Synthesis and photochromic properties of novel nonsymmetric dihetarylethenes based on benzindole and thiophene

Article abstract of DOI:10.1007/s11172-010-0288-8

Novel nonsymmetric dihetarylethenes 3-(5-methoxy-1,2-dimethyl-1H-benzo[g] indol-3-yl)-4-(3-thienyl)-furan-2,5-dione and 1-alkyl- and 1-aryl-3-(5-methoxy- 1,2-dimethyl-1H-benzo[g]indol-3-yl-4-(3-thienyl)-1(H)-pyrrole-2,5-diones were synthesized. The substitution of the furandione moiety for pyrroledione gives rise to the radiation and photochemical channels of deactivation of the electron excitation energy of dihetarylethenes. The products of photolysis of pyrrolediones undergo recyclization in both the ground and excited states.

Full text of DOI:10.1007/s11172-010-0288-8

Russian Chemical Bulletin, International Edition, Vol. 59, No. 8, pp. 1639—1644, August, 2010
1639
Synthesis and photochromic properties of novel nonsymmetric
dihetarylethenes based on benzindole and thiophene
A. V. Metelitsa,a V. P. Rybalkin,b N. I. Makarova,a P. V. Levchenko,a V. S. Kozyrev,a
E. N. Shepelenko,b L. L. Popova,a V. A. Bren´,a,b and V. I. Minkina,b
aInstitute of Physical and Organic Chemistry, Southern Federal University,
194/2 prosp. Stachki, 344090 RostovꢀonꢀDon, Russian Federation.
Eꢀmail: photo@ipoc.rsu.ru
bSouthern Scientific Center of the Russian Academy of Sciences,
41 ul. Chekhova, 344006 RostovꢀonꢀDon, Russian Federation
Novel nonsymmetric dihetarylethenes 3ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indolꢀ
3ꢀyl)ꢀ4ꢀ(3ꢀthienyl)ꢀfuranꢀ2,5ꢀdione and 1ꢀalkylꢀ and 1ꢀarylꢀ3ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀ
benzo[g]indolꢀ3ꢀylꢀ4ꢀ(3ꢀthienyl)ꢀ1(H)ꢀpyrroleꢀ2,5ꢀdiones were synthesized. The substitution
of the furandione moiety for pyrroledione gives rise to the radiation and photochemical
channels of deactivation of the electron excitation energy of dihetarylethenes. The products
of photolysis of pyrrolediones undergo recyclization in both the ground and excited states.
Key words: benzo[g]indole, dihetarylethene, maleinimide, synthesis, photochromism,
fluorescence, photocolorability, molecular switches.
formed due to the acylation of compound 4 with oxalyl
chloride, and the reaction of acid chloride 5 with
3ꢀthienylacetic acid affords, similarly to the synthesis of
indolemaleic anhydrides,10 3ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ
1Hꢀbenzo[g]indolꢀ3ꢀyl)ꢀ4ꢀ(3ꢀthienyl)furanꢀ2,5ꢀdione
(6). The reaction of furandione 6 with alkylꢀ and arylꢀ
amines gives 1ꢀalkylꢀ and 1ꢀarylꢀ3ꢀ(5ꢀmethoxyꢀ1,2ꢀdiꢀ
methylꢀ1Hꢀbenzo[g]indolꢀ3ꢀyl)ꢀ4ꢀ(3ꢀthienyl)ꢀ1(H)pyrꢀ
roleꢀ2,5ꢀdiones 7a—d (Scheme 1).
In recent decades, demands of optoelectronics, moꢀ
lecular electronics, and chemosensor engineering of novel
polyfunctional materials became a powerful stimulus for
the creation of various types of photochromic comꢀ
pounds,1—5 among which dihetarylethenes can be first
distinguished due to high thermal stability of their isoꢀ
meric forms and resistance to photodegradation.4,6 Fluoꢀ
rescence of one of the isomeric forms provides possibiliꢀ
ties for optical information recording and creation of moꢀ
lecular switches with the fluorescent signal function.5—7
Many dihetarylethenes with various heterocyclic substituꢀ
ents, such as thiophene, benzothiophene, furan, benzoꢀ
furan, thiazole, indole, pyrazole, and pyrrole moieties,
have been synthesized to the present time. In the most
part of cases, these are symmetric systems. With the purꢀ
pose to extend the range of structural types of dihetarylꢀ
ethenes and to study their reactivity and photochromism,
we synthesized and studied nonsymmetric ethenes
(furanꢀ and pyrrolediones) containing the thiophene and
benzo[g]indole moieties as hetaryl residues.
