TfOH-SiO2 as an efficient and recyclable catalyst for synthesis of 3-arylbenzofurans

Article abstract of DOI:10.3987/COM-15-13351

A convenient process for the synthesis of 3-arylbenzofurans and their derivatives by 2-phenoxy-1-phenylethanones via TfOH-SiO₂ catalyzed is developed. This method provides several advantages such as simple work-up procedure, simple post-treatme

Full text of DOI:10.3987/COM-15-13351

HETEROCYCLES, Vol. 92, No. 1, 2016, pp. -. © 2016 The Japan Institute of Heterocyclic Chemistry
Received, 25th October, 2015, Accepted, 25th November, 2015, Published online, 4th December, 2015
DOI: 10.3987/COM-15-13351
TfOH-SiO2 AS AN EFFICIENT AND RECYCLABLE CATALYST FOR
SYNTHESIS OF 3-ARYLBENZOFURANS
Baolong Wang,1 Jiaxing Hu,2 Fanglin Zhang,1 and Hua Zheng1*
1
School of Chemistry, Chemical Engineering and Life Sciences, Wuhan
2
University of Technology, Wuhan 430070, Hubei, P.R. China.
Pharmaceutical, Linhai, Taizhou 317000, Zhejiang, P.R. China.
E-mail: zhenghuawhut@163.com
Huahai
Abstract – A convenient process for the synthesis of 3-arylbenzofurans and their
derivatives by 2-phenoxy-1-phenylethanones via TfOH-SiO2 catalyzed is
developed. This method provides several advantages such as simple work-up
procedure, simple post-treatment process, high yields, broad applicability,
practicability, and recycling of the catalyst.
Following the principles of “green chemistry”, the search for more environmentally friendly forms of
catalysis has gained extensive attentions due to economic and environmental considerations, and one of
the leading contenders for environmentally acceptable alternatives is solid-supported catalysis.1 In the
past several years, some Brønsted acids, such as H2SO4, HClO4, etc.4 have been successfully supported
onto silica gel and applied as solid acids in various catalytic reactions. TfOH supported on functionalized
silica also had immerged as a powerful catalyst in organic transformations, but the study of TfOH
supported on unmodified chromatographic silica gel is still very rare.5
2
3
Benzofurans are ubiquitous structural motifs in both natural products and synthetic pharmaceuticals.6
Numerous natural products containing the benzofuran framework have been reported to display
significant biological activities such as antitumor,7 antiviral,8 antioxidative,9 and antifungal properties.10
Their broad range of biological activities and significant pharmacological potentials have led to the
development of many methods for their synthesis. Many methods such as palladium-catalyzed
cross-coupling cyclization reaction from alkynes and o-halophenols, palladium-catalyzed enolate
arylation, cyclofragmentation of oxiranes have been developed to synthesize benzofurans.11 These
processes often required tedious work-up and led to large amount of catalysts waste in Lewis acid
catalysis system; And a part of transition metal catalysts were often highly expensive and provided hard
separation of the products. Therefore, the development of a simple, fast and flexible method to generate

libraries of such compounds was desirable.
Our recent studies have been focusing on the development of new synthetic pathways for the preparation
of heterocyclic compounds.12 In this paper, we would like to describe an efficient route to benzofurans via
TfOH-SiO2 catalyzed intramolecular Friedel-Crafts reaction of 2-phenoxy-1-phenylethanones (Scheme 1).
It can obtain target products 3-arylbenzofurans in a high yields and no by-products 2-arylbenzofurans. To
the best of our knowledge, there are no reports for the immobilized Brønsted acid-mediated reaction of
2-phenoxy-1-arylethanones.
Scheme 1. Synthesis of 3-phenylbenzofuran derivatives
Initially,
we
started
to
optimize
the
reaction
conditions
by
using
2-(4-methoxyphenoxy)-1-phenylethanone13 1a as a model substrate (Table 1). Firstly, we chose
1,2-dichloroethane as reaction solvent, the process was investigated in different immobilized catalysts
including HClO4-SiO2, H2SO4-SiO2, TfOH-SiO2 under reflux (Table 1, entries 1-3), the product was
obtained in 22-45% yields, and we observed that the reaction took place smoothly to give the
corresponding product 2a in the best yield in TfOH-SiO2 system.
