Synthesis of Novel 4,4-Dialkyl- and 4,4-Diarylindeno[1,2-b]Thiophenes and their 2-Bromo Derivatives

Article abstract of DOI:10.1007/s10593-014-1605-1

A series of new 4,4-dialkyl- and 4,4-diaryl-4H-indeno[1,2-b]thiophenes and their 2-bromo derivatives were synthesized and characterized. An economical one-pot method for the preparation of the key starting material 2-(2-thienyl)benzoic acid and improved p

Full text of DOI:10.1007/s10593-014-1605-1

DOI 10.1007/s10593-014-1605-1
Chemistry of Heterocyclic Compounds, Vol. 50, No. 10, January, 2015 (Russian Original Vol. 50, No. 10, October, 2014)
SYNTHESIS OF NOVEL 4,4-DIALKYL- AND
4,4-DIARYLINDENO[1,2-b]THIOPHENES AND
THEIR 2-BROMO DERIVATIVES*
J. Bucevicius1, P. Adomenas2, and S. Tumkevicius1**
A series of new 4,4-dialkyl- and 4,4-diaryl-4H-indeno[1,2-b]thiophenes and their 2-bromo derivatives were
synthesized and characterized. An economical one-pot method for the preparation of the key starting
material 2-(2-thienyl)benzoic acid and improved procedures for the synthesis of indeno[1,2-b]thiophen-
4-one and 4,4-dialkyl-4H-indeno[1,2-b]thiophenes have been developed. The described methods were
shown to be efficient for the preparation of the title compounds on a multigram scale.
Keywords: indeno[1,2-b]thiophenes, sulfur heterocycles, alkylation, bromination, Kumada coupling.
4H-Indeno[1,2-b]thiophene is an attractive molecule with potentially interesting properties owing to its
unique structure highly reminiscent to fluorene. Compounds possessing this heterocyclic moiety were found to
display a wide range of functional material properties and are useful for the construction of sensitizers for dye-
sensitized solar cells [1, 2], p-type organic semiconductors for organic thin film transistors [3-6], chromophores in
luminescent materials [7], or as spacers in D-π-A [8] dyes for liquid or solid state solar cells. Continuing our program
focused on the search of novel heterocyclic compounds with valuable properties [9-11], we present herein a
synthesis of the title compounds and some improved procedures for the preparation of intermediates.
For the construction of 4H-indeno[1,2-b]thiophene ring system, 2-(2-thienyl)benzoic acid or the
corresponding benzoates are the most often used starting materials [3, 12]. These compounds, as well as their
precursor, 2-(2-thienyl)benzonitrile, can be obtained by Ullmann coupling [12], palladium-catalyzed desulfinylative
[13, 14] or Stille [15, 16] reactions, or using manganese-catalyzed oxidative cross coupling of the corresponding
Grignard reagents [17].
Taking into account that manganese-catalyzed reactions require large excess of one of the components
and palladium prices are steadily rising, the purpose of the present investigation was to establish a more
economical synthesis method, suitable for the preparation of the title compounds on a multigram scale. In this
connection, for the synthesis of 2-(2-thienyl)benzoic acid (4) we decided to apply the Kumada-type
Ni(0)-catalyzed cross-coupling reaction between 2-chlorobenzonitrile (1) and 2-thienylmagnesium bromide (2)
(Scheme 1). Upon optimization of the reaction conditions, it was noticed that the success of the cross-coupling
_______
*Dedicated to Academician G. Duburs on the occasion of his 80th birthday.
**To whom correspondence should be addressed, e-mail: sigitas.tumkevicius@chf.vu.lt.
1Vilnius University, 24 Naugarduko St., Vilnius LT-03225, Lithuania.
2Fine synthesis Ltd., 201E Kalvarijų St., Vilnius LT-08311, Lithuania; е-mail: p.adomenas@gmail.com.
_________________________________________________________________________________________
Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1537-1544, October, 2014. Original
article submitted May 27, 2014.
0009-3122/15/5010-1413©2015 Springer Science+Business Media New York
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reaction depends on the amount of catalyst. When 2 mol% NiCl2(PPh3)2 were used only 10% conversion of nitrile 1
to the desired product 3 was observed. Increase of catalyst loading up to 4 mol% raised the conversion to 30%, and
2-chlorobenzonitrile (1) was completely consumed in 8 h when 8 mol% NiCl2(PPh3)2 was employed in the reaction.
