Synthesis, structures, and photochromic properties of 2-methylthieno[3,2-b] [1]benzothiophen-3-ylfulgide

Article abstract of DOI:10.1007/s11172-007-0382-8

The novel heterocyclic fulgide, 3-(1-methylethylidene)-4-[1-(2- methylthieno[3,2-b]-[1]benzothiophen-3-yl)ethylidene]dihydrofuran-2,5-dione, was obtained and isolated as a Z-isomer. Its structure was confirmed by electronic absorption spectroscopy, ¹H NMR spectroscopy, and X-ray diffraction analysis. The novel thienothiophene fulgide is photochromic in both solutions and the crystalline state. Its colored cyclic form resists photodegradation and is thermally stable. When benzothiophene is annulated with the thienyl fragment, the long-wavelength absorption peak of the cyclic isomer of the novel fulgide experiences a bathochromic shift compared to the earlier described 3-thienylfulgide. The TD B3LYP/6-311G**-calculated spectroscopic characteristics of the fulgide isomers suggest the formation of their photostationary mixture under irradiation with λ = 365 nm.

Full text of DOI:10.1007/s11172-007-0382-8

Russian Chemical Bulletin, International Edition, Vol. 56, No. 12, pp. 2400—2406, December, 2007
2400
Synthesis, structures, and photochromic properties
of 2ꢀmethylthieno[3,2ꢀb][1]benzothiophenꢀ3ꢀylfulgide
S. K. Balenko,a N. I. Makarova,a O. G. Karamov,a V. P. Rybalkin,b I. V. Dorogan,a L. L. Popova,a

E. N. Shepelenko,b A. V. Metelitsa,a V. V. Tkachev,c S. M. Aldoshin,c V. A. Bren,a,b and V. I. Minkina,b
aResearch Institute of Physical and Organic Chemistry, Southern Federal University,
194/2 prosp. Stachki, 344090 RostovꢀonꢀDon, Russian Federation.
Eꢀmail: dubon@ipoc.rsu.ru
bSouthern Scientific Center of the Russian Academy of Sciences,
41 ul. Chekhova, 344006 RostovꢀonꢀDon, Russian Federation
cInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Eꢀmail: sma@icp.ac.ru
The novel heterocyclic fulgide, 3ꢀ(1ꢀmethylethylidene)ꢀ4ꢀ[1ꢀ(2ꢀmethylthieno[3,2ꢀb]ꢀ
[1]benzothiophenꢀ3ꢀyl)ethylidene]dihydrofuranꢀ2,5ꢀdione, was obtained and isolated as a
Zꢀisomer. Its structure was confirmed by electronic absorption spectroscopy, 1H NMR
spectroscopy, and Xꢀray diffraction analysis. The novel thienothiophene fulgide is photochroꢀ
mic in both solutions and the crystalline state. Its colored cyclic form resists photodegradation
and is thermally stable. When benzothiophene is annulated with the thienyl fragment,
the longꢀwavelength absorption peak of the cyclic isomer of the novel fulgide experiences a
bathochromic shift compared to the earlier described 3ꢀthienylfulgide. The TD
B3LYP/6ꢀ311G**ꢀcalculated spectroscopic characteristics of the fulgide isomers suggest the
formation of their photostationary mixture under irradiation with λ = 365 nm.
Key words: thieno[3,2ꢀb][1]benzothiophene, fulgide, synthesis, structure, photochromism,
quantumꢀchemical calculations, density functional theory.
Because of the high thermal stability of their isomers
acid (1)5 gave thieno[3,2ꢀb][1]benzothiophene (2). The
Vilsmeier reaction of the latter afforded thieno[3,2ꢀb][1]ꢀ
benzothiopheneꢀ2ꢀcarbaldehyde (3) in high yield. Aldeꢀ
hyde 3 was reduced to 2ꢀmethylthieno[3,2ꢀb][1]benzoꢀ
thiophene (4) according to the Kishner reaction. The
Friedel—Crafts acetylation of compound 4 with acetyl
chloride in the presence of anhydrous SnCl4 gave 1ꢀ(2ꢀ
methylthieno[3,2ꢀb][1]benzothiophenꢀ3ꢀyl)ethanone 5
(Scheme 1).
