Triflic Acid-Catalyzed Cycloisomerization Reactions of Donor-Acceptor Cyclopropanes: Access to Alkyl 5-Arylfuran-2-carboxylates

Article abstract of DOI:10.1021/acs.joc.6b00161

A direct synthetic strategy starting from alkyl 1-alkoxy-2-aroylcyclopropanecarboxylates was developed for the construction of alkyl 5-arylfuran-2-carboxylates. These donor-acceptor cyclopropanes smoothly undergo a simple ring-opening reaction or/and cycl

Full text of DOI:10.1021/acs.joc.6b00161

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Triflic Acid Catalyzed Cycloisomerization Reactions of Donor
-Acceptor Cyclopropanes: Access to Alkyl 5-Arylfuran-2-carboxylates
Yuequan Zhu, Panpan Xu, and Yuefa Gong
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b00161 • Publication Date (Web): 08 May 2016
Downloaded from http://pubs.acs.org on May 8, 2016
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Triflic Acid Catalyzed Cycloisomerization Reactions of Donor−Acceptor
Cyclopropanes: Access to Alkyl 5-Arylfuran-2-carboxylates
Yuequan Zhu, Panpan Xu and Yuefa Gong*
School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology,
1037 Luoyu Road, Wuhan 430074, People’s Republic of China
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RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to
the journal that you are submitting your paper to)
* To whom correspondence should be addressed. gongyf@mail.hust.edu.cn. Phone: +86 027 87543232. Fax: +86
027 87543632.
X
O
TfOH
DCM, rt
COOR
Ar
Ar
COOR
O
18 examples
yield up to 99%
A direct synthetic strategy starting from alkyl 1-alkoxy-2-aroylcyclopropanecarboxylates was
developed for the construction of alkyl 5-arylfuran-2-carboxylates. These donor-acceptor
cyclopropanes smoothly undergo simple ring-opening reaction or/and cycloisomerization reaction in
the presence of acid at room temperature, greatly depending on the property of the acids used in the
experiments. Alkyl 5-arylfuran-2-carboxylates were afforded in high yields in triflic acid, whereas
alkyl 2,5-dioxo-5-phenylpentanoate became the major product in other protic acids and Lewis acids.
2, 5-Disubstituted furans are one kind of the most important polysubstituted furans. This feature
structure is not only widely present in many natural products1 and pharmaceuticals2, but also can be
utilized as versatile synthetic building block.3 Although some synthetic methods for substituted
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furans have already been reported,4 the main approaches to 2, 5-disubstituted furans involve the
introduction of designated groups in existing furan precursors,5 and the generation of furan ring by
metal-catalyzed cyclization of unsaturated alcohols, unsaturated ketones, and haloalkynes or 1,
3-diynes with ketones or aldehydes.6 These methods, however, suffer from different disadvantages
such as limitation of substrates, harsh reaction conditions, or poor chemoselectivity. Therefore, it is
still of great importance to develop new and efficient synthetic strategy for various 2, 5-disubstituted
furans.
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As useful three-carbon synthon, cyclopropanes with donor and acceptor substituents in the
vicinal positions (donor-acceptor cyclopropanes) have attracted much attention from synthetic
chemists for their successful application in the construction of natural products.7 Since the high
polarization of one of three C-C bonds of the ring, donor-acceptor cyclopropanes are readily
transformed into useful 1, 3-dipoles via ring-opening reaction by treatment with Lewis acids or bases.
These 1, 3-dipoles easily participate in formal [3 + n] (n = 2, 3, 4) cycloaddition reactions with
various suitable dipolarophiles to yield carbocyclic or heterocyclic compounds.8 In addition,
donor-acceptor cyclopropanes as appropriate candidates can also undergo cyclodimerization in the
absence of dipolarophiles or other reagents.9 Recently, we reported a cycloisomerization between
alkyl 2-acyl-1-chlorocyclopropanecarboxylates with aliphatic amines under basic conditions, which
mainly gave 2-pyrone derivatives.10 The key intermediate was assigned to be alkyl
2-acyl-1-aminocyclopropanecarboxylates generated in situ in the above reaction. The analogous
alkyl 2-acyl-1-alkoxycyclopropanecarboxylates 1, however, could not undergo spontaneous
cycloisomerization under the above conditions. Interestingly, a cycloisomerization product, ethyl
5-phenylfuran-2-carboxylate 2a, was obtained when the substrate 1a was treated with triflic acid. In
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fact, the cycloisomerization of donor-acceptor cyclopropanes to substituted furans was scarcely
reported.11 To our knowledge, this is the first transition metal-free example for direct construction of
2, 5-disubstituted furans from donor-acceptor cyclopropanes. Therefore, the reaction details were
carefully investigated and depicted as follows.
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At the beginning of our study, the reaction of substrate 1a, prepared easily by treatment of alkyl
2-acyl-1-chlorocyclopropanecarboxylates with phenol in presence of Cs2CO3 in acetonitrile, was
used as a probe for evaluating the effect of the properties of acids and solvents on the reaction. The
observed results are summarized in Table 1. Treatment of 1a with one equivalent amount of
concentrated H2SO4, CH3SO3H or BF3.Et2O in dichloromethane (DCM) at room temperature mainly
afforded ethyl 2,5-dioxo-5-phenylpentanoate 3a in 72%, 98% or 69% yields within 10 h, respectively,
as well as a little amount of the desired product 2a (Table 1, entries 1-3). Typical Lewis acids such as
anhydrous FeCl3 and AlCl3 were also tested, and besides the main product 3a, the cycloisomerization
product 2a was also isolated in 19% and 14% yields, respectively (Table 1, entries 4, 5). In order to
assess the effect of acid strength on the reaction, triflic acid (TfOH) as the strongest protic acid was
also employed to promote the above reaction. An unexpected result was observed in this case, where
2a was isolated in 75% yield as the main product without any 3a (Table 1, entry 6). A detectable
decline in the yield of 2a appeared when the loading of TfOH was decreased from 1.0 equiv. to 0.5
equiv. (Table 1, entry 7). On the contrary, increasing the loading of TfOH from 1.0 equiv. to 1.5 or
2.0 equiv. can markedly accelerate the reaction, and a satisfied yield of 2a was obtained in the case
of 2.0 equiv. (Table 1, entries 8, 9). These observations clearly indicate that the acid property plays
an important role in this transformation.
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Next, the influence of solvent on the reaction was estimated using TfOH as the promoter. Some
common solvents such as toluene, CH3CN and DMF were chosen for the purpose. As shown in Table
1, the yield observed in toluene was slightly lower than that in DCM (entry 10), and a further decline
appeared in CH3CN (entry 11). To our surprise, almost no any reaction occurred when the reaction
was conducted in DMF, a well-known aprotic polar solvent with certain alkalinity, even with
extending the reaction time to 24 h (Table 1, entry 12). Therefore, we believe that the property of
solvent also has a marked influence on the reaction, and nonpolar and weakly polar solvents favored
this tandem process. Based on the above observations, 2.0 equiv. of TfOH and DCM were employed
as the suitable acid and solvent in the following experiments.