Formation of compound 3 was confirmed, and conversion of the starting material was estimated by GC/MS (m/z
185.1 [M]+). Distillation of the crude product under reduced pressure gave a mixture consisting of 2-(2-thienyl)-
benzonitrile (3) and triphenylphosphine. This mixture was used in the next step without any further purification.
Hydrolysis of compound 3 with KOH in ethylene glycol furnished 2-(2-thienyl)benzoic acid (4) in overall two-step
yield 44%.
Scheme 1
Literature survey revealed that the synthesis of the key intermediate, 4H-indeno[1,2-b]thiophen-4-one
(5) is explored insufficiently. To our knowledge, the only method of synthesis of compound 5 from benzoic acid
4 described in the literature includes the synthesis of the corresponding benzoyl chloride and its subsequent
cyclization with SnCl4 in dry benzene [3, 12]. Therefore, we decided to investigate other well-known
cyclization reactions. First, we tried to apply the direct cyclization reactions using POCl3 or PPA. However, the
reaction of compound 4 with POCl3 did not yield even traces of product. Heating compound 4 with PPA at
100°C afforded 4H-indeno[1,2-b]thiophen-4-one (5) in low yield (18%). Further, the corresponding chloro-
anhydride was obtained by treating compound 4 with SOCl2. Various Lewis acids were tested in intramolecular
Friedel–Crafts acylation reaction. Using FeCl3, AlCl3, and TiCl4 in dichloroethane afforded compound 5 in 36%,
46%, and 52% yields, respectively. The best result was achieved using in situ generated AlCl3–MeNO2 complex:
indenothiophenone 5 was obtained in 70% yield over two steps (Scheme 1). Wolff–Kishner reduction of compound
5 afforded 4H-indeno[1,2-b]thiophene (6) [12] in 82% yield. Methylation of compound 6 with methyl iodide
using phase transfer catalyst benzyltriethylammonium chloride in the two-phase solvent system after 96 h of
stirring at room temperature afforded compound 7a in 82% yield. Alkylation of compound 6 under the same
reaction conditions with alkyl halides, which had longer carbon chains, showed even longer reaction times, and
4,4-dialkyl-4H-indeno[1,2-b]thiophenes 7b-e could not be separated from the monoalkylated by-products. In
order to reduce the reaction time and increase yields of dialkylated compounds 7a-e, the alkylation reaction
using an excess of potassium tert-butoxide with alkyl halides was carried out (Scheme 1). This method
produced 4,4-dialkyl-4H-indeno[1,2-b]thiophenes 7a-e in good yields without any traces of monoalkylated
by-products. The total reaction time was 2 h. The method works well with both alkyl bromides and alkyl
iodides.
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The synthetic route towards 4,4-diarylindeno[1,2-b]thiophenes is outlined in Scheme 2. Ester 8,
prepared from acid 4, reacted with an excess of aryl Grignard reagents to give the corresponding alcohols 9a,b
as intermediates. Without further purification, these alcohols were subjected to acid-catalyzed intramolecular
annelation to afford 4,4-diaryl-4H-indeno[1,2-b]thiophenes 10a,b [7].
Scheme 2
S
S
MeOH, p-TsOH
RC6H4MgBr
THF, , 3 h
, 14 h
92%
CO2H
CO2Me
4
8
S
S
AcOH, H2SO4
80°C, 2 h
OH
R
R
R
R
10 a (38%), b (28%)
9a,b
a R= 4-C6H13, b R = 3-C6H13
The obtained 4,4-dialkylindeno[1,2-b]thiophenes 7a-e and 4,4-diaryl-4H-indeno[1,2-b]thiophenes 10a,b
were selectively brominated at position 2 by NBS in DMF under exclusion of light to give compounds 11a-g in
high yields (Scheme 3).
Scheme 3
In summary, we have synthesized and characterized a series of new 4,4-dialkyl- and 4,4-diaryl-
4H-indeno[1,2-b]thiophenes and their 2-bromo derivatives. The synthesized compounds can find application as
precursors or substrates for the development of novel functional materials with valuable light-emitting and
semiconductive properties. Improved procedures for the synthesis of 2-(2-thienyl)benzoic acid and 4,4-dialkyl-
4H-indeno[1,2-b]thiophenes allow the preparation of the title compounds on a multigram scale.