The Stobbe condensation of ketone 5 with diethyl
isopropylidenesuccinate gave earlier unknown (4Z)ꢀ3ꢀ(1ꢀ
methylethylidene)ꢀ4ꢀ[1ꢀ(2ꢀmethylthieno[3,2ꢀb][1]benzoꢀ
thiophenꢀ3ꢀyl)ethylidene]dihydrofuranꢀ2,5ꢀdiꢀ
one (6) (Scheme 2).
and the high number of cyclic photochromic transformaꢀ
tions, heterocyclic fulgides are a promising class of phoꢀ
tochromic compounds for use in optical recording sysꢀ
tems.1 It is known that annulation of the benzene ring
additionally stabilizes an aromatic heterocyclic system,
thus enhances the resistance of fulgides to photodegradaꢀ
tion during photochromic transformations.2 One can exꢀ
pect that annulation of a heterocyclic aromatic fragment
will produce a similar effect.
The goal of the present work was to study the effect of
the annulation of benzo[b]thiophene fragment with the
thienyl ring of 3ꢀthienylfulgide3,4 on the characteristics of
the photochromic system.
The IR spectra of fulgide 6 contain characteristic bands
at 1755 and 1810 cm–1 due to two exocyclic carbonyl
groups in succinic anhydride. The 1H NMR spectra show
highꢀfield signals for four methyl groups and lowꢀfield
signals for four aromatic protons. The absence of the sinꢀ
glet signal for the ethylidene Me group from the 1H NMR
spectrum at δ 2.5 suggests the Z configuration of fulgide 6
with respect to the heterylethylidene double bond,6 which
is structurally not ready for a photoinitiated electrocyclic
Results and Discussion
We developed a procedure for the synthesis of 3ꢀacetylꢀ
2ꢀmethylthieno[3,2ꢀb][1]benzothiophene containing two
methyl groups, which prevent oxidative aromatization of
the colored cyclic form of the fulgide. Thermal decarboxꢀ
ylation of thieno[3,2ꢀb][1]benzothiopheneꢀ2ꢀcarboxylic
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2318—2324, December, 2007.
1066ꢀ5285/07/5612ꢀ2400 © 2007 Springer Science+Business Media, Inc.

2ꢀMethylthieno[3,2ꢀb][1]benzothiophenꢀ3ꢀylfulgide Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007 2401
Scheme 1
Scheme 2
Table 1. Selected interatomic distances (d) in structure 6
reaction. This conclusion was confirmed by Xꢀray difꢀ
fraction data. Structure 6 is shown in Fig. 1; selected
interatomic distances are given in Table 1.
Bond
d/Å
Bond
d/Å
The atoms of thieno[3,2ꢀb][1]benzothiophene fragꢀ
ment are coplanar to within 0.023 Å. The C(5) and C(12)
S(1)—C(11)
S(2)—C(13)
O(1)—C(2)
O(2)—C(1)
C(1)—C(4)
C(3)—C(7)
C(4)—C(5)
C(5)—C(6)
C(7)—C(8)
C(10)—C(13)
C(13)—C(20)
C(14)—C(19)
C(16)—C(17)
C(18)—C(19)
1.722(4)
1.745(4)
1.395(6)
1.186(5)
1.487(6)
1.349(6)
1.359(5)
1.502(5)
1.505(6)
1.426(5)
1.366(5)
1.419(5)
1.388(6)
1.389(5)
S(1)—C(20)
S(2)—C(14)
O(1)—C(1)
O(3)—C(2)
C(2)—C(3)
C(3)—C(4)
C(5)—C(10)
C(7)—C(9)
C(10)—C(11) 1.383(5)
C(11)—C(12) 1.495(5)
C(14)—C(15) 1.395(6)
C(15)—C(16) 1.372(6)
C(17)—C(18) 1.382(6)
C(19)—C(20) 1.429(5)
1.723(4)
1.746(4)
1.397(5)
1.191(5)
1.473(6)
1.470(5)
1.470(5)
1.490(6)
O(1)
O(2)
C(1)
O(3)
C(12)
S(1)
C(11)
C(2)
C(3)
C(8)
C(18)
C(19)
C(20)
C(10)
C(6)
C(4)
C(5)
C(17)
C(16)
C(14)
C(13)
C(7)
C(9)
C(15)
S(2)
Fig. 1. Structure 6 with atomic thermal displacement ellipsoids
(30% probability).

