A general approach to arylated furans, pyrroles, and thiophenes

Article abstract of DOI:10.1016/j.tet.2014.09.025

A general and practical synthetic method for aryl-substituted five-membered heterocycles has been developed. In the presence of KOH (30%), 1,4-diaryl-1,3-butadiynes undergo the cyclocondensation reaction with water, primary amines, and Na₂S·9H₂O in DMSO at 80 °C to afford 2,5-diarylfurans, 1,2,5-trisubstituted pyrroles, and 2,5-diarylthiophenes in good to high yields. Further studies have disclosed that aryl-substituted five-membered heterocycles can be also synthesized by a one-pot, two-step strategy from the terminal alkynes in DMSO firstly catalyzed by CuCl, and then via addition of KOH to promote the cyclocondensation of 1,3-butadiynes generated in situ.

Full text of DOI:10.1016/j.tet.2014.09.025

Tetrahedron 70 (2014) 8252e8256
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A general approach to arylated furans, pyrroles, and thiophenes
*
Qingwei Zheng, Ruimao Hua , Jianhua Jiang, Lei Zhang
Department of Chemistry, Tsinghua University, Beijing 100084, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 June 2014
Received in revised form 30 August 2014
Accepted 9 September 2014
Available online 18 September 2014
A general and practical synthetic method for aryl-substituted five-membered heterocycles has been
developed. In the presence of KOH (30%), 1,4-diaryl-1,3-butadiynes undergo the cyclocondensation re-
action with water, primary amines, and Na2S$9H2O in DMSO at 80 ꢀC to afford 2,5-diarylfurans, 1,2,5-
trisubstituted pyrroles, and 2,5-diarylthiophenes in good to high yields. Further studies have disclosed
that aryl-substituted five-membered heterocycles can be also synthesized by a one-pot, two-step
strategy from the terminal alkynes in DMSO firstly catalyzed by CuCl, and then via addition of KOH to
promote the cyclocondensation of 1,3-butadiynes generated in situ.
Keywords:
Cyclocondensation
1,3-Butadiynes
Furans
Ó 2014 Elsevier Ltd. All rights reserved.
Pyrroles
Thiophenes
1. Introduction
2. Results and discussion
Cyclocondensation of alkynes represent one of the most pow-
erful methods for the synthesis of cyclic compounds with the sig-
nificant advantages of high-atom efficiency and easy availability of
starting materials, which has been well applied in the synthesis of
highly functionalized cyclic compounds.1 Development of efficient
and practical synthetic methods to synthesize functionalized five-
membered heterocycles of furans, pyrroles, and thiophenes is one
of important research topics in synthetic chemistry, since they have
interesting biological and physiological activities, and versatile
applications in the synthesis of other heterocycles. On the other
hand, 1,3-butadiyne derivatives have been applied as important
building blocks for the synthesis of various carbo- and heterocyclic
compounds, and recently, a number of reports on the transition
metal-catalyzed synthesis of naphthalenes,2 furans,3 thio-
phenes,3d,4 pyrroles,3b,5 and other cyclic compounds6 using 1,3-
butadiyne derivatives as starting materials have appeared in the
literature. Encouraged by our previous success in the preparation of
pyrroles,5c furans,3e and benzo[f]quinazolines7 via the cycloaddi-
tion of 1,3-butadiynes with primary amines, water, and nitriles,
respectively, we investigated the possibility in this paper to es-
tablish a general procedure for the synthesis of five-membered
heterocycles using 1,4-disubstituted 1,3-butadiynes as one of the
reactants and without use of transition metal complex as catalyst.
