Synthesis and photochromic properties of tetrakis(3,5-dimethyl-2-thienyl)- and tetrakis(2,5-dimethyl-3-thienyl)ethylenes

Article abstract of DOI:10.1007/s11172-005-0382-5

Tetrakis(3,5-dimethyl-2-thienyl)ethylene and tetrakis(2,5-dimethyl-3- thienyl)ethylene were obtained from the corresponding dithienyl ketones by the McMurry reaction. The photochromic properties of the compounds obtained were studied.

Full text of DOI:10.1007/s11172-005-0382-5

1208
Russian Chemical Bulletin, International Edition, Vol. 54, No. 5, pp. 1208—1213, May, 2005
Synthesis and photochromic properties of tetrakis(3,5ꢀdimethylꢀ2ꢀthienyl)ꢀ
and tetrakis(2,5ꢀdimethylꢀ3ꢀthienyl)ethylenes*
ꢀ
L. I. Belen´kii, G. P. Gromova, A. V. Kolotaev, B. V. Nabatov, and M. M. Krayushkin
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Eꢀmail: libel@ioc.ac.ru
Tetrakis(3,5ꢀdimethylꢀ2ꢀthienyl)ethylene and tetrakis(2,5ꢀdimethylꢀ3ꢀthienyl)ethylene
were obtained from the corresponding dithienyl ketones by the McMurry reaction. The photoꢀ
chromic properties of the compounds obtained were studied.
Key words: dihetarylethenes, photochromes, McMurry reaction, thiophenes, ketones.
Scheme 1
Photochromic compounds and materials are capable
of being transformed reversibly, so that substance A
(photochrome) exposed to light is converted into prodꢀ
uct B, which differs from A in absorption spectrum (color)
and other physicochemical properties. Photochromes are
used in actinometers, dosimeters, various optoelectronic
devices, and such common goods as sun glasses; presꢀ
ently, they are considered to be extremely promising sysꢀ
tems for data storage.1
The possibility of using photochromes as optical storꢀ
age elements is determined first of all by two specific
properties: the number of the interconversions A
B
until 20% of a sample has decomposed2 (fatigue resisꢀ
tance) and the thermal irreversibility of phototransforꢀ
mations. 1,2ꢀDihetarylethenes are ones of the best therꢀ
mally irreversible photochromes, their fatigue resistance
being high (up to 10 000 cycles).3 Since only cisꢀ1,2ꢀdiꢀ
hetarylethenes are capable of photocyclization of the deꢀ
sired type, cisꢀtrans isomerization must be prevented. This
is attained by fixing the cisꢀform in cyclic ethene fragꢀ
ments (most often, these are the residues of perfluoroꢀ
cyclopentene, maleic anhydride, and maleimide)
(Scheme 1).1,2
At the same time, it is evident that if triꢀ or tetraꢀ
substituted ethylene contains three or four identical hetaryl
residues, its cisꢀtrans isomerization is degenerate and such
compounds retain the ability to photocyclize. In the
present work, we describe the syntheses of tetrakis(3,5ꢀdiꢀ
methylꢀ2ꢀthienyl)ethylene (1) and tetrakis(2,5ꢀdimethylꢀ
3ꢀthienyl)ethylene (2) and the primary data on their
photochromic properties.
(Scheme 2). The starting ketones were prepared by seꢀ
quential reactions: formylation of dimethylthiophenes 5
and 6, oxidation of aldehydes 7 and 8 into acids 9 and 10,
their transformation into acid chlorides, and final acylaꢀ
tion of dimethylthiophenes 5 and 6.
The McMurry reaction, which is a reductive coupling
of carbonyl compounds in the presence of lowꢀvalence
titanium reagents (see reviews4,5), has been repeatedly
used to synthesize photochromic dithienylethenes with
perfluorocyclopentene and cycloalkene fragments6,7 and
2,5ꢀdihydrothiophene as the ethene bridge.8,9 Nonꢀ
photochromic tetra(2ꢀthienyl)ethylene has also been obꢀ
tained by this reaction.10 However, for the syntheses of
the target compounds 1 and 2, thorough optimization of
the reaction conditions was required.
