General approach to benzo[b]thiophenes, benzo[b]furans, and dibenzofurans via gold-catalyzed cyclization of 1-heteroarylalka-2,3-dienyl acetates

Article abstract of DOI:10.1016/j.tet.2013.04.099

An efficient and mild route to a series of benzo[b]thiophenes, benzo[b]furans, and dibenzofurans through gold-catalyzed benzannulation of 1-heteroarylalka-2,3-dienyl acetates was developed. Two possible pathways of this reaction involving gold carbene and aryl gold intermediates have been proposed on the basis of mechanistic studies.

Full text of DOI:10.1016/j.tet.2013.04.099

Tetrahedron 69 (2013) 6305e6312
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
General approach to benzo[b]thiophenes, benzo[b]furans, and
dibenzofurans via gold-catalyzed cyclization of 1-heteroarylalka-
2,3-dienyl acetates
*
Youai Qiu, Dengke Ma, Chunling Fu, Shengming Ma
Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University, 310027 Hangzhou, Zhejiang, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient and mild route to a series of benzo[b]thiophenes, benzo[b]furans, and dibenzofurans through
gold-catalyzed benzannulation of 1-heteroarylalka-2,3-dienyl acetates was developed. Two possible
pathways of this reaction involving gold carbene and aryl gold intermediates have been proposed on the
basis of mechanistic studies.
Received 13 March 2013
Received in revised form 14 April 2013
Accepted 23 April 2013
Available online 28 April 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Gold-catalysis
Benzannulation
Benzo[b]thiophenes
Benzo[b]furans
Dibenzofurans
R3
1. Introduction
R3
Benzo[b]thiophenes,1 benzo[b]furans,2 and dibenzofurans3 are
important heterocyclic scaffolds because of their widespread oc-
currence among natural products and material chemistry. Thus, the
synthesis of functionalized heterocycles is an important topic in
synthetic organic chemistry,4 and many methodologies for the
construction of benzo[b]thiophenes, benzo[b]furans, and other
fused-ring compounds by metal-catalyzed cyclization reactions
have been developed.5 However, there still remain some limita-
tions such as low yields, harsh reaction conditions, and not readily
available starting materials in these methods. Thus, a mild, efficient,
regiocontrolled, and diversified preparation of these compounds is
still desirable.
PtCl2
R2
R2
toluene
N
N
OH
R1
R1
R1
R1
HO
M
R2
R2
X
X
X= S, O
Scheme 1. Cyclization of 2,3-allenols for the formation of the benzene ring.
We recently reported a route to construct carbazole alkaloids via
the PtCl2-catalyzed cyclization of 1-(indol-2-yl)-2,3-allenols.6 Then,
we described a Au-catalyzed approach to a series of naturally car-
bazoles.7 Considering the interests in synthesis of heterocyclic
compounds, we reasoned that benzo[b]thiophenes, benzo[b]fu-
rans, and dibenzofurans could be afforded by using thiophenes,
furans, and benzo[b]furans instead of the indole unit in the starting
material (Scheme 1). In this paper, we wish to report our recent
observation on efficient synthesis of benzo[b]thiophenes, benzo[b]
furans, and dibenzofurans through gold-catalyzed cyclization of 1-
heteroarylalka-2,3-dienyl acetates.
2. Results and discussion
Initially, we tried the reaction of 2-phenyl-1-(3-thienyl)buta-
2,3-dienol (1a) in toluene under the catalysis of PtCl2 (5 mol %),6
however, 1a was recovered in 92% (Scheme 2). With AuCl as the
catalyst,8 the cycloisomerization product 4 was afforded in 71%
yield, instead of the expected benzo[b]thiophene derivative (3a).
* Corresponding author. Fax: þ86 (0)2162609305; e-mail address: masm@
sioc.ac.cn (S. Ma).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.04.099

6306
Y. Qiu et al. / Tetrahedron 69 (2013) 6305e6312
Table 2
Gold-catalyzed cyclization of 1-heteroarylalka-2,3-dienyl acetatesa
Entry
X
R1
R2
Time (h)
Yield of 3b (%)
1
2
3
4
5
6c
7
8
S
S
S
S
S
S
S
O
Ph
Bu
C7H15
CH2OEt
Ph
Ph
p-MeC6H4
Ph
Ac (2a)
Ac (2b)
Ac (2c)
Ac (2d)
Me (2e)
Ac (2a)
Ac (2f)
Ac (2g)
12
10
24
12
12
24
12
24
84 (3a)
85 (3b)
89 (3c)
89 (3d)
87 (3e)
88 (3a)
93 (3f)
85 (3g)
Scheme 2. Metal-catalyzed cyclization of allenol 1a.
Interestingly, 5-phenylbenzo[b]thiophene 3a was formed in 5%
NMR yield together with cycloisomerization product 4 in 29% NMR
yield when AuCl(PPh3)/AgBF4 was used.
a
Thus, the hydroxy group was protected in order to prevent the
cycloisomerization reaction forming the dihydrofuran product. The
reaction of 2-phenyl-1-(3-thienyl)buta-2,3-dienyl acetate 2a in DCE
with AuCl(PPh3)/AgBF4 gave the desired product 3a in only 8% yield
(entry 1, Table 1). Fortunately, the yield was improved to 84% when
THF was used instead of DCE (entry 2, Table 1). Notably, the solvent
effect was obvious, further study showed that dioxane was the best
solvent for this transformation, affording 3a in 95% yield (entry 5,
Table 1)! Then, several combinations of AuCl(PPh3) with different
silver salts were tested, among which AgBF4 was still the best
(entries 5e10, Table 1). Thus, we defined the standard conditions as
Reaction conditions: 1.0 mmol 2 and 0.05 mmol AuCl(PPh3)/AgBF4 in 10 mL of
dioxane.
b
c
Isolated yield.
The reaction was conducted with 4 mmol (1.0811 g) scale of 2a.
We found that even the crude residue 2 without any purification
can be used directly for the gold-catalyzed cyclization reactions.
Thus, as shown in Table 3, R1 could be H (entries 3 and 4, Table 3),
aryl (entry 1, Table 3), or alkyl group (entries 2 and 5e7, Table 3). R2
could be H (entries 1e2 and 5e7, Table 3), phenyl (entry 4, Table 3),
or alkyl group (entry 3, Table 3). Benzo[b]furans were also afforded
under standard reaction conditions (entries 5e7,Table 3).
follows:
5 mol % of AuCl(PPh3)/AgBF4 in dioxane at room
temperature.
Table 3
Synthesis of benzothiophenes and benzofurans from 1-arylalka-2,3-dienols
Table 1
Optimization of reaction conditions for the cyclization reaction of 2-phenyl-1-(3-
thienyl)buta-2,3-dienyl acetate (2a)a
Entry
X
R1
R2
t1/t2 (h)
Yield of 3 (%)a
1
2
3
4
5
6
7
S
S
S
S
O
O
O
p-MeOC6H4
Allyl
H
H
Bu
H (2h)
H (2i)
Pr (2j)
Ph (2k)
H (2l)
24/12
24/48
12/24
18/12
12/36
12/30
12/18
73 (3h)
38 (3i)
44 (3j)
62 (3k)
52 (3l)
60 (3m)
53 (3n)
Entry
[Ag]
Solvent
Yield of 3ab (%)
1
2
3
4
5
6
7
8
AgBF4
AgBF4
AgBF4
AgBF4
DCE
THF
Et2O
Toluene
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
8
84
52
18
95
85
77
90
d
d
C7H15
CH2OEt
H (2m)
H (2n)
a
Isolated yield ( from 1 to 3).
