Facile strategy for the synthesis of furans utilizing silver(i)-promoted addition/oxidative cyclization of 1,3-dicarbonyl compounds and alkynoates

Article abstract of DOI:10.1080/00397911.2011.615102

The addition/oxidative cyclization of alkynoates with 1,3-dicarbonyl compounds in the presence of Ag(I) leads to polysubstituted furans. The reaction corresponds to the construction of a furan fragment, which also provides a new way to form the C-O bond.

Full text of DOI:10.1080/00397911.2011.615102

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Facile Strategy for the Synthesis of
Furans Utilizing Silver(I)-Promoted
Addition/Oxidative Cyclization of 1,3-
Dicarbonyl Compounds and Alkynoates
Wei-Bing Liu a , Cui Chen a & Qing Zhang a
a School of Chemistry and Life Science, Guangdong University of
Petrochemical Technology, Maoming, China
Accepted author version posted online: 22 Feb 2012.Version of
record first published: 07 Jan 2013.
To cite this article: Wei-Bing Liu , Cui Chen & Qing Zhang (2013): Facile Strategy for the Synthesis
of Furans Utilizing Silver(I)-Promoted Addition/Oxidative Cyclization of 1,3-Dicarbonyl Compounds
and Alkynoates, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 43:7, 951-960
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Synthetic Communications1, 43: 951–960, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.615102
FACILE STRATEGY FOR THE SYNTHESIS OF FURANS
UTILIZING SILVER(I)-PROMOTED ADDITION/
OXIDATIVE CYCLIZATION OF 1,3-DICARBONYL
COMPOUNDS AND ALKYNOATES
Wei-Bing Liu, Cui Chen, and Qing Zhang
School of Chemistry and Life Science, Guangdong University of
Petrochemical Technology, Maoming, China
GRAPHICAL ABSTRACT
Abstract The addition/oxidative cyclization of alkynoates with 1,3-dicarbonyl compounds
in the presence of Ag(I) leads to polysubstituted furans. The reaction corresponds to the
construction of a furan fragment, which also provides a new way to form the C-O bond.
Keywords Addition=oxidative cyclization; furan; silver
INTRODUCTION
Over the past few decades, transition metal–catalyzed reactions have emerged
as powerful and general methods for the synthesis of organic compounds.[1]
Especially late transition metals, the so-called coinage metals, have been widely used
for various organic transformations in organic synthesis.[2] In the coinage metal ser-
ies, silver and gold exhibit special properties because of the availability of the orbitals
and relativistic contraction of their electron cloud. The applications of silver salts,
mainly Ag (I), in organic synthesis today can be classified into two well-defined
Received June 11, 2011.
Address correspondence to Wei-Bing Liu, School of Chemistry and Life Science, Guangdong
University of Petrochemical Technology, 2 Guangdu Road, Maoming 525000, China. E-mail: lwb409@
yahoo.com.cn
951

952
W.-B. LIU, C. CHEN, AND Q. ZHANG
areas: silver-promoted oxidation processes[3] and homogeneous silver-mediated cat-
alyzed reactions.[4] In this article, we disclose an expeditious method in which the
Ag(I) is used not only as the catalyst but also as the oxidant to construct furan deri-
vatives.[5] As we all know, furans are some of the most important heteroaromatic
compounds with widespread occurrence in nature[6] and are frequently found in
many natural products arising from plants and marine organisms.[7] In addition,
many of the naturally occurring furans have shown interesting biological activities,
such as antiallergic and antiasthamatic activities,[8] as well as cytotoxic and antitu-
mor properties,[9] antidiabetic activity,[10] and several other potentially useful
activities.[11]
RESULTS AND DISCUSSION
Our preliminary investigations were focused on the systematic evaluation of
different silver catalysts for the desired addition=oxidative cyclization of diethyl
but-2-ynedioate (1a) and 1-phenylbutane-1,3-dione (2a) (Table 1). As shown in
Table 1. Optimization of reaction conditionsa
Entry
Additive
Solvent
Time (h)
Yield (%)b
1
AgOAc
Ag2CO3
AgBF4
DCE
DCE
5
5
5
5
5
5
5
5
5
5
5
5
5
5
2
2
3
4
45
23
2
3
DCE
DCE
Np
Np
Trace
Np
Trace
52
4
AgOTf
Ag2O
5
DCE
DCE
DCE
6
AgNO3
AgClO4
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
CH3CO2Na
AgOAc
AgOAc
AgOAc
7
8
CH3CN
DMSO
DMA
Dioxane
Benzene
DMA
DMA
DMA
DMA
DMA
DMA
9
57
71
10
11
12
13
14
15c
16d
17d
18d
48
37
Trace
78
70
79
84
84
aReaction conditions: 1a (0.25 mmol), 2a (0.25 mmol), additive (1.2 equiv.), in 2 mL solvent at 80 ꢀC for
5 h.
bIsolated yields.
c100 ꢀC.
d120 ꢀC.

