Silver-catalyzed one-pot cyclization reaction of electron-DEficient alkynes and 2-Yn-1-ols: An efficient domino process to polysubstituted furans

Article abstract of DOI:10.1002/adsc.200900685

Transition metal-catalyzed domino reactions have been used as powerful tools for the preparation of polysubstituted furans in a one-pot manner. In this paper, an efficient synthetic method was developed for the construction of tri- or tetrasubstituted furans from electron-deficient alkynes and 2-yn-1-ols by a silver-catalyzed domino reaction. It is especially noteworthy that a 2,3,5-trisubstituted 4-ynylfuran was formally obtained in an extremely direct manner without tedious stepwise synthesis. In addition, regio-isomeric furans were observed when substituted aryl alkynyl ketones were employed. This methodology represents a highly efficient synthetic route to electron-deficient furans for which catalytic approaches are scarce. The reaction proceeds efficiently under mild conditions with commercially available catalysts and materials.

Full text of DOI:10.1002/adsc.200900685

FULL PAPERS
DOI: 10.1002/adsc.200900685
Silver-Catalyzed One-Pot Cyclization Reaction of Electron-
Deficient Alkynes and 2-Yn-1-ols: An Efficient Domino
Process to Polysubstituted Furans
Hua Cao,a Huanfeng Jiang,a,* Ronghuan Mai,a Shifa Zhu,a and Chaorong Qia
a
School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, Peopleꢀs
Republic of China
Fax : (+86)-20-8711-2906; e-mail: jianghf@scut.edu.cn
Received: October 1, 2009; Revised: November 16, 2009; Published online: December 30, 2009
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200900685.
Abstract: Transition metal-catalyzed domino reac- tion, regio-isomeric furans were observed when sub-
tions have been used as powerful tools for the prepa- stituted aryl alkynyl ketones were employed. This
ration of polysubstituted furans in a one-pot manner. methodology represents a highly efficient synthetic
In this paper, an efficient synthetic method was de- route to electron-deficient furans for which catalytic
veloped for the construction of tri- or tetrasubstitut- approaches are scarce. The reaction proceeds effi-
ed furans from electron-deficient alkynes and 2-yn-1- ciently under mild conditions with commercially
ols by a silver-catalyzed domino reaction. It is espe- available catalysts and materials.
cially noteworthy that a 2,3,5-trisubstituted 4-ynyl-
furan was formally obtained in an extremely direct Keywords: cyclization; domino process; furans; ho-
manner without tedious stepwise synthesis. In addi- mogeneous catalysis; one-pot reaction; silver
Introduction
Very recently, our group has reported a one-pot,
copper-catalyzed domino process for the synthesis of
The rapid synthesis of elaborate and diverse organic highly
functionalized
polysubstituted
furans
molecules in one single operation without isolation of (Scheme 1).[10] During our further investigation of dif-
intermediates is one of the current concerns of the ferent metal catalysts in this sequential system, we
chemical community[1] that attracts increasing interest. were delighted to find that the product diethyl 5-
To this end, transition metal-catalyzed domino reac- methylfuran-2,3-dicarboxylate (3aa) can be detected
tions[2] have been used as powerful tools for the prep- with the AgBF4/DMF catalytic system at 808C
aration of various compounds in a one-pot manner. (Scheme 2). Herein we report a one-pot, Ag-catalyzed
Furan derivatives are important targets of these
metal-catalyzed methods,[3] because functionalized
furans have exhibited a broad range of biological ac-
tivities[4] and been found as key structural units in
many natural products.[5] They have also been exten-
sively used as building blocks for the synthesis of
Scheme 1. One-pot copper-catalyzed synthesis of diethyl 5-
more elaborate heterocyclic compounds[6] and as com-
formylfuran-2,3-dicarboxylate.
municating moieties in molecular materials.[7] Thus,
the search for efficient transition metal-catalyzed syn-
theses of polysubstituted furans continues to attract
the interest of synthetic chemists. In spite of several
methodologies that were developed during the last
decade,[8] there is still an intrinsic need for improved
routes for the expedient synthesis of more diverse
furans under mild conditions and with a simple cata-
Scheme 2. AgBF4-catalyzed synthesis of diethyl 5-methylfur-
an-2,3-dicarboxylate.
lytic system.[9]
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atom-economical domino process synthesis of poly- AuCl3 with 5 mol% of PPh3 gave the desired furan
substituted furans from electron-deficient alkynes and 3aa in 11% and 13% yields, respectively (Table 1, en-
alkynols without the aid of traditional catalysts such tries 9 and 10). To our surprise, when toluene was
as Au and Pt. This methodology represents a highly used as the solvent, it was found that the yield of 3aa
efficient synthetic route to electron-deficient furans was increased to 76% (Table 1, entry 11). Other sol-
for which catalytic approaches are scarce.
vents, such as 1,2-dichloroethane, 1,4-dioxane, which
were employed, led to moderate yields (Table 1, en-
tries 12 and 13). Different temperatures were
scanned, and 508C was found the most optimal one
for the domino reaction (Table 1, entries 14 and 15).
Results and Discussion
Initial efforts were focused on searching for potential After systematically tuning the different conditions,
catalysts and suitable reaction conditions, and sub- the optimized conditions were found as indicated in
strates 1a and 2a were used as the starting materials. entry 14 in Table 1.