Compounds 1 and 2 were obtained from the correꢀ
sponding ketones 3 and 4 by the McMurry reaction
The reduction of bis(3,5ꢀdimethylꢀ2ꢀthienyl) ketone
(3) with a lowꢀvalence titanium reagent generated in
the TiCl4—Zn system led to tetrakis(3,5ꢀdimethylꢀ2ꢀ
* Dedicated to the Academician N. K. Kochetkov on the occaꢀ
sion of his 90th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1177—1181, May, 2005.
1066ꢀ5285/05/5405ꢀ1208 © 2005 Springer Science+Business Media, Inc.

Tetrakis(dimethylthienyl)ethylenes
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 5, May, 2005
1209
Scheme 2
Reagents and conditions: a. Me2NCHO/POCl3 (in the synthesis of compound 1) or MeOCHCl2/TiCl4 (in the synthesis of comꢀ
pound 2); b. CrO3, H2SO4, acetone; c. SOCl2; d. 2,4ꢀdimethylthiophene (in the synthesis of compound 1) or 2,5ꢀdimethylthiophene
(in the synthesis of compound 2), AlCl3, CH2Cl2; e. TiCl3—LiAlH4.
thienyl)ethane (11) in 65% yield. When starting from
bis(2,5ꢀdimethylꢀ3ꢀthienyl) ketone (4), we obtained
a mixture of ethylene 2 and tetrakis(2,5ꢀdimethylꢀ3ꢀ
thienyl)ethane (12) in the nearly 1 : 1 ratio; the overall
yield of these compounds was 40%.
tetramethylꢀ2,5ꢀdihydrothiophene as the expected prodꢀ
uct of the McMurry reaction; instead, this compound
underwent reductive desulfurization leading to 3ꢀisoꢀ
butyroylꢀ2,5ꢀdimethylthiophene. When a titanium reagent
was generated in the TiCl3—LiAlH4 system, a mixture of
a desulfurization product and 3,4ꢀbis(2,5ꢀdimethylꢀ3ꢀ
thienyl)ꢀ2,2,5,5ꢀtetramethylꢀ2,3,4,5ꢀtetrahydrothiophene
was obtained; however, no formation of the target dihydroꢀ
thiophene derivative was observed.
The use of the TiCl3—LiAlH4 system for generation of
a lowꢀvalence titanium reagent for ketones 3 and 4 yielded
mixtures 1 + 11 and 2 + 12 in the 3 : 1 and 6 : 1 ratios,
respectively. The target products, namely, tetrakis(3,5ꢀdiꢀ
methylꢀ2ꢀthienyl)ethylene (1) and tetrakis(2,5ꢀdimethylꢀ
3ꢀthienyl)ethylene (2), were isolated from the reaction
mixtures. The structures of substituted ethylenes 1 and 2
and substituted ethanes 11 and 12 were confirmed by
1H NMR and mass spectra and elemental analysis data.
In particular, the 1H NMR spectrum of compound 1
agrees with the published data for its close analogs,
namely, tetra(2ꢀthienyl)ethylene and its derivatives
It is worth noting that the intramolecular McMurry
reaction with the same system afforded 3,4ꢀbis(2,5ꢀdiꢀ
methylꢀ3ꢀthienyl)ꢀ2,5ꢀdihydrothiophene only in 11%
yield8,9 (no other products were mentioned). Earlier,11 an
attempted cyclization of 2,4ꢀdimethylꢀ2,4ꢀbis(2,5ꢀdiꢀ
methylꢀ3ꢀthenoyl)ꢀ3ꢀthiapentane under the same condiꢀ
tions gave no 3,4ꢀbis(2,5ꢀdimethylꢀ3ꢀthienyl)ꢀ2,2,5,5ꢀ

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Russ.Chem.Bull., Int.Ed., Vol. 54, No. 5, May, 2005
Belen´kii et al.
