in acetonitrile were recorded (Figure 1). The ab-
sorption maxima of compounds 5а and 6а are in the range
250–330 nm, so a mercury lamp was chosen as a light
DOI: 10.1055/a-1392-2209; Art ID: st-2021-v0017-l
Abstract 4-{[(2-Iodoaryl)oxy]methyl}thiophene-2-carbaldehydes
and 5-iodo-4-(aryloxymethyl)thiophene-2-carbaldehydes were ob-
tained by the reaction of phenols with 4-(chloromethyl)thiophene-2-
carbaldehyde or its 5-iodo analogue, respectively. These products un-
derwent ring closure upon irradiation with UV light (254 nm) to form
the corresponding 4H-thieno[3,2-c]chromene-2-carbaldehydes in high
yield. The formation of intermediate radical species was detected by
EPR spectroscopy. Comparative analysis of ring-closure methods
showed that photochemical cyclization of 5-iodo-4-(aryloxymeth-
yl)thiophene-2-carbaldehyde is superior to Pd-catalyzed intramolecular
arylation. A series of substituted 4H-thieno[3,2-c]chromene-2-carbal-
dehydes were synthesized by the photochemical cyclization of the cor-
responding precursors, and the photophysical properties of the prod-
ucts were studied. The 4H-thieno[3,2-c]chromene-2-carbaldehydes can
be used as covert marking pigments.
Key words photochemistry, cyclization, thienochromenes, lumines-
cence, arylation, pigments
4H-Thieno[3,2-c]chromene derivatives are of interest as
biologically active compounds. Among them are substances
that exhibit analgesic,1 mucoregulating,2 antiosteoporotic,3
antiinflammatory, anti-Parkinsonian,4 or antiulcer effects.5
Some are also used to treat diabetes, hyperlipidemia,6 or
cancer.7 Substituted 4H-thieno[3,2-c]chromenes are lumi-
nophores, and their luminescent properties permit their lo-
calization and transformation within cells. Consequently,
luminescent probes for medical and biological use,8 as well
as materials for organic electronics,9 have been developed.
Currently, several approaches are used to synthesize
4H-thieno[3,2-c]chromenes. These are based on annulation
reactions of benzopyrans with a thiophene core10 or on the
formation of a pyran ring.11–13 In the latter case, cross-cou-
© 2021. Thieme. All rights reserved. Synlett 2021, 32, 790–794
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

791
E. B. Ulyankin et al.
Letter
Synlett
source. Irradiation with UV radiation (254 nm, 32 W) of 10
mM solutions of compounds 5а and 6а in acetonitrile both
gave 4H-thieno[3,2-c]chromene-2-carbaldehyde (7a) in
90% yield (Table 1, entries 1 and 2). The changes in the con-
centrations of the reaction product 7а and the reactant 5а
or 6а were recorded by HPLC.
