Palladium-Catalyzed Dehydrogenation Coupling-Cyclization Reactions of Acetylenic Acids with Iodonium Ylides for the Synthesis of 2(5 H)-Furanones

Article abstract of DOI:10.1055/s-0035-1560554

A new route for the synthesis of 2(5H)-furanones is presented via Pd(PPh₃)₄-catalyzed cascade reaction of acetlenic acids with iodonium ylides using K₂CO₃ as the base. The cascade proceeds through dehydrogenatio

Full text of DOI:10.1055/s-0035-1560554

SYNLETT
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© Georg Thieme Verlag Stuttgart · New York
2016, 27, 794–798
letter
794
W.-G. Li et al.
Letter
Synlett
Palladium-Catalyzed Dehydrogenation Coupling–Cyclization Re-
actions of Acetylenic Acids with Iodonium Ylides for the Synthesis
of 2(5H)-Furanones
Wen-Guang Li
Bo Cai
O
R3
R2
O
O
Pd(PPh3)4 (3 mol%)
K2CO3 (2 equiv)
O
R1
Hong-Bo Xiao
Shao-Feng Pi*
Han-Zhou Sun
HOOC
R1
R2
+
R3
O
CH2Cl2, r.t.
IPh
O
R1 = aryl, alkyl
R2, R3 = aryl, alkyl, alkoxy
74–98%, 10 examples
Institute of Applied Chemistry Central South University
of Forestry and Technology, Changsha, Hunan 410004,
P. R. of China
psfhunan@163.com
Received: 08.09.2015
Accepted after revision: 15.11.2015
Published online: 14.12.2015
MeO
OH
HO
OH
F
DOI: 10.1055/s-0035-1560554; Art ID: st-2015-w0689-l
HO
Abstract A new route for the synthesis of 2(5H)-furanones is present-
ed via Pd(PPh3)4-catalyzed cascade reaction of acetlenic acids with io-
donium ylides using K2CO3 as the base. The cascade proceeds through
dehydrogenation coupling and cyclization under mild conditions.
O
O
O
O
O
O
HO
vitamin C
VU0487836
sotolon
O
O
O
Key words palladium, dehydrogenation, acetylenic acids, iodonium
ylides, 2(5H)-furanones
O
S
O
OH
O
HN
S
H
H
OHC
2(5H)-Furanones (butenolides), important classes of ox-
ygen-containing heterocyclic compounds, are ubiquitous in
natural products, drugs, and materials, and important in-
termediates in organic synthesis (Figure 1).1–4 2(5H)-Fura-
none derivatives have been considered as potential insecti-
cides, fungicides, antibiotics, bactericides, anticancer
agents, allergy inhibitors, cyclooxygenase inhibitors, phos-
pholipase A2 inhibitors, etc.5 For these reasons, consider-
able efforts have been devoted to the synthesis of 2(5H)-fu-
ranone and its derivatives.6 The transition-metal-promoted
or -catalyzed cyclization reaction of 2,3-allenoic acids/es-
ters was one of useful methods for the construction of
2(5H)-furanones.7 However, those methods were mostly
limited by the structure of the starting materials. Thus, the
development of new methods for the synthesis of 2(5H)-fu-
ranones is still attractive.
Transition-metal-catalyzed cascade reactions have
proven to be a powerful shortcut for the assembly of com-
plex ring systems in organic synthesis. Among these pro-
cesses, the cyclization of alkynes is a particularly effective
and atom-economical step for the construction of heterocy-
cles. The Toste8 and Yang9 groups reported transition-met-
al-catalyzed Conia-ene reaction of 1,3-dicarbonyl com-
pounds with alkynes. The Liang group10 also demonstrated
Ph
H
OH
O
O
O
H
O
rofecoxib
Figure 1 Examples of important 2(5H)-furanones
calactin
nickel(II)-catalyzed cyclization reactions of propargylic
compounds for the indene formation. In connection with
our ongoing projects on the synthesis of 2(5H)-furanones,
we herein report a palladium-catalyzed cascade reaction of
acetylenic acids with iodonium ylides at room temperature
(Scheme 1) that proceeds through a cascade of dehydroge-
nation coupling and cyclization.
