An aquatic pseudo-four-component reaction for the synthesis of highly substituted thiophenes

Article abstract of DOI:10.1055/s-0032-1316866

A novel and simple procedure was developed for the construction of fully substituted thiophenes. A series of α-haloacetophenone derivatives were converted into fully substituted thiophenes by treatment with sodium sulfide in the presence of 1,8-diazabicyc

Full text of DOI:10.1055/s-0032-1316866

PAPER
▌913
paper
An Aquatic Pseudo-Four-Component Reaction for the Synthesis of Highly
Substituted Thiophenes
Synthesis of Highly Substituted Thiophenes
Hassan Zali-Boeini,* Maryam Ghani
Department of Chemistry, University of Isfahan, 81746-73441, Isfahan, Iran
Fax +98(311)6689732; E-mail: h.zali@chem.ui.ac.ir
Received: 10.12.2012; Accepted after revision: 16.02.2013
catalytic amount of sodium iodide at 85 °C, we obtained
the corresponding trisubstituted thiophene 2 in a good
yield (67–71%) (Scheme 1).
Abstract: A novel and simple procedure was developed for the
construction of fully substituted thiophenes. A series of α-haloace-
tophenone derivatives were converted into fully substituted thio-
phenes by treatment with sodium sulfide in the presence of 1,8-
diazabicyclo[5.4.0]undec-7-ene and sodium iodide in aqueous eth-
anol under aerobic conditions. A mechanism for the reaction is pro-
posed.
Ar
O
base, HTAB (cat.)
Ar
NaI (cat.)
3
Br
Ar
Na2S
+
Ar
EtOH–H2O
85 °C, 90 min
S
O
Key words: sulfur, heterocycles, alkyl halides, coupling, dehydro-
genation, multicomponent reactions
1a,b
O
2a–c
67–71%
HTAB: Me(CH2)15N+Me3Br–
Scheme 1 Synthesis of trisubstituted thiophenes
Thiophenes are undoubtedly an important class of sulfur
heterocycles, and their synthesis has attracted a great deal
of research because of their presence in natural products,1
conducting polymers,2 and hole-transport materials for or-
ganic light-emitting diodes,3 and their use in medicinal
chemistry as isosteric replacements for the phenyl group.4
At the start of our study, we dissolved 2-bromo-1-(4-bro-
mophenyl)ethanone (1a; 3 mmol) as a model compound
in N,N-dimethylformamide and treated the solution with 5
M aqueous sodium sulfide (0.22 mL) in the presence of
1,8-diazabicyclo[5.4.0]undec-7-ene as base and a catalyt-
ic amount of HTAB at 85 °C. The reaction proceeded
sluggishly with the formation of various tarry and colored
materials together with small amounts of the thiophene
derivative 2a (33%). To optimize our reaction conditions,
we examined the effects of various solvents and bases on
the reaction of dibromo ketone 1a with 5 M sodium sul-
fide solution at various temperatures. The results of this
study are summarized in Table 1.
The most general method for the preparation of highly
substituted thiophenes is the Gewald method, in which el-
emental sulfur reacts with a molar equivalent of an acti-
vated acetonitrile and a carbonyl compound in the
presence of a suitable base.5 Another route to fully substi-
tuted thiophenes, known as the Hinsberg method, relies on
the condensation reaction between a diketone and a sul-
fide containing reactive methylene groups.6 We and other
research groups have previously shown that a one-pot
thio-Claisen reaction and a ring closure of thioacetomor-
pholides with propargyl bromide leads to trisubstituted
thiophenes via an α-allenyl thioacetomorpholide interme-
diate.7 We have also reported an efficient method for the
synthesis of fully substituted thiophenes that is based on
the reaction between thioacetomorpholides and α-bromo-
acetophenone derivatives.8
Table 1 Effects of Various Solvents, Bases, and Temperatures on
the Synthesis of Thiophene 2a
Entry
Solvent
Base
Yield (%)
At 85 °C At 110 °Ca
1
2
3
4
5
6
7
8
DMF
K2CO3
DBU
22
33
<5
25
42
29
71
38c
31
32
11
27
35
31
66
–
DMF
In continuation of our research in this area, we report a
new, one-pot, convenient route to fully substituted thio-
phenes through the reaction of α-haloacetophenone deriv-
atives with sodium sulfide in the presence of 1,8-
diazabicyclo[5.4.0]undec-7-ene in aqueous ethanol as the
reaction medium.