As depicted in Scheme 1, the five-membered heterocycles are
expected to form via the cycloaddition of 1,3-butadiynes with EeH
bond (E¼O, S, and N). The challenging work is to optimize a general
catalytic system, which can promote both intermolecular addition
and intramolecular cycloaddition of EeH bond across CeC triple
bonds. On the basis of the previous reports, it seems that the
presence of basic additives is one of the crucial factors to promote
the transformation of 1,3-butadiynes to furan derivatives in the
presence of Cu3d and Pd.3e Therefore we examined the reaction of
1,4-diphenyl-1,3-butadiyne (1a) with water in presence of a variety
of basic compounds without the use of transition metal catalyst to
investigate the possibility to synthesize 2,5-diarylfuran (2a).
R
E
H
R
R
+ HE
H
addition
H
R
cycloisomerization
R
R
E
Scheme 1. Formation of five-membered heterocycles via the cyclocondensation of
1,3-butadiyne.
As concluded in Table 1, it proved possible to obtain the desir-
able 2a in high isolated yield when 30% of KOH was used as catalyst
in DMSO at 80 ꢀC for 4 h (entry 7), although other inorganic bases,
such as NaHCO3, Na2CO3, K2CO3, K3PO4, Cs2CO3 (entries 1e5), and
organic bases such as DBU (1,8-diazabicyclo[5.4.0]undec-7-ene),
* Corresponding author. Fax: þ86 10 62771149; e-mail address: ruimao@mail.
tsinghua.edu.cn (R. Hua).
http://dx.doi.org/10.1016/j.tet.2014.09.025
0040-4020/Ó 2014 Elsevier Ltd. All rights reserved.

Q. Zheng et al. / Tetrahedron 70 (2014) 8252e8256
8253
Table 1
Formation of 2,5-diphenylfuran from the cyclocondensation of 1,4-diphenyl-1,3-butadiyne with water under different conditionsa
Entry
Base
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
NaHCO3
Na2CO3
K2CO3
K3PO4
CS2CO3
NaOH
KOH
KOH
KOH
KOH
KOH
KOH
DBU
NEt3
DABCO
KOH
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
0
0
0
0
<5
67
96 (92)
37
13
<5
0
0
<5
0
9
THF
10
11
12
13
14
15
16c
17d
18
CH3CN
1,4-Dioxane
1,2-DCE
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
0
88
72
0
KOH
d
a
Reaction conditions: 1a (1.0 mmol), H2O (2.0 mmol), and base (0.3 mmol) in solvent (2.0 mL) at 80 ꢀC for 4 h.
GC yield of 2a, and isolated yield in parenthesis.
KOH of 20 mol % was used.
b
c
d
KOH of 10 mol % was used.
Et3N, and DABCO (1,4-diazabicyclo[2.2.2]octane) (entries 13e15)
decrease of yields (entries 16 and 17). In addition, it was confirmed
that no 2a was formed in the absence of KOH (entry 18).
In fact, KOH/DMSO as the superbasic medium showing versatile
diverse catalytic activity has been well applied in a variety of
organic transformation reported by Trofimov,8 Bolm,9 and other
groups.10
showed no catalytic activity at all. It was also found that NaOH in
DMSO showed moderate catalytic activity (entry 6), and the cata-
lytic activity of KOH greatly depended on the nature of solvents.
When DMF, THF, and CH3CN were used as solvents, KOH showed
fair and low catalytic activity (entries 8e10), and in 1,4-dioxane and
1,2-DCE, no catalytic activity was observed (entries 11 and 12).
Decrease of the amount of KOH resulted in the considerable
The results shown in Table 2 verify the scope and generality for
the formation of 2,5-diarylfurans using KOH/DMSO catalyst system.