In order to further improve the efficiency of this procedure, different solvents, including water, methanol,
ethanol, acetonitrile, tetrahydrofuran, dichloromethane, acetone and toluene were used (Table 1, entries
4-10). Results show that the yield of the reaction increased to 77% in the presence of toluene (Table 1,
entry 11). Meanwhile the catalyst loading have a major influence on the yield, when 40 mol% catalysts
resulted in higher reaction yield (Table 1, entry 12). Consequently, the optimum reaction conditions were
determined to be TfOH-SiO2 (40 mol%) in toluene under reflux conditions.
Table 1. Optimization of the reaction conditionsa
MeO
O
catalyst
O
O
solvent
OMe
1a
2a
Entry
1
Catalyst (eq.)
Solvent
Yield (%)b
27
HClO4-SiO2 (0.2 eq.) ClCH2CH2Cl

2
3
H2SO4-SiO2 (0.2 eq.) ClCH2CH2Cl
22
45
TfOH-SiO2 (0.2 eq.)
TfOH-SiO2 (0.2 eq.)
TfOH-SiO2 (0.2 eq.)
TfOH-SiO2 (0.2 eq.)
TfOH-SiO2 0.2 eq.)
TfOH-SiO2 (0.2 eq.)
TfOH-SiO2 (0.2 eq.)
TfOH-SiO2 (0.2 eq.)
TfOH-SiO2 (0.2 eq.)
TfOH-SiO2 (0.4 eq.)
ClCH2CH2Cl
H2O
4
<10
<10
<10
<10
<10
43
5
MeOH
EtOH
6
7
MeCN
THF
8
9
CH2Cl2
acetone
toluene
toluene
10
11
12
49
77
94
a
Reaction condition: Different catalysts were added to a stirred solution of the
2-(4-methoxyphenoxy)-1-phenylethanone (242 mg, 1 mmol) in different solvents (5
mL). The mixture was refluxed for 6 h. Then the crude product was purified by
column chromatography give product 2a. b Isolated yields.
To explore the substrate scope of this protocol, the optimized reaction conditions were applied to
synthesis a series of 3-arylbenzofuran compounds. 2-Phenoxy-1-phenylethanone compounds 1 were
synthesized by using phenols and bromoacetophenones as materials (Table 2). Firstly, the scope of the
substrates with different groups on phenoxy ring was explored. It was pleased to find that the reactions
proceed well. A wide range of functional groups including F, Cl, Br, Me, 4-tert-butyl, 3,4-dimethyl could
be well tolerated, leading to the products in moderate to good yields (Table 2, entries 1-8). Then, a range
of 2-Phenoxy-1-phenylethanone with electronically different substituents on phenylethanone ring were
investigated (Table 2, entries 11-18). The results showed that 2-phenoxy-1-phenylethanone bearing
different groups such as Me, Cl, Br, OMe, also afforded the corresponding 3-phenylbenzofurans 2i-2p in
good to high yields.
Table 2. The reaction of various substrates for the synthesis of 3-phenylbenzofuran derivativesa

Entry
1
R1
H
R2
4-OMe
H
Yield (%)b
94 (2a)
84 (2b)
73 (2c)
88 (2d)
86 (2e)
85 (2f)
93 (2g)
86 (2h)
82 (2i)
2
H
3
H
4-F
4
H
4-Cl
5
H
4-Br
6
H
4-Me
7
H
4-tert-butyl
3,4-dimethyl
4-OMe
4-OMe
4-OMe
4-OMe
4-OMe
4-OMe
4-OMe
4-OMe
8
H
9
2-Cl
4-Cl
4-Br
2-Me
3-Me
4-Me
4-tert-butyl
4-OMe
10
11
12
13
14
15
16
85 (2j)
81 (2k)
88 (2l)
84 (2m)
92 (2n)
74 (2o)
86 (2p)
a
Reaction condition: TfOH-SiO2 (0.4 eq.) was added to a stirred solution of the
2-phenoxy-1-phenylethanone derivatives (1 mmol) in toluene (5 mL). The mixture was
refluxed for 8 h. Then the crude product was purified by column chromatography to give
corresponding product. b Isolated yields.
