Palladium-catalyzed synthesis of 2,3,4-trisubstituted furans via cascade reactions of aryloxy-enynes with aryl halides

Article abstract of DOI:10.1021/jo3012545

A highly efficient palladium-catalyzed cascade reactions of aryloxy-enynes with aryl halides under mild reaction conditions has been developed. This methodology offers rapid access to 2,3,4-trisubstituted furans in good to excellent yields in a regioselective manner.

Full text of DOI:10.1021/jo3012545

Note
pubs.acs.org/joc
Palladium-Catalyzed Synthesis of 2,3,4-Trisubstituted Furans via
Cascade Reactions of Aryloxy-enynes with Aryl Halides
Ende Li, Xingcan Cheng, Chengyu Wang, Yushang Shao, and Yanzhong Li*
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, 500
Dongchuan Road, Shanghai, 200241, People’s Republic of China
S
* Supporting Information
ABSTRACT: A highly efficient palladium-catalyzed cascade reactions of
aryloxy-enynes with aryl halides under mild reaction conditions has been
developed. This methodology offers rapid access to 2,3,4-trisubstituted furans in
good to excellent yields in a regioselective manner.
The requisite (E)-1-aryloxy-1-en-3-ynes with an ester group
ubstituted furans are important structural units which are
Sfound in many biologically active natural and artificial on C-2 (1) were synthesized via the Sonogashira coupling of
compounds.1,2 They are also versatile building blocks in
the corresponding 2-bromo-3-aryloxypropenoates and terminal
alkynes.13 First, the reaction of (E)-1-phenoxy-1-en-3-yne with
an ethyl ester group on C-2 (1a) with ethyl 4-iodobenzoate
(2a) was carried out using PdCl2(PPh3)2 (5 mol %) as the
catalyst and Cs2CO3 (2 equiv) as the base in dioxane at 70 °C.
However, the desired furan 3a was produced in only 35% yield
after 6 h (Table 1, entry 1). When the catalyst was changed to
Pd(PPh3)4, the yield of 3a increased to 66% (Table 1, entry 3).
It is interesting that PdCl2(PPh3)2 combined with DMF
afforded 3a in 87% yield within 2 h (Table 1, entry 2). It seems
that DMF is better than dioxane, and Pd(0) is more efficient
than Pd(II) in our system. Then the combination of Pd(PPh3)4
and DMF was tested; satisfyingly, the desired trisubstituted
furan was produced quantitatively (Table 1, entry 4). Lowering
the catalyst loading to 2 mol % gave 75% yield (Table 1, entry
5). When the reaction was carried out at 40 °C, no desired
product could be detected (Table 1, entry 8). Pd2(dba)3
resulted in moderate yield of the desired furan (Table 1,
entry 17). When 2a was reduced to 1.0 equiv, the yield of 3a
was decreased to 83% (Table 1, entry 7). Changing the solvent
to THF, toluene, DMA (N,N-dimethylacetamide), or DMSO,
3a was produced in relatively lower yields (Table 1, entries 9−
12). The use of other bases such as K2CO3, Na2CO3, NaOAc,
or K3PO4 gave no better results than that of Cs2CO3 (Table 1,
entries 13−16). Therefore, the optimized reaction condition
was to use 5 mol % of Pd(PPh3)4 as the catalyst, 2.0 equiv of
Cs2CO3 as the base, and DMF as the solvent at 70 °C. One of
the advantages of this method to furans is that the
regioselective introduction of substituents on the furan ring
comes down to the appropriate choice of the aryloxy-enyne and
aryl halide, which allows for considerable versatility.
synthetic organic chemistry.3 As a consequence, a variety of
synthetic routes toward furan ring formation have been
disclosed,4 the majority of which include the classical
approaches, such as Paal−Knorr synthesis,5 Feist−Benary
method,6 and O-annulation reactions from acyclic starting
materials. Among the many approaches to substituted furans,
the intramolecular attack of a nucleophilic oxygen atom onto a
C−C triple bond offers a straightforward access to furan
derivatives either by the electrophilic cyclization of functionally
substituted alkynes or the transition-metal-catalyzed cyclization.