The presence of the anhydride moiety in molecule 6
predetermines the appearance of the IR spectral bands at
1760 and 1830 cm—1 in the range of absorption of carboꢀ
nyl groups. The imide structure of compounds 7a—d is
confirmed by the presence of bands at 1690 and 1750 cm–1
.
The 1H NMR spectra of ethenes 6 and 7a—d contain
signals of benzindole and thiophene moieties, whereas for
compounds 7a—d they contain additionally signals of the
substituents at the imide nitrogen atom (see Experimenꢀ
tal). In addition, no signals of aliphatic protons at the
sp3ꢀhybridized carbon atom of the annulated thiophene
moiety makes it possible to ascribe the structure of the
open form A to compounds 6 and 7a—d (Scheme 2).
The electronic absorption spectra of dihetarylethenes
6 and 7a—d (form А) are characterized by longꢀwaveꢀ
length absorption bands with maxima in the range from
442 to 451 nm and the molar absorption coefficients
7190—9570 L mol–1 cm–1 (see Table 1, Fig. 1). An insigꢀ
nificant bathochromic shift of the longꢀwavelength
absorption maxima of pyrroleꢀ2,5ꢀdiones 7a, 7b, 7c, and
Results and Discussion
The methylation of ethyl 5ꢀhydroxyꢀ1,2ꢀdimethylꢀ1Hꢀ
indoleꢀ3ꢀcarboxylate (1)8 yielded ethyl 5ꢀmethoxyꢀ1,2ꢀ
dimethylꢀ1Hꢀbenzo[g]indoleꢀ3ꢀcarboxylate (2),9 which
was hydrolyzed to acid 3. Benzindole 4 was obtained by
the decarboxylation of acid 3. 2ꢀ(5ꢀMethoxyꢀ1,2ꢀdiꢀ
methylꢀ1Hꢀbenzo[g]indolꢀ3ꢀyl)oxoacetyl chloride (5) was
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1596—1601, August, 2010.
1066ꢀ5285/10/5908ꢀ1639 © 2010 Springer Science+Business Media, Inc.

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Metelitsa et al.
Scheme 1
1
2
7: R = Bui (a), CH2Ph (b), Ph (c), 3ꢀpyridylmethyl (d)
of pyrrolediones 7a—d, the Δλ value reflects the contribuꢀ
tion of the substituents at the nitrogen atom to the electron
density delocalization of the main chromophoric core.
Pyrroleꢀ2,5ꢀdione derivatives 7a—d in the open form
А manifest fluorescence properties at room temperature
in heptane solutions, unlike furandione 6 that does not
fluoresce under these conditions. The fluorescence band
maxima of compounds 7a—d range from 542 to 560 nm.
The excitation fluorescence spectra agree well with the
longꢀwavelength absorption bands of pyrrolediones in
form А (see Table 1). The fluorescence quantum yields of
dihetarylethenes 7a,b several times exceed the values of
fluorescence efficiency of compounds 7c,d (see Table 1).
