Synthesis, structures, and photochromic properties of 3-[(E)-alk-1-enyl]-4- (1-alkyl-5-methoxy-2-methyl-1H-indol-3-yl)furan-2,5-diones

Article abstract of DOI:10.1007/s11172-011-0172-1

New hetarylethenes, viz., 3-[(E)-alk-1-enyl]-4-(1-alkyl-5-methoxy-2-methyl- 1H-indol-3-yl)furan-2,5-diones, exhibiting photochromic properties in solution were synthesized. The molecular and crystal structure of 3-(5-methoxy-1,2- dimethyl-1H-indol-3-yl)-4

Full text of DOI:10.1007/s11172-011-0172-1

Russian Chemical Bulletin, International Edition, Vol. 60, No. 6, pp. 1090—1095, June, 2011
1090
Synthesis, structures, and photochromic properties of 3ꢀ[(E)ꢀalkꢀ1ꢀenyl]ꢀ
4ꢀ(1ꢀalkylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ3ꢀyl)furanꢀ2,5ꢀdiones
N. I. Makarova,a P. V. Levchenko,a V. V. Tkachev,b E. N. Shepelenko,c A. V. Metelitsa,a
V. P. Rybalkin,c L. L. Popova,a V. A. Bren´,a S. M. Aldoshin,b and V. I. Minkina,c
aInstitute of Physical and Organic Chemistry, Southern Federal University,
194/2 prosp. Stachki, 344090 RostovꢀonꢀDon, Russian Federation.
Eꢀmail: dubon@ipoc.rsu.ru
bInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Eꢀmail: sma@icp.ac.ru
cSouthern Scientific Center of Russian Academy of Sciences,
41 ul. Chekhova, 344006 RostovꢀonꢀDon, Russian Federation
New hetarylethenes, viz., 3ꢀ[(E)ꢀalkꢀ1ꢀenyl]ꢀ4ꢀ(1ꢀalkylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ
3ꢀyl)furanꢀ2,5ꢀdiones, exhibiting photochromic properties in solution were synthesized. The
molecular and crystal structure of 3ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ4ꢀ[(E)ꢀpropꢀ1ꢀ
enyl]furanꢀ2,5ꢀdione was determined by Xꢀray diffraction. The initial and photoinduced forms
of hetarylethenes are characterized by thermal stability. The openꢀring isomers of furandiones
exhibit fluorescence with quantum yields of up to 0.1.
Key words: furanꢀ2,5ꢀdione, synthesis, structure, Xꢀray diffraction study, photochromism,
fluorescence, molecular switches.
Nꢀmethylꢀ and Nꢀbenzylindolylꢀsubstituted furanꢀ2,5ꢀ
diones.
Dihetarylethenes, including hetarylꢀsubstituted furanꢀ
diones (maleic anhydrides), whose photochromic transꢀ
formations occur by the mechanism involving the reversꢀ
ible hexatrieneꢀcyclohexadiene rearrangement, are generꢀ
ally characterized by thermal stability of isomeric forms
and high resistance to photodegradation. Due to this fact,
dihetarylethenes are considered as one of the most promꢀ
ising classes of molecular systems for the use in optical
memory devices and as molecular switches.1,2
In addition, to determine the geometric parameters
and the degree of preparedness of the molecules in the
solid state for exhibiting optical properties, we obtained
single crystals of 3ꢀ[(E)ꢀbutꢀ1ꢀenyl]ꢀ4ꢀ(5ꢀmethoxyꢀ1,2ꢀ
dimethylꢀ1Hꢀindolꢀ3ꢀyl)furanꢀ2,5ꢀdione and studied
them by Xꢀray diffraction.