EXPERIMENTAL
1H and 13C NMR spectra were recorded on a Varian Inova spectrometer (300 and 75 MHz, respectively)
1
in CDCl3. The NMR chemical shifts were referenced to residual solvent peaks (7.29 and 77.3 ppm for H and
13C nuclei, respectively). Mass spectra and conversion of compounds were acquired on an Agilent 5975 GC/MS
instrument with EI ionization (70 eV). Elemental analysis was performed on a ThermoFischer Scientific Flash
2000 Elemental Analyzer. Melting points were determined in open capillaries with a digital melting point
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ThermoFischer Scientific IA900 series apparatus and are uncorrected. Thin-layer chromatography was
performed using TLC-aluminum sheets with silica gel Merck 60 F254. Visualization was accomplished by UV
light. Column chromatography was performed using Merck Silica gel 60 (0.040-0.063 mm). All reagents,
catalysts, and solvents were purchased from Sigma-Aldrich and were used without further purification.
2-(2-Thienyl)benzoic Acid (4). A mixture of NiCl2(PPh3)2 (144.5 g, 0.221 mol), PPh3 (115.8 g, 0.442 mol),
and Zn (14.3 g, 0.221 mol) was stirred at room temperature for 30 min under argon atmosphere till the reaction
mixture became dark-red. Then a solution of 2-chlorobenzonitrile (1) (379.5 g, 2.760 mol) in THF (1000 ml)
was added to the reaction mixture. Thiophene Grignard reagent (2), prepared by reacting 2-bromothiophene (500 g,
3.07 mol) with magnesium turnings (76.5 g, 3.15 mol) in THF (1000 ml), was added dropwise to the reaction
mixture at such a speed that temperature would not rise above 30°C. The reaction mixture was stirred at room
temperature for 2 h and left overnight, then poured into ice water, acidified with concentrated hydrochloric acid
to pH 2-4, and extracted with CH2Cl2 (2×750 ml). The combined extracts were dried over Na2SO4 and filtered.
After the removal of the solvent from the filtrate, the obtained viscous dark-brown residue was distilled under
vacuum and the fraction with bp 145-155°C/1 mbar was collected to give 300.0 g of 2-(2-thienyl)benzonitrile
(3) as a viscous yellow oil. The obtained crude 2-(2-thienyl)benzonitrile (3) was added to a mixture of ethylene
glycol (1200 ml), H2O (50 ml), and KOH (320 g, 5.7 mol). The reaction mixture was stirred at 130-140°C for 24 h.
After cooling to room temperature, the mixture was poured into water, acidified with concentrated HCl to pH 1-2,
and extracted with CH2Cl2 (3×500 ml). After removal of the solvent, the brown residue was recrystallized from
hexane to give 250 g (44%) of compound 4 as a white solid, mp 91-93°C (hexane) (mp 92-94°C (Et2O) [3]). 1H
NMR spectrum, δ, ppm (J, Hz): 7.08-7.14 (2H, m, H-3,4 thienyl); 7.39 (1H, dd, J = 4.8, J = 1.5, H-5 thienyl);
7.41-7.54 (2H, m, H-4,5 Ph); 7.57 (1H, dd, J = 7.5, J = 1.5, H-3 Ph); 7.94 (1H, dd, J = 7.5, J = 1.5, H-6 Ph);
10,09 (1H, s, COOH). 13C NMR spectrum, δ, ppm: 126.4; 127.1; 127.5; 128.1; 130.5; 130.8; 132.1; 132.2;
135.4; 141.9; 173.9. Found, %: C 64.32; H 3.96. C11H8O2S. Calculated, %: C 64.69; H 3.95.
4H-Indeno[1,2-b]thiophen-4-one (5). A mixture of 2-(2-thienyl)benzoic acid (4) (150 g, 0.735 mol),
SOCl2 (88 g, 0.74 mol), and 1,2-dichloroethane (250 ml) was refluxed for 8 h. Then the reaction mixture was
cooled to -18°C, and a solution of AlCl3 (103 g, 0.75 mol) and MeNO2 (122 g, 2 mol) in 1,2-dichloroethane
(300 ml) was added dropwise within 1 h. After the addition was complete, the reaction mixture was left to warm
to room temperature for 1 h. The mixture was poured into 5 M HCl (500 ml) and stirred for 30 min. The organic
layer was separated, washed twice with water, dried over Na2SO4, and filtered. After removal of the solvent
from the filtrate, the obtained dark-brown residue was distilled under vacuum at 122°C/0.5 mbar and
recrystallized from hexane to give 96 g (70%) of compound 5 as orange crystals, mp 101-102°C (hexane) (mp
1
99-101°C (benzene) [12]). H NMR spectrum, δ, ppm (J, Hz): 7.13-7.22 (4H, m, H-2,3,6,8); 7.35 (1H, td,
13
J = 7.5, J = 0.9, H-7); 7.46 (1H, dd, J = 7.5, J = 0.9, H-5). C NMR spectrum, δ, ppm: 119.5; 121.7; 123.9;
128.7; 129.3; 134.1; 136.7; 139.0; 142.2; 159.2; 187.5. Found, %: C 70.69; H 3.24. C11H6OS. Calculated, %:
C 70.94; H 3.25.