In a typical procedure, 1a (0.5 mmol), 2a (0.5 mmol)
On the basis of the above optimization, we pro-
and DABCO in CH2Cl2 were stirred for 10 min at ceeded to probe the scope of the AgOAc/PPh3-cata-
room temperature.[11] Then the solution was evaporat- lyzed conversion of propargyl vinyl ethers to a variety
ed to dryness under reduced pressure. Subsequently, of polysubstituted furans in Table 2. It was pleasing to
various silver catalysts were added. Based on the ex- find that all the reactions proceeded efficiently and
perience of our previous work, we first examined the afforded the desired products in good to excellent
reaction in the presence of 5 mol% of AgBF4 and yields. To examine the scope of this cyclization, we
10 mol% PPh3. The desired product was obtained first investigated reactions of 1a with prop-2-yn-1-ol
after stirring at 1008C in DMF (Table 1, entry 1). (2a) or but-2-yn-1-ol (2b) or pent-2-yn-1-ol (2c), as
Other Ag(I) catalysts, such as 5 mol% AgOAc, depicted in Table 2. Tetrasubstituted furans (3aa–3ac)
5 mol% AgNO3, 5 mol% Ag2CO3 were next exam- were obtained in 64–71% yields (Table 2, entries 1–3).
ined (Table 1, entries 2–4). Interestingly, AgOAc was The furan products were formed in good yields (en-
found to catalyze the reaction more effectively. Other tries 4–13), when 2a–2c were replaced by 2d–2m.
transition metal salts, such as PdCl2, Pd
ACHTUNGRTEN(NNUG OAc)2, These results showed that aliphatic groups could work
Pd(dba)2 and Ru3(CO)12 (Table 1, entries 5–8), were as well as aryl groups. Both electron-rich aryl groups
ACHTUNGTRENNUNG
employed, no conversion was observed in the above and electron-withdrawing groups furnished good
cases due to the complete recovery of compound 2a’. yields in this reaction. Subsequently, ethyl 3-phenyl-
Treatment of 2a’ with 3 mol% of AuCl3 or 3 mol% of propiolate was examined and the product (3bh) was
Table 1. Optimization of reaction conditions.
Entry
Catalyst
Solvent
Temperature [oC]
Yield [%][a]
1
2
3
4
5
6
7
8
5 mol% AgBF4/10% PPh3
5 mol% AgOAc/10% PPh3
5 mol% AgNO3/10% PPh3
5 mol% AgCO3/10% PPh3
5 mol% PdCl2/10% PPh3
DMF
DMF
DMF
DMF
CH2Cl2
DMF
DMF
DMF
DMF
100
100
100
100
50
100
100
100
100
100
100
100
100
50
37
68
32
trace
–
–
–
–
11
13
76
40
46
79
–
5 mol% Pd
5 mol% Pd
U
5 mol% Ru3(CO)12
3 mol% AuCl3
9
10
11
12
13
14
15
3 mol% AuCl3/5 mol% PPh3
5 mol% AgOAc/10 mol% PPh3
5 mol% AgOAc/10 mol% PPh3
5 mol% AgOAc/10 mol% PPh3
5 mol% AgOAc/10 mol% PPh3
5 mol% AgOAc/10 mol% PPh3
DMF
toluene
1,2-dichloroethane
1,4-dioxane
toluene
toluene
r.t.
[a]
Yield determined by GC.
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Silver-Catalyzed One-Pot Cyclization Reaction of Electron-Deficient Alkynes and 2-Yn-1-ols
Table 2. Ag(I)-catalyzed formation of polysubstituted furans.
Entry
1
Electron-deficient alkyne
2-Yn-1-ol
Product
Yield [%][a]
71
1a
2a
2b
2c
2d
3aa
3ab
3ac
3ad
2
3
4
1a
1a
1a
70
64
68
5
6
1a
1a
2e
2f
3ae
3af
68
59
7
1a
2g
3ag
69
8
1a
1a
1a
1a
2h
2i
3ah
3ai
66
55
67
53
9
10
11
2j
3aj
3ak
2k
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Table 2. (Continued)
Entry
Electron-deficient alkyne
2-Yn-1-ol
Product
Yield [%][a]
62
12
1a
1a
2l
3al
13
2m
3am
64
79
14[b]
1b
1c
2h
2n
3bh
3cn
15
16
70
68
1c
1d
1e
2o
2n
2n
3co
3dn
3en
17[b]
75
72
18[b]
[a]
Isolated yields.
PBu3 substituted DABCO as a catalyst.
[b]
obtained in 79% yield (entry 14). Furthermore, 5-phe-
The above studies dealt with 1a, 1b, 1c, 1d, and 1e
nylpenta-2,4-diyn-1-ol (2n) and 5-p-tolylpenta-2,4- as the starting materials. As an extension of the above
diyn-1-ol (2o) were tested. Interestingly, the desired study (Table 2), we devised other electronic-deficient
products 3cn, 3co, 3dn and 3en were formed in 70%, compounds, such as substituted aryl alkynyl ketones
68%, 75%, 72% yields, respectively (entries 15–18), (1e–1h), to investigate the possibility of this transfor-
when 1c, 1d, and 1e were reacted with 2n or 2o. No mation. In contrast to but-2-ynedioates, phenyl alkyn-
formation of other regioisomers was observed by GC/ yl ketone (1e) gave the corresponding rearrangement
MS. It is especially noteworthy that a novel 2,3,5-tri- products (3ea, 3ed) with good yields only upon the
substituted 4-ynylfuran was formally formed in an ex- initiation of tributylphosphine (Bu3P)[12] (Scheme 3)
tremely direct manner without tedious stepwise syn- since the DABCO-catalyzed reaction of 1e with 2a
thesis.[13]
could not take place. Interestingly, substrates bearing
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Silver-Catalyzed One-Pot Cyclization Reaction of Electron-Deficient Alkynes and 2-Yn-1-ols
tained in reasonable yields. To the best of our knowl-
edge, this transformation had not been reported in
previous work.[14] The molecular structure of repre-
sentative product 4fd was confirmed by an X-ray dif-
fraction study (Figure 1).
