A new synthetic approach to thiophenes

Article abstract of DOI:10.1055/s-2001-18054

A new simple and efficient way to 3-hydroxy(methoxy)thiophenes is described. The reactions of (ethylsulfanyl)acetyl fluoride/boron trifluoride (1) and 2-(ethylsulfanyl)butanoyl fluoride/boron trifluoride (6) complexes with acetylenes give rise to the 5-membered cyclic sulfonium salts (3a-f). The last ones (3e, 3f) after being refluxed with thiourea in methanol or acetonitrile are converted into 3-methoxythiophenes or 3-(2H)-thiophenones respectively. Several 3-methoxythiophenes unsubstituted in the 2-position were obtained by the reactions of 1 with acetylenes. Reactions of 6 with acetylenes allows the synthesis of 2-ethylsubsituted 3-methoxythiophenes. The method allows the synthesis of a variety of mono-, di-, tri- and tetrasubsituted thiophenes.

Full text of DOI:10.1055/s-2001-18054

2
124
PAPER
A New Synthetic Approach to Thiophenes
A
M
N
ewSynthetic
A
ppr
i
oachto
k
Thiophene sh ail V. Lebedev, Valentine G. Nenajdenko,* Elizabeth S. Balenkova*
Department of Chemistry, Moscow State University, 119899 Moscow, Russia
Fax +7(095)9328846; E-mail: Nen@acylium.chem.msu.ru
Received 27 April 2001; revised 27 July 2001
The carbonyl group (electrophilic center) linked by two
Abstract: A new simple and efficient way to 3-hydroxy(meth-
oxy)thiophenes is described. The reactions of (ethylsulfanyl)acetyl
fluoride/boron trifluoride (1) and 2-(ethylsulfanyl)butanoyl fluo-
ride/boron trifluoride (6) complexes with acetylenes give rise to the
CH -groups to the sulfide moiety (nucleophilic center) in
2
the complex b-(ethylsulfanyl)propionyl fluoride◊BF ,
3
made the intramolecular acylsulfonium salts very interest-
5
-membered cyclic sulfonium salts (3a–f). The last ones (3e, 3f) af- ing molecules to study. From this point further investiga-
ter being refluxed with thiourea in methanol or acetonitrile are con- tions of homologous complexes seemed logical.
verted into 3-methoxythiophenes or 3-(2H)-thiophenones
We have found that the complex ethylsulfanyl acetyl flu-
respectively. Several 3-methoxythiophenes unsubstituted in the 2-
oride◊BF (1) reacts with acetylenes analogously to its ho-
position were obtained by the reactions of 1 with acetylenes. Reac-
tions of 6 with acetylenes allows the synthesis of 2-ethylsubsituted mologue, i.e. the reactions proceed as a conjugated
-methoxythiophenes. The method allows the synthesis of a variety addition reaction of acyl and sulfide moeties to the car-
of mono-, di-, tri- and tetrasubsituted thiophenes.
3
3
bon-carbon triple bond. The reaction was carried out in
Key words: acylation, thiophene, acylsulfonium salt, alkynes, dichloromethane at –60 °C to –40 °C and the cyclic five-
electrophilic addition
membered sulfonium tetrafluoroborates were obtained.
They are quite stable pale colored solids or in several cas-
es oils, which can be easily isolated by treatment of the re-
In our previous work we found that dimethylacylsulfo- action mixture with ether.
nium salts formed by the reaction of acyltetrafluorobo-
rates with dimethyl sulfide are useful reagents for the
1
synthesis of unsaturated ketones. Certain types of dime-
thylacylsulfonium salts are milder reagents than the acyli-
um salts which tend to polymerize olefins. Reaction of
acylsulfonium salts with alkenes, acetylenes and dienes
proceeds as a conjugate addition of the acyl group and
dimethyl sulfide to the unsaturated C-C bond and results
in the formation of unsaturated ketones. We used this
principle further to propose a new trifluoroacylating re-
agent a complex of dimethyl sulfide borontrifluoride and
Scheme 1
2
trifluoroacetic anhydride.