AgBF4
AgSbF6
AgOTf
AgPF6
AgOAc
AgOOCCF3
In addition, we have tested the reaction of the benzofuran-
derived substrate 1-(benzofuran-2-yl)-2-phenylbuta-2,3-dienyl
acetate 2o in dioxane under the catalysis of AuCl(PPh3)/AgBF4
(10 mol %) to give dibenzofuran 3o in 48% yield (Scheme 3).
9c
10d
a
The reaction was conducted with 2a (0.2 mmol) and catalyst (0.01 mmol) in
2 mL of solvent at room temperature.
b
Determined by 1H NMR of crude product using dibromomethane as internal
standard.
c
The recovery of 2a was 97%.
The recovery of 2a was 87%.
d
Then, other substrates were screened under the optimal re-
action condition. The R1 group could be aryl (entries 1 and 5e8,
Table 2) or alkyl group (entries 2e4, Table 2). In addition to acetate,
the protecting group could also be methyl ether (entry 5, Table 2). It
is noteworthy that this reaction shows an interesting exclusive
elimination of the OAc group to form the benzothiophene ring even
when R1 is CH2OEt (entry 4, Table 2). Moreover, the reaction can be
easily conducted in a scale of 4 mmol (1.0811 g) in a slightly higher
yield (entry 6, Table 2). Interestingly, benzo[b]furan was also
formed in a good yield, when furan was used instead of thiophene
(entry 8, Table 2).
Scheme 3. Synthesis of dibenzofuran through the gold-catalyzed cyclization.
In order to unveil the mechanism, we added D2O to the re-
action mixture of 2a, the reaction proceeded smoothly to afford
3a-D in 62% yield with 29% D-incorporation at the 6-position of
benzothiophene 3a-D. The result shows that the reaction may
proceed through a carbocation gold intermediate, final proto-
nolysis would release the gold catalyst into the catalytic cycle to
afford benzothiophene 3a-D. Then, we prepared the deuterium-
labeled 2k-D. To our surprise, the 3k-D was afforded in 55%
yield with 52% D-incorporation at the ortho-position of phenyl

Y. Qiu et al. / Tetrahedron 69 (2013) 6305e6312
6307
group (Scheme 4). This means that the reaction may also involve
a gold carbene intermediate, subsequent 1,2-D shift would afford
3k-D.
chromatography was performed on silica gel. Et2O and dioxane were
refluxed in the presenceof sodium using diphenyl ketone as indicator
and distilled right before use. AuCl(PPh3) was purchased from Alfa.
HO
AcO
AuCl(PPh3)/AgBF4 (5 mol%)
dioxane, rt, 24 h
H/D
Ac2O, DMAP
(52% D)
Ph
Ph
Et3N, Et2O
rt, 12 h
Ph
S
D
D
S
S
3k-D
1k-D
2k-D
combined yield: 55%
Scheme 4. The deuterium-labeling reactions.
On the basis of these results, we proposed two possible mech-
anistic pathways for this reaction.6,9 The reaction of cationic gold
with 2a would form the intermediate M1 via the coordination of
the allene moiety with gold atom followed by nucleophilic attack of
the C2 in the thiophene ring. Subsequent elimination of ꢀOAc
would afford gold carbene intermediate M2 followed by 1,2-H shift
to afford the final product 3a with regeneration of the catalytically
cationic gold species. Alternatively, elimination of acetic acid would
form aromatic gold intermediate M3, which would be followed by
protonolysis to release the catalytically active species by pro-
tonation to afford the target product 3a (Scheme 5).
4.2. Synthesis of 1-heteroarylalka-2,3-dienyl acetates 2ae2d,
2fe2g, and 2o
4.2.1. 2-Phenyl-1-(3-thienyl)buta-2,3-dienyl acetate (2a).
Typical procedure: To a solution of 1a6,9b,10 (1.5626 g, 6.86 mmol)
and Et2O (40 mL) were added DMAP (0.1676 g, 1.37 mmol), Et3N
(4.0 mL, d¼0.73 g/mL, 2.92 g, 28.9 mmol), and Ac2O (2.6 mL, d¼1.08 g/
mL, 2.79 g, 27.4 mmol). The resulting mixture was stirred at room
temperature until the reaction was complete as monitored by TLC.
After being stirred for 12 h, the reaction mixture was quenched with
a saturated aqueous solution of NaHCO3 (20 mL), and extracted with
diethyl ether (20 mLꢁ3), then washed by water (10 mL). The ether
layer was dried over anhydrous Na2SO4. Filtration, evaporation, and
column chromatography on silica gel afforded 2a (1.7207 g, 93%)
(petroleum ether/ethyl acetate¼20:1, it should be noted that the
columnpacked with silicagel waseluted witha mixture ofpetroleum
ether and triethylamine (100:1) before loading the sample) as a liq-
Scheme 5. Two proposed pathways.
uid: 1H NMR (300 MHz, CDCl3)
d 7.41e7.31 (m, 2H, ArH), 7.30e7.11 (m,
5H, ArH), 7.16 (dd, J1¼5.1 Hz andJ2¼0.9 Hz,1H, thienyleH), 6.95 (s,1H,
3. Conclusions
OCH), 5.26 (d, J¼1.8 Hz, 2H, ]CH2), 2.13 (s, 3H, CH3); 13C NMR
(75 MHz, CDCl3) d 208.6, 169.8, 139.3, 133.5, 128.3, 127.0, 126.7, 126.5,
In conclusion, we have developed a general Au-catalyzed re-
action of 1-heteroarylalka-2,3-dienyl acetates, providing a series of
benzo[b]thiophenes, benzo[b]furans, and dibenzofurans. Two pos-
sible pathways of this reaction are involved in the reaction as in-
dicated by the mechanistic studies. Due to the easy availability of
the starting materials, mild conditions, and the potential of the
products, this method may be useful in organic synthesis, material
science, and medicinal chemistry. Further studies on synthesis
applications of this reaction are being carried out in our laboratory.
125.7,123.4,106.5, 80.4, 69.5, 20.9; IR (KBr) n
(cmꢀ1) 3105, 3057, 3033,
2979, 2937, 1941, 1747, 1597, 1578, 1495, 1450, 1423, 1368, 1228, 1152,
1077, 1024; MS (70 eV, EI) m/z (%) 227 (Mþ-CH3CO, 33.11), 43 (100).
Elemental analysis calcd for C16H14O2S: C, 71.08; H, 5.22. Found: C,
71.06; H, 5.27.
The following compounds 2be2d, 2fe2g, and 2o were prepared
according to this procedure.
4.2.2. 2-Butyl-1-(3-thienyl)buta-2,3-dienyl acetate (2b).