We found that the starting openꢀring isomers of 3ꢀ[(E)ꢀ
alkꢀ1ꢀenyl]ꢀ4ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ
furanꢀ2,5ꢀdiones exhibit efficient fluorescence.3 The fluoꢀ
rescence of one of isomeric forms shows promise for the
design of media for 3D data recording and molecular
switches with a fluorescent signaling property.4—7
With the aim of studying the influence of substituents
of different nature in the indole and maleic anhydride
moieties of 3ꢀ[(E)ꢀalkꢀ1ꢀenyl]ꢀ4ꢀ(1,2ꢀalkylꢀ5ꢀmethoxyꢀ
1Hꢀindolꢀ3ꢀyl)furanꢀ2,5ꢀdiones on their photochromic
and fluorescence properties and investigating the energy
and structural mechanisms of photoinduced transformaꢀ
tions, we synthesized new 3ꢀ[(E)ꢀalkꢀ1ꢀenyl]ꢀ4ꢀ(1ꢀbenꢀ
zylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ3ꢀyl)furanꢀ2,5ꢀdiones
containing different alkyl substituents in the heterocyclic
and olefinic moieties and performed a comparative study
of the spectroscopic and photochromic properties of
Results and Discussion
The starting compounds, viz., 5ꢀmethoxyꢀ1,2ꢀdimeꢀ
thylindole (1) and 1ꢀbenzylꢀ5ꢀmethoxyꢀ2ꢀmethylindole
(2), were synthesized according to known procedures.8,9
The acylation of indoles 1 and 2 with oxalyl chloride10
afforded the corresponding acid chlorides 3 and 4. The
reactions of compounds 3 and 4 with (E)ꢀ3ꢀalkenoic acids
gave 3ꢀ[(E)ꢀalkꢀ1ꢀenyl]ꢀ4ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀ
indolꢀ3ꢀyl)furanꢀ2,5ꢀdiones (5a—с) and 3ꢀ[(E)ꢀalkꢀ1ꢀ
enyl]ꢀ4ꢀ(1ꢀbenzylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ
furanꢀ2,5ꢀdiones (5d,e) (Scheme 1).
The IR spectra of compounds 5a—e show characterisꢀ
tic bands at 1750 and 1820 cm–1 corresponding to vibraꢀ
tions of two exocyclic carbonyl groups of the furandione
moiety. The 1H NMR spectra of compounds 5a—e in
CDCl3 contain all signals of the indole and (E)ꢀalkꢀ1ꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1065—1070, June, 2011.
1066ꢀ5285/11/6006ꢀ1090 © 2011 Springer Science+Business Media, Inc.

Photochromism of furanꢀ2,5ꢀdiones
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 6, June, 2011
1091
Scheme 1
1, 3: R1 = Me; 2, 4: R1 = Bn; 5: R1 = R2 = Me (a); R1 = Me, R2 = Et (b); R1 = Me, R2 = C6H13 (c); R1 = Bn, R2 = Me (d); R1 = Bn, R2 = Et (e)
Scheme 2
enyl substituents. At low field, there are two signals
for ethylene protons with the spinꢀspin coupling constant
J = 16 Hz and the characteristic spinꢀspin coupling of
these protons with the protons at the carbon atom of the
alkyl substituent nearest to the double bond. This indiꢀ
cates that the compounds were isolated in the open form A
containing the alkenyl substituent in the E configuration
(see Scheme 2 and the Experimental section).
The structure of 3ꢀ[(E)ꢀbutꢀ1ꢀenyl]ꢀ4ꢀ(5ꢀmethoxyꢀ
1,2ꢀdimethylꢀ1Hꢀindolꢀ3ꢀyl)furanꢀ2,5ꢀdione (5b) in the
crystalline state was determined by Xꢀray diffraction
(Fig. 1). It was shown that there are two crystallographiꢀ
C(18)
O(3)
O(24)
C(17)
C(16)
C(19)
C(26)
C(14)
C(15)
C(32)
C(25)
C(27)
C(12)
C(5)
O(2)
C(13)
C(24)
C(28)
O(4)
C(11)
C(4)
C(3)
C(29)
C(23)
C(38)
C(39)
N(21)
C(21)
C(2)
C(1)
C(6)
C(7)
C(22)
C(31)
C(36)
C(35)
C(37)
C(34)
C(8)
C(30)
C(10)
N(1)
C(9)
C(33)
O(21)
O(23)
O(22)
Fig. 1. Xꢀray diffraction structures of two independent molecules in the crystal structure of compound 5b (the numbering of the second
molecule was set by adding 20 to the numbers of the corresponding atoms in the first molecule).

