A simple route to benzo[b]thiophenes: Sulfanylation-acylation of C-H acids with 2-(chlorosulfanyl)benzoyl chloride

Article abstract of DOI:10.1080/10426500902855117

A convenient procedure for the preparation of 2,2-disubstituted benzo[b]thiophen3(2H)-ones and 2-substituted 3-hydroxybenzo[b]thiophenes from β-diketones, β-keto- and β-cyanoesters, and β-cyanoketones, diethyl malonate, malonitrile, and anthrone has been

Full text of DOI:10.1080/10426500902855117

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A Simple Route to
Benzo[b]thiophenes:
Sulfanylation–Acylation
of C─H Acids with 2-
(Chlorosulfanyl)benzoyl
Chloride
Jacek Młochowski a & Piotr Potaczek a
a Faculty of Chemistry, Wrocław University of
Technology, Wrocław, Poland
Published online: 28 Apr 2009.
To cite this article: Jacek Młochowski & Piotr Potaczek (2009) A Simple
Route to Benzo[b]thiophenes: Sulfanylation–Acylation of C─H Acids with 2-
(Chlorosulfanyl)benzoyl Chloride, Phosphorus, Sulfur, and Silicon and the Related
Elements, 184:5, 1115-1123, DOI: 10.1080/10426500902855117
To link to this article: http://dx.doi.org/10.1080/10426500902855117
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Phosphorus, Sulfur, and Silicon, 184:1115–1123, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902855117
A Simple Route to Benzo[b]thiophenes:
Sulfanylation–Acylation of C H Acids with
2-(Chlorosulfanyl)benzoyl Chloride
Jacek Mlochowski and Piotr Potaczek
ꢀ
Faculty of Chemistry, Wrocꢀlaw University of Technology, Wroclaw,
ꢀ
Poland
A convenient procedure for the preparation of 2,2-disubstituted benzo[b]thiophen-
3(2H)-ones and 2-substituted 3-hydroxybenzo[b]thiophenes from β-diketones, β-
keto- and β-cyanoesters, and β-cyanoketones, diethyl malonate, malonitrile, and
anthrone has been developed. The tandem sulfanylation–acylation of these C
H
acids resulting in the formation of a thiophene ring occurs upon treatment with
2-(chlorosulfanyl)benzoyl chloride in the presence of triethylamine.
Keywords Acylations; cyclizations; heterocycles; sulfur; tandem reactions
INTRODUCTION
The synthesis of benzo[b]thiophenes has been of broad interest owing
to their biological activity or application in organic materials employed
in electronics.1−6 The extensive research on chemistry and biology of
benzo[b]thiophenes substituted in the heterocylic ring led to the drug
Ralofixen, which is used for prevention and treatment of osteoporo-
sis in postmenopausal women.7 Other potential applications of this
drug, e.g., for the treatment of Alzheimer’s disease, have also been
reported recently.8 Moreover 3-(4-pyridinyl)aminobenzo[b]thiophenes
may be useful for the treatment of central nervous system disorders,9,10
and some 2,3-disubstituted benzo[b]thiophenes were found to be active
as antimicrobials.11
Received 14 November 2007; accepted 24 February 2008.
Dedicated to Professor Marian Mikolajczyk, CBMiM PAN in Lo´dz´, Poland, on the
ꢀ
ꢀ
occasion of his 70th birthday.
The authors would like to express their thanks to Ministry of Science and Information
for financial support (Grant N204022 31/0458).