We found that photocyclization of 6a proceeded com-
pletely in five hours, whereas the conversion of aldehyde 5a
into thienochromene 7a occurred twice as slowly, requiring
irradiation for ten hours (Figure 2).17
The rate-limiting stage of the reaction is probably the
formation of a radical, which proceeds faster in the case of
compound 6а. No signals were observed in the EPR spec-
trum upon UV irradiation of acetonitrile solutions of sub-
strate 5а or 6а (mercury lamp, 100 W) at room tempera-
ture. This absence of EPR signals might be associated with a
low concentration or a short lifetime (less than 10–8 s) of
the radical species that is formed. However, irradiation of
compounds 5a and 6a as glass solutions in acetonitrile at 77
K led to the appearance of signals in the EPR spectra (Figure
Table 1 Synthesis of 4H-Thieno[3,2-c]chromene-2-carbaldehydes 7a–p
R2
OH
R2
Cl
I
(CH2O)n
3a–c
Method A or B
O
I
AlCl3
CHCl3
K2CO3, DMF, KI
CHO
S
1
CHO
5a–c
O
R4
S
NIS, H+
R3
CHO
R3
R3
S
R2
R2
R1
R4
CHO
S
R1 7a–p
R2
Method C or D
R4
R1
Cl
OH
4a–o
O
I
K2CO3, DMF, KI
CHO
S
2
I
CHO
S
6a–o
Method A/C: hν 254 nm, 32 W, 10 mM in MeCN, 33–90%
Method B: Pd(OAc)2, P(Ph)3, C16H33NMe3Br, K2CO3, DMF, 110 °C, 5–6 h, 44–85%
Method D: Pd(OAc)2, P(Ph)3, C16H33NMe3Br, K2CO3, MeCN, 80 °C, 5 h, 20–69%
Entry
R1
R2
R3
R4
Ether 5 or 6 Yield (%) of Time (h)
6 (5)
Product
Yield (%) of 7
Yield (%) of 7
[Method А/C] [Method D12 or (B)11
]
1
2
H
H
H
H
5a
6a
6b
6c
6d
6e
6f
47
65
67
72
76
87
64
73
81
83
87
65
82
54
47
92
–
10
5
7a
7a
7b
7c
7d
7e
7f
90
90
50
67
84
20a
57
87
74
75
67
65
64
33
35
51
51a
– (85)c
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
63b
3
Me
H
H
7
62b (69)c
4
Cl
H
H
5
75b (20)c
5
H
H
Cl
7
74b
44b
82b
83b
17
33
–
6
H
Cl
H
7
7
OMe
H
H
14
20
30
26
10
7
8
O(CH2)5Me
H
H
6g
6h
6i
7g
7h
7i
9
H
NO2
H
I
H
CO2Me
10
11
12
13
14
15
16
17
H
H
H
NO2
H
6j
7j
H
6k
6l
7k
7l
–
F
H
H
11
5
–
H
H
N(Me)2
N(Bu)2
H
H
6m
6n
6o
6e
7m
7n
7o
7p
–
H
4
–
–CH=CH–CH=CH–
Cl
H
5
-
H
H
H
7
–
a Isomeric products 7e and 7p (entries 6 and 17) were obtained as a mixture using Method C in a 2:5 ratio according to the NMR data.
b According to the literature data.12
c According to the literature data.11
© 2021. Thieme. All rights reserved. Synlett 2021, 32, 790–794

792
E. B. Ulyankin et al.
Letter
Synlett
3). This indicated the formation of radical species during
the photochemical reaction. Analyses of the solutions after
irradiation showed the progress of cyclization. A blank ex-
periment with UV irradiation of acetonitrile at 77 K in the
absence of substrates did not reveal the formation of any
significant amounts of any radical species. The spectra of
compounds 5a and 6a contain broadened multiplet signals
due to the coupling of the 1H and 13C nuclei. The higher val-
ue of the g-factor for substrate 6a (2.0050) compared with
that of compound 5a (2.0032) indicates the localization of
the unpaired electron in the thiophene ring. Such an in-
crease in the g-factor value of an unpaired electron in a sul-
fur-containing heterocycle is explained by the higher spin–
orbit coupling constant of the S atom compared with that of
the C atom.18
Because the photochemical cyclization of 5-iodo-4-
(phenoxymethyl)thiophene-2-carbaldehyde (6а) proceed-
ed faster than that of 5a, compounds 6a–o were used to
synthesize thienochromenes 7a–p. The cyclization was per-
formed under the same conditions as those used for com-
pound 6a, and the reaction progress was monitored by TLC.
Complete cyclization of compounds 6b–o required irradia-
tion for 4–30 hours and the yields of thienochromenes 7b–
p were in the range 33–90% (Table 1, entries 3–17).