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Table 1. Optimization of the Reaction Parameters a
O
O
O
Ph
COOEt
COOEt
OPh
acid
COOEt
Ph
+
Ph
solvent, rt
O
2a
3a
1a
yield (%)b
entry
catalyst
solvent
T (h)
2a
3a
72
98
69
64
64
--
1
2
3
4
5
6
7
8
H2SO4 (1 equiv.)
CH3SO3H (1 equiv.)
BF3.Et2O (1 equiv.)
FeCl3 (1 equiv.)
DCM
DCM
DCM
DCM
DCM
DCM
10
10
10
10
10
10
10
3
trace
trace
trace
19
AlCl3 (1 equiv.)
14
CF3SO3H (1 equiv.)
75
CF3SO3H (0.5 equiv.) DCM
CF3SO3H (1.5 equiv.) DCM
55
--
76
--
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CF3SO3H (2 equiv.)
CF3SO3H (2 equiv.)
CF3SO3H (2 equiv.)
CF3SO3H (2 equiv.)
DCM
2
80
76
70
--
--
--
--
--
10
11
12
toluene
CH3CN
DMF
1
1
24
a General conditions: 1a (0.2 mmol), catalyst, solvent (3.0 mL) at r.t.. b Isolated yield.
With the optimal conditions in hand, various donor-acceptor cyclopropanes were next examined.
All the observed results are listed in Table 2. It is clear that the electronic property of 2-aroyl group
exerts a definite influence on both the reaction time and the product yield. Substrates 1b-c with
electron-donating Me and MeO groups showed a relatively lower reactivity in comparison with
substrates 1d-f with electron-withdrawing Cl and Br groups (Table 2, entries 4-6). For example, the
reaction of 1c bearing a 4-MeO group was completed after 3 h, whereas that of 1f with a 2-Br group
finished within 0.5 h. In the case of 1g with a 4-biphenyl group, the reaction proceeded quickly,
giving the desired product 2g in an excellent yield of 91% (entry 7). In addition, the reaction of
substrate 1h with a 2-furanyl group gave a complicated mixture (Table 2, entry 8), whereas that of
substrate 1i with 2-thienyl group gave the desired product 2i in 63% yield (Table 2, entry 9). The big
difference in product distribution may be due to the facile polymerization of furan derivative caused
by the strong acid TfOH.
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Table 2. Effect of Ar Group on the Cycloisomerization Reactions of Donor-acceptor
Cyclopropanesa
O
TfOH
OPh
O
Ar
COOEt
Ar
COOEt
DCM, rt
1a-1i
2a-2i
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entry
Ar
T (h)
2
product
yield (%)b
1
1
2
3
4
5
6
7
8
C6H5
80
87
83
84
78
97
91
1a
1b
1c
1d
1e
1f
2a
2b
2c
2d
2e
2f
4-MeC6H4
4-MeOC6H4
4-ClC6H4
4-BrC6H4
2-BrC6H4
4-PhC6H4
2-furyl
2
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3
1
1
0.5
1
1g
1h
1i
2g
--c
2i
0.5
1
9
2-thienyl
63
a
General conditions: 1 (0.2 mmol), TfOH (0.4 mmol) in DCM (3.0 mL) at room
temperature. b Isolated yield. c Complicated mixture.
Moreover, steric effect of ester group on the reaction was also investigated. The results listed in
Table 3 clearly show that the methyl ester 1j-1m provided the highest yield (Table 3, entries 1-4),
and the bulky t-butyl ester 1n gave a complicated mixture, owing to its chemical instability (t-Bu+)
(Table 3, entry 5). When R was (CH2)2Cl and benzyl, this reaction also can occur under the same
conditions in moderate yields (Table 3, entries 6, 7). Next, substrates with different substituted
phenoxy groups were explored under the optimized conditions. In fact, the leaving phenoxy group
had scarcely effect on the reaction (Table 3, entries 8, 9). The presence of 2-propynyloxy or
morpholinyl groups instead of phenoxy group, led to the formation of a small amount of hydrolysis
product 3a, besides the deserved product 2a (Table 3, entries 10, 11). The reaction did not happen
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when X is Cl, on account of its electronic property (Table 3, entry 12). Obviously, the electronic
property of leaving group has a big effect on the cycloisomerization of this reaction.
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Table 3. Effect of Ester group and X group on Cycloisomerization Reactions of Donor-acceptor
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Cyclopropanesa
O
X
O
TfOH
Ar
COOR
Ar
COOR
DCM, rt
1j-1u
2j-2p
entry substrate 1
T (h)
1
product
yield (%)b
1
Ar=C6H5, R=Me, X=OPh 1j
80
2j
2
Ar=4-MeOC6H4, R=Me, X=OPh 1k
Ar=4-ClC6H4, R=Me, X=OPh 1l
Ar=4-PhC6H4, R=Me, X=OPh 1m
Ar=C6H5, R=t-Bu, X=OPh 1n
1
78
2k
2l
3
1
94
4
0.5
1
99
2m
--
5c
6
--
Ar=C6H5, R=(CH2)2Cl, X=OPh 1o
Ar=C6H5, R=Bn, X=OPh 1p
1
2o
2p
2j
60
7
1
36
8
Ar=C6H5, R=Me, X=4-MeOC6H4O 1q
Ar=C6H5, R=Me, X=4-ClC6H4O 1r
Ar=C6H5, R=Et, X=OCH2C≡CH 1s
Ar=C6H5, R=Et, X=morpholinyl 1t
Ar=C6H5, R=Et, X=Cl 1u
1
85
9
1
84
2j
10
11
12
12
24
54(21)d
57(36)d
--
2a
2a
--
12e
a
General conditions: 1 (0.2 mmol), TfOH (0.4 mmol) in DCM (3.0 mL) at room
b
c
d
e
temperature. Isolated yield. Complex mixture. Yield of 3a in parentheses. No
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reaction.
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In order to understand the mechanistic detail of this tandem reaction, some control experiments
were also performed (Scheme 1). In the presence of 50% aqueous TfOH, the substrate 1a can also be
converted into 3a completely in 80% yield, almost without the formation of the desired product 2a
(eq. a). Moreover, when additional 2 equiv. of TfOH was added into the untreated reaction mixture
obtained by treatment of 1a with 1 equiv. of CH3SO3H in DCM at room temperature, the reaction
continued and gave the expected product 2a in 86% yield (eq. b). Furthermore, 2-ketoester 3a
isolated from the reaction mixture can directly turn into ethyl 5-phenylfuran-2-carboxylate 2a in the
presence of 2 equiv. TfOH at room temperature in DCM in 78% yield (eq. c). From the above
observations, we believe that the acid strength has a crucial role in the tandem reaction, and
2-ketoester 3 would be the key intermediate of this reaction.
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Scheme 1. Mechanistic Study for the Cycloisomerization
O
O
50%TfOH/
2 equiv.
DCM, rt
COOEt
OPh
COOEt
Ph
(a)
Ph
O
1a
3a 80%
O
O
CH3SO3H/
1 equiv.
DCM, rt
TfOH/
O
COOEt
OPh
COOEt
Ph
2 equiv.
DCM, rt
Ph
Ph
(b)
1a
2a 86%
TfOH/ 2 equiv.