Table 1. Photochromic and fluorescent properties of solutions of compounds 1 and 2 in
acetonitrile (c = 1•10–4 mol L–1
)
A
Comꢀ
pound
λ /nm
DA
λ /nm
DB
λ
Fl/nm
IA
Fl
/rel. unit
∆λ/nm
A
B
1
255
288
382
314
1.71
1.72
1.12
0.81
255
288
382
313
451
1.76
1.55
0.89
1.02
0.14
330
530
0.75
0.2
42
148
2
400
0.95
86
Note. The exposure time was 3 min.
tetra(5ꢀmethylꢀ2ꢀthienyl)ꢀ and tetra(5ꢀmethylthioꢀ2ꢀ
thienyl)ethylenes.10
We estimated the photochromic and fluorescent propꢀ
erties of compounds 1 and 2. The results obtained are
given in Table 1.
bands appeared in the visible range; the position and shape
of the persistent absorption band at λ = 382 nm remained
unchanged, although its optical density decreased or inꢀ
creased in proportion to the irradiation duration and the
light wavelength. Simultaneously, opposite changes were
observed in the UV range from 250 to 290 nm (Fig. 1, a).
Note that after an irradiated sample of compound 1 was
kept in the dark for 10 days, its optical densities at λ = 382
and 250—290 nm changed noticeably, approaching the
initial (preirradiation) values. Compound 1 fluoresces (two
When compound 1 was alternately irradiated with light
at wavelengths of 365 and 313 nm, no new absorption
D
2.0
5
emission bands at λA = 330 and 530 nm). Compound 2
Fl
1
a
exhibits both photochromic (the closed form with an abꢀ
sorption maximum at 450 nm (Fig. 2, b)) and fluorescent
properties (the band at 400 nm).
1
1.5
5
382 nm
1
5
Thus, with tetrathienylethylene 2 as an example, we
discovered a route to photochromic systems of this type.
The behavior of compound 1 calls for further discussion.
Earlier,12 it was found that the electronic absorption specꢀ
trum of Nꢀcyanomethylꢀ2,3ꢀbis(3,4ꢀdimethylꢀ5ꢀphenylꢀ
2ꢀthienyl)maleimide, which also contains the 2ꢀthienyl
fragments, remained unchanged upon irradiation with visꢀ
ible and UV light at any wavelength. This was associated12
with the inefficiency of photocyclization and a high quanꢀ
tum yield of ring opening. Apparently, compound 1 is a
1.0
0.5
300
400
500
600
700
λ/nm
D
3.0
2.5
2.0
1.5
1.0
0.5
1
b
5
314 nm
5
5
1
1
450 nm
300
400
500
600
700
λ/nm
Fig. 1. Electronic absorption spectra of solutions of comꢀ
pounds 1 (a) and 2 (b) in acetonitrile at 298 K for a 1ꢀcmꢀthick
layer: (1) the initial solutions; (2)—(5) the solutions exposed to
light with λ = 365 (for 1) or 313 nm (for 2) for 0.5 (2), 1 (3),
2 (4), and 3 min (5).

Tetrakis(dimethylthienyl)ethylenes
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 5, May, 2005
1211
sure—opening cycle was repeated several times to check the
photochromic properties of this compound.
thermally reversible inverse photochrome, in which
cyclic form 1B provides less efficient conjugation
(di(vinylthio)butadiene fragment C=C—S—C=C—
C=C—S—C=C) than open form 1A (decapentaene fragꢀ
ment C=C—C=C—C=C—C=C—C=C).
At the same time, in the photochromic transformation
of tetra(βꢀthienyl)ethylene 2A, the di(vinylthio)hexatriene
The fluorescence spectra of compound 2 were recorded as
described for compound 1. Excitation of the initial solution with
light at λEx = 340 nm resulted in its luminescence at 400 nm.
