Photochromic dihetarylethenes 11. Synthesis and photochromic properties of diarylethenes containing furan or furopyrimidine bridges

Article abstract of DOI:10.1023/A:1015004101130

Procedures were developed for the synthesis of substituted bis(2,5-dimcthyl-3-thienyl)furans based on 1,2-bis(2.5-dimethyl-3-thienyl)-2-hydroxycthanone. Dithienylethene structures in which the ethene fragment is involved in the furan or furopyrimidine sys

Full text of DOI:10.1023/A:1015004101130

2424
Russian Chemical Bulletin, International Edition, Vol. 50, No. 12, pp. 2424—2427, December, 2001
Photochromic dihetarylethenes
11.* Synthesis and photochromic properties of diarylethenes
containing furan or furopyrimidine bridges
M. M. Krayushkin,a« S. N. Ivanov,a A. Yu. Martynkin,a B. V. Lichitsky,a A. A. Dudinov,a and B. M. Uzhinovb
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. E-mail: mkray@ioc.ac.ru
bDepartment of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119899 Moscow, Russian Federation.
Fax: +7 (095) 932 8846. E-mail: uzhinov@light.chem.msu.su
Procedures were developed for the synthesis of substituted bis(2,5-dimethyl-3-thienyl)furans
based on 1,2-bis(2,5-dimethyl-3-thienyl)-2-hydroxyethanone. Dithienylethene structures in
which the ethene fragment is involved in the furan or furopyrimidine system possess
photochromic properties and their open forms exhibit fluorescence.
Key words: furan, furopyrimidines, α-hydroxyketone, photochromes, 1,2-dithienylethenes,
fluorescence.
Scheme 1
Photochromic thermally irreversible dihetarylethenes
are being extensively studied as elements of optical
memory, photoswitches, dosimeters, etc.2,3 Previously,
we have synthesized dithienylethenes containing triaz-
ine4 or azole5 bridges and demonstrated that the former
compounds do not possess photochromic properties,
whereas the azole derivatives bearing electron-donating
substituents are photochromes. As part of continuing
studies aimed at searching for new readily accessible
compounds exhibiting photochromic activity, we devel-
oped procedures for the synthesis of substituted
bis(2,5-dimethyl-3-thienyl)furans in which the ethene
bridges are involved in the furan or furopyrimidine
systems.
HO
O
CH2(CN)2
DBU
Me
Me
S
S
Me Me
1
NH2
CN
O
Me
Me
Structures of this type are often synthesized with the
use of 1,2-bifunctional compounds.6,7 In the present
work, we used thenoin 1, viz., 1,2-bis(2,5-dimethyl-3-
thienyl)-2-hydroxyethanone, as the starting compound.
Its synthesis has been reported previously.4
S
S
Me Me
2
whose reaction with hydroxylamine yielded aminofuro-
pyrimidine N-oxide 6 (Scheme 3).
Treatment of compound 2 with dimedone produced
enaminone 7. According to a procedure developed by us
previously,8 the reaction of the latter compound with
arylmethylidenemalononitrile afforded furopyrimido-
quinoline 8 (Scheme 4).
We examined the photochromic and spectroscopic
characteristics of compounds 2—4, 6, and 8 (solutions
in MeCN). In the absorption spectra of the open forms
of compounds 2, 3, 6, and 8, the long-wavelength bands
are observed in the narrow range of 304—310 nm. The
spectrum of hydroxypyrimidine 4 has the analogous
band at 375 nm, i.e., it is shifted bathochromically by
∼65 nm. The conversion of aminopyrimidine 3 into
Results and Discussion
The reaction of thenoin 1 with malononitrile in the
presence of DBU afforded furan derivative 2 (Scheme 1).
Treatment of compound 2 with formamide or formic
acid gave rise to the amino or oxo derivatives of
furopyrimidine (3 or 4), respectively, in good yields
(Scheme 2).
By analogy with the known procedure,6 we used
compound 2 for the synthesis of amidine 5,
* For Part 10, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2315—2318, December, 2001.