On the basis of these experimental results and pre-
vious reports,[14–16] a plausible reaction mechanism is
shown in Scheme 4. The PBu3-promoted nucleoaddi-
tion of propargyl alcohol to electron-deficient alkynes
formed enyne adduct A. Alkyne-coordinated silver B
was generated from the intermediate A and Ag(I).
The complex C which underwent rearrangement to
Scheme 3. Formation of the desired products 3 from 1e and
2.
different substituents gave a pair of regioisomers. As form complex D, was then formed via 5-endo cycliza-
summarized in Table 3, we examined the domino re- tion. Since two carbonyl groups in complex D were
action of alkynyl ketones bearing different aryl both active in the following cyclization reaction, re-
groups with 2-yn-1-ols. The rearrangement products gioisomers would be produced in an around 1:1 ratio
(3fa–3hd) and their regioisomers (4fa–4hd) were ob- by different attack directions (Paths I and II).
Table 3. Cyclization of alkynyl ketones with 2-yn-1-ol.
Entry
1
Electron-deficient alkyne
2-Yn-1-ol
Product
Yield [%][a]
73 (50:50)[b]
1f
2a
3fa+4fa
2
3
4
1f
1g
1h
2d
2a
2a
2d
3fd+4fd
3ga+4ga
3ha+4ha
3hd+4hd
64ACTHNGUTERNNUG
(45:55)[b]
72 (50:50)[b]
83 (53:47)[c]
40 (50:50)[c]
5
1h
[a]
Isolated yields.
The ratio was determined by HPLC.
Ratio was determined by H NMR.
[b]
[c]
1
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Hua Cao et al.
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tions of the domino reactions are ongoing in our labo-
ratory.
Experimental Section
General Remarks
All reactions were performed at the room temperature
under air atmosphere in a round-bottom flask equipped
with a magnetic stir bar. 1H NMR spectra and 13H NMR
spectra were recorded using a Bruker Avance 400 MHz
NMR spectrometer and referenced to 7.24 ppm and
77.0 ppm for chloroform solvent, respectively, with TMS as
internal standard. IR spectra were obtained as potassium
bromide pellets or as liquid films between two potassium
bromide pellets with a Brucker Vector 22 spectrometer.
Mass spectra were recorded on
a Shimadzu GCMS-
QP5050A at an ionization voltage of 70 eV equipped with a
DB-WAX capillary column (internal diameter=0.25 mm,
length=30 m). Elemental analysis was performed on a
Vario EL elemental analyzer. TLC was performed using
commercially prepared 100–400 mesh silica gel plates
(GF254), and visualization was effected at 254 nm. All the
other chemicals were purchased from Aldrich Chemicals.
Figure 1. X-ray structure of compound 4fd.
Conclusions
We have developed a facile one-pot, Ag-catalyzed
atom-economical domino reaction which provides ef-
ficient access to highly substituted furans from elec-
tron-deficient alkynes and alkynols. Different from
previous work,[13] the 2,3,5-trisubstituted 4-ynyl-furan
was obtained from electron-deficient alkynes (1c–1e)
and 2n or 2o in a one-pot manner. The reaction pro-
ceeds efficiently under mild conditions with commer-
cially available catalysts. Further studies and applica-
General Procedure for the Synthesis of Diethyl 5-
Methylfuran-2,3-dicarboxylate (3aa)
Diethyl acetylenedicarboxylate (1a 0.5 mmol), prop-2-yn-1-
ol (2a 0.5 mmol), DABCO (0.05 mmol) in CH2Cl2 were
stirred for 10 min at room temperature. And then the solu-
tion was evaporated to dryness under reduced pressure. Sub-
sequently, AgOAc/PPh3 and toluene were added at 508C.
After completion of the reaction (as monitored by TLC),
the solution was evaporated to dryness under reduced pres-
Scheme 4. Plausible reaction mechanism.
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Silver-Catalyzed One-Pot Cyclization Reaction of Electron-Deficient Alkynes and 2-Yn-1-ols
sure and then water (8 mL) was added. The aqueous solu-
tion was extracted with diethyl ether (3ꢂ8 mL) and the
combined extract was dried with anhydrous MgSO4. The sol-
vent was removed and the crude product was separated by
column chromatography to give a pure sample of 3aa.
(CDCl3, 100 Hz): d=164.0, 157.8, 152.6, 139.4, 138.1, 130.6,
129.4, 128.5, 128.4, 126.7, 125.8, 122.7, 61.6, 61.2, 21.3, 14.1,
13.9, 12.6; MS (EI): m/z (%)=316, 271, 243, 199, 91; anal.
calcd. for C18H20O5: C 68.34, H 6.37; found: C 68.13, H 6.45.
Diethyl 5-methyl-4-o-tolylfuran-2,3-dicarboxylate (3af):
Yellowish viscous oil; IR (KBr): n=3048, 2983, 1732, 1560,
1450, 1177, 758 cmÀ1 1H NMR (CDCl3, 400 Hz): d=7.11–
;
General Procedure for the Synthesis of (5-Methyl-2-
phenylfuran-3-yl)ACHTUNGTRENNUNG(phenyl)methanone (3ea)
7.26 (m, 4H), 4.39 (q, J=8.0 Hz, 2H), 4.14 (q, J=8.0 Hz,
2H), 2.21 (s, 3H), 2.15 (s, 3H), 1.37 (t, J=8.0 Hz, 3H), 1.08
(t, J=8.0 Hz, 3H); 13C NMR (CDCl3, 100 Hz): d=163.3,
157.9, 152.7, 140.0, 137.4, 130.4, 129.9, 128.3, 126.9, 125.5,
122.4, 111.3, 61.2, 60.6, 19.7, 14.2, 13.7, 12.3; MS (EI): m/z
(%)=316, 270, 242, 198, 170, 115, 91; anal. calcd. for
C18H20O5: C 68.34, H 6.37; found: C 68.25, H 6.44.