Address correspondence to Jacek Mlochowski, Department of Organic Chemistry,
ꢀ
Faculty of Chemistry, Wroclaw University of Technology, Wybrzez˙e Wyspian´skiego 27,
ꢀ
50-370 Wroclaw, Poland. E-mail: jacek.mlochowski@pwr.wroc.pl
ꢀ
1115

1116
J. M lochowski and P. Potaczek
ꢀ
Our ongoing interest in the chemistry of organoselenium and
organosulfur compounds is focused on the reactions that result in
the ring closure and formation of selenium or sulfur-containing het-
erocycles. The well known reactions of this type are selenenylation–
acylation or sulfanylation–acylation of a primary amino group with
2-(chloroselenyl)- or 2-(chlorosulfanyl)benzoyl chloride 1. Both of
these reagents can act as biselectrophiles, with the hard elec-
trophilic center located on the carbonyl carbon atom and the soft
one located on the chalcogen atom. Sulfonylation (or selenenyla-
tion) followed by acylation results in ring closure at the nitro-
gen atom, and benzisothiazolin-2(2H)-ones or benzisoselenazol-3(2H)-
ones are produced, respectively.12−15Although the selenenylation–
acylation of an active methylene group in ketones is reported to afford
benzo[b]selenophenes,16,17 the reaction of 1 with enolizable ketones and
other C H acids is to our knowledge still unknown.
RESULTS AND DISCUSSION
In this work, 2-(chlorosulfanyl)benzoyl chloride 1 was used as the agent
for tandem sulfanylation–acylation of different compounds having an
active methylene group, which results in the formation of a thiophene
ring. This easy-to-prepare, stable compound, was obtained in a two-
step synthesis starting from 2,2ꢀ-dithiodibenzoic acid. The acid when
refluxed with thionyl chloride in benzene gave 2,2ꢀ-dithiobisbenzoyl
chloride, which was dissolved in carbon tetrachloride and chlorinated
with dry, gaseous chlorine to give the chloride 1.18 We found that this
reagent easily reacted with common C H acids 2 having two hydrogen
atoms in an activated methylene group, such as β-diketones, β-keto- and
β-cyanoesters, β-cyanoketones, diethyl cyanomethyl-phosphonate, di-
ethyl malonate, malononitrile, and 9(10H)-anthracenone. The reaction,
carried out at −15◦C or 20◦C in the presence of triethylamine as a base,
was completed after 2.5 h. It resulted in a ring closure at the methylene
carbon atom, and, depending on the substrate used, 2,2’-disubstituted
benzo[b]thiophen-3(2H)-ones 3 and/or 3-hydroxybenzo[b]thiophenes 4
were produced (Table I). Monoketones, such as acetone and cyclohex-
anone, reacted more slowly than β-diketones, and complex mixtures of
products were formed.
When C H acids such as β-cyanoesters 2d–e, malononitrile 2f,
β-cyanoacetophenone 2g, 9(10H)-anthracenone (anthrone) 2h, and
5,5dimethyl-1,3-cyclohexanedione (dimedone) 2i were treated with 2-
(chlorosulfanyl)benzoyl chloride 1, the corresponding 2,2-disubstituted
benzo[b]thiophen-3(2H)-ones 3d–i were produced. Compounds 3d–i

Simple Route to Benzo[b]thiophenes
1117
TABLE I Reaction of 2-(Chlorosulfanyl)benzoyl Chloride with C−H
Acids
Substrate
R2
Method
Yield (%)
Products
Yield (%)
2
R1
3
4
2a
COPh
COMe
COPh
COOEt
CN
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
3a
3a
3b
3b
3c
3c
3d
3d
3e
3e
3f
84
42
74
31
92
36
54
46
97
59
86
63
84
80
87
4a
4a
4b
4b
4b
4b
4d
4d
4e
4e
4f
—
23
—
45
—
32
—
—
—
—
—
—
—
—
—
2b
2c
2d
2e
2f
COOEt
COOEt
COOEt
CN
P(O)(OEt)2
CN
CN
3f
4f
2g
2h
CN
COPh
3g
3g
3h
4g
4g
4h
B
3h
87
4h
—
2i
A
B
3i
3i
68
70
4i
4i
—
—
2j
COMe
COMe
COMe
A
B
A
B
A
B
A
3j
3j
3k
3k
3l
3l
3m
3m
81
—
—
—
—
—
—
4j
4j
—
93
82
82
98
74
69
2k
2l
COOEt
4b
4b
4lb
4lb
4mc
2m
B
—
4mc
60
aIsolated yield.
bFor 4l R1 = COCH2CH2COOH.
cFor 4m R1 = COCH2CH2CH2COOH.