Table 2
Synthesis of 2,5-diarylfurans from the reaction of 1,4-diaryl-1,3-butadiyne with watera
Entry
Ar, Ar0
Yield of 2b (%)
1
2
3
4
5
6
7
8
Ar¼Ar0¼p-tolyl
Ar¼Ar0¼o-tolyl
Ar¼Ar0¼m-tolyl
Ar¼Ar0¼p-EtC6H4
Ar¼Ar0¼p-nPrC6H4
Ar¼Ar0¼p-nBuC6H4
Ar¼Ar0¼p-nC5H11C6H4
Ar¼Ar0¼p-MeOC6H4
Ar¼Ar0¼3,5-Me2C6H3
Ar¼Ar0¼2-naphthyl
Ar¼Ar0¼p-ClC6H4
Ar¼Ar0¼p-FC6H4
Ar¼Ar0¼p-CF3C6H4
Ar¼Ar0¼2-thienyl
Ar¼Ph
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
2p
92
83
90
90
87
89
86
91
87
87
90
88
85
90
91
9
10
11
12
13
14
15
Ar0¼p-EtOC6H4
Ar¼Ph
16
17
1q
1r
2q
2r
86
90
Ar0¼2-Naphthyl
Ar¼p-nPrC6H4
Ar0¼p-EtOC6H4
a
Unless otherwise noted, the reactions were carried out using 1 (1.0 mmol), H2O (2.0 mmol), and KOH (0.3 mmol) in DMSO (2.0 mL) at 80 ꢀC for 4 h.
b
Isolated yield.

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Q. Zheng et al. / Tetrahedron 70 (2014) 8252e8256
It was found that both electron-donating and electron-
withdrawing groups on the benzene rings were insensitive to the
formation of furans, all of the reactions afforded the corresponding
furan derivatives in high yields. The cyclocondensation of 1,4-bis(2-
thienyl)-1,3-butadiyne (1o) with H2O gave the high yield of the
expected five-membered heterocyclic trimer (2o), which has in-
teresting electrical and/or optical properties.11
In addition, in order to verify the practicality of the present
procedure, a 15-fold scale-up reaction of 1a was also performed. As
shown in Eq. 1, the expected product 2a was obtained on a gram-
level with a similar yield as shown in entry 7 of Table 1.
In addition, under the similar conditions, the corresponding 2,5-
diarylthiophenes could be also obtained in high yields by the re-
action of 1,3-butadiynes with 2.0 equiv of Na2S$9H2O as shown in
Table 4.
It should be noted that although there have been several reports
on the formation of 2,5-diarylthiophenes via the cyclocondensation
of 1,4-diaryl-1,3-butadiynes using different sulfur sources under
different conditions (e.g., H2S gas/NaOH in methanol,12 Na2S$9H2O
in DMF13), the present transformation provides an alternative and
practical procedure for the synthesis of 2,5-diarylthiophenes, par-
ticularly for the formation of terthiophene (5d) efficiently under
mild conditions.
In our previous work, we developed an efficient oxidative
homocoupling reaction of terminal alkynes to form 1,4-
disubstituted 1,3-diyne (1) catalyzed by CuCl/piperidine,14 we
then investigated the possibility to develop a one-pot, two-step
strategy for the synthesis of five-membered heterocycles directly
using terminal alkynes as one of the reaction partners. Therefore
we re-optimized the reaction conditions for the formation of 1, and
fortunately found that in DMSO, CuCl could efficiently catalyze the
formation of 1 from terminal alkynes at 80 ꢀC without use of any
additive. As shown in Table 5, 2,5-diarylfurans could be synthesized
from aromatic terminal alkynes as starting materials by a one-pot,
two-step sequential procedure involving the formation of 1,4-
diaryl-1,3-butadiynes in situ and cyclocondensation with water
by addition catalytic amount of KOH. The yields of the desired furan
derivatives in this manner are comparable to those achieved by the
reaction of 1,4-diaryl-1,3-butadiynes with water as shown in
Table 2.
ð1Þ
The simplicity of the KOH-catalyzed formation of furan de-
rivatives (2) makes the procedure highly attractive as a preparative
method, and it can probably be considered efficient in the synthesis
of other five-membered heterocycles. Therefore the reaction con-
ditions indicated in entry 7 of Table 1 were applied as the standard
conditions in the transformation of 1,3-butadiynes into pyrroles
and thiophenes.