1,3-Diphenylprop-2-yn-1-one (1c 0.5 mmol), prop-2-yn-1-ol
(2a 0.5 mmol), and PBu3 (0.1 mmol) in CH2Cl2 were stirred
for 30 min at room temperature. And then the solution was
evaporated to dryness under reduced pressure. Subsequent-
ly, AgOAc and toluene were added at 508C. After comple-
tion of the reaction (as monitored by TLC), the solution
was evaporated to dryness under reduced pressure and then
water (8 mL) was added. The aqueous solution was extract-
ed with diethyl ether (3ꢂ8 mL) and the combined extract
was dried with anhydrous MgSO4. The solvent was removed
and the crude product was separated by column chromatog-
raphy to give a pure sample of 3ea.
Diethyl 4-(4-acetylphenyl)-5-methylfuran-2,3-dicarboxy-
late (3ag): Yellowish viscous oil; IR (KBr): n=3046, 2983,
1
1729, 1612, 1573, 1046 cmÀ1; H NMR (CDCl3, 400 Hz): d=
8.05 (d, J=8.0 Hz, 2H), 7.34 (t, J=8.0 Hz, 2H), 4.37 (q, J=
8.0 Hz, 2H), 4.26 (q, J=8.0 Hz, 2H), 3.90 (s, 3H), 2.39 (s,
3H), 1.33 (t, J=8.0 Hz, 3H), 1.19 (t, J=8.0 Hz, 3H);
13C NMR (CDCl3, 100 Hz): d=166.6, 163.6, 157.6, 153.0,
152.9, 140.0, 135.5, 129.8, 128.8, 126.1, 121.8, 61.8, 61.4, 52.1,
14.1, 13.9, 12.7; MS (EI): m/z (%)=360, 329, 315, 288, 211,
143, 128, 58; anal. calcd. for C19H20O7: C 63.33, H 5.59;
found: C 63.02 H 5.63.
Diethyl 5-methylfuran-2,3-dicarboxylate (3aa): Yellowish
viscous oil; IR (KBr): n=2980, 1725, 1603, 1581, 1138 cmÀ1
;
1H NMR (CDCl3, 400 Hz): d=6.30 (s, 1H), 4.25–4.31 (m,
4H), 2.30 (s, 3H), 1.26–1.32 (m, 6H); 13C NMR (CDCl3,
100 Hz): d=162.7, 157.8, 155.4, 142.0, 125.1, 109.2, 61.2,
14.1, 14.0, 13.5; MS (EI): m/z (%)=226, 198, 181, 153, 126,
109; anal. calcd. for C11H14O5: C 58.40, H 6.24; found: C
58.26, H 6.32.
Diethyl 4-(4-methoxyphenyl)-5-methylfuran-2,3-dicarbox-
ylate (3ah): Yellowish viscous oil; IR (KBr): n=3041, 2983,
1
1737, 1606, 1560, 773 cmÀ1; H NMR (CDCl3, 400 Hz): d=
7.22 (d, J=8.0 Hz, 2H), 6.94 (t, J=9.6 Hz, 2H), 4.39 (q, J=
8.0 Hz, 2H), 4.27 (q, J=8.0 Hz, 2H), 3.82 (s, 3H), 2.39 (s,
3H), 1.36 (t, J=7.2 Hz, 3H), 1.24 (t, J=7.2 Hz, 3H);
13C NMR (CDCl3, 100 Hz): d=164.0, 159.1, 157.8, 152.4,
139.3, 130.0, 126.7, 122.9, 122.2, 114.0, 61.6, 61.2, 55.2, 14.1,
13.9, 12.5; MS (EI): m/z (%)=332, 304, 287, 259, 232, 187,
115; anal. calcd. for C18H20O6: C 65.05, H 6.07; found: C
65.22, H 5.93.
Diethyl 4,5-dimethylfuran-2,3-dicarboxylate (3ab): Yel-
lowish viscous oil; IR (KBr): n=2983, 1722, 1556,1092 cmÀ1
;
1H NMR (CDCl3, 400 Hz): d=4.27–4.35 (m, 4H), 2.25 (s,
3H), 1.96 (s, 3H), 1.29–1.35 (m, 6H); 13C NMR (CDCl3,
100 Hz): d=163.9, 157.9, 152.0, 140.0, 126.5, 116.5, 61.3,
61.0, 14.2, 14.1, 11.7, 8.50; MS (EI): m/z (%)=240, 229, 194,
166, 137; anal. calcd. for C12H16O5: C 59.99, H 6.71, found:
C 60.24, H 6.63.
Diethyl 4-(2-methoxyphenyl)-5-methylfuran-2,3-dicarbox-
ylate (3ai): Yellowish viscous oil; IR (KBr): n=3044, 2971,
Diethyl 4-ethyl-5-methylfuran-2,3-dicarboxylate (3ac):
Yellowish viscous oil; IR (KBr): n=2981, 1730, 1603, 1528,
1
1731, 1609, 1561, 1156 cmÀ1; H NMR (CDCl3, 400 Hz): d=
1105 cmÀ1
;
1H NMR (CDCl3, 400 Hz): d=4.28–4.36 (m,
7.97 (d, J=8.0 Hz, 1H), 7.49 (t, J=7.6 Hz, 1H), 7.42 (t, J=
7.6 Hz, 1H), 7.22 (d, J=7.6 Hz, 1H), 4.36 (q, J=6.8 Hz,
2H), 4.09 (q, J=6.8 Hz, 2H), 3.72 (s, 3H), 2.20 (s, 3H), 1.34
(t, J=7.2 Hz, 3H), 1.03 (t, J=7.2 Hz, 3H); 13C NMR
(CDCl3, 100 Hz): d=167.1, 162.8, 158.0, 152.2, 140.4, 131.9,
131.6, 131.1, 130.5, 128.2, 126.1, 122.7, 61.2, 61.1, 52.1, 14.1,
13.6, 12.2; MS (EI): m/z (%)=332, 314, 242, 226; anal.
calcd. for C18H20O6: C 65.05, H 6.07; found: C 65.20, H 5.95.