4. Experimental section
4.1. General information
1H and 13C nuclear magnetic resonance spectra were recorded
with an instrument operated at 300 MHz for 1H NMR and 75 MHz for
13C NMR.CDCl3 wasused assolventinall NMRexperiments. Chemical
shifts (
d
) are given in parts per million (ppm). Infrared spectra were
The reaction of 1b (0.6869 g, 3.3 mmol), Et2O (20 mL), DMAP
(0.0812 g, 0.66 mmol), Et3N (2.0 mL, d¼0.73 g/mL, 1.46 g,
14.5 mmol), and Ac2O (1.25 mL, d¼1.08 g/mL, 1.35 g, 13.2 mmol) at
recorded on an FT-IR spectrometer. Mass spectra were carried out in
EI mode. HRMS spectra were carried out in EI mode. Flash column

6308
Y. Qiu et al. / Tetrahedron 69 (2013) 6305e6312
room temperature for 16 h afforded 2b (0.6568 g, 80%) (petroleum
ether/ethyl acetate¼40:1, it should be noted that the column
packed with silica gel was eluted with a mixture of petroleum ether
and triethylamine (100:1) before loading the sample) as a liquid: 1H
4.2.5. 2-(p-Methylphenyl)-1-(3-thienyl)buta-2,3-dienyl acetate (2f)
NMR (300 MHz, CDCl3)
d 7.32e7.21 (m, 2H, thienyleH), 7.06 (d,
J¼4.8 Hz, 1H, thienyleH), 6.27 (s, 1H, OCH), 4.82e4.61 (m, 2H, ]
CH2), 2.10 (s, 3H, CH3), 1.94e1.83 (m, 2H, CH2), 1.46e1.21 (m, 4H,
2ꢁCH2), 0.86 (t, J¼7.1 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3)
d
205.8, 169.9, 139.7, 126.6, 125.8, 122.9, 104.1, 78.5, 71.8, 29.5, 27.7,
22.2, 21.1, 13.9; IR (neat)
n
(cmꢀ1) 3106, 2957, 2930, 2860, 1958,
1746, 1369, 1231, 1024; MS (70 eV, EI) m/z (%) 251 (Mþþ1, 2.03), 250
(Mþ, 16.31), 249 (100); HRMS calcd for C14H18O2S (Mþ): 250.1028,
found: 250.1028.
.
The reaction of 1f (0.7268 g, 3.0 mmol), Et2O (20 mL), DMAP
(0.0738 g, 0.6 mmol), Et3N (2.0 mL, d¼0.73 g/mL, 1.46 g,
14.5 mmol), and Ac2O (1.1 mL, d¼1.08 g/mL, 1.22 g, 12.0 mmol) at
room temperature for 24 h afforded 2f (0.6424 g, 75%) (petroleum
ether/ethyl acetate¼20:1, it should be noted that the column
packed with silica gel was eluted with a mixture of petroleum
ether and triethylamine (100:1) before loading the sample) as
a solid: mp 72.9e74.5 ꢂC (n-hexane/ethyl acetate); 1H NMR
4.2.3. 2-Heptyl-1-(3-thienyl)buta-2,3-dienyl acetate (2c).
(300 MHz, CDCl3)
ArH), 6.76 (s, 1H, OCH), 5.10 (s, 2H, ]CH2), 2.20 (s, 3H, CH3), 2.00
(s, 3H, CH3); 13C NMR (75 MHz, CDCl3)
208.5, 169.9, 139.5, 136.8,
130.5, 129.1, 126.8, 126.5, 125.8, 123.5, 106.4, 80.4, 69.7, 21.1, 21.0;
d 7.30e7.17 (m, 4H, ArH), 7.07e6.90 (m, 3H,
d
The reaction of 1c (0.6256 g, 2.5 mmol), Et2O (20 mL), DMAP
(0.0613 g, 0.5 mmol), Et3N (2.0 mL, d¼0.73 g/mL, 1.46 g, 14.5 mmol),
and Ac2O (0.94 mL, d¼1.08 g/mL, 1.02 g, 10.0 mmol) at room tem-
perature for 12 h afforded 2c (0.6710 g, 92%) (petroleum ether/ethyl
acetate¼50:1, it should be noted that the column packed with silica
gel was eluted with a mixture of petroleum ether and triethylamine
(100:1) before loading the sample) as a liquid: 1H NMR (300 MHz,
IR (KBr)
n
(cmꢀ1) 1941, 1745, 1606, 1512, 1432, 1369, 1229, 1151,
1079, 1030; MS (70 eV, EI) m/z (%) 284 (Mþ, 0.30), 243 (Mþ-CH3CO,
28.28), 242 (100). Elemental analysis calcd for C17H16O2S: C, 71.80;
H, 5.67. Found: C, 71.62; H, 5.72.
4.2.6. 1-(3-Furyl)-2-phenylbuta-2,3-dienyl acetate (2g).
CDCl3)
d
7.33e7.18 (m, 2H, thienyleH), 7.05 (dd, J1¼4.7 Hz and
J2¼1.5 Hz, 1H, thienyleH), 6.27 (s, 1H, OCH), 4.90e4.75 (m, 2H, ]
CH2), 2.10 (s, 3H, CH3), 1.94e1.81 (m, 2H, CH2), 1.47e1.33 (m, 2H,
CH2), 1.33e1.16 (m, 8H, 4ꢁCH2), 0.87 (t, J¼6.8 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3) d 205.8, 169.9, 139.7, 126.6, 125.8, 122.8, 104.2, 78.4,
71.9, 31.8, 29.1, 29.0, 28.1, 27.3, 22.6, 21.1, 14.0; IR (neat)
n )
(cmꢀ1
3107, 2955, 2927, 2856, 1958, 1746, 1465, 1368, 1230, 1150, 1079,
1021; MS (70 eV, EI) m/z (%) 292 (Mþ, 1.35), 147 (100); HRMS calcd
for C17H24O2S (Mþ): 292.1497, found: 292.1502.
The reaction of 1g (0.6786 g, 3.2 mmol), Et2O (20 mL), DMAP
(0.0786 g, 0.64 mmol), Et3N (2.0 mL, d¼0.73 g/mL, 1.46 g,
14.5 mmol), and Ac2O (1.2 mL, d¼1.08 g/mL, 1.31 g, 12.8 mmol) at
room temperature for 24 h afforded 2g (0.7779 g, 96%) (petroleum
ether/ethyl acetate¼30:1, it should be noted that the column
packed with silica gel was eluted with a mixture of petroleum ether
and triethylamine (100:1) before loading the sample) as a liquid: 1H
4.2.4. 2-(Ethoxymethyl)-1-(3-thienyl)buta-2,3-dienyl acetate (2d).