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Russ.Chem.Bull., Int.Ed., Vol. 60, No. 6, June, 2011
Makarova et al.
cally independent molecules in the crystal structure of
compound 5b.
compared to Nꢀbenzylindolylꢀsubstituted furanꢀ2,5ꢀdiꢀ
ones 5d,e.
It should be noted that two independent molecules have
similar structures with the only difference that the hydroꢀ
gen atoms of the methyl groups at the nitrogen atoms
N(1) and N(21) are rotated by approximately 60° with
respect to the plane of the pyrrole ring and, corresponꢀ
dingly, with respect to each other upon superimposition.
The distances between the reactive carbon atoms in
compound 5b are 4.399 and 4.402 Å in two independent
molecules, which are shorter than that in the nonꢀphotoꢀ
chromic crystal of 3ꢀ(1,2ꢀdimethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ4ꢀ
[(E)ꢀpropꢀ1ꢀenyl]furanꢀ2,5ꢀdione (6);10 however, these
distances are too long for the photocyclization to occur in
the crystal to form the cyclohexadiene ring. In solutions of
compound 5b, the free rotation around single bonds,
through which the indole and alkenyl moieties are bound
to the furandione ring, provides the necessary distance
between the reaction centers.
An increase in the length of the alkyl substituent in the
alkenyl moiety at position 4 of furanꢀ2,5ꢀdione in going
from 4ꢀ[(E)ꢀpropꢀ1ꢀenyl]ꢀ (5a,d) to 4ꢀ[(E)ꢀbutꢀ1ꢀenyl]ꢀ
(5b,e) and then to 4ꢀ[(E)ꢀoctꢀ1ꢀenyl]furanꢀ2,5ꢀdione (5c)
has virtually no effect on the spectralꢀabsorption characꢀ
teristics of the isomers A (see Table 1).
Solutions of the compounds under study in heptane at
room temperature were found to exhibit fluorescence with
maxima at 523—528 nm for hetarylethenes 5a—e and at
522 nm for compound 6 (see Table 1). Figure 2 illustrates
the fluorescence excitation and emission spectra of a soluꢀ
tion of compound 5c in heptane. The fluorescence excitaꢀ
tion spectra are in good agreement with the absorption
spectra, which unambiguously indicates that the observed
fluorescence corresponds to the open isomers A (see Table 1).
The fluorescence quantum yields of compounds 5a—e are
0.06—0.09, and they are two—three times higher than that
of compound 6 (0.03 in heptane).
The UV irradiation of solutions of compounds 5a—e
and 6 in heptane with a mercury lamp (λ = 436 nm) leads
to their coloration associated with the appearance of new
bands in the longꢀwavelength region of the electronic abꢀ
sorption spectra with maxima at 528—530 nm (see Table
1 and Fig. 3). This absorption is characteristic of the closed
isomeric forms B of dihetarylethenes1,10 (see Scheme 2).
The positions of the longꢀwavelength absorption maxima
of the cyclic isomers B are virtually independent of the
structures of compounds 5a—e. It should be noted that the
presence of the methoxy group in the indole moiety of
hetarylethenes 5a—e leads to a bathochromic shift of the
longꢀwavelength absorption maximum of the form B in
these compounds by more than 30 nm compared to model
compound 6.