4H-Indeno[1,2-b]thiophene (6). A mixture of 4H-indeno[1,2-b]thiophen-4-one (5) (40 g, 0.215 mol),
hydrazine hydrate (36 g of 50% solution in water, 0.36 mol), and diethylene glycol (150 ml) was heated at
110°C for 3 h, then cooled to 40°C, and KOH (36 g, 0.645 mol) was added. The reaction mixture was heated to
110°C and stirred for 4 h. After cooling to room temperature, the mixture was poured into water (400 ml) and
extracted with CH2Cl2 (3×150 ml). The organic layer was separated and washed with water until neutral
reaction (pH 7). After removal of the solvent, the solid was recrystallized from hexane to give 32 g (82%) of
1
compound 6 as a yellowish solid, mp 68-70°C (hexane) (mp 68-69°C (Et2O) [12]). H NMR spectrum, δ, ppm
(J, Hz): 3.74 (2H, s, CH2); 7.16 (1H, d, J = 4.5, H-3); 7.24-7.34 (2H, m, H-5,8); 7.35 (1H, d, J = 4.5, H-2);
13
7.52-7.55 (2H, m, H-6,7). C NMR spectrum, δ, ppm: 34.2; 119.0; 122.9; 125.0; 125.3; 127.1; 127.3; 139.1;
143.4; 146.3; 147.4. Mass spectrum, m/z (Irel, %): 172 [M]+ (100), 139 (10), 127 (20), 86 (14). Found, %:
C 76.46; H 4.63. C11H8S. Calculated, %: C 76.70; H 4.68.
Synthesis of 4,4-Dimethyl-4H-indeno[1,2-b]thiophene (7a) Under Phase Transfer Catalysis. A
mixture of 4H-indeno[1,2-b]tiophene (6) (2.00 g, 11.60 mmol), benzyltriethylammonium chloride (0.18 g,
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0.79 mmol), MeI (2.5 ml, 40 mmol), DMSO (20 ml), and 50% aqueous solution of NaOH (20 ml) was stirred at
room temperature for at least 96 h. The reaction mixture was quenched with water and extracted with CH2Cl2.
After removal of the solvent, the product was purified by column chromatography on silica gel (eluent hexane)
1
to give compound 7a. Yield 1.90 g (82%), white powder, mp 84-85°C (2-PrOH). H NMR spectrum: δ, ppm
(J, Hz): 1.52 (6H, s, 2CH3); 7.08 (1H, d, J = 5.1, H-3); 7.24-7.32 (2H, m, H-5,8); 7.34 (1H, d, J = 5.1, H-2);
7.48-7.50 (2H, m, H-6,7). 13C NMR spectrum, δ, ppm: 26.3; 45.7; 119.1; 120.9; 122.6; 125.4; 127.2; 127.8;
136.8; 140.0; 156.5; 158.6. Found, %: C 77.45; H 6.04. C13H12S. Calculated, %: C 77.95; H 6.04.
4,4-Dialkyl-4H-indeno[1,2-b]thiophenes 7a-e (General Method). Potassium tert-butoxide (3.9 g, 34.8
mmol) was added to a solution of 4H-indeno[1,2-b]-thiophene (6) (2.0 g, 11.6 mmol) in THF (30 ml). The
reaction mixture was stirred at room temperature for 1 h. Then the corresponding alkyl iodide (for compounds
7a,b,e) or bromide (for compounds 7c,d) (34.8 mmol) was added, and the reaction mixture was stirred for an
additional hour. The reaction was quenched with water and extracted with CH2Cl2 (3×50 ml); the organic layer
was separated and washed with water until neutral reaction (pH 7). After evaporation of the solvent, the product
was recrystallized from 2-PrOH (compound 7a) or purified by column chromatography (eluent hexane)
(compounds 7b-e).