2402
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007
Balenko et al.
atoms deviate from the plane on both sides by 0.063(4)
and 0.093(5) Å, respectively. An analysis of the structure
of the fulgide fragment containing the C(5) and C(6)
atoms shows that the formal plane passes through the
O(1), O(2), O(3), C(1), and C(2) atoms to within 0.013 Å;
the C(3), C(7), C(8), and C(9) atoms deviate by 0.08(1),
0.62(2), 0.96(2), and 1.00(2) Å, respectively, on one side
and the C(4), C(5), C(6), and C(10) atoms deviate by
0.19(1), 0.80(2), 1.52(2), and 0.85(2) Å, respectively, on
the other side. Obviously, this is due to the mutual arꢀ
rangement of the C(6) and C(9) atoms and their hydroꢀ
gen atoms (the H...H and C(6)...C(9) distances are
2.21 and 3.14 Å, respectively). The angle between the
planes of the thieno[3,2ꢀb][1]benzothiophene and fulgide
fragments calculated as an angle between the perpendicuꢀ
lars to the planes of these fragments is 81°; the torsion
angles C(11)—C(10)—C(5)—C(4) and C(10)—C(5)—
C(4)—C(1) are –52.4(5)° and –25.1(5)°, respectively;
the C(7)—C(11) distance is 5.27 Å.
c
b
0
a
Fig. 3. Arrangement of the molecules of compound 6 along the
axis c.
O(2) atom to one of the H atoms at the C(12) atom is
2.707 Å; i.e., no steric interactions occur between these
atoms. The C(4)—C(5) and C(3)—C(7) distances are 1.36
and 1.35 Å, which is only slightly longer than an ordinary
double bond of this type.
Arrangement of the molecules of compound 6 along
the axis c is shown in Fig. 3. The shortest distances
(2.488 Å) between the fulgide O(2) atoms and one of the
H atoms at the C(9) atom, which are related by translaꢀ
tions in the unit cell along the axis a, are indicated with
dashed lines. Using the 6ꢀexp potential with appropriate
parameters,8 we calculated the energies of the intermoꢀ
lecular interactions. The total energy of the crystal lattice
of compound 6 was found to be 36.1 kcal mol–1. The major
contributions to the energy of the crystal lattice are made
by the energies of pair intermolecular interactions:
between the molecules related by the center of inversion
and translations (011) (15.33 kcal mol–1), (112)
(10.72 kcal mol–1), and (111) (6.99 kcal mol–1) and beꢀ
tween the molecules related by the helical axis and transꢀ
lations (01–1 and 010) (6.13 kcal mol–1). The volume of
the molecule is 259.4 Å3 and the free volume fraction (the
fraction of the free volume per molecule in the unit cell)
is K = 176.3 Å3. This parameter was calculated by the
formula K = (Vcell – ZVmol)/Z, where Vcell and Vmol are
the unit cell volume and the molecule volume, respecꢀ
tively; Z is the number of formula units in the unit cell.
In the unit cell with such parameters, the Zꢀisomer
can transform itself into the Eꢀisomer by rotating about
the C(4)—C(5) bond in the solid state, because the moleꢀ
cules in the leftꢀ and rightꢀhand chains in Fig. 3 are
shifted by half the translation along the plane of the figure.
In this case, the photoreaction E → C becomes quite
possible.
The mutual arrangement of the fragments of strucꢀ
ture 6 and the earlier7 studied 4ꢀ[2ꢀ(9ꢀanthryl)ꢀ5ꢀ
methyl]oxazolylfulgide (7) is shown in Fig. 2 so that their
fulgide fragments coincide (their structures are identical
to within the error of determination and have the same
orientation relative to the central part of the molecule).
Ant is anthryl
Note that fulgide 7 also exists as the Zꢀisomer and
irradiation of its solutions with λ = 365 nm results in Z/E
isomerization yielding a thermally stable cyclic form; light
irradiation with λ = 436 nm produces the starting
Eꢀisomer.
When considering the structure of the central part of
the molecule, note that the shortest distance from the
O(1)
O(3)
O(2)
C(2)
C(1)
C(3)
C(4)
S(2)
The electronic absorption
spectra of fulgide Zꢀ6 in toluꢀ
ene show a longꢀwavelength
absorption peak at 340 nm
C(7)
C(5)
C(6)
C(8)
C(9)
C(10)
S(1)
(Fig. 4, curve 1).
The molar absorption coꢀ
efficient ε at the absorption
Fig. 2. Mutual arrangement of the fragments of structure 6 and
4ꢀ[2ꢀ(9ꢀanthryl)ꢀ5ꢀmethyl]oxazolylfulgide.
peak is 7340 L mol–1 cm–1
.

2ꢀMethylthieno[3,2ꢀb][1]benzothiophenꢀ3ꢀylfulgide Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007 2403
A
not accompanied by restoration of the original absorption
of the UVꢀnonirradiated solution (see Fig. 4, curve 3).
At the same time, in subsequent photocoloration—phoꢀ
todecoloration cycles, the spectroscopic characteristics of
the colored and decolorized solutions were reproducible.
Such changes in the absorption spectra are due to the
presence of the isomer Eꢀ6 in the irradiated solutions.