The electronic absorption spectra of solutions of furanꢀ
2,5ꢀdiones 5a—e are characterized by longꢀwavelength
absorption bands of a similar shape with maxima at
442—445 nm and the molar extinction coefficients of
9760—10980 L mol–1 cm–1 (Table 1). The introduction of
the electronꢀreleasing methoxy group at position 5 of the
indole moiety in compounds 5a—e causes a bathochromic
shift (Δλ are 6, 7, 8, 5, and 8 nm, respectively) of the longꢀ
wavelength absorption maximum of the form A compared
to the open form A of model compound 6, viz., 3ꢀ(1,2ꢀ
dimethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ4ꢀ[(E)ꢀpropꢀ1ꢀenyl]furanꢀ2,5ꢀ
dione,10 whose longꢀwavelength absorption maximum
abs
is observed at lower wavelengths (λmax
= 437 nm,
ε = 7330 L mol–1 cm–1). NꢀMethylindole derivatives 5a—c
are characterized by a weak (Δλ = 1—3 nm) bathochromic
shift of the longꢀwavelength absorption of the form A
Table 1. Spectralꢀabsorption and fluorescence characteristics of
the isomeric starting (A) and photoinduced (B) forms of comꢀ
pounds 5a—e and 6 in heptane at 293 K
IF (a.u.)
1
1000
800
600
400
200
0
2
Comꢀ
pound
Form A
Form B
Absorption
Absorption
abs/nm
Fluorescence
λ
abs/nm
max
λ
max
ex
em
max
λ
λ
Φ
(ε •10–3
/
max
max
L mol–1 cm–1
)
5a
5b
5c
5d
5e
6
443 (8.84)
444 (10.93)
445 (10.34)
442 (9.76)
442 (10.98)
437 (7.33)
446
448
450
448
446
442
524
525
525
528
523
522
0.09
0.07
0.09
0.06
0.08
530
528
530
530
530
200
300
400
500
600 700
800 λ/nm
0.03 495 shoulder
Fig. 2. Fluorescence excitation (1) and emission (2) spectra of
Note. λ ex and λ em are the fluorescence excitation and emisꢀ
sion maxima, respectively; Φ is the fluorescence quantum yield.
a solution of compound 5c in heptane (C = 4•10–5 mol L–1
T = 293 K).
,
max
max

Photochromism of furanꢀ2,5ꢀdiones
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 6, June, 2011
1093
(εmaxB) corresponding to one of the concepts of "photoꢀ
A (a.u.)
colorability".11
→
B
The efficiencies of the photocyclization reactions A
of furanꢀ2,5ꢀdiones 5a—e in heptane at room temperature
in terms of the photocolorability (ΦAB•εmaxB) are given in
Table 2.
The photocyclization quantum yields (ΦAB) estimated
with the use of the average molar extinction coefficient
εmaxB = 7300 L mol–1 cm–1 (see Refs 12—17) are 0.10—0.16
for compounds 5a—e and 0.11 (0.10 in hexane10) for comꢀ
pound 6.
1.2
0.6
0
The efficiencies of the photorecyclization reactions
B
B→A estimated as ΦBA•εmax (see Table 2) depend
200
300
400
500
600
λ/nm
only slightly on the nature of the substituents and are
2190—2493 L mol–1 cm–1 for compounds 5a—e and
2488 L mol–1 cm–1 for compound 6.
Fig. 3. Electronic absorption spectra of compound 5с in heptane
(C = 4•10–5 mol L–1, T = 293 K) before (1) and after irradiation
at 436 nm for 1 (2), 2 (3), 3 (4), 5 (5), 10 (6), and 20 min (7).
The ratios of the quantum yields of the forward and
backward photoreactions (ΦAB/ΦBA) for compounds 5a—e
are 0.32—0.55. This indicates that the efficiency of the
ringꢀopening photoreactions is much higher (see Table 2).
The estimated quantum yields of the backward photoreꢀ
actions are 0.30—0.34 for compounds 5a—e and 0.34 for
compound 6 (0.32 for compound 6 in hexane10).