NMR (300 MHz, CDCl3) d 7.45e7.34 (m, 3H, ArH), 7.34e7.23 (m, 3H,
ArH), 7.18 (t, J¼7.2 Hz, 1H, ArH), 6.76 (s, 1H, furyl-H), 6.40 (s, 1H,
OCH), 5.24e5.18 (m, 2H, ]CH2), 2.06 (s, 3H, CH3); 13C NMR
(75 MHz, CDCl3)
123.6, 109.7, 106.1, 80.6, 66.7, 21.0; IR (neat)
1598, 1496, 1450, 1429, 1370, 1232, 1159, 1023; MS (70 eV, EI) m/z
(%) 254 (Mþ, 1.14), 212 (100); HRMS calcd for C16H14O3 (Mþ):
254.0943, found: 254.0943.
d
208.6, 170.0, 143.0, 141.1, 133.5, 128.4, 127.1, 126.5,
(cmꢀ1) 1942, 1746,
The reaction of 1d (0.5698 g, 2.7 mmol), Et2O (20 mL), DMAP
(0.0677 g, 0.54 mmol), Et3N (2.0 mL, d¼0.73 g/mL, 1.46 g,
14.5 mmol), and Ac2O (1.0 mL, d¼1.08 g/mL, 1.10 g, 10.8 mmol) at
room temperature for 12 h afforded 2d (0.5756 g, 84%) (petroleum
ether/ethyl acetate¼10:1, it should be noted that the column
packed with silica gel was eluted with a mixture of petroleum ether
and triethylamine (100:1) before loading the sample) as a liquid: 1H
n
4.2.7. 1-(Benzofuran-2-yl)-2-phenylbuta-2,3-dienyl acetate (2o).
NMR (300 MHz, CDCl3)
d 7.38e7.18 (m, 2H, thienyleH), 7.09 (dd,
J1¼4.8 Hz and J2¼0.9 Hz, 1H, thienyleH), 6.41 (s, 1H, OCH),
5.03e4.77 (m, 2H, ]CH2), 4.12e3.82 (m, 2H, OCH2), 3.58e3.30 (m,
2H, OCH2), 2.08 (s, 3H, CH3), 1.16 (t, J¼7.1 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3) d 206.4, 169.6, 139.1, 126.5, 125.7, 123.0, 101.7, 78.3,
69.4, 68.7, 65.2, 20.9, 14.9; IR (neat)
n
(cmꢀ1) 3105, 2975, 2930,
2865, 1958, 1744, 1369, 1231, 1094, 1024; MS (70 eV, EI) m/z (%) 252
(Mþ, 0.02), 209 (Mþꢀ43, 0.48), 43 (100). Elemental analysis calcd
for C13H16O3S: C, 61.88; H, 6.39. Found: C, 61.66; H, 6.34.
The reaction of 1o (1.2839 g, 4.9 mmol), Et2O (30 mL), DMAP
(0.1216 g, 0.98 mmol), Et3N (3.0 mL, d¼0.73 g/mL, 2.19 g,

Y. Qiu et al. / Tetrahedron 69 (2013) 6305e6312
6309
21.7 mmol), and Ac2O (1.85 mL, d¼1.08 g/mL, 2.00 g, 19.6 mmol) at
room temperature for 12 h afforded 2o (1.3620 g, 91%) (petroleum
ether/ethyl acetate¼50:1) as a liquid: 1H NMR (300 MHz, CDCl3)
CDCl3)
2H, ArH), 7.67 (dd, J1¼8.4 Hz and J2¼1.2 Hz, 1H, ArH), 7.60e7.49 (m, 3H,
ArH), 7.49e7.39 (m, 2H, ArH); 13C NMR (75 MHz, CDCl3)
141.3, 140.1,
d
8.10 (s,1H, ArH), 8.00 (d, J¼8.7 Hz,1H, ArH), 7.74 (d, J¼7.5 Hz,
d
d
7.49 (t, J¼8.9 Hz, 2H, ArH), 7.41 (d, J¼7.2 Hz, 2H, ArH), 7.32e7.13
138.7,137.6,128.8,127.4,127.1,127.0,124.0,123.8,122.6,121.9;IR(KBr)n
(m, 5H, ArH), 6.95 (s, 1H, ArH), 6.74 (s, 1H, OCH), 5.34e5.23 (m, 2H,
]CH2), 2.14 (s, 3H, CH3); 13C NMR (75 MHz, CDCl3)
208.7, 169.5,
154.9, 153.4, 133.1, 128.4, 127.2, 126.3, 124.5, 122.7, 121.1, 111.3, 106.3,
(cmꢀ1) 1537, 1487,1447, 1436,1410, 1180,1153, 1054,1031; MS (70 eV,
EI) m/z (%) 211 (Mþþ1, 16.79), 210 (Mþ, 100). Elemental analysis calcd
for C14H10S: C, 79.96; H, 4.79. Found: C, 79.80; H, 4.72.
The following compounds 3be3g, and 3o were prepared
according to this procedure.
d
104.4, 81.0, 67.3, 20.8; IR (KBr) n
(cmꢀ1) 1942,1747, 1598, 1496, 1453,
1370, 1254, 1225, 1027; MS (70 eV, EI) m/z (%) 304 (Mþ, 1.36), 262
(100); HRMS calcd for C20H16O3 (Mþ): 304.1099, found: 304.1098.
4.4.2. 5-Butylbenzo[b]thiophene (3b).
4.3. Synthesis of methyl 2-phenyl-1-(3-thienyl)buta-2,3-
dienyl ether (2e)
The reaction of AgBF4 (10.8 mg, 0.055 mmol), AuCl(PPh3)
(24.8 mg, 0.05 mmol), and 2b (250.7 mg, 1.0 mmol) in dioxane
(10 mL) at room temperature for 10 h afforded 3b (162.2 mg, 85%)
(eluent: petroleum ether) as a liquid: 1H NMR (300 MHz, CDCl3)
To a solution of NaH (0.2228 g, 5.55 mmol) and THF (10 mL) was
added dropwise 1e (0.8449, 3.7 mmol)/THF (10 mL) at 0 ꢂC with
stirring under a nitrogen atmosphere within 15 min. Then the
mixture was allowed to warm up to room temperature. After being
stirred for 1.5 h, TBAB (0.1236 g, 0.37 mmol) and MeI (0.35 mL,
d¼2.28 g/mL, 7.88 g, 5.55 mmol) were added. The resulting mixture
was stirred at room temperature until the reaction was complete as
monitored by TLC. After being stirred for 16 h, the reaction mixture
was quenched with a saturated aqueous solution of NH4Cl (10 mL),
and extracted with diethyl ether (20 mLꢁ3), then washed by water
(10 mL) and brine (10 mL). The ether layer was dried over anhy-
drous Na2SO4, filtration, evaporation, and column chromatography
on silica gel afforded 2a (0.4554 g, 51%) (petroleum ether/ethyl
d
7.93 (d, J¼8.1 Hz, 1H, ArH), 7.78 (s, 1H, ArH), 7.52 (d, J¼5.4 Hz, 1H,
ArH), 7.40 (d, J¼5.4 Hz, 1H, ArH), 7.34 (d, J¼8.1 Hz, 1H, ArH), 2.89 (t,
J¼7.8 Hz, 2H, CH2), 1.91e1.76 (m, 2H, CH2), 1.63e1.48 (m, 2H, CH2),
1.13 (t, J¼7.4 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3)
d 139.9, 138.9,
137.1, 126.2, 125.4, 123.5, 122.9, 122.0, 35.5, 33.9, 22.3, 14.0; IR (neat)
n
(cmꢀ1) 2955, 2927, 2856, 1605, 1502, 1437, 1421, 1089, 1050; MS
(70 eV, EI) m/z (%) 191 (Mþþ1, 3.51), 190 (Mþ, 20.32), 147 (100);
HRMS calcd for C12H14S (Mþ): 190.0816, found: 190.0821.