1118
J. M lochowski and P. Potaczek
ꢀ
were isolated in 46–97% yield from the reaction mixture by solvent
evaporation and recrystallization of the residue (Method A) or by silica
gel column chromatography (Method B). When compounds 2a–c were
used as starting materials and the reaction mixture was worked up ac-
cording to Method A, only benzo[b]thiophen-3(2H)-ones 3a–c were ob-
tained, while chromatography on silica gel (Method B) resulted in mix-
tures containing also 3-hydroxybenzo-[b]thiophenes 4a or 4b. The re-
action of 1 with ethyl acetoacetate 2k and the cyclic β-diketones 2l and
2 m gave only 2-substituted 3-hydroxybenzo[b]thiophenes 4b, 4l, and4
m, respectively. Most probably in these cases, the initially formed 2,2-
disubstituted benzo[b]thiophenes underwent deacylation and conver-
sion to 3-hydroxybenzo[b]thiophenes by treatment with water (Method
A), or in the presence of moisture, adsorbed on silica gel during the
separation by column chromatography (Method B). Similar conversion
was observed when a solution of 3b in dichloromethane and silica gel
was allowed to stand with stirring at room temperature for 24 h. After
this period, 65% of the substrate was converted into 2-ethoxycarbonyl-
3-hydroxybenzo[b]thiophene 4b.
Benzo[b]thiophenes 3d–g substituted at 2-position with a cyano
group as well as derivatives of 9(10H)-anthracenone 3h and 5,5-
dimethyl-1,3-cyclohexanedione 3i remained resistant towards decom-
position, while 2,2-diacetylbenzo[b]thiophen-3(2H)-one 3j was con-
verted on a silica gel column into 4j almost quantitatively.
It should be noted that although unsubstituted benzo[b]thiophen-
3(2H)-one exists preferentially as the oxo tautomer, introduction of a
2-acyl group promotes enolization, presumably by virtue of the extra
stabilization conferred by intramolecular hydrogen bonding. The broad
. . .
absorption band νOH O, observed in the IR spectra of the compounds
4 in the range 2983–1920 cm−1 and bands νC=O at 1622–1537 cm−1
are similar to those reported for enol forms of other 1,3-diketones.19
1
In addition, the signal of an acid proton present in H NMR spectra
between 10.9 and 13.5 provides good evidence that these compounds
exist in the enol form as 2-substituted 3-hydroxybenzo[b]thiophenes,
represented by formula 4 given in Figure 1. The enol form seems to
be stabilized by intramolecular hydrogen bonding, similar to what was
observed earlier for 3-hydroxybenzo[b]selenophenes.16,17
EXPERIMENTAL
Solvents were dried according to standard procedures and distilled.
Silica gel 70–230 mesh (Fluka) was used for column chromatography.
Melting points were measured using Digital Melting Point Apparatus

Simple Route to Benzo[b]thiophenes
1119
FIGURE 1 2-Substituted 3-hydroxybenzo[b]thiophenes.
Electrothermal IA 91100. IR spectra were recorded with a Perkin-
1
Elmer 2000 FT spectrometer. H and 13C NMR spectra were recorded
using a Bruker DRX300 spectrometer. Chemical shifts are given
in ppm. The reagents were purchased from Aldrich and Fluka. 2-
(Chlorosulfanyl)benzoyl chloride was prepared according to procedures
given in the literature.18
Sulfanylation-Acylation of C H Acids: General Procedure
To a stirred solution of the C H acid 2a–m (3.3 mmol) and triethy-
lamine (0.668 g, 6.6 mmol) in dry dichloromethane (30 mL), a solu-
tion of 2-(chlorosulfanyl)benzoyl chloride (1) (0.621 g, 3.0 mmol) in dry
dichloromethane (20 mL) was added dropwise at room temperature (for
2i, 2l: acetone and cyclohexanone, −15◦C) during 30 min, and the re-
action was continued for an additional 2 h. The reaction mixture was
washed with acidified water (50 mL H2O and 1 mL HCl) and then
with water (2 × 50 mL). The organic layer was dried with anhydrous
Na2SO4, the solvent was evaporated in vacuo, and the residue was re-
crystallized from a suitable solvent (Method A). Alternatively (Method
B), from the reaction mixture the solvent was evaporated in vacuo, and
the residue was purified by silica gel column chromatography using
ethyl acetate (for 3e–f, 4l–m), chloroform (for 4j), ethyl acetate:hexane
1:3 (for 4k), and dichloromethane (in all other cases) as eluent.