As summarized in Table 3, aniline (3a), n-propylamine (3b),
p-methoxyaniline (3c), and p-fluoroaniline (3d) underwent the
cyclocondensation smoothly to afford the corresponding 1,2,3-
triaryl pyrroles in high isolated yields.
In addition, as exampled in Eqs. 2 and 3, the present sequential
CuCl and KOH-catalyzed one-pot strategy could be successfully
Table 3
Synthesis of 1,2,5-triarylpyrrolesa
Entry
Ar, Ar0
R
Yield of 4b (%)
1
2
3
4
5
6
7
Ar¼Ar0¼Ph
1a
1a
1a
1e
1i
Ph
3a
3b
3c
3d
3a
3a
3a
4a
4b
4c
4d
4e
4f
84
82
87
91
84
85
87
Ar¼Ar0¼Ph
n-C3H7
p-MeOC6H4
p-FC6H4
Ph
Ph
Ph
Ar¼Ar0¼Ph
Ar¼Ar0¼p-EtC6H4
Ar¼Ar0¼p-MeOC6H4
Ar¼Ar0¼2-thienyl
Ar¼Ph
1o
1q
4g
Ar0¼2-naphthyl
a
Unless otherwise noted, the reactions were carried out using 1 (1.0 mmol), amine 3 (1.5 mmol), and KOH (0.3 mmol) in DMSO (2.0 mL) at 80 ꢀC for 4 h.
b
Isolated yield.
Table 4
Synthesis of 2,5-diarylthiophenesa
Entry
Ar
Yield of 5b (%)
1
2
3
4
Ph
1a
1g
1n
1o
5a
5b
5c
5d
97
92
93
93
p-nBuC6H4
p-FC6H4
2-Thienyl
a
Unless otherwise noted, the reactions were carried out using 1 (1.0 mmol), H2O (2.0 mmol), and KOH (0.3 mmol) in DMSO (2.0 mL) at 80 ꢀC for 4 h.
Isolated yield.
b

Q. Zheng et al. / Tetrahedron 70 (2014) 8252e8256
8255
Table 5
One-pot synthesis of 2,5-diarylfurans from the reaction of terminal alkynes with watera
Entry
Ar
Diyne 1
Yield of 2b (%)
1
2
3
4
5
6
Ar¼Ph
1a
1d
1f
1i
1n
1o
2a
2d
2f
2i
2n
2o
90
86
84
86
87
82
Ar¼m-tolyl
Ar¼p-nPrC6H4
Ar¼p-MeOC6H4
Ar¼p-FC6H4
Ar¼2-thienyl
a
Reaction conditions for first step: terminal alkyne (2.0 mmol) and CuCl (5 mol %, 10.0 mg) in DMSO (2.0 mL) in air was heated with stirring at 80 ꢀC for 8 h; second step: H2O
(2.0 mmol) and KOH (0.3 mmol, 16.8 mg) were added to the reaction mixture of the first step, and then heated at 80 ꢀC for 4 h.
b
Isolated yield.
applied to the synthesis of 1,3,5-triphenylpyrrole (4a) and 2,5-
diphenylthiophene (5a) in high yields by the reactions of phenyl-
acetylene with aniline and Na2S$9H2O, respectively.
the synthesis of five-membered heterocycles, the present pro-
cedures have the merits of easily available starting materials and
one-pot reaction with high-atom efficiency.
4. Experimental section
4.1. General method
ð2Þ
ð3Þ
All organic starting materials are analytically pure and used
without further purification. 1,4-Diaryl-1,3-butadiynes were pre-
pared by an oxidative homocoupling reaction of terminal alkynes
according to a known catalytic system.14 The purity of KOH is
99.99%. 1H NMR (300 MHz) chemical shifts (
TMS and 13C NMR (75 MHz) chemical shifts (
d
) were referenced to
) were referenced to
d
internal solvent resonance. GC analyses of organic compounds
were performed on a GC instrument with a 30 M capillary column.