Obviously, UV irradiation of solutions of fulgide 6 first
initiates the isomerization Z → E since cyclic product Cꢀ6
cannot be formed directly from the Zꢀform of the fulgide.
Because the absorption bands of the isomers Eꢀ6 and Zꢀ6
overlap greatly, both the Zꢀ and Eꢀforms are photoinꢀ
duced by UV irradiation and the electrocyclic transforꢀ
mation E → C becomes possible. We found that the conꢀ
version into the colored form remains incomplete even
on prolonged irradiation of solutions of fulgide 6. This
can be associated with overlap of the absorption bands
due to the transitions S0 → S2 in cyclic isomers Cꢀ6 with
the absorption bands due to the transitions S0 → S1 in the
Eꢀ and Zꢀisomers. Under the conditions of the reverse
photoreaction C → E and the photoisomerization E → Z,
UV irradiation produces the photostationary state conꢀ
sisting of the Eꢀ, Zꢀ, and Cꢀisomers; their ratio is deterꢀ
mined by the wavelength of exciting UV light (Scheme 3).
The formation of a mixture of three isomers was conꢀ
firmed by the 1H NMR spectrum of fulgide Zꢀ6 recorded
in deuterated toluene after irradiation with λ = 365 nm.
The spectrum contains signals for the methyl groups of all
the three isomers. Subsequent full photodecoloration of
the solution with visible light gave a mixture consisting
only of the isomers Eꢀ6 and Zꢀ6; the content of the Eꢀform
in the mixture is increased by the amount of the Cꢀform in
the mixture of three isomers (1H NMR data for the colꢀ
ored solution before and after irradiation with λ = 546 nm).
Fulgide 6 is resistant to photodegradation. After ten phoꢀ
tocoloration—photodecoloration cycles, the optical density
of the colored solution remained unchanged (Fig. 5).
1
1.0
0.8
0.6
0.4
0.2
3
2
300
400
500
600
λ/nm
Fig. 4. Electronic absorption spectra of fulgide 6 in toluene
(4•10–5 mol L–1): (1) before irradiation; (2) photostationary
state under light irradiation with λ = 365 nm; (3) after subseꢀ
quent light irradiation with λ = 546 nm.
The spectroscopic characteristics of the Zꢀisomer of
fulgide 6 are close to the corresponding parameters
of the Zꢀform of thienylfulgide 8 absorbing at 344 nm
(ε = 7010 L mol–1 cm–1).3
Solutions of compound Zꢀ6 in toluene do not fluoꢀ
resce at room temperature.
When irradiated with UV light corresponding to the
longꢀwavelength absorption peak of the Zꢀform (λexc
=
365 nm), solutions of fulgide Zꢀ6 in toluene became colꢀ
ored and their spectra show an absorption band at 561 nm.
This absorption is characteristic of the cyclic Cꢀisomers
(see Fig. 4, curve 2); the Cꢀisomer of thienylfulgide 8
absorbs at the shorter wavelengths (526 nm).3 The cyclic
form Cꢀ6 is thermally stable: the reverse dark reaction
C → E at 293 K was not observed for 72 h.
The colored form Cꢀ6 of 2ꢀmethylthieno[3,2ꢀb][1]ꢀ
benzothiophene does not fluoresce in toluene, in contꢀ
rast to the cyclic isomers of fulgides based on naphꢀ
tho[1,2ꢀb]furan and benzo[g]indole we have described earꢀ
lier.9
Fulgide 6 exhibits photochromism in the solid state.
When irradiated with UV light (λexc = 365 nm), goldish
yellow crystals of the isomer Zꢀ6 turned dark violet. The
electronic absorption spectrum of a solution of dark violet
crystals in toluene shows a band at 561 nm. Apparently,
Irradiation of colored solutions of fulgide Cꢀ6 with
visible light (λ = 546 nm) decolorized them. The decrease
in the intensity of the absorption peak of the Cꢀform was
Scheme 3

2404
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007
Balenko et al.
A
0.16
0.12
0.08
0.04
1.493
1.195
1.473
1.361
1.770
1.393
1.478
1.761
1.438
1.491
1.391
1.390
18.94
59.88
1.380
1.376
1.417
1.396
1.193
1.402
1.435
1.739
1.403
1.751
1.387
0
Zꢀ6
1
2
3
4
5
6
7
8
9
10 n
Fig. 5. Change in the optical density of the absorption peak
(561 nm) of the C form of fulgide 6 in toluene in repeated cycles
coloration (light irradiation with λ = 365 nm for 10 min)—
decoloration (light irradiation with λ = 546 nm for 10 min); n is
the number of cycles.