Further work in our group on the intramolecular acylsul-
fonium salts, resulted in these salts being obtained by the
treatment of alkylsulfanyl substituted acyl fluorides with
borontrifluoride at –60 °C, significally increased the syn-
To investigate a broad range of acetylenes which could
undergo reaction with complex 1 we carried out several
reactions with a variety of terminal and non-terminal acet-
ylenes 2a–f, bearing both alkyl and aryl substituents, in-
cluding cyclooctyne and phenylsulfanyl acetylene. In all
cases the formation of five-membered sulfonium salts 3a–
f was observed (Scheme 1). The reactions proceeded re-
giospecifically, in good yields and without significant
amounts of side products forming. Unfortunately, the
acetylenes with electron withdrawing substituents could
not react with complex 1 in this manner; even the propar-
gyl chloride remained unreacted after several hours at
3
thetic applications of acylsulfonium salts. Thus the reac-
tions of b-(ethylsulfanyl)propionyl fluoride◊BF complex
3
with alkenes leads initially to the formation of a 6-mem-
bered sulfonium salt, which is then converted to the ethyl-
sulfanyl substituted a,b-unsaturated ketone. The complex
formed with alkynes gives rise to divinylketones with a
sulfide moiety or to the substituted thiapyran-4-ones. Also
the complex b-(ethylsulfanyl)propionyl fluoride◊BF re-
3
acts with various aromatic compounds and could be used
for the simple synthesis of aryl vinyl ketones and conju-
gated thiapyranones.
–
40 °C due to the deactivating -I-effect.
The synthesis of the corresponding thiophene derivatives
from the cyclic sulfonium salts was achieved using thio-
urea as a dealkylating agent. However, after the reaction
of 3a with thiourea in methanol we have isolated the 3-
methoxythiophene 5a, instead of expected thophenone
Synthesis 2001, No. 14, 26 10 2001. Article Identifier:
4
a. Replacing methanol with acetonitrile allowed the iso-
1
©
437-210X,E;2001,0,14,2124,2128,ftx,en;E03301SS.pdf.
Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881
lation of thiophenone 4a (Scheme 2).

PAPER
A New Synthetic Approach to Thiophenes
2125
ide◊BF complex undergoes a reaction with acetylenes,
3
which permits the direct synthesis of thiophene deriva-
tives with a substituent in the 2-position.
To illustrate this last hypothesis we have synthesized the
fluoroanhydride of 2-ethylsulfanyl butyric acid. This can
be viewed as ethylsulfanyl acetyl fluoride with ethyl in the
a-position. 2-Ethylsulfanyl butyroyl fluoride reacts with
BF to give complex (6), the structure of which seems to
3
Scheme 2
be analogous to 1. It is shown (Scheme 4) that complex 6
reacts with acetylenes with the formation of the cyclic sul-
fonium salts (7a–c).
The observed difference in the reaction products obtained
in acetonitrile and methanol proved to be true also for the
other sulfonium salts 3a–f. The products are the deriva-
tives of 3-(2H)-thiophenone (4a, 4d, 4e) in the first case
and 3-methoxythiophenes (5a–f) in the second case. The
most common and frequently used synthetic methods for
substituted 3-hydroxythiophenes is the Fiesselmann con-
4
densation and its different modifications. The thiophenes
synthesized by those methods usually contain electron
withdrawing substituents.
It should also be noted that few examples of the thiophene
ring synthesis from the C-C-S and C-C fragments (see
Scheme 3) are known at the present time. In our method
Scheme 4
5
the C-C-S fragment is derived from the fluoroanhydride
of ethylsulfanylacetic acid and the C-C fragment is a triple
bond of acetylene.