The irradiation of solutions of furandione 6 at 293 K
gives no noticeable changes in the electronic absorption
spectra. On the contrary, solutions of pyrrolediones 7a—d
are colored upon photolysis and this is accompanied by
spectral changes characteristic of (2π+2π+2π) photoꢀ
cyclization reactions of dihetarylethenes.4 For example,
the irradiation of solutions of compounds 7a—d in hepꢀ
tane gives rise to new longꢀwavelength absorption bands
with maxima at 589—603 nm, indicating the formation
of cyclic isomers B (see Scheme 2, Table 1, Fig. 1). The
influence of the substituents at the nitrogen atom of the
pyrroledione moiety on the position of the longꢀwaveꢀ
Scheme 2
Х = NR
7d compared to the maximum of the corresponding
absorption band of furanꢀ2,5ꢀdione 6 by Δλ = 2, 5, 9, and
8 nm, respectively, is observed (see Table 1). In the series

Photochromic properties of dihetarylethenes
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
1641
Table 1. Spectral absorption and fluorescence characteristics of the isomeric forms of dihetarylethenes 6
and 7a—d in heptane at 293 K
Comꢀ
pound
Initial form А
Photoinduced
form В,
absorption, λmax/nm
Absorption
Fluorescence
λmax/nm Quantum
λ
max/nm
ε
max
/L mol—1 cm–1
yield
excitation
emission
6
442
444
447
451
450
9570
7190
7280
7300
8480
—
—
—
—
7a
7b
7c
7d
445
445
450
450
542
555
557
560
0.030
0.020
0.004
0.005
589
591
603
595
the photoreaction (Ф) by the molar absorption coeffiꢀ
cient value at the longꢀwavelength absorption maximum
A
1
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
of the photoinduced form (ε B) corresponding to one
2
3
max
of concepts about "photocolorability" (see Ref. 11). The
4
5
efficiencies of cyclization photoreactions expressed in
"photocolorability" terms (ФAB•ε
B) are given in
max
Table 2. The estimation of the quantum yields of photoꢀ
cyclization ФАВ at the averaged value of the molar absorpꢀ
tion coefficient ε B = 10 000 L mol–1 cm–1, taken from
max
published data,12—17 gives values of 0.04—0.06.
A backward thermal process (very slow at room
temperature) returning the system to the initial state is
observed after the end of irradiation. The recyclization
kinetics obeys the monoexponential law (Fig. 2). The
rate constants of thermal reactions B → A at 293 K
in heptane are listed in Table 2 and lie in the range
300
400
500
600
700 λ/nm
Fig. 1. Electronic absorption spectra of a solution of dihetarylꢀ
ethene 7a in heptane before (1) and after irradiation with the
light with the wavelength 436 nm for 1 (2), 2 (3), 3 (4), and 8 s (5)
(c = 3.1•10–5 mol L–1, T = 293 K).
(0.29—3.63)•10–5 s–1
.
The backward photoreaction is characteristic of pyrꢀ
rolediones 7a—d along with thermal recyclization. The
values obtained for efficiencies for the photorecyclization
reaction B → A are estimated by ФВА•εmax and depend
insignificantly on the substituents at the nitrogen atom of
the pyrroledione moiety (see Table 2). The ratio of the
quantum yields of the direct and backward photoreacꢀ
tions (ФАВ/ФВА) for compounds 7a—d is 0.19—0.28 and
indicates a substantially higher efficiency of ring opening,
which has been observed earlier for the photochromic
length absorption maxima of the forms B appears to the
same extent as for the noncyclic isomers А: the conjugaꢀ
tion of the pyrroledione ring with the πꢀsystem of the
substituent at the nitrogen atom in the series 7a, 7b, 7d,
and 7c leads to the bathochromic shift of the longꢀwaveꢀ
length absorption maximum. Unlike the initial forms А,
the cyclic isomers B have no fluorescence. For quantitaꢀ
tive characterization of phototransformations, we used
the parameter, being the product of the quantum yield of
Table 2. Characteristics of photochromic transformations of dihetarylethenes 7a—d
in heptane at 293 K
Comꢀ
pound
Photochemical processes
Coloration, Decoloration,
Thermal decoloration
ФAB/ФBA
kBA•10–5
B*
B*
ФAB•ε
•102
ФBA•ε
•102
/s–1
max
max
7a
7b
7c
7d
5.3
6.5
4.2
4.2
22.1
23.0
22.1
20.9
0.24
0.28
0.19
0.20
1.10
0.29
0.89
3.63
* In L mol–1 cm–1
.