Diethyl 4-(4-ethylphenyl)-5-methylfuran-2,3-dicarboxylate
(3aj): Yellowish viscous oil; IR (KBr): n=3039, 2975, 1728,
4H), 2.39 (d, J=7.6 Hz, 2H), 2.27 (s, 3H), 1.29–1.36 (m,
6H), 1.07 (t, J=7.6 Hz, 3H); 13C NMR (CDCl3, 100 Hz):
d=164.1, 157.9, 151.8, 139.7, 122.8, 110.8, 61.4, 61.0, 16.9,
14.7, 14.1, 14.0, 11.7; MS (EI): m/z (%)=254, 208, 179, 162,
135, 108; anal. calcd. for C13H18O5: C 61.40, H 7.14; found:
C 61.16, H 7.20.
Diethyl 5-methyl-4-phenylfuran-2,3-dicarboxylate (3ad):
Yellowish viscous oil; IR (KBr): n=3059, 2984, 1732, 1558,
1
1177, 700 cmÀ1; H NMR (CDCl3, 400 Hz): d=7.22–7.34 (m,
1
1600, 1577, 765 cmÀ1; H NMR (CDCl3, 400 Hz): d=7.19 (s,
5H), 4.29 (q, J=7.2 Hz, 2H), 4.21 (q, J=7.2 Hz, 2H), 2.34
(s, 3H), 1.31 (t, J=7.2 Hz, 3H), 1.14 (t, J=7.2 Hz, 3H);
13C NMR (CDCl3, 100 Hz): d=163.9, 157.8, 152.6, 139.5,
131.7, 130.7, 128.8, 128.3, 127.7, 126.6, 122.6, 111.4, 61.6,
61.2, 14.2, 13.9, 12.6; MS (EI): m/z (%)=302, 257, 229, 202,
185, 128, 77; anal. calcd. for C17H18O5: C 67.54, H 6.00;
found: C 67.30, H 6.14.
4H), 4.35 (q, J=7.2 Hz, 2H), 4.25 (q, J=7.2 Hz, 2H), 2.63
(q, J=7.6 Hz, 2H), 2.38 (s, 3H), 1.33 (t, J=6.8 Hz, 3H),
1.18–1.25 (m, 6H); 13C NMR (CDCl3, 100 Hz): d=164.0,
157.8, 152.5, 143.8, 139.4, 128.7, 128.0, 127.9, 126.7, 122.6,
61.6, 61.2, 28.5, 15.3, 14.2, 13.9, 12.6; MS (EI): m/z=(%):
330, 315, 285, 258, 77; anal. calcd. for C19H22O5: C 69.07, H
6.71; found: C 69.29, H 6.57.
Diethyl 5-methyl-4-m-tolylfuran-2,3-dicarboxylate (3ae):
Yellowish viscous oil; IR (KBr): n=3052, 2984, 2935, 1733,
Diethyl 4-(2-ethylphenyl)-5-methylfuran-2,3-dicarboxylate
(3ak): Yellowish viscous oil; IR (KBr): n=3042, 2985, 1727,
1
1610, 1557, 1096, 789 cmÀ1; H NMR (CDCl3, 400 Hz): d=
1608, 1562, 763 cmÀ1 1H NMR (CDCl3, 400 Hz): d=7.25–
;
7.19–7.21 (m, 1H), 7.02–7.09 (m, 3H), 4.31 (q, J=7.2 Hz,
2H), 4.21 (q, J=7.2 Hz, 2H), 2.34 (s, 3H), 2.30 (s, 3H), 1.29
(t, J=6.8 Hz, 3H), 1.16 (t, J=6.8 Hz, 3H); 13C NMR
7.33 (m, 2H), 7.06–7.15 (m, 2H), 4.35 (q, J=8.0 Hz, 2H),
4.18 (q, J=8.0 Hz, 2H), 2.50 (q, J=7.6 Hz, 2H), 2.30 (s,
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FULL PAPERS
3H), 1.33 (t, J=7.2 Hz, 3H), 1.14 (t, J=7.2 Hz, 3H), 0.99 (t,
J=7.2 Hz, 3H); 13C NMR (CDCl3, 100 Hz): d=163.1, 157.7,
153.6, 140.5, 131.3, 129.9, 126.3, 124.0, 118.6, 116.8, 115.8,
61.4, 61.3, 46.2, 14.1, 13.7, 12.6, 11.5; MS (EI): m/z (%)=
330, 315, 285, 257, 77; anal. calcd. for C19H22O5: C 69.07, H
6.71; found: C 70.42, H 6.65.
(EI): m/z (%)=390, 223, 207, 119, 105, 91, 77; anal. calcd.
for C28H22O2: C 86.13, H 5.68; found: C 85.90, H 5.70.