A comparative analysis of Methods A–D shows that the
use of the more accessible 5-iodo-4-(phenoxymethyl)thio-
phene-2-carbaldehyde (6а) as a starting compound is more
rational. The yields of compounds 7b and 7f with electron-
donor substituents in the benzene ring obtained by palladi-
um-catalyzed cyclization of 6b and 6f, respectively, were
slightly higher than those of the photochemical reaction
(Table 1, entries 3 and 7), whereas photochemical cycliza-
tion of compounds 6h and 6i bearing electron-withdrawing
substituents proceeds with significantly higher yields of
thienochromenes 7h and 7i, respectively (entries 9 and 10).
The photochemical cyclization of 6m–o gave compounds
7m–o, respectively, as the sole reaction products (entries
14–16). Only in the case of 6e were the isomeric 4H-thie-
no[3,2-c]chromene-2-carbaldehydes 7e (entry 6) and 7p
(entry 17) obtained in a 2:5 ratio according to NMR data.
However, compound 7e was the main product in the case of
Pd-catalyzed cyclization 6e using method D.12
The UV spectra of 4H-thieno[3,2-c]chromene-2-carbal-
dehydes have been reported only for compounds 7a–f.19
The main emission band in the luminescence spectra of
Figure 1 Absorption spectra of compounds 5а, 6a, and 7a
O
H
hν
S
CHO
6a
I
7a + HI
O
hν
I
5a
H
CHO
S
Figure 3 In situ experimental (black curves) and simulated (red curves)
EPR spectra of glass solutions of compounds 6a (Spectrum 1) and 5a
(Spectrum 2) in acetonitrile after UV irradiation at 77 K
Figure 2 Plot of ln(C/C0) against the exposure time for compounds 5a
and 6a
© 2021. Thieme. All rights reserved. Synlett 2021, 32, 790–794

793
E. B. Ulyankin et al.
Letter
Synlett
Table 2 UV and Luminescence Spectral Parameters of Acetonitrile Solutions of 4H-Thieno[3,2-c]chromene-2-carbaldehydes 7e–o and [(8-Fluoro-4H-
thieno[3,2-c]chromen-2-yl)methylene]malononitrile (8)a
UV absorption
Luminescence
max (nm)
ex (nm)
em (nm)
Stokes shiftb (nm) (eV)
Фfl
0.33c
7e
7g
7h
7i
241, 259, 291, 311, 368
215, 257, 289, 321, 389
262, 290, 318, 360
229, 295, 357
360, 370
380, 390
350, 360
355
454
522
453
–
86 (0.64)
133 (0.81)
93 (0.70)
–
0.45c
0.18c
0.00
7j
231, 276, 367
365
–
–
0.00
7k
7l
218, 263, 293, 317, 372
236, 254, 291, 311, 371
211, 264, 296, 427
212, 268, 438
365, 375
360, 370
420, 430
425, 435
390, 400
430
467
468
535
538
484
–
95 (0.68)
97 (0.69)
108 (0.58)
100 (0.53)
86 (0.56)
–
0.35d
0.65d
0.55c
0.62c
0.57d
0.00
7m
7n
7o
8
218, 238, 272, 337, 398
211, 262, 311, 340, 432
a c = 2.4 × 10–5 mol/L.
b Minimum Stokes shift.
c Quantum yield relative to that of a solution of coumarin in EtOH (Φf = 0.38).
d Quantum yield relative to that of a solution of perylene in EtOH (Φf = 0.92).
these compounds is known to be due to intramolecular
charge transfer, which should be influenced by substituents
on the benzene ring (Scheme 1).
O
O
hν
S
O
S
O
Figure 4 Photographs (a) in UV light and (b) in daylight of strips of raw
paper (1), strips of paper moistened with a solution of compound 7l in
ethanol and then dried (2), and strips of paper treated with compound
7l and a developer (1% malonodinitrile with a catalytic amount of Et3N
in ethanol) after drying.