Extension of these results into a bicyclic series gave the expected product naphtho[2,1-b]furan by cyclize
the 2-naphthoxy-1-phenylethanone. The cyclization of both methyl substituted and halogen substituted
2-naphthoxy-1-phenylethanone proceeded smoothly to afford the corresponding naphthofuran in
moderate to good yields (Table 3).
Table 3. The synthesis of 3-phenylnaphthofuran derivativesa
Entry
1
R1
H
Yield (%)b
86 (2q)

2
3
2-Br
72 (2r)
70 (2s)
3-Me
a
Reaction condition: TfOH-SiO2 (0.4 eq.) was added to a stirred solution of the
2-naphthoxy-1-phenylethanone derivatives (1 mmol) in toluene (5 mL). The mixture was
refluxed for 12 h. Then the crude product was purified by column chromatography to give
corresponding product. b Isolated yields.
Series of benzofuran derivatives having been readily obtained, we decided to evaluate the scope of this
reaction further. Polycyclic compounds 2t-2v were also obtained under the optimum conditions (Scheme
2), it was found that the ring closing reaction proceeded perfectly to generate the product.
Scheme 2. Synthesis of polycyclic compounds
Table 4. The recycling of 0.5 mmol/g of TfOH-SiO2
Entry
Times
Yield (%)a
1
2
3
4
2
3
4
5
92
88
87
87

5
6
85
a Isolated yields. Reaction time was 6 h.
Next,
we
investigated
the
reusability
and
recycling
of
TfOH-SiO2.
2-(4-methoxyphenoxy)-1-phenylethanone was selected as a model reaction under the optimized
conditions. When the reaction was completed, the catalyst was separated by simple filtration and
recovered. TfOH-SiO2 was reused in subsequent reactions without significant decrease in activity even
after six runs (Table 4).
In conclusion, a series of 3-arylbenzofuran derivatives have been synthesized with the catalysis of an
efficient and recyclable solid acid catalyst through direct absorption of TfOH onto very cheap
chromatographic silica gel. TfOH-SiO2 has been applied as the catalyst for intramolecular Friedel-Crafts
reaction of various 2-phenoxy-1-phenylethanones and gave the products in moderate to excellent yields.
The catalyst TfOH-SiO2 can readily be recovered and reused with almost stable reactivity and yields in 6
runs. In comparison with the homogeneous reactions catalyzed by TfOH, the reaction provides a mildness
of the conversion, simple experimental procedure which possesses the potential for application in industry.
Further investigations and the design of new synthetic crafts to expand the usage of this TfOH-SiO2
catalyst to more catalytic organic reactions are ongoing in our laboratory.
EXPERIMENTAL
General. All anhydrous solvents were purified according to standard methods. All commercially
available reagents were used without further purification. Reactions were monitored by thin-layer
chromatography (TLC) on GF 254 plates. Column chromatography was conducted on silica gel (200-300
1
mesh) using compound-appropriate mixtures of petroleum ether and EtOAc as eluent. H- and 13C-NMR
spectra were obtained on a 400 or 500 MHZ NMR spectrometer.
Preparation for catalyst TfOH-SiO2. TfOH (3.06 g, 20 mmol) was added to a stirred Et2O (100 mL) of
silica gel (40.0 g, 200-300 mesh). The mixture was stirred for 60 min at rt. Then, Et2O was removed in
vacuo and the residue was dried at 110 °C for 2 h to afford TfOH-SiO2 (0.5 mmol࣭g-1) as a white powder.
Synthesis of 3-phenylbenzofuran. 1 was dissolved in 5 mL toluene, 40 mol% TfOH-SiO2 was added
and the mixture refluxed for 6-12 h. The reaction was monitored by TLC, the mixture was collected by
filtration after the reaction was finished. The filtrate was purified by column chromatography using
EtOAc/ petroleum ether to give corresponding product 3-arylbenzofuran 2.