1066-5285/01/5012-2424 $25.00 © 2001 Plenum Publishing Corporation

Photochromic dihetarylethenes
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 12, December, 2001 2425
Scheme 2
Scheme 4
N
N
O
O
NH2
HCONH2
2
O
HN
CN
O
Me
Me
HCOOH
S
S
4-ClC6H4CH C(CN)2
O
Me Me
2
3
Me
Me
N
S
S
NH
Me Me
O
7
O
O
C6H4Cl-4
CN
Me
Me
S
S
Me Me
4
N
N
O
N-oxide 6 is accompanied by the hypsochromic shift of
the long-wavelength band in the absorption spectrum of
the cyclic form by 10 nm.
NH2
All products, except for furopyrimidoquinoline 8,
exhibit photochromic properties (Scheme 5; Table 1).
The cyclic forms of the photochromes appeared to be
unstable. After storage at room temperature for one day,
their optical densities in the maximum of the long-
wavelength absorption band were halved. Fatigue resis-
tance2,3 of these compounds is rather low. Thus after
three—five transitions from the open to the cyclic form
and back (on irradiation), the optical density of the
Me
Me
S
S
Me Me
8
Scheme 5
hν1
hν2
Scheme 3
Me
Me
Me
Me
S
S
S
S
Me Me
Me Me
N
N
cyclic form was recovered by, at most, 80%. Taking into
account the results obtained previously,5 it can be as-
sumed that low fatigue resistance in solutions is typical
of bis(2,5-dimethyl-3-thienyl)ethenes.
CN
O
(MeO)2CHNMe2
NH2OH
2
Me
Me
S
S
Table 1. Maxima of the long-wavelength bands of the elec-
tronic absorption spectra (λmax/nm) and the fluorescence spec-
tra (λfl/nm) for the open (A) and cyclic (B) forms of com-
pounds 2—4, 6, and 8
Me Me
5
–
+
N
O
N
Compound
λmax
λfl(A)
O
NH2
A
B
2
3
4
6
8
304
307
375
310
304
483
505
506
515
—
405
380
510
415
—
Me
Me
S
S
Me Me
6

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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 12, December, 2001
Krayushkin et al.
Earlier, we have demonstrated9,10 that the fluores-
of 0.267 g (81%), m.p. 186—187 °C. Found (%): C, 61.85;
H, 5.06; N, 8.12; S, 19.97. C17H16N2OS2. Calculated (%):
C, 62.17; H, 4.91; N, 8.53; S, 19.52. 1H NMR (DMSO-d6), δ:
1.98, 2.04, 2.30, and 2.39 (all s, 3 H each, Me); 6.46 and 6.61
(both s, 1 H each, CH); 7.50 (s, 2 H, NH2).
4-Amino-5,6-bis(2,5-dimethyl-3-thienyl)furo[2,3-d]pyrim-
idine (3). One—two drops of Ac2O were added to a solution of
compound 2 (0.130 g, 0.4 mmol) in HCONH2 (2 mL). The
reaction mixture was refluxed for 4 h and then cooled. Water
(5 mL) was added and the precipitate that formed was filtered
off. The product was recrystallized from dioxane and com-
cence properties of dithienylethene photochromes are
favored by the presence of benzooxazole- or oxadiazole-
containing substituents in the thiophene rings as well as
by the formation of thienothiophenes. Although the
structures of compounds 2—4 and 6 do not contain the
above-mentioned aromatic fragments, their open forms
fluoresce in acetonitrile solutions. It should be empha-
sized that this is the first example of fluorescence of
dithienylethenes resulting from the characteristic struc-
tural features of the ethene bridge. The quantum yield of
fluorescence is low (<0.1). Based on the measurements
of the lifetime of the excited state, the observed fluores-
cence can be assigned to emission from the π—π* state.
The cyclic forms of the photochromes under study do
not exhibit fluorescence.