4,4-Dimethyl-4H-indeno[1,2-b]thiophene (7a). Yield 2.0 g (86%).
4,4-Dibutyl-4H-indeno[1,2-b]thiophene (7b). Yield 2.5 g (76%), yellow oil. H NMR spectrum, δ,
1
ppm (J, Hz): 0.69-0.85 (4H, m, 2CH2CH2CH2CH3); 0.75-0.87 (6H, t, J = 7.5, 2CH3); 1.13-1.21 (4H, m,
2CH2CH2CH2CH3 ); 1.89-1.99 (4H, m, 2CH2CH2CH2CH3); 7.20 (1H, d, J = 4.8, H-3); 7.31-7.33 (3H, m,
13
H-5,6,7); 7.38 (1H, d, J = 4.8, H-2); 7.45 (1H, d, J = 7.5, H-8). C NMR spectrum, δ, ppm: 14.1; 23.3; 26.6;
39.0; 54.0; 118.8; 121.8; 122.8; 125.2; 126.9; 127.3; 138.5; 141.4; 154.1; 155.6. Found, %: C 80.22; H 9.03.
C19H24S. Calculated, %: C 80.22; H 8.59.
1
4,4-Dipentyl-4H-indeno[1,2-b]thiophene (7c). Yield 2.3 g (64%), yellow oil. H NMR spectrum, δ,
ppm (J, Hz): 0.71-0.89 (4H, m, 2CH2CH2(CH2)2CH3); 0.83 (6H, t, J = 7.2, 2CH3); 1.14-1.23 (8H, m,
2(CH2)2(CH2)2CH3); 1.97-2.07 (4H, m, 2CH2(CH2)3CH3); 7.04 (1H, d, J = 4.8, H-3); 7.30-7.36 (3H, m,
13
H-5,6,7); 7.39 (1H, d, J = 4.8, H-2); 7.51 (1H, d, J = 7.2, H-8). C NMR spectrum, δ, ppm: 14.3; 22.6; 24.1;
32.6; 39.3; 54.1; 118.9; 121.8; 122.8; 125.3; 127.0; 127.4; 138.6; 141.5; 154.2; 155.6. Mass spectrum, m/z (Irel,
%): 312 [M]+ (70), 241 (90), 185 (100), 171 (35), 152 (14). Found, %: C 80.7; H 9.03. C21H28S. Calculated, %:
C 80.71; H 9.03.
4,4-Dihexyl-4H-indeno[1,2-b]thiophene (7d). Yield 2.8 g (71%), yellow oil. 1H NMR spectrum, δ, ppm
(J, Hz): 0.72-0.89 (4H, m, 2CH2CH2(CH2)3CH3); 0.88 (6H, t, J = 7.5, 2CH3); 1.12-1.21 (12H, m,
2(CH2)2(CH2)3CH3); 1.96-2.06 (4H, m, 2CH2(CH2)4CH3); 7.07 (1H, d, J = 4.8, H-3); 7.27-7.38 (3H, m, H-5,6,7);
7.38 (1H, d, J = 4.8, H-2); 7.51 (1H, d, 7.2, H-8). 13C NMR spectrum, δ, ppm: 14.3; 22.9; 24.4; 30.0; 31.9; 39.3;
54.1; 118.9; 121.8; 122.8; 125.2; 127.0; 127.4; 138.6; 141.5; 154.1; 155.6. Mass spectrum, m/z (Irel, %): 340 [M]+
(63), 255 (85), 185 (100), 171 (32), 152 (12). Found, %: C 80.92; H 9.44. C23H32S. Calculated, %: C 81.11; H 9.47.
1
4,4-Diheptyl-4H-indeno[1,2-b]thiophene (7e). Yield 3.6 g (84%), yellow oil. H NMR spectrum, δ,
ppm (J, Hz): 0.75-0.91 (4H, m, 2CH2CH2(CH2)4CH3); 0.91 (6H, t, J = 7.2, 2CH3); 1.17-1.29 (16H, m,
2(CH2)2(CH2)4CH3); 1.91-2.07 (4H, m, 2CH2(CH2)5CH3); 7.03 (1H, d, J = 5.1, H-3); 7.24-7.36 (3H, m,
13
H-5,6,7); 7.36 (1H, d, J = 5.1, H-2); 7.47 (1H, d, J = 7.2, H-8). C NMR spectrum, δ, ppm: 14.3; 22.8; 24.4;
29.3; 30.3; 32.1; 39.3; 54.1; 118.9; 121.8; 122.8; 125.3; 127.0; 127.3; 138.5; 141.4; 154.1; 155.6. Found, %:
C 80.96; H 9.87. C25H36S. Calculated, %: C 81.46; H 9.84.