2-Acetyl-2-benzoylbenzo[b]thiophen-3(2H)-one (3a)
White needles from ethyl acetate, mp 146–148◦C. IR (KBr): ν = 1729,
1663, 1249 cm−1. 1H NMR (CDCl3): δ = 2.59 (s, 3H, CH3), 7.38–7.43 (m,
1H, arom-H), 7.49–7.54 (m, 1H, arom-H), 7.58–7.67 (m, 3H, arom-H),
7.72–7.77 (m, 1H, arom-H), 7.84 (d, J = 8.1 Hz, 1H, arom-H), 8.32 (d,
J = 7.2 Hz, 2H, arom-H). 13C NMR (CDCl3): δ = 29.4, 122.9; 123.4;
125.2, 128.3, 129.0, 130.6, 133.0, 134.5, 138.4, 164.0, 190.7. Anal. Calcd
for C17H12O3S: C, 68.89; H, 4.09; S, 10.82%. Found: C, 68.95; H, 4.18;
S, 10.90%.

1120
J. M lochowski and P. Potaczek
ꢀ
2-Benzoyl-2-ethoxycarbonylbenzo[b]thiophen-3(2H)-one (3b)
White prisms from hexane, mp 90–93◦C. IR (KBr): ν = 1742, 1702,
1378, 1292, 1255, 1088 cm−1. 1H NMR (CDCl3): δ = 1.19 (t, J = 7.1 Hz,
3H, CH3), 4.29 (q, J = 7.1 Hz, 2H, CH2), 7.42 (t, J = 7.1 Hz, 1H, arom-
H), 7.49–7.59 (m, 3H, arom-H), 7.66–7.72 (m, 1H, arom-H), 7.75 (d,
J = 8.1 Hz, 1H, arom-H), 7.80 (d, J = 8.1 Hz, 1H, arom-H), 8.31 (d,
J = 8.5 Hz, 2H, arom-H). 13C NMR (CDCl3): δ = 14.1, 61.5, 122.3, 123.1,
125.1, 128.0, 128.9, 130.6, 133.1, 134.0, 138.1, 145.1, 161.4, 164.1. Anal.
Calcd. for C18H14O4S: C, 66.24; H, 4.33; S, 9.82%. Found: C, 66.44; H,
4.34; S, 9.95%.
2,2-Diethoxycarbonylbenzo[b]thiophen-3(2H)-one (3c)
Yellow oil. IR (KBr): ν = 2984, 1737, 1247 cm−1.1H NMR (CDCl3):
δ = 1.28 (t, J = 7.1 Hz, 6H, CH3), 4.29 (q, J = 7.1 Hz, 4H, CH2), 7.25
(t, J = 7.8 Hz, 1H, arom-H), 7.38 (d, J = 7.8 Hz, 1H, arom-H), 7.58 (t,
J = 7.1 Hz, 1H, arom-H), 7.78–7.81 (m, 1H, arom-H). 13C NMR (CDCl3):
δ = 13.8, 63.4, 123.8, 125.8, 128.0, 136.6, 150.5, 164.4, 190.2. Anal.
Calcd. for C14H14O5S: C, 57.12; H, 4.80; S, 10.89%. Found: C, 57.21; H,
4.92; S, 10.92%.
2-Cyano-2-ethoxycarbonylbenzo[b]thiophen-3(2H)-one (3d)
White needles from hexane, mp 97–98◦C. IR (KBr): ν = 2979, 2252,
1744, 1713, 1576, 1452, 1238 cm−1
.