To summarize, we have developed procedures
for the synthesis of substituted bis(2,5-dimethyl-3-
thienyl)ethenes in which the ethene fragment is involved
in the furan or furopyrimidine systems. It was found for
the first time that dihetarylethenes containing the
2,5-dimethylthienyl fragments fluoresce due to the char-
acteristic features of the heterocyclic bridging system.
pound
3 was obtained in a yield of 0.090 g (63%),
m.p. 211—212 °C. Found (%): C, 60.43; H, 4.95; N, 12.20;
S, 18.59. C18H17N3OS2. Calculated (%): C, 60.82; H, 4.82;
N, 11.82; S, 18.04. 1H NMR (DMSO-d6), δ: 2.02, 2.21, 2.32,
and 2.44 (all s, 3 H each, Me); 6.53 (s, 1 H, CH); 6.62 (br.s,
2 H, NH2); 6.75 (s, 1 H, CH); 8.23 (s, 1 H, CH arom.).
5,6-Bis(2,5-dimethyl-3-thienyl)-3,4-dihydrofuro[2,3-d]pyr-
imidin-4-one (4). A mixture of compound 2 (0.164 g, 0.5 mmol)
and HCOOH (2 mL) was refluxed for 8 h and then cooled.
Water (5 mL) was added and the precipitate that formed was
filtered off. The product was recrystallized from dioxane and
compound 4 was obtained in a yield of 0.098 g (55%), m.p.
143—144 °C. Found (%): C, 60.28; H, 4.47; N, 8.09; S, 18.32.
C
18H16N2O2S2. Calculated (%): C, 60.65; H, 4.52; N, 7.86;
S, 17.99. 1H NMR (DMSO-d6), δ: 1.96, 2.03, 2.34, and 2.38
(all s, 3 H each, Me); 6.59 and 6.62 (both s, 1 H each, CH);
8.14 (d, 1 H, CH arom., J = 2.1 Hz); 12.62 (br.s, 1 H, NH).
N-[3-Cyano-4,5-bis(2,5-dimethyl-3-thienyl)-2-furyl]-N,N´-
dimethylformimidamide (5). A mixture of compound 2 (0.450 g,
1.4 mmol) and (MeO)2CHNMe2 (0.245 g, 2.1 mmol) in
anhydrous MeOH (2 mL) was refluxed with stirring for 2 h and
then cooled. Water (3 mL) was added and the precipitate was
filtered off. The product was recrystallized from aqueous EtOH
and compound 5 was obtained in a yield of 0.455 g (85%),
m.p. 93—94 °C. Found (%): C, 62.41; H, 5.64; N, 11.23;
S, 16.89. C20H21N3OS2. Calculated (%): C, 62.63; H, 5.52;
N, 10.96; S, 16.72. 1H NMR (DMSO-d6), δ: 2.01, 2.08, 2.31,
2.39, 3.04, and 3.15 (all s, 3 H each, Me); 6.54 and 6.63
(both s, 1 H each, CH); 8.32 (s, 1 H, N=CH).
Experimental
The 1H NMR spectra were recorded on Bruker AM-300
(300.13 MHz) and Bruker WM-250 (250.13 MHz) instruments
in DMSO-d6 and CDCl3. The melting points were measured
on a Boetius heating stage and were not corrected. The mass
spectrum (EI) was obtained on a Kratos MS-30 instrument
with direct inlet of the sample into the ion source; the energy
of ionizing electrons was 70 eV. The course of the reactions
and the purities of the products were monitored by TLC on
Silica gel 60 F254 plates (Merck) using an AcOEt—hexane
solvent system.
The photochromic characteristics of compounds 2—4, 6,
and 8 were examined for solutions in MeCN. Acetonitrile of
special-purity grade was used in the measurements. Samples
were irradiated with a DRSh-500 mercury lamp using light
filters to separate lines of the mercury spectrum (λ = 313, 546,
and 578 nm). The intensity of radiation of the mercury lamp
was determined using an F4 photodetector calibrated using a
ferrioxalate actinometer11 for λ = 313 nm and using an
actinometer based on the Reinecke salt12 for λ = 546 and
578 nm. The electronic absorption spectra were recorded on a
Shimadzu UV-3100 spectrophotometer. The fluorescence spec-
tra were measured on an Elyumin-2M spectrofluorometer with
excitation in the maximum of the absorption spectrum of the
compound under study. Since the fluorescence excitation spectra
of the open forms corrected for the intensity of the exciting
light are identical with the electronic absorption spectra of
these forms, the observed fluorescence is attributable to emis-
sion of the open forms of the compounds under study.