DCM, rt
O
COOEt
COOEt
2a 78%
Ph
(c)
O
3a
On the basis of our above findings, we proposed a possible mechanism for this tandem process
to rationalize the formation of substituted furans (Scheme 2). At the beginning, the donor acceptor
cyclopropane was protonated in the presence of TfOH, and the protonation weakened the C1-C2
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bond of donor-acceptor cyclopropanes by polarization. The presence of electron-donating group at
C1 site prompted the ring-opening reaction to furnish the reactive intermediate I. The latter was
smoothly transformed into the product 5-phenylfuran-2-carboxylates through the cycloisomerization
and removal of phenol. Simultaneously, the presence of water caused the competitive hydrolysis of
the intermediate I to afford 2-ketoester 3. Actually in presence of TfOH, 2-ketoeste 3 can be directly
converted into alkyl 5-phenylfuran-2-carboxylates via continuous cycloisomerization and
dehydration.
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Scheme 2. Proposed Mechanism for Cycloisomerization
O
O
COOR
TfOH
Ar
X
Ar
COOR
DCM, rt
2
1
H
t
r
O
f
,
T
M
C
H
O
D
COOR
O
Ar
COOR
O
H
COOR
Ar
O
X
3
X
Ar
n
H2O
o
i
t
a
z
i
r
r
i
n
e
H
O
g
OR
m
o
o
s
O
p
i
e
o
l
n
c
y
i
n
Ar
X
c
g
I
In conclusion, we have developed a simple and direct approach for the synthesis of alkyl
5-phenylfuran-2-carboxylates from donor-acceptor cyclopropanes under transition metal-free
conditions. The operational simplicity, ready availability of starting materials, and good chemical
yields make this novel synthetic method appealing in diversity-oriented synthesis. And this protocol
is expected to find considerable applications in the synthesis of functionized furans, a structural
motif for a large number of pharmaceuticals and functional materials.
Experiment Section
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General Methods All reagents and solvents were of commercial grade and purified prior to use
when necessary. Reactions were monitored by TLC analysis using silica gel 60 Å F-254 thin layer
plates. Flash column chromatography was performed on silica gel 60 Å, 10-40 μm. All 1H NMR and
13C NMR spectra were recorded on a 400 MHz spectrometer with solvent resonances as the internal
standard (1H NMR: CDCl3 at 7.26 ppm; 13C NMR: CDCl3 at 77.0 ppm). The following abbreviations
are used to describe peak patterns where appropriate: s = singlet, d = doublet, t = triplet q = quartet,
m = multiplet, and br s = broad signal. All coupling constants (J) are given in Hz. IR spectra were
recorded on an infrared spectrometer. Melting point was recorded on a melting point detector. HRMS
was measured on a TOF-Q mass spectrometer equipped with an ESI technique.
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Typical Procedure for Synthesis of ethyl 2-benzoyl-1-phenoxycyclopropanecarboxylate 1a
Ethyl 2-benzoyl-1-chlorocyclopropanecarboxylate (10 mmol) was added to a solution of phenol (10
mmol) and Cs2CO3 (22 mmol) in 20mL CH3CN, the mixture was stirred at room temperature. The
reaction was monitored by TLC until the ethyl 2-benzoyl-1-chlorocyclopropanecarboxylate
disappeared completely. The mixture was quenched with water and extracted with CH2Cl2.
Combined extracts were dried over anhydrous Na2SO4 and concentrated under reduced pressure. The
residue was purified by silica gel column chromatography using petroleum ether and ethyl acetate as
eluent to afford the corresponding product 1a in 97% yield. Unless otherwise specified, all other
products 1 were synthesized according to this typical procedure.
Typical Procedure for the Preparation of 5-phenylfuran-2-carboxylate 2a
To a solution of TfOH (0.034 mL; 0.4 mmol) in anhydrous dichloromethane (3 mL) was slowly
added donor acceptor cyclopropane 1a (0.2 mmol). The reaction mixture was stirred at room
temperature and followed by TLC until all the substrate 1a disappeared. The mixture was quenched
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with water, and the organic layer was separated. The layer was washed with water and dried
(anhydrous Na2SO4), and the solvent was removed under reduced pressure. The crude product was
purified by flash chromatography (silica gel, petroleum ether-EtOAc, 30:1) to afford the product 2a.
Unless otherwise specified, all other products 2 were obtained according to this typical procedure.
Typical Experiment Procedure for Product 3a
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Compounds 1a (0.2 mmol) and CH3SO3H (0.2 mmol) were added into 3 mL of anhydrous DCM, and
the mixture was stirred at room temperature. The reaction was followed by TLC until all the
substrate 1a disappeared. The mixture was quenched with water, and the organic layer was separated.
The layer was washed with water and dried (anhydrous Na2SO4), and the solvent was removed under
reduced pressure. The residue was purified by silica gel column chromatography using petroleum
ether and ethyl acetate as eluent to afford the product 3a.
Ethyl 2-benzoyl-1-phenoxycyclopropanecarboxylate (1a)
Colorless viscous liquid (total 3.0 g, 97% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 8.00 –
7.94 (m, 2H), 7.51 – 7.42 (m, 3H), 7.20 – 7.13 (m, 2H), 6.94 – 6.89 (m, 1H), 6.85 – 6.80 (m, 2H),
4.35 – 4.27 (m, 2H), 3.64 (dd, J = 8.9, 7.8 Hz, 1H), 2.27 (dd, J = 7.7, 5.4 Hz, 1H), 2.02 (dd, J = 9.0,
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5.4 Hz, 1H), 1.24 (t, J = 7.1 Hz, 3H). C NMR (101 MHz, CDCl3) δ 191.5, 170.7, 157.2, 137.7,
133.3, 129.2, 128.7, 128.4, 122.0, 115.8, 63.9, 62.3, 33.8, 20.0, 14.2. HRMS (ESI) m/z: Calcd for
C19H18O4Na [M+Na]+: 333.1103. Found: 333.1112.
Ethyl 2-(4-methylbenzoyl)-1-phenoxycyclopropanecarboxylate (1b)
Yellowish viscous liquid (total 3.2 g, 98% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.76
(d, J = 8.2 Hz, 2H), 7.12 (d, J = 7.9 Hz, 2H), 7.03 (t, J = 7.9 Hz, 2H), 6.77 (dd, J = 14.1, 6.8 Hz, 1H),
6.70 (t, J = 8.2 Hz, 2H), 4.21 – 4.11 (m, 2H), 3.51 (dd, J = 8.8, 7.9 Hz, 1H), 2.26 (s, 3H), 2.13 (dt, J
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= 11.0, 5.5 Hz, 1H), 1.88 (dd, J = 9.0, 5.4 Hz, 1H), 1.10 (t, J = 7.1 Hz, 3H). C NMR (101 MHz,
CDCl3) δ 190.9, 170.6, 157.3, 144.1, 135.3, 129.4, 129.2, 128.5, 121.9, 115.8, 63.8, 62.2, 33.7, 21.7,
19.8, 14.2. HRMS (ESI) m/z: Calcd for C20H20O4Na [M+Na]+: 347.1259. Found: 347.1264.