Mass spectra were obtained on a low-resolution GCeMS spec-
trometer, and high-resolution mass spectra (ESI) were obtained
with a micro TOF mass spectrometer.
It has been well-known that carbonecarbon triple bond of
alkynes easily undergoes the nucleophilic addition and then
cycloisomerization to afford cyclic compounds. On the basis of the
proposed route for the formation of five-membered heterocycles as
shown in Scheme 1, the present formation of five-membered
heterocycles is reasonably considered to be resulted from the nu-
cleophilic addition of 1,3-butadiynes with nucleophilic species such
as HOꢁ, RNHꢁ or HSꢁ under basic conditions, and subsequent
protonation and cycloisomerization.
4.2. General procedure for the synthesis of 2,5-diaryl-
substituted furans, pyrroles, and thiophenes from the
reaction of 1,4-diaryl-1,3-butadiyne with water, primary
amines or sodium sulfide nonahydrate
A solution of 1,4-diaryl-1,3-butadiynes (1) (1.0 mmol), KOH
(0.3 mmol), and H2O (2.0 mmol), or RNH2 (1.5 mmol), or Na2S$9H2O
(2.0 mmol) in DMSO (2.0 mL) was heated at 80 ꢀC with stirring for
4 h. The reaction mixture was then cooled to room temperature,
and the volatiles were removed under reduced pressure. The
obtained residue was subjected to silica gel column chromatogra-
phy (eluting with CH2Cl2/petroleum ether: 0:1 to 1:10) to give
2,5-diaryl-substituted five-membered heterocycles.
3. Conclusion
We have developed a general synthetic method for the forma-
tion of 2,5-diarylfurans, 1,2,5-triarylpyrroles or 2,5-diarylpyrroles,
and 2,5-diarylthiophenes by the cyclocondensation of 1,4-diaryl-
1,3-butadiynes with water, primary amines, and sodium sulfide
nonahydrate, respectively, in the presence of KOH in DMSO at 80 ꢀC.
The present procedure provides a promising protocol using simple
and cheap catalytic system for the construction of five-membered
heterocycles bearing a variety of electron-rich and electron-
deficient aryl groups in good to high yields. Interestingly, the
five-membered heterocycles can be also obtained by a one-pot,
two-step procedure from terminal alkynes sequentially catalyzed
by CuCl and KOH in DMSO. Compared to the known procedures for
4.3. A typical procedure for the synthesis of 2,5-phenylfuran
(2a) from phenylacetylene (Table 5, entry 1)
A mixture of phenylacetylene (204.0 mg, 2.0 mmol) and CuCl
(10.0 mg, 0.1 mmol) in DMSO (2.0 mL) in an atmosphere of air was
heated with stirring at 80 ꢀC for 8 h, and then the reaction mixture
was cooled to room temperature, and KOH (16.8 mg, 0.3 mmol) was
added. The obtained mixture was further heated at 80 ꢀC for 4 h.

8256
Q. Zheng et al. / Tetrahedron 70 (2014) 8252e8256
After work-up and isolation as mentioned-above, 2a (198.0 mg,
0.90 mmol, 90%) was obtained as colorless solid.
91 (2), 77(8); HRMS m/z calcd for C20H21O [MþH]þ: 277.1586, found
277.1585.
4.4. Characterization data of new products
Acknowledgements
Compounds 2c, 2f, 2g, 2h, and 2j are new compounds and
characterized by 1H, 13C NMR, mass spectrum, and HRMS (ESI).
Other products are known compounds, which were characterized
by 1H, 13C NMR and mass spectra, see Supplementary data.
This project was supported by the National Natural Science
Foundation of China (21473097, 21032004, 21273125), and the
Specialized Research Fund for the Doctoral Program of Higher Ed-
ucation (20110002110051).
