Catalyst-free synthesis of 1-phenylnaphtho[2,1-b]furan derivatives under microwave irradiation

Article abstract of DOI:10.3987/COM-16-13487

An environmentally benign and efficient method has been developed for the synthesis of naphtho[2,1-b]furan from (E)-(2-nitrovinyl)benzene and naphthalen-2-ol in brine media under catalyst-free conditions through microwave-assisted technology. The advantag

Full text of DOI:10.3987/COM-16-13487

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HETEROCYCLES, Vol. 92, No. 8, 2016
HETEROCYCLES, Vol. 92, No. 8, 2016, pp. 1468 - 1478. © 2016 The Japan Institute of Heterocyclic Chemistry
Received, 21st April, 2016, Accepted, 10th June, 2016 Published online, 24th June, 2016
DOI: 10.3987/COM-16-13487
CATALYST-FREE SYNTHESIS OF 1-PHENYLNAPHTHO[2,1-b]FURAN
DERIVATIVES UNDER MICROWAVE IRRADIATION
Baolong Wang,1 Jinfu Zhang,1 Jianhong Liao,1 Yiyuan Peng,2* and Hua
Zheng1*
1School of Chemistry, Chemical Engineering and Life Sciences, Wuhan
2
University of Technology, Wuhan, Hubei, P. R. China. School of Chemistry,
Jiangxi Normal University, Nanchang, Jiangxi, P. R. China
E-mail:zhenghuawhut@163.com
Abstract – An environmentally benign and efficient method has been developed
for the synthesis of naphtho[2,1-b]furan from (E)-(2-nitrovinyl)benzene and
naphthalen-2-ol in brine media under catalyst-free conditions through
microwave-assisted technology. The advantages of this process are that it is
catalyst-free, has an easy work-up, provides good yields, and uses brine as the
solvent which is considered to be relatively environmentally benign.
Green chemistry, which emphasizes the development of environmentally benign chemical processes and
technologies has attracted much attention in recent years.1 Organic solvents represent the biggest
pollution problem in many synthetic organic processes.2 Water as a green reaction medium has gained
considerable interest in view of its low cost, safety, and environmentally benign properties.3 Furthermore,
catalyst-free reaction protocols in water will also be one of the most suitable strategies, which will meet
the requirements of green chemistry as well as develop libraries of medicinal scaffolds.4
Heterocyclic rings are of remarkable biological and chemical significance in many fields,5 including
biological field and pharmaceutical field. Naphthofurans are important classes of heterocyclic compounds
that are present as key structural motifs in many pharmaceuticals and biologically active natural products6
(Figure 1). Some naturally occurring substances in this family exhibit a variety of interesting
pharmacological properties such as anticancer,7 anti-inflammatory,8 regulators of the nuclear receptor
HNF4R,9 and imaging agents for β-amyloid plaques in the brain10 and many others.11

HETEROCYCLES, Vol. 92, No. 8, 2016
1469
Figure 1. Biologically important molecules of naphtho[2,1-b]furan compounds
Considerable attention has been directed toward the synthesis of compounds with naphtho[2,1-b]furan
framework because of their remarkable biological activities. In more recent years, a wider variety of
efficient methods have been developed for the synthesis of naphtho[2,1-b]furan. Among which. the more
approaches are via the cyclization reactions of allyl naphthols or allyl iodonaphthyl ethers promoted by
metal catalysts such as Cu and Pd.12 More recently, Rao and his co-workers also reported an efficient and
simple strategy using sequential hydroarylation of naphthols and alkynes in the presence of In(OTf)3
under microwave irradiation followed by one-pot Heck-oxyarylation of generated
1-substituted-α-hydroxystyrenes.13 And Hajra also used In(OTf)3 catalyst for the coupling of nitroalkenes
with naphthols into naphthofurans.14 In addition, there is another way to synthesis naphthofurans, that is
using acid-catalyst.15 It also can prepare naphthofurans in a high yield.
A number of methods have been developed for the synthesis of 2,3-diarylbenzofurans, but synthetic
routes for naphthofurans are limited. Most of the existing methods suffer from certain liminations with
respect to yield, substrate scope, or apparative requirements, and are not suitable for the preparation of
compound libraries.16 The synthesis of diversified naphthofurans still presents a major challenge in
organic synthesis. Therefore, the development of a versatile method to synthesize substituted
naphtho[2,1-b]furans is highly desired.
Our recent studies have been focusing on the development of new synthetic pathways for the preparation
of heterocyclic compounds.17 We report herein an environmentally benign and efficient method for the
synthesis of naphtho[2,1-b]furans from naphthalen-2-ol and (E)-(2-nitrovinyl)benzene via tandem
reaction through microwave-assisted technology. To the best of our knowledge, this is the first report of
the synthesis of naphtho[2,1-b]furan derivatives under catalyst-free conditions in aqueous media.
Initially, we explored the tandem reaction of (E)-(2-nitrovinyl)benzene 1a (29.8 mg, 0.2 mmol) and
o
naphthalen-2-ol 2a (57.6 mg, 0.4 mmol) in different solvents (5 mL) at 170 C for 25 min under