[5-Methyl-2-phenyl-4-(phenylethynyl)furan-3-yl]-
AHCTUNGTERG(NNNU phenyl)methanone (3en): Yellowish viscous oil; IR (KBr):
1
n=3029 1738, 1632 cmÀ1; H NMR (CDCl3, 400 Hz): d=7.94
(d, J=7.2 Hz, 2H), 7.08–7.65 (m, 13H), 2.54 (s, 3H);
13C NMR (CDCl3, 100 Hz): d=191.3, 154.8, 151.9, 137.2,
132.7, 130.7, 129.6, 128.8, 128.4, 128.3, 128.2, 128.1, 127.9,
127.8, 127.6, 127.5, 126.7, 126.1, 122.5, 121.7, 105.7, 94.7,
79.4, 12.3; MS (EI): m/z (%)=390, 223, 207, 119, 105, 91,
77; anal. calcd. for C26H18O2: C 86.16, H 5.01, found: C
86.41, H 4.97.
Diethyl 4-(2-fluorophenyl)-5-methylfuran-2,3-dicarboxy-
late (3al): Yellowish viscous oil; IR (KBr): n=3057, 2986,
1
1732, 1612, 1575, 1027 cmÀ1; H NMR (CDCl3, 400 Hz): d=
7.30–7.33 (m, 2H), 7.07–7.15 (m, 2H), 4.36 (q, J=7.2 Hz,
2H), 4.21 (q, J=8.0 Hz, 2H), 2.31 (s, 3H), 1.32 (t, J=
7.2 Hz, 3H), 1.15 (t, J=7.2 Hz, 3H); 13C NMR (CDCl3,
100 Hz): d=163.1, 157.7, 153.6, 140.5, 131.3, 129.9, 129.8
126.3, 124.1, 118.6, 115.8, 115.6, 61.4, 61.3, 14.1, 13.8, 12.7;
MS (EI): m/z (%)=320, 275, 247, 220, 203, 116; anal. calcd.
for C17H17FO5: C 63.74, H 5.35; found: C, 63.56, H 5.42.
Diethyl 5-methyl-4-(thiophen-2-yl)furan-2,3-dicarboxylate
(3am): Yellowish viscous oil; IR (KBr): n=3057, 2986, 1732,
(5-Methyl-2-phenylfuran-3-yl)ACTHUNTGRNEUNG(phenyl)methanone (3ea):
Yellowish viscous oil; IR (KBr): n=3037, 1746, 1612, 1582,
1
1031 cmÀ1; H NMR (CDCl3, 400 Hz): d=7.81 (d, J=9.6 Hz,
2H), 7.64–7.66 (m, 2H), 7.25–7.49 (m, 6H), 6.28 (s, 1H),
2.39 (s, 3H); 13C NMR (CDCl3, 100 Hz): d=191.9, 154.4,
151.1, 138.2, 132.6,130.0, 129.6, 128.9, 128.6, 128.5, 128.4,
128.2, 127.2, 121.7, 109.7, 13.3; MS (EI): m/z (%)=262, 185,
105, 77; anal. calcd. for C18H14O2: C 82.42, H 5.38; found: C
82.03, H 5.42.
1
1612, 1575, 1027 cmÀ1; H NMR (CDCl3, 400 Hz): d=7.33–
7.34 (m, 1H), 7.05–7.06 (m, 2H), 4.30–4.39 (m, 4H), 2.49 (s,
3H), 1.28–1.37 (m, 6H); 13C NMR (CDCl3, 100 Hz): d=
163.7, 157.6, 153.2, 139.5, 132.9, 127.3 126.9, 125.9, 116.1,
111.6, 61.9, 61.4, 14.2, 13.9, 13.0; MS (EI): m/z (%)=308,
263, 235, 208, 163, 135, 91; anal. calcd. for C15H16O5S: C
58.43, H 5.23; found: C 58.26, H 5.17.
(5-Methyl-2,4-diphenylfuran-3-yl)ACTHNUTRGNE(NUG phenyl)methanone
(3ed): Yellowish viscous oil; IR (KBr): n=3032, 1749, 1604,
1
1576 cmÀ1; H NMR (CDCl3, 400 Hz): d=7.81 (d, J=9.6 Hz,
2H), 7.55–7.57 (d, J=8.4 Hz, 2H), 7.35–7.39 (m, 1H), 7.14–
7.27 (m, 10H), 2.45 (s, 3H); 13C NMR (CDCl3, 100 Hz): d=
193.7, 150.8, 148.1, 137.5, 133.1, 132.2, 130.0, 129.8, 129.7,
129.3, 129.0, 128.9, 128.7, 128.6, 128.4, 128.2, 128.0, 126.8,
126.2, 123.5, 121.7, 12.2; MS (EI): m/z (%)=262, 141, 105,
77; anal. calcd. for C24H18O2: C 85.18, H 5.36; found: C
84.92, H 5.43.
Ethyl 4-(4-methoxyphenyl)-5-methyl-2-phenylfuran-3-car-
boxylate (3bh): white solid, mp 100.8–102.78C; IR (KBr):
n=3057, 2986, 1732, 1612, 1575, 1027 cmÀ1
;
1H NMR
(CDCl3, 400 Hz): d=7.83 (d, J=7.2 Hz, 2H), 7.36–7.44 (m,
3H), 7.26 (d, J=8.0 Hz, 2H), 6.93 (d, J=7.6 Hz, 2H), 4.13
(q, J=6.8 Hz, 2H), 3.85 (s, 3H), 2.32 (s, 3H), 1.05 (t, J=
6.8 Hz, 3H); 13C NMR (CDCl3, 100 Hz): d=164.6, 158.7,
153.7, 148.2, 130.7, 130.2, 128.5, 128.0, 127.5, 125.2, 122.5,
115.0, 113.4, 60.3, 55.2, 13.6, 11.9; MS (EI): m/z (%)=336,
308, 291, 105, 77; anal. calcd. for C21H20O4: C 74.98, H 5.99;
found: C 74.76, H 6.02.