2,4ꢀDimethylthiophene (5) was prepared according to
a known procedure13 by the Kishner—Wolff reduction of
2,4ꢀthiophenedicarbaldehyde.14
fragment
C=C—S—C=C—C=C—C=C—S—C=C
2,5ꢀDimethylthiophene (6) was prepared as described earꢀ
lier15 from acetonylacetone and phosphorus pentasulfide.
3,5ꢀDimethylthiopheneꢀ2ꢀcarbaldehyde (7). Phosphorus oxyꢀ
chloride (5.1 mL, 8.54 g, 55.8 mmol) was added at 10 °C to
DMF (9.7 g, 132.8 mmol). The resulting complex was kept at
75—80 °C for 10 min and cooled to 10 °C and 2,4ꢀdimethylꢀ
thiophene (5 g, 44.6 mmol) was added. The resulting brown
solution was heated at 70—75 °C for 3 h and cooled to ~20 °C.
The thick mixture was decomposed with 15% CH3COONa
(aq, 30 mL). The product was extracted with chloroform
(5×30 mL), washed with water, and dried over MgSO4. The
solvent was distilled off to give aldehyde 7 (4.15 g, 66%), b.p.
120 °C (15 Torr), which agrees with the literature data.16
2,5ꢀDimethylthiopheneꢀ3ꢀcarbaldehyde (8). Solutions of
α,αꢀdichlorodimethyl ether (7.3 g, 90.6 mmol) in CH2Cl2
(15 mL) and 2,5ꢀdimethylthiophene (7.8 g, 69.6 mmol) in
CH2Cl2 (15 mL) were added simultaneously from two funnels at
T < 5 °C to a solution of TiCl4 (33.1 g, 19.1 mL, 174 mmol) in
CH2Cl2 (20 mL). The mixture was kept at this temperature
for 2 h (until the evolution of HCl was ceased), warmed to room
temperature over 30 min, poured into ice acidified with HCl,
washed with water, and dried over MgSO4. The solvent was
removed and the residue was distilled to give aldehyde 8 (5.85 g,
60%), b.p. 114 °C (20 Torr), which agrees with the literaꢀ
ture data.17
changes into the octatetraene fragment C=C—C=C—
C=C—C=C in cyclic form 2B. It is also possible that
the formation of a new C—C bond in the transformaꢀ
tion 1A → 1B requires more energy hν than that transꢀ
ferred during the irradiation with this (minimum posꢀ
sible) wavelength.
Experimental
1
H NMR spectra were recorded on Bruker AMꢀ300 and
Bruker ACꢀ200 instruments in CDCl3. Mass spectra (EI) were
recorded on a Kratos instrument (70 eV, direct inlet probe).
Melting points were determined on a Boetius microscope stage
and are given uncorrected. The course of the reactions was
monitored and the purity of the products was checked by TLC
on Silica gel 60 F254 plates (Merck); spots were visualized under
UV light). Column chromatography was carried out on SiO2ꢀ60
silica gel (0.060—0.200 mm; Merck).
Titanium tetrachloride, zinc powder (highꢀpurity grade),
lithium aluminum hydride, titanium trichloride, and α,αꢀdiꢀ
chlorodimethyl ether (Aldrich Co.) were used. Acetonitrile
(99% purity, Acros Co.) was employed for spectroscopic meaꢀ
surements.
The absorption and fluorescence spectra of solutions of comꢀ
pounds 1 and 2 irradiated with visible and UV light were reꢀ
corded on a Varian Cary 50 Bio spectrophotometer and a
Fluoratꢀ02 Panorama spectrofluorimeter using an OIꢀ18A luꢀ
minescent illuminator fitted with a DRKꢀ120 mercury quartz
lamp. The concentrations of compounds 1 and 2 in acetonitrile
were 1•10–4 mol L–1. Measurements were carried out in 10ꢀmm
quartz cuvettes under the following conditions: monochromator
step 1 nm, slit width 3 nm, and averaging over three to five
points in each step. The results obtained are given in Table 1.