2-Amino-4,5-bis(2,5-dimethyl-3-thienyl)furan-3-carbo-
nitrile (2). Diazabicycloundecene (DBU) (0.228 g, 1.5 mmol)
was added to a solution of thenoin 1 4 (0.280 g, 1 mmol) and
malononitrile (0.110 g, 1.66 mmol) in EtOH (3 mL). The
reaction mixture was heated with stirring at 65—70 °C for 4 h
and then cooled. Water (3 mL) was added and the precipitate
that formed was filtered off. The product was recrystallized
from aqueous EtOH and compound 2 was obtained in a yield
4-Amino-5,6-bis(2,5-dimethyl-3-thienyl)furo[2,3-d]pyr-
imidine 3-oxide (6). A mixture of compound 5 (0.100 g,
0.3 mmol) and NH2OH•HCl (0.070 g, 1 mmol) in EtOH
(1.5 mL) was refluxed for 5—6 h and then cooled. Water
(5 mL) was added and the precipitate was filtered off.
The product was recrystallized from EtOH and com-
pound 6 was obtained in a yield of 0.085 g (76%), m.p.
109—110 °C. Found (%): C, 57.97; H, 4.54; N, 11.64; S, 16.88.
C18H17N3O2S2. Calculated (%): C, 58.20; H, 4.61; N, 11.31;
S, 17.26. 1H NMR (DMSO-d6), δ: 2.03, 2.23, 2.32, and 2.44
(all s, 3 H each, Me); 6.51 and 6.71 (both s, 1 H each, CH);
7.09 (br.s,
2 H, NH2); 8.69 (s, 1 H, CH arom.). MS,
m/z (Irel (%)): 371 [M+] (20).
2-[(5,5-Dimethyl-3-oxocyclohex-1-enyl)amino]-4,5-
bis(2,5-dimethyl-3-thienyl)furan-3-carbonitrile (7). A solution
of dimedone (0.140 g, 1 mmol), compound 2 (0.329 g, 1 mmol),
and p-toluenesulfonic acid (0.02 g, 0.0001 mol) in benzene
(5 mL) was refluxed with the use of a Dean—Stark trap for 5 h.
Then the reaction mixture was cooled and the precipitate of
the product that formed was filtered off and washed on a filter
with a small amount of benzene. Enaminoketone 7 was ob-
tained in a yield of 0.328 g (73%), m.p. 88—89 °C. Found (%):
C, 66.78; H, 5.71; N, 6.51; S, 14.01. C25H26N2O2S2. Calcu-
lated (%): C, 66.64; H, 5.82; N, 6.22; S, 14.23. 1H NMR
(DMSO-d6), δ: 1.06 (s, 6 H, 2 Me); 2.01 and 2.11 (both s,
3 H each, Me); 2.15 (s, 2 H, CH2); 2.31 and 2.42 (both s,

Photochromic dihetarylethenes
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 12, December, 2001 2427
3 H each, Me); 2.45 (s, 2 H, CH2); 5.69, 6.51, and 6.69 (all s,
1 H each, CH); 10.32 (s, 1 H, NH).
5. M. M. Krayushkin, S. N. Ivanov, A. Yu. Martynkin, B. V.
Lichitsky, A. A. Dudinov, and B. M. Uzhinov, Izv. Akad.
Nauk, Ser. Khim., 2001, 113 [Russ. Chem. Bull., Int. Ed.,
2001, 50, 116].
6. F. S. Babichev, Yu. A. Sharanin, V. K. Promonenkov,
V. P. Litvinov, and Yu. M. Volovenko, Vnutrimolekulyarnoe
vzaimodeistvie nitril´noi i aminogrupp [Intramolecular Inter-
actions of the Nitrile and Amino Groups], Naukova Dumka,
Kiev, 1987, 240 pp. (in Russian).