(2-Chlorophenyl)(5-methyl-2-phenylfuran-3-yl)methanone
1
(3fa): IR (KBr): n=3027, 1723, 1608, 1542 cmÀ1; H NMR
(CDCl3, 400 Hz): d=7.76–7.78 (m, 2H), 7.20–7.36 (m, 7H),
6.23 (s, 1H), 2.37 (s, 3H); 13C NMR (CDCl3, 100 Hz): d=
189.8, 156.9, 151.5, 139.7, 131.3, 130.9, 130.0, 129.7, 129.2,
129.1, 128.9, 128.0, 127.9, 126.3, 122.5, 109.0, 13.3; MS (EI):
m/z (%)=296, 185, 139, 77; anal. calcd. for C18H13ClO2: C
72.85, H 4.42; found: C 72.73, H 4.49.
Dimethyl 5-methyl-4-(2-phenylethynyl)furan-2,3-dicarbox-
ylate (3cn): IR (KBr): n=3051 2969, 1730, 1647, 1582,
1027 cmÀ1
;
1H NMR (CDCl3, 400 Hz): d=7.45–7.47 (m,
(2-Chlorophenyl)(4-methyl-2-phenylfuran-3-yl)methanone
(4fa): Yellowish viscous oil; IR (KBr): n=3029, 1720, 1600,
2H), 7.31–7.33 (m, 3H), 3.93 (s, 3H), 3.89 (s, 3H), 2.49 (s,
3H); 13C NMR (CDCl3, 100 Hz): d=162.6, 159.4, 157.8,
140.6, 131.6, 128.7, 128.5, 126.4, 122.7, 106.5, 94.9, 52.7, 52.5,
13.2; MS (EI): m/z (%)=298, 267, 211, 152, 59; anal. calcd.
for C17H14O5: C 68.45, H 4.73; found: C 68.59, H 4.69.
1
1537 cmÀ1; H NMR (CDCl3, 400 Hz): d=7.74 (d, J=8.0 Hz,
2H), 7.37–7.43 (m, 2H), 7.22–7.33 (m, 3H), 7.16–7.20 (m,
2H), 6.46 (s, 1H), 2.43 (s, 3H); 13C NMR (CDCl3, 100 Hz):
d=191.0, 152.4, 138.0, 133.5, 132.2, 131.9, 130.1, 129.8, 129.7,
129.3, 127.8, 126.3, 124.3, 108.2, 13.4; MS (EI): m/z (%)=
296, 261, 130, 77; anal. calcd. for C18H13ClO2: C 72.85, H
4.42; found: C 72.42, H 4.46.
Dimethyl 5-methyl-4-(p-tolylethynyl)furan-2,3-dicarboxy-
late (3co): white solid, mp 123.9–125.48C; IR (KBr): n=
1
3055 2973, 1728, 1650 cmÀ1; H NMR (CDCl3, 400 Hz): d=
7.37 (d, J=8.0 Hz, 2H), 7.13 (d, J=7.2 Hz, 2H), 3.95 (s,
3H), 3.91 (s, 3H), 2.50 (s, 3H), 2.36 (s, 3H); 13C NMR
(CDCl3, 100 Hz): d=162.0, 158.5, 157.2, 140.0, 138.3, 130.9,
128.6, 125.9, 119.1, 106.0, 94.5, 52.0, 51.8, 20.9, 12.5; MS
(EI): m/z (%)=312, 297, 281, 167, 59; anal. calcd. for
C18H16O5: C 69.22, H 5.16; found: C 69.43, H 5.19.
(2-Chlorophenyl)(5-methyl-2,4-diphenylfuran-3-yl)metha-
none (3fd): Yellowish viscous oil; IR (KBr): n=3018, 1732
1609, 1561 cmÀ1 1H NMR (CDCl3, 400 Hz): d=7.71–7.73
;
(m, 2H), 7.42–7.44 (m, 1H), 7.14–7.32 (m, 11H), 2.47 (s,
3H); 13C NMR (CDCl3, 100 Hz): d=191.9, 150.7, 149.1,
137.6, 133.4, 132.5, 132.1, 132.0, 130.1, 129.8, 129.6, 129.4,
129.3, 128.1, 127.7, 126.8, 126.4, 124.2, 122.8, 12.3; MS (EI):
m/z (%)=372, 261, 139, 111, 105, 77; anal. calcd. for
C24H17ClO2: C 77.31, H 4.60; found: C 77.13, H 4.68.
[5-Methyl-4-(phenylethynyl)-2-p-tolylfuran-3-yl]ACTHNUGRTNEUNG(p-tolyl)-
methanone (3dn): white solid, mp 142.5–144.38C; IR (KBr):
1
n=3035, 2950, 1742, 1645 cmÀ1; H NMR (CDCl3, 400 Hz):
d=7.84 (d, J=8.0 Hz, 2H), 7.53 (d, J=8.0 Hz, 2H), 7.06–
7.22 (m, 9H), 2.53 (s, 3H), 2.38 (s, 3H), 2.31 (s, 3H);
13C NMR (CDCl3, 100 Hz): d=191.1, 154.4, 151.8, 143.4,
138.2, 134.8, 130.6, 129.8, 128.6, 128.5, 127.5, 127.4, 126.2,
126.0, 122.7, 121.2, 105.6, 94.5, 79.6, 21.4, 20.7, 12.3; MS
[2-(2-Chlorophenyl)-5-methyl-4-phenylfuran-3-yl]-
AHCTUNGTRENNUNG
;
400 Hz): d=7.70–7.73 (m, 2H), 7.29–7.35 (m, 5H), 7.16–7.25
(m, 7H), 2.37 (s, 3H); 13C NMR (CDCl3, 100 Hz): d=191.0,
150
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Adv. Synth. Catal. 2010, 352, 143 – 152

Silver-Catalyzed One-Pot Cyclization Reaction of Electron-Deficient Alkynes and 2-Yn-1-ols
154.5, 148.4, 138.4, 132.6, 132.0, 131.7, 131.0, 129.6, 129.3,
128.9, 128.5, 128.1, 127.9, 127.7, 127.5, 126.8, 125.9, 123.3,
12.0; MS (EI): m/z (%)=372, 337, 105, 77; anal. calcd. for
C24H17ClO2: C 77.31, H 4.60; found: C 77.54, H 4.51.