DMF
Et3N
MeCN
MeCN
EtOH–H2Ob
EtOH–H2Ob
H2Oc
K2CO3
DBU
K2CO3
DBU
We found that when we treated an α-bromoacetophenones
1 with sodium sulfide in aqueous ethanol as the solvent in
the presence of a base, a phase-transfer catalyst (N,N,N-
trimethylhexadecylammonium bromide; HTAB), and a
DBU
a Colored or tarry byproducts were also formed.
b In the presence of HTAB (5.5 mol%) and NaI (10 mol%).
c Reflux conditions.
SYNTHESIS 2013, 45, 0913–0918
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DOI: 10.1055/s-0032-1316866; Art ID: SS-2012-N0952-OP
© Georg Thieme Verlag Stuttgart · New York

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H. Zali-Boeini, M. Ghani
PAPER
S2¯
air (O2)
2Na
Na I¯
aqueous phase
organic phase
Br¯
N
10
O
O
O
O
O
S
O
S
S
aerobic oxidation
– H2O
DBU
– HI
Ar
Ar
Ar
Ar
Ar
Ar
O
Ar
Ar
Ar
2
Br
I¯
+
HTAB
I
2
Ar
5
4
1
– Br¯
Na2S
– H2O
DBU
O
O
O
O
S
+
I
I
+
2
Ar
Ar
Ar
Ar
– I¯
3
Scheme 2 Proposed mechanism for the formation of substituted thiophenes
As is clear from Table 1, the use of 1,8-diazabicyc- proach. Fortunately, however, we found that trisubstituted
lo[5.4.0]undec-7-ene (DBU) as the base in aqueous etha- and fully substituted thiophenes bearing different aryl
nol containing HTAB (5.5 mol%) and sodium iodide (10 groups could prepared by the treatment under the opti-
mol%) as the catalyst system at 85 °C provided the best mized reaction conditions of an α-substituted α-bromo-
conditions for obtaining a good yields of the highly sub- acetophenone 4 with a sulfide 3, formed in situ by reaction
stituted thiophene 2a. We also showed that the reaction of two equivalents of an α-bromoacetophenone 1 with so-
proceeded better in the presences of catalytic amount of dium sulfide (Scheme 3).
sodium iodide (10 mol%), because the reaction of 1a with
sodium sulfide under identical conditions in the absence
of sodium iodide resulted in a marked decrease in the
yield of product 2a (57%).
O
Br
2
Na2S
+
Ar1
O
1
A mechanism for the reaction has been proposed and is
shown in Scheme 2.
O
O
S
3
Ar1
Ar1
Ar1
It seems likely that the α-bromoacetophenone 1 undergoes
halogen exchange to form the corresponding iodo deriva-
tive, which reacts with sodium sulfide to form the sulfide
3. Condensation of 3 with a second molecule of 1 gives in-
termediate 4, which undergoes elimination of hydrogen
iodide to form intermediate 5. Aerobic oxidation of this
intermediate leads to the corresponding thiophene 2. Note
that our attempts to isolate intermediates 4 and 5 were un-
successful, whereas intermediate 3 could be isolated.
O
S
base, HTAB (cat.)
NaI (cat.)
+
Ar1
Ar2
EtOH–H2O
85 °C, 70 min
O
R
2d–k
Br
Ar2
55–80%
4
R
R = aryl, alkyl, H
Scheme 3 Two-step preparation of tri- and tetrasubstituted thio-
phenes bearing different aryl groups
The proposed mechanism implies that the presence of air
is necessary for the final step of the reaction to proceed.
Interestingly, when a stream of air (or oxygen) was bub-
bled through the reaction mixture, the product yield was
not significantly altered. The use of manganese dioxide as
a mild oxidant for oxidative dehydrogenation produced
only very slightly higher yields of the product than those
obtained in the original form of the reaction. Unfortunate-
ly, we failed in our attempts to produce trisubstituted thio-
phenes under our optimized conditions by using α-
chloroacetophenone derivatives as the α-halo ketones.
We confirmed the generality of our method by the suc-
cessful synthesis of eleven diverse thiophene derivatives
in moderate-to-good yields (58–80%) under rather mild
conditions (Table 2).
In conclusion, we have developed a novel, general, and ef-
ficient method for the construction of fully substituted
thiophenes from α-bromoacetophenone derivatives as
readily available starting materials. The reaction occurs
under reasonably mild conditions in aqueous ethanol as a
nonpolluting, safe, and green medium.