Ethyl 2-(4-methoxybenzoyl)-1-phenoxycyclopropanecarboxylate (1c)
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Yellowish viscous liquid (total 2.8 g, 81% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.97
(t, J = 9.2 Hz, 2H), 7.14 (t, J = 8.0 Hz, 2H), 6.90 (dd, J = 13.0, 7.0 Hz, 2H), 6.85 – 6.78 (m, 3H),
4.27 (qd, J = 7.1, 2.7 Hz, 2H), 3.80 (s, 3H), 3.64 – 3.57 (m, 1H), 2.24 (dd, J = 7.7, 5.4 Hz, 1H), 1.98
(dd, J = 9.0, 5.4 Hz, 1H), 1.21 (t, J = 7.1 Hz, 3H). 13C NMR (101 MHz, CDCl3) δ 189.8, 170.7,
163.7, 157.3, 130.7, 129.2, 121.9, 115.8, 113.9, 63.7, 62.3, 55.5, 33.5, 19.8, 14.2. HRMS (ESI) m/z:
Calcd for C20H20O5Na [M+Na]+: 363.1208. Found: 363.1211.
Ethyl 2-(4-chlorobenzoyl)-1-phenoxycyclopropanecarboxylate (1d)
Yellowish viscous liquid (total 3.1 g, 89% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.79
(t, J = 8.4 Hz, 2H), 7.30 (t, J = 5.2 Hz, 2H), 7.04 (ddd, J = 12.3, 6.6, 4.9 Hz, 2H), 6.79 (t, J = 7.4 Hz,
1H), 6.69 (dd, J = 7.6, 4.1 Hz, 2H), 4.21 – 4.12 (m, 2H), 3.49 (dd, J = 8.9, 7.8 Hz, 1H), 2.20 – 2.12
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(m, 1H), 1.90 (dt, J = 17.2, 8.6 Hz, 1H), 1.10 (t, J = 7.1 Hz, 3H). C NMR (101 MHz, CDCl3) δ
190.4, 170.5, 157.2, 139.7, 136.0, 129.8, 129.2, 129.0, 122.1, 115.8, 64.0, 62.4, 33.6, 20.1, 14.1.
HRMS (ESI) m/z: Calcd for C19H17ClO4Na [M+Na]+: 367.0713. Found: 367.0719.
Ethyl 2-(4-bromobenzoyl)-1-phenoxycyclopropanecarboxylate (1e)
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Yellow solid (total 3.4 g, 88% yield): mp 44-46 C; Major isomer: H NMR (400 MHz, CDCl3) δ
7.85 – 7.78 (m, 2H), 7.64 – 7.58 (m, 2H), 7.20 – 7.13 (m, 2H), 6.93 (t, J = 7.4 Hz, 1H), 6.80 (dd, J =
8.7, 0.9 Hz, 2H), 4.30 (qd, J = 7.1, 2.1 Hz, 2H), 3.58 (dd, J = 8.9, 7.8 Hz, 1H), 2.26 (dd, J = 7.7, 5.5
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Hz, 1H), 2.02 (dd, J = 9.0, 5.5 Hz, 1H), 1.24 (t, J = 7.1 Hz, 3H). C NMR (101 MHz, CDCl3) δ
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190.5, 170.5, 157.1, 136.4, 132.0, 129.8, 129.2, 128.5, 122.1, 115.8, 63.9, 62.4, 33.6, 20.1, 14.1.
HRMS (ESI) m/z: Calcd for C19H17BrO4Na [M+Na]+: 411.0208. Found: 411.0217.
Ethyl 2-(2-bromobenzoyl)-1-phenoxycyclopropanecarboxylate (1f)
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Yellowish viscous liquid (total 3.8 g, 98% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.60
(d, J = 7.7 Hz, 1H), 7.33 (d, J = 4.1 Hz, 2H), 7.30 – 7.27 (m, 1H), 7.23 (dd, J = 8.5, 7.5 Hz, 2H), 6.99
(dd, J = 9.1, 5.7 Hz, 1H), 6.89 (d, J = 7.8 Hz, 2H), 4.28 – 4.22 (m, 2H), 3.53 (dd, J = 8.8, 7.8 Hz, 1H),
2.24 (dd, J = 7.7, 5.5 Hz, 1H), 2.09 (dd, J = 8.9, 5.5 Hz, 1H), 1.21 (t, J = 7.1 Hz, 3H). 13C NMR (101
MHz, CDCl3) δ 194.5, 170.1, 157.4, 141.2, 133.8, 132.2, 129.9, 129.3, 127.5, 122.2, 119.6, 116.0,
65.1, 62.3, 37.3, 21.4, 14.2. HRMS (ESI) m/z: Calcd for C19H17BrO4Na [M+Na]+: 411.0208. Found:
411.0201.
Ethyl 2-(biphenylcarbonyl)-1-phenoxycyclopropanecarboxylate (1g)
Yellowish viscous liquid (total 3.8 g, 99% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 8.04
(d, J = 8.3 Hz, 2H), 7.69 (d, J = 8.4 Hz, 2H), 7.66 – 7.61 (m, 2H), 7.47 (t, J = 7.5 Hz, 2H), 7.41 (d, J
= 7.3 Hz, 1H), 7.17 (dd, J = 11.3, 4.7 Hz, 2H), 6.92 (t, J = 7.4 Hz, 1H), 6.84 (d, J = 8.0 Hz, 2H), 4.36
– 4.26 (m, 2H), 3.67 (dd, J = 8.8, 7.9 Hz, 1H), 2.29 (dd, J = 7.7, 5.5 Hz, 1H), 2.03 (dt, J = 13.1, 6.5
Hz, 1H), 1.25 (t, J = 7.1 Hz, 3H). 13C NMR (101 MHz, CDCl3) δ 191.0, 170.7, 157.3, 145.9, 139.9,
136.4, 129.2, 129.0, 129.0, 128.3, 127.3, 122.0, 115.6, 63.9, 62.3, 33.9, 20.0, 14.2. HRMS (ESI) m/z:
Calcd for C25H22O4Na [M+Na]+: 409.1416. Found: 409.1409.
Ethyl 2-(furan-2-carbonyl)-1-phenoxycyclopropanecarboxylate (1h)
White solid (total 2.6 g, 86% yield): mp 46-49 oC; Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.61
(d, J = 0.9 Hz, 1H), 7.23 – 7.12 (m, 3H), 6.90 (dd, J = 14.8, 7.4 Hz, 1H), 6.88 – 6.80 (m, 2H), 6.53
(dd, J = 3.6, 1.7 Hz, 1H), 4.35 – 4.22 (m, 2H), 3.65 (dd, J = 9.0, 7.9 Hz, 1H), 2.27 (dd, J = 7.8, 5.4
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Hz, 1H), 1.98 (dd, J = 9.1, 5.4 Hz, 1H), 1.22 (t, J = 7.1 Hz, 3H). C NMR (101 MHz, CDCl3) δ
179.9, 170.4, 157.2, 153.4, 146.5, 129.1, 121.9, 117.2, 115.6, 112.6, 63.9, 62.3, 33.3, 19.8, 14.1.
HRMS (ESI) m/z: Calcd for C17H16O5Na [M+Na]+: 323.0895. Found: 323.0902.