Scheme 1 Intramolecular charge transfer in 4H-thieno[3,2-
c]chromene-2-carbaldehyde (7a)
The parameters of the UV and luminescence spectra of
compounds 7g–o are presented in Table 2. The introduction
of an electron-accepting substituent such as a methoxycar-
bonyl (7h) or nitro group (7i and 7g) onto the benzene ring,
which hinders charge transfer, led to a significant decrease
in or complete quenching of luminescence, whereas the
presence of an electron-donating substituent such as an
alkoxy (7f) or dialkylamino group (7m, 7n) led to an in-
crease in luminescence. Note that some compounds have an
abnormally large Stokes shift in excess of 100 nm. More-
over, their absorption bands are outside the visible region,
making these compounds colorless in daylight. Such lumi-
nophores are used in preventing counterfeiting of
banknotes, securities, or other important documents.
Compound 7l and malonodinitrile in the presence of a
base undergo a Knoevenagel condensation to form the con-
jugated structure 8, which has a deeper color (Scheme 2).
The optical properties of condensation product 8 are pre-
sented in Table 2. The absorption bands of compound 7l lie
outside the visible region (236–371 nm), in contrast to the
emission band (468 nm). This makes the strips of paper
treated with compound 7l colorless in daylight (2b), but
colored in UV light (2a) (Figure 4). The authenticity of the
luminophore is checked using a developer. A strip of paper
(2) turned yellow after treatment with 1% alcohol solution
of malonodinitrile (3).
To demonstrate a practical application of our synthesized
compounds, Figure 4 shows photographs of paper treated
with a solution of compound 7l in ethanol before and after
development by visible light or UV radiation (Figure 4).
In summary, a method has been developed for the
preparation of 4H-thieno[3,2-c]chromene-2-carbaldehydes
through photochemical cyclization of 5-iodo-4-(aryl-
oxymethyl)thiophene-2-carbaldehydes. The optical proper-
ties of the synthesized compounds were studied. A possibil-
ity of their use as covert marking pigments was shown.
© 2021. Thieme. All rights reserved. Synlett 2021, 32, 790–794

794
E. B. Ulyankin et al.
Letter
Synlett
(c) Wu, H.; Fan, H.; Xu, S.; Ye, L.; Guo, Y.; Yi, Y.; Ade, H.; Zhu, X.
Small 2019, 15, 1. (d) Xiao, Z.; Yang, S.; Yang, Z.; Yang, J.; Yip, H. L.;
Zhang, F.; He, F.; Wang, T.; Wang, J.; Yuan, Y.; Yang, H.; Wang, M.;
Ding, L. Adv. Mater. 2019, 31, 1.
CH2(CN)2
Et3N
O
O
NC
CN
CHO
S
S
7l
8
F
F
(10) (a) He, X.-K.; Cai, B.-G.; Yang, Q.-Q.; Wang, L.; Xuan, J. Chem.
Asian J. 2019, 14, 3269. (b) Sperança, A.; Godoi, B.; Costa, M. D.;
Menezes, P. H.; Zeni, G. Tetrahedron Lett. 2019, 52, 388.
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Mabon, R.; Pabba, P.; Tarver, J. Jr.; Terranova, K. M.; Tunoori, A.;
Xu, X. US 20120302562, 2012.
Scheme 2 Reaction of compound 7l with malonodinitrile
(11) Katsiel, A. L.; Sharipova, A. N.; Fisyuk, A. S. Mendeleev Commun.
2008, 18, 169.
Conflict of Interest
(12) Fisyuk, A. S.; Bogza, Y. P.; Belyaeva, L. V.; Belyaev, V. B. Chem.
Heterocycl. Compd. 2012, 48, 1078.
The authors declare no conflict of interest.
(13) (a) Kunz, T.; Knochel, P. Angew. Chem. Int. Ed. 2012
(b) Mori, A.; Arai, N.; Hatta, T.; Monguchi, D. Heterocycles 2010
103. (c) Reddy, C. R.; Valleti, R. R.; Reddy, M. D. J. Org. Chem. 2013
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51, 1958.