Methyl 2-(2-Thienyl)benzoate (8). A mixture of 2-(2-thienyl)benzoic acid (4) (30 g, 0.147 mol),
p-TsOH (5 g, 0.022 mol), and MeOH (100 ml) was refluxed for 14 h. Then the reaction mixture was cooled and
poured into ice water (300 ml) and extracted with CH2Cl2 (2×100 ml). Removal of the solvent gave 29 g (91%)
1
of yellowish oil (slightly-yellow oil [3]). H NMR spectrum, δ, ppm (J, Hz): 3.77 (3H, s, COOCH3); 7.06-7.10
(2H, m, H-3,4 thienyl); 7.37 (1H, dd, J = 5.0, J = 1.5, H-2 thienyl); 7.43-7.52 (3H, m, H-4,5,6 Ph); 7.75 (1H, td,
13
J = 7.6, J = 1.5, H-3 Ph). C NMR spectrum, δ, ppm: 52.2; 125.9; 126.3; 127.2; 127.7; 129.4; 131.0; 131.1;
131.7; 134.1; 142.0; 169.1.
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4,4-Diaryl-4H-indeno[1,2-b]thiophenes 10a,b (General Method). Grignard reagent prepared from
1-bromo-4-hexylbenzene or 1-bromo-3-hexylbenzene (13.3 g, 0.055 mol) and magnesium turnings (1.45 g,
0.06 mol) in THF (25 ml) was added to a stirred solution of methyl 2-(2-thienyl)benzoate (8) (5 g, 0.023 mol) in
THF (50 ml). After the addition was complete, the reaction mixture was refluxed for 3 h, then cooled to room
temperature and poured into 1 M NH4Cl solution (200 ml), extracted with CH2Cl2, and washed with water
twice. After removal of the solvent, the obtained yellow oil was dissolved in acetic acid (40 ml) and heated to
80°C. When the required temperature was reached, 2 drops of concentrated H2SO4 was added, and stirring at
80°C was continued for 2 h. The reaction mixture was poured to ice water, extracted with CH2Cl2, and washed
with water 3 times. Removal of the solvent gave the crude product, which was recrystallized from 2-PrOH.
4,4-Bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophene (10a). Yield 4.3 g (38%), white solid, mp 61-63°C
(2-PrOH). 1H NMR spectrum, δ, ppm (J, Hz): 0.94 (6H, t, J = 6.0, 2CH3); 1.35-1.63 (16H, m, 2CH2(CH2)4CH3);
2.59 (4H, t, J = 7.5, 2CH2(CH2)4CH3); 7.08-7.24 (10H, m, H-2,3, H-2,3,5,6 2Ar); 7.31-7.35 (2H, m, H-6,7);
7.43 (1H, d, J = 7.5, H-5); 7.51 (1H, d, J = 7.5, H-8). 13C NMR spectrum, δ, ppm: 14.3; 22.8; 29.3; 31.6; 31.9;
35.8; 63.1; 119.5; 123.4; 125.8; 126.6; 127.5; 128.0; 128.1; 128.5; 137.5; 141.2; 141.5; 142.2; 154.0; 156.2.
Mass spectrum, m/z (Irel, %): 492 [M]+ (100), 459 (9), 407 (18), 331 (16), 260 (14). Found, %: C 85.02; H 7.89.
C35H40S. Calculated, %: C 85.31; H 8.18.