The initial solution of compound 1 at the aforesaid concenꢀ
tration is colored pale yellow with a greenish tinge. This solution
was alternately (alternation was effected every 4 min) irradiated
through light filters for λ = 365 and 313 nm and its absorption
spectra were recorded. The color of the irradiated solution reꢀ
mained virtually unchanged.
3,5ꢀDimethylthiopheneꢀ2ꢀcarboxylic acid (9). The Jones reꢀ
agent (12 mL) prepared from CrO3 (39 g), water (117 mL), and
conc. H2SO4 (30 mL) was added to a stirred solution of aldeꢀ
hyde 7 (1.8 g, 12.9 mmol) in acetone (40 mL) cooled in a water
bath (<20 °C). The addition rate was regulated so that the orꢀ
ange color disappeared. The mixture was stirred at room temꢀ
perature for 6 h. The solution was decanted from the green
precipitate of Cr2O3 and concentrated to ~1/10 of the volume
and the precipitate was washed with ether. The ethereal extract
was combined with the concentrated solution in acetone and
washed with water to remove sulfuric acid. Acid 9 was extracted
with a saturated solution of NaHCO3. Acidification with conc.
HCl gave acid 9 (0.86 g), m.p. 170—173 °C, which agrees with
the literature data.16 The ethereal extract was concentrated and
the residue (0.6 g) containing the starting aldehyde was reoxidized
with the Jones reagent to give an additional crop of acid 9
(0.25 g). Its total yield was 1.11 g (~55%).
The fluorescence spectra of compound 1 were recorded beꢀ
fore irradiation of its solution by scanning the emission waveꢀ
2,5ꢀDimethylthiopheneꢀ3ꢀcarboxylic acid (10) was obtained
as described for acid 9. The yield of compound 10 was 65%, m.p.
114—115 °C, which agrees with the literature data.18
Ex
length range for two excitation wavelengths: λ 1 = 300 nm and
Ex
λ
= 380 nm. The spectra contained two fluorescence bands
2
with the emission maxima at 330 and 530 nm.
The initial solution of compound 2 was transparent in the
visible range of the spectrum. The irradiated solution turned
3,5ꢀDimethylthiopheneꢀ2ꢀcarbonyl chloride was obtained by
the action of thionyl chloride (1.24 g, 0.75 mL) on acid 9 (1.47 g,
9.4 mmol) in the presence of a catalytic amount of DMF. The
mixture was stirred at room temperature for 3 h, SOCl2 was
removed, and the residue was distilled. The yield of the acid
chloride was 1.85 g (62.5%), b.p. 97 °C (2.5 Torr). The product
was used without additional purification.
pale yellow because of the formation of cyclic form 2B with the
B
absorption maximum λ
= 450 nm. Irradiation of the soluꢀ
max
tion at the wavelength of this new band caused the cyclic form to
undergo opening, the solution becoming colorless. Such a cloꢀ

1212
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 5, May, 2005
Belen´kii et al.
2,5ꢀDimethylthiopheneꢀ3ꢀcarbonyl chloride was obtained
analogously from acid 10 in 65% yield.
1.05 mmol), a Zn powder (0.15 g, 2.25 mmol), and pyridine
(0.086 mL) in dry THF (5 mL) was refluxed under argon for 7 h.
The resulting thick mass was treated with 10% K2CO3 (50 mL)
and the products were extracted with CH2Cl2. The extract was
washed with water, dried over MgSO4, and concentrated. Benꢀ
zene (3 mL) was added to the residue and a substance (0.04 g)
with m.p. 230—248 °C was separated. According to 1H NMR
data, the substance was tetrakis(2,5ꢀdimethylꢀ3ꢀthienyl)ethane
(12) with an admixture of ethene 2. The benzene solution was
concentrated to an oil, from which a substance (0.05 g) with
m.p. ~200 °C was precipitated with hexane. According to
1H NMR data, the substance was tetrakis(2,5ꢀdimethylꢀ3ꢀ
thienyl)ethylene (2) with an admixture of ethane 12. The overall
yield of compounds 2 and 12 was ~40%.