1H NMR (CDCl3): δ = 1.33 (t,
J = 7.1 Hz, 3H, CH3), 4.35 (q, J = 7.1 Hz, 2H, CH2), 7.38 (t, J = 7.5 Hz,
1H, arom-H), 7.45 (d, J = 8.0 Hz, 1H, arom-H), 7.68–7.74 (m, 1H, arom-
H), 7.90 (d, J = 7.5 Hz, 1H, arom-H). 13C NMR (CDCl3): δ = 13.8,
65.0, 113.1, 124.2, 126.5, 126.9, 129.1, 137.6, 149.9. Anal. Calcd. for
C12H9NO3S: C, 58.28; H, 3.67; N, 5.66; S, 12.96%. Found: C, 58.39; H,
3.73; N, 5.70; S, 13.03%.
2-Cyano-2-diethylphosphonylbenzo[b]thiophen-3(2H)-one (3e)
Orange oil. IR (KBr): ν = 2986, 2222, 1529, 1366, 1284, 1038 cm−1.1H
NMR (CDCl3): δ = 1.40 (t, J = 6.1 Hz, 6H, CH3), 4.39 (q, J = 6.1 Hz,
4H, CH2), 7.46–7.58 (m, 2H, arom-H), 7.74 (d, J = 8.0 Hz, 1H, arom-
H), 8.03 (d, J = 7.7 Hz, 1H, arom-H).13C NMR (CDCl3): δ = 16.1, 16.2,
66.0, 66.1, 112.1, 122.9, 123.1, 126.0, 128.4, 129.0, 158.5. Anal. Calcd.
for C13H14NO4PS: C, 50.15; H, 4.54; N, 4.50; S, 10.30%. Found: C, 50.23;
H, 4.62; N, 4.59; S, 10.42%.
2,2-Dicyanobenzo[b]thiophen-3(2H)-one (3f)
Yellow needles from hexane-ethyl acetate, mp 224–227◦C. IR (KBr):
ν = 2975, 2256, 1671, 1410, 1266 cm−1. 1H NMR (DMSO): δ = 7.30–7.38

Simple Route to Benzo[b]thiophenes
1121
(m, 1H, arom-H), 7.44–7.57 (m, 1H, arom-H), 7.60–7.65 (m, 1H, arom-
H), 7.93–8.02 (m, 1H, arom-H).13C NMR (DMSO): δ = 112.2, 124.2,
125.9, 126.8, 127.2, 129.2, 136.6, 152.2. Anal. Calcd. for C10H4N2OS: C,
59.99; H, 2.02; N, 13.99; S, 16.01%. Found: C, 60.11; H, 2.18; N, 14.12
S, 16.15%.
2-Benzoyl-2-cyanobenzo[b]thiophen-3(2H)-one (3g)
Yellow prisms from ethyl acetate, mp 118◦C. IR (KBr): ν = 2220,
1754, 1231, 1057 cm−1. 1H NMR (CDCl3): δ = 7.46–7.51 (m, 1H, arom-
H), 7.59 (t, J = 7.7 Hz, 3H, arom-H), 7.71–7.76 (m, 2H, arom-H), 7.83
(d, J = 8.2 Hz, 1H, arom-H), 8.30 (d, J = 7.1 Hz, 2H, arom-H).13C NMR
(CDCl3): δ = 112.0, 122.5, 123.1, 125.9, 127.6, 128.8, 129.0, 130.8, 134.7,
138.5, 149.9, 163.1. Anal. Calcd. for C16H9NO2S: C, 68.80; H, 3.25; N,
5.02 S, 11.48%. Found: C, 68.98; H, 3.34; N, 5.13 S, 11.55%.
2,2-[10,10-(9-Anthacenonyl)]benzo[b]thiophen-3(2H)-one (3h)
White needles from acetonitrile, mp 205–208◦C. IR (KBr): ν = 1703,
1
1657, 1586, 1245, 1317, 1271 cm−1. H NMR (CDCl3): δ = 7.35 (t, J =
7.0 Hz, 1H, arom-H), 7.49–7.54 (m, 6H, arom-H), 7.61 (d, J = 8.0 Hz,
1H, arom-H), 7.70–7.76 (m, 1H, arom-H), 7.78–7.80 (m, 1H, arom-H),
8.38–8.44 (m, 2H, arom-H). 13C NMR (CDCl3): δ = 123.9, 126.0, 126.9,
127.4, 128.1, 129.0, 129.1, 131.9, 133.7, 136.7, 139.7, 153.3, 182.8, 198.5.