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Ethyl 1-phenoxy-2-(thiophene-2-carbonyl)cyclopropanecarboxylate (1i)
White solid (total 3.1 g, 99% yield): mp 44-47 oC; Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.81
(dd, J = 3.8, 0.9 Hz, 1H), 7.62 (dd, J = 4.9, 0.9 Hz, 1H), 7.15 (ddd, J = 17.0, 6.2, 2.9 Hz, 3H), 6.91 (t,
J = 7.4 Hz, 1H), 6.87 – 6.82 (m, 2H), 4.35 – 4.22 (m, 2H), 3.57 (dd, J = 9.0, 7.7 Hz, 1H), 2.24 (dd, J
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= 7.6, 5.5 Hz, 1H), 2.00 (dd, J = 9.1, 5.5 Hz, 1H), 1.22 (t, J = 7.1 Hz, 3H). C NMR (101 MHz,
CDCl3) δ 183.7, 170.5, 157.2, 144.9, 134.1, 132.3, 129.2, 128.2, 122.0, 115.8, 63.8, 62.3, 34.3, 20.1,
14.1. HRMS (ESI) m/z: Calcd for C17H16O4SNa [M+Na]+: 339.0667. Found: 339.0659.
Methyl 2-benzoyl-1-phenoxycyclopropanecarboxylate (1j)
Colorless viscous liquid (total 2.7 g, 92% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 8.01 –
7.89 (m, 2H), 7.57 (dd, J = 14.8, 7.4 Hz, 1H), 7.45 (t, J = 7.6 Hz, 2H), 7.16 (t, J = 8.0 Hz, 2H), 6.90
(dd, J = 16.6, 9.3 Hz, 1H), 6.81 (d, J = 8.5 Hz, 2H), 3.81 (s, 3H), 3.65 (t, J = 8.4 Hz, 1H), 2.27 (dd, J
= 7.7, 5.5 Hz, 1H), 2.02 (dd, J = 9.0, 5.5 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 191.3, 171.2, 157.2,
137.6, 133.3, 129.3, 128.7, 128.3, 122.1, 115.8, 63.7, 53.2, 33.9, 20.1. HRMS (ESI) m/z: Calcd for
C18H16O4Na [M+Na]+: 319.0946. Found: 319.0939.
Methyl 2-(4-methoxybenzoyl)-1-phenoxycyclopropanecarboxylate (1k)
White solid (total 2.9 g, 90% yield): mp 73-75 oC; Major isomer: 1H NMR (400 MHz, CDCl3) δ 8.04
(d, J = 8.7 Hz, 2H), 7.28 (t, J = 7.6 Hz, 2H), 7.00 (t, J = 9.0 Hz, 2H), 6.92 (t, J = 7.4 Hz, 2H), 6.81 (d,
J = 8.0 Hz, 1H), 3.81 (s, 3H), 3.49 (s, 3H), 3.17 (t, J = 9.4 Hz, 1H), 2.45 (dd, J = 8.1, 6.3 Hz, 1H),
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1.68 (dt, J = 16.6, 8.3 Hz, 1H). C NMR (101 MHz, CDCl3) δ 190.8, 168.9, 163.9, 156.7, 130.9,
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129.6, 122.1, 115.7, 115.5, 113.9, 63.5, 63.4, 55.5, 52.5, 35.5, 19.8. HRMS (ESI) m/z: Calcd for
C19H18O5Na [M+Na]+: 349.1054. Found: 349.1049.
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Methyl 2-(4-chlorobenzoyl)-1-phenoxycyclopropanecarboxylate (1l)
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Yellowish viscous liquid (total 3.0 g, 91% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.89
(d, J = 8.5 Hz, 2H), 7.43 (d, J = 8.6 Hz, 2H), 7.17 (t, J = 8.0 Hz, 2H), 6.92 (t, J = 7.4 Hz, 1H), 6.80
(d, J = 8.0 Hz, 2H), 3.82 (s, 3H), 3.61 (dd, J = 15.3, 6.6 Hz, 1H), 2.27 (dd, J = 7.6, 5.6 Hz, 1H), 2.03
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(dd, J = 9.0, 5.5 Hz, 1H). C NMR (101 MHz, CDCl3) δ 190.2, 171.1, 157.1, 139.8, 135.9, 129.7,
129.3, 129.0, 122.2, 115.7, 63.8, 53.3, 33.7, 20.2. HRMS (ESI) m/z: Calcd for C18H15ClO4Na
[M+Na]+: 353.0557. Found: 353.0548.
Methyl 2-(biphenylcarbonyl)-1-phenoxycyclopropanecarboxylate (1m)
White solid (total 3.2 g, 85% yield): mp 95-97 oC; Major isomer: 1H NMR (400 MHz, CDCl3) δ 8.03
(d, J = 8.3 Hz, 2H), 7.68 (d, J = 8.4 Hz, 2H), 7.65 – 7.60 (m, 2H), 7.49 – 7.42 (m, 2H), 7.39 (dd, J =
13.4, 6.1 Hz, 1H), 7.17 (t, J = 8.0 Hz, 2H), 6.92 (t, J = 7.4 Hz, 1H), 6.83 (d, J = 8.4 Hz, 2H), 3.82 (s,
3H), 3.68 (t, J = 8.4 Hz, 1H), 2.29 (dd, J = 7.6, 5.5 Hz, 1H), 2.04 (dd, J = 9.0, 5.4 Hz, 1H). 13C NMR
(101 MHz, CDCl3) δ 190.8, 171.3, 157.2, 146.0, 139.8, 136.4, 129.3, 129.0, 129.0, 128.3, 127.3,
122.1, 115.8, 63.7, 53.3, 34.0, 20.1. HRMS (ESI) m/z: Calcd for C24H20O4Na [M+Na]+: 395.1259.
Found: 395.1248.
t-Butyl 2-benzoyl-1-phenoxycyclopropanecarboxylate (1n)
Yellowish viscous liquid (total 3.3 g, 99% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 8.03
– 7.88 (m, 2H), 7.56 (dd, J = 14.6, 7.3 Hz, 1H), 7.51 – 7.41 (m, 2H), 7.17 – 7.11 (m, 2H), 6.88 (dd, J
= 13.9, 6.6 Hz, 1H), 6.83 (t, J = 9.7 Hz, 2H), 3.61 (t, J = 8.3 Hz, 1H), 2.29 – 2.21 (m, 1H), 2.03 –
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128.7, 128.3, 121.8, 115.7, 83.1, 64.4, 33.2, 27.9, 19.8. HRMS (ESI) m/z: Calcd for C21H22O4Na
[M+Na]+: 361.1416. Found: 361.1411.
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2-Chloroethyl 2-benzoyl-1-phenoxycyclopropanecarboxylate (1o)
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Yellowish viscous liquid (total 2.9 g, 83% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.99
(dd, J = 11.8, 4.6 Hz, 2H), 7.58 (t, J = 7.4 Hz, 1H), 7.47 (t, J = 7.7 Hz, 2H), 7.17 (dt, J = 10.0, 5.0 Hz,
2H), 6.96 – 6.90 (m, 1H), 6.84 (d, J = 7.9 Hz, 2H), 4.58 – 4.42 (m, 2H), 3.72 – 3.63 (m, 3H), 2.29 (dt,
J = 9.3, 4.6 Hz, 1H), 2.11 – 1.99 (m, 1H). 13C NMR (101 MHz, CDCl3) δ 191.2, 170.3, 157.1, 137.6,
133.3, 129.3, 128.7, 128.4, 122.2, 115.9, 65.2, 63.5, 41.3, 34.1, 19.9. HRMS (ESI) m/z: Calcd for
C19H17ClO4Na [M+Na]+: 367.0713. Found: 367.0708.