,
80,
Funding Information
,
This work was supported by the Russian Science Foundation (Grant
78, 6495. (d) Do, S.; Goldsmith, R.; Heffron, T.; Kolesnikov, A.;
Staben, S.; Olivero, A. G.; Siu, M.; Sutherlin, D. P.; Zhu, B.-Y.;
Goldsmith, P.; Bayliss, T.; Folkes, A.; Pegg, N. US 20090247567,
2009. (e) Lipshutz, B. H.; Kayser, F.; Maullin, N. Tetrahedron Lett.
No. 20-73-10043).
R
usia
n
S
cience
F
o
u
n
datio
n
(20-73-1
0
0
4
3)
Supporting Information
1994, 35, 815.
(14) 5-Iodo-4-(aryloxymethyl)thiophene-2-carbaldehydes 6a–o;
General Procedure
Supporting information for this article is available online at
https://doi.org/10.1055/a-1392-2209.
S
u
p
p
ortingI
n
formati
o
nS
u
p
p
ortingInformati
o
n
K2CO3 (138 mg, 1 mmol) and KI (17 mg, 0.1 mmol) were added to
a solution of the appropriate phenol 4a–o (1.1 mmol) and alde-
hyde 2 (287 mg, 1 mmol) in anhyd DMF (3 mL) under an inert
atmosphere, and the mixture was stirred for 60 h. The resulting
mixture was poured into cold H2O and extracted with Et2O (3 × 5
mL). The organic layer was washed sequentially with H2O and
brine, dried (MgSO4), and concentrated in vacuum. Crystalline
products were purified by recrystallization from EtOH whereas
liquid products were purified by column chromatography.
(15) Gol’dfarb, Y. L.; Karmanova, I. B.; Vol’kenshtein, Y. B.; Belen’kii,
L. I. Chem. Heterocycl. Compd. 1978, 11, 1196.
(16) (a) Wolf, W.; Kharasch, N. J. Org. Chem. 1965, 30, 2493.
(b) Martelli, G.; Spagnolo, P.; Tiecco, M. J. Chem. Soc. B 1968,
901. (c) D’Auria, M.; De Mico, A.; D’Onofrio, F.; Piancatelli, G.
J. Chem. Soc., Perkin Trans. 1 1987, 1777.
(17) Thieno[3,2-c]chromene-2-carbaldehydes 7a–p; General Pro-
cedure
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The appropriate ether 5a or 6a–o (1 mmol) was dissolved in
anhyd MeCN (100 mL) and the solution was added to a 2.5 cm-
diameter quartz tube with a volume of 150 mL. The stirred
solution was irradiated by four low-pressure Hg lamps (Philips
TUV G8 T5, max = 254 nm; 32W in total) while it was cooled by
a fan. The solvent was then evaporated in vacuum, and the
residue was purified by column chromatography.
8-Fluoro-4H-thieno[3,2-c]chromene-2-carbaldehyde (7l)
Yellow solid; yield: 150 mg (64%); mp 170–171 °С (EtOH). IR
(KBr): 1656 (С=O) cm–1. 1H NMR (400 MHz, CDCl3):  = 5.27 (s, 2
H, CH2). 6.91–7.01 (m, 2 H, H-6,7), 7.10 (dd, 3J = 8.12, 4J = 2.64, 1
H, H-9), 7.55 (s, H-3, 1 H), 9.88 (s, 1 H, CHO). 13C NMR (101 MHz,
CDCl3):  = 65.50, 110.28, 117.60, 118.30, 119.80, 132.69,
133.38, 141.28, 142.05, 148.82, 157.43, 182.86.
(18) Buchachenko, A. L.; Wasserman, A. M. In Khimija, 1st ed.
Moscow, 1973; 409.
(19) Bogza, Y. P.; Rastrepin, A. A.; Nider, V. V.; Zheleznova, T. Y.;
Stasyuk, A. J.; Kurowska, A.; Laba, K.; Ulyankin, E. B.; Domagala,
W.; Fisyuk, A. S. Dyes Pigm. 2018, 159, 419.
© 2021. Thieme. All rights reserved. Synlett 2021, 32, 790–794