According to NMR data ( H and 13C), the reaction pro-
ceeds diastereospecifically with only one diastereomer of
sulfonium salts 7a-c obtained. In the case of sulfonium
salt 7a the structure was secured by means of X-ray anal-
ysis (Figure), with the ethyl-substituents in the trans-posi-
tion relatively to each other.
1
Scheme 3
Thus, we present a new synthetic approach to the
thiophene ring construction, the key step of which is the
reaction of complex 1 with acetylenes. It opens a simple
way to various 4- and 5-substituted 3-(2H)-thiophenones
and 3-hydroxythiophenes. Both, the first step, acylation of
acetylene and the second, dealkylation of the initially
formed sulfonium salt, proceed under very mild condi-
tions in good to excellent yields.
It should be mentioned that methods for the synthesis of
3
-methoxy(hydroxy)thiophenes
essentially
allows
thiophenes with a substituent in the 2-position, while the
preparation of 2-unsubstituted heterocycles needs addi-
tional steps. In our case, the reaction of the ethylsulfanyl
Figure Crystal structure of sulfonium salt 7a
acetyl fluoride◊BF complex (1) with acetylenes leads to
3
the 3-methoxy derivatives of thiophenes with an unsubsti-
tuted 2-position which is additionally activated by the ad- The dealkylation of sulfonium salts 7a,7b occured in
jacent methoxy-group and could be easy functionalized methanol yielding the 2-ethyl-3-methoxy derivatives of
with different electrophiles.
thiophene (Scheme 5). 2,3,5-Trisubstituted thiophene
8a) was synthesized from phenylacetylene, and the reac-
tion of complex 6 with 1-phenylpropyne-1 furnished the
tetra-substituted thiophene (8b).
(
We have also shown the possibility of introducing the 2-
substituent earlier on, in the synthesis of 3-methox-
ythiophenes. a-Substituted ethylsulfany acetyl fluor-
Synthesis 2001, No. 14, 2124–2128 ISSN 0039-7881 © Thieme Stuttgart · New York

2
126
M. V. Lebedev et al.
PAPER
1
H NMR: d = 7.56–7.31 (m, 5 H), 7.19 (s, 1 H), 4.15 (d, 1 H,
J = 17.5 Hz), 3.93 (d, 1 H, J = 17.5 Hz), 3.42–3.18 (m, 2 H), 1.27 (t,
3
H, J = 7.2 Hz).
1
3
C NMR: d = 192.89, 158.37, 133.82, 130.93, 129.58, 127.39,
1
26.67, 42.03, 39.01, 7.09.
Anal. Calcd for C H BF OS: C, 49.34; H, 4.49. Found: C, 49.25;
1
2
13
4
H, 4.36.
Scheme 5
5
-Phenyl-3-(2H)-thiophenone (4a)
6
Yield 69%; mp 75–77 °C, lit. mp 78 °C.
Thus, we have proposed a new simple two-step synthetic
approach to thiophenes, based on the reaction of boron tri-
fluoride complexes of a-alkylsulfanyl substituted carbox-
-
1
IR (Nujol): 3100–3450, 1700, 1680 cm .
1
H NMR: ketone: d = 7.51–7.22 (m, 5 H), 6.36 (s, 1 H), 3.61 (s, 2
ylic acids fluoroanhydrides with acetylenes, which allows H); enol: d = 6.86 (s, 1 H), 6.11 (s, 1 H); ketone–enol, 10:1.
1
3
the synthesis of various 3-oxygen substituted thiophenes
bearing both heteroatoms, alkyl and aryl groups.
C NMR: ketone: d = 201.22, 177.30, 131.07, 127.41, 124.97
123.60, 116.79, 38.54; enol: d = 153.27, 131.07, 127.16, 125.83,
23.60, 114.34, 97.41.
1
Anal Calcd for C H OS: C, 68.15; H, 4.58. Found: C, 68.18; H,
Melting points were determined in sealed capillaries. NMR spectra
were recorded on Varian VXR-400 and Bruker AM 400C spectrom-
eters in CD CN or CD Cl for sulfonium salts (3a-f, 7a,7b), CDCl
10
8
4
.44.