Benzyl 2-benzoyl-1-phenoxycyclopropanecarboxylate (1p)
Yellowish viscous liquid (total 3.3 g, 90% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.90
(d, J = 8.3 Hz, 2H), 7.52 (t, J = 7.4 Hz, 1H), 7.45 – 7.36 (m, 2H), 7.27 (dd, J = 8.4, 5.1 Hz, 2H), 7.19
(dd, J = 6.4, 2.6 Hz, 3H), 7.16 – 7.10 (m, 2H), 6.89 (dd, J = 10.8, 3.9 Hz, 1H), 6.83 – 6.78 (m, 2H),
5.25 (d, J = 2.8 Hz, 2H), 3.63 – 3.54 (m, 1H), 2.30 – 2.22 (m, 1H), 2.02 (dd, J = 9.0, 5.5 Hz, 1H). 13C
NMR (101 MHz, CDCl3) δ 191.3, 170.5, 157.2, 137.6, 135.3, 133.3, 129.3, 128.7, 128.6, 128.5,
128.4, 128.1, 122.1, 115.9, 67.8, 63.8, 33.9, 19.8. HRMS (ESI) m/z: Calcd for C24H20O4Na [M+Na]+:
395.1259. Found: 395.1251.
Methyl 2-benzoyl-1-(4-methoxyphenoxy)cyclopropanecarboxylate (1q)
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White solid (total 3.2 g, 97% yield): mp 118-119 C; Major isomer: H NMR (400 MHz, CDCl3) δ
7.96 (d, J = 7.4 Hz, 2H), 7.56 (t, J = 7.2 Hz, 1H), 7.50 – 7.42 (m, 2H), 6.76 (t, J = 8.4 Hz, 2H), 6.70
(d, J = 9.1 Hz, 2H), 3.84 (s, 3H), 3.70 (s, 3H), 3.66 – 3.58 (m, 1H), 2.25 (dd, J = 7.6, 5.5 Hz, 1H),
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133.2, 128.7, 128.3, 116.9, 114.4, 64.4, 55.6, 53.2, 34.2, 20.0. HRMS (ESI) m/z: Calcd for
C19H18O5Na [M+Na]+: 349.1052. Found: 349.1046.
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Methyl 2-benzoyl-1-(4-chlorophenoxy)cyclopropanecarboxylate (1r)
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Yellowish viscous liquid (total 3.0 g, 92% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 8.02
– 7.87 (m, 2H), 7.58 (t, J = 7.3 Hz, 1H), 7.47 (t, J = 7.6 Hz, 2H), 7.15 – 7.09 (m, 2H), 6.79 – 6.73 (m,
2H), 3.82 (s, 3H), 3.65 (dt, J = 19.1, 9.5 Hz, 1H), 2.26 (dd, J = 7.7, 5.5 Hz, 1H), 2.01 (dd, J = 9.1, 5.5
Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 191.2, 170.8, 155.8, 137.5, 133.4, 129.2, 128.7, 128.3,
127.1, 117.1, 63.9, 53.3, 33.7, 20.0. HRMS (ESI) m/z: Calcd for C18H15ClO4Na [M+Na]+: 353.0557.
Found: 353.0548.
Ethyl 2-benzoyl-1-(prop-2-ynyloxy)cyclopropanecarboxylate (1s)
Yellowish viscous liquid (total 2.1 g, 77% yield); Major isomer: 1H NMR (400 MHz, CDCl3) δ 7.98
(d, J = 7.4 Hz, 2H), 7.57 (t, J = 7.3 Hz, 1H), 7.46 (t, J = 7.7 Hz, 2H), 4.37 – 4.29 (m, 2H), 4.21 –
4.10 (m, 1H), 3.44 – 3.36 (m, 1H), 2.44 – 2.37 (m, 2H), 1.75 (dd, J = 8.9, 5.3 Hz, 1H), 1.36 (t, J =
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7.1 Hz, 3H), 0.99 (q, J = 6.9 Hz, 1H). C NMR (101 MHz, CDCl3) δ 191.8, 171.0, 137.5, 133.3,
128.7, 128.3, 78.7, 75.3, 66.3, 62.1, 58.5, 33.7, 18.9, 14.2. HRMS (ESI) m/z: Calcd for C16H16O4Na
[M+Na]+: 295.0946. Found: 295.0937.
Ethyl 2-benzoyl-1-morpholinocyclopropanecarboxylate (1t)
o
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Yellow solid (total 2.7 g, 88% yield): mp 209-211 C; Major isomer: H NMR (400 MHz, CDCl3) δ
7.63 (dd, J = 8.1, 1.4 Hz, 2H), 7.41 – 7.29 (m, 3H), 5.22 (t, J = 2.7 Hz, 1H), 4.36 – 4.29 (m, 2H),
3.84 – 3.69 (m, 4H), 3.10 (qd, J = 18.0, 2.7 Hz, 2H), 2.97 – 2.84 (m, 2H), 2.68 – 2.55 (m, 2H), 1.34
13
(t, J = 7.1 Hz, 3H). C NMR (101 MHz, CDCl3) δ 170.3, 155.2, 130.1, 128.6, 128.3, 125.2, 101.2,
92.4, 66.8, 61.9, 46.3, 38.2, 14.2. HRMS (ESI) m/z: Calcd for C17H21NO4Na [M+Na]+: 326.1368.
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Found: 326.1357.
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Ethyl 5-phenylfuran-2-carboxylate (2a).12a
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Yellow liquid (35 mg, 80% yield); H NMR (400 MHz, CDCl3) δ 7.86 – 7.71 (m, 2H), 7.41 (t, J =
7.5 Hz, 2H), 7.34 (t, J = 7.3 Hz, 1H), 7.23 (d, J = 3.6 Hz, 1H), 6.73 (d, J = 3.6 Hz, 1H), 4.38 (q, J =
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7.1 Hz, 2H), 1.39 (t, J = 7.1 Hz, 3H); C NMR (101 MHz, CDCl3) δ 158.9, 157.5, 143.9, 129.6,
128.9, 128.8, 124.8, 119.8, 106.8, 60.9, 14.4; IR (neat): ν 2982, 2931, 1717, 1530, 1481, 1450, 1374,
1302, 1272, 1217, 1141, 1019, 763 cm-1. HRMS (ESI) m/z: Calcd for C13H12O3Na [M+Na]+:
239.0684. Found: 239.0681.
Ethyl 5-p-tolylfuran-2-carboxylate (2b).12a
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Yellow liquid (40 mg, 87% yield); H NMR (400 MHz, CDCl3) δ 7.67 (d, J = 8.2 Hz, 2H), 7.23 –
7.17 (m, 3H), 6.67 (d, J = 3.6 Hz, 1H), 4.37 (q, J = 7.1 Hz, 2H), 2.37 (s, 3H), 1.39 (t, J = 7.1 Hz, 3H);
13C NMR (101 MHz, CDCl3) δ 158.9, 157.8, 143.5, 139.0, 129.5, 126.9, 124.8, 119.9, 106.2, 60.8,
21.4, 14.4; IR (neat): ν 2982, 2924, 1721, 1537, 1488, 1373, 1302, 1272, 1215, 1140, 1019, 798, 760
cm-1. HRMS (ESI) m/z: Calcd for C14H14O3Na [M+Na]+: 253.0841. Found: 253.0837.