1.196
1.391
1.489
1.361
1.771
1.394
1.758
1.477
1.389
1.394
1.196
1.474
1.436
1.417
1.376
1.492
55.56
1.402
1.380
the same sequence of isomerization and cyclization phoꢀ
toreactions Z → E and E → C occurs in both the solid state
and solutions. These crystals turned again yellow upon
irradiation with visible light.
1.435
1.403
1.386
1.740
1.757
Eꢀ6
To elucidate the nature of the observed absorption
bands of fulgide 6, we performed TD B3LYP/6ꢀ311G**
calculations of the first three singlet transitions of its isoꢀ
mers whose optimized structures are shown in Fig. 6.
The theoretically predicted structural parameters of
the Zꢀisomer agree well with Xꢀray diffraction data. The
largest discrepancy between the experimental and calcuꢀ
lated bond lengths does not exceed 0.03 Å. The shorter
C—S bonds and the difference in the torsion angles beꢀ
tween the planes of the thieno[3,2ꢀb][1]benzothiophene
and fulgide fragments in the crystal compared to the calꢀ
culated values for the gas phase can be explained by packꢀ
ing effects. The spectroscopic characteristics of the sinꢀ
glet transitions for the isomers of compound 6 are given in
Table 2.
1.195
1.382
1.444
1.765
1.395
1.370
1.429
1.498
1.357
1.388
1.761
1.378
1.407
1.196
1.469
1.514
1.544
1.890
1.405
1.429
1.406
1.565
1.752
1.384
Cꢀ6
Fig. 6. B3LYP/6ꢀ311G**ꢀcalculated geometrical parameters of
the Zꢀ, Eꢀ, and Cꢀisomers of fulgide 6; bond lengths (Å) and
dihedral angles (deg) are indicated.
According to theoretical estimations, the transition
S0 → S1 in both the open forms corresponds to the charge
transfer band associated with the electron density redistriꢀ
bution between the thieno[3,2ꢀb][1]benzothiophene and
fulgide fragments. It has low intensity and most likely
corresponds to the weakly pronounced shoulder in the
longꢀwavelength part of the spectrum. The second singlet
transition of the π → π* type is responsible for the observed
longꢀwavelength absorption peak at 340 nm (3.65 eV). The
deviations of the calculated excitation energies of this
transition from the experimental values are 0.25 and
0.13 eV for the structures Zꢀ6 and Eꢀ6, respectively. The
shortꢀwavelength absorption band at 300 nm is due to
third and higher singlet transitions. As assumed, the abꢀ
sorption bands of the isomers Zꢀ6 and Eꢀ6 overlap strongly.
Table 2. DFTꢀcalculated excitation energies (Eexc) and the osꢀ
cillating forces (f) of the first three singlet transitions for the Zꢀ,
Eꢀ, and Cꢀisomers of fulgide 6 (TD B3LYP/6ꢀ311G**)
Structure
Transition
Eexc/eV
f
Zꢀ6
S0 → S1
S0 → S2
S0 → S3
S0 → S1
S0 → S2
S0 → S3
S0 → S1
S0 → S2
S0 → S3
3.13
3.40
3.90
3.28
3.52
4.07
2.13
3.09
3.50
0.023
0.112
0.005
0.009
0.086
0.107
0.189
0.122
0.007
Eꢀ6
Cꢀ6

2ꢀMethylthieno[3,2ꢀb][1]benzothiophenꢀ3ꢀylfulgide Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007 2405
The extract was washed with water and steamꢀdistilled. The
resulting compound 4 was extracted with chloroform and the
organic layer was separated and dried with CaCl2. The solvent
was evaporated in a rotary evaporator. The yield was 52%, m.p.
39—40 °C. Found (%): C, 64.39; H, 4.16. C11H8S2. Calculated
(%): C, 64.67; H, 3.95. 1H NMR, δ: 2.67 (s, 3 H, Me);
7.45—7.53, 7.85—8.00 (both m, 2 H each, H arom.); 8.05 (s,
1 H, H arom.).
According to our calculations, the longꢀwavelength
peak of the isomer Cꢀ6 is due to the transition π → π*; its
energy (2.13 eV) is close to the experimental value
(2.21 eV; 561 nm). The transition S0 → S2 is less intense
than the first one and is contributed by the transition
π → π* and the charge transfer transition. This absorption
band of the Cꢀisomer overlaps with the charge transfer
band in the spectra of the open forms. The third singlet
transition of the n → π* type for the structure Cꢀ6 appears
at 355 nm, overlapping with the intense longꢀwavelength
absorption band of the open forms. Thus, according to
the calculated data, irradiation with λ = 365 nm can inꢀ
duce the reverse photoreaction, which can explain the
experimentally observed formation of a photostationary
mixture of all three isomers (Z, E, and C) of fulgide 6.