3
2
2
3
4
-Methoxy-2-phenylthiophene (5a)
for thiophenes (5a-f, 8a,8b) and thiophenones (4a,4d,4e) and
CD Cl/CF COOH (1/1) for salt 7c with TMS as an internal stan-
Yield 61%; oil.
3
3
1
dard. The IR spectra were obtained with UR-20 spectrometer. Col-
umn chromatography was performed on silica gel (63-200 mesh,
Merck). All solvents used were dried and distilled according to the
standard procedures. Ethylsulfanylacetyl fluoride was prepared ac-
cording to the literature procedure from thioglycolic acid (Merck).
H NMR: d = 7.61–7.28 (m, 5H), 7.03 (d, 1 H, J = 1.8 Hz), 6.23 (d,
1 H, J = 1.8 Hz), 3.79 (s, 3 H).
1
3
C NMR d = 158.63, 142.86, 134.27, 128.78, 127.72, 125.44,
1
15.32, 96.19, 57.14.
Anal Calcd for C H OS: C, 69.44; H, 5.30. Found: C, 69.30; H
1
1
10
5
.38.
X-ray Structural Analysis (7a):
Empirical formula C H BF OS, formula weight 320.15, orthor-
1
4
17
4
4
-Methyl-3-oxo-5-phenyl-1-ethyl-2,3-dihydrothiopheniumTe-
hombic, space group Pna2 , wavelength 0.71073 Å, a = 13.486 (3),
1
3
trafluoroborate (3b)
Yield 77%; oil.
b = 13.592 (4), 8.493 (1) Å, V = 1554.7 (6) Å , Z = 4, density (cal-
culated) 1.368 mg/m , Reflections collected: 2413, Unique: 2305,
3
R1 = 0.051. Crystallographic data (excluding structure factors) for
the structure have been deposited at the Cambridge Crystallograph-
ic Data Centre CCDC 163723.
IR (Nujol): 1720, 1620 cm-1.
1
H NMR: d = 7.69–7.66 (m, 5 H), 4.39 (d, 1 H, J = 17.8 Hz), 4.21
(
d, 1 H, J = 17.8 Hz), 3.53–3.30 (m, 2 H), 2.15 (s, 3 H), 1.20 (t, 3 H,
J = 7.3 Hz).
Sulfonium Salts (3); General Procedure
13C NMR: 193.93, 150.61, 143.60, 133.22, 130.56, 129.14, 128.53,
42.17, 39.86, 12.70, 8.65.
A well-stirred solution of ethylsulfanylacetyl (a-ethylsulfanyl buty-
royl) fluoride (0.02 mol) in CH Cl (40 mL) was saturated by gas-
2
2
eous BF at –60 °C. A solution of acetylene (0.02 mol) in CH Cl
2
3
2
Anal Calcd for: C H BF OS: C, 51.01; H, 4.94. Found: C, 49.86;
H, 5.10.
1
3
15
4
(10 mL) was added dropwise. After stirring for 15 min at –40 °C the
temperature was allowed to rise to 0 °C and the mixture was stirred
for 2 h at this temperature. The reaction mixture was poured into an-
3
-Methyl-4-methoxy-2-phenylthiophene (5b)
hyd Et O (80 mL). The precipitated sulfonium salt was collected by
2
Yield 84%; mp 41–43 °C.
vacuum filtration, washed with anhyd Et O (20 mL), cold MeOH
2
1
H NMR: d = 7.45–7.24 (m, 5 H), 6.16 (s, 1 H), 3.82 (s, 3 H), 2.15
s, 3 H).
(
10 mL), anhyd Et O (30 mL) and dried in vacuo.
2
(
3
-Methoxythiophenes (5); General Procedure
13
C NMR: d = 157.07, 136.86, 135.06, 128.73, 128.45, 127.30,
24.83, 94.53, 56.92, 11.68.