It initially appeared that only trisubstituted thiophenes
bearing identical aryl groups could be prepared by this ap-
Synthesis 2013, 45, 913–918
© Georg Thieme Verlag Stuttgart · New York

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Synthesis of Highly Substituted Thiophenes
915
Table 2 Efficient Preparation of Various Highly Substituted Thiophenes
Entry
Ar1
Ar2
Ar3
R
Producta
Yield (%)b
O
O
S
Br
2a
Cl
1
4-BrC6H4
4-BrC6H4
4-BrC6H4
H
71
Br
Br
O
O
S
2
3
4
5
6
7
4-ClC6H4
4-ClC6H4
4-ClC6H4
H
H
H
H
H
H
67
63
69
77
80
66
Cl
Cl
2b
O
O
S
4-Tol
4-Tol
Ph
2c9
O
O
O
O
O
O
O
O
S
S
S
S
Br
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-Tol
Br
Br
Br
Br
2d
Br
4-O2NC6H4
4-ClC6H4
4-MeOC6H4
O2N
2e
Br
Cl
2f
Br
MeO
2g
© Georg Thieme Verlag Stuttgart · New York
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916
H. Zali-Boeini, M. Ghani
PAPER
Table 2 Efficient Preparation of Various Highly Substituted Thiophenes (continued)
Entry
Ar1
Ar2
Ar3
R
H
Producta
Yield (%)b
O
O
S
Br
8
4-BrC6H4
4-BrC6H4
4-AcNHC6H4
58
AcHN
Br
2h
O
O
S
9
10
11
Ph
Ph
Ph
Ph
Ph
H
65
67
61
2i9
O
O
S
4-BrC6H4
4-BrC6H4
Ph
Br
Br
2j
O
O
S
N
N
4-pyridyl
4-pyridyl
4-pyridyl
N
2k9
a All compounds were characterized by 1H NMR, 13C NMR, HRMS, and IR spectroscopy.
b Isolated yields.
All reagents, unless otherwise stated, were used as received from
commercial suppliers. TLC was performed on aluminum plates
coated with UV-active silica gel (silica gel 60 F254). Flash chroma-
tography was performed on silica gel (60 Å, 230–400 mesh) with
elution by reagent-grade solvents. NMR spectra were recorded at
400 MHz (1H NMR) or 100 MHz (13C NMR) on a Bruker Avance
400 spectrometer and are referenced to residual solvent. High-reso-
lution mass spectra were obtained with a ZAB high-resolution mass
spectrometer (Vacuum Generators). IR spectra were recorded on a
PerkinElmer Spectrum 1000 spectrophotometer.
were added NaI (15 mg, 0.1 mmol), HTAB (20 mg, 0.055 mmol),
and a second α-bromoacetophenone 4 (1.1 mmol). DBU (2 mmol,
0.3 ml) was then added and the mixture was vigorously stirred at 85
°C for 70 min. The thiophene product was isolated and purified as
described in Method A.
[3-(4-Bromophenyl)thiene-2,5-diyl]bis[(4-bromophenyl)metha-
none] (2a)
White solid; yield: 430 mg (71%); mp 178.2 °C.
IR (KBr): 3122, 2847, 1642, 1508, 1131, 763 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.91 (d, J = 8.0 Hz, 2 H), 7.72–
7.67 (m, 3 H), 7.54 (d, J = 8.0 Hz, 2 H), 7.20–7.31 (m, 6 H).
13C NMR (100 MHz, CDCl3): δ = 188.5, 186.5, 144.8, 144.6, 142.4,
136.0, 135.4, 135.3, 133.2, 132.1, 131.8, 131.7, 131.2, 130.8, 130.4,
128.9, 128.3, 122.9.
Trisubstituted Thiophenes 2; General Procedure (Method A)
5 M aq Na2S (0.22 ml, 1.1 mmol) was added slowly to a stirred
warm (50 °C) soln of α-bromoacetophenone 1 (3 mmol) in EtOH
(10 mL) containing NaI (15 mg, 0.1 mmol) and HTAB (20 mg,
0.055 mmol). The mixture was stirred for 20 min before DBU (2
mmol, 0.30 mL) was added. The mixture was then heated to 85 °C
with vigorous stirring for a further 70 min, cooled to r.t., and poured
into cold H2O (10 mL). The precipitated gummy product was ex-
tracted with EtOAc (15 mL). The EtOAc soln was concentrated un-
der vacuum, and the residue was purified by flash column
chromatography [silica gel, EtOAc–hexane (1:5)].
HRMS (EI): m/z calcd for C24H13Br3O2S: 605.1358; found:
605.1349.
[3-(4-Chlorophenyl)thiene-2,5-diyl]bis[(4-chlorophenyl)metha-
none](2b)
White solid; yield: 316 mg (67%); mp 178.2 °C.
IR (KBr): 3122, 2847, 1642, 1508, 1131, 763 cm–1.