O
R3
R2
O
O
Pd(PPh3)4 (3 mol%)
K2CO3 (2 equiv)
O
R1
O
HOOC
R1
R2
R3
+
CH2Cl2, r.t.
IPh
1
O
3
2
Scheme 1 Dehydrogenation coupling–cyclization reactions of acety-
lenic acids with iodonium ylides
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, 794–798

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Our initial investigations focused on the dehydrogena-
tion coupling–cyclization of 3-phenylpropiolic acid (1a)
with dimethyl 2-(phenyl-λ3-iodanylidene)malonate (2a, Ta-
ble 1). Gratifyingly, treatment of the substrate 3-phenyl-
propiolic acid (1a) with 2a, Pd(PPh3)4, and K2CO3 in CH2Cl2
at room temperature for six hours afforded the desired
product dimethyl 5-oxo-3-phenylfuran-2,2(5H)-dicarbox-
ylate (3aa, Figure 2) in 98% yield (Table 1, entry 1).11 A serial
of other palladium catalysts, including Pd(dba)2,
PdCl2(PPh3)2, Pd(OAc)2, and PdCl2 were tested, and the re-
sults showed that they were less effective than Pd(PPh3)4
(Table 1, entries 2–5). For example, 90% yield of 3aa was ob-
tained when Pd(dba)2 was used as catalyst, while 75% yield
of 3aa was afforded when Pd(OAc)2 was used. However, no
product 3aa was detected by GC–MS in the absence of pal-
ladium catalyst (Table 1, entry 6). Screening revealed that
the amount of catalyst affected the reaction: The identical
yield of 3aa was obtained at a loading of 5 mol% Pd(PPh3)4
(Table 1, entry 7), while only 73% yield of 3aa was isolated
in the presence of 1 mol% Pd(PPh3)4 (Table 1, entry 8). In
light of these results, a series of other bases, namely Cs2CO3,
KOH, and organic base Et3N, were tested (Table 1, entries 9–
11). The results showed that they were less effective than
K2CO3 (Table 1, entry 1 vs. entries 9–11). The amount of
K2CO3 was also examined, and the results demonstrated
that two equivalents of K2CO3 were more efficient (Table 1,
entry 1 vs. entries 12 and 13). Others solvents such as DCE,
MeCN, toluene, and THF were less effective (Table 1, entries
14–17). Among the reaction temperatures tested, the yield
of 3aa decreased from 98% at room temperature to 90% at
40 °C and 95% at 10 °C. It turned out that the reaction at
room temperature gave the best results (Table 1, entry 1 vs.
entries 18 and 19).
Table 1 Screening of the Optimal Conditionsa
O
OMe
O
O
MeO
[Pd], base
solvent
O
Ph
MeO
OMe
HOOC
Ph
+
O
I
Ph
O
1a
Entry Pd (mol%)
2a
3aa
Base (equiv)
Solvent
Isolated yield (%)
1
2
Pd(PPh3)4 (3)
Pd(dba)2 (3)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
Cs2CO3 (2)
KOH (2)
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DCE
98
90
76
75
82
0b
3
PdCl2(PPh3)2 (3)
Pd(OAc)2 (3)
PdCl2 (3)
4
5
6
–
7
Pd(PPh3)4 (5)
Pd(PPh3)4 (1)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
Pd(PPh3)4 (3)
97
73
93
73
68
98
90
95
39
46
41
90
95
8
9
10
11
12
13
14
15
16
17
18c
19d
Et3N (2)
K2CO3 (3)
K2CO3 (1)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
MeCN
toluene
THF
CH2Cl2
CH2Cl2
a Reaction conditions: 1a (0.2 mmol), 2a (1.2 equiv), [Pd], base, and solvent
(2 mL) under Ar atmosphere at r.t.
b Dimethyl 2-[(3-phenylpropioloyl)oxy]malonate (4) was isolated in 85%
yield.
c At 40 °C.
d At 10 °C.