To a solution of sulfonium salt (0.003 mol) in MeOH (15 mL), thio-
urea (2.3 g, 0.03 mol) and HClO (1 mL of 70% aq solution) were
added. After 2–24 h (monitored by TLC) at reflux the reaction mix-
ture was poured onto H O (100 mL) and extracted with CH Cl (4
1
4
Anal Calcd for C H OS: C, 70.58; H, 5.88. Found: C, 70.97; H,
1
2
12
5
.80.
2
2
2
¥
10 mL). The combined organic phases were dried (Na SO ), fil-
tered and concentrated at reduced pressure. The crude product was
2 4
3
-Oxo-4,5-diphenyl-1-ethyl-2,3-dihydrothiopheniumTetra-
fluoroborate (3c)
Yield 80%; mp 149–153 °C (dec.).
purified by column chromatography (EtOAc–hexane, 9:1).
-
1
3
-(2H)- Thiophenones 4; General Procedure
IR (Nujol): 1720, 1620 cm .
The procedure is the same as for 3-methoxythiophenes, except
1
H NMR: d = 7.61–7.09 (m, 10 H), 4.62 (d, 1 H, J = 17.9 Hz), 4.40
d, 1 H, J = 17.9 Hz), 3.56–3.29 (m, 2 H), 1.19 (t, 3 H, J = 7.2 Hz).
CH CN is used as solvent.
3
(
1
3
C NMR: d = 193.15, 153.41, 144.38, 133.67, 131.74, 131.57,
3
-Oxo-5-phenyl-1-ethyl-2,3-dihydrothiopheniumTetra-
1
30.77, 130.24, 129.93, 129.66, 128.85, 43.51, 40.57, 9.08.
fluoroborate (3a)
Yield 72%; mp 128–130 °C (dec).
Anal Calcd for: C H BF OS: C, 58.72; H, 4.65; Found: C, 58.40;
18 17 4
-
1
H, 4.70.
IR (Nujol): 1730, 1610 cm .
Synthesis 2001, No. 14, 2124–2128 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
-Methoxy-2,3-diphenylthiophene (5c)
A New Synthetic Approach to Thiophenes
2127
4
13C NMR: 202.82, 185.73, 120.69, 40.67, 33.50, 30.51, 22.08,
13.61.
Yield 79%; mp 108–111 °C.
1
H NMR: d = 7.38–7.21 (m, 10 H), 6.35 (s, 1 H), 3.75 (s, 3 H).
Anal Calcd for C H OS: C, 61.50; H, 7.74. Found: C, 61.24; H,
7.73.
8
12
1
3
C NMR: d = 161.41, 139.00, 134.72, 134.31, 130.44, 129.59,
1
28.89, 128.26, 128.03, 127.33, 127.00, 95.62, 57.15.
2
-Butyl-4-methoxythiophene (5e)
Anal Calcd for C H OS: C, 76.66; H, 5.30. Found: C, 76.69; H,
5
16
1
7
14
Yield 96%; nD 1.4110.
.24.
1
H NMR: d = 6.48 (s, 1 H), 6.03 (s, 1 H), 3.78 (s, 3 H), 2.8–2.6 (m,
2
H), 1.73–1.55 (m, 2 H), 1.51–1.25 (m, 2 H), 0.93 (t, 3 H, J = 7.2
3
-Oxo-5-(phenylsulfanyl)-1-ethyl-2,3-dihydrothiopheniumTe-
Hz).
trafluoroborate (3d)
Yield 92%; mp 89–92 °C.
1
3
C NMR: d = 157.64, 144.95, 116.61, 93.57, 56.94, 33.38, 30.21,
-
1
22.14, 13.80.
IR (Nujol): 1720 cm .
1
Anal Calcd for C H14OS: C, 63.49; H, 8.29. Found: C, 63.13; H,
9
H NMR: d = 7.72–7.45 (m, 5 H), 6.39 (s, 1 H), 4.45 (d, 1 H,
7
.98.