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Metelitsa et al.
ethene solutions were detected directly during irradiation on a
Cary 50 spectrophotometer equipped with a thermostat. A xenon
lamp with the monochromator for picking out narrow spectral
lines (Newport) was used as a radiation source. The optical
radiation intensity was determined with a Newport 2935 power
meter of optical radiation. The optical radiation intensity
at the wavelengths used (460 and 580 nm) was 4.17•1015 and
ln(Ai – A )/(A0 – A )
A
∝
∝
0
–2
–4
0.08
0.06
0.04
0.02
0
1.33•1015 photon s–1, respectively. To determine the parameters
B
ФAB•ε
and ФBA•ε B, the slope ratio of the tangent was
max
max
0
10000 20000 30000 40000
t/s
calculated at the initial time moment from the kinetic photoꢀ
coloration and photodecoloration curves. Equal absorbances of
solutions of the dihetarylethenes at the irradiation wavelengths
B
were selected in experiments on the determination of ФAB•ε
max
0
10000
20000
30000
40000
t/s
B
and ФBA•ε
.
max
Fig. 2. Kinetic curve of the thermal relaxation of dihetarylethene
7d in heptane (c = 3.6•10–5 mol L–1, T = 318 K). inset: linear
anamorphosis of the kinetic curve of thermal relaxation.
The IR spectra of samples in Nujol were recorded on a
Specord 75 IR instrument. The 1H NMR spectra in CDCl3 were
obtained on a Varian Unityꢀ300 instrument (300 MHz) using
HMDS as the external standard.
rearrangements of bis(2ꢀthienyl)perfluorocyclopentene18
(see Table 2). The estimated quantum yield values for the
photoreactions B → A are 0.21—0.23. The ratios obtained
for the quantum yields of direct and backward photoreacꢀ
tions explain the low level of the content of colored
isomers in the photostationary state estimated by a low
value of absorbances achieved at the absorption band
maxima of the photoinduced forms. The appearance of
the photostationary state due to very low rate constants of
the backward thermal processes is mainly related to the
strong overlapping (see Fig. 1) of the absorption bands,
which is caused by the transition S0 → S1 of the initial
form А and the transition S0 → S2 of the photoinduced
isomer В, which upon the excitation of the form А ineviꢀ
tably results in the excitation of the form В.
Thus, we developed the procedure of synthesis and
synthesized novel representatives of the class of nonꢀ
symmetric dihetarylethenes: 3ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ
1Hꢀbenzo[g]indolꢀ3ꢀyl)ꢀ4ꢀ(3ꢀthienyl)furanꢀ2,5ꢀdione
and 1ꢀalkylꢀ and 1ꢀarylꢀ3ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀ
benzo[g]indolꢀ3ꢀyl)ꢀ4ꢀ(3ꢀthienyl)ꢀ1(H)ꢀpyrroleꢀ2,5ꢀdiones.
Unlike furandione, pyrrolediones exhibit photochromic
and fluorescence properties in solutions. Recyclization
processes of the photolysis products of pyrrolediones
occur in both the ground and excited states. The quantum
yields of photocoloration of pyrrolediones are by 4—5 times
lower than the photodecoloration quantum yields.
Ethyl 5ꢀhydroxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indoleꢀ3ꢀcarbꢀ
oxylate (1). Acetic acid (20—25 mL) was added to 1,4ꢀnaphꢀ
thoquinone (11 g, 0.07 mol) until an easily stirred mixture
was obtained. Then ethyl Nꢀmethyl βꢀaminocrotonate (10 mL,
0.007 mol) was added by small portions at 5—10 °C with
thorough stirring. The reaction mixture turned pink and gradually
thickened. The reaction mixture was stored for ~14 h. A preꢀ
cipitate of acid 1 that formed was filtered off, thoroughly washed
with a small amount of acetic acid and then with methanol,
and dried in air. Recrystallization from a mixture of butanol
(20 mL) and DMF (60 mL) gave pale pink crystals in 93% yield,
m.p. 279—280 °C (cf. Ref. 8: m.p. 279—280 °C). 1H NMR
(DMSOꢀd6), δ: 1.46 (t, 3 H, Me, J = 7.1 Hz); 2.78 (s, 3 H, Me);
4.12 (s, 3 H, NMe); 4.35 (q, 2 H, J = 7.1 Hz); 7.30—7.55 (m,
2 H, Ar); 7.64 (s, 1 H, Ar); 8.22—8.30, 8.40—8.48 (both m, 1 H
each, Ar); 9.42 (s, 1 H, OH). Found (%): C, 72.19; H, 6.10;
N, 4.80. C17H17NO3. Calculated (%): C, 72.07; H, 6.05; N, 4.94.