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HETEROCYCLES, Vol. 92, No. 8, 2016
microwave-assisted condition. As shown in Table 1, we attempted a range of solvents including dimethyl
sulfoxide, dimethylformamide, acetonitrile, ethyl alcohol and water (Table 1, entries 1-9). It was pleased
to find that the reaction using water-ethanol mixtures as the solvent gave the product 3a in higher yields,
and the yields increased with the increasing of proportion of water (Table 1, entries 5-8). And the
corresponding product was obtained in 65% yield in the presence of pure water. Other mixed solvent such
as t-butyl alcohol-water also yielded a lower result for this conversion (Table 1, entry 9). From the above
results, the reaction showed a good reactivity in high polar solvent. In order to further improve the yield,
saturated brine was tested for this reaction, the results showed that the yield of the reaction increased to
70% in the presence of 5 mL saturated brine (Table 1, entry 10). It may be assumed that brine has a high
concentration and great polarity. When saturated brine was used as a solvent, the reaction temperature can
increase stably and rapidly. And reaction temperature is higher than the pure water's boiling point.
Meanwhile reactant molecule can vibrate at a high speed. So the reaction can complete in a short period
of time. Further investigation reveals the reaction time also affects the addition result (Table 1, entries
11-13), meanwhile 25 min was found to be the most suitable time for the reaction. But when acids, such
as TsOH, or weak bases, such as NaHCO3 or K2CO3 were employed as promoter, the yields of products
were moderate (Table 1, entries 15-17). From the economical and environmental point of view, saturated
brine was chosen as the reaction medium for all further reactions.
To further explore the scope of this protocol, we decided to investigate the reaction of
(E)-(2-nitrovinyl)benzene 1 and naphthalen-2-ol 2 in saturated brine as solvent under catalyst-free
conditions (Table 2). The scope of the reaction was examined and the results are shown in Table 2.
Table 1. Optimization of reaction conditionsa

HETEROCYCLES, Vol. 92, No. 8, 2016
1471
Entry
1
Solvent
DMSO
Time
25 min
25 min
25 min
25 min
25 min
25 min
25 min
25 min
25 min
25 min
10 min
20 min
30 min
10 h
Yield (%)b
21
2
DMF
25
3
MeCN
27
4
EtOH
37
5
EtOH:H2O=1:5
EtOH:H2O=1:10
EtOH:H2O=1:20
H2O
49
6
55
7
60
8
65
9
t-BuOH:H2O=1:20
saturated brine
saturated brine
saturated brine
saturated brine
saturated brine
saturated brine
saturated brine
saturated brine
51
10
11
12
13
14c
15d
16e
17f
70
60
63
68
46
12 h
34
12 h
59
12 h
43
a A mixture of (E)-(2-nitrovinyl)benzene 1a (29.8 mg, 0.2 mmol) and naphthalen-2-ol
2a (57.6 mg, 0.4 mmol) without a catalyst in different solvents (5 mL) was placed
into a sealed glass vessel together with a Teflon-coated magnetic stirring bar and
o
b
c
heated in a microwave reactor for the time at the 170 C. Isolated yields. The
d
reaction was carried out under reflux conditions. Under reflux conditionsˈnot
microwave irradiation conditions, TsOH as promoter. e Under reflux conditionsˈ not
f
microwave irradiation conditions, NaHCO3 as promoter. Under reflux conditionsˈ
not microwave irradiation conditions, K2CO3 as promoter.