1
5-Methoxy-3-phenylbenzofuran (2a). Yellow oil (211 mg, 94%): H-NMR (400 MHz, CDCl3): δ 7.81
(s, 1H), 7.71 – 7.67 (m, 2H), 7.57 – 7.48 (m, 3H), 7.44 (t, J = 7.4 Hz, 1H), 7.35 (d, J = 2.6 Hz, 1H), 7.03
(dd, J = 8.9, 2.6 Hz, 1H), 3.92 (s, 3H); 13C-NMR (100 MHz, CDCl3): δ 156.4, 150.9, 142.2, 132.2, 129.0,
127.5, 127.4, 127.1, 122.4, 113.4, 112.2, 103.0, 56.0. HRMS (ESI) calcd for [C15H12O2+Na]+: 247.0730,
found: 247.0732.
1
3-Phenylbenzofuran (2b). Yellow oil (163 mg, 84%): H-NMR (400 MHz, CDCl3): δ 8.03 – 8.00 (m,
1H), 7.92 (s, 1H), 7.82 – 7.79 (m, 2H), 7.72 (d, J = 8.8 Hz, 1H), 7.64 – 7.60 (m, 2H), 7.54 – 7.49 (m, 2H),
13
7.48 – 7.45 (m, 1H); C-NMR (100MHz, CDCl3): δ 156.0, 141.5, 132.2, 129.1, 127.7, 127.6, 126.6,
124.7, 123.2, 122.4, 120.6, 111.9. HRMS (ESI) calcd for [C14H10O+Na]+: 217.0624, found: 217.0626.
5-Fluoro-3-phenylbenzofuran (2c). Yellow oil (155 mg, 73%): 1H-NMR (400 MHz, CDCl3): δ 7.88 (s,
1H), 7.71 (d, J = 7.3 Hz, 2H), 7.66 – 7.55 (m, 4H), 7.52 (t, J = 7.4 Hz, 1H), 7.21 (m, 1H); 13C-NMR (100
MHz, CDCl3): δ 160.8, 158.5, 152.1, 143.1, 131.7, 129.2, 127.8, 127.4, 122.7, 112.6, 112.5, 106.3.
HRMS (ESI) calcd for [C14H9OF+Na]+: 235.0530, found: 235.0532.
5-Chloro-3-phenylbenzofuran (2d). Yellow oil (201 mg, 88%): 1H-NMR (400 MHz, CDCl3): δ 7.85 (d,
J = 2.0 Hz, 1H), 7.82 (s, 1H), 7.66 – 7.62 (m, 2H), 7.56 – 7.49 (m, 3H), 7.44 (t, J = 7.4 Hz, 1H), 7.36 (dd,
13
J = 8.7, 2.1 Hz, 1H); C-NMR (100 MHz, CDCl3): δ 154.2, 142.5, 131.3, 129.1, 128.8, 127.9, 127.8,
127.5, 124.9, 122.1, 120.1, 112.8. HRMS (ESI) calcd for [C14H9OCl+Na]+: 251.0234, found: 251.0237.
1
5-Bromo-3-phenylbenzofuran (2e). Yellow solid (234 mg, 86%). H-NMR (400 MHz, CDCl3): δ 8.00
(d, J = 1.8 Hz, 1H), 7.81 (s, 1H), 7.63 (d, J = 7.2 Hz, 2H), 7.55 – 7.49 (m, 2H, 7.49 – 7.41 (m, 3H);
13C-NMR (100MHz, CDCl3): δ 154.5, 142.4, 131.3, 129.1, 128.5, 127.8, 127.6, 127.5, 123.2, 122.0,
116.3, 113.3. HRMS (ESI) calcd for [C14H9OBr+Na]+: 271.9837, found: 271.9838.