1ꢀ(2ꢀMethylthieno[3,2ꢀb][1]benzothiophenꢀ3ꢀyl)ethanone
(5). Compound 4 (200 mg, 0.98 mmol) was triturated with dry
benzene (2 mL) and cooled to 0—5 °C. Acetyl chloride (80 mg,
1.18 mmol) was added with stirring and then SnCl4 (260 mg,
1.2 mmol) was added. The reaction mixture was stirred at ~20 °C
for 1 h, 10% HCl (2 mL) was added under cooling, and the
solvent was removed in water aspirator vacuum. The residue was
filtered off, washed with water, and dried in air. The yield was
83%, m.p. 158—160 °C (from ethanol). Found (%): C, 63.29;
H, 4.26. C13H10OS2. Calculated (%): C, 63.38; H, 4.09. IR,
ν/cm–1: 1750, 1800 (C=O). 1H NMR, δ: 2.67, 2.92 (both s, 3 H
each, Me); 7.30—7.45, 7.75—7.92 (both m, 2 H each, H arom.).
(4Z)ꢀ3ꢀ(1ꢀMethylethylidene)ꢀ4ꢀ[1ꢀ(2ꢀmethylthieno[3,2ꢀb]ꢀ
[1]benzothiophenꢀ3ꢀyl)ethylidene]dihydrofuranꢀ2,5ꢀdione (Zꢀ6).
A solution of compound 5 (2.95 g, 0.012 mol), diethyl isopropyꢀ
lidenesuccinate (2.8 g, 0.013 mol), and diisopropylamine
(1.4 mL, 0.01 mol) in THF (20 mL) was added at ~20 °C to a
stirred suspension of NaH (0.36 g, 0.015 mol) in THF (10 mL).
The reaction mixture was stirred at 30 °C for 2 h. The solvent
was removed in water aspirator vacuum. The residue was treated
with 10% HCl (10 mL). The precipitate of monoethyl ester that
formed was filtered off, and refluxed with 10% KOH (10 mL) in
methanol for 2 h. On cooling, the mixture was diluted with
water and treated with 10% HCl (30 mL). The precipitate of
dicarboxylic acid that formed was filtered off and dried in air.
The dicarboxylic acid was dissolved under heating in acetyl chloꢀ
ride (2 mL). The solvent was removed in vacuo. The product was
purified by column chromatography on silica gel with chloroꢀ
form as eluent and recrystallized from acetonitrile to give goldꢀ
ish yellow crystals. The yield was 3%, m.p. 211—213 °C. Found
(%): C, 65.00; H, 4.12. C20H16S2O3. Calculated (%): C, 65.19;
H, 4.38. IR, ν/cm–1: 1755; 1810 (C=O). UV, λmax/nm (ε): 340
(7340). 1H NMR, δ: 1.29, 1.72, 2.06, 2.23 (all s, 3 H each, Me);
6.92—7.15, 7.34—7.53 (both m, 2 H each, H arom.).
Experimental
Electronic absorption spectra were recorded on a Carryꢀ100
spectrophotometer (Varian). Photolysis of solutions in toluene
(C = 4•10–5 mol L–1) was carried out with a DRShꢀ250 highꢀ
pressure mercury lamp fitted with a set of interference light
filters. IR spectra (Nujol) were recorded on a Specord IRꢀ75
instrument. 1H NMR spectra were recorded on a Varian Unityꢀ
300 instrument (300 MHz) in CDCl3 with HMDS as the exterꢀ
nal standard.
Thieno[3,2ꢀb][1]benzothiopheneꢀ2ꢀcarboxylic acid (1) was
prepared as described earlier.5 The yield was 92%, m.p. 265 °C
(decomp.).
Thieno[3,2ꢀb][1]benzothiophene (2). Acid 1 (2 g, 8.53 mmol)
was heated in an open flask at 240—250 °C for 50 min. On
cooling, the reaction mixture was dissolved in benzene (120 mL)
and the solution was washed with 1% NaOH (25 mL) and water.
The benzene layer was separated, dried with CaCl2, treated with
activated charcoal (0.5 g), and filtered off. A greater part of the
solvent was removed and the product was precipitated with light
petroleum. The yield was 88%, m.p. 94—97 °C. Found (%):
C, 63.19; H, 3.26. C10H6S2. Calculated (%): C, 63.12; H, 3.18.