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Table 2. Reaction of substituted naphtho[2,1-b]furans under optimized conditionsa
R1
NO2
MW, 170 oC
OH
R1
+
R2
O
saturated brine
R2
2
1
3
3a, 63%
3e, 70%
3i, 52%
3m, 64%
3b, 88%
3f, 54%
3j, 53%
3n, 77%
3c, 76%
3g, 59%
3k, 60%
3o, 62%
3d, 72%
3h, 64%
3l, 80%
3p, 0%
a Reaction conditions: 1 (0.2 mmol), 2 (0.4 mmol) were stirred in
saturated brine in sealing microwave reaction tube. Isolated yields based
on 1. The average yields of 3 times reactions
Firstly, we investigated a variety of (E)-(2-nitrovinyl)benzenes under the similar reaction conditions.
Most of products got moderate to good yields, especially when the nitro was touched to the ring of
benzene (Table 2, 3b-3d). However, substrates with electron-donating groups and halogen groups
(chlorine and bromine) afforded lower yields (Table 2, 3f-3j). In summary we added different group onto
the benzene ring of the 2-naphthol or the (E)-(2-nitrovinyl)benzene, Obviously, those almost reacted well

HETEROCYCLES, Vol. 92, No. 8, 2016
1473
(Table 2, 3k-3o). It is a pity that methyl 1-(p-tolyl)naphtho[2,1-b]furan-7-carboxylate does not react with
(E)-1-methyl-4-(2-nitrovinyl)benzene under the reaction conditions described above (Table 2, 3p). For
synthetic
utility,
(E)-1-methyl-4-(2-nitrovinyl)benzene
(1e,
10
mmol)
and
(E)-1-bromo-4-(2-nitrovinyl)benzene (1j, 10 mmol) react with naphthalen-2-ol (20 mmol) on the
condition to give the corresponding products in 49% and 31% yields, respectively.
Presumably, this process involves Michael addition of naphthols to unsaturated nitroalkenes followed by
subsequent cyclization, thereby leading to the final product. We assumed that the formation of the final
product need two steps (A and B), as shown in Scheme 1. We thought that the initial formation of Michael
adduct (A) leads to the furan moiety after successive intramolecular cyclization followed by elimination
-
of H2 and nitroxyl (HNO2 ) from the intermediate (B). Although it was so hard to detect for the detailed
process, we deduced that the Michael adduct gave the final product in high yield at specific conditions.
All in all, it is clear that the selected conditions enhanced the rate of formation of the final product.
OH
MW, 170 oC
NO2
O
saturated brine, 25 min
-H2
-HNO2
O
H
N OH
H
O
Ph
Ph
H
N
H
O
OH
O
A
B
Scheme 1. Proposed mechanism for the efficient reaction
We have developed an efficient, catalyst-free, step-economic, and eco-friendly method for the synthesis
of naphtho[2,1-b]furan from (E)-(2-nitrovinyl)benzene and naphthalen-2-ol under microwave irradiation
conditions in saturated brine media as a green reaction medium. The simple work-up, mild reaction
conditions and high yields make this new strategy attractive for the preparation of a wide variety of
biologically relevant naphtho[2,1-b]furan. The investigation of the applications and the design of new
synthetic crafts for these products are ongoing in our laboratory.
EXPERIMENTAL