The acyclic precursors involve allenyl ketones,7 alkynyl
ketones,8 2-(1-alkynyl)-2-alken-1-ones,9 enynols or phenols,10
1,3-enynyl ketones,11 and others.12 Although these methods are
efficient for the substituted furan formation, the development
of synthetic procedures that allow the facile assembly of
substituted furans from readily available starting materials still
remains an important task in organic chemistry. Recently, we
reported a Au-catalyzed methodology for the preparation of
2,4-disubstituted furans from aryloxy-enynes.13 We envisioned
that one more substituent might be introduced to the C-3
position of the furan ring from the same starting materials by
the proper choice of metal catalyst, such as palladium catalyst,
and resulting in the trisubstituted furans. It is well-known that
Pd(II) species are efficient catalysts for the C−C triple bond
activation,14 and it can be generated conveniently from Pd(0)
and aryl halide (Scheme 1). Herein, we would like to report the
effective synthesis of 2,3,4-trisubstituted furans through the Pd-
catalyzed cascade reactions of aryloxy-enyne and aryl halides.
Scheme 1
With the optimized reaction conditions in hand, we next
examined the substrate scope of this catalytic method for the
Received: June 22, 2012
Published: August 13, 2012
© 2012 American Chemical Society
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The Journal of Organic Chemistry
Note
coupling of the initially formed C-3 TMS-substituted furan with
iodobenzene catalyzed by the Pd catalyst (Table 2, entry 14).
Very interestingly, a mixture of 1a (E/Z = 1:1) could also
afford the desired 3a in high yield under the optimal conditions
(eq 1). This result may further broaden the substrate scope of
this method.
Table 1. Optimization of Reaction Conditions for the
Formation of 3a
ab
,
time
(h)
yield
(%)
entry
catalyst
base (n equiv)
solvent
1
2
PdCl2(PPh3)2
PdCl2(PPh3)2
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd2(dba)3
Cs2CO3 (2.0)
Cs2CO3 (2.0)
Cs2CO3 (2.0)
Cs2CO3 (2.0)
Cs2CO3 (2.0)
Cs2CO3(1.0)
Cs2CO3 (2.0)
Cs2CO3 (2.0)
Cs2CO3 (2.0)
Cs2CO3 (2.0)
Cs2CO3 (2.0)
Cs2CO3 (2.0)
K2CO3 (2.0)
Na2CO3 (2.0)
NaOAc (2.0)
K3PO4 (2.0)
Cs2CO3 (2.0)
dioxane
DMF
dioxane
DMF
DMF
DMF
DMF
DMF
THF
6
2
35
87
66
99
75
26
83
3
12
1.5
2
According to our previous results, one possibility of the
reaction pathway is that the enynyl ether 1 is hydrolyzed to the
corresponding carbonyl group by H2O, and then undergo an
O-cyclization.13 To prove this point, we carried out an isotopic
labeling experiment using 1a and 2a with 3 equiv of H218O and
found that 43% of 18O was incorporated in the final furan ring;
the desired furan was obtained in 97% yield in 3 h (Scheme 2).
On the basis of the above observations and the reported
work, a possible reaction mechanism is proposed in Scheme 3.
First, oxidative addition of aryl iodide to Pd(0) gives Pd(II),
which may act as a Lewis acid12j,14 to activate the enone moiety
of compound 1, then nucleophilic attack of H2O to the C−C
double bond followed by elimination of PhOH gives
intermediate 5 or 6. Then 6 is activated by the coordination
of the alkynyl moiety to Pd(II) which enhances the
electrophilicity of the triple bond and facilitates an intra-
molecular cyclization of the enol oxygen onto the alkyne to
afford 8. Reductive elimination of 8 with regeneration of the
Pd(0) catalyst furnishes the desired furan 3.
4
c
5
6
2
d
e
7
2
8
6
9
12
12
1.5
1.5
19
24
24
7
86
50
91
80
70
12
50
74
59
10
11
12
13
14
15
16
17
Tol
DMA
DMSO
DMF
DMF
DMF
DMF
DMF
2
a
Unless otherwise noted, all reactions were carried out using 5 mol %
of catalyst with the ratio of 1a/2a = 1:1.5. Isolated yield. 2 mol % of
Pd catalyst was used. Ratio of 1a/2a = 1:1. Reaction was carried out
at 40 °C.
b
c
d
e
In conclusion, we have shown that 2,3,4-trisubstituted furans
can be efficiently prepared by the Pd-catalyzed cascade
reactions using aryloxy-enynes and aryl iodides. Aryl, alkyl,
and trimethylsilyl substituents on the acetylene terminus are
compatible in the annulation reaction, furnishing the desired
furans in good to high yields. In this procedure, the
regioselective introduction of substituents on the furan ring
comes down to the appropriate choice of the aryloxy-enyne and
aryl halide, which allows for considerable versatility.