7. T. Hayashi and M. Kagawa, Bull. Chem. Soc. Jpn., 1970,
43, 3290.
8. B. V. Lichitsky, S. N. Ivanov, A. A. Dudinov, S. A.
Woznesensky, and M. M. Krayushkin, Izv. Akad. Nauk,
Ser. Khim., 2001, 2319 [Russ. Chem. Bull., Int. Ed., 2001,
50, 2428].
4-Amino-7-(4-chlorophenyl)-10,10-dimethyl-2,3-bis(2,5-
dimethyl-3-thienyl)-8-oxo-8,9,10,11-tetrahydro-7H-
furo[3´,2´:5,6]pyrimido[1,2-a]quinoline-6-carbonitrile (8). Sev-
eral drops of DBU were added to a solution of enaminoketone
7 (0.292 g, 0.65 mmol) and p-chlorobenzylidenemalononitrile
(0.123 g, 0.65 mmol) in EtOH (3 mL). The reaction mixture
was refluxed for 4 h and then cooled. The precipitate that
formed was filtered off and washed on a filter with a small
amount of EtOH. Furopyrimidoquinoline 8 was obtained in a
yield of 0.162 g (39%), m.p. 262—263 °C. Found (%): C, 65.52;
H, 4.81; Cl, 5.73; N, 8.94; S, 9.76. C35H31ClN4O2S2. Calcu-
lated (%): C, 65.76; H, 4.89; Cl, 5.55; N, 8.76; S, 10.03.
1H NMR (DMSO-d6), δ: 1.00, 1.15, 2.05, and 2.17 (all s,
3 H each, Me); 2.25—2.48 (m, 9 H, Me + CH2); 2.85 (d, 1 H,
CH2, J = 18 Hz); 4.68 (s, 1 H, CH); 5.17 (br.s, 1 H, NH);
6.31 and 6.70 (both br.s, 1 H each, CH); 7.29 (m, 4 H,
H arom.); 8.10 (br.s, 1 H, NH).
9. M. M. Krayushkin, V. N. Yarovenko, F. M. Stoyanovich,
O. Yu. Zolotarskaya, E. I. Chernoburova, I. V. Zavarzin,
A. Yu. Martynkin, and B. M. Uzhinov, Khim. Geterotsikl.
Soedin., 2002, No. 2 [Chem. Heterocycl. Compd., 2002
(Engl. Transl.)].
10. M. M. Krayushkin, F. M. Stoyanovich, O. Yu. Zolotarskaya,
I. V. Murav´ev, A. Yu. Martynkin, L. G. Vorontsova, Z. A.
Starikova, V. L. Ivanov, and B. M. Uzhinov, Izv. Akad.
Nauk, Ser. Khim., 2001, 107 [Russ. Chem. Bull., Int. Ed.,
2001, 50, 110].
11. C. B. Hatchard and C. A. Parker, Proc. Roy. Soc., 1956,
A235, 518.
12. E. W. Wagner and A. W. Adamson, J. Am. Chem. Soc.,
1966, 88, 394.
References
1. M. M. Krayushkin, F. M. Stoyanovich, O. Yu. Zolotarskaya,
I. V. Murav´ev, A. Yu. Martynkin, and B. M. Uzhinov,
Izv. Akad. Nauk, Ser. Khim., 2001, 2311 [Russ. Chem.
Bull., Int. Ed., 2001, 50, 2420].
2. M. M. Krayushkin, Khim. Geterotsikl. Soedin., 2001, 19
[Chem. Heterocycl. Compd., 2001 (Engl. Transl.)].
3. M. Irie, Chem. Rev., 2000, 100, 1685.
4. S. N. Ivanov, B. V. Lichitsky, A. A. Dudinov, A. Yu.
Martynkin, M. M. Krayushkin, and B. M. Uzhinov, Khim.
Geterotsikl. Soedin., 2001, 89 [Chem. Heterocycl. Compd.,
2001 (Engl. Transl.)].
Received April 24, 2001;
in revised form June 14, 2001