Anal. Calcd. for C21H12O2S: C, 76.80; H, 3.69; S, 9.76%. Found: C, 76.95;
H, 3.78; S, 9.90%.
2,2-[(3,3-Dimethyl)glutaryl]benzo[b]thiophen-3(2H)-one (3i)
White needles from hexane, mp 137–139◦C. IR (KBr): ν = 2936, 1742,
1
1699, 1288, 1219 cm−1. H NMR (CDCl3): δ = 0.97 (s, 3H, CH3), 1.26
(s, 3H, CH3), 2.67 (d, J = 14.2 Hz, 2H, CH2), 3.32 (d, J = 14.2 Hz, 2H,
CH2), 7.21 (t, J = 7.9 Hz, 1H, arom-H), 7.43 (d, J = 7.9 Hz, 1H, arom-
H), 7.54–7.59 (m, 1H, arom-H), 7.64–7.67 (m, 1H, arom-H). 13C NMR
(CDCl3): δ = 27.8, 30.0, 51.5, 124.2, 126.2, 128.2, 135.0, 136.8, 152.6,
190.5, 196.2. Anal. Calcd. for C15H14O3S: C, 65.66; H, 5.15; S, 11.68%.
Found: C, 65.79; H, 5.22; S, 11.70%.
2,2-Diacetylbenzo[b]thiophen-3(2H)-one (3j)
Yellow needles from hexane, mp 75–77◦C. IR (KBr): ν = 1730, 1667,
1253 cm−1. 1H NMR (CDCl3): δ = 2.35 (s, 6H, CH3), 7.28–7.33 (m, 1H,
arom-H), 7.46 (d, J = 8.0 Hz, 1H, arom-H), 7.60–7.65 (m, 1H, arom-
H), 7.82 (d, J = 7.8 Hz, 1H, arom-H). 13C NMR (CDCl3): δ = 27.3,
124.3, 126.2, 128.0, 129.6, 136.8, 150.6, 192.4, 196.2. Anal. Calcd. for

1122
J. M lochowski and P. Potaczek
ꢀ
C12H10O3S: C, 61.52; H, 4.30; S, 13.69%. Found: C, 61.79; H, 4.32; S,
13.70%.
2-Benzoyl-3-hydroxybenzo[b]thiophene (4a)
Yellow needles from ethyl acetate, mp 116–118◦C. IR (KBr): ν =
2940–1980, 1593, 1517, 1342, 1294, 1227 cm−1.1H NMR (CDCl3):
δ = 7.44 (t, J = 7.5 Hz, 1H, arom-H), 7.53–7.65 (m, 4H, arom-H), 7.74
(d, J = 8.1 Hz, 1H, arom-H), 8.07 (t, J = 6.4 Hz, 3H, arom-H), 13.45
(s, 1H, OH). 13C NMR (CDCl3): δ = 123.0, 124.0, 124.8, 128.4, 128.7,
130.4, 132.6, 138.3, 140.8, 165.5, 191.8. Anal. Calcd. for C15H10O2S: C,
70.84; H, 3.97; S, 12.61%. Found: C, 70.96; H, 4.04; S, 12.69%.