synthesis of 2,3,4-trisubstituted furans using a variety of (E)-1-
aryloxy-1-en-3-ynes and aryl iodides, and the results are shown
in Table 2. We first investigated the electronic effects of the
aromatic substituents on the triple bond. It was found that
electron-donating aryl groups such as −Me (1b) or −2,3,4-
trimethoxyl (1c) reacted with 4-iodobenzoate (2a) to afford the
corresponding products 3b and 3c in 82 and 91% yields,
respectively (Table 2, entries 1 and 2). An electron-with-
drawing (−Cl) aryl group afforded the corresponding furan 3d
in 78% yield (Table 2, entry 3). Naphthyl-substituted 1e gave a
good result (Table 2, entry 4). The substituents on the triple
bond could also be alkyl groups, such as n-butyl (1f), n-pentyl
(1g), and phenylethyl (1h), furnishing 3f, 3g, and 3h in 66, 72,
and 50% yields, respectively (Table 2, entries 5−7). Enynyl
ether 1a reacted smoothly with iodobenzene (2b) to give 3i in
92% yield (Table 2, entry 8). The aryl iodides could also be 4-
methyl (2c) or 4-nitroiodobenzene (2d), and the correspond-
ing furans were produced in 87% (3j) and 82% (3k) yields,
respectively (Table 2, entries 9 and 10). The structure of 3k
was further confirmed by X-ray crystallographic analysis. 2-
Bromo-1-iodobenzene could also be employed in the reaction,
providing the desired 3l in good yield, and the −Br group was
well-tolerated during the reaction (Table 2, entry 11).
Heteroaryl idodide such as 2-iodothiophene (2f) led to the
formation of 3m in 64% yield (Table 2, entry 12). When the
ester group of enynyl ether was methyl ester, the corresponding
furan 3n was produced in 57% yield (Table 2, entry 13). It is
worthy to note when the trimethylsilyl-substituted enynyl ether
1j was used to react with 2.5 equiv of iodobenzene, 3i was
obtained in 63% yield. It might due to the further desilylation
EXPERIMENTAL SECTION
■
Typical Procedure for the Pd-Catalyzed Formation of Ethyl
4-(4-(Ethoxycarbonyl)phenyl)-5-phenylfuran-3-carboxylate
(3a). Pd(PPh3)4 (12 mg, 0.01 mmol), (E)-ethyl-2-(phenoxymethy-
lene)-4-phenylbut-3-ynoate (58 mg, 0.2 mmol) in DMF (2 mL), ethyl
4-iodobenzoate (0.05 mL, 0.3 mmol), and Cs2CO3 (130 mg, 0.4
mmol) were added to a Schlenk tube under nitrogen. The resulting
solution was stirred at 70 °C. After the reaction was complete as
monitored by thin-layer chromatography, the mixture was treated with
water and extracted with EA. The extract was washed with water and
dried over anhydrous Na2SO4. The solvent was evaporated under the
reduced pressure, and the residue was purified by chromatography on
silica gel to afford the 2,3,4-trisubstituted furan derivative 3a (72 mg,
99%) as a yellow oil: 1H NMR (400 MHz, CDCl3, Me4Si) δ 1.17 (t, J
= 7.2 Hz, 3H), 1.41 (t, J = 7.2 Hz, 3H), 4.17 (q, J = 7.2 Hz, 2H), 4.41
(q, J = 7.2 Hz, 2H), 7.22−7.26 (m, 3H), 7.32−7.34 (m, 2H), 7.42−
7.44 (m, 2H), 8.07−8.09 (m, 2H), 8.13 (s, 1H); 13C NMR (100.6
MHz, CDCl3, Me4Si) δ 14.0, 14.3, 60.3, 60.9, 120.4, 120.5, 125.9,
128.1, 128.4, 129.4, 129.6, 129.7, 130.4, 137.4, 147.3, 150.9, 162.6,
166.5; HRMS (EI) calcd for C22H20O5 364.1311, found 364.1312.