Tri- and Tetrasubstituted Thiophenes 2; General Procedure
(Method B)
Diketo sulfide 3 was prepared in situ by treatment of a first α-bro-
moacetophenone derivative 1 (2 mmol) with 5 M aq Na2S, (0.22
mL, 1.1 mmol) in EtOH (15 mL) at 85 °C. To the resulting soln
1H NMR (400 MHz, CDCl3): δ = 7.83 (d, J = 8.4 Hz, 2 H), 7.71 (d,
J = 8.4 Hz, 2 H), 7.59 (d, J = 8.4 Hz, 2 H), 7.47 (d, J = 8.4 Hz, 2 H),
7.39 (d, J = 8.4 Hz, 2 H), 7.38 (s, 1 H), 7.14 (d, J = 8.4 Hz, 2 H).
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Synthesis of Highly Substituted Thiophenes
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13C NMR (100 MHz, CDCl3): δ = 188.4, 186.9, 144.8, 144.6, 142.6,
135.9, 135.4, 135.3, 133.2, 132.1, 131.8, 131.7, 131.2, 130.8, 130.4,
128.9, 128.3, 122.9.
1H NMR(400 MHz, CDCl3): δ = 7.74 (d, J = 8.4 Hz, 2 H), 7.62 (d,
J = 8.4 Hz, 2 H), 7.61 (s, 1 H), 7.51 (d, J = 8.4 Hz, 2 H), 7.37 (d,
J = 8.8 Hz, 2 H), 7.31 (d, J = 8.8 Hz, 2 H), 7.05 (d, J = 8.4 Hz, 2 H),
3.92 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 185.5, 184.6, 144.8, 144.6, 142.3,
135.8, 135.4, 135.3, 133.2, 132.1, 131.8, 131.7, 131.2, 130.8, 130.4,
128.9, 128.3, 123.0, 47.7.
HRMS (EI): m/z calcd for C24H13Cl3O2S: 471.7828; found:
471.7823.
(3-Phenylthiene-2,5-diyl)bis[(4-tolyl)methanone] (2c)
White solid; yield: 250 mg (63%); mp 181 °C.
IR (KBr): 3110, 2925, 1648, 1502, 1120, 831 cm–1.
HRMS (EI): m/z calcd for C25H16Br2O3S: 556.2657; found:
556.2650.
1H NMR (400 MHz, CDCl3): δ = 7.83 (d, J = 8.8 Hz, 2 H), 7.72 (d,
J = 8.8 Hz, 2 H), 7.59 (d, J = 8.4 Hz, 2 H), 7.47 (d, J = 8.4 Hz, 2 H),
7.42–7.40 (m, 3 H), 7.15 (s, 1 H), 7.14 (d, J = 8.4 Hz, 2 H), 2.23 (s,
3 H), 2.22 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 188.4, 186.4, 144.8, 144.5, 142.4,
140.1, 139.7, 135.5, 135.4, 134.9, 134.7, 132.8, 131.2, 130.7, 130.1,
129.1, 128.8, 128.7, 32.1, 31.8.
N-{4-[2,5-Bis(4-bromobenzoyl)-3-thienyl]phenyl}acetamide
(2h)
Off-white solid; yield: 338 mg (58%); mp 164.5 °C.
IR (KBr): 3093, 2898, 1649, 1503, 1125, 830 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.83 (s, 1 H), 7.71 (d, J = 8.4 Hz,
2 H), 7.69 (d, J = 8.4 Hz, 2 H), 7.59 (d, J = 8.0 Hz, 2 H), 7.47 (d,
J = 8.0 Hz, 2 H), 7.39 (d, J = 8.4 Hz, 2 H), 7.15 (s, 1 H), 7.14 (d,
J = 8.4 Hz, 2 H), 2.29 (s, 3 H).
HRMS (EI): m/z calcd for C26H20O2S: 396.5008; found: 396.5015.
13C NMR (100 MHz, CDCl3): δ = 188.5, 186.6, 169.9, 144.8, 144.6,
142.3, 135.8, 135.4, 135.3, 133.2, 132.1, 131.8, 131.7, 131.2, 130.8,
130.4, 128.9, 128.3, 122.9, 35.9.
[3-(4-Tolyl)thiene-2,5-diyl]bis[(4-bromophenyl)methanone]
(2d)
White solid; yield: 373 mg (69%); mp 162.4 °C.
IR (KBr): 3120, 2845, 1640, 1507, 1123, 753 cm–1.