Ethyl 5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indoleꢀ3ꢀcarbꢀ
oxylate (2). Anhydrous DMSO (23 mL), NaOH thoroughly
milled in a mortar (1.84 g, 46 mmol), and 3ꢀcarboethoxyꢀ
5ꢀhydroxyꢀ1,2ꢀdimethylꢀbenzo[g]indole (6.51 g) were placed
in a 100ꢀmL threeꢀnecked flask equipped with a stirrer and
a dropping funnel. Benzoindole was partially dissolved, and
the reaction mixture turned dark green. At 5 °C CH3I (7.1 mL,
114 mmol) was added dropwise to this mixture with stirring for
1 h. The reaction mixture gradually became homogeneous
and turned pale pink, and a white precipitate began to form.
The mixture was stirred for 4 h more and stored for ~14 h. The
reaction mixture was poured to 200 mL of water with ice. An oil
that formed solidified after trituration with methanol. The
precipitate was filtered off, washed with water and recrystallized
from a heavy petroleum ether—toluene (1 : 3) mixture. The yield
was 70.2%, m.p.. 143—145 °C (cf. Ref. 9: m.p. 228—229 °C).
1H NMR, δ: 1.48 (t, 3 H, Ме, J = 7.1 Hz); 2.82 (s, 3 H, Ме);
4.07 (s, 3 H, NМе); 4.15 (s, 3 H, OМе); 4.42 (q, 2 H, CH2,
J = 7.1 Hz); 7.40—7.60 (m, 2 H, Ar); 7.75 (s, 1 H, Ar);
8.37—8.48 (m, 2 H, Ar). Found (%): C, 72.59; H, 6.33; N, 4.80.
C18H19NO3. Calculated (%): C, 72.71; H, 6.44; N, 4.71.
5ꢀMethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indoleꢀ3ꢀcarboxylic
acid (3). Ester 2 (8.9 g, 0.03 mol) was added by portions with
stirring to a melt of KOH (16.8 g, 0.3 mol) and H2О (4.2 g)
heated to 155—160 °C. The mixture was thoroughly stirred
at this temperature for 30 min. Then the melt was heated to
Experimental
Electronic absorption spectra were recorded on a Cary 100
spectrophotometer (Varian). Fluorescence measurements were
carried out on a Cary Eclipse spectrofluorimeter (Varian).
Fluorescence quantum yields were determined by the Parker—
Reis method19 using 3ꢀmethoxybenzanthrone in toluene (ϕ = 0.1,
λ
= 365 nm) as a standard luminophore.20 Solutions in a
exc
quartz cell (l = 1 cm) were irradiated with a DRShꢀ250 mercury
lamp with a set of interference light filters to pick out lines of the
mercury spectrum. Kinetic curves of photocoloration of dihetarylꢀ

Photochromic properties of dihetarylethenes
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
1643
200—210 °C and stirred at this temperature to solidification.
After cooling the solid residue was dissolved in water (700 mL).
The resulting solution was treated with active carbon, filtered,
and acidified with dilute hydrochloric acid to the acidic
pH. A precipitate of acid 3 that formed was filtered off,
and thoroughly washed with water. The yield was 93%,
decomp. temp. 210—220 °C. 1H NMR (DMSOꢀd6), δ: 2.80 (s,
3 H, Ме); 4.00 (s, 3 H, NМе); 4.17 (s, 3 H, OМе); 7.32—7.60,
8.13—8.60 (both m, 2 H each, Ar); 7.72 (s, 1 H, Ar); 11.82 (br.s,
1 H, ОH). Found (%): C, 71.52; H, 5.83; N, 5.17. C16H15NO3.
Calculated (%): C, 71.36; H, 5.61; N, 5.20.