Maleic anhydrides 5a—e exhibit resistance to photoꢀ
degradation. The repeated ten photocolorationꢀphotoꢀ
bleaching cycles showed that the spectroscopic characterꢀ
istics of the colored and bleached solutions remained unꢀ
changed.
To sum up, we synthesized new photochromic hetarylꢀ
ethenes containing the 5ꢀmethoxyꢀsubstituted indole moiety.
These compounds are characterized by a high content of
colored forms in the photostationary state compared
to the unsubstituted analog. Due to the thermal stability
of isomeric forms, quite efficient fluorescence of openꢀ
ring isomers, and resistance to photodegradation, the reꢀ
sulting hetarylethenes can be considered as promising
compounds for the design of materials for optical data
recording and molecular switches with a fluorescentꢀsigꢀ
naling property.
Unlike the starting open form A, the closed isomers B
of hetarylethenes do not exhibit fluorescence.
The irradiation of colored solutions of compounds 5a—e
and 6 at longꢀwavelength absorption bands of the cyclic
forms B (λ = 546 nm) leads to their bleaching accompaꢀ
nied by the recovery of the initial (before irradiation at
436 nm) spectral patterns. This is evidence for the backꢀ
ward photoreaction B→A, resulting in the recovery to the
initial state of the system. The isomeric forms A and B are
thermally stable (after the irradiation was stopped, the
contents of the forms A and B remained unchanged with
time even as the temperature was increased). Therefore,
hetarylethenes 5a—e exhibit photochromic properties and
possess bistability, i.e., they can exist in two thermally
stable structurallyꢀmediated states.
The continuous irradiation of solutions of compounds
5a—e and 6 at the longꢀwavelength absorption band of the
form A does not lead to the complete conversion into the
colored form B but results in the establishment of the
photostationary state as a consequence of the substantial
overlap of the longꢀwavelength absorption bands of the
photoactive isomeric forms A and B. Since the presence of
the methoxy group at position 5 of the indole moiety of
hetarylethenes 5a—e leads to a bathochromic shift of the
longꢀwavelength absorption maxima of the closed isomers
B compared to unsubstituted compound 6, whereas the
positions of the longꢀwavelength absorption maxima of
the open forms A remain virtually unchanged, the content
of the colored forms in the photostationary state of comꢀ
pounds 5a—e is higher than that of the previously syntheꢀ
sized hetarylethene 6.
Table 2. Characteristics of the photochromic transformations of
compounds 5a—e and 6 in heptane at 293 K
B
B
Comꢀ
pound
Φ
•ε
АВ max
Φ
•ε
Φ
АВ/Φ
ВA max
ВА
L mol–1 cm–1
5a
5b
5c
5d
5e
6
1095
2275
2493
2307
2238
2190
2468
0.41
0.48
0.55
0.32
0.34
0.32
930
1164
724
755
796
To quantitatively characterize the phototransformaꢀ
tions of furanꢀ2,5ꢀdiones 5a—e in heptane, we used
the product of the quantum yield (Φ) of the photoreacꢀ
tion by the molar extinction coefficient at the longꢀwaveꢀ
length absorption maximum of the photoinduced form
B
Note. Φ •ε B is photocoloration (cyclization) and Φ •ε
AB max
BA max
is photobleaching (recyclization).

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Makarova et al.
3ꢀ(5ꢀMethoxyꢀ1,2ꢀdimethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ4ꢀ[(E)ꢀoctꢀ1ꢀ
enyl]furanꢀ2,5ꢀdione (5c) was synthesized by analogy with comꢀ
pound 5a from dimethylindole 1 and (E)ꢀdecꢀ3ꢀenoic acid. The
yield was 0.3 g (26.4%), red crystals, m.p. 112—114 °C. IR,
ν/cm–1: 1750, 1820 (C=O). 1H NMR, δ: 0.86 (br.t, 3 H, Me,
J = 7.0 Hz); 1.16—1.35 (m, 6 H, CH2); 1.36—1.48 (m, 2 H, CH2);
2.20 (q, 2 H, CH2, J = 7.0 Hz); 2.42, 3.73, and 3.79 (all s,
3 H each, NMe, C(2)Me, OMe); 6.21 (br.d, 1 H, CH, J = 16.0 Hz);
6.78 (d, 1 H, HAr, J = 2.3 Hz); 7.16—7.30 (m, 2 H, HAr).