SYNTHESIS OF FURANS
953
Table 2. Synthesis of polyfunctional furans from alkynoates and 1,3-dicarbonyl compoundsa
Entry
1
2
Product
Yieldb (%)
1
81
2
3
4
1a
1a
1a
77
80
82
5
1a
88
6
2a
50
(Continued )

954
W.-B. LIU, C. CHEN, AND Q. ZHANG
Table 2. Continued
Entry
1
2
Product
Yieldb (%)
7
1b
2b
65
8
9
1b
2d
2a
53
78
10
1c
2b
71
11
12
13
1c
1c
1c
2c
2d
2e
73
76
75
aAll the reactions are carried out using 1.0 mmol of 1, 1.0 mmol of 2, 1.2 equivalence of AgOAc in DMA
(2.0 mL) at 120 ꢀC for 3 h.
bIsolated yield.

SYNTHESIS OF FURANS
955
Scheme 1. Plausible reaction mechanism.
Table 1, the AgOAc showed the greatest activity and afforded the best result in
1,2-dichloroethane (DCE) (entries 1–7). By changing the reaction solvents (entries
8–12), we found that the reaction was not sensitive to the solvent medium and that
N,N-dimethylacetamide (DMA) led to the best result (entry 10). We next investi-
gated the dosage of AgOAc (entries 13 and 14), the results showed that 1.2 equiva-
lents of AgOAc was the preferable dosage. Finally, it was interesting to find that
when increasing the reaction temperature of this transformation, a significant
increase of the yield was observed (entries 14–16) and the practical reaction tempera-
ture was 120 ꢀC (entry 16). The optimum reaction time was 3 h (entry 17).
Under the optimized conditions, we explored the scope of the reaction, and the
results are summarized in Table 2. A wide variety of 1,3-dicarbonyl compounds
could successfully react with alkynoates to afford the corresponding furan deriva-
tives (Table 2). However, the electronic property of the substituents on the alkynes
has an obvious influence on the reaction. This reaction proceeded smoothly and
afforded the desired product in good to excellent yields for those alkynes substituted
with two electron-withdrawing groups. For example, the diethyl but-2-ynedioate (1a)
reacted with 2a–2e and led to 3aa–3ae in good isolated yield, whereas ethyl 3-phenyl-
propiolate led to inferior result or even traces of the desired product. Methyl propio-
late (1c) was a desirable partner of 1a, and when it was employed in the reaction with
1,3-dicarbonyl compounds, it would produce the products in reasonable isolated
yield.
A plausible mechanism for the described addition=oxidative cyclization, exem-
plified by the formation of diethyl 4-acetyl-5-phenylfuran-2, 3-dicarboxylate 3aa, can
be rationalized as shown in Scheme 1. The 1,3-dicarbonyl compound 2a is first oxi-
dized by silver(I)[12] metal to generate the a -oxoalkyl radical 4, which then attacks
the C-C triple bond of diethyl but-2-ynedioate to give the radical 5. The nucleophilic
adduct 5 now undergoes fast nucleophilic attack by carbonyl oxygen to a benzylic
radical 6, which oxidizes to the desired furan product 3aa by oxygen of air.
CONCLUSION
In conclusion, a facile and expeditious addition=oxidative cyclization method
a
to construct
furan framework was developed from alkynoates and