Ethyl 4-(4-(Ethoxycarbonyl)phenyl)-5-p-tolylfuran-3-carbox-
ylate (3b). Column chromatography on silica gel (eluent: n-hexane/
ethyl acetate = 50:1) afforded the title product 3b in 82% isolated yield
as a yellow oil: 1H NMR (400 MHz, CDCl3, Me4Si) δ 1.17 (t, J = 6.8
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Note
Table 2. Synthesis of Various of 2,3,4-Trisubstituted Furans
a
b
Isolated yields. Unless noted, all of the reactions were carried out using 5 mol % of Pd(PPh3)4 and 2.0 equiv of Cs2CO3 in DMF at 70 °C. The
c
reaction time was 12 h. 2.5 equiv of 2b was used.
a
Scheme 2. Isotopic Experiment
a
[a] Determined by MS.
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The Journal of Organic Chemistry
Note
Ethyl 4-(4-(Ethoxycarbonyl)phenyl)-5-pentylfuran-3-carbox-
ylate (3g). Column chromatography on silica gel (eluent: n-hexane/
ethyl acetate = 50:1) afforded the title product 3g in 72% isolated yield
as a light white oil: 1H NMR (400 MHz, CDCl3, Me4Si) δ 0.84 (t, J =
7.2 Hz, 3H), 1.19 (t, J = 7.2 Hz, 3H), 1.22−1.26 (m, 4H), 1.40 (t, J =
7.2 Hz, 3H), 1.59−1.62 (m, 2H), 2.57 (t, J = 7.2 Hz, 2H), 4.17 (q, J =
6.8 Hz, 2H), 4.40 (q, J = 7.2 Hz, 2H), 7.36−7.38 (m, 2H), 7.98 (s,
1H), 8.06−8.08 (m, 2H); 13C NMR (100.6 MHz, CDCl3, Me4Si) δ
13.8, 14.1, 14.3, 22.2, 26.0, 27.9, 31.1, 60.1, 60.8, 118.6, 120.0, 129.0,
129.1, 130.0, 137.1, 146.8, 155.1, 163.0, 166.5; HRMS (EI) calcd for
C21H26O5 358.1780, found 358.1776.
Scheme 3. Proposed Reaction Pathway
Ethyl 4-(4-(Ethoxycarbonyl)phenyl)-5-phenethylfuran-3-car-
boxylate (3h). Column chromatography on silica gel (eluent: n-
hexane/ethyl acetate = 50:1) afforded the title product 3h in 50%
1
isolated yield as a yellow oil: H NMR (400 MHz, CDCl3, Me4Si) δ
1.17 (t, J = 7.2 Hz, 3H), 1.39 (t, J = 6.8 Hz, 3H), 2.83−2.87 (m, 2H),
2.91−2.94 (m, 2H), 4.15 (q, J = 6.8 Hz, 2H), 4.38 (q, J = 7.6 Hz, 2H),
6.99−7.01 (m, 2H), 7.05−7.08 (m, 2H), 7.18−7.25 (m, 3H), 7.95−
7.98 (m, 2H), 8.01 (s, 1H); 13C NMR (100.6 MHz, CDCl3, Me4Si) δ
14.0, 14.3, 28.2, 34.3, 60.2, 60.9, 118.7, 121.0, 126.2, 128.3, 128.4,
128.9, 129.1, 130.0, 136.7, 140.3, 147.0, 153.5, 162.9, 166.5; HRMS
(EI) calcd for C24H24O5 392.1624, found 392.1620.
Ethyl 4,5-Diphenylfuran-3-carboxylate (3i). Column chroma-
tography on silica gel (eluent: n-hexane/ethyl acetate = 50:1) afforded
the title product 3i in 92% isolated yield as a yellow oil: 1H NMR (400
MHz, CDCl3, Me4Si) δ 1.15 (t, J = 7.2 Hz, 3H), 4.15 (q, J = 6.8 Hz,
2H), 7.20−7.22 (m, 3H), 7.33−7.40 (m, 7H), 8.10 (s, 1H); 13C NMR
(100.6 MHz, CDCl3, Me4Si) δ 14.0, 60.1, 120.7, 121.5, 125.8, 127.6,
127.8, 128.2, 128.3, 130.1, 130.2, 132.4, 147.0, 150.6, 162.8; HRMS
(EI) calcd for C19H16O3 292.1099, found 292.1098.