4.4.3. 5-Heptylbenzo[b]thiophene (3c).
acetate¼50:1) as a liquid: 1H NMR (500 MHz, CDCl3)
d 7.41 (d,
J¼7.5 Hz, 2H, ArH), 7.29e7.20 (m, 4H, ArH), 7.19e7.14 (m, 1H, ArH),
7.07 (dd, J1¼4.8 Hz and J2¼1.3 Hz, 1H, thienyleH), 5.27 (s, 1H, OCH),
5.18 (dd, J1¼12.5 Hz and J2¼1.5 Hz, 1H, one proton of ]CH2), 5.14
(dd, J1¼12.3 Hz and J2¼0.8 Hz, 1H, one proton of ]CH2), 3.44 (s, 3H,
CH3); 13C NMR (125 MHz, CDCl3)
126.9, 126.7, 125.4, 122.2, 106.1, 79.7, 79.0, 56.7; IR (neat)
d
209.4, 141.8, 134.1, 128.3, 127.0,
(cmꢀ1
n
)
The reaction of AgBF4 (10.8 mg, 0.055 mmol), AuCl(PPh3)
(25.0 mg, 0.05 mmol), and 2c (292.1 mg, 1.0 mmol) in dioxane
(10 mL) at room temperature for 24 h afforded 3c (206.8 mg, 89%)
(eluent: petroleum ether) as a liquid: 1H NMR (300 MHz, CDCl3)
3055, 2981, 2819, 1938, 1597, 1495, 1450, 1415, 1317, 1217, 1187, 1150,
1091; MS (70 eV, EI) m/z (%) 243 (Mþþ1, 2.26), 242 (Mþ, 9.93), 127
(100); HRMS calcd for C15H14OS (Mþ): 242.0765, found: 242.0769.
d
7.82 (d, J¼8.1 Hz, 1H, ArH), 7.66 (s, 1H, ArH), 7.43 (d, J¼5.4 Hz, 1H,
4.4. Synthesis of 3ae3g and 3o
ArH), 7.31 (d, J¼5.4 Hz, 1H, ArH), 7.22 (d, J¼8.1 Hz, 1H, ArH), 2.76 (t,
J¼7.7 Hz, 2H, CH2),1.80e1.64 (m, 2H, CH2),1.47e1.23 (m, 8H, 4ꢁCH2),
0.93 (t, J¼6.8 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3)
d 139.9, 139.0,
4.4.1. 5-Phenylbenzo[b]thiophene (3a).
137.1,126.3,125.4,123.6,122.9,122.1, 35.9, 31.9, 31.8, 29.3, 29.2, 22.7,
14.1; IR (neat)
n
(cmꢀ1) 2954, 2926, 2853, 1459, 1437, 1420, 1089,
1050; MS (70 eV, EI) m/z (%) 233 (Mþþ1, 2.25), 232 (Mþ, 13.35), 147
(100); HRMS calcd for C15H20S (Mþ): 232.1286, found: 232.1287.
4.4.4. 5-(Ethoxymethyl)benzo[b]thiophene (3d).
Typical procedure: A dry Schlenk tube was charged with AgBF4
(10.2 mg, 0.052 mmol, weighed in a glove box), AuCl(PPh3) (25.1 mg,
0.05 mmol), 2a (271.8 mg, 1.0 mmol), and dioxane (10 mL) under N2.
The resulting mixture was stirred at room temperature until the re-
action was complete as monitored by TLC. Filtration through a short
column of silica gel (eluent: Et2O), evaporation, and column chroma-
tography on silica gel afforded 3a (177.8 mg, 84%) (petroleum ether) as
a solid: mp 98.5e99.2 ꢂC (n-hexane/ethyl acetate); 1H NMR (300 MHz,
The reaction of AgBF4 (10.3 mg, 0.053 mmol), AuCl(PPh3)
(24.6 mg, 0.05 mmol), and 2d (252.6 mg, 1.0 mmol) in dioxane

6310
Y. Qiu et al. / Tetrahedron 69 (2013) 6305e6312
(10 mL) at room temperature for 12 h afforded 3d (170.8 mg, 89%)
(eluent: petroleum ether/petroleum ether/ethyl acetate¼100:1)
4.4.8. 5-Phenylbenzo[b]furan (3g).
as a liquid: 1H NMR (300 MHz, CDCl3)
d
7.82 (d, J¼8.4 Hz, 1H, ArH),
7.77 (s, 1H, ArH), 7.39 (d, J¼5.4 Hz, 1H, ArH), 7.35e7.24 (m, 2H, ArH),
4.59 (s, 2H, CH2), 3.54 (q, J¼7.0 Hz, 2H, CH2), 1.24 (t, J¼7.1 Hz, 3H,
CH3); 13C NMR (75 MHz, CDCl3)
123.7, 122.6, 122.3, 72.7, 65.6, 15.2; IR (neat)
d 139.6, 138.9, 134.7, 126.6, 124.2,
n
(cmꢀ1) 2973, 2928,
2862, 1436, 1373, 1354, 1325, 1148, 1097, 1050, 1015; MS (70 eV, EI)
m/z (%) 193 (Mþþ1, 3.71),192 (Mþ, 27.41),147 (100); HRMS calcd for
C11H12OS (Mþ): 192.0609, found: 192.0611.
The reaction of AgBF4 (10.8 mg, 0.055 mmol), AuCl(PPh3)
(25.0 mg, 0.05 mmol), and 2g (254.1 mg, 1.0 mmol) in dioxane
(10 mL) at room temperature for 24 h afforded 3g11 (164.6 mg, 85%)
(eluent: petroleum ether/petroleum ether/ethyl acetate¼100:1)
as a solid: mp 58.6e59.9 ꢂC (n-hexane/ethyl acetate); 1H NMR
4.4.5. 5-Phenylbenzo[b]thiophene (2e).
(300 MHz, CDCl3)
J¼7.7 Hz, 2H, ArH), 7.47 (t, J¼7.2 Hz, 1H, ArH), 6.90 (d, J¼1.5 Hz, 1H,
ArH); 13C NMR (75 MHz, CDCl3)
154.5, 145.4, 141.6, 136.4, 128.7,
127.9, 127.4, 126.8, 123.9, 119.6, 111.4, 106.7; IR (KBr)
(cmꢀ1) 1601,
d 7.92 (s, 1H, ArH), 7.79e7.62 (m, 5H, ArH), 7.57 (t,
d
n
1536, 1463, 1428, 1330,1296, 1261, 1229, 1160, 1132, 1111, 1031, 1015;
MS (70 eV, EI) m/z (%) 195 (Mþþ1, 15.43), 194 (Mþ, 100).