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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
13
mesh) using compound-appropriate mixtures of petroleum ether and EtOAc as eluent. H and C NMR
spectra were obtained on a 500 or 600 MHZ NMR spectrometer.
Synthesis of 1-phenylnaphtho[2,1-b]furan derivatives. Compound 1 (0.2 mmol) and compound 2 (0.4
mmol) were stirred in saturated brine in sealing microwave reaction tube. Then the reaction irradiated in a
o
microwave reactor for 25 min at the 170 C. After the completion of the reaction, the solution was
extracted by EtOAc (3×10 mL). The organic solution removed under reduced pressure and the residue
was purified by column chromatography to afford the desired products 3.
1
1-Phenylnaphtho[2,1-b]furan (3a). (31 mg, 63%): H NMR (500 MHz, CDCl3) δ 8.13 (d, J = 8.3 Hz,
1H), 8.03 (d, J = 8.1 Hz, 1H), 7.85 (d, J = 9.0 Hz, 1H), 7.78 (dd, J = 13.7, 7.5 Hz, 2H), 7.71 (dt, J = 3.4,
13
1.9 Hz, 2H), 7.63 – 7.51 (m, 4H), 7.46 (ddd, J = 8.2, 7.0, 1.3 Hz, 1H). C NMR (126 MHz, CDCl3) δ
153.28, 141.80, 133.23, 130.94, 129.98, 129.03, 128.70, 128.46, 127.97, 126.09, 126.07, 124.56, 124.47,
123.49, 120.84, 112.75. IR (KBr) ν (cm-1): 3055, 2960, 1814, 1584, 1444, 1385, 1252, 1027, 948.
1-(2-Nitrophenyl)naphtho[2,1-b]furan (3b). (48 mg, 88%): 1H NMR (500 MHz, CDCl3) δ 8.18 (dd, J =
8.1, 1.3 Hz, 1H), 7.98 (d, J = 8.1 Hz, 1H), 7.83 (dd, J = 9.1, 5.3 Hz, 1H), 7.78 – 7.68 (m, 3H), 7.64 (tdd, J
= 9.0, 6.4, 2.7 Hz, 2H), 7.56 (dd, J = 9.6, 5.2 Hz, 1H), 7.47 (ddd, J = 8.1, 7.0, 1.2 Hz, 1H), 7.38 (ddd, J =
13
10.6, 5.9, 2.4 Hz, 1H). C NMR (126 MHz, CDCl3) δ 152.96, 149.90, 141.53, 133.51, 132.97, 130.89,
129.53, 129.10, 128.12, 127.98, 126.47, 126.38, 124.68, 124.62, 122.46, 121.38, 119.45, 112.67. IR (KBr)
ν (cm-1): 3063, 2965, 1815, 1614, 1528, 1447, 1348, 1263, 1146, 996. HRMS (ESI) calcd for
[C18H11NO3+Na]+: 312.0637, found: 312.0633.
1
1-(4-Nitrophenyl)naphtho[2,1-b]furan (3c). (44 mg, 76%): H NMR (500 MHz, CDCl3) δ 8.40 (d, J =
8.6 Hz, 2H), 7.99 (t, J = 8.4 Hz, 1H), 7.91 (d, J = 8.3 Hz, 1H), 7.87 – 7.71 (m, 5H), 7.50 (dd, J = 11.1, 3.9
13
Hz, 1H), 7.46 – 7.40 (m, 1H). C NMR (126 MHz, CDCl3) δ 153.59, 147.59, 142.27, 140.33, 131.00,
130.50, 129.29, 127.88, 126.75, 126.43, 124.78, 123.92, 122.98, 122.82, 119.85, 112.67. IR (KBr) ν
(cm-1): 3070, 2960, 1886, 1601, 1516, 1443, 1344, 1251, 1059, 863.
1
1-(3-Nitrophenyl)naphtho[2,1-b]furan (3d). (40 mg, 72%): H NMR (500 MHz, CDCl3) δ 8.51 (t, J =
1.9 Hz, 1H), 8.43 – 8.33 (m, 1H), 8.03 – 7.94 (m, 2H), 7.89 – 7.81 (m, 2H), 7.78 – 7.69 (m, 3H), 7.53 –