1H NMR, δ: 7.32 (d, 1 H, H arom., J = 5 Hz); 7.32—7.45
(m, 2 H, H arom.); 7.51 (d, 1 H, H arom., J = 5 Hz); 7.84—7.86
(m, 2 H, thiophene).
Thieno[3,2ꢀb][1]benzothiopheneꢀ2ꢀcarbaldehyde (3). A mixꢀ
ture of compound 2 (0.5 mg, 2.60 mmol), Nꢀmethylformanilide
(0.39 g, 2.86 mmol), and POCl3 (0.44 g, 2.86 mmol) was stirred
at ~20 °C for 4 h and then heated at 50—55 °C for 0.5 h. On
cooling, the reaction mixture was kept for 12 h and treated with
water with ice (25 mL). The precipitate that formed was thorꢀ
oughly triturated with water, filtered off, washed with water
several times, and dried in air. The yield was 99%, m.p.
100—102 °C (from ethanol). Found (%): C, 60.39; H, 2.54.
4,10a,11,11ꢀTetramethylꢀ10a,11ꢀdihydro[1]benzoꢀ
thiopheno[2´,3´:4,5]thieno[2,3ꢀf][2]benzofuranꢀ1,3ꢀdione (Cꢀ6)
was obtained in a tube of the NMR spectrometer as a mixture
with the isomers Zꢀ6 and Eꢀ6 upon 3ꢀh irradiation of a solution
of fulgide Zꢀ6 in deuterated toluene (C = 2.4•10–2 mol L–1
)
with λexc = 365 nm. 1H NMR, δ: 1,15, 1.26, 1.42, 2.25 (all s, 3 H
each, Me); 6.90—7.15 (m, 4 H, H arom.).
(4E)ꢀ3ꢀ(1ꢀMethylethylidene)ꢀ4ꢀ[1ꢀ(2ꢀmethylthieno[3,2ꢀb]ꢀ
[1]benzothiophenꢀ3ꢀyl)ethylidene]dihydrofuranꢀ2,5ꢀdione
(Eꢀ6). A. The isomer was obtained as described for Cꢀ6 as a
mixture with the isomers Zꢀ6 and Cꢀ6 upon 3ꢀh irradiation
of a solution of fulgide Zꢀ6 in deuterated toluene
(C = 2.4•10–2 mol L–1) with λexc = 365 nm.
B. The isomer was obtained from the isomer Cꢀ6 in a tube of
the NMR spectrometer as a mixture with Zꢀ6 upon 3ꢀh irradiaꢀ
tion of a solution containing all three isomers in deuterated
toluene (C = 2.4•10–2 mol L–1) with λexc = 546 nm. 1H NMR,
δ: 0.68, 1.08, 1.54, 2.57 (all s, 3 H each, Me); 6.90—7.15,
7.34—7.53 (both m, 2 H each, H arom.).
C11H6O2S2. Calculated (%): C, 60.52; H, 2.77. IR, ν/cm–1
:
1
1770 (C=O). H NMR, δ: 7.45—7.53, 7.85—8.00 (both m, 2 H
each, H arom.); 8.00 (s, 1 H, H arom.); 10.01 (s, 1 H, CHO).
2ꢀMethylthieno[3,2ꢀb][1]benzothiophene (4). A mixture of
aldehyde 3 (450 mg, 2.06 mmol), NaOH (300 mg, 7.5 mmol),
and 85% hydrazine hydrate (0.8 mL, 13.5 mmol) was refluxed in
diethylene glycol (5 mL) for 3 h. The solution was diluted with
water (25 mL) and the product was extracted with chloroform.

2406
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007
Balenko et al.
Xꢀray diffraction analysis. A 3D set of reflection intenꢀ
sities were collected and the unit cell parameters of the crystal
were determined on a Bruker Pꢀ4 automated diffractometer
(MoꢀKα radiation, graphite monochromator). Crystals of
compound 6 are monoclinic, C20H16O3S2, M = 368.45; a =
7.772(2) Å, b = 28.634(7) Å, c = 8.235(2) Å, β = 108.00(1)°,
Southern Scientific Center of the Russian Academy of Sciencꢀ
es], 2005, 2, 58 (in Russian).
3. A. P. Glazo, S. A. Harris, H. G. Heller, W. Johncock, S. N.
Oliver, P. J. Strydom, and J. Whittal, J. Chem. Soc., Perkin
Trans., 1985, 957.
4. A. Tomoda, A. Kaneko, H. Tsuboi, and R. Matsushima,
Bull. Chem. Soc. Jpn, 1992, 65, 1262.