1
5-Methyl-3-phenylbenzofuran (2f). Pale yellow solid (177 mg, 85%): H-NMR (400 MHz, CDCl3): δ
7.87 (s, 1H), 7.82 – 7.77 (m, 3H), 7.65 – 7.56 (m, 3H), 7.55 – 7.47 (m, 1H), 7.34 – 7.28 (m, 1H), 2.63 (s,
3H); 13C-NMR (100 MHz, CDCl3): δ 154.4, 141.6, 132.6, 132.4, 129.1, 127.6, 127.5, 126.7, 126.0, 122.1,
120.3, 111.4, 21.6. HRMS (ESI) calcd for [C15H12O+Na]+: 231.0780, found: 231.0782.
1
5-(tert-Butyl)-3-phenylbenzofuran (2g). White solid (233 mg, 93%): H-NMR (400 MHz, CDCl3): δ
7.99 (s, 1H), 7.88 (d, J = 1.9 Hz, 1H), 7.83 – 7.76 (m, 2H), 7.67 – 7.60 (m, 3H), 7.59 – 7.47 (m, 2H), 1.55
13
(s, 9H); C-NMR (100 MHz, CDCl3): δ 154.2, 146.2, 141.7, 132.5, 129.1, 127.7, 127.6, 127.5, 126.2,
122.7, 122.6, 116.4, 111.2, 35.0, 32.1. HRMS (ESI) calcd for [C18H18O+Na]+: 273.1250, found:
273.1252.
1
5,6-Dimethyl-3-phenylbenzofuran (2h). Yellow oil (191 mg, 86%): H-NMR (400 MHz, CDCl3): δ
7.91 (d, J = 1.7 Hz, 1H), 7.86 – 7.80 (m, 2H), 7.70 – 7.61 (m, 3H), 7.58 – 7.51 (m, 1H), 7.16 (s, 1H), 2.70
13
(d, J = 23.6 Hz, 3H), 2.64 (s, 3H); C-NMR (100 MHz, CDCl3): δ 153.5, 141.4, 132.7, 129.1, 127.7,
127.4, 127.0, 126.2, 122.4, 121.6, 117.8, 21.6, 15.2. HRMS (ESI) calcd for [C16H14O+Na]+: 245.0937,

found: 245.0938.
1
3-(2-Chlorophenyl)-5-methoxybenzofuran (2i). Yellow oil (212 mg, 82%): H-NMR (400 MHz,
CDCl3): δ 7.86 (s, 1H), 7.61 – 7.55 (m, 2H), 7.51 (d, J = 5.9 Hz, 1H), 7.42 – 7.35 (m, 2H), 7.08 (d, J = 1.7
Hz, 1H), 7.02 (dd, J = 5.9, 1.7 Hz, 1H), 3.87 (s, 3H); 13C-NMR (100 MHz, CDCl3): δ 156.2, 150.1, 144.3,
133.5, 131.5, 130.8, 130.3, 128.9, 127.6, 127.0, 119.5, 113.5, 112.2, 103.2, 56.0. HRMS (ESI) calcd for
[C15H11O2Cl+Na]+: 281.0340, found: 281.0340.
1
3-(4-Chlorophenyl)-5-methoxybenzofuran (2j). Yellow oil (219 mg, 85%): H-NMR (400 MHz,
CDCl3): δ 7.76 (s, 1H), 7.59 – 7.55 (m, 2H), 7.50 – 7.45 (m, 3H), 7.24 (d, J = 2.6 Hz, 1H), 7.00 (dd, J =
13
9.0, 2.6 Hz, 1H), 3.89 (s, 3H); C-NMR (100 MHz, CDCl3): δ 156.4, 150.8, 142.3, 133.2, 130.6, 129.2,
128.6, 126.7, 121.4, 113.4, 112.3, 102.7, 56.0. HRMS (ESI) calcd for [C15H11O2Cl+Na]+: 281.0340,
found: 281.0342.
1
3-(4-Bromophenyl)-5-methoxybenzofuran (2k). Yellow oil (245 mg, 81%): H-NMR (400 MHz,
CDCl3): δ 7.76 (s, 1H), 7.64 – 7.61 (m, 2H), 7.52 – 7.46 (m, 3H), 7.24 (d, J = 2.6 Hz, 1H), 7.01 (dd, J =
13
9.0, 2.6 Hz, 1H), 3.89 (s, 3H); C-NMR (100 MHz, CDCl3): δ 156.4, 150.8, 142.3, 132.2, 131.1, 128.9,
126.6, 121.4, 121.3, 113.4, 112.3, 102.7, 56.0. HRMS (ESI) calcd for [C15H11O2Br+Na]+: 324.9835,
found: 324.9836.