HETEROCYCLES, Vol. 92, No. 8, 2016
1475
7.46 (m, 1H), 7.42 (ddd, J = 8.2, 7.0, 1.3 Hz, 1H). 13C NMR (126 MHz, CDCl3) δ 153.46, 148.49, 142.29,
135.87, 135.11, 130.96, 129.61, 129.28, 127.91, 126.65, 126.43, 124.73, 124.54, 122.89, 122.79, 122.44,
119.99, 112.68. IR (KBr) ν (cm-1): 3050, 2959, 1898, 1593, 1515, 1430, 1349, 1251, 1059, 867. HRMS
(ESI) calcd for [C18H11NO3+Na]+: 312.0637, found: 312.0639.
1
1-(p-Tolyl)naphtho[2,1-b]furan (3e). (36 mg, 70%): H NMR (500 MHz, CDCl3) δ 8.16 (d, J = 8.3 Hz,
1H), 8.03 (d, J = 7.9 Hz, 1H), 7.84 (d, J = 9.0 Hz, 1H), 7.81 – 7.74 (m, 2H), 7.60 (d, J = 8.0 Hz, 2H), 7.53
(ddd, J = 9.3, 6.6, 2.6 Hz, 1H), 7.46 (ddd, J = 8.2, 6.9, 1.3 Hz, 1H), 7.41 (d, J = 7.8 Hz, 2H), 2.57 (s, 3H).
13C NMR (126 MHz, CDCl3) δ 153.24, 141.71, 137.69, 130.91, 130.14, 129.84, 129.41, 128.99, 128.52,
126.02, 125.95, 124.46, 124.41, 123.53, 120.95, 112.74, 21.43. IR (KBr) ν (cm-1): 3048, 2946, 1884, 1594,
1498, 1443, 1341, 1251, 1059, 861.
1
1-(4-Methoxyphenyl)naphtho[2,1-b]furan (3f). (30 mg, 54%): H NMR (500 MHz, CDCl3) δ 8.18 –
8.13 (m, 1H), 8.02 (d, J = 7.6 Hz, 1H), 7.84 (d, J = 9.0 Hz, 1H), 7.78 (dd, J = 7.3, 3.6 Hz, 1H), 7.74 (s,
1H), 7.63 – 7.59 (m, 2H), 7.53 (ddd, J = 8.1, 7.0, 1.3 Hz, 1H), 7.47 (ddd, J = 10.4, 5.9, 2.4 Hz, 1H), 7.16
13
– 7.11 (m, 2H), 3.97 (s, 3H). C NMR (126 MHz, CDCl3) δ 159.53, 153.20, 141.67, 131.10, 130.92,
129.01, 128.54, 126.06, 125.94, 125.29, 124.42, 124.12, 123.45, 121.08, 114.16, 112.75, 55.40. IR (KBr)
ν (cm-1): 3001, 2952, 1880, 1591, 1497, 1461, 1342, 1242, 1062, 947.
1-(2-Methoxyphenyl)naphtho[2,1-b]furan (3g). (32 mg, 59%): 1H NMR (500 MHz, CDCl3) δ 8.01 (d, J
= 8.1 Hz, 1H), 7.89 – 7.77 (m, 4H), 7.60 – 7.48 (m, 3H), 7.46 – 7.41 (m, 1H), 7.21 – 7.13 (m, 2H), 3.77 (s,
13
3H). C NMR (126 MHz, CDCl3) δ 158.01, 153.01, 142.00, 131.99, 130.80, 129.81, 128.90, 128.67,
125.85, 125.71, 124.25, 123.53, 122.15, 121.79, 120.76, 120.51, 112.78, 111.01, 55.49. IR (KBr) ν (cm-1):
3055, 2933, 1906, 1626, 1510, 1462, 1343, 1239, 1061, 948. HRMS (ESI) calcd for [C19H14O2+Na]+:
297.0891, found: 297.0890.
1-(2-Chlorophenyl)naphtho[2,1-b]furan (3h). (36 mg, 64%): 1H NMR (500 MHz, CDCl3) δ 8.04 (d, J =
8.1 Hz, 1H), 7.87 (d, J = 9.0 Hz, 1H), 7.82 (t, J = 7.3 Hz, 2H), 7.77 (d, J = 8.3 Hz, 1H), 7.70 (dd, J = 8.0,
13
1.2 Hz, 1H), 7.64 – 7.59 (m, 1H), 7.50 (m, 4H). C NMR (126 MHz, CDCl3) δ 152.99, 142.22, 135.29,
132.52, 132.36, 130.87, 129.94, 129.80, 128.89, 128.49, 126.99, 126.37, 126.16, 124.59, 123.16, 121.39,
121.38, 112.76. IR (KBr) ν (cm-1): 3059, 2926, 1925, 1670, 1526, 1468, 1342, 1226, 1079, 950. HRMS
(ESI) calcd for [C18H11OCl+Na]+: 301.0396, found: 301.0398.
1
1-(4-Chlorophenyl)naphtho[2,1-b]furan (3i). (29 mg, 52%): H NMR (500 MHz, CDCl3) δ 8.01 (dd, J
= 11.8, 4.1 Hz, 2H), 7.82 (d, J = 9.0 Hz, 1H), 7.75 (d, J = 9.0 Hz, 1H), 7.70 (d, J = 6.2 Hz, 1H), 7.60 –