956
W.-B. LIU, C. CHEN, AND Q. ZHANG
1,3-diketones=b-ketoesters. The silver(I) plays a dual role in the reaction, in which
Ag (I) is used not only as the catalyst but also as the oxidant. The scope, mechanism,
and synthetic applications of this protocol are currently under investigation.
EXPERIMENTAL
All the reactions were carried out at 120 ꢀC in a Schlenk tube equipped with
1
magnetic stir bar. Solvents and all reagents were used as received. H NMR spectra
were recorded in CDCl3 at 400 MHz, and 13C NMR spectra were recorded in CDCl3
at 100 MHz. GC–MS was obtained using electron ionization (EI). Infrared (IR)
spectra were obtained as potassium bromide pellets or as liquid films between two
potassium bromide pellets with a Brucker Vector 22 spectrometer. Thin-layer chro-
matography (TLC) was performed using commercially prepared 100- to 400-mesh
silica-gel plates (GF254), and visualization was effected at 254 nm. All the other che-
micals were purchased from Aldrich Chemicals.
General Procedure for the Synthesis of Diethyl 4-Acetyl-5-
phenylfuran-2,3-dicarboxylate 3aa
To a stirring mixture of diethyl but-2-ynedioate (1a, 170 mg, 1.0 mmol) and
1-phenylbutane-1,3-dione (2a, 162 mg, 1.0 mmol), 2 mL DMA and AgOAc
(200.4 mg, 1.2 mmol) were added successively. The mixture was stirred at 120 ꢀC
for 3 h in a Schlenk tube. After cooling, the solution was directly subjected to iso-
lation by PTLC (GF254) and eluted with a 10:2 petroleum ether–diethyl ether mix-
ture to furnish the desired product 3aa (300.1 mg, 91%) as a pale yellow viscous oil.
Diethyl 4-Acetyl-5-phenylfuran-2,3-dicarboxylate (3aa)[13]
Pale yellow viscous oil: IR vmax (KBr): 3065, 2996, 2938, 1724, 1659, 1597,
1
1410, 1252, 1171, 1060, 942, 910, 864, 772, 697 cmꢁ1; H NMR (400 MHz, CDCl3):
d 7.72–7.70 (m, 2H), 7.57–7.53 (m, 1H), 7.45–7.41 (m, 2H), 4.36 (q, 2H, J ¼ 7.2 Hz),
3.94 (q, 2H, J ¼ 7.2 Hz), 2.41 (s, 3H), 1.34 (t, 3H, J ¼ 7.2 Hz), 1.05 (t, 3H, J ¼ 7.2 Hz);
13C NMR (100 MHz, CDCl3): d 189.8, 262.2, 159.3, 157.4, 140.4, 137.8, 133.2, 128.8,
128.5, 125.5, 122.1, 67.8, 61.7, 14.0, 13.9, 13.5; GC–MS m=z (% rel. inten.): 330.07
(Mþ, 69.67), 240.92 (100).
Diethyl 4-Benzoyl-5-phenylfuran-2,3-dicarboxylate (3ab)[13]
Pale yellow viscous oil: IR vmax (KBr): 3053, 2964, 2935, 1725, 1667, 1596,
1
1234, 1078, 1038, 903, 860, 812, 771, 693 cmꢁ1; H NMR (400 MHz, CDCl3): d
7.81–7.79 (m, 2H), 7.61–7.59 (m, 2H), 7.50–7.48 (m, 1H), 7.38–7.24 (m, 5H), 4.41
(q, 2H, J ¼ 7.2 Hz), 4.06 (q, 2H, J ¼ 7.2 Hz), 1.38 (t, 3H, J ¼ 7.2 Hz), 1.07 (t, 3H,
J ¼ 7.2 Hz); 13C NMR (100 MHz, CDCl3): d 190.2, 161.6, 157.5, 155.2, 141,4,
136.9, 133.7, 130.2, 129.0, 128.8, 128.6, 127.8, 127.4, 126.2, 121.5, 61.8, 14.1, 13.6;
GC–MS m=z (% rel. inten.): 392.08 (Mþ, 100).