J = 17.6 Hz), 4.17 (d, 1 H, J = 17.6 Hz), 3.84–3.56 (m, 2 H), 1.46 (t,
3
H, J = 7.2 Hz).
3
-Oxo-1-ethyl-2,3,4,5,6,7,8,9-Octahydrocycloocta-[b]-thiophe-
1
3
C NMR: d = 190.46, 164.06, 135.02, 132.50, 131.28, 130.25,
25.85, 43.94, 40.61, 7.81.
nium Tetrafluoroborate (3f)
Yield 85%, mp 110-112 °C.
IR (Nujol): 1720, 1630 cm-1.
1
Anal Calcd for C H BF OS : C, 44.46; H, 4.04. Found: C, 44.87;
H, 4.23.
12
13
4
2
1
H NMR: d = 4.54 (d, 1 H, J = 18.4 Hz), 4.29 (d, 1 H, J = 18.4 Hz),
4
3
.02–3.70 (m, 2 H), 3.13–2.69 (m, 4 H), 2.19–1.65 (m, 8 H), 1.58 (t,
H, J = 7.4 Hz).
5
-(Phenylsulfanyl)-3(2H)-thiophenone (4d)
Yield 70%; oil.
13C NMR: 193.39, 155.17, 149.11, 41.95, 38.60, 29.11, 28.38,
2
4
-
1
IR (Nujol): 1680, 1660 cm .
7.75, 25.53, 25.51, 27.78, 8.44. Anal Calcd for C H BF OS: C,
12 19 4
1
H NMR: d = 7.62–7.33 (m, 5 H), 5.86 (s, 1 H), 3.62 (s, 2 H).
8.34; H, 6.42. Found: C, 48.01; H, 6.36.
-Methoxy-4,5,6,7,8,9-hexahydrocycloocta-[b]-thiophene (5f)
1
3
C NMR: d = 198.65, 183.45, 135.28, 130.77, 129.57, 127.56,
17.12, 41.41.
3
1
Yield 92%, oil.
Anal Calcd for C H OS : C, 57.66; H, 3.87. Found: C, 57.91; H,
4
1
0
8
2
1
H NMR: d = 5.96 (s, 1 H), 3.80 (s, 3 H), 2.81–2.67 (m, 4 H), 1.70–
.06.
1
.35 (m, 8 H).
4
-Methoxy-2-(phenylsulfanyl)-thiophene (5d)
13
C NMR: d = 156.06, 137.48, 129.38, 92.26, 57.10, 31.96, 29.35,
7.79, 26.07, 25.50, 23.51.
Yield 84%, oil.
2
1
H NMR: d = 7.28–7.12 (m, 5 H), 6.92 (d, 1 H, J = 2.0 Hz), 6.33 (d,
Anal Calcd forC H OS: C, 67.30; H, 8.21. Found: C, 67.55; H,
1
1
16
1
H, J = 2.0 Hz), 3.75 (s, 3 H).
7
.95.
1
3
C NMR: d = 157.81, 137.86, 130.78, 128.94, 127.50, 127.09,
26.25, 102.37, 57.07.
3
-Oxo-5-phenyl-1,2-diethyl-2,3-dihydrothiophenium
1
Tetrafluoroborate (7a)
Yield 82%; mp 153–156 °C (dec).
Anal Calcd for C H OS : C, 59.43; H, 4.53. Found: C, 59.20; H,
4
11
10
2
.77.
-
1
IR (Nujol): 1720, 1610 cm .
5
-Butyl-3-oxo-1-ethyl-2,3-dihydrothiopheniumTetrafluoro-
1
H NMR: d = 7.90–7.45 (m, 5 H), 7.40 (s, 1 H), 4.48 (dd, 1 H,
borate (3e)
Yield 76%; oil.