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HETEROCYCLES, Vol. 92, No. 8, 2016
7.48 (m, 5H), 7.45 (ddd, J = 8.2, 7.0, 1.4 Hz, 1H). 13C NMR (126 MHz, CDCl3) δ 153.29, 141.79, 134.00,
131.66, 131.20, 130.91, 129.10, 128.91, 128.23, 126.24, 126.20, 124.55, 123.39, 123.22, 120.51, 112.69.
IR (KBr) ν (cm-1): 3065, 2924, 1900, 1621, 1521, 1482, 1381, 1226, 1058, 859.
1
1-(4-Bromophenyl)naphtho[2,1-b]furan (3j). (37 mg, 53%): H NMR (500 MHz, CDCl3) δ 8.03 (dd, J
= 15.9, 8.1 Hz, 2H), 7.83 (d, J = 9.0 Hz, 1H), 7.76 (d, J = 8.9 Hz, 1H), 7.70 (dd, J = 6.2, 4.3 Hz, 3H), 7.56
13
– 7.49 (m, 3H), 7.48 – 7.44 (m, 1H). C NMR (126 MHz, CDCl3) δ 153.34, 141.77, 132.17, 131.88,
131.53, 130.94, 129.14, 128.25, 126.29, 126.25, 124.60, 123.43, 123.25, 122.16, 120.45, 112.71. IR (KBr)
ν (cm-1): 3062, 2955, 1902, 1621, 1550, 1479, 1381, 1178, 1098, 945. HRMS (ESI) calcd for
[C18H11OBr+Na]+: 344.9891, found: 344.9889.
1
1-(Naphthalen-1-yl)naphtho[2,1-b]furan (3k). (35 mg, 60%): H NMR (500 MHz, CDCl3) δ 8.10 –
7.95 (m, 3H), 7.91 – 7.79 (m, 4H), 7.74 – 7.63 (m, 2H), 7.59 – 7.52 (m, 1H), 7.44 – 7.31 (m, 3H), 7.15
13
(ddd, J = 8.2, 7.0, 1.1 Hz, 1H). C NMR (126 MHz, CDCl3) δ 153.03, 142.54, 133.72, 133.06, 130.84,
130.57, 128.78, 128.70, 128.35, 128.34, 128.27, 126.55, 126.40, 126.23, 126.15, 126.08, 125.58, 124.37,
123.56, 122.24, 121.97, 112.73. IR (KBr) ν (cm-1): 3055, 2926, 1928, 1624, 1554, 1449, 1382, 1187, 1059,
931.
1-(p-Tolyl)naphtho[2,1-b]furan-8-ol (3l). (44 mg, 80%): 1H NMR (500 MHz, CDCl3) δ 7.86 (d, J = 8.8
Hz, 1H), 7.71 (d, J = 8.9 Hz, 1H), 7.65 (s, 1H), 7.57 (dd, J = 8.9, 3.9 Hz, 1H), 7.53 – 7.49 (m, 2H), 7.35
13
(dt, J = 14.2, 6.9 Hz, 3H), 7.06 (dd, J = 8.8, 2.5 Hz, 1H), 5.35 – 4.96 (m, 1H), 2.48 (s, 3H). C NMR
(126 MHz, CDCl3) δ 153.74, 153.66, 141.29, 137.68, 130.84, 130.01, 129.82, 129.64, 129.34, 125.91,
125.79, 124.19, 119.76, 115.47, 110.33, 106.42, 21.33. IR (KBr) ν (cm-1): 3364, 3069, 2917, 1900, 1625,
1529, 1439, 1319, 1178, 1022, 864. HRMS (ESI) calcd for [C19H14O2+Na]+: 297.0891, found: 297.0892.
1
7-Bromo-1-(p-tolyl)naphtho[2,1-b]furan (3m). (45 mg, 64%): H NMR (600 MHz, CDCl3) δ 8.12 (s,
1H), 7.96 (d, J = 8.9 Hz, 1H), 7.77 – 7.70 (m, 2H), 7.68 (d, J = 9.0 Hz, 1H), 7.55 – 7.46 (m, 3H), 7.38 (d,
13
J = 7.7 Hz, 2H), 2.54 (s, 3H). C NMR (151 MHz, CDCl3) δ 153.16, 142.05, 137.88, 132.16, 130.86,
129.68, 129.64, 129.48, 129.14, 126.87, 125.12, 124.85, 124.22, 121.03, 118.10, 113.76, 21.42. IR (KBr)
ν (cm-1): 3052, 2941, 1893, 1562, 1452, 1467, 1301, 1089, 890.
3-(p-Tolyl)naphtho[1,2-b]furan (3n). (40 mg, 77%): 1H NMR (500 MHz, CDCl3) δ 8.39 (d, J = 8.2 Hz,
1H), 7.99 (d, J = 8.2 Hz, 1H), 7.95 – 7.88 (m, 2H), 7.76 (d, J = 8.6 Hz, 1H), 7.68 – 7.60 (m, 3H), 7.59 –
13
7.52 (m, 1H), 7.35 (d, J = 7.8 Hz, 2H), 2.47 (s, 3H). C NMR (126 MHz, CDCl3) δ 151.42, 140.28,
137.30, 131.51, 129.72, 129.25, 128.29, 127.58, 126.42, 125.32, 123.58, 123.44, 122.08, 121.66, 120.14,