Ethyl 5-Phenyl-4-p-tolylfuran-3-carboxylate (3j). Column
chromatography on silica gel (eluent: n-hexane/ethyl acetate = 50:1)
afforded the title product 3j in 87% isolated yield as a light yellow
solid: 1H NMR (400 MHz, CDCl3, Me4Si) δ 1.18 (t, J = 6.8 Hz, 3H),
2.39 (s, 3H), 4.17 (q, J = 7.2 Hz, 2H), 7.18−7.24 (m, 7H), 7.37−7.40
(m, 2H), 8.08 (s, 1H); 13C NMR (100.6 MHz, CDCl3, Me4Si) δ 14.0,
21.3, 60.1, 120.7, 121.6, 125.7, 127.9, 128.3, 129.0, 129.2, 130.0, 130.2,
137.2, 146.9, 150.5, 162.8; HRMS (EI) calcd for C20H18O3 306.1256,
found 306.1255.
Hz, 3H), 1.41 (t, J = 6.8 Hz, 3H), 2.29 (s, 3H), 4.16 (q, J = 7.2 Hz,
2H), 4.40 (q, J = 7.2 Hz, 2H), 7.02−7.04 (m, 2H), 7.20−7.22 (m,
2H), 7.41−7.44 (m, 2H), 8.07−8.09 (m, 2H), 8.10 (s, 1H); 13C NMR
(100.6 MHz, CDCl3, Me4Si) δ 14.0, 14.3, 21.1, 60.2, 60.9, 119.8,
120.3, 125.9, 126.8, 129.1, 129.4, 129.5, 130.4, 137.5, 138.1, 147.0,
151.2, 162.7, 166.5; HRMS (EI) calcd for C23H22O5 378.1467, found
378.1463.
E t h y l 4 - ( 4 -( E t h o x y c a r b onyl)ph enyl)-5-(3, 4, 5-
trimethoxyphenyl)furan-3-carboxy- late (3c). Column chroma-
tography on silica gel (eluent: n-hexane/ethyl acetate = 50:1) afforded
the title product 3c in 91% isolated yield as a light white crystalline
solid: mp 105−107 °C; 1H NMR (300 MHz, CDCl3, Me4Si) δ 1.18 (t,
J = 6.9 Hz, 3H), 1.41 (t, J = 6.9 Hz, 3H), 3.61 (s, 6H), 3.82 (s, 3H),
4.17 (q, J = 7.2 Hz, 2H), 4.41 (q, J = 7.2 Hz, 2H), 6.58 (s, 2H), 7.46−
7.49 (m, 2H), 8.11−8.13 (m, 2H), 8.13 (s, 1H); 13C NMR (100.6
MHz, CDCl3, Me4Si) δ 13.9, 14.2, 55.6, 60.2, 60.7, 60.9, 103.0, 120.1,
120.5, 124.9, 129.4, 129.6, 130.4, 137.7, 137.8, 146.8, 150.6, 153.0,
162.5, 166.2; HRMS (EI) calcd for C25H26O8 454.1628, found
454.1626.
Ethyl 5-(4-Chlorophenyl)-4-(4-(ethoxycarbonyl)phenyl)-
furan-3-carboxylate (3d). Column chromatography on silica gel
(eluent: n-hexane/ethyl acetate = 50:1) afforded the title product 3d in
78% isolated yield as a yellow oil: 1H NMR (400 MHz, CDCl3, Me4Si)
δ 1.17 (t, J = 7.2 Hz, 3H), 1.41 (t, J = 7.2 Hz, 3H), 4.17 (q, J = 6.8 Hz,
2H), 4.41 (q, J = 6.8 Hz, 2H), 7.18−7.21 (m, 2H), 7.24−7.26 (m,
2H), 7.40−7.43 (m, 2H), 8.08−8.10 (m, 2H), 8.12 (s, 1H); 13C NMR
(100.6 MHz, CDCl3, Me4Si) δ 14.0, 14.3, 60.3, 61.0, 120.6, 121.0,
127.1, 128.1, 128.7, 129.5, 129.9, 130.2, 134.0, 137.0, 147.4, 149.8,
162.4, 166.3; HRMS (EI) calcd for C22H19O5Cl 398.0921, found
398.0922.