HRMS (EI): m/z calcd for C26H17Br2NO3S: 583.2911; found:
1H NMR (400 MHz, CDCl3): δ = 7.82 (d, J = 8.4 Hz, 2 H), 7.72 (d,
J = 8.8 Hz, 2 H), 7.71 (s, 1 H), 7.59 (d, J = 8.4 Hz, 2 H), 7.47 (d,
J = 8.4 Hz, 2 H), 7.39 (d, J = 8.4 Hz, 2 H), 7.14 (d, J = 8.8 Hz, 2 H),
2.19 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 188.5, 186.6, 144.8, 144.6, 142.3,
135.8, 135.4, 135.3, 133.2, 132.1, 131.9, 131.7, 131.2, 130.8, 130.4,
128.9, 128.3, 122.9, 30.9.
583.2906.
(3,4-Diphenylthiene-2,5-diyl)bis[(4-bromophenyl)methanone]
(2j)
White solid; yield: 403 mg (67%); mp 176 °C.
IR (KBr): 3098, 2905, 1651, 1507, 1126, 829 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.87–2.92 (m, 9 H), 7.38–7.51 (m,
9 H).
HRMS (EI): m/z calcd for C25H16Br2O2S: 540.2663; found:
540.2655.
13C NMR (100 MHz, CDCl3): δ = 185.8, 138.7, 135.3, 134.0, 132.7,
129.1, 129.0, 128.9, 128.8, 128.5, 127.2.
[3-(4-Nitrophenyl)thiene-2,5-diyl]bis[(4-bromophenyl)metha-
none] (2e)
Light-yellow solid; yield: 440 mg (77%); mp 188 °C.
HRMS (EI): m/z calcd for C30H18Br2O2S: 602.3357; found:
602.3349.
IR (KBr): 3100, 2915, 1645, 1500, 1123, 830 cm–1.
(3-Pyridin-4-ylthiene-2,5-diyl)bis(pyridin-4-ylmethanone) (2k)
Light-yellow solid; yield: 227 mg (61%); mp 169 °C.
1H NMR (400 MHz, CDCl3): δ = 7.74 (d, J = 8.4 Hz, 2 H), 7.62 (d,
J = 8.4 Hz, 2 H), 7.61 (s, 1 H), 7.50 (d, J = 8.4 Hz, 2 H), 7.38 (d,
J = 8.4 Hz, 2 H), 7.31 (d, J = 8.4 Hz, 2 H), 7.05 (d, J = 8.4 Hz, 2 H).
13C NMR(100 MHz, CDCl3): δ = 191.5, 189.6, 144.8, 144.6, 142.3,
135.8, 135.4, 135.3, 133.2, 132.1, 131.8, 131.7, 131.2, 130.8, 130.4,
128.9, 128.3, 122.9.
IR (KBr): 3100, 2911, 1657, 1509, 1131, 834 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.91 (d, J = 8.8 Hz, 2 H), 8.71 (s,
1 H), 8.67 (d, J = 8.8 Hz, 2 H), 8.54 (d, J = 8.8 Hz, 2 H), 8.30 (d,
J = 8.8 Hz, 2 H), 8.20–8.26 (m, 4 H).
13C NMR (100 MHz, CDCl3): δ = 191.5, 189.6, 154.8, 152.3, 145.8,
HRMS (EI): m/z calcd for C24H13Br2NO4S: 571.2373; found:
145.4, 143.2, 142.1, 141.8, 141.5, 140.8, 140.4, 139.3, 138.9, 138.8.
571.2365.
HRMS (EI): m/z calcd for C21H13N3O2S: 371.4118; found:
371.4125.
[3-(4-Chlorophenyl)thiene-2,5-diyl]bis[(4-bromophenyl)metha-
none] (2f)
White solid; yield: 448 mg (80%); mp 179 °C.
Acknowledgment
IR (KBr): 3092, 2905, 1655, 1510, 1113, 825 cm–1.
We are grateful to the University of Isfahan Research Council for
financial support of this work.
1H NMR (400 MHz, CDCl3): δ = 7.83 (d, J = 8.8 Hz, 2 H), 7.73 (d,
J = 8.4 Hz, 2 H), 7.71 (s, 1 H), 7.59 (d, J = 8.8 Hz, 2 H), 7.47 (d,
J = 8.4 Hz, 2 H), 7.39 (d, J = 8.4 Hz, 2 H), 7.14 (d, J = 8.4 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 188.5, 186.6, 144.8, 144.6, 142.3,
135.8, 135.4, 135.3, 133.2, 132.1, 131.8, 131.7, 131.2, 130.8, 130.4,
128.9, 128.3, 122.9.
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(8) Matloubi Moghaddam, F.; Zali Boeini, H. Tetrahedron
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(9) Compounds 2c, 2i, and 2k have been reported, see: Yuji, M.;
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Synthesis 2013, 45, 913–918
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