4.4.1. 2,5-Bis(o-tolyl)furan (2c). White solid, mp 81e83 ꢀC; 1H
Supplementary data
NMR (300 MHz, CDCl3)
d
7.79 (d, 2H, J¼7.6 Hz), 7.29e7.21 (m, 6H),
6.67 (s, 2H), 2.57 (s, 6H); 13C NMR (75 MHz, CDCl3)
d
152.8, 134.6,
General method, characterization data of known products, and
copies of 1H, 13C NMR charts of all products. Supplementary data
associated with this article can be found in the online version, at
http://dx.doi.org/10.1016/j.tet.2014.09.025.
131.4, 130.2, 127.5, 126.9, 126.2, 110.6, 22.3; GCeMS m/z (% rel
inten.) 248 (Mþ, 100), 233 (2), 205 (9), 129 (24), 119 (14), 91 (4), 65
(7); HRMS (ESI) calcd for C18H17O [MþH]þ: 249.1273, found
249.1274.
References and notes
4.4.2. 2,5-Bis(p-n-propylphenyl)furan
(2f). White
7.64 (d, 4H, J¼7.9 Hz), 7.19 (d,
solid,
mp
83e85 ꢀC; 1H NMR (300 MHz, CDCl3)
d
1. Selected reviews, see: (a) Saito, S.; Yamamoto, Y. Chem. Rev. 2000, 100, 2901; (b)
Varela, J. A.; Saa, C. Chem. Rev. 2003, 103, 3787; (c) Nakamura, I.; Yamamoto, Y.
Chem. Rev. 2004, 104, 2127; (d) Hua, R.; Abrenica, M. V. A.; Wang, P. Curr. Org.
Chem. 2011, 15, 712.
2. (a) Sun, H.; Wu, X.; Hua, R. Tetrahedron Lett. 2011, 52, 4408; (b) Singha, R.;
Nandi, S.; Ray, J. K. Tetrahedron Lett. 2012, 53, 6531.
ꢀ
4H, J¼7.9 Hz), 6.65 (s, 2H), 2.59 (t, 4H, J¼7.2 Hz), 1.72e1.59 (m, 4H),
0.95 (t, 6H, J¼7.6 Hz); 13C NMR (75 MHz, CDCl3)
d 153.4,142.0,128.9,
128.6, 123.8, 106.6, 37.9, 24.6, 13.9; GCeMS m/z (% rel inten.) 304
(Mþ, 86), 275 (100), 259 (4), 246 (48), 202 (8), 152 (4), 123 (18), 110
(9), 90 (9), 77 (5); HRMS (ESI) calcd for C22H25O [MþH]þ: 305.1899,
found 305.1903.
3. (a) Pridmore, S. J.; Slatford, P. A.; Williams, J. M. J. Tetrahedron Lett. 2007, 48,
€
5111; (b) Kramer, S.; Madsen, J. L. H.; Rottlander, M.; Skrydstrup, T. Org. Lett.
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L.; Fu, W. J. Org. Chem. 2012, 77, 5179; (e) Zheng, Q.; Hua, R.; Yin, T. Curr. Org.
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4.4.3. 2,5-Bis(p-n-butylphenyl)furan
(2g). White
7.66 (d, 4H, J¼8.3 Hz), 7.22
solid,
mp
87e88 ꢀC; 1H NMR (300 MHz, CDCl3)
d
(d, 4H, J¼8.3 Hz), 6.67 (s, 2H), 2.64 (t, 4H, J¼7.6 Hz), 1.68e1.54 (m,
4H), 1.45e1.27 (m, 4H), 0.95 (t, 6H, J¼7.2 Hz); 13C NMR (75 MHz,
CDCl3) d 153.4, 142.3, 128.9, 128.6, 123.8, 106.6, 35.6, 33.7, 22.5, 14.1;
GCeMS m/z (% rel inten.) 332 (Mþ, 99), 289 (100), 246 (54), 202 (7),
128 (6), 115 (5), 103 (4), 90 (8), 77 (4); HRMS (ESI) calcd for C24H29
O
[MþH]þ: 333.2212, found 333.2208.