SYNTHESIS OF FURANS
957
Triethyl 5-Phenylfuran-2,3,4-tricarboxlate (3ac)
Yellow viscous oil: IR vmax (KBr): 3066, 2964, 1937, 1723, 1606, 1548, 1388,
1
1371, 1283, 1164, 1071, 938, 847, 771, 694 cmꢁ1; H NMR (400 MHz, CDCl3): d
7.93–7.90 (m, 2H), 7.46–7.43 (m, 3H), 4.43–4.34 (m, 4H), 4.26 (q, 2H, J ¼ 7.2 Hz),
1.41–1.33 (m, 3H), 1.25 (t, 3H, J ¼ 7.2 Hz); 13C NMR (100 MHz, CDCl3): d 163.1,
161.4, 159.5, 157.3, 139.7, 130.8, 129.2, 128.2, 128.0, 127.7, 127.4, 62.2, 61.8, 61.4,
14.1, 14.0, 13.9; GC–MS m=z (% rel inten.): 359.95 (Mþ, 100). Anal. calcd. for
C19H20O7: C, 63.33; H, 5.59. Found: C, 63.58; H, 5.40.
Diethyl 4-Acetyl-5-methylfuran-2,3-dicarboxylate (3ad)[13,14]
Pale yellow viscous oil: IR vmax (KBr): 2965, 2936, 1709, 1675, 1547, 1411,
1
1295, 1207, 1156, 1055, 1020, 958, 896, 860, 774, 682 cmꢁ1; H NMR (400 MHz,
CDCl3): d 4.40 (q, 2H, J ¼ 7.2 Hz), 4.33 (q, 2H, J ¼ 7.2 Hz), 2.64 (s, 3H), 2.38 (s,
3H), 1.37 (t, 3H, J ¼ 7.2 Hz), 1.33 (t, 3H, J ¼ 7.2 Hz); 13C NMR (100 MHz, CDCl3):
d 191.7, 163.8, 160.9, 157.3, 139.2, 125.5, 122.3, 62.3, 61.7, 29.4, 15.0, 14.1, 13.9; GC–
MS m=z (% rel. inten.): 368.04 (Mþ, 18.14), 221.96 (100).
Triethyl 5-Methylfuran-2,3,4-tricarboxylate (3ae)[13]
Yellow viscous oil: IR vmax (KBr): 2985, 2938, 1722, 1609, 1566, 1373, 1251,
1175, 1058, 1022, 982, 908, 860, 786, 705, 684 cmꢁ1; 1H NMR (400 MHz, CDCl3): d
4.39–4.23 (m, 6H), 2.62 (s, 3H), 1.37–1.27 (m, 9H); 13C NMR (100 MHz, CDCl3): d
163.2, 162.2, 161.6, 157.2, 139.0, 126.1, 114.0, 62.0, 61.6, 60.9, 14.1, 14.0; GC–MS
m=z (% rel. inten.): 297.98 (Mþ, 21.74), 251.84 (100).
Ethyl 4-Benzoyl-3,5-diphenylfuran-2-carboxylate (3bb)
Yellow solid, mp: 109–110 ꢀC; IR vmax (KBr): 2961, 2896, 1815, 1710, 1659,
1
1401, 1270, 1236, 1173, 1029, 973, 900, 863, 765, 688 cmꢁ1; H NMR (400 MHz,
CDCl3): d 7.74–7.72 (m, 1H), 7.66–7.65 (m, 1H), 7.30–7.28 (m, 1H), 7.24–7.18 (m,
7H), 4.27 (q, 2H, J ¼ 7.2 Hz), 1.23 (t, 3H, J ¼ 7.2 Hz); 13C NMR (100 MHz, CDCl3):
d 192.4, 158.7, 154.1, 138.6, 136.9, 135.3, 133.6, 130.2, 129.7, 128.6, 128.5, 128.4,
128.3, 128.2, 127.6, 127.0, 123.4, 61.0, 14.0; GC–MS m=z (% rel. inten.): 396.14
(Mþ, 73.45), 104.98 (100). Anal. calcd. for C26H20O4: C, 78.77; H, 5.09. Found:
C, 78.60; H, 4.89.
Ethyl 4-Acetyl-5-methyl-3-phenylfuran-2-carboxylate (3bd)
Yellow viscous oil: IR vmax (KBr): 3061, 2983, 2931, 1725, 1674, 1366, 1355,
1292, 1228, 1095, 1040, 976, 918, 867, 804, 692 cmꢁ1; 1H NMR (400 MHz, CDCl3): d
7.70–7.67 (m, 2H), 7.40–7.35 (m, 3H), 4.32 (q, 2H, J ¼ 7.2 Hz), 2.54 (s, 3H), 2.42 (s,
3H), 1.29 (t, 3H, J ¼ 7.2 Hz); 13C NMR (100 MHz, CDCl3): d 194.3, 164.8, 155.6,
152.0, 129.5, 128.9, 128.4, 126.9, 123.8, 113.9, 61.6, 30.1, 14.0, 13.9; GC–MS m=z
(% rel inten.): 271.95 (Mþ, 35.64), 225.68 (100). Anal. calcd. for C16H16O4: C,
70.57; H, 5.92. Found: C, 70.69; H, 5.98.