Found (%): C, 72.86; H, 7.01; N, 3.54. C23H27NO4. Calculatꢀ
ed (%): C, 73.00; H, 7.15; N, 3.68.
3ꢀ(1ꢀBenzylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ4ꢀ[(E)ꢀ
propꢀ1ꢀenyl]furanꢀ2,5ꢀdione (5d) was synthesized by analogy with
compound 5a from 1ꢀbenzylindole 2 and (E)ꢀpentꢀ3ꢀenoic acid.
The yield was 0.29 g (31%), red crystals, m.p. 150—152 °C. IR,
ν/cm–1: 1750, 1820 (C=O). 1H NMR, δ: 1.95 (dd, 3 H, Me,
J1 = 7.0 Hz, J2 = 1.6 Hz); 2.38 (s, 3 H, Me); 3.80 (s, 3 H, OMe);
5.36 (s, 2 H, CH2); 6.24—6.32 (dq, 1 H, CH, J1 = 16.0 Hz,
J2 = 1.6 Hz); 6.82—6.95 (m, 2 H, HAr); 7.00—7.12 (m, 2 H, HAr);
7.14—7.22 (m, 2 H, HAr); 7.24—7.38 (m, 3 H, HAr). Found (%):
C, 74.36; H, 5.41; N, 3.60. C24H21NO4. Calculated (%): C, 74.40;
H, 5.46; N, 3.62.
Experimental
The electronic absorption spectra were measured on a Cary
100 spectrophotometer (Varian); the optical path length was
1 cm. The fluorescence measurements were carried out on a Cary
Eclipse spectrofluorimeter (Varian). The fluorescence quantum
yields were determined by the Parker—Rees method18 with the
use of a solution of 3ꢀmethoxybenzanthrone in toluene as the
reference luminophore.19 The solutions were irradiated in
a quartz cell (l = 1 cm) with a DRShꢀ250 mercury lamp equipped
with a kit of interference light filters to select lines of the mercuꢀ
ry spectrum. The kinetic curves for the photocoloration of soluꢀ
tions of dihetarylethenes were measured directly during irradiaꢀ
tion on a Cary 50 spectrophotometer (Varian) equipped with
a temperatureꢀcontrolled cell holder. A xenon lamp equipped
with a monochromator to produce narrow spectral lines (Newꢀ
port) was used as the radiation source. The optical radiation
intensity was determined with a Newport 2935 optical power
meter. The optical radiation intensity at the wavelengths used
(436 and 546 nm) was 2.94•1015 and 6.30•1015 photon s–1, reꢀ
spectively. To determine the photocolorability (Φ •ε B), the
AB max
slope of the tangent line at the initial instant was calculated from
the kinetic curves for the photocoloration.
3ꢀ(1ꢀBenzylꢀ5ꢀmethoxyꢀ2ꢀmethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ4ꢀ[(E)ꢀ
butꢀ1ꢀenyl]furanꢀ2,5ꢀdione (5e) was synthesized by analogy with
compound 5a from 1ꢀbenzylindole 2 and (E)ꢀhexꢀ3ꢀenoic acid.