5-Methoxy-3-(o-tolyl)benzofuran (2l). White solid (210 mg, 88%): 1H-NMR (400 MHz, CDCl3): δ 7.71
(s, 1H), 7.60 – 7.50 (m, 2H), 7.50 – 7.38 (m, 3H), 7.12 – 7.02 (m, 2H), 3.90 (s, 3H), 2.46 (s, 3H);
13C-NMR (100MHz, CDCl3): δ 156.3, 150.2, 143.2, 137.1, 131.1, 130.7, 130.5, 128.5, 128.0, 126.0,
121.7, 113.5, 112.2, 102.9, 56.0, 20.6. HRMS (ESI) calcd for [C16H14O2+Na]+: 261.0886, found:
261.0885.
1
5-Methoxy-3-(m-tolyl)benzofuran (2m). White solid (200 mg, 84%): H-NMR (400 MHz, CDCl3): δ
7.86 – 7.81 (m, 1H), 7.59 – 7.52 (m, 3H), 7.52 – 7.45 (m, 1H), 7.45 – 7.39 (m, 1H), 7.30 (d, J = 9.9 Hz,
1H), 7.12 – 7.05 (m, 1H), 3.97 (s, 3H), 2.56 (s, 3H); 13C-NMR (100 MHz, CDCl3): δ 156.3, 150.9, 142.3,
138.7, 132.2, 129.0, 128.3, 128.2, 127.2, 124.6, 122.5, 113.2, 112.2, 103.2, 56.0, 21.6. HRMS (ESI) calcd
for [C16H14O2+Na]+: 261.0886, found: 261.0884.
5-Methoxy-3-(p-tolyl)benzofuran (2n). Yellow oil (219 mg, 92%): 1H-NMR (400 MHz, CDCl3): δ 7.84
(s, 1H), 7.65 (d, J = 8.1 Hz, 2H), 7.56 (d, J = 8.9 Hz, 1H), 7.42 (d, J = 2.9 Hz, 2H), 7.40 (s, 1H), 7.10 (dd,
13
J = 8.9, 2.6 Hz, 1H), 3.97 (s, 3H), 2.54 (s, 3H); C-NMR (100 MHz, CDCl3): δ 156.4, 150.9, 142.1,
137.3, 129.8, 129.3, 127.4, 127.3, 122.4, 113.3, 112.2, 103.1, 56.0, 21.3. HRMS (ESI) calcd for
[C16H14O2+Na]+: 261.0886, found: 261.0888.
1
3-(4-(tert-Butyl)phenyl)-5-methoxybenzofuran (2o). White solid (207 mg, 74%): H-NMR (400 MHz,
CDCl3): δ 7.81 (s, 1H), 7.69 – 7.64 (m, 2H), 7.60 (dd, J = 8.1, 1.2 Hz, 2H), 7.54 – 7.50 (m, 1H), 7.39 (s,
1H), 7.08 – 7.03 (m, 1H), 3.94 (s, 3H), 1.48 (s, 9H); 13C-NMR (100 MHz, CDCl3): δ 156.3, 150.9, 150.5,

142.1, 129.3, 127.2, 126.6, 122.3, 113.4, 112.2, 103.0, 56.0, 34.7, 31.4. HRMS (ESI) calcd for
[C19H20O2+Na]+: 303.1356, found: 303.1356.
1
5-Methoxy-3-(4-methoxyphenyl)benzofuran (2p). White solid (218 mg, 86%): H-NMR (400 MHz,
CDCl3): δ 7.73 (s, 1H), 7.60 – 7.57 (m, 2H), 7.47 (d, J = 5.9 Hz, 1H), 7.28 (d, J = 1.7 Hz, 1H), 7.08 –
13
7.04 (m, 2H), 7.01 – 6.96 (m, 1H), 3.90 (s, 3H), 3.90 (s, 3H); C-NMR (100 MHz, CDCl3): δ 159.1,
156.2, 150.7, 141.6, 128.6, 127.3, 126.4, 124.5, 122.0, 114.5, 114.2, 113.2, 112.2, 102.8, 56.0, 55.9, 55.4.