The reaction ofAgBF4 (10.6 mg, 0.054 mmol), AuCl(PPh3) (25.0mg,
0.05 mmol), and 2e (243.1 mg,1.0 mmol) in dioxane (10 mL) at room
temperature for 12 h afforded 3e (184.0 mg, 87%) (eluent: petroleum
ether/petroleum ether/ethyl acetate¼100:1) as a solid: 1H NMR
4.4.9. 3-Phenyldibenzofuran (3o).
(300 MHz, CDCl3)
d
8.14 (d, J¼1.2 Hz, 1H, ArH), 8.03 (d, J¼8.4 Hz, 1H,
ArH), 7.78 (d, J¼7.2 Hz, 2H, ArH), 7.70 (dd, J1¼8.3 Hz and J2¼1.4 Hz,1H,
ArH), 7.63e7.42 (m, 5H, ArH); 13C NMR (75 MHz, CDCl3)
d
141.2, 140.1,
138.7, 137.6, 128.8, 127.3, 127.1, 126.9, 124.0, 123.8, 122.6, 121.9.
4.4.6. 5-Phenylbenzo[b]thiophene (3a).
The reaction of AgBF4 (20.1 mg, 0.1 mmol), AuCl(PPh3) (49.8 mg,
0.1 mmol), and 2o (304.6 mg, 1.0 mmol) in dioxane (10 mL) at room
temperature for 48 h afforded 3o (118.0 mg, 48%) (eluent: petroleum
ether/petroleum ether/dichloromethane¼10:1) as a solid: mp
131.9e132.9 ꢂC (n-hexane/ethyl acetate); 1H NMR (300 MHz, CDCl3)
d
8.06e7.96 (m, 2H, ArH), 7.85 (s, 1H, ArH), 7.78e7.71 (m, 2H, ArH),
7.68e7.61 (m, 2H, ArH), 7.58e7.37 (m, 5H, ArH); 13C NMR (75 MHz,
CDCl3) 156.7, 156.5, 140.9, 140.6, 128.8, 127.4, 127.3, 127.0, 124.0,
123.2, 122.7, 122.1, 120.7, 120.6, 111.6, 110.0; IR (KBr)
(cmꢀ1) 1597,
1571,1514,1484,1456,1416,1356, 1299, 1228, 1175, 1103; MS (70 eV,
EI) m/z (%) 245 (Mþþ1, 18.42), 244 (Mþ, 100). Elemental analysis
calcd for C18H12O: C, 88.50; H, 4.95. Found: C, 88.40; H, 4.98.
The reaction of AgBF4 (39.6 mg, 0.2 mmol), AuCl(PPh3) (98.6 mg,
0.2 mmol), and 2a (1081.1 mg, 4.0 mmol) in dioxane (40 mL) at
room temperature for 24 h afforded 3a (739.2 mg, 88%) (eluent:
petroleum ether/petroleum ether/ethyl acetate¼100:1) as
d
n
a solid: 1H NMR (300 MHz, CDCl3)
d
8.14 (d, J¼1.2 Hz, 1H, ArH), 8.03
(d, J¼8.1 Hz, 1H, ArH), 7.83e7.73 (m, 2H, ArH), 7.70 (dd, J1¼8.6 Hz
and J2¼1.4 Hz, 1H, ArH), 7.63e7.42 (m, 5H, ArH); 13C NMR (75 MHz,
CDCl3)
d
141.2, 140.1, 138.7, 137.6, 128.7, 127.3, 127.0, 126.9, 124.0,
4.5. Synthesis of 3he3n
123.8, 122.6, 121.9.
4.5.1. 5-(p-Methoxyphenyl)benzo[b]thiophene (3h).
4.4.7. 5-(p-Methylphenyl)benzo[b]thiophene (3f).
Typical procedure: To a solution of 1h (0.2418 g, 0.94 mmol) and
Et2O (10 mL) were added DMAP (0.0246 g, 0.2 mmol), Et3N (1.0 mL,
d¼0.73 g/mL, 0.73 g, 7.2 mmol), and Ac2O (0.38 mL, d¼1.08 g/mL,
0.41 g, 4.0 mmol). The resulting mixture was stirred at room tem-
perature until the reaction was complete as monitored by TLC. After
being stirred for 12 h, the reaction mixture was quenched with
a saturated aqueous solution of NaHCO3 (10 mL), and extracted with
diethyl ether (20 mLꢁ3), then washed by water and brine. The ether
layer was dried over anhydrous Na2SO4. Filtration through a short
column ofsilica gel(eluent:Et2O), evaporation, andfiltrationthrough
a short column of silica gel (eluent: Et2O) and evaporation afforded
2h. The product 2h was then used without further purification.
The reaction ofAgBF4 (10.3 mg, 0.053 mmol), AuCl(PPh3) (25.0mg,
0.05 mmol), and 2f (285.6 mg, 1.0 mmol) in dioxane (10 mL) at room
temperature for 12 h afforded 3f (208.7 mg, 93%) (eluent: petroleum
ether) as a solid: mp 121.8e123.9 ꢂC (n-hexane/ethyl acetate); 1H
NMR (300 MHz, CDCl3)
d
8.00 (s,1H, ArH), 7.91 (d, J¼8.7 Hz,1H, ArH),
7.62e7.50 (m, 3H, ArH), 7.45 (d, J¼5.4 Hz, 1H, ArH), 7.36 (d, J¼5.1 Hz,
1H, ArH), 7.26 (d, J¼8.1 Hz, 2H, ArH), 2.40 (s, 3H, CH3); 13C NMR
(75 MHz, CDCl3) d 140.2, 138.5, 138.4, 137.6, 136.9, 129.5, 127.2, 126.9,
124.0,123.8,122.6,121.7, 21.1; IR (KBr) n
(cmꢀ1) 1542,1519,1497,1437,
1421, 1401, 1177, 1158, 1115,1089, 1057, 1025; MS (70 eV, EI) m/z(%)225
(Mþþ1, 20.00), 224 (Mþ,100). Elemental analysis calcd for C15H12S: C,
80.31; H, 5.39. Found: C, 80.38; H, 5.39.
A
dry Schlenk tube was charged with AgBF4 (10.3 mg,
0.053 mmol, weighed in a glove box), AuCl(PPh3) (24.6 mg,

Y. Qiu et al. / Tetrahedron 69 (2013) 6305e6312
6311
0.05 mmol), 2h (prepared in the previous step), and dioxane (10 mL)
under N2. The resulting mixture was stirred at room temperature
until the reaction was complete as monitored by TLC. Filtration
through a short column of silica gel (eluent: Et2O), evaporation, and
column chromatography on silica gel afforded 3h (163.8 mg, 73%,
from 1h to 3h) (eluent: petroleum ether/petroleum ether/ethyl
acetate¼50:1) as a solid: mp 140.6e141.8 ꢂC (n-hexane/ethyl ace-
1571, 1461, 1394, 1378, 1250, 1109, 1087, 1036; MS (70 eV, EI) m/z (%)
177 (Mþþ1, 4.69),176 (Mþ, 35.42), 84 (100); HRMS calcd for C11H12
S
(Mþ): 176.0660, found: 176.0662.
