A mild approach to diarylfuranones via functionalized 2-arylfurans

Article abstract of DOI:10.1016/j.tet.2013.03.101

5,5- and 3,5-Diarylfuranones have been obtained in a three-step one-pot manner. The procedure starts from photooxygenation of easily accessible arylfurans followed by in situ base treatment and finally by triflic anhydride mediated acylation of activated

Full text of DOI:10.1016/j.tet.2013.03.101

Tetrahedron xxx (2013) 1e6
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A mild approach to diarylfuranones via functionalized 2-arylfurans
*
Marina DellaGreca , Simona Zuppolini, Armando Zarrelli, Maria R. Iesce, Lucio Previtera
ꢀ
UdR Napoli 4 Consorzio INCA, IC-REACH, Dipartimento di Scienze Chimiche, Universita Federico II, Complesso Universitario di Monte S. Angelo,
via Cintia 4, I-80126 Naples, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
5,5- and 3,5-Diarylfuranones have been obtained in a three-step one-pot manner. The procedure starts
from photooxygenation of easily accessible arylfurans followed by in situ base treatment and finally by
triflic anhydride mediated acylation of activated aromatic substrates. The regioselectivity of the acylation
reaction depends on the reaction conditions and/or activation of both acid and aromatic reagents. The
5,5-diarylfuranone products have the same carbon skeleton as some rearranged tetrahydrofuran lignans.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 5 October 2012
Received in revised form 21 February 2013
Accepted 18 March 2013
Available online xxx
Keywords:
2-Furanone
Furan
Singlet oxygen
FriedeleCrafts acylation
Triflic anhydride
1. Introduction
conditions (low temperature, neat, high equivalents) otherwise
leading to 3-aroyl-regioisomers.3 In our effort to search for
Furans are a class of heterocycles widely distributed in a large
number of natural compounds, in aromatic forms, reduced forms
as tetrahydrofurans, and oxidized forms as furanones.1 This het-
erocycle has a prominent role in synthetic chemistry due to its
ability to undergo a wide range of reactions, amongst these, oxi-
dation to versatile 1,4-enedione or to the widely diffuse furanone
ring.2 Polysubstituted furans are important building blocks for the
synthesis of natural and non-natural products.2 In a previous study
we reported a strategy allowing the preparation of some furans as
precursors of lignan-like compounds.3 Lignans are widespread
plant secondary metabolites displaying a large series of bio-
activities.4 Their isolation from natural sources is a laborious ex-
pensive process and the yields are generally low. Hence, several
routes to natural and synthetic derivatives have been proposed
over the years. We obtained 4-aroyl-3-carbomethoxy-2-
new synthetic methods for lignan-like compounds,3,7 and
stimulated by the potentiality of the Tf2O-mediated acylation,
we decided to explore further applications of the above method-
ology using 4-oxo-2-alkenoic acids prepared from 2-aryl-3,4-
dicarbomethoxyfurans.
2. Results and discussion
It is reported that 4-oxoalkenoic acids can be obtained from
furans via oxidation with sodium chlorite in an acidic aqueous so-
lution followed by treatment with pyridine.8 We have prepared
these acids via dye-sensitized photooxygenation followed by in situ
addition of diethylamine. The dye-sensitized photooxygenation is
one of the most used and environmentally friendly furan oxidation
procedures, often representing the key step in the synthesis of in-
teresting natural compounds.9e11 The methylene blue (MB)-sensi-
tized photooxygenation of furans 1aec, synthesized according to
a reported procedure,12 was carried out at ꢀ20 ꢁC. Endoperoxides 2
were obtained quantitatively and exhibited a sufficient thermal
stability due to the presence of two electron-withdrawing groups.9
The in situ treatment with diethylamine at rt gave monoacids 3
almost quantitatively (Scheme 1).
phenylfurans, having a b-b
0-linked C6C3eC3C6 backbone typical
of lignans, starting from a unique easily accessible furoic acid
precursor via trifluoromethanesulfonic anhydride (Tf2O)-mediated
acylation.3 Tf2O is of high current interest in FriedeleCrafts (FC)
acylation of carboxylic acids5 and other substrates.6 It can be used
directly without the use of a catalyst and it reacts in short times
and within a large range of temperatures.3,5 Our method was
based on tunable Tf2O-mediated FC acylation under controlled
Acids 3 were the only products even using other bases as trie-
thylamine and 1,4-diazabicyclo[2.2.2]octane. The base treatment of
a
- or
a conversion to
probable that the once formed lactone rapidly converts to the
a,a
0-unsubstituted furan endoperoxides generally produces
g
-hydroxybutenolides.9,10,13 In our cases it is
* Corresponding author. Tel.: þ39 81 674162; fax: þ39 81 674393; e-mail
address: dellagre@unina.it (M. DellaGreca).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.03.101
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2
M. DellaGreca et al. / Tetrahedron xxx (2013) 1e6
MeO2C
CO2Me
MeO2C
MeO2C
CO2Me
Et2NH
CO2Me
COOH
,
O2, hν MB
CH2Cl2, -20 °C
O
O
O
O
2
O
R
R
R
3
1
a R = H
b R = Br
c R = OMe
Scheme 1. Singlet oxygenation of furans 1 and base-assisted transformation of endoperoxides 2.
corresponding acid open form 3 because of the particular sub-
stitution and high conjugation. On the other hand, the base-
mediated conversion of butenolides into open structures is
known.8
diaylfuranone 6a is promoted by the presence of the aroyl
group that directs the aryl addition also to the 3-position by
means of conjugation and/or steric effects.16 Interestingly, 5,5-
diarylfuranone 5a had a structure similar to some rare natural
lignans, for example, sacidumlignan D (Fig. 1), that is, a peculiar
Initially, investigation of the Tf2O-mediated acylation was
proven starting from pure acid 3a and using anisole (4a) as the
aryl reagent. The reaction was carried out at low temperature
using 2.5 equiv of Tf2O and neat anisole as solvent. Unexpectedly
the reaction led to a mixture of cyclic acylated products, e.g., 5,5-
diarylfuranone 5a and 3,5-diarylfuranones 6a and 60a (Scheme 2).
When the reaction was performed in dichloromethane as solvent
using an excess of anisole (5 equiv) and 2.5 equiv of Tf2O, the
result did not change while it appeared to slightly increase the
amounts of 3,5-diarylfuranones 6a and 60a (Scheme 2). Further
experiments changing the stoichiometry or using a highly polar
solvent were unsuccessful. The use of equimolecular amounts of
3a and 4a in the presence of 1.5 equiv of Tf2O in dichloromethane
gave poor yield (27%). A lower yield (42%) was also obtained using
acetonitrile as solvent while nitromethane gave a very complex
reaction mixture.
rearranged
a
,
a
-diaryltetrahydrofuran lignan.17
MeO
HO
MeO
MeO
O
OMe
HO
Fig. 1. Sacidumlignan D, a lignan with a rare structure.
MeO2C
Ph
MeO2C
Ph
MeO2C
Ph
CO2Me
C6H4-o-OMe
CO2Me
O
CO2Me
OMe
C6H4-p-OMe
+
+
O
O
3a
+
O
O
O
MeO-p-C6H4
5a
6a
6'a
4a
-20 °C, neat, Tf2O (2.5 equiv), 60% (5a:6a:6'a = 8:<1:1)
-15 °C, CH2Cl2, Tf2O (2.5 equiv), 56% (5a:6a:6'a = 7:1:2)
Scheme 2. Tf2O-assisted FriedeleCrafts acylation of anisole (4a) with acid 3a.
Cyclic products by FC acylation indicated an intramolecular
addition of the carbonyl to the activated carboxylic function and
the possible formation of pseudo anhydrides 7 (or a carbocation).
These intermediates should undergo FC reaction to result in the
cyclic arylated 5 and 6 (Scheme 3). The formation of pseudo an-
hydrides 7 is supported by 1H NMR spectra acquired immediately
after the addition of Tf2O. A shift at higher field of ortho aryl
protons was observed indicating the possible presence of the
pseudo anhydrides. Few examples of obtaining furanones in FC
reactions are reported in the literature such as the FC acylation of
phthalic acids14 or alkylated acrylic acids,15 both leading to 5-
arylfuranones. It is probable that the formation of 3,5-
These considerations induced us to verify the scope of the re-
action. Preliminary experiments showed that starting from crude 3a
very similar results were obtained with regards to the final yields
and the molar ratio of furanones 5a, 6a, and 60a for both optimized
acylation approaches (with and without dichloromethane). Hence,
we decided to apply the one-pot reaction to furans 1b,c using both
conditions (Table 1). Moreover, to extend the scope in the prepara-
tion of lignan-like compounds, starting from furans 1a and 1c the
acylation was performed using other aromatic substrates, with
lignan-typical aryl substitution, such as 1,2-dimethoxybenzene (4b,
R1¼R2¼OMe), 3-benzodioxole (4c, R1, R2¼eOCH2Oe) and phenol
(4d, R1¼OH, R2¼H). Since triflic acid is generated the acylation was
MeO2C
Ar
CO2Me
CO2Tf
MeO2C
CO2Me
MeO2C
Ar
CO2Me
OTf
O
Tf2O
4
+
5, 6
3
Ar
O
O
O
O
TfO
7
Scheme 3. Proposed conversion of acid 3 to furanones 5 and 6.
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M. DellaGreca et al. / Tetrahedron xxx (2013) 1e6
3
Table 1
One-pot preparation of furanones 5 and 6
MeO2C
CO2Me
O
CO2Me
MeO2C
R
i.1O2
R1
+
ii. Et2NH
O
O
R2
O
R2
1
+
R
iii. Tf2O, 4
R1
4
6
R1
R2
5
1
R
4
R1
R2
5/6
FC-acylation condition
Yielda (%)
5/6 Ratiob
Entry
Solvent
T (ꢁC)/time (h)
a
b
c
H
a
a
a
OMe
OMe
OMe
OMe
eOCH2Oe
OH
OMe
H
a
b
c
1
2
3
4
5
6
7
8
9
Neat
CH2Cl2
Neat
CH2Cl2
Neat
CH2Cl2
Neat
CH2Cl2
CH2Cl2
Neat
CH2Cl2
CH2Cl2
ꢀ20 to rt/20
ꢀ15/2.5
52 (70)
48 (73)
53 (72)
35 (55)
72 (97)
40 (61)
39 (61)
34 (55)
39 (60)
89
88:12c (82:18)
83:17c (57:43)
77:23c (72:28)
45:55c (34:66)
60:40 (42:58)
20:80 (25:75)
61:39 (55:45)
55:45 (54:46)
46:54 (45:55)
23:77
Br
H
ꢀ20 to rt/20
ꢀ10/2.5
OMe
H
ꢀ20/21
ꢀ20/21
a
a
a
c
H
H
H
OMe
b
c
d
b
OMe
d
e
f
ꢀ10 to 10/8
ꢀ15 to rt/20
ꢀ20 to rt/2.5
ꢀ20 to rt/18
ꢀ10/2
H
OMe
g
10
11
12
50 (76)
98
18:82 (29:71)
6:94
c
OMe
c
eOCH2Oe
h
ꢀ10/20
a
b
c
Isolated yield from column chromatography. In parenthesis yield for the reaction performed in the presence of 2,6-lutidine (2.5 equiv).
Ratio for the reaction performed in the presence of 2,6-lutidine (2.5 equiv).
These reactions gave a mixture of 6 and 60 isomers in ratio: entry 1 (1:11), entry 2 (7:10), entry 3 (10:13), and entry 4 (20:35). Similar isomeric ratios were obtained for the
reactions performed in the presence of 2,6-lutidine (2.5 equiv).
CO2Me
MeO2C
O
O
OMe
R
6'
also performed in the presence of a non-nucleophilic base, such as
2,6-lutidine. As shown in Table 1, higher yields were obtained while
the product ratio was little, if at all, altered.
4. Experimental section
4.1. General information
In all cases diarylfuranones 5 and 6 were formed. Starting from
furans 1a and 1b with anisole (4a) o-isomers 60 were also found.
The molecular structures were elucidated by 1H and 13C NMR
spectroscopy, 2D NMR experiments, and MS data. As shown in
Table 1, the nature of the aryl substituent on acids 3 has no effect
on the furanone formation while the use of the solvents generally
decreases the yield. Low temperatures and the absence of a sol-
vent favor 5,5-diarylfuranones 5 (compare entries 1 and 2, 3 and 4,
5 and 6). In some cases, the use of the solvent was effective in
reversing the regioselectivity of the acylation in favor of 3,5-diaryl
NMR spectra were recorded on 500 MHz spectrometer; 1H NMR
recorded at 500 MHz and 13C NMR recorded at 126 MHz. Chemical
shifts (d) are reported in parts per million (ppm) relative to the
residual solvent signal (CDCl3: dH 7.26, dC 77.0). All reactions in-
volving air or moisture sensitive reagents were carried out under
a dry argon or nitrogen atmosphere using commercially dry sol-
vents (SigmaeAldrich 99.7%) stored over molecular sieves. When
necessary, compounds were dried by azeotropic removal of water
with toluene under reduced pressure. Analytical thin layer chro-
matography (TLC) was performed on aluminum plates precoated
with Merck Silica Gel 60 F254 as the adsorbent. The plates were
developed with 5% H2SO4 ethanolic solution and then heating to
130 ꢁC. Column chromatography was performed on Merck Kieselgel
60 (63e200 mesh).
isomers
6 (compare entries 5 and 6). This also occurs in-
dependently from the reaction conditions in the presence of the
highly activated acid 3c and aromatic compound 4b (compare
entries 10 and 11).
Dimethyl 2-phenylfuran-3,4-dicarboxylate (1a, 70%), dimethyl
2-(4-bromophenyl)furan-3,4-dicarboxylate (1b, 34%), and dimethyl
2-(4-methoxyphenyl)furan-3,4-dicarboxylate (1c, 60%) were pre-
pared according to a literature procedure.11
3. Conclusion
In summary, we have prepared various novel 5,5- and 3,5-
diarylfuranones 5 and 6 in a three-step one-pot manner starting
from furans 1 under mild conditions. The key step is a Tf2O-medi-
ated acylation and the addition of a non-nucleophilic base increases
the yields. Arylfuranones have been rarely obtained by FC acylation,
especially 3-arylfuranones.14e16 The furanone structural motif is
widespread in bioactive natural products, also lignans,18 as well as
in synthetic products, also diarylderivatives,19 with a wide range of
activities such as antibiotic, antifungal, and anticancer agents.1
Noteworthy, 5,5-diarylfuranones 5 combine the presence of a fur-
anone moiety with a carbon skeleton of some recently isolated rare
lignans.17
4.2. Preparation of diarylfuranones 5 and 6
4.2.1. General procedure for synthesis of acids (3). A solution of dry
2-aryl-3,4-dicarboxymethyl furan 1 (1a, 130 mg, 0.5 mmol) in dry
CH2Cl2 (27.8 mL, 0.018 M) was irradiated at ꢀ20 ꢁC in the presence
of methylene blue (MB, 1 mg, 3ꢂ10ꢀ3 mmol) while dry oxygen was
bubbled through the solution. The progress of the reaction was
checked by periodically monitoring (1H NMR) until the disap-
pearance of 1 (typically 2e3 h) and the intermediate endoperoxide
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4
M. DellaGreca et al. / Tetrahedron xxx (2013) 1e6
2 was identified by its 1H NMR spectroscopic data. Then, irradiation
was stopped, diethylamine (62 L, 0.6 mmol, 1.2 equiv) was added,
and the mixture was kept at rt for 30 min. The solvent was evap-
orated and the crude acrylic acid 3 was dried in the presence of
anhydrous P2O5 for 5 h in order to remove diethylamine.
CDCl3) d 191.6, 166.8, 165.5, 163.6, 145.2, 135.4, 131.9, 131.7, 130.3,
m
128.0, 53.0, 52.4; HRMS (ESI) (m/z): found 371.9770 [MþH]þ; calcd
79
for C H BrO7 370.9766.
14 11
4.2.9. (Z)-4-Methoxy-3-(4-methoxybenzoyl)-2-(methoxycarbonyl)-
4-oxobut-2-enoic acid (3c). Amorphous powder. IR (CH2Cl2)
3590e3480 (br), 2957, 1740, 1738, 1685, 1600, 1513, 1436, 1172,
n
4.2.2. General procedure for Tf2O-mediated FriedeleCrafts acylation
of acids (3). Crude reagent 3 (3a, 144 mg, 0.493 mmol) was dis-
solved in aromatic compound 4 (35 equiv, neat conditions) or in dry
1030, 842 cmꢀ1; 1H NMR (500 MHz, CDCl3)
d
7.92 (d, J¼8.8 Hz, 2H),
6.91 (d, J¼8.8 Hz, 2H), 3.90 (s, 3H), 3.84 (s, 3H), 3.67 (s, 3H); 13C
solvent (CH2Cl2, 2 mL) and then anisole (268
m
L, 5 equiv) was
NMR (126 MHz, CDCl3) d 191.0, 166.7, 166.3, 164.2, 163.3, 140.0,
added. The mixture was cooled to ꢀ20 ꢁC and Tf2O (207
mL,
131.5, 130.9, 130.0, 113.6, 55.4, 52.7, 52.5; HRMS (ESI) (m/z): found
1.23 mmol, 2.5 equiv) was added dropwise at this temperature. The
resulting mixture was stirred under N2 atmosphere at the tem-
perature and for the time reported in Table 1. In the acylation with
323.0772 [MþH]þ; calcd for C15H14O8 323.0767.
4.2.10. Dimethyl 2-(4-methoxyphenyl)-5-oxo-2-phenyl-2,5-dihydro-
phenol (entry 9), Tf2O (207
mL, 1.23 mmol, 2.5 equiv) was added
furan-3,4-dicarboxylate (5a, Table 1, entry 1). Yellow oil (88 mg,
dropwise in the acrylic acid 3a (96.0 mg, 0.325 mmol) solution (dry
CH2Cl2, 2 mL) cooled at ꢀ20 ꢁC. The mixture was stirred for 30 min,
then phenol was added and the resulting mixture warmed to rt for
2.5 h. On completion of the reaction (controlled by TLC), each
mixture was washed with saturated aq NaHCO3 solution and
extracted twice with ethyl ether. The organic layer was collected,
dried over anhydrous Na2SO4, filtered, and concentrated to give
a residue that was chromatographed on silica gel with a gradient of
petrol ether and ethyl acetate. Mixture of p- and o-isomers 6 and 60
was subsequently separated by HPLC using RP-18 column and H2O/
MeOH/MeCN as eluent.
46%). Rf (25% EtOAc/hexane): 0.27. IR (CH2Cl2)
1602, 1441, 1170, 1036, 980, 890 cmꢀ1 1H NMR (500 MHz, CDCl3)
7.38e7.29 (m, 5H), 7.23 (d, J¼8.8 Hz, 2H), 6.88 (d, J¼8.8 Hz, 2H),
3.92 (s, 3H), 3.81 (s, 3H), 3.75 (s, 3H); 13C NMR (126 MHz, CDCl3)
165.6, 161.5, 161.0, 160.5, 160.3, 136.8, 129.3, 128.6, 128.5, 128.2,
127.7, 126.7, 113.9, 91.9, 55.3, 53.2, 53.1; HRMS (ESI) (m/z): found
383.1136 [MþH]þ; calcd for C21H18O7 383.1131.
n 2960, 1760, 1738,
;
d
d
4.2.11. Dimethyl 3-(4-methoxyphenyl)-2-oxo-5-phenyl-2,3-dihydro-
furan-3,4-dicarboxylate (6a, Table 1, entry 2). Yellow oil (5 mg,
3%). Rf (25% EtOAc/hexane): 0.38, separated from 60a by RP-HPLC
H2O/MeOH/MeCN (3:3:4 v/v/v). IR (CH2Cl2)
n
2980, 1812, 1755,
4.2.3. General procedure for Tf2O-mediated FriedeleCrafts acylation
of acids (3) using 2,6-lutidine. Crude reagent 3 (3a, 144 mg,
0.493 mmol) was dissolved in anisole (1.87 mL, 35 equiv, neat
conditions) or in dry solvent (CH2Cl2, 2 mL) and then anisole
1717, 1607, 1510, 1460, 1170, 1032, 970, 841 cmꢀ1
;
1H NMR
(500 MHz, CDCl3)
d
7.99 (d, J¼7.8 Hz, 2H), 7.53e7.41 (m, 5H), 6.92 (d,
J¼8.8 Hz, 2H), 3.83 (s, 3H), 3.81 (s, 3H), 3.68 (s, 3H); 13C NMR
(126 MHz, CDCl3)
d 170.2, 166.8, 162.6, 161.7, 160.0, 132.1, 129.6,
(268
m
L, 5 equiv) was added. The mixture was cooled to ꢀ20 ꢁC and
128.9, 128.8, 128.5, 128.2, 114.1, 114.0, 63.8, 55.1, 54.0, 52.0; HRMS
Tf2O (207
m
L, 1.23 mmol, 2.5 equiv) added dropwise at this tem-
(ESI) (m/z): found 383.1136 [MþH]þ; calcd for C21H18O7 383.1131.
perature. Then 2,6-lutidine (143 mL, 2.5 equiv) was added at the
same temperature. The resulting mixture was stirred under N2 at-
mosphere at the temperature and for the time reported in Table 1.
4.2.12. Dimethyl 3-(2-methoxyphenyl)-2-oxo-5-phenyl-2,3-dihydro-
furan-3,4-dicarboxylate (60a, Table 1, entry 1). Yellow oil (6 mg,
6%). Rf (25% EtOAc/hexane): 0.38, separated from 6a by RP-HPLC
4.2.4. Dimethyl 1-phenyl-2,3,7-trioxa-bicyclo[2.2.1]hept-5-ene-5,6-
H2O/MeOH/MeCN (3:3:4 v/v/v). IR (CH2Cl2)
1711, 1600, 1515, 1465, 1174, 1030, 974, 843 cmꢀ1
(500 MHz, CDCl3)
7.88 (d, J¼7.1 Hz, 2H), 7.57e7.43 (m, 5H), 7.33 (t,
J¼8.8 Hz, 1H), 7.03 (t, J¼7.7 Hz, 1H), 3.90 (s, 3H), 3.77 (s, 3H), 3.56 (s,
3H); 13C NMR (126 MHz, CDCl3)
170.3, 166.5, 162.5, 160.9, 156.5,
n
2982, 1815, 1752,
dicarboxylate (2a). 1H NMR (500 MHz, CDCl3)
d
7.75 (d, J¼8.3 Hz,
;
1H NMR
2H), 7.59e7.56 (m, 2H), 7.48e7.44 (m, 1H), 6.81 (s, 1H), 3.72 (s, 3H),
d
3.68 (s, 3H).
d
4.2.5. Dimethyl 1-(4-bromophenyl)-2,3,7-trioxa-bicyclo[2.2.1]hept-5-
131.5, 131.4, 130.1, 129.8, 129.4, 128.1, 127.5, 123.6, 120.9, 111.9, 63.1,
55.8, 53.8, 51.4; HRMS (ESI) (m/z): found 383.1133 [MþH]þ; calcd
for C21H18O7 383.1131.
ene-5,6-dicarboxylate (2b). 1H NMR (500 MHz, CDCl3)
d 7.61 (d,
J¼8.6 Hz, 2H), 7.47 (d, J¼8.6 Hz, 2H), 6.81 (s, 1H), 3.88 (s, 3H), 3.74 (s,
3H).
4.2.13. Dimethyl
2,5-dihydrofuran-3,4-dicarboxylate (5b, Table 1, entry 3). Yellow oil
(43 mg, 41%). Rf (25% EtOAc/hexane): 0.28. IR (CH2Cl2) 3090, 2930,
1750, 1740, 1658, 1608, 1513, 1436, 1343, 1220, 927, 834 cmꢀ1 1H
NMR (500 MHz, CDCl3)
7.50 (d, J¼8.7 Hz, 2H), 7.21 (d, J¼8.8 Hz,
2H), 7.19 (d, J¼8.8 Hz, 2H), 6.88 (d, J¼8.7 Hz, 2H), 3.92 (s, 3H), 3.82
(s, 3H), 3.77 (s, 3H); 13C NMR (126 MHz, CDCl3)
165.4, 161.3, 160.5,
2-(4-bromophenyl)-2-(4-methoxyphenyl)-5-oxo-
4.2.6. Dimethyl 1-(4-methoxyphenyl)-2,3,7-trioxa-bicyclo[2.2.1]hept-
5-ene-5,6-dicarboxylate (2c). 1H NMR (500 MHz, CDCl3)
d
7.53 (d,
n
J¼9.1 Hz, 2H), 6.97 (d, J¼9.1 Hz, 2H), 6.78 (s, 1H), 3.87 (s, 3H), 3.84 (s,
;
3H), 3.75 (s, 3H).
d
4.2.7. (Z)-3-Benzoyl-4-methoxy-2-(methoxycarbonyl)-4-oxobut-2-
d
enoic acid (3a). Amorphous powder. IR (CH2Cl2)
n
3595e3478 (br),
160.3, 160.1, 136.0, 131.7, 129.4, 129.2, 128.1, 127.1, 123.8, 114.0, 91.3,
2950, 1742, 1720, 1675, 1605, 1513, 1436, 1172, 1030, 850 cmꢀ1
;
1H
55.3, 53.3, 53.2; HRMS (ESI) (m/z): found 461.0240 [MþH]þ; calcd
79
NMR (500 MHz, CDCl3)
d
7.89 (d, J¼7.6 Hz, 2H), 7.50 (t, J¼7.6 Hz,1H),
for C H BrO7 461.0236.
21 17
7.40 (t, J¼7.6 Hz, 2H), 3.86 (s, 3H), 3.65 (s, 3H); 13C NMR (126 MHz,
CDCl3)
d
192.5, 166.9, 165.6, 163.9, 145.0, 136.6, 134.5, 132.9, 128.6,
4.2.14. Dimethyl
5-(4-bromophenyl)-3-(4-methoxyphenyl)-2-oxo-
128.4, 52.8, 52.4; HRMS (ESI) (m/z): found 293.0664 [MþH]þ; calcd
2,3-dihydrofuran-3,4-dicarboxylate (6b, Table 1, entry 4). Yellow oil
for C14H12O7 293.0661.
(6.7 mg, 7%). Rf (25% EtOAc/hexane): 0.45, separated from 60b by RP-
HPLC H2O/MeOH/MeCN (2:5:3 v/v/v). IR (CH2Cl2)
n
2928, 1816,
7.81
4.2.8. (Z)-3-(4-Bromobenzoyl)-4-methoxy-2-(methoxycarbonyl)-4-
1608, 1590, 1512, 1172, 1149 cmꢀ1; 1H NMR (500 MHz, CDCl3)
d
oxobut-2-enoic acid (3b). Amorphous powder. IR (CH2Cl2)
n
(d, J¼8.5 Hz, 2H), 7.64 (d, J¼8.4 Hz, 2H), 7.21 (d, J¼8.9 Hz, 2H), 6.85
3590e3480 (br), 2960,1742,1718,1680,1601,1512,1430,1170,1040,
(d, J¼8.9 Hz, 2H), 3.87 (s, 3H), 3.81 (s, 3H), 3.80 (s, 3H); 13C NMR
830 cmꢀ1; 1H NMR (500 MHz, CDCl3)
d
7.76 (d, J¼8.5 Hz, 2H), 7.56
(126 MHz, CDCl3) d 169.9, 166.3, 162.4, 159.7, 156.4, 131.4, 130.9,
129.9, 126.2, 123.4, 120.9, 114.2, 111.9, 63.4, 55.8, 53.8, 51.5; HRMS
(d, J¼8.5 Hz, 2H), 3.87 (s, 3H), 3.67 (s, 3H); 13C NMR (126 MHz,
Please cite this article in press as: DellaGreca, M.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.03.101

M. DellaGreca et al. / Tetrahedron xxx (2013) 1e6
5
79
(ESI) (m/z): found 461.0239 [MþH]þ; calcd for C21
H
BrO7
129.4, 128.6, 128.5, 127.6, 127.5, 122.0, 108.5, 108.0, 101.6, 91.7, 53.3,
17
461.0236.
53.2; HRMS (ESI) (m/z): found 397.0929 [MþH]þ; calcd for
C21H16O8 397.0923.
4.2.15. Dimethyl 5-(4-bromophenyl)-3-(2-methoxyphenyl)-2-oxo-
2,3-dihydrofuran-3,4-dicarboxylate (60b, Table 1, entry 4). Yellow oil
(11.4 mg,12%). Rf (25% EtOAc/hexane): 0.45, separated from 6b by RP-
4.2.21. Dimethyl 3-(benzo[d][1,3]dioxol-5-yl)-2-oxo-5-phenyl-2,3-
dihydrofuran-3,4-dicarboxylate (6e, Table 1, entry 8). Yellow oil
HPLC H2O/MeOH/MeCN (2:5:3 v/v/v). IR (CH2Cl2)
n
2930,1800,1602,
7.78 (d,
(12 mg, 15%). Rf (27% EtOAc/hexane): 0.52. IR (CH2Cl2)
1815, 1748, 1720, 1605, 1515, 1485, 1176, 1156, 1008, 974, 852 cmꢀ1
1H NMR (500 MHz, CDCl3)
n 3010, 2956,
1592, 1512, 1172, 1150 cmꢀ1 1H NMR (500 MHz, CDCl3)
;
d
;
J¼8.8 Hz, 2H), 7.61 (d, J¼8.8 Hz, 2H), 7.48 (dd, J¼7.9, 1.5 Hz, 1H), 7.33
d
7.98 (d, J¼7.4 Hz, 2H), 7.55 (br d,
(td, J¼8.0,1.5 Hz,1H), 7.04 (t, J¼7.8 Hz,1H), 6.90 (d, J¼7.7 Hz,1H), 3.90
J¼7.3 Hz, 1H), 7.50 (t, J¼7.5 Hz, 2H), 7.13 (br s, 1H), 6.92 (dd, J¼8.2,
(s, 3H), 3.75 (s, 3H), 3.57 (s, 3H); 13C NMR (126 MHz, CDCl3)
d 169.9,
1.8 Hz, 1H), 6.79 (d, J¼8.3 Hz, 1H), 5.98 (s, 2H), 3.83 (s, 3H), 3.69 (s,
166.3,162.4,159.7,156.4, 131.6,131.4,130.9,129.9,129.3,126.2,123.4,
3H); 13C NMR (126 MHz, CDCl3)
d 170.0, 166.6, 162.5, 161.8, 148.2,
120.9, 114.2, 111.9, 63.2, 55.8, 53.8, 51.5; HRMS (ESI) (m/z): found
147.9,132.1,129.6,128.2,126.8,126.6,121.5,115.5,109.3,108.0,101.4,
64.0, 53.7, 52.1; HRMS (ESI) (m/z): found 397.0936 [MþH]þ; calcd
for C21H16O8 397.0939.
79
461.0238 [MþH]þ; calcd for C21
H Br O7 461.0236.
17
4.2.16. Dimethyl 2,2-bis(4-methoxyphenyl)-5-oxo-2,5-dihydrofuran-
3,4-dicarboxylate (5c, Table 1, entry 5). Yellow oil (45 mg, 43%). Rf
4.2.22. Dimethyl 2-(4-hydroxyphenyl)-5-oxo-2-phenyl-2,5-dihydro-
(40% EtOAc/hexane): 0.32. IR (CH2Cl2)
1180, 1033, 978, 895 cmꢀ1 1H NMR (500 MHz, CDCl3)
J¼9.0 Hz, 4H), 6.88 (d, J¼8.9 Hz, 4H), 3.92 (s, 3H), 3.82 (s, 6H), 3.76
(s, 3H); 13C NMR (126 MHz, CDCl3)
165.8, 161.6, 161.3, 160.5, 160.2,
129.2, 128.6, 126.3, 113.8, 91.8, 55.3, 53.2, 53.1; HRMS (ESI) (m/z):
found 413.1242 [MþH]þ; calcd for C22H20O8 413.1236.
n
2930, 1780, 1741, 1608, 1461,
furan-3,4-dicarboxylate (5f, Table 1, entry 9). Yellow oil (21.5 mg,
;
d
7.24 (d,
18%). Rf (35% EtOAc/hexane): 0.24. IR (CH2Cl2)
1758, 1715, 1600, 1510, 1491, 1180, 1010, 981, 846 cmꢀ1
(500 MHz, CDCl3)
7.43e7.34 (m, 3H), 7.32 (dd, J¼8.1, 1.5 Hz, 2H),
7.16 (d, J¼8.8 Hz, 2H), 6.80 (d, J¼8.7 Hz, 2H), 3.92 (s, 3H), 3.75 (s, 3H);
13C NMR (126 MHz, CDCl3)
165.9, 161.5, 161.3, 160.5, 156.9, 136.6,
n
3009, 2958, 1780,
;
1H NMR
d
d
d
129.5, 129.4, 128.5, 128.4, 127.7, 126.5, 115.4, 92.1, 53.3, 53.2; HRMS
4.2.17. Dimethyl 3,5-bis(4-methoxyphenyl)-2-oxo-2,3-dihydrofuran-
3,4-dicarboxylate (6c, Table 1, entry 6). Yellow oil (15 mg, 32%). Rf
(ESI) (m/z): found 369.0973 [MþH]þ; calcd for C20H16O7 369.0969.
(40% EtOAc/hexane): 0.40. IR (CH2Cl2)
1606, 1512, 1461, 1172, 1028, 971, 839 cmꢀ1
CDCl3)
8.06 (d, J¼9.0 Hz, 2H), 7.46 (d, J¼9.1 Hz, 2H), 6.99 (d,
J¼9.0 Hz, 2H), 6.94 (d, J¼9.1 Hz, 2H), 3.89 (s, 3H), 3.82 (s, 3H), 3.81
(s, 3H), 3.68 (s, 3H); 13C NMR (126 MHz, CDCl3)
170.3, 167.1, 162.9,
162.6, 161.8, 159.8, 131.8, 131.4, 129.4, 125.5, 118.8, 113.9, 113.6, 63.7,
55.5, 55.3, 53.6, 51.9; HRMS (ESI) (m/z): found 413.1240 [MþH]þ;
calcd for C22H20O8 413.1236.
n
2956, 1813, 1758, 1720,
;
4.2.23. Dimethyl 3-(4-hydroxyphenyl)-2-oxo-5-phenyl-2,3-dihydro-
furan-3,4-dicarboxylate (6f, Table 1, entry 9). Yellow oil (25.5 mg,
1H NMR (500 MHz,
d
21%). Rf (35%EtOAc/hexane):IR(CH2Cl2)
n
3001, 2956,1810,1762,1720,
1601, 1490, 1158, 1008, 980, 850 cmꢀ1
;
1H NMR (500 MHz, CDCl3)
d
d
7.98 (d, J¼7.5Hz, 2H), 7.54 (br t, J¼7.3 Hz,1H), 7.50 (brt, J¼7.8Hz, 2H),
7.40 (d, J¼8.7 Hz, 2H), 6.84 (d, J¼8.7 Hz, 2H), 3.83 (s, 3H), 3.68 (s, 3H);
13C NMR (126 MHz, CDCl3)
170.2, 166.9, 162.7, 161.8, 156.2, 132.1,
d
129.6,128.2, 126.6,125.3,115.5,110.7, 63.7, 53.8, 52.1; HRMS (ESI) (m/
z): found 369.0975 [MþH]þ; calcd for C20H16O7 369.0969.
4.2.18. Dimethyl 2-(3,4-dimethoxyphenyl)-5-oxo-2-phenyl-2,5-
dihydrofuran-3,4-dicarboxylate (5d, Table 1, entry 7). Yellow oil
4.2.24. Dimethyl 2-(3,4-dimethoxyphenyl)-2-(4-methoxyphenyl)-5-
(20 mg, 24%). Rf (30% EtOAc/hexane): 0.19. IR (CH2Cl2)
1748, 1720, 1605, 1507, 1465, 1175, 1018, 968, 838 cmꢀ1
(500 MHz, CDCl3)
n
2950, 1797,
;
oxo-2,5-dihydrofuran-3,4-dicarboxylate (5g, Table 1, entry 10).
1H NMR
Yellow oil (17 mg, 18%). Rf (30% EtOAc/hexane): 0.20. IR (CH2Cl2)
3009, 2928, 1780, 1741, 1605, 1514, 1464, 1180, 1027, 995, 841 cmꢀ1
1H NMR (500 MHz, CDCl3)
7.23 (d, J¼9.0 Hz, 2H), 6.92e6.81 (m,
5H), 3.92 (s, 3H), 3.89 (s, 3H), 3.82 (s, 3H), 3.78 (s, 3H), 3.76 (s, 3H);
13C NMR (126 MHz, CDCl3)
165.8, 161.7, 160.3, 149.8, 148.7, 134.0,
n
d
7.40e7.34 (m, 3H), 7.32 (dd, J¼8.0,1.5Hz, 2H), 6.90
;
(dd, J¼8.4, 2.2 Hz, 1H), 6.83 (d, J¼9.0 Hz, 1H), 6.81 (d, J¼2.0 Hz, 1H),
d
3.92 (s, 3H), 3.89 (s, 3H), 3.78 (s, 3H), 3.76 (s, 3H); 13C NMR (126 MHz,
CDCl3)
d
165.7, 161.6, 161.4, 160.4, 149.9, 148.9, 136.8, 129.4, 128.8,
d
128.5, 127.7, 126.3, 120.7, 111.1, 110.7, 91.9, 56.0, 55.9, 53.3, 53.2; HRMS
131.8, 129.3, 125.9, 124.0, 120.5, 113.8, 113.7, 110.9, 110.5, 91.5, 55.9,
55.8, 55.3, 53.3, 53.2; HRMS (ESI) (m/z): found 443.1349 [MþH]þ;
calcd for C23H22O9 443.1342.
(ESI) (m/z): found 413.1239 [MþH]þ; calcd for C22H20O8 413.1236.
4.2.19. Dimethyl 3-(3,4-dimethoxyphenyl)-2-oxo-5-phenyl-2,3-
dihydrofuran-3,4-dicarboxylate (6d, Table 1, entry 7). Yellow oil
4.2.25. Dimethyl 3-(3,4-dimethoxyphenyl)-5-(4-methoxyphenyl)-2-
oxo-2,3-dihydrofuran-3,4-dicarboxylate (6g, Table 1, entry
10). Yellow oil (68 mg, 54%). Rf (30% EtOAc/hexane): 0.30. IR
(13 mg, 15%). Rf (30% EtOAc/hexane): 0.25. IR (CH2Cl2)
1756, 1718, 1608, 1505, 1465, 1178, 1032, 971, 839 cmꢀ1
(500 MHz, CDCl3)
n
2980, 1811,
;
1H NMR
d
7.99 (d, J¼7.4 Hz, 2H), 7.58e7.53 (m, 1H), 7.50 (t,
(CH2Cl2)
n ;
3010, 2933, 1810, 1740, 1600, 1518, 1466, 1037, 844 cmꢀ1
J¼7.5 Hz, 2H), 7.22 (d, J¼2.2 Hz,1H), 6.95 (dd, J¼8.5, 2.2 Hz,1H), 6.84
(d, J¼8.5 Hz, 1H), 3.91 (s, 3H), 3.88 (s, 3H), 3.84 (s, 3H), 3.69 (s, 3H);
1H NMR (500 MHz, CDCl3)
d
8.05 (d, J¼8.9 Hz, 2H), 7.21 (d, J¼2.1 Hz,
1H), 6.99 (d, J¼9.0 Hz, 2H), 6.95 (dd, J¼8.5, 2.2 Hz, 1H), 6.83 (d,
J¼8.5 Hz,1H), 3.90 (s, 3H), 3.89 (s, 3H), 3.87 (s, 3H), 3.82 (s, 3H), 3.69
13C NMR (126 MHz, CDCl3)
d 170.1, 166.8, 162.7, 161.7, 149.6, 148.9,
132.1, 129.6, 128.2, 126.7, 125.5, 125.3, 120.1, 112.1, 110.8, 63.8, 56.0,
55.9, 53.7, 52.1; HRMS (ESI) (m/z): found 413.1240 [MþH]þ; calcd
for C22H20O8 413.1236.
(s, 3H); 13C NMR (126 MHz, CDCl3)
d 170.2, 167.0, 163.0, 162.7, 161.7,
149.6, 148.8, 131.7, 125.8, 120.2, 118.8, 113.7, 113.6, 112.2, 110.6, 63.5,
56.0, 55.8, 55.4, 53.6, 51.9; HRMS (ESI) (m/z): found 443.1352
[MþH]þ; calcd for C23H22O9 443.1342.
4.2.20. Dimethyl 2-(benzo[d][1,3]dioxol-5-yl)-5-oxo-2-phenyl-2,5-
dihydrofuran-3,4-dicarboxylate (5e, Table 1, entry 8). Yellow oil
4.2.26. Dimethyl 2-(benzo[d][1,3]dioxol-5-yl)-2-(4-methoxyphenyl)-
(16 mg, 19%). Rf (27% EtOAc/hexane): 0.43. IR (CH2Cl2)
1795, 1758, 1718, 1604, 1508, 1491, 1182, 1157, 1008, 978, 852 cmꢀ1
1H NMR (500 MHz, CDCl3)
n
3008, 2958,
5-oxo-2,5-dihydrofuran-3,4-dicarboxylate (5h, Table 1, entry
;
12). Yellow oil (3 mg, 6%). Rf (40% EtOAc/hexane): IR (CH2Cl2)
3010, 2956, 1780, 1759, 1718, 1601, 1510, 1481, 1185, 1160, 982,
850 cmꢀ1 1H NMR (500 MHz, CDCl3)
7.22 (d, J¼6.9 Hz) and
7.00e7.84 (m) (together 7H), 6.00 (s, 2H), 3.92 (s, 3H), 3.82 (s, 3H),
3.78 (s, 3H); 13C NMR (126 MHz, CDCl3)
165.4, 161.0, 160.8, 160.0,
n
d
7.43e7.35 (m, 3H), 7.33 (d, J¼6.9 Hz,
2H), 6.80 (dd, J¼9.0, 1.4 Hz, 1H), 6.79 (d, J¼1.5 Hz, 1H), 6.74 (d,
;
d
J¼8.5 Hz, 1H), 5.99 (s, 2H), 3.92 (s, 3H), 3.77 (s, 3H); 13C NMR
(126 MHz, CDCl3)
d
165.5, 161.4, 161.0, 160.4, 147.9, 136.6, 130.3,
d
Please cite this article in press as: DellaGreca, M.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.03.101

6
M. DellaGreca et al. / Tetrahedron xxx (2013) 1e6
2. Wong, H. N. C.; Yeung, K.-S.; Yang, Z. In Comprehensive Heterocyclic Chemistry III;
Katritzky, A. R., Ramsden, C. A., Scriven, E. F. V., Taylor, R., Eds.; Elsevier: London,
UK, 2008; pp 407e496.
3. Comegna, D.; DellaGreca, M.; Iesce, M. R.; Previtera, L.; Zarrelli, A.; Zuppolini, S.
Org. Biomol. Chem. 2012, 10, 1219.
147.9, 146.5, 136.6, 130.3, 129.4, 128.6, 127.6, 124.5, 121.0, 108.5,
108.0, 101.6, 90.7, 55.0, 53.3, 53.2; HRMS (ESI) (m/z): found 427.1041
[MþH]þ; calcd for C22H18O9 427.1029.
4. (a) Pan, J.-Y.; Chen, S.-L.; Yang, M.-H.; Wu, J.; Sinkkonen, J.; Zou, K. Nat. Prod.
Rep. 2009, 26, 1251; (b) Saleem, M.; Kim, H. J.; Ali, M. S.; Lee, Y. S. Nat. Prod. Rep.
2005, 22, 696.
5. (a) Khodaei, M. M.; Alizadeh, A.; Nazari, E. Tetrahedron Lett. 2007, 48, 4199; (b)
Khodaei, M. M.; Nazari, E. B. Bull. Korean Chem. Soc. 2011, 32, 1784.
6. (a) Spange, S.; Bauer, M.; Walfort, B.; Lang, H. J. Org. Chem. 2006, 71, 7850; (b)
Grundl, M. A.; Kaster, A.; Beaulieu, E. D.; Trauner, D. Org. Lett. 2006, 8, 5429; (c)
Harmata, M.; Jones, D. E. Tetrahedron Lett. 1996, 37, 783; (d) Martinez, A. G.;
Barcina, J. O.; Albert, A.; Cano, F. H.; Subramanian, L. R. Tetrahedron Lett. 1993,
34, 6753.
4.2.27. Dimethyl 3-(benzo[d][1,3]