HRMS (ESI) calcd for [C16H14O3+Na]+: 277.0835, found: 277.0836.
1
3-Penylnaphtho[1,2-b]furan (2q). White solid (210 mg, 86%): H-NMR (400 MHz, CDCl3): δ 8.45 –
8.42 (m, 1H), 8.22 – 8.17 (m, 1H), 7.99 (d, J = 0.8 Hz, 2H), 7.92 (s, 1H), 7.91 – 7.87 (m, 2H), 7.78 – 7.64
13
(m, 5H); C-NMR (100 MHz, CDCl3): δ 153.5, 142.0, 133.5, 131.2, 130.2, 129.3, 128.9, 128.7, 128.2,
126.4, 124.8, 124.7, 123.8, 121.1, 113.0. HRMS (ESI) calcd for [C18H12O+Na]+: 267.0780, found:
267.0782.
1
3-(2-Bromophenyl)naphtho[1,2-b]furan (2r). Yellow oil (232 mg, 72%): H-NMR (500 MHz, CDCl3):
δ 8.46 (d, J = 8.2 Hz, 1H), 8.02 (t, J = 4.1 Hz, 2H), 7.83 (dd, J = 8.0, 1.0 Hz, 1H), 7.76 (d, J = 8.6 Hz, 1H),
7.72 – 7.65 (m, 2H), 7.59 (ddd, J = 8.0, 4.2, 1.8 Hz, 2H), 7.47 (m, J = 7.5, 0.9 Hz, 1H), 7.32 (m, J = 7.8,
1.7 Hz, 1H).13C NMR (126 MHz, CDCl3): δ 150.72, 142.41, 133.56, 132.93, 131.97, 131.65, 129.34,
128.42, 127.54, 126.56, 125.46, 123.93, 123.60, 122.80, 122.37, 121.69, 120.16, 119.34. HRMS (ESI)
calcd for [C18H11BrO+Na]+: 321.9991, found: 321.9993. IR (KBr) ν (cm-1): 3138, 3060, 2962, 2962, 2925,
2850, 1952, 1921, 1811, 1749, 1601, 1563, 1522, 1465, 1431, 1384, 1219, 1154, 1112, 1050, 755, 726.
3-(m-Tolyl)naphtho[1,2-b]furan (2s). Yellow oil (180 mg, 70%): 1H NMR (500 MHz, CDCl3): δ 8.46 (d,
J = 8.2 Hz, 1H), 8.04 (d, J = 8.2 Hz, 1H), 7.99 (t, J = 4.3 Hz, 1H), 7.80 (d, J = 8.6 Hz, 1H), 7.74 – 7.67
13
(m, 1H), 7.61 (dd, J = 11.0, 4.0 Hz, 1H), 7.52 – 7.45 (m, 1H), 7.31 (d, J = 7.5 Hz, 1H), 2.55 (s, 1H). C
NMR (126 MHz, CDCl3): δ 151.52, 140.56, 138.73, 132.20, 131.60, 128.99, 128.45, 128.36, 128.35,
126.49, 125.40, 124.86, 123.68, 123.66, 122.08, 121.73, 120.21, 118.93, 21.64. HRMS (ESI) calcd for
[C19H14O+Na]+: 258.1043, found: 258.1045. IR (KBr) ν (cm-1): 3133, 3058, 2922, 2854, 1943, 1811,
1744, 1610, 1520, 1456, 1383, 1255, 1113, 1035, 775, 746.