With the optimized reaction conditions in hand, the
scope of the cascade reaction was investigate with a variety
of propiolic acids 1 and iodonium ylides 2 (Scheme 2). Ini-
tially, dimethyl 2-(phenyl-λ3-iodanylidene)malonate (2a)
reacted with two different propiolic acids 1b and 1c, in the
presence of Pd(PPh3)4 and K2CO3. The results demonstrated
both aryl and alkyl propiolic acids were found to be suitable
substrates for the reaction (products 3ba and 3ca). For ex-
ample, substrate 1c, an alkyl propiolic acid, was trans-
formed into product 3ca in 74% yield. Subsequently, a num-
ber of iodonium ylides 2b–i were examined under the opti-
mal conditions, and they were found to be suitable
substrates for the reaction. To our surprise, the reaction
preferably delivered the nonquaternary carbon products,
dihydrofuranones 3ab and 3ac, in good yields via C–C bond
cleavage from substrates ethyl propionate 2b and methyl
butyrate 2c. We were happy to observe that substrates
bearing a phenyl group (2d), an allyl group (2e), and an al-
Figure 2 X-ray crystal structure of 3aa
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, 794–798

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W.-G. Li et al.
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kyl group (2f–h) could also react with 3-phenylpropiolic
acid efficiently in moderate to good yields (products 3ad–
ah). Notably, 1a and ketone iodonium ylide 2i reacted
smoothly in a 75% yield under the standard conditions
(product 3ai).
O
OMe
O
O
OMe
OMe
Pd(PPh3)4 (3 mol%)
K2CO3 (2 equiv)
MeO
O
O
O
Ph
(1)
O
CH2Cl2, r.t.
Ph
O
4
3aa, 99%
O
R3
O
OMe
R2
Pd(PPh3)4 (3 mol%)
K2CO3 (2 equiv)
O
O
O
O
OMe
MeO
O
O
O
R1
Pd(PPh3)4 (3 mol%)
CH2Cl2, r.t.
HOOC
R1 R2
+
R3
O
Ph
O
OMe
O
(2)
CH2Cl2, r.t.
IPh
O
Ph
O
1
2
3
3aa, 21%
4
EtO
O
O
O
O
O
O
O
O
O
Scheme 3 Control experiments
O
O
O
Ph
OMe
O
O
O
O
O
O
O
3ba, 88%
3ca, 74%
3ab,a 80%
MeO
OMe
MeO
OMe
O
O
O
OEt
MeO
I
I
Ph
O
O
Ph
Ph
2a
O
Ph
O
Ph
O
O
O
A
Ph
HOOC
Ph
K2CO3
O
O
1a
3ac,b 83%
3ad, 96%
3ae, 82%
PhI
O
O
O
OMe
O
O
O
OMe
O
MeO
O
OMe
OMe
O
Ph
MeO
OMe
Pd(PPh3)4
K2CO3
O
Ph
O
O
Ph
O
Ph
O
Ph
O
O
O
O
O
Ph
Ph
O
O
O
O
O
3aa
Scheme 4 Proposed mechanism
4
3af, 88%
3ag, 78%
3ah, 78%
3ai, 75%
Scheme 2 Screening scope of propiolic acids 1 and iodonium ylides.
Reagents and conditions: 1 (0.2 mmol), 2 (1.2 equiv), Pd(PPh3)4 (3
mol%), K2CO3 (0.4 mmol), and CH2Cl2 (2 mL) at r.t. under Ar atmo-
sphere for 6 h. a R1 = Me. b R1 = Et.
ence of Pd(PPh3)4 and K2CO3, acetylenic acids successfully
underwent the dehydrogenation coupling–cyclization tan-
dem reaction with iodonium ylides at room temperature to
afford the corresponding 2(5H)-furanones in moderate to
good yields. Notably, 2(5H)-furanones are an important
skeleton in natural products and exhibit a broad range of bi-
ological activities. Work to probe the detailed mechanism
and apply the reaction in organic synthesis is currently in
progress.
To understand the mechanism, two experiments were
done. As shown in Table 1, entry 6, 85% yield of product 4
was isolated in the absence palladium catalyst. Compound
4 could transform to the desired product 3aa in the pres-
ence of 3 mol% P(PPh3)4 and two equivalents K2CO3
(Scheme 3, eq. 1). However, product 3aa was obtained with
a lower yield under only palladium catalyst conditions
(Scheme 3, eq. 2). This implies that the reaction proceeds
via a dehydrogenation coupling and then cyclization of
alkynes in a tandem pathway.
Acknowledgment
Proposed reaction mechanism based on the above re-
sults and previous reports12 are shown in Scheme 4. Initial-
ly, dehydrogenation coupling of intermediate A with 3-
phenylpropiolic acid (1a) to yield intermediate 4 and phe-
nyl iodide, followed by intramolecular cyclization of inter-
mediate 4 to afford the desired 2(5H)-furanones.
In summary, we have developed a mild and general cas-
cade reaction of acetylenic acids with an iodonium ylide
protocol for the synthesis of 2(5H)-furanones. In the pres-
This research was supported by the NSFC (Nos. 21202206), Scientific
Innovation Fund for Graduate of Hunan Province (CX2015B298), and
Scientific Innovation Fund for Graduate of Central South University of
Forestry and Technology (CX2013B16).
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1560554.
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© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, 794–798

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W.-G. Li et al.
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(11) Typical Experimental Procedure for the Palladium-Catalyzed
Dehydrogenation Coupling–Cyclization Reactions of Acety-
lenic Acids with Iodonium Ylides
To a Schlenk tube were added 3-phenylpropiolic acid (1a, 29.2
mg, 0.2 mmol), dimethyl 2-(phenyl-λ3-iodanylidene)malonate
(2a, 80.2 mg, 0.24 mmol), Pd(PPh3)4 (13.8 mg, 0.06 mmol),
K2CO3 (60.8 mg, 0.4 mmol), and CH2Cl2 (2 mL). Then the tube
was charged with argon and was stirred at r.t. for the indicated
time until complete consumption of starting material as moni-
tored by TLC and GC–MS analysis. After the reaction was fin-
ished, the reaction diluted in Et2O and concentrated in vacuum,
and the resulting residue was purified by silica gel column chro-
matography (hexane–EtOAc) to afford the desired product 3aa
(54.1 mg, 98%).
Dimethyl 5-Oxo-3-phenylfuran-2,2(5H)-dicarboxylate (3aa)
Yield: 54.1 mg (98%); white solid; mp 104–106 °C. 1H NMR (400
MHz, CDCl3, 25 °C): δ = 7.56 (d, J = 8.0 Hz, 2 H), 7.42–7.37 (m, 3
H), 6.46 (s, 1 H), 3.76 (s, 6 H). 13C NMR (100 MHz, CDCl3, 25 °C):
δ = 170.13, 164.61, 162.24, 131.86, 128.86, 128.54, 116.20,
99.99, 88.06, 54.05. IR (neat): 2958, 2852, 1779, 1749, 1262,
797cm–1. LRMS (EI, 70 eV): m/z (%) = 276 (5) [M], 232 (9), 188
(77), 161 (100), 115 (32), 102 (60). ESI-HRMS: m/z calcd for
C
10H13O6 [M + H]+: 227.0712; found: 277.0708.
Dimethyl 3-(4-Methoxyphenyl)-5-oxofuran-2,2(5H)-dicar-
boxylate (3ba)
Yield: 53.8 mg (88%); colorless oil. 1H NMR (400 MHz, CDCl3, 25
°C): δ = 7.56 (d, J = 8.0 Hz, 2 H), 6.88 (d, J = 8.0 Hz, 2 H), 6.33 (s, 1
H), 3.86 (s, 6 H), 3.84 (s, 3 H). 13C NMR (100 MHz, CDCl3, 25 °C):
δ = 164.89, 162.80, 130.98, 120.91, 114.28, 113.19, 60.42, 55.50,
54.00, 53.87. IR (neat): 2924, 2855, 1761, 1376, 1265, 743 cm–1
.
LRMS (EI, 70 eV): m/z (%): 307 (1) [M], 247 (10), 219 (27), 189
(3), 175 (3), 132 (37), 117 (15), 59 (100). ESI-HRMS: m/z calcd
for C10H13O6 [M + H]+: 307.0818; found: 307.0812.
Dimethyl 3-Ethyl-5-oxofuran-2,2(5H)-dicarboxylate (3ca)
Yield: 33.8 mg (74%); colorless oil. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 7.92 (s, 1 H), 3.82 (d, J = 12.0 Hz, 6 H), 2.56–2.50 (m, 2
H), 1.19 (d, J = 8.0 Hz, 3 H). 13C NMR (100 MHz, CDCl3, 25 °C): δ =
170.36, 169.22, 164.31, 117.00, 88.7, 60.41, 53.90, 21.59, 11.20.
IR (neat): 2954, 2924, 2854, 2361, 1784, 1755, 1458, 742, 684
cm–1. LRMS (EI, 70 eV): m/z (%) = 226 (9) [M], 184 (20) [M], 168
(16), 141 (100), 126 (17). ESI-HRMS: m/z calcd for C10H13O6 [M +
H]+: 229.0712; found: 229.0707.
Ethyl 5-Oxo-3-phenyl-2,5-dihydrofuran-2-carboxylate (3ab)
Yield: 37.2 mg (80%); white solid; mp 93–95 °C. 1H NMR (400
MHz, CDCl3, 25 °C): δ = 7.54 (t, J = 4.0 Hz, 2 H), 7.42–7.39 (m, 3
H), 6.37 (s, 1 H), 5.81 (s, 1 H), 4.11 (m, 2 H), 1.11 (m, 6 H).
13CNMR (100 MHz, CDCl3, 25 °C): δ = 172.18, 166.16, 162.43,
132.02, 129.18, 128.71, 127.49, 114.50, 80.06, 62.71, 13.83. IR
(neat): 3108, 2919, 2850, 1763, 1465, 1155, 763 cm–1. LRMS (EI,
70 eV): m/z (%) = 233 (3) [M], 203 (25), 146 (100), 131 (29). ESI-
HRMS: m/z calcd for C13H13O4 [M + H]+: 233.0814; found:
233.0808.
(7) (a) Ma, S. Acc. Chem. Res. 2003, 36, 701. (b) Ma, S.; Shi, Z. Chem.
Commun. 2002, 540. (c) Ma, S.; Yu, Z. Angew. Chem. Int. Ed. 2002,
41, 1775; Angew. Chem. 2002, 114, 2874. (d) Gu, Z.-H.; Wang, X.-
K.; Shu, W.; Ma, S. J. Am. Chem. Soc. 2007, 129, 10948. (e) Chen,
G.-F.; Zeng, R.; Gu, Z.-H.; Fu, C.-L.; Ma, S. Org. Lett. 2008, 10,
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, 794–798

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W.-G. Li et al.
Letter
Synlett
Methyl 5-Oxo-3-phenyl-2,5-dihydrofuran-2-carboxylate (3ac)
Yield: 36.2 mg (83%); white solid; mp 75–76 °C. 1H NMR (400
MHz, CDCl3, 25 °C): δ = 7.54 (t, J = 4.0 Hz, 2 H), 7.44–7.40 (m, 3
H), 6.38 (s, 1 H), 5.85 (s, 1 H), 3.65 (s, 3 H). 13C NMR (100 MHz,
CDCl3, 25 °C): δ = 172.15, 166.71, 162.32, 132.09, 129.29,
128.85, 128.82, 128.60, 171.44, 114.45, 53.38. IR (neat): 2957,
1766, 1621, 1437, 1158, 788, 688 cm–1. LRMS (EI, 70 eV): m/z (%)
= 218 (10) [M], 159 (100), 146 (20), 77 (56). ESI-HRMS: m/z
calcd for C12H10O4 [M + H]+: 219.0657; found: 219.0650.
Ethyl 2-Benzoyl-5-oxo-3-phenyl-2,5-dihydrofuran-2-carbox-
ylate (3ad)
eV): m/z (%) = 274 (6) [M], 259 (14), 200 (37), 146 (100), 77 (30).
ESI-HRMS: m/z calcd for C15H14O5 [M + H]+: 274.0841; found:
275.0837.
Methyl 2-Butyryl-5-oxo-3-phenyl-2,5-dihydrofuran-2-car-
boxylate (3ag)
Yield: 44.9 mg (78%); white solid; mp 113–117. 1H NMR (400
MHz,CDCl3, 25 °C): δ = 7.61–7.59 (d, J = 8.0 Hz, 2 H), 7.49–7.41
(m, 3 H), 6.54 (s, 1 H), 3.83 (s, 3 H), 2.77–2.71 (m, 1 H), 2.58–
2.40 (m, 1 H), 1.66–1.55 (m, 2 H), 0.89–0.86 (t, J = 4.0 Hz, 3 H).
13C NMR (75 MHz, CDCl3, 25 °C): δ = 198.0, 170.4, 165.6, 164.2,
162.8, 162.6, 131.8, 129.1, 128.9, 128.7, 127.5, 115.9, 114.5,
92.7, 80.2, 71.8, 26.0, 21.5, 21.3. IR (neat): 2937, 2811, 2359,
1789, 1345, 741 cm–1. LRMS (EI, 70 eV): m/z (%) = 288 (1) [M],
240 (12), 210 (13) 160 (6), 77 (100). ESI-HRMS: m/z calcd for
1
Yield: 64.5 mg (96%); light yellow solid; mp 48–50 °C. H NMR
(400 MHz, CDCl3, 25 °C): δ = 7.96 (d, J = 8.0 Hz, 2 H), 7.60 (d, J =
8.0 Hz, 3 H), 7.43–7.36 (m, 5 H), 6.50 (s, 1 H), 4.16–4.10 (m, 2 H),
1.02 (t, J = 6.0 Hz, 3 H). 13C NMR (75 MHz, CDCl3, 25 °C): δ =
189.13, 170.15, 165.88, 164.38, 134.15, 134.02, 131.64, 129.63,
129.29, 129.23, 128.73, 128.67, 116.49, 63.49, 13.67. IR (neat):
2925, 2854, 1767, 1712, 1450, 1262, 1028, 712 cm–1. LRMS (EI,
70 eV): m/z (%) = 337 (1) [M], 207 (1), 105 (100), 103 (2), 77
(28). ESI-HRMS: m/z calcd for C20H17O5 [M + H]+: 337.1076;
found: 337.1071.
C
16H16O5 [M + H]+: 288.0997; found: 288.0992.
Methyl 2-Isobutyryl-5-oxo-3-phenyl-2,5-dihydrofuran-2-
carboxylate (3ah)
Yield: 44.9 mg (78%); white solid; mp 110.3–112.0 1H NMR (400
MHz,CDCl3, 25 °C): δ = 7.60–7.40 (m, 2 H), 7.45–7.41 (m, 3 H),
6.55 (s, 1 H), 3.84 (s, 3 H), 3.09 (t, J = 6.0 Hz, 1 H), 1.23–1.21 (d,
J = 8.0 Hz, 3 H), 1.01–0.99 (d, J = 8.0 Hz, 3 H). 13C NMR (75 MHz,
CDCl3, 25 °C): δ = 204.68, 170.51, 165.49, 162.99, 131.86,
128.90, 128.71, 115.96, 92.92, 53.89, 36.56, 19.21, 19.17. IR
(neat): 2957, 2851, 2359, 1776, 1255, 739 cm–1. LRMS (EI, 70
eV): m/z (%) = 274 (6) [M], 259 (14), 200 (37) 146 (100), 77 (30).
ESI-HRMS: m/z calcd for C16H16O5 [M + H]+: 288.2951; found:
288.2946.
Vinyl 2-Acetyl-5-oxo-3-phenyl-2,5-dihydrofuran-2-carboxyl-
ate (3ae)
Yield: 44.6 mg (82%); pale yellow oil. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 7.47–7.45 (m, 2 H), 7.42–7.37 (m, 3 H), 6.49 (s, 1 H),
5.42–5.35 (m, 1 H), 5.00–4.90 (m, 2 H), 2.12 (s, 3 H). 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 203.09, 117.82, 164.87, 131.71,
129.35, 129.06, 127.64, 121.02, 116.56, 93.90, 37.11, 29.71,
24.06. IR (neat): 2923, 2852, 1766, 1188, 769 cm–1. LRMS (EI, 70
eV): m/z (%) = 272 (6) [M], 245 (14), 201 (37), 158 (100), 77 (30).
ESI-HRMS: m/z calcd for C15H13O5 [M + H]+: 273.0763; found:
273.0758.
4-Acetyl-4-benzoyl-3-phenylcyclopent-2-enone (3ai)
Yield 47.4 mg (75%); yellow solid; mp 52–55 °C. 1H NMR (400
MHz, CDCl3, 25 °C): δ = 7.89 (d, J = 8.0 Hz, 2 H), 7.62 (t, J = 10.0
Hz, 3 H),7.49–7.43 (m, 5 H), 6.67 (s, 1 H), 2.39 (s, 3 H). 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 170.51, 164.29, 134.08, 132.01,
129.70, 129.26, 128.87, 115.84, 24.78. IR (neat): 2925, 2854,
1770, 1693, 1450, 1266, 713, 685 cm–1. LRMS (EI, 70 eV): m/z (%)
= 306 (0.02) [M], 218 (4), 189 (6), 173 (27), 158 (65), 105 (100).
ESI-HRMS: m/z calcd for C20H17O3 [M + H]+: 306.3121; found:
306.0892.
Methyl
5-Oxo-3-phenyl-2-propionyl-2,5-dihydrofuran-2-
carboxylate (3af)
Yield: 48.2 mg (88%); white solid; mp 101–103. 1H NMR (400
MHz,CDCl3, 25 °C): δ = 7.61–7.59 (d, J = 8.0 Hz, 2 H), 7.49–7.27
(m, 3 H), 6.54 (s, 1 H), 3.83 (s, 3 H), 2.87–2.77 (m, 1 H), 2.65–
2.55 (m, 1 H), 1.09–1.05 (t, J = 8.0 Hz, 3 H). 13C NMR (75 MHz,
CDCl3, 25 °C): δ = 201.0, 170.4, 165.4, 162.8, 131.9, 120.3, 128.8,
128.8, 128.7, 127.4, 115.7, 92.5, 92.5, 79.0 , 77.4, 53.9, 31.4. IR
(neat): 2957, 2851, 2359, 1776, 1255, 739 cm–1. LRMS (EI, 70
(12) (a) Deng, C.-L.; Song, R.-J.; Guo, S.-M.; Wang, Z.-Q.; Li, J.-H. Org.
Lett. 2007, 9, 5111. (b) Deng, C.-L.; Zou, T.; Wang, Z.-Q.; Song, R.-
J.; Li, J.-H. J. Org. Chem. 2009, 74, 412. (c) Huang, X.-C.; Liu, Y.-L.;
Liang, Y.; Pi, S.-F.; Wang, F.; Li, J.-H. Org. Lett. 2008, 10, 1525.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, 794–798