Ethyl 4-(4-(Ethoxycarbonyl)phenyl)-5-(naphthalen-1-yl)-
furan-3-carboxylate (3e). Column chromatography on silica gel
(eluent: n-hexane/ethyl acetate = 50:1) afforded the title product 3e in
60% isolated yield as a yellow oil: 1H NMR (300 MHz, CDCl3, Me4Si)
δ 1.26 (t, J = 6.8 Hz, 3H), 1.33 (t, J = 6.8 Hz, 3H), 4.26 (q, J = 7.2 Hz,
2H), 4.31 (q, J = 6.8 Hz, 2H), 7.26−7.33 (m, 4H), 7.43−7.48 (m,
2H), 7.82−7.88 (m, 5H), 8.29 (s, 1H); 13C NMR (75.5 MHz, CDCl3,
Me4Si) δ 14.0, 14.2, 60.4, 60.8, 119.3, 123.1, 125.0, 125.4, 126.1, 126.7,
126.8, 128.4, 128.9, 129.1, 129.3, 129.8, 130.2, 131.8, 133.6, 136.4,
148.4, 152.0, 162.8, 166.4; HRMS (EI) calcd for C26H22O5 414.1467,
found 414.1463.
Ethyl 4-(4-Nitrophenyl)-5-phenylfuran-3-carboxylate (3k).
Column chromatography on silica gel (eluent: n-hexane/ethyl acetate
= 50:1) afforded the title product 3k in 82% isolated yield as a yellow
crystalline solid: mp 119−121 °C; 1H NMR (300 MHz, CDCl3,
Me4Si) δ 1.21 (t, J = 7.2 Hz, 3H), 4.20 (q, J = 7.2 Hz, 2H), 7.26−7.31
(m, 5H), 7.53−7.55 (m, 2H), 8.16 (s, 1H), 8.24−8.27 (m, 2H); 13C
NMR (100.6 MHz, CDCl3, Me4Si) δ 14.1, 60.5, 119.4, 120.1, 123.4,
126.2, 128.6, 128.6, 129.2, 131.5, 139.7, 147.3, 147.6, 151.4, 162.5;
HRMS (EI) calcd for C19H15NO5 337.0950, found 337.0948.
Ethyl 4-(2-Bromophenyl)-5-phenylfuran-3-carboxylate (3l).
Column chromatography on silica gel (eluent: n-hexane/ethyl acetate
= 50:1) afforded the title product 3l in 78% isolated yield as a yellow
1
oil: H NMR (300 MHz, CDCl3, Me4Si) δ 1.11 (t, J = 6.9 Hz, 3H),
4.13 (q, J = 7.5 Hz, 2H), 7.22−7.36 (m, 8H), 7.68−7.71 (m, 1H), 8.14
(s, 1H); 13C NMR (75.5 MHz, CDCl3, Me4Si) δ 13.8, 60.2, 120.3,
121.0, 125.2, 127.4, 128.0, 128.5, 129.4, 129.8, 131.6, 132.6, 134.2,
146.8, 150.6, 162.6; HRMS (EI) calcd for C19H15O3Br 370.0205,
found 370.0204.
Ethyl 5-Phenyl-4-(thiophen-2-yl)furan-3-carboxylate (3m).
Column chromatography on silica gel (eluent: n-hexane/ethyl acetate
= 50:1) afforded the title product 3m in 64% isolated yield as a light
Ethyl 5-Butyl-4-(4-(ethoxycarbonyl)phenyl)furan-3-carboxy-
late (3f). Column chromatography on silica gel (eluent: n-hexane/
ethyl acetate = 50:1) afforded the title product 3f in 66% isolated yield
as a light white oil: 1H NMR (400 MHz, CDCl3, Me4Si) δ 0.84 (t, J =
7.2 Hz, 3H), 1.19 (t, J = 7.2 Hz, 3H), 1.24−1.30 (m, 2H), 1.40 (t, J =
7.2 Hz, 3H), 1.57−1.61 (m, 2H), 2.58 (t, J = 7.2 Hz, 2H), 4.17 (q, J =
6.8 Hz, 2H), 4.39 (q, J = 7.2 Hz, 2H), 7.36−7.38 (m, 2H), 7.98 (s,
1H), 8.06−8.08 (m, 2H); 13C NMR (100.6 MHz, CDCl3, Me4Si) δ
13.6, 14.1, 14.3, 22.1, 25.8, 30.3, 60.1, 60.9, 118.6, 120.0, 129.0, 129.1,
130.1, 137.1, 146.8, 155.0, 163.0, 166.5; HRMS (EI) calcd for
C20H24O5 344.1624, found 344.1627.