8. Selected reports, see: (a) Trofimov, B. A. Sulfur Rep. 1992, 11, 207; (b) Trofimov,
B. A.; Vasil’tsov, A. M.; Schmidt, E. Y.; Zaitsev, A. B.; Mikhaleva, A. I.; Afonin, A. V.
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2010, 16, 8516; (f) Schmidt, E. Y.; Zorina, N. V.; Skitaltseva, E. V.; Ushakov, I. A.;
Mikhaleva, A. I.; Trofimov, B. A. Tetrahedron Lett. 2011, 52, 3772; (g) Trofimov, B.
A.; Schmidt, E. Y.; Bidusenko, I. A.; Ushakov, I. A.; Protsuk, N. I.; Zorina, N. V.;
Mikhaleva, A. I. Tetrahedron 2012, 68, 1241.
4.4.4. 2,5-Bis(p-n-pentylphenyl)furan (2h). White solid, mp
90e93 ꢀC; 1H NMR (300 MHz, CDCl3)
d
7.65 (d, 3H, J¼8.3 Hz), 7.54
(d, 1H, J¼8.3 Hz), 7.25e7.18 (m, 4H), 6.67 (s, 2H), 2.63 (t, 4H,
J¼7.6 Hz), 1.69e1.55 (m, 6H), 1.36e1.26 (m, 6H), 0.91 (t, 6H,
J¼7.6 Hz); 13C NMR (75 MHz, CDCl3)
d 153.4, 142.3, 129.1, 128.9,
123.8,106.6, 35.9, 31.6, 31.2, 22.7,14.2; GCeMS m/z (% rel inten.) 360
(Mþ, 99), 303 (100), 259 (9), 246 (50), 233 (4), 215 (4), 159 (5), 128
(5), 90 (8), 77 (4); HRMS (ESI) calcd for C26H33O [MþH]þ: 361.2525,
found 361.2528.
ꢀ
9. (a) Yuan, Y.; Thome, I.; Kim, S. H.; Chen, D.; Beyer, A.; Bonnamour, J.; Zuidema,
E.; Chang, S.; Bolm, C. Adv. Synth. Catal. 2010, 352, 2892; (b) Beyer, A.; Reucher,
C. M. M.; Bolm, C. Org. Lett. 2011, 13, 2876.
4.4.5. 2,5-Bis(3,5-dimethylphenyl)furan (2j). White solid, mp
ꢀ
10. (a) Bernard, M. K. Tetrahedron 2000, 56, 7273; (b) Cano, R.; Ramon, D. J.; Yus, M.
110e112 ꢀC; 1H NMR (300 MHz, CDCl3)
d 7.39 (s, 4H), 6.93 (s, 2H),
J. Org. Chem. 2011, 76, 654.
6.70 (s, 2H), 2.39 (s, 12H); 13C NMR (75 MHz, CDCl3)
d 153.6, 138.3,
11. Beaujuge, P. M.; Reynolds, J. R. Chem. Rev. 2010, 110, 268.
12. Potts, K. T.; Nye, S. A.; Smith, K. A. J. Org. Chem. 1992, 57, 3895.
13. Tang, J.; Zhao, X. RSC Adv. 2012, 2, 5488.
130.9, 129.2, 121.7, 107.1, 21.5; GCeMS m/z (% rel inten.) 276 (Mþ,
100), 233 (5), 218 (4), 203 (3), 143 (14), 138 (13), 123 (11), 105 (10),
14. Zheng, Q.; Hua, R.; Wan, Y. Appl. Organomet. Chem. 2010, 24, 314.