Ethyl 5-(4-methoxyphenyl)furan-2-carboxylate (2c).12a
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Yellow liquid (41 mg, 83% yield); H NMR (400 MHz, CDCl3) δ 7.85 – 7.52 (m, 2H), 7.22 (d, J =
3.6 Hz, 1H), 6.94 (t, J = 5.8 Hz, 2H), 6.60 (d, J = 3.6 Hz, 1H), 4.37 (q, J = 7.1 Hz, 2H), 3.84 (s, 3H),
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1.39 (t, J = 7.1 Hz, 3H); C NMR (101 MHz, CDCl3) δ 160.2, 159.0, 157.7, 143.3, 126.4, 122.5,
120.0, 114.3, 105.4, 60.8, 55.4, 14.4; IR (neat): ν 2981, 2939, 2838, 1719, 1613, 1591, 1538, 1488,
1373, 1303, 1256, 1139, 1065, 1021, 960, 922, 835, 796, 759 cm-1. HRMS (ESI) m/z: Calcd for
C14H14O4Na [M+Na]+: 269.0790. Found: 269.0783.
Ethyl 5-(4-chlorophenyl)furan-2-carboxylate (2d).12a
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Yellow solid (40 mg, 84% yield): mp 72-74 oC; 1H NMR (400 MHz, CDCl3) δ 7.75 – 7.66 (m, 2H),
7.38 (d, J = 8.6 Hz, 2H), 7.22 (d, J = 3.6 Hz, 1H), 6.71 (d, J = 3.6 Hz, 1H), 4.38 (q, J = 7.1 Hz, 2H),
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1.39 (t, J = 7.1 Hz, 3H); C NMR (101 MHz, CDCl3) δ 158.7, 156.3, 144.1, 134.7, 129.1, 128.0,
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126.0, 119.8, 107.2, 61.0, 14.4; IR (neat): ν 2984, 2937, 1724, 1586, 1529, 1477, 1411, 1371, 1301,
1276, 1217, 1142, 1095, 1018, 962, 833, 800, 760 cm-1. HRMS (ESI) m/z: Calcd for C13H11ClO3Na
[M+Na]+: 273.0294. Found: 273.0293.
Ethyl 5-(4-bromophenyl)furan-2-carboxylate (2e).12b
o
1
Yellow solid (46 mg, 78% yield): mp 84-86 C; H NMR (400 MHz, CDCl3) δ 7.63 (d, J = 8.6 Hz,
2H), 7.53 (d, J = 8.6 Hz, 2H), 7.22 (d, J = 3.6 Hz, 1H), 6.72 (d, J = 3.6 Hz, 1H), 4.38 (q, J = 7.1 Hz,
2H), 1.39 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 158.7, 156.3, 144.2, 132.0, 128.5,
126.3, 123.0, 119.8, 107.3, 61.0, 14.4. IR (neat): ν 2987, 2908, 1723, 1579, 1519, 1470, 1368, 1297,
1214, 1145, 1110, 1020, 1007, 922, 864, 802, 763 cm-1. HRMS (ESI) m/z: Calcd for C13H11BrO3Na
[M+Na]+: 316.9789. Found: 316.9784.
Ethyl 5-(2-bromophenyl)furan-2-carboxylate (2f).
Yellow liquid (57 mg, 97% yield); 1H NMR (400 MHz, CDCl3) δ 7.91 (dd, J = 7.9, 1.6 Hz, 1H), 7.72
– 7.60 (m, 1H), 7.44 – 7.34 (m, 1H), 7.26 (d, J = 3.7 Hz, 1H), 7.23 (d, J = 3.6 Hz, 1H), 7.18 (td, J =
13
8.0, 1.7 Hz, 1H), 4.39 (q, J = 7.1 Hz, 2H), 1.39 (t, J = 7.1 Hz, 3H); C NMR (101 MHz, CDCl3) δ
158.8, 154.7, 143.9, 134.2, 130.1, 129.8, 129.7, 127.6, 120.4, 119.1, 112.3, 61.0, 14.4; IR (neat): ν
2981, 2932, 1725, 1581, 1560, 1519, 1465, 1432, 1372, 1300, 1246, 1214, 1145, 1020, 963, 923, 808,
760 cm-1. HRMS (ESI) m/z: Calcd for C13H11BrO3Na [M+Na]+: 316.9789. Found: 316.9781.
Ethyl 5-(4-diphenyl)furan-2-carboxylate (2g).12c
White solid (53 mg, 91% yield): mp 99-101 oC; 1H NMR (400 MHz, CDCl3) δ 7.82 (t, J = 10.6 Hz,
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2H), 7.69 – 7.55 (m, 4H), 7.44 (t, J = 7.5 Hz, 2H), 7.35 (t, J = 7.3 Hz, 1H), 7.24 (d, J = 3.6 Hz, 1H),
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6.74 (d, J = 3.6 Hz, 1H), 4.38 (q, J = 7.1 Hz, 2H), 1.39 (t, J = 7.1 Hz, 3H); C NMR (101 MHz,
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CDCl3) δ 158.9, 157.3, 144.0, 141.6, 140.3, 128.9, 128.5, 127.70, 127.5, 127.0, 125.3, 119.9, 107.0,
60.9, 14.4; IR (neat): ν 2985, 2925, 1723, 1535, 1502, 1411, 1372, 1303, 1216, 1154, 1021, 919, 838,
800, 760 cm-1. HRMS (ESI) m/z: Calcd for C19H16O3Na [M+Na]+: 315.0997. Found: 315.0993.
Ethyl 5-(thiophen-2-yl)furan-2-carboxylate (2i).12d
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Yellow liquid (28 mg, 63% yield); 1H NMR (400 MHz, CDCl3) δ 7.45 (dd, J = 3.6, 0.9 Hz, 1H), 7.33
(dd, J = 5.0, 1.0 Hz, 1H), 7.20 (d, J = 3.6 Hz, 1H), 7.07 (dd, J = 5.0, 3.7 Hz, 1H), 6.57 (d, J = 3.6 Hz,
1H), 4.37 (q, J = 7.1 Hz, 2H), 1.39 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 158.7, 152.9,
143.4, 132.3, 127.9, 126.2, 125.1, 119.9, 106.7, 60.9, 14.4; IR (neat): ν 3115, 2982, 1721, 1595, 1543,
1494, 1486, 1420, 1379, 1347, 1301, 1259, 1223, 1206, 1139, 1016, 957, 893, 849, 797, 759 cm-1.
HRMS (ESI) m/z: Calcd for C11H10O3SNa [M+Na]+: 245.0248. Found: 245.0243.