1
yellow solid: H NMR (300 MHz, CDCl3, Me4Si) δ 1.21 (t, J = 6.9
Hz, 3H), 4.20 (q, J = 6.9 Hz, 2H), 7.04−7.11 (m, 2H), 7.25−7.28 (m,
3H), 7.41−7.47 (m, 3H), 8.10 (s, 1H); 13C NMR (100.6 MHz,
CDCl3, Me4Si) δ 14.0, 60.2, 113.9, 121.3, 126.0, 126.7, 127.1, 128.2,
128.4, 128.5, 129.7, 132.4, 147.0, 152.2, 162.5; HRMS (EI) calcd for
C17H14O3S 298.0664, found 298.0660.
Methyl 4,5-Diphenylfuran-3-carboxylate (3n).14c Column
chromatography on silica gel (eluent: n-hexane/ethyl acetate = 50:1)
afforded the title product 3n in 57% isolated yield as a light yellow
solid: 1H NMR (400 MHz, CDCl3, Me4Si) δ 3.71 (s, 3H), 7.21 −7.24
7747
dx.doi.org/10.1021/jo3012545 | J. Org. Chem. 2012, 77, 7744−7748

The Journal of Organic Chemistry
Note
(m, 2H), 7.35−7.41 (m, 8H), 8.10 (s, 1H); 13C NMR (100.6 MHz,
CDCl3, Me4Si) δ 51.2, 120.3, 121.6, 125.9, 127.8, 127.9, 128.4, 128.4,
130.1, 130.3, 132.3, 147.2, 150.8, 163.3; HRMS (EI) calcd for
C18H14O3 278.0943, found 278.0948.
67, 2365. (c) Zhang, G.; Cui, L.; Wang, Y.; Zhang, L. J. Am. Chem. Soc.
2010, 132, 1474.
(11) (a) Patil, N. T.; Wu, H.; Yamamoto, Y. J. Org. Chem. 2005, 70,
4531. (b) Jin, T.; Yamamoto, Y. Org. Lett. 2008, 10, 3137.
(12) For selected examples, see: (a) Hashmi, A. S. K.; Sinha, P. Adv.
Synth. Catal. 2004, 346, 432. (b) Karpov, A. S.; Merkul, E.; Oeser, T.;
Muller, T. J. J. Chem. Commun. 2005, 2581. (c) Suhre, M. H.; Reif, M.;
Kirsch, S. F. Org. Lett. 2005, 7, 3925. (d) Feng, X.; Tan, Z.; Chen, D.;
Shen, Y.; Guo, C.-C.; Xiang, J.; Zhu, C. Tetrahedron Lett. 2008, 49,
4110. (e) Kao, T.-T.; Syu, S.-E.; Jhang, Y.-W.; Lin, W. Org. Lett. 2010,
12, 3066. (f) Yang, J.; Wang, C.; Xie, X.; Li, H.; Li, E.; Li, Y. Org.
Biomol. Chem. 2011, 9, 1342. (g) Li, Y.; Wheeler, K. A.; Dembinski, R.
Eur. J. Org. Chem. 2011, 2767. (h) Chen, K.-W.; Syu, S.-E.; Jang, Y.-J.;
Lin, W. Org. Biomol. Chem. 2011, 9, 2098. (i) Barluenga, J.; Riesgo, L.;
Vicente, R.; Lopez, L. A.; Tomas, M. J. Am. Chem. Soc. 2008, 130,
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7364.
ASSOCIATED CONTENT
* Supporting Information
■
S
NMR spectra for new products and X-ray crystallography of
compound 3k. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Fax: (+86) 021-54340096. E-mail: yzli@chem.ecnu.edu.cn.
■
Notes
(13) Li, E.; Yao, W.; Xie, X.; Wang, C.; Shao, Y.; Li, Y. Org. Biomol.
Chem. 2012, 10, 2960.
The authors declare no competing financial interest.
(14) (a) Trost, B. M.; Lumb, J.-P.; Azzarelli, J. M. J. Am. Chem. Soc.
2011, 133, 740. (b) Gaunt, M. J.; Spencer, J. B. Org. Lett. 2001, 3, 25.
(c) Gabriele, B.; Veltri, L.; Mancuso, R.; Plastina, P.; Salerno, G.;
Costa, M. Tetrahedron Lett. 2010, 51, 1663. For review, see: (d) Tsuji,
J. Palladium Reagents and Catalysts; John Wiley & Sons Ltd.:
Chichester, UK, 1996.
ACKNOWLEDGMENTS
■
We thank the National Natural Science Foundation of China
(Grant No. 20872037) for financial support.
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