according to the general procedure from furandione 6
and isobutylamine. The yield was 33.3%. Orange crystals,
m.p. 150—151 °C. IR, ν/cm–1: 1690, 1750 (C=О). 1H NMR, δ:
1.00 (d, 6 H, Ме, J = 7.2 Hz); 2.06—2.24 (m, 1 H, CH); 2.43
(s, 3 H, Ме); 3.51 (m, 2 H, CH2); 3.64 (s, 3 H, NМе); 4.21 (s,
3 H, ОМе); 6.40, 8.12 (both s, 1 H each, Ar); 7.04—7.20,
7.40—7.62, 8.36—8.52 (all m, 2 H each, Ar). Found (%):
C, 70.69; H, 5.65; N, 6.03. C27H26N2O3S. Calculated (%):
C, 70.72; H, 5.71; N, 6.11.
1ꢀBenzylꢀ3ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indolꢀ
3ꢀyl)ꢀ4ꢀ(3ꢀthienyl)ꢀ1Hꢀpyrroleꢀ2,5ꢀdione (7b) was synꢀ
thesized from furandione 6 and benzylamine according to
the general procedure. The yield was 73.5%. Orange crystals,
m.p. 199—200 °C. IR, ν/cm–1: 1690, 1750 (C=О). 1H NMR, δ:
2.43 (s, 3 H, Ме); 3.64 (s, 3 H, NМе); 4.21 (s, 3 H, ОМе); 4.85
(s, 2 H, CH2); 7.05—7.30 (m, 10 H, Ar); 8.11 (s, 1 H, Ar); 8.35
(d, 1 H, Ar, J = 8.6 Hz); 8.94 (d, 1 H, Ar, J = 8.9 Hz). Found (%):
C, 73.11; H, 4.87; N, 5.61. C30H24N2O3S. Calculated (%):
C, 73.15; H, 4.91; N, 5.69.
3ꢀ(5ꢀMethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indolꢀ3ꢀyl)ꢀ
4ꢀ(3ꢀthienyl)ꢀ1ꢀphenylꢀ1Hꢀpyrroleꢀ2,5ꢀdione (7c) was synꢀ
thesized from furandione 6 and aniline according to the
general procedure. The yield was 80.7%. Orange crystals,
m.p. 235—236 °C. IR, ν/cm–1: 1690, 1750 (C=О). 1H NMR, δ:
2.52 (s, 3 H, Ме); 3.66 (s, 3 H, NМе); 4.28 (s, 3 H, ОМе);
6.44 (s, 1 H, Ar); 7.10—7.28 (m, 2 H, Ar); 7.36—7.68 (m, 7 H,
Ar); 8.21 (m, 1 H, Ar); 8.36—8.52 (m, 2 H, Аr). Found (%):
C, 72.71; H, 4.57; N, 5.80. C29H22N2O3S. Calculated (%):
C, 72.78; H 4.63; N, 5.85.
3ꢀ(5ꢀMethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indolꢀ3ꢀyl)ꢀ1ꢀmethylꢀ
pyridinꢀ3ꢀylꢀ4ꢀ(3ꢀthienyl)ꢀ1Hꢀpyrroleꢀ2,5ꢀdione (7d) was synꢀ
thesized from furandione 6 and 3ꢀpyridylmethylamine according
to the general procedure. The yield was 62.5%. Orange crystals,
m.p. 200—201 °C. IR, ν/cm–1: 1690, 1750 (C=О). 1H NMR, δ:
2.44 (s, 3 H, Ме); 3.62 (s, 3 H, NМе); 4.20 (s, 3 H, ОМе);
4.80—4.98 (m, 2 H, CH2); 6.38 (s, 1 H, Ar); 7.08—7.20,
7.32—7.48 (both m, 2 H each, Ar); 7.54—7.66, 7.90—7.98, 8.08,
8.80 (all m, 1 H each, Ar); 8.32—8.64 (m, 3 H, Ar). Found (%):
C, 70.52; H, 4.66; N, 8.48. C29H23N3O3S. Calculated (%):
C, 70.57; H, 4.70; N, 8.51.
5ꢀMethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indole (4). Acid 3
(5 g) was heated at 230—245 °C until carbon dioxide
stopped evolving (5—10 min). Upon cooling the resulting solid
product was recrystallized from butanol. The yield was 90%,
1
m.p. 123—124 °C. H NMR, δ: 2.50 (s, 3 H, Ме); 4.02 (s, 3 H,
NМе); 4.13 (s, 3 H, OМе); 6.33, 7.0 (both s, 1 H each, Ar);
7.36—7.58 (m, 2 H, Ar); 8.35—8.50 (m, 2 H, Ar). Found (%):
C, 79.7; H, 6.03; N, 6.70. C15H15NO. Calculated (%): C, 79.97;
H, 6.71; N, 6.22.
2ꢀ(5ꢀMethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indolꢀ3ꢀyl)oxoꢀ
acetyl chloride (5). A solution of benzoindole 4 (450 mg, 2 mmol)
in diethyl ether (20 mL) was cooled to 0 °C, and oxalyl chloride
(0.25 mL) was slowly added dropwise. Orangeꢀyellow needles
gradually precipitated from the solution. The mixture was stored
for 40 min at ~20 °C. A precipitate of oxoacetyl chloride 5 was
filtered off and washed with ether. The yield was 87%. 1H NMR,
δ: 2.74 (s, 3 H, Ме); 4.07 (s, 3 H, NМе); 4.19 (s, 3 H, ОМе);
7.25—7.45 (m, 3 H, Ar), 8.35—8.48 (m, 2 H, Ar). Found (%):
C, 63.47; H, 4.50; N, 4.79. C16H14ClNO3. Calculated (%):
C, 63.27; H, 4.65; N, 4.61.
3ꢀ(5ꢀMethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indolꢀ3ꢀyl)ꢀ4ꢀ
(3ꢀthienyl)furanꢀ2,5ꢀdione (6). 3ꢀThienylacetic acid (142 mg,
1 mmol) and freshly distilled triethylamine (0.3 mL) were added
to a solution of oxoacetyl chloride 5 (315 mg, 1 mmol) in
anhydrous benzene (8 mL). The solution turned orangeꢀred,
and triethylamine hydrochloride precipitated. The reaction
mixture was stored for ~14 h. The precipitate was filtered off.
Benzene was removed on a rotary evaporator. The yield of
furandione 6 was 36.5%. The product obtained was purified by
column chromatography (silica gel—chloroform), chloroform
was distilled off, and the residue was twice recrystallized from
This work was financially supported by the Federal
Target Program "Scientific and Pedagogical Specialists
of Innovation Russia for 2009—2013" (State Contract
of the Federal Agency on Science and Innovations
No 02.740.11.0456) and the Russian Foundation for
Basic Research (Project No. 09ꢀ03ꢀ00813).
MeCN. Redꢀorange crystals, m.p. 259—260 °C. IR, ν/cm–1
:
1760, 1830 (C=О). 1H NMR, δ: 2.48 (s, 3 H, Ме); 3.66 (s,
3 H, NМе); 4.24 (s, 3 H, ОМе); 6.30 (s, 1 H, Ar); 7.18—7.28,
7.42—7.66, 8.36—8.52 (all m, 2 H each, Ar); 8.20 (m, 1 H, Ar).
Found (%): C, 68.59; H, 4.35; N, 3.41. C23H17NO4S. Calculꢀ
ated (%): C, 68.47; H, 4.25; N, 3.47.
Synthesis of 3ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀbenzo[g]indolꢀ
3ꢀyl)ꢀ4ꢀ(3ꢀthienyl)ꢀ1Hꢀpyrroleꢀ2,5ꢀdiones 7a—d (general proceꢀ
dure). The corresponding amine (3.9 mmol) was added to
furandione 6 (0.13 mmol), and the mixture was heated for
10 min. Then isopropyl alcohol (10 mL) was poured to the
reaction mixture, and the mixture was refluxed for 15 min.
The mixture was cooled, and the solvent was distilled off. The
pyrrolediones obtained were purified by column chromatography
(silica gel—chloroform), and chloroform was distilled off. The
products were dried in air. The yields of pyrrolediones were
33—80%.
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Received March 10, 2010;
in revised form April 30, 2010