J = 5.4, 8.2 Hz), 3.70–3.46 (m, 2 H), 2.35–2.05 (m, 2 H), 1.23 (t, 3
H, J = 7.2 Hz), 1.11 (t, 3 H, J = 7.3 Hz).
-
1
IR (Nujol): 1730, 1610 cm .
13
C NMR: d = 196.36, 158.28, 135.52, 132.75, 131.56, 129.17,
1
128.14, 63.21, 41.26, 23.62, 11.74, 9.18.
H NMR: d = 6.92 (s, 1 H), 4.16 (d, 1 H, J = 18.0 Hz), 4.02 (d, 1 H,
J = 18.0 Hz), 3.70–3.51 (m, 2 H), 2.81–2.60 (m, 2 H), 1.79–1.58 (m,
Anal Calcd for C H BF OS: C, 52.52; H, 5.35. Found: C, 52.77;
H, 5.51.
1
4
17
4
2
H), 1.50–1.35 (m, 2 H), 1.32 (t, 3 H, J = 7.2 Hz), 0.92 (t, 3 H,
J = 7.2 Hz).
1
3
4-Methyl-3-oxo-5-phenyl-1,2-diethyl-2,3-dihydrothiophenium-
Tetrafluoroborate (7b)
Yield 76%; mp 123–126 °C (dec).
C NMR d = 195.08, 165.65, 135.80, 43.10, 39.98, 31.33, 30.15,
2
2.62, 13.19, 8.64.
Anal Calcd for C H BF OS: C 44.14, H 6.30; Found: C 43.88, H
6
10
17
4
-
1
IR (Nujol): 1710, 1630 cm .
.21.
1
H NMR: d = 7.70–7.55 (m, 5 H), 4.48 (dd, 1 H, J = 4.8, 7.3 Hz),
5
-Butyl-3-(2H)-thiophenone (4e)
3
.52–3.45 (m, 2 H), 2.50–2.14 (m, 2 H), 2.14 (s, 3 H), 1.24 (t, 3 H,
Yield 95%; oil.
J = 7.1 Hz), 1.12 (t, 3 H, J = 7.2 Hz).
-
1
IR (Neat): 1690, 1660 cm .
1H NMR: 6.01 (br s, 1 H), 3.62 (s, 2 H), 2.65–2.55 (m, 2 H), 1.7–1.5
13
C NMR: d = 195.23, 149.07, 143.86, 133.21, 130.42, 129.08,
127.89, 62.59, 40.60, 22.85, 13.06, 11.34, 9.33.
(
m, 2 H), 1.45–1.25 (m, 2 H), 0.9 (t, 3 H, J = 7.2 Hz).
Anal Calcd for C H BF OS: C, 53.91; H, 5.73. Found: C, 54.12;
1
5
19
4
H, 5.82.
Synthesis 2001, No. 14, 2124–2128 ISSN 0039-7881 © Thieme Stuttgart · New York

2
128
M. V. Lebedev et al.
PAPER
3
-Oxo-4,5-diphenyl-1,2-diethyl-2,3-dihydrothiopheniumTe-
Acknowledgement
trafluoroborate (7c)
Financial support from Russian Fundamental Investigation Found-
ation (Grant N 00-03-32763a) is gratefully acknowledged.
Yield 92%; mp 205–210 °C (dec).
-
1
IR (Nujol): 1720, 1620 cm .
1
H NMR: d = 7.39–7.20 (m, 10 H), 4.48 (m, 1 H), 3.42–3.24 (m, 2
References
H), 2.33–2.04 (m, 2 H), 1.14 (t, 3 H, J = 7.2 Hz), 0.98 (t, 3 H, J = 7.2
Hz).
(
1) (a) Vertelezkij, P. V.; Balenkova, E. S. Zh. Org. Khim. 1990,
26, 2446. (b) Vertelezkij, P. V.; Nenajdenko, V. G.;
Balenkova, E. S. Vestnik MGU. Ser. 2. Khim. 1996, 540.