4.5.4. 7-Phenylbenzo[b]thiophene (3k).
tate); 1H NMR (300 MHz, CDCl3)
d
8.01 (d, J¼0.9 Hz,1H, ArH), 7.94 (d,
J¼8.4 Hz, 1H, ArH), 7.67e7.55 (m, 3H, ArH), 7.49 (d, J¼5.1 Hz, 1H,
ArH), 7.39 (d, J¼5.7 Hz, 1H, ArH), 7.03 (d, J¼9.0 Hz, 2H, ArH), 3.88 (s,
3H, CH3); 13C NMR (75 MHz, CDCl3)
d 159.0,140.2,138.1,137.3,133.8,
128.3, 126.9, 124.0, 123.6, 122.6, 121.4, 114.2, 55.3; IR (KBr) n )
(cmꢀ1
The reaction of 1k (0.2290 g, 1.0 mmol), Et2O (10 mL), DMAP
(0.0240 g, 0.2 mmol), Et3N (1.0 mL, d¼0.73 g/mL, 0.73 g, 7.2 mmol),
and Ac2O (0.38 mL, d¼1.08 g/mL, 0.41 g, 4.0 mmol) at room tem-
perature for 18 h afforded 2k. The product 2k was then used
without further purification.
1607, 1575, 1523, 1496, 1303, 1283, 1264, 1249, 1092, 1034, 1016; MS
(70 eV, EI) m/z (%) 241 (Mþþ1, 14.98), 240 (Mþ, 100). Elemental
analysis calcd for C15H12OS: C, 74.97; H, 5.03. Found: C, 74.97, H, 5.33.
The following compounds 3ie3n were prepared according to
this procedure.
The reaction of AgBF4 (10.8 mg, 0.055 mmol), AuCl(PPh3)
(25.1 mg, 0.05 mmol), and 2k (prepared in the previous step) in
dioxane (10 mL) at room temperature for 12 h afforded 3k
(130.0 mg, 62%, from 1k to 3k) (eluent: petroleum ether) as a liq-
4.5.2. 5-Allylbenzo[b]thiophene (3i).
uid: 1H NMR (300 MHz, CDCl3)
(m, 7H, ArH); 13C NMR (75 MHz, CDCl3)
d
8.01e7.82 (m, 3H, ArH), 7.70e7.44
140.6, 140.3, 138.8, 136.7,
d
128.7, 128.1, 127.8, 126.6, 124.8, 124.23, 124.20, 122.6; IR (neat)
n
(cmꢀ1) 3100, 3056, 3027, 1602, 1574, 1510, 1490, 1457, 1444, 1378,
1347, 1217, 1181, 1099, 1076, 1042, 1028; MS (70 eV, EI) m/z (%) 211
(Mþþ1, 16.23), 210 (Mþ, 100); HRMS calcd for C14H10S (Mþ):
210.0503, found: 210.0500.
The reaction of 1i (0.1930 g, 1.0 mmol), Et2O (10 mL), DMAP
(0.0246 g, 0.2 mmol), Et3N (1.0 mL, d¼0.73 g/mL, 0.73 g, 7.2 mmol),
and Ac2O (0.38 mL, d¼1.08 g/mL, 0.41 g, 4.0 mmol) at room tem-
perature for 24 h afforded 2i. The product 2i was then used without
further purification.
4.5.5. 5-Butylbenzo[b]furan (3l).
The reaction of AgBF4 (10.7 mg, 0.055 mmol), AuCl(PPh3)
(25.0 mg, 0.05 mmol), and 2i (prepared in the previous step) in
dioxane (10 mL) at room temperature for 48 h afforded 3i (65.6 mg,
38%, from 1i to 3i) (eluent: petroleum ether) as a liquid: 1H NMR
(300 MHz, CDCl3)
d
7.77 (d, J¼8.1 Hz, 1H, ArH), 7.61 (s, 1H, ArH), 7.37
The reaction of 1l (0.1906 g, 1.0 mmol), Et2O (10 mL), DMAP
(0.0246 g, 0.2 mmol), Et3N (1.0 mL, d¼0.73 g/mL, 0.73 g, 7.2 mmol),
and Ac2O (0.38 mL, d¼1.08 g/mL, 0.41 g, 4.0 mmol) at room tem-
perature for 12 h afforded 2l. The product 2l was then used without
further purification.
The reaction of AgBF4 (10.8 mg, 0.055 mmol), AuCl(PPh3)
(25.1 mg, 0.05 mmol), and 2l (prepared in the previous step) in
dioxane (10 mL) at room temperature for 36 h afforded 3l
(90.5 mg, 52%, from 1l to 3l) (eluent: petroleum ether) as a liquid:
(d, J¼5.1 Hz, 1H, ArH), 7.24 (d, J¼5.4 Hz, 1H, ArH), 7.16 (dd, J1¼8.1 Hz
and J2¼0.6 Hz, 1H, ArH), 6.09e5.89 (m, 1H, ]CH), 5.18e4.97 (m, 2H,
]CH2), 3.48 (d, J¼6.6 Hz, 2H, CH2); 13C NMR (75 MHz, CDCl3)
d
139.9, 137.6, 137.5, 136.1, 126.5, 125.4, 123.6, 123.2, 122.3, 115.8,
40.1; IR (neat)
n
(cmꢀ1) 3075, 3003, 2976, 2901, 1638, 1606, 1503,
1435, 1421, 1327, 1259, 1222, 1158, 1143, 1089, 1050; MS (70 eV, EI)
m/z (%) 175 (Mþþ1, 17.35), 174 (Mþ, 100); HRMS calcd for C11H10
S
(Mþ): 174.0503, found: 174.0502.
1H NMR (300 MHz, CDCl3)
d
7.63 (d, J¼1.8 Hz, 1H, ArH), 7.51e7.40
4.5.3. 7-Propylbenzo[b]thiophene (3j).
(m, 2H, ArH), 7.17 (dd, J1¼8.3 Hz and J2¼1.7 Hz, 1H, ArH), 6.75 (d,
J¼1.5 Hz, 1H, ArH), 2.76 (t, J¼7.7 Hz, 2H, CH2), 1.77e1.62 (m, 2H,
CH2), 1.52e1.36 (m, 2H, CH2), 1.00 (t, J¼7.4 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3)
d 153.5, 144.9, 137.3, 127.4, 124.9, 120.3, 110.8,
106.3, 35.5, 34.3, 22.3, 13.9; IR (neat)
n
(cmꢀ1) 3022, 2956, 2929,
2857, 1614, 1590, 1538, 1469, 1444, 1378, 1329, 1262, 1196, 1127,
1110, 1032; MS (70 eV, EI) m/z (%) 175 (Mþþ1, 2.93), 174 (Mþ,
18.85), 131 (100); HRMS calcd for C12H14O (Mþ): 174.1045, found:
174.1044.
The reaction of 1j (0.1932 g, 1.0 mmol), Et2O (10 mL), DMAP
(0.0250 g, 0.2 mmol), Et3N (1.0 mL, d¼0.73 g/mL, 0.73 g, 7.2 mmol),
and Ac2O (0.38 mL, d¼1.08 g/mL, 0.41 g, 4.0 mmol) at room tem-
perature for 12 h afforded 2j. The product 2j was then used without
further purification.