958
W.-B. LIU, C. CHEN, AND Q. ZHANG
Methyl 4-Acetyl-5-phenylfuran-2-carboxylate (3ca)
Yellow solid; mp: 68–70 ꢀC; IR vmax (KBr): 1710, 1682, 1585, 1265, 1173,
1
1080, 996, 884, 840, 798, 710, 683 cmꢁ1; H NMR (400 MHz, CDCl3): d 7.95–7.93
(m, 2H), 7.52 (s, 1H), 7.45–7.44 (m, 3H), 3.91 (s, 3H), 2.43 (s, 3H); 13C NMR
(100 MHz, CDCl3): d 190.0, 163.0, 158.7, 141.8, 138.1, 132.6, 128.7, 128.3, 122.0,
119.4, 52.0, 14.4; GC–MS m=z (% rel inten.): 244.03 (Mþ, 62.76), 228.86 (100). Anal.
calcd. for C14H12O4: C, 68.85; H, 4.95. Found: C, 70.10; H, 4.88.
Methyl 4-Benzoyl-5-phenylfuran-2-carboxylate (3cb)
Yellow solid; mp: 87–89 ꢀC; IR vmax (KBr): 1722, 1650, 1441, 1385, 1023, 921,
885, 770, 688 cmꢁ1; 1H NMR (400 MHz, CDCl3): d 7.82–7.76 (m, 4H), 7.55–7.53 (m,
1H), 7.41–7.32 (m, 6H), 3.91 (s, 3H); 13C NMR (100 MHz, CDCl3): d 190.6, 158.8,
158.5, 142.3, 137.3, 133.3, 130.2, 129.7, 128.5, 128.0, 122.2, 121.0, 52.2; GC–MS m=z
(% rel. inten.): 306.07 (Mþ, 100). Anal. calcd. for C19H14O4: C, 74.50; H, 4.61.
Found: C, 74.50; H, 4.66.
4-Ethyl 2-Methyl 5-Phenylfuran-2,4-dicarboxylate (3cc)
Colorless solid; mp: 72–73 ꢀC; IR vmax (KBr): 2983, 2930, 1732, 1660, 1428,
;
1327, 1191, 1084, 997, 865, 765, 691 cmꢁ1 1H NMR (400 MHz, CDCl3): d
8.04–8.02 (m, 2H), 7.56 (s, 1H), 7.44–7.42 (m, 3H), 4.29 (q, 2H, J ¼ 7.2 Hz), 3.90
(s, 3H), 1.32 (t, 3H, J ¼ 7.2 Hz); 13C NMR (100 MHz, CDCl3): d 162.2, 160.1,
158.7, 142.4, 130.4, 128.9, 128.5, 120.6, 115.5, 60.9, 52.1, 14.1; GC–MS m=z (%
rel. inten.): 273.90 (Mþ, 100). Anal. calcd. for C15H14O4: C, 65.69; H, 5.15. Found:
C, 65.60; H, 5.31.
Methyl 4-Acetyl-5-methylfuran-2-carboxylate (3cd)
Yellow solid; mp: 86–88 ꢀC; IR vmax (KBr): 1726, 1647, 1540, 1362, 1172,
1
1121, 1020, 995, 764, 706 cmꢁ1; H NMR (400 MHz, CDCl3): d 7.37 (s, 1H), 3.88
(s, 3H), 2.64 (s, 3H), 2.41 (s, 3H); 13C NMR (100 MHz, CDCl3): d 193.2, 162.1,
158.6, 142.0, 122.8, 118.2, 52.1, 29.0, 14.7; GC–MS m=z (% rel inten.): 181.97
(Mþ, 38.35), 166.95 (100). Anal. calcd. for C9H10O4: C, 59.34; H, 5.53. Found: C,
59.55; H, 5.62.
4-Ethyl 2-Methyl 5-Methylfuran-2,4-dicarboxylate (3ce)
Pale yellow viscous oil; IR vmax (KBr): 2987, 2958, 1727, 1637, 1442, 1095,
1
1032, 963, 896, 805, 714 cmꢁ1; H NMR (400 MHz, CDCl3): d 7.71 (s, 1H), 4.29
(q, 2H, J ¼ 7.2 Hz), 3.80 (s, 3H), 2.48 (s, 3H), 1.32 (t, 3H, J ¼ 7.2 Hz); 13C NMR
(100 MHz, CDCl3): d 163.1, 162.7, 159.1, 145.3, 118.8, 113.5, 60.7, 51.8, 14.1,
13.4; GC–MS m=z (% rel. inten.): 212.02 (Mþ, 17.62), 165.99 (100). Anal. calcd.
for C10H12O5: C, 56.60; H, 5.70. Found: C, 56.61; H, 5.77.

SYNTHESIS OF FURANS
959
ACKNOWLEDGMENT
The authors thank the Guangdong University of Petrochemical Technology of
China for financial support of this work.
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