4,4-Bis(3-hexylphenyl)-4H-indeno[1,2-b]thiophene (10b). Yield 3.2 g (28%), white solid, mp 45-46°C
(2-PrOH). 1H NMR spectrum, δ, ppm (J, Hz): 0.91 (6H, t, J = 6.0, 2CH3); 1.25-1.57 (16H, m, 2CH2(CH2)4CH3);
2.53 (4H, t, J = 7.8, CH2(CH2)4CH3); 6.96-7.08 (7H, m, H-2, H-2,4,6 2Ar); 7.16 (2H, t, J = 7.5, H-5 2Ar); 7.22
(1H, d, J = 7.5, H-5); 7.30-7.41 (3H, m, H-3,6,7); 7.51 (1H, d, J = 7.5, H-8). 13C NMR spectrum, δ, ppm: 14.3;
22.8; 29.1; 31.7; 31.9; 36.2; 63.6; 119.5; 123.3; 125.2; 125.8; 126.5; 127.0; 127.6; 128.1; 128.2; 128.5; 137.5;
141.3; 143.1; 144.9; 153.8; 156.0. Mass spectrum, m/z (Irel, %): 492 [M]+ (100), 459 (10), 407 (20), 331 (16),
260 (14). Found, %: C 84.96; H 8.11. C35H40S. Calculated, %: C 85.31; H 8.18.
2-Bromo-4,4-dialkyl- and 4,4-Diaryl-4H-indeno[1,2-b]thiophenes 11a-g (General Method). NBS
(1.47 g, 8.25 mmol) was added in portions to a solution of the corresponding 4,4-dialkyl- or 4,4-diaryl-
4H-indeno[1,2-b]thiophene 7a-e, 10a,b (7.5 mmol) in DMF (25 ml), cooled to 0°C, and protected from the
daylight. The reaction mixture was stirred at 0°C for 2 h and then allowed to reach room temperature. The
reaction was quenched with water (100 ml) and extracted with CH2Cl2. After removal of the solvent, the
products were purified by column chromatography on silica gel (eluent hexane).
2-Bromo-4,4-dimethyl-4H-indeno[1,2-b]thiophene (11a). Yield 1.9 g (90%), white solid, mp 54-55°C
(hexane). 1H NMR spectrum, δ, ppm: 1.48 (6H, s, 2CH3); 7.08 (1H, s, H-3); 7.25-7.33 (2H, m, H-5,6); 7.38-7.40
(2H, m, H-7,8). 13C NMR spectrum, δ, ppm: 26.1; 46.7; 113.7; 119.0; 122.0; 124.2; 125.7; 127.3; 136.4; 140.2;
155.1; 157.4. Found, %: C 56.23; H, 3.98. C13H11BrS. Calculated, %: C 55.92; H 3.97.
2-Bromo-4,4-dibutyl-4H-indeno[1,2-b]thiophene (11b). Yield 2.2 g (82%), white solid, mp 61-63°C
1
(hexane). H NMR spectrum, δ (J, Hz): 0.73-0.84 (4H, m, 2CH2CH2CH2CH3); 0.77 (6H, t, J = 7.2, 2CH3);
1.12-1.17 (4H, m, 2CH2CH2CH2CH3); 1.81-1.92 (4H, m, 2CH2CH2CH2CH3); 7.02 (1H, s, H-3); 7.20-7.29 (2H,
13
m, H-5,6); 7.31-7.39 (2H, m, H-7,8). C NMR spectrum, δ, ppm: 14.1; 23.2; 26.5; 38.9; 55.0; 113.3; 118.8;
122.8; 124.8; 125.5; 127.1; 138.1; 141.7; 152.7; 154.4. Mass spectrum, m/z (Irel, %): 364 [M]+ (60), 307 (50),
251 (20), 226 (100), 198 (46), 184 (75), 139 (24). Found, %: C 63.13; H 6.55. C19H23BrS. Calculated, %:
C 62.80; H 6.38.
1
2-Bromo-4,4-dipentyl-4H-indeno[1,2-b]thiophene (11c). Yield 2.7 g (92%), yellow oil. H NMR
spectrum, δ, ppm (J, Hz): 0.77-0.82 (4H, m, 2CH2CH2(CH2)2CH3); 0.81 (6H, t, J = 6.9, 2CH3); 1.11-1.16 (8H,
m, 2(CH2)2(CH2)2CH3); 1.72-1.98 (4H, m, 2CH2(CH2)3CH3); 7.01 (1H, s, H-3); 7.20-7.30 (2H, m, H-5,6);
13
7.31-7.41 (2H, m, H-7,8). C NMR spectrum, δ, ppm: 14.2; 22.6; 24.0; 32.4; 39.1; 55.1; 113.3; 118.8; 122.8;
124.8; 125.5; 127.1; 138.1; 141.7; 152.7; 154.7. Found, %: C 64.92; H 7.06. C21H27BrS. Calculated, %:
C 64.44; H 6.95.