The yield was 0.29 g (30%), red crystals, m.p. 148—149 °C. IR,
ν/cm–1: 1750, 1820 (C=O). 1H NMR, δ: 1.05 (t, 3 H, Me,
J = 7.3 Hz); 2.27 (q.d, 2 H, CH2, J1 = 7.2 Hz, J2 = 1.5 Hz); 2.37
(s, 3 H, Me); 3.80 (s, 3 H, OMe); 5.36 (s, 2 H, CH2); 6.25 (dt, 1 H,
CH, J1 = 16.0 Hz, J2 = 1.5 Hz); 6.82—6.95 (m, 2 H, CH, HAr);
7.00—7.12 (m, 2 H, HAr); 7.14—7.22 (m, 2 H, HAr); 7.28—7.40
(m, 3 H, HAr). Found (%): C, 74.77; H, 5.69; N, 3.44. C25H23NO4.
Calculated (%): C, 74.80; H, 5.77; N, 3.49.
The IR spectra in Nujol mulls were recorded on a Varian
Excalibur 3100 FTꢀIR instrument. The 1H NMR spectra
were measured in CDCl3 on a Varian Unityꢀ300 instrument
(300 MHz) with hexamethyldisiloxane as the external standard.
5ꢀMethoxyꢀ1,2ꢀdimethylindole (1) was synthesized accordꢀ
ing to a known procedure,8 m.p. 67—68 °C.
1ꢀBenzylꢀ5ꢀmethoxyꢀ2ꢀmethylindole (2) was synthesized acꢀ
cording to a procedure published earlier,9 m.p. 114—115 °C.
3ꢀ(5ꢀMethoxyꢀ1,2ꢀdimethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ4ꢀ[(E)ꢀpropꢀ1ꢀ
enyl]furanꢀ2,5ꢀdione (5a). Oxalyl chloride (0.26 mL, 3 mmol)
was added dropwise to a solution of dimethylindole 1 (0.53 g,
3 mmol) in dry 1,2ꢀdichloroethane (5 mL) at 5 °C. The reaction
mixture was stirred at 5 °C for 10 min. Then a solution of
(E)ꢀpentꢀ3ꢀenoic acid (0.3 mL, 3 mmol) and triethylamine
(1 mL, 3.2 mmol) in 1,2ꢀdichloroethane (7 mL) was added dropꢀ
wise at 5 °C. The reaction mixture was stirred for 1 h, and the
solution was concentrated in vacuo. The residue was purified by
column chromatography on silica gel (chloroform as the eluent).
The yield of the product was 0.26 g (28%), red crystals, m.p.
185—187 °C. IR, ν/cm–1: 1750, 1820 (C=O). 1H NMR, δ: 1.94
(dd, 3 H, Me, J1 = 7.0 Hz, J2 = 1.7 Hz); 2.43 (s, 3 H, Me); 3.74
(s, 3 H, NMe); 3.80 (s, 3 H, OMe); 6.26 (dq, 1 H, CH, J1 = 16.0 Hz,
3ꢀ(1,2ꢀDimethylꢀ1Hꢀindolꢀ3ꢀyl)ꢀ4ꢀ[(E)ꢀpropꢀ1ꢀenyl]furanꢀ
2,5ꢀdione (6) was synthesized according to a known procedure,10
m.p. 199—200 °C.
Xꢀray diffraction study. The unit cell parameters were meaꢀ
sured and the threeꢀdimensional Xꢀray diffraction data set was
collected on an EnrafꢀNonius CADꢀ4 automated diffractometer
(MoꢀKα radiation, graphite monochromator) at room temperaꢀ
ture. Darkꢀred transparent crystals of compound 5b (C19H19NO4,
M = 325.35) are triclinic, space group P–1, a = 10.463(3) Å,
b = 11.118(3) Å, с = 17.107(4) Å, α = 71.66(2)°, β = 76.54(3)°,
γ = 62.72(3)°, V = 1669.6(8) Å3, Z = 4, dcalc = 1.294 g cm–3
,
μ(MoKα) = 0.91 cm–1. The intensities of 6220 reflections were
measured in the angle range 2θ ≤ 50.04° using the ω/2θ scanning
technique from a single crystal of dimensions 0.42×0.25×0.25 mm;
5887 reflections (Rint = 0.071) were independent, 4057 reflecꢀ
tions were with F2 > 4σ(F2). The structure was solved by direct
methods using the SHELXTL program package20 and refined by
the fullꢀmatrix leastꢀsquares method based on F2 with anisotroꢀ
pic displacement parameters for nonhydrogen atoms using the
SHELXTL program package.20 All hydrogen atoms were locatꢀ
ed in difference Fourier maps. Then the atomic coordinates and
the isotropic temperature factors for all H atoms were refined by
the leastꢀsquares method using a riding model. In the last cycle
of the fullꢀmatrix refinement, the absolute shifts of all 434 variꢀ
able parameters of the crystal structure of 5b were smaller than
0.001σ. The final R factors were R1 = 0.054, wR1 = 0.150
based on 4057 observed reflections with I ≥ 2σ(I); R2 = 0.081,
wR2 = 0.163 based on all measured reflections; GOOF = 1.004.