4.5.6. 5-Heptylbenzo[b]furan (3m).
The reaction of AgBF4 (10.3 mg, 0.052 mmol), AuCl(PPh3)
(25.0 mg, 0.05 mmol), and 2j (prepared in the previous step) in
dioxane (10 mL) at room temperature for 24 h afforded 3j (76.3 mg,
44%, from 1j to 3j) (eluent: petroleum ether) as a liquid: 1H NMR
(300 MHz, CDCl3)
d
7.73 (d, J¼7.8 Hz, 1H, ArH), 7.46 (d, J¼5.1 Hz, 1H,
ArH), 7.42e7.32 (m, 2H, ArH), 7.21 (d, J¼6.9 Hz, 1H, ArH), 2.93 (t,
J¼7.5 Hz, 2H, CH2), 2.00e1.80 (m, 2H, CH2), 1.07 (t, J¼7.4 Hz, 3H,
The reaction of 1m (0.2343 g, 1.0 mmol), Et2O (10 mL), DMAP
(0.0250 g, 0.2 mmol), Et3N (1.0 mL, d¼0.73 g/mL, 0.73 g, 7.2 mmol),
and Ac2O (0.38 mL, d¼1.08 g/mL, 0.41 g, 4.0 mmol) at room
CH3); 13C NMR (75 MHz, CDCl3)
d 139.7, 139.6, 136.6, 125.5, 124.5,
123.4, 121.3, 37.1, 22.4, 14.1; IR (neat)
n
(cmꢀ1) 2958, 2930, 2870,

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Y. Qiu et al. / Tetrahedron 69 (2013) 6305e6312
temperature for 12 h afforded 2m. The product 2m was then used
without further purification.
The reaction of AgBF4 (10.8 mg, 0.055 mmol), AuCl(PPh3)
(25.1 mg, 0.05 mmol), and 2m (prepared in the previous step) in
dioxane (10 mL) at room temperature for 30 h afforded 3m
(130.0 mg, 60%, from 1m to 3m) (eluent: petroleum ether) as
References and notes
1. (a) Qin, Z.; Kasrati, I.; Chandrasena, R. E. P.; Liu, H.; Yao, P.; Petukhov, P. A.;
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McCulloch, I.; Heeney, M.; Chabinyc, M. L.; DeLongchamp, D.; Kline, R. J.;
a liquid: 1H NMR (300 MHz, CDCl3)
d
7.63 (d, J¼2.1 Hz, 1H, ArH),
€
Colle, M.; Duffy, W.; Fischer, D.; Gundlach, D.; Hamadani, B.; Hamilton, E.;
7.52e7.39 (m, 2H, ArH), 7.18 (d, J¼8.4 Hz, 1H, ArH), 6.84e6.66 (m,
1H, ArH), 2.76 (t, J¼7.5 Hz, 2H, CH2), 1.80e1.63 (m, 2H, CH2),
1.48e1.26 (m, 8H, 4ꢁCH2), 0.96 (t, J¼6.5 Hz, 3H, CH3); 13C NMR
Richter, L.; Salleo, A.; Shkunov, M.; Sparrowe, D.; Tierney, S.; Zhang, W. Adv.
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(75 MHz, CDCl3) d 153.5,144.9,137.4,127.4,124.9,120.3,110.9,106.4,
35.9, 32.2, 31.9, 29.3, 29.2, 22.7, 14.1; IR (neat) n
(cmꢀ1) 2955, 2927,
2. (a) Greve, H.; Meis, S.; Kassack, M. U.; Kehrasus, S.; Krick, A.; Wright, A. D.;
€
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2855, 1538, 1468, 1444, 1262, 1197, 1128, 1110, 1033; MS (70 eV, EI)
m/z (%) 217 (Mþþ1, 3.97), 216 (Mþ,19.82),131 (100); HRMS calcd for
C15H20O (Mþ): 216.1514, found: 216.1515.
Kimura, E.; Iwashita, H.; Uno, Y.; Onishi, T.; Uchiyama, N.; Kawamoto, T.;
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4.5.7. 5-(Ethoxymethyl)benzo[b]furan (3n).
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The reaction of 1n (0.1943 g, 1.0 mmol), Et2O (10 mL), DMAP
(0.0250 g, 0.2 mmol), Et3N (1.0 mL, d¼0.73 g/mL, 0.73 g, 7.2 mmol),
and Ac2O (0.38 mL, d¼1.08 g/mL, 0.41 g, 4.0 mmol) at room tem-
perature for 12 h afforded 2n. The product 2n was then used
without further purification.
The reaction of AgBF4 (10.8 mg, 0.055 mmol), AuCl(PPh3)
(24.6 mg, 0.05 mmol), and 2n (prepared in the previous step) in
dioxane (10 mL) at room temperature for 18 h afforded 3n
(92.6 mg, 53%, from 1n to 3n) (eluent: petroleum ether/ethyl
acetate¼100:1 to 50:1) as a liquid: 1H NMR (300 MHz, CDCl3)
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d
7.62 (d, J¼2.1 Hz, 1H, ArH), 7.60 (s, 1H, ArH), 7.49 (d, J¼8.4 Hz, 1H,
ArH), 7.31 (dd, J1¼8.4 Hz and J2¼1.2 Hz, 1H, ArH), 6.76 (d, J¼1.5 Hz,
1H, ArH), 4.61 (s, 2H, CH2), 3.58 (q, J¼6.9 Hz, 2H, CH2), 1.28 (t,
€
2011, 696, 277; (f) Schmidt, A. W.; Reddy, K. R.; Knolker, H.-J. Chem. Rev. 2012,
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J¼7.1 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3)
d
154.5, 145.2, 133.1,
(cmꢀ1
127.4, 124.3, 120.5, 111.1, 106.5, 72.8, 65.5, 15.2; IR (neat)
n
)
2975, 2930, 2864, 1538, 1470, 1444, 1375, 1355, 1329, 1264, 1197,
1128, 1108, 1032; MS (70 eV, EI) m/z (%) 177 (Mþþ1, 2.02), 176 (Mþ,
17.47), 131 (100); HRMS calcd for C11H12O2 (Mþ): 176.0837, found:
176.0835.
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€
Acknowledgements
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Financial support from the National Natural Science Foundation
of China (21232006) and the National Basic Research Program
(2009CB825300) is greatly appreciated. S.M. is a Qiu Shi Adjunct
Professor at Zhejiang University. We thank Mr. Bukeyan Miao in this
group for reproducing the results presented in entries 1 and 8 of
Table 2, entry 2 of Table 3.
ꢀ
ꢁ
ꢀ~
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Supplementary data
ꢀ
ꢀ
ꢀ
Supplementary data related to this article can be found in the
online version, at http://dx.doi.org/10.1016/j.tet.2013.04.099.
11. Varela-Fernandez, A.; Gonzalez-Rodríguez, C.; Varela, J. A.; Castedo, L.; Saa, C.
Org. Lett. 2009, 11, 5350.