Methyl 5-phenylfuran-2-carboxylate (2j).12a
o
1
White solid (32 mg, 80% yield): mp 58-60 C; H NMR (400 MHz, CDCl3) δ 7.82 – 7.75 (m, 2H),
7.42 (t, J = 7.5 Hz, 2H), 7.35 (dd, J = 8.4, 6.3 Hz, 1H), 7.25 (d, J = 3.6 Hz, 1H), 6.74 (d, J = 3.6 Hz,
13
1H), 3.91 (s, 3H); C NMR (101 MHz, CDCl3) δ 159.2, 157.6, 143.6, 129.5, 129.0, 128.8, 124.9,
120.1, 106.9, 51.9; IR (neat): ν 292844, 1712, 1529, 1481, 1450, 1371, 1305, 1273, 1219, 1192, 1139,
1066, 1027, 991, 921, 797, 763 cm-1. HRMS (ESI) m/z: Calcd for C12H10O3Na [M+Na]+: 225.0630.
Found: 225.0623.
Methyl 5-(4-methoxyphenyl)furan-2-carboxylate (2k).12e
o
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White solid (36 mg, 78% yield): mp 83-85 C; H NMR (400 MHz, CDCl3) δ 7.86 – 7.59 (m, 2H),
7.23 (d, J = 3.6 Hz, 1H), 7.00 – 6.87 (m, 2H), 6.60 (d, J = 3.6 Hz, 1H), 3.90 (s, 3H), 3.84 (s, 3H); 13C
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NMR (101 MHz, CDCl3) δ 160.3, 159.3, 157.8, 142.9, 126.4, 122.5, 120.3, 114.3, 105.4, 55.4, 51.8;
IR (neat): ν 2942, 2843, 1730, 1614, 1588, 1489, 1432, 1368, 1318, 1256, 1187, 1146, 1065, 985,
919, 829, 789, 754 cm-1. HRMS (ESI) m/z: Calcd for C13H12O4Na [M+Na]+: 255.0633. Found:
255.0627.
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Methyl 5-(4-chlorophenyl)furan-2-carboxylate (2l).12e
White solid (44 mg, 94% yield): mp 130-132 oC; 1H NMR (400 MHz, CDCl3) δ 7.81 – 7.58 (m, 2H),
7.44 – 7.34 (m, 2H), 7.23 (d, J = 3.6 Hz, 1H), 6.72 (d, J = 3.6 Hz, 1H), 3.91 (s, 3H); 13C NMR (101
MHz, CDCl3) δ 159.1, 156.4, 143.8, 134.8, 129.1, 128.0, 126.1, 120.0, 107.2, 51.9; IR (neat): ν 3134,
2948, 1730, 1583, 1565, 1529, 1474, 1408, 1364, 1299, 1213, 1105, 1090, 1025, 987, 911, 805, 756
cm-1. HRMS (ESI) m/z: Calcd for C12H9ClO3Na [M+Na]+: 259.0138. Found: 259.0132.
Methyl 5-(4-diphenyl)furan-2-carboxylate (2m).
White solid (55 mg, 99% yield): mp 159-161 oC; 1H NMR (400 MHz, CDCl3) δ 7.74 (d, J = 8.5 Hz,
2H), 7.58 – 7.48 (m, 4H), 7.35 (t, J = 7.5 Hz, 2H), 7.29 – 7.24 (m, 1H), 7.16 (d, J = 3.6 Hz, 1H), 6.65
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(d, J = 3.6 Hz, 1H), 3.82 (s, 3H); C NMR (101 MHz, CDCl3) δ 159.3, 157.4, 143.6, 141.6, 140.2,
128.9, 128.4, 127.7, 127.5, 127.0, 125.3, 120.2, 107.0, 51.9; IR (neat): ν 2925, 2375, 1707, 1584,
1539, 1504, 1434, 1411, 1366, 1303, 1220, 1189, 1072, 1029, 987, 919, 805, 760 cm-1. HRMS (ESI)
m/z: Calcd for C18H14O3Na [M+Na]+: 301.0841. Found: 301.0837.
2-Chloroethyl 5-phenylfuran-2-carboxylate (2o).
Yellow liquid (30 mg, 60% yield); 1H NMR (400 MHz, CDCl3) δ 7.85 – 7.73 (m, 2H), 7.43 (dd, J =
10.3, 4.6 Hz, 2H), 7.39 – 7.32 (m, 1H), 7.30 (d, J = 3.6 Hz, 1H), 6.75 (d, J = 3.6 Hz, 1H), 4.57 (t, J =
13
5.8 Hz, 2H), 3.80 (t, J = 5.8 Hz, 2H); C NMR (101 MHz, CDCl3) δ 158.3, 158.1, 143.0, 129.4,
129.1, 128.9, 124.9, 120.8, 107.0, 64.2, 41.5; IR (neat): ν 3125, 2960, 1723, 1573, 1528, 1478, 1450,
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1384, 1309, 1271, 1217, 1140, 1014, 961, 921, 804, 762 cm-1. HRMS (ESI) m/z: Calcd for
C13H11ClO3Na [M+Na]+: 273.0294. Found: 273.0286.
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Benzyl 5-phenylfuran-2-carboxylate (2p).
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Yellow liquid (20 mg, 80% yield); 1H NMR (400 MHz, CDCl3) δ 7.78 (d, J = 7.4 Hz, 2H), 7.45 (t, J
= 7.1 Hz, 2H), 7.40 (d, J = 8.0 Hz, 3H), 7.38 – 7.31 (m, 2H), 7.27 (d, J = 3.6 Hz, 1H), 7.24 – 7.15 (m,
1H), 6.73 (d, J = 3.6 Hz, 1H), 5.37 (s, 2H); 13C NMR (101 MHz, CDCl3) δ 158.7, 157.8, 143.5,
135.8, 129.5, 129.0, 128.8, 128.7, 128.6, 128.4, 124.9, 120.3, 106.9, 66.4; IR (neat): ν 3033, 2956,
2926, 1720, 1573, 1528, 1478, 1451, 1379, 1298, 1271, 1216, 1135, 1066, 1026, 970, 921, 804, 783,
762 cm-1. HRMS (ESI) m/z: Calcd for C18H14O3Na [M+Na]+: 301.0841. Found: 301.0839.
Ethyl 2,5-dioxo-5-phenylpentanoate (3a).10
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Yellow liquid (46 mg, 98% yield); H NMR (400 MHz, CDCl3) δ 8.04 – 7.97 (m, 2H), 7.63 – 7.57
(m, 1H), 7.49 (dd, J = 10.5, 4.7 Hz, 2H), 4.39 (q, J = 7.1 Hz, 2H), 3.42 (t, J = 6.1 Hz, 2H), 3.29 (dd,
13
J = 7.0, 5.6 Hz, 2H), 1.42 (t, J = 7.1 Hz, 3H); C NMR (101 MHz, CDCl3) δ 197.5, 193.2, 160.8,
136.3, 133.4, 128.6, 128.1, 62.5, 33.1, 32.6, 14.0; IR (KBr) v 2963, 2909, 1725, 1666, 1604, 1447,
1405, 1369, 1254, 1088, 1022, 865, 800 cm-1; HRMS (ESI) m/z calcd for C13H14O4Na[M+Na]+
257.0790, found 257.0786.
Acknowledgements
This work was supported by grants from National Natural Science Foundation of China (no.
21472053, 21172082). The Analysis and Testing Centre of Huazhong University of Science and
Technology is acknowledged for characterization of the new compounds.
Supporting Information Available.
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Copies of H, C NMR spectra for all compounds. This material is available free of charge via the
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