10-Methyl-5,6-dihydronaphtho[2,1-b]benzofuran (2t). Yellow oil (101 mg, 43%): 1H NMR (500 MHz,
CDCl3): δ 7.84 – 7.76 (m, 1H), 7.43 (d, J = 8.3 Hz, 1H), 7.40 – 7.35 (m, 1H), 7.30 (dd, J = 10.2, 3.4 Hz,
1H), 7.22 (m, J = 7.4, 1.2 Hz, 1H), 7.15 (dd, J = 8.3, 1.2 Hz, 1H), 3.20 (t, J = 7.9 Hz, 1H), 3.08 (dd, J =
13
12.0, 4.6 Hz, 1H), 2.57 (s, 1H). C NMR (126 MHz, CDCl3): δ 156.83, 153.65, 133.54, 132.55, 131.86,
128.10, 126.91, 125.82, 124.54, 122.74, 119.99, 113.26, 110.90, 29.38, 22.42, 21.61. HRMS (ESI) calcd
for [C17H14O+Na]+: 234.1047, found: 234.1045. IR (KBr) ν (cm-1): 3056, 3019, 2925, 2851, 1948, 1907,
1862, 1739, 1619, 1500, 1465, 1378, 1340, 1230, 1151, 1020, 765, 745, 732.
1
5,6-Dihydrodinaphtho[1,2-b:1’,2’-d]furan (2u). Yellow oil (178 mg, 66%): H NMR (500 MHz,

CDCl3): δ 8.50 (d, J = 8.2 Hz, 1H), 8.14 (d, J = 8.6 Hz, 1H), 8.08 (d, J = 8.2 Hz, 1H), 7.98 (d, J = 7.7 Hz,
1H), 7.85 (d, J = 8.5 Hz, 1H), 7.80 – 7.73 (m, 1H), 7.68 – 7.61 (m, 1H), 7.50 (td, J = 7.4, 1.1 Hz, 1H),
13
7.40 (d, J = 6.9 Hz, 1H), 7.35 (td, J = 7.4, 1.0 Hz, 1H), 3.31 – 3.26 (m, 2H), 3.26 – 3.20 (m, 2H). C
NMR (126 MHz, CDCl3): δ 155.77, 150.55, 133.85, 131.95, 131.02, 128.50, 128.35, 127.13, 126.53,
126.16, 124.96, 123.78, 122.97, 121.63, 121.22, 120.02, 118.99, 114.89, 29.66, 22.58. HRMS (ESI) calcd
for [C20H14O+Na]+: 270.1046, found: 270.1045. IR (KBr) ν (cm-1): 3053, 2933, 2904, 2840, 1941, 1797,
1695, 1617, 1570, 1524, 1449, 1374, 1341, 1235, 1075, 760, 742, 727.
1
8,9-Dihydrodinaphtho[2,1-b:1’,2’-d]furan-2-ol (2v). Yellow oil (115 mg, 40%): H NMR (400 MHz,
CDCl3): δ 8.08 (dd, J = 10.4, 4.7 Hz, 1H), 7.88 (d, J = 8.8 Hz, 1H), 7.68 (d, J = 8.8 Hz, 1H), 7.53 (d, J =
8.8 Hz, 1H), 7.36 (d, J = 7.6 Hz, 1H), 7.22 (d, J = 6.8 Hz, 1H), 7.14 (dd, J = 8.8, 2.4 Hz, 1H), 6.01 (s, 1H),
3.12 (d, J = 7.5 Hz, 1H), 3.01 (d, J = 7.6 Hz, 1H). 13C NMR (101 MHz, CDCl3): δ 157.36, 153.55, 153.52,
134.94, 132.19, 130.98, 129.18, 128.29, 126.84, 126.28, 125.88, 125.06, 124.84, 119.04, 116.19, 115.60,
110.08, 108.14, 30.29, 22.78. HRMS (ESI) calcd for [C20H14O2+Na]+: 286.0995, found: 286.0994. IR
(KBr) ν (cm-1): 3503, 3459, 3046, 2942, 2888, 2827, 1906, 1770, 1710, 1620, 1529, 1462, 1355, 1284,
1177, 1027, 762, 740.
ACKNOWLEDGEMENTS
This work was supported by National Natural Science Foundation of China (51273156).
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14. The products 2a, 2b, 2d, 2e, 2f, 2g, 2j, 2n, 2p and 2q are known compounds.