HETEROCYCLES, Vol. 92, No. 8, 2016
1477
118.85, 21.28. IR (KBr) ν (cm-1): 3052, 2919, 1908, 1597, 1516, 1457, 1385, 1082, 1015, 808. HRMS
(ESI) calcd for [C19H14O+Na]+: 281.0942, found: 281.0943.
1
8-Methoxy-1-(p-tolyl)naphtho[2,1-b]furan (3o). (36 mg, 62%): H NMR (500 MHz, CDCl3) δ 7.87 (d,
J = 8.9 Hz, 1H), 7.78 – 7.68 (m, 2H), 7.59 (dd, J = 17.1, 8.3 Hz, 3H), 7.46 – 7.33 (m, 3H), 7.18 – 7.10 (m,
13
1H), 3.65 (s, 3H), 2.52 (s, 3H). C NMR (126 MHz, CDCl3) δ 157.77, 153.69, 141.17, 137.63, 130.29,
130.10, 129.98, 129.61, 129.14, 125.77, 125.63, 124.21, 120.25, 116.24, 110.20, 103.17, 54.97, 21.35. IR
(KBr) ν (cm-1): 3019, 2952, 1907, 1628, 1522, 1471, 1378, 1228, 1022, 822. HRMS (ESI) calcd for
[C19H14O+Na]+: 311.1048, found: 311.1051.
ACKNOWLEDGEMENTS
This work was supported by National Natural Science Foundation of China (51273156).
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