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A. M. Echavarren, J. Am. Chem. Soc. 2006, 128, 5033–
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(5-Methyl-2-phenylfuran-3-yl)(thiophen-2-yl)methanone
(3ga): Yellowish viscous oil; IR (KBr): n=3020, 1728 1610,
1540 cmÀ1
;
1H NMR (CDCl3, 400 Hz): d=7.78–7.80 (m,
2H), 7.63–7.66 (m, 2H), 7.30–7.39 (m, 3H), 7.06–7.08 (m,
1H), 6.44 (s, 1H), 2.45 (s, 3H); 13C NMR (CDCl3, 100 Hz):
d=183.4, 153.6, 151.3, 144.8, 134.2, 133.9, 133.0, 130.8, 130.0,
128.6, 128.3, 127.8, 127.0, 121.6, 109.3, 13.4; MS (EI): m/z
(%)=268, 235, 165, 111, 77; anal. calcd. for C16H12O2S: C
71.62, H 4.51; found: C 71.84, H 4.14.
[5-Methyl-2-(thiophen-2-yl)furan-3-yl]ACHTGNUTERN(UGNN phenyl)methanone
1
(4ga): IR (KBr): n=3025, 1726, 1602, 1530 cmÀ1; H NMR
(CDCl3, 400 Hz): d=7.88–7.90 (m, 3H), 7.48–7.60 (m, 3H),
7.38–7.40 (m, 1H), 7.08–7.10 (m, 1H), 6.29 (s, 1H), 2.41 (s,
3H); 13C NMR (CDCl3, 100 Hz): d=190.5, 150.4, 138.9,
132.2, 132.0, 129.3, 128.2, 127.6, 127.3, 127.1, 120.3, 109.7,
13.3; MS (EI): m/z (%)=268, 191, 105, 77; anal. calcd. for
C16H12O2S: C 71.62, H 4.51; found: C 71.76, H 4.15.
(5-Methyl-2-phenylfuran-3-yl)
N
(3ha)
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and (5-methyl-2-p-tolylfuran-3-yl)ACHTUNGTRENNNUG
1H NMR (CDCl3, 400 Hz): d=7.87 (d, J=8.0 Hz, 2H), 7.82
(d, J=8.0 Hz, 2H), 7.74 (d, J=8.0 Hz, 2H), 7.64 (d, J=
8.0 Hz, 2H), 7.38–7.43 (m, 3H), 7.30–7.32 (m, 3H), 7.21 (d,
J=8.0 Hz, 2H), 7.14 (d, J=8.0 Hz, 2H), 6.31 (s, 2H), 2.42
(s, 3H) , 2.41 (s, 3H) , 2.39 (s, 3H) , 2.34 (s, 3H); 13C NMR
(CDCl3, 100 Hz): d=191.9, 191.7, 154.9, 153.9, 151.0, 150.8,
143.5, 138.7, 138.4, 135.8, 132.5, 132.3, 130.1, 129.9, 129.6,
129.4, 129.0, 128.9, 128.6, 128.4, 128.3, 128.2, 128.1, 127.3,
127.2, 127.1, 127.1, 121.9, 121.1, 109.8, 109.7, 21.6, 21.3, 13.5,
13.4; MS (EI): m/z (%)=276, 105, 91, 55; anal. calcd. for
C16H12O2: C 82.58, H 5.84; found: C 82.15, H 5.90.
(5-Methyl-2,4-diphenylfuran-3-yl)
ACHTUNGTRENNUNG
(3hd) and (5-methyl-4-phenyl-2-p-tolylfuran-3-yl)AHCTUNGTRENNUNG
1
methanone (4hd): H NMR (CDCl3, 400 Hz): d=7.85 (d, J=
8.0 Hz, 2H), 7.80 (d, J=8.0 Hz, 2H), 7.62 (d, J=7.2 Hz,
2H), 7.53 (d, J=8.0 Hz, 2H), 7.38–7.43 (m, 2H), 7.25–7.32
(m, 16H), 7.08–9.10 (m, 4H), 2.50 (s, 3H), 2.49 (s, 3H) ,
2.32 (s, 3H) , 2.31 (s, 3H); 13C NMR (CDCl3, 100 Hz): d=
194.0, 193,8, 148.3, 144.4, 138.3, 133.3, 132.6, 132.5, 130.2,
130.0, 129.4, 129.3, 128.7, 128.5, 128.4, 128.2, 127.1, 126.4,
126.2, 123.7, 21.8, 21.4, 12.6, 12.5; MS (EI): m/z (%)=352,
105, 91, 77, 55; anal. calcd. for C16H12O2: C 85.20, H 5.72;
found: C 85.77, H 5.68.
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ˇ
A. V. Kelin, V. Gevorgyan, J. Am. Chem. Soc. 2008,
Acknowledgements
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Yap, D. Chernyak, V. Gevorgyan, J. Am. Chem. Soc.
2007, 129, 9868–9878; c) L. Peng, X. Zhang, M. Ma,
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We thank the National Natural Foundation of China (Nos.
20625205, 20772034 and 20932002) and Guangdong Natural
Science Foundation (No. 07118070) for financial support.
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