1
2-Bromo-4,4-dihexyl-4H-indeno[1,2-b]thiophene (11d). Yield 2.8 g (89%), yellow oil. H NMR
spectrum, δ, ppm (J, Hz): 0.79-0.85 (4H, m, 2CH2CH2(CH2)3CH3); 0.82 (6H, t, J = 6.9, 2CH3); 1.15-1.22 (12H,
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m, 2(CH2)2(CH2)3CH3); 1.81-198 (4H, m, 2CH2(CH2)4CH3); 7.03 (1H, s, H-3); 7.21-7.32 (2H, m, H-5,6);
13
7.37-7.44 (2H, m, H-7,8). C NMR spectrum, δ, ppm: 14.2; 22.8; 24.3; 29.8; 31.8; 39.0; 55.1; 113.3; 118.8;
122.8; 124.9; 125.5; 127.1; 138.1; 141.7; 152.7; 154.6. Found, %: C 65.69; H 7.43. C23H31BrS. Calculated, %:
C 65.86; H 7.45.
1
2-Bromo-4,4-diheptyl-4H-indeno[1,2-b]thiophene (11e). Yield 2.61 g (78%), yellow oil. H NMR
spectrum, δ, ppm (J, Hz): 0.78-0.84 (4H, m, 2CH2CH2(CH2)4CH3); 0.86 (6H, t, J = 7.0, 2CH3); 1.12-126 (16H,
m, 2(CH2)2(CH2)4CH3); 1.78-1.95 (4H, m, 2CH2(CH2)5CH3); 7.01 (1H, s, H-3); 7.20-7.30 (2H, m, H-5,6);
7.32-7.39 (2H, m, H-7,8). 13C NMR spectrum, δ, ppm: 14.3; 22.8; 24.3; 29.2; 30.2; 32.0; 39.1; 55.1; 113.3;
118.8; 122.8; 124.9; 125.5; 127.1; 138.1; 141.7; 152.7; 154.5. Found, %: C 66.93; H 7.92. C25H35BrS.
Calculated, %: C 67.10; H 7.88.
2-Bromo-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophene (11f). Yield 3.8 g (89%), white powder,
1
mp 93-95°C (hexane). H NMR spectrum, δ, ppm (J, Hz): 0.94 (6H, t, J = 6.6, 2CH3); 1.36-1.63 (16H, m,
2CH2(CH2)4CH3); 2.61 (4H, t, J = 7.8, 2CH2(CH2)4CH3); 7.08-7.19 (8H, m, H-2,3,5,6 2Ar); 7.14 (1H, s, H-3);
7.23-7.45 (4H, m, H-5,6,7,8). 13C NMR spectrum, δ, ppm: 14.3; 22.8; 29.4; 31.6; 32.0; 35.8; 63.9; 114.2; 119.5;
120.6; 126.1; 126.5; 127.8; 127.9; 128.6; 137.1; 141.5; 141.6; 141.8; 152.8; 155.0. Found, %: C 73.52; H 6.96.
C35H39BrS. Calculated, %: C 73.54; H 6.88.
2-Bromo-4,4-bis(3-hexylphenyl)-4H-indeno[1,2-b]thiophene (11g). Yield 3.0 g (70%), yellow
1
viscous oil. H NMR spectrum, δ, ppm (J, Hz): 0.92 (6H, t, J = 6.9, 2CH3); 1.29-1.61 (16H, m,
2CH2(CH2)4CH3); 2.56 (4H, t, J = 7.8, 2CH2(CH2)4CH3); 6.97 (2H, dt, J = 7,5, J = 1.5, H-6 2Ar); 7.05 (2H, s,
H-2 2Ar); 7.07-7.14 (3H, m, H-3, H-4 2Ar); 7.17 (2H, t, J = 7.5, H-5 2Ar); 7.23 (1H, dd, J = 7.5, J = 0.9, H-5);
13
7.33 (1H, td, J = 7.5, J = 0.9, H-6); 7.37-7.45 (2H, m, H-7,8). C NMR spectrum, δ, ppm: 14.3; 22.9; 29.1;
31.6; 31.9; 36.2; 64.5; 114.2; 119.5; 125.1; 126.1; 126.3; 126.5; 127.2; 127.7; 128.4; 128.4; 137.1; 141.5;
143.2; 144.3; 152.6; 154.8. Found: C 73.54; H 6.91. C35H39BrS. Calculated, %: C 73.54; H 6.88.
The research was funded by a grant (No. MIP-027/2013) from the Research Council of Lithuania.
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