J2 = 1.7 Hz); 6.79 (d, 2 H, HAr, J = 2.4 Hz); 6.90 (dd, 1 H, HAr
,
J1 = 8.9 Hz, J2 = 2.4 Hz); 7.10—7.30 (m, 2 H, HAr). Found (%):
C, 69.32; H, 5.41; N, 4.46. C18H17NO4. Calculated (%): C, 69.44;
H, 5.50; N, 4.50.
3ꢀ[(E)ꢀButꢀ1ꢀenyl]ꢀ3ꢀ(5ꢀmethoxyꢀ1,2ꢀdimethylꢀ1Hꢀindolꢀ4ꢀ
yl)furanꢀ2,5ꢀdione (5b) was synthesized by analogy with comꢀ
pound 5a from dimethylindole 1 and (E)ꢀhexꢀ3ꢀenoic acid. The
yield was 0.32 g (32.7%), red crystals, m.p. 175—177 °C. IR,
ν/cm–1: 1750, 1820 (C=O). 1H NMR, δ: 1.05 (t, 3 H, Me,
J = 7.4 Hz); 2.26 (q.d, 2 H, CH2, J1 = 7.3 Hz, J2 = 1.6 Hz); 2.44
(s, 3 H, Me); 3.75 (s, 3 H, NMe); 3.80 (s, 3 H, OMe); 6.22 (dt, 1 H,
CH, J1 = 16.0 Hz, J2 = 1.6 Hz); 6.78 (d, 1 H, HAr, J = 2.4 Hz);
6.90 (dd, 1 H, HAr, J1 = 8.9 Hz, J2 = 2.4 Hz); 7.16—7.30 (m, 2 H,
HAr). Found (%): C, 70.02; H, 5.63; N, 4.21. C19H19NO4. Calꢀ
culated (%): C, 70.14; H, 5.69; N, 4.30.

Photochromism of furanꢀ2,5ꢀdiones
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 6, June, 2011
1095
10. T. Yamaguchi, M. Irie, Chem. Lett., 2005, 34, 64.
11. P. Appriou, R. Guglielmetti, F. Garnier, J. Photochem., 1978,
8, 145.
12. S. Pu, M. Li, C. Fan, G. Liu, L. Shen, J. Mol. Struct., 2009,
919, 100.
13. Y.ꢀC. Jeong, D. G. Park, I. S. Lee, S. I. Yang, K.ꢀH. Ahn,
J. Mater. Chem., 2009, 19, 97.
This study was financially supported by the Federal
Agency for Science and Innovations (Federal Targeted
Program "Scientific and ScientificꢀPedagogical Personꢀ
nel of the Innovative Russia in 2009ꢀ2013," State Conꢀ
tract P2260) and the Russian Foundation for Basic Reꢀ
search (Project No. 09ꢀ03ꢀ00813).
14. M. Ohsumi, T. Fukaminato, M. Irie, Chem. Commun.,
2005, 3921.
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Received March 4, 2011;
in revised form April 4, 2011