(c) Nenajdenko, V. G.; Lebedev, M. V.; Shevchenko, N. E.;
Balenkova, E. S. Zh. Org. Khim. 1998, 34, 1026.
1
3
C NMR: d = 194.64, 150.60, 143.67, 133.82, 131.03, 130.37,
29.50, 129.21, 129.04, 128.00, 127.06, 63.34, 40.29, 22.97, 10.80,
.55.
1
8
Anal Calcd for C H BF OS: C, 60.62; H, 5.34. Found: C, 60.27;
H, 5.55.
2
0
21
4
(
4
d) Kiselyov, A.; Harvey, R. Tetrahedron Lett. 1995, 36,
005.
2) (a) Nenajdenko, V. G.; Balenkova, E. S. Zh. Org. Khim.
992, 28, 600. (b) Nenajdenko, V. G.; Balenkova, E. S. Zh.
(
3
-Methoxy-5-phenyl-2-ethylthiophene (8a)
1
Yield 78%; oil.
Org. Khim. 1993, 29, 687. (c) Nenajdenko, V. G.;
Leshcheva, I. F.; Balenkova, E. S. Tetrahedron 1994, 50,
1
H NMR: d = 7.55–7.20 (m, 5 H), 7.03 (s, 1 H), 3.84 (s, 3 H), 2.75
q, 2 H, J = 7.5 Hz), 1.24 (t, 3 H, J = 7.5 Hz).
(
775. (d) Nenajdenko, V. G.; Gridnev, I. D.; Balenkova, E. S.
1
3
Tetrahedron 1994, 50, 11023. (e) Nenajdenko, V. G.;
Balenkova, E. S. Tetrahedron 1994, 50, 12407.
C NMR: d = 153.10, 137.74, 134.69, 128.70, 127.07, 124.90,
1
7
24.03, 112.90, 59.01, 19.19, 15.57. Anal Calcd for C H OS: C,
1.52; H, 6.46. Found: C, 71.18; H, 6.62.
13 14
(
f) Nenajdenko, V. G.; Sanin, A. V.; Balenkova, E. S. Zh.
Org. Khim. 1994, 30, 531.
(
3) (a) Nenajdenko, V. G.; Lebedev, M. V.; Balenkova, E. S.
Tetrahedron Lett. 1995, 36, 6317. (b) Nenajdenko, V. G.;
Lebedev, M. V.; Balenkova, E. S. Synlett 1995, 1133.
3
-Methyl-4-methoxy-2-phenyl-5-ethylthiophene (8b)
Yield 91%; oil.
1
H NMR: d = 7.50–7.20 (m, 5 H), 3.79 (s, 3 H), 2.82 (q, 2 H, J = 7.6
Hz), 2.21 (s, 3 H), 1.31 (t, 3 H, J = 7.6 Hz).
(c) Lebedev, M. V.; Nenajdenko, V. G.; Balenkova, E. S.
Tetrahedron 1998, 5599. (d) Lebedev, M. V.; Nenajdenko,
V. G.; Balenkova, E. S. Synthesis 1998, 89.
1
3
C NMR: d = 152.38, 135.29, 129.48, 129.43, 128.75, 127.38,
26.87, 100.13, 61.25, 19.55, 15.57, 12.24.
1
(4) Lissavetzky, J.; Manzanares, I. Heterocycles 1996, 43, 775.
(
5) Coppola, G. M.; Damon, R. E.; Yu, H. J. Heterocyclic
Chem. 1996, 33, 687.
6) Kosak, A. I.; Palchak, R. J. F.; Steele, W. A.; Selwitz, C. M.
J. Am. Chem. Soc. 1954, 76, 4450.
Anal Calcd for C H OS: C, 72.37; H, 6.94. Found: C, 72.33; H,
1
4
16
7
.11.
(
Synthesis 2001, No. 14, 2124–2128 ISSN 0039-7881 © Thieme Stuttgart · New York