2-Ethoxycarbonyl-3-hydroxybenzo[b]thiophene (4b)
White needles from hexane, mp 73–75◦C. IR (KBr): ν = 3487, 2983,
1
2950–1920, 1532, 1304, 1227 cm−1. H NMR (CDCl3): δ = 1.43 (t, J =
7.1 Hz, 3H, CH3), 4.43 (q, J = 7.1 Hz, 2H, CH2), 7.38–7.43 (m, 1H,
arom-H), 7.48–7.53 (m, 1H, arom-H), 7.74 (d, J = 8.1 Hz, 1H, arom-H),
7.95 (d, J = 7.8 Hz, 1H, arom-H), 10.19 (s, 1H, OH). 13C NMR (CDCl3,):
δ = 14.4, 61.4, 123.0, 123.1, 124.4, 128.8, 130.5, 138.9, 159.5, 167.4.
Anal. Calcd. for C11H10O3S: C, 59.44; H, 4.54; S, 14.42%. Found: C,
59.53; H, 4.56; S, 14.50%.
2-Acetyl-3-hydroxybenzo[b]thiophene (4j)
White needles from hexane, mp 79–80◦C. IR (KBr): ν = 2920–1905,
1622, 1520, 1357, 1298, 1221 cm−1.1H NMR (CDCl3): δ = 2.51 (s, 3H,
CH3), 7.40–7.45 (m, 1H, arom-H), 7.52–7.57 (m, 1H, arom-H), 7.74 (d,
J = 8.2 Hz, 1H, arom-H), 8.00 (d, J = 8.0 Hz, 1H, arom-H), 12.27 (s,
1H, OH). 13C NMR (CDCl3): δ = 28.2, 111.5, 123.3, 123.8, 124.8, 129.8,
139.1, 161.7, 196.7. Anal. Calcd. for C10H8O2S: C, 62.47; H, 4.20; S,
16.68%. Found: C, 62.59; H, 4.34; S, 16.75%.
2-(3-Carboxypropionyl)-3-hydroxybenzo[b]thiophene (4l)
White needles from acetonitrile, mp 189–192◦C. IR (KBr): ν = 3325–
2165, 1710, 1617, 1521, 1402, 1247 cm−1. 1H NMR (DMSO): δ = 2.59 (t,
J = 6.4 Hz, 2H, CH2), 3.22 (t, J = 6.4 Hz, 2H, CH2), 7.43 (t, J = 7.1 Hz,
1H, arom-H), 7.53 (t, J = 7.1 Hz, 1H, arom-H), 7.88 (d, J = 8.0 Hz, 1H,
arom-H), 8.10 (d, J = 8.0 Hz, 1H, arom-H), 11.91 (s, 2H, OH, COOH).
13C NMR (DMSO): δ = 28.2, 36.5, 117.0, 123.9, 124.0, 125.0, 129.3,
132.4, 138.7, 155.5, 174.3, 194.0. Anal. Calcd. for C12H10O4S: C, 57.58;
H, 4.03; S, 12.81%. Found: C, 57.70; H, 4.14; S, 12.90%.

Simple Route to Benzo[b]thiophenes
1123
2-(4-Carboxybutyl)-3-hydroxybenzo[b]thiophene (4m)
White needles from acetonitrile, mp 154–156◦C. IR (KBr): ν = 3057,
2946–2005, 1708, 1587 cm−1. 1H NMR (DMSO): δ = 1.90 (quintet, J =
7.3 Hz, 2H, CH2), 2.34 (t, J = 7.3 Hz, 2H, CH2), 3.04 (t, J = 7.3 Hz,
2H, CH2), 7.45 (t, J = 7.6 Hz, 1H, arom-H), 7.56 (t, J = 7.6 Hz, 1H,
arom-H), 7.91 (d, J = 8.1 Hz, 1H, arom-H), 8.11 (d, J = 8.1 Hz, 1H,
arom-H), 12.09 (s, 2H, OH, COOH). 13C NMR (DMSO): δ = 29.3, 37.2,
117.3, 123.9, 124.7, 125.0, 129.9, 133.4, 139.1, 156.5, 175.9, 195.6. Anal.
Calcd. for C13H12O4S: C, 59.08; H, 4.58; S, 12.13%. Found: C, 59.20; H,
4.54; S, 12.10%.
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