5. P. Cagniant, M.ꢀM. Briola, and G. Kirsch, C. R. Seances
Acad. Sci., Ser. C, 1977, 285, 21.
V = 1742.9(3) Å3, Z = 4, ρ
= 1.404 g cm–3, µ(MoꢀKα) =
calc
0.32 mm–1, space group P21/c. The intensities of 3658 reflections
were measured in the quadrant of reciprocal space (2θ ≤ 50°) in
the ω/2θ scan mode for a single crystal 0.1Ѕ0.3Ѕ0.4 mm. After
systematic absences were excluded and the intensities of equivaꢀ
lent reflections were averaged, the working array of measured
F2(hkl) and σ(F2) included 2709 independent reflections; the
number of reflections with F2 > 4σ(F2) was 1764. The structure
was solved by the direct method with the SHELXSꢀ97 proꢀ
gram10 and refined by the fullꢀmatrix leastꢀsquares method on
F2 with the SHELXLꢀ97 program10 in the anisotropic approxiꢀ
mation for nonꢀhydrogen atoms. In the crystal structure 6, all
hydrogen atoms were located from the electron density differꢀ
ence map; the coordinates and isotropic thermal parameters of
all the H atoms were refined by the leastꢀsquares method in the
rider model.10 The fullꢀmatrix refinement was continued until
the absolute differences for all 226 variable parameters of strucꢀ
ture 6 were less than 0.001σ. Final residuals were R1 = 0.050 and
wR2 = 0.14 for 1764 observed reflections with I ≥ 2σ(I) and
R1 = 0.093 and wR2 = 0.11 for all 2709 measured reflections;
GOF = 1.039. The residual maximum and minimum electron
densities were 0.247 and –0.258 e Å–3, respectively.
6. H. G. Heller and S. N. Oliver, J. Chem. Soc., Perkin Trans.,
1981, 197.
7. V. P. Rybalkin, E. N. Shepelenko, V. V. Tkachev, G. V.
Shilov, S. K. Balenko, A. V. Tsukanov, L. L. Popova, A. D.
Dubonosov, S. M. Aldoshin, V. A. Bren, and V. I. Minkin,
Izv. Akad. Nauk, Ser. Khim., 2006, 97 [Russ. Chem. Bull.,
Int. Ed., 2006, 55, 101].
8. G. V. Timofeeva, N. I. Chernikova, and P. M. Zorkii, Usp.
Khim., 1980, 69, 966 [Russ. Chem. Rev., 1980, 69 (Engl.
Transl.)].
9. S. K. Balenko, V. P. Rybalkin, E. N. Shepelenko, L. L.
Popova, N. I. Makarova, A. V. Metelitsa, V. A. Bren, and
V. I. Minkin, Zh. Org. Khim., 2006, 42, 1869 [Russ. J. Org.
Chem., 2006, 42, 1861 (Engl. Transl.)].
10. G. M. Sheldrick, The SHELXꢀ97, University of Göttingen,
Göttingen (Germany), 1997.
11. A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
12. C. Lee, W. Yang, and R. G. Parr, Phys. Rev. B, 1988, 37, 785.
13. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr.,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth,
P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapꢀ
prich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz,
Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Steꢀ
fanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. AlꢀLaham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill,
B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, and J. A.
Pople, GAUSSIAN 03, Revision D.01, Gaussian, Inc., Wallꢀ
ingford CT, 2004.
Quantumꢀchemical calculations. The geometrical parameꢀ
ters of the isomers of fulgide 6 were optimized in terms of density
functional theory (DFT) with the B3LYP hybrid exchangeꢀcorꢀ
relation functional11,12 using the 6ꢀ311G** basis set. Spectroꢀ
scopic characteristics were calculated in terms of TD DFT using
the same basis set. All calculations were performed with the
Gaussian 03 program package.13
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 06ꢀ03ꢀ
32988), the Ministry of Education and Science of the
Russian Federation (Branch Scientific Program "Develꢀ
opment of the scientific potential of higher school", Project
RNP 2.1.1.1938), and the Council on Grants of the Presꢀ
ident of the Russian Federation (Program for State Supꢀ
port of Leading Scientific Schools of the Russian Federaꢀ
tion, Grant NShꢀ4849.2006.3).
References
1. Y. Yokoyama, Chem. Rev., 2000, 100, 1717.
2. V. A. Bren, A. D. Dubonosov, and V. I. Minkin, Vestn.
Yuzhn. Nauchn. Tsentra Ross. Akad. Nauk [Bulletin of the
Received June 21, 2007;
in revised form September 12, 2007