B. A mixture of TiCl3 (0.25 g, 1.6 mmol), LiAlH4 (0.03 g,
0.8 mmol), and ketone 4 (0.2 g, 0.8 mmol) in dry THF (8 mL)
was prepared as described for ketone 3 (procedure B). The mixꢀ
ture was refluxed for 7.5 h and treated with THF (5 mL), ether
(5 mL), and water (10 mL). The organic layer was sepaꢀ
rated and the products from the aqueous layer were extracted
with ether. The extract was washed with water, dried over
MgSO4, and concentrated to an oil containing compounds 2
and 12 in the ratio 6 : 1 (1H NMR data). A solid was isolated
by addition of hexane (3 mL); the solid was ethylene 2 (90%
purity; 1H NMR data). The residue was separated by column
chromatography with light petroleum—ethyl acetate (50 : 1) as
an eluent to give additional crops of ethylene 2 (0.02 g) and
ethane 12 (~0.02 g). The total yield of compound 2 was
0.11 g (58%).
Bis(3,5ꢀdimethylꢀ2ꢀthienyl) ketone (3). Aluminum trichloꢀ
ride (0.68 g, 5.1 mmol) was added in portions to a stirred soluꢀ
tion of the chloride (0.8 g, 4.58 mmol) obtained from acid 9 and
2,4ꢀdimethylthiophene (5) (0.52 g, 4.68 mmol) in CH2Cl2
(10 mL). The mixture was kept for 4 h and poured into water.
The product was extracted with CH2Cl2 and the extract was
dried over MgSO4. The solvent was removed and the residue was
recrystallized from hexane. The yield of compound 3 was 72%,
m.p. 60 °C. Found (%): C, 62.26; H, 6.19; S, 25.05. C13H14OS2.
Calculated (%): C, 62.36; H, 5.64; S, 25.61.
Bis(2,5ꢀdimethylꢀ3ꢀthienyl) ketone (4) was obtained analoꢀ
gously from 2,5ꢀdimethylthiophene (6). The yield of comꢀ
pound 4 was 85%, m.p. 65 °C, which agrees with the literaꢀ
ture data.18
McMurry condensation of bis(3,5ꢀdimethylꢀ2ꢀthienyl) ketone
(3). A. Titanium tetrachloride (0.63 g, 3.3 mmol) was added
dropwise in an atmosphere of argon at T < 5 °C to dry THF
(10 mL). Then a Zn powder (0.425 g, 6.6 mmol) and a solution
of ketone 3 (0.55 g, 2.2 mmol) in THF (6 mL) were added in
portions. The resulting black mixture was kept at T < 5 °C for 2 h
and dry pyridine (0.2 mL) was added. The mixture was reꢀ
fluxed to decoloration (10 h) and treated with a solution of
K2CO3 (2 g) in water (20 mL). The inorganic precipitate that
formed was filtered off and washed with ether. The organic
products from the aqueous solution were extracted with ether.
The combined ethereal extracts were dried over MgSO4 and
concentrated.
Tetrakis(3,5ꢀdimethylꢀ2ꢀthienyl)ethane (11) was precipitated
by addition of several milliliters of hexane to the residue. The
yield of compound 11 was 0.34 g (65%), m.p. 207—210 °C (from
hexane). Found (%): C, 66.19; H, 6.47; S, 26.68. C26H30S4.
Tetrakis(2,5ꢀdimethylꢀ3ꢀthienyl)ethylene (2) was isolated by
washing the above mixture with hexane; m.p. 198 °C. Found (%):
C, 66.27; H, 6.14; S, 27.43. C26H28S4. Calculated (%): C, 66.62;
H, 6.02; S, 27.35. 1H NMR, δ: 1.89 (s, 12 H, 4 Me); 2.24 (s,
12 H, 4 Me); 6.15 (s, 4 H, Hthioph). MS, m/z (Irel (%)): 468 [M]+
(33), 235 [M/2+H]+ (100).
1
Calculated (%): C, 66.33; H, 6.42; S, 27.24. H NMR, δ: 1.99
(s, 12 H, 4 Me); 2.31 (s, 12 H, 4 Me); 4.91 (s, 2 H, 2 Hethane);
6.27 (s, 4 H, Hthioph). MS, m/z (Irel (%)): 235 [M/2]+ (100).
B. Titanium trichloride (0.36 g, 2.4 mmol) and LiAlH4
(0.045 g, 1.2 mmol) were added successively in an atmosphere of
argon to cooled dry THF (8 mL). The resulting mixture was
refluxed to the formation of a reductive black mixture (30 min).
The mixture was cooled and ketone 3 (0.3 g, 1.2 mmol) in dry
THF (2 mL) was added. The mixture was kept at ~20 °C for
15 min and refluxed to decoloration (6.5 h). Tetrahydrofuran
(15 mL) and ether (15 mL) were added and the mixture was
poured into water (10 mL). The precipitate that formed was
filtered off, the organic layer was separated, and the products
from the aqueous layer were extracted with ether. The combined
extracts were washed with water, dried over MgSO4, and conꢀ
centrated. The residue was additionally purified on silica gel
with light petroleum—ethyl acetate (100 : 1) as an eluent. The
eluent was removed to give a mixture of compounds 1 and 11
in the ratio 4.5 : 1 (1H NMR data). The overall yield was
0.27 g (70%).
Tetrakis(2,5ꢀdimethylꢀ3ꢀthienyl)ethane (12) was isolated by
chromatography; m.p. 247—250 °C. Found (%): C, 66.15;
H, 6.54; S, 26.91. C26H30S4. Calculated (%): C, 66.33; H, 6.42;
S, 27.24. 1H NMR, δ: 2.08 (s, 12 H, 4 Me); 2.25 (s, 12 H, 4 Me);
4.31 (s, 2 H, 2 Hethane); 6.47 (s, 4 H, Hthioph). MS, m/z:
235 [M/2]+.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 04ꢀ03ꢀ32878)
and the International Scientific and Technical Center
(Project No. 2117).
References
1. M. M. Krayushkin, Khim. Geterotsikl. Soedin., 2001, 19
[Chem. Heterocycl. Compd., 2001 (Engl. Transl.)].
2. M. Irie, Chem. Rev., 2000, 100, 1685.
3. M. Irie and M. Mohri, J. Org. Chem., 1988, 53, 803.
4. J. E. McMurry, Acc. Chem. Res., 1983, 16, 405.
5. D. Lenoir, Synthesis, 1989, 883.
Tetrakis(3,5ꢀdimethylꢀ2ꢀthienyl)ethylene (1) was isolated by
washing the above mixture with hexane; m.p. 170—173 °C.
Found (%): C, 66.42; H, 6.13; S, 27.05. C26H28S4. Calcuꢀ
lated (%): C, 66.62; H, 6.02; S, 27.35. 1H NMR, δ: 1.80 (s,
12 H, 4 Me); 2.35 (s, 12 H, 4 Me); 6.35 (s, 4 H, Hthioph). MS,
m/z (Irel (%)): 468 [M]+ (27), 235 [M/2+H]+ (100).
6. L. N. Lucas, J. van Esch, R. M. Kellogg, and B. L. Feringa,
Chem. Commun., 1998, 2313.
McMurry condensation of bis(2,5ꢀdimethylꢀ3ꢀthienyl) ketone
(4). A. A mixture of ketone 4 (0.25 g, 1 mmol), TiCl4 (0.2 g,
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Received March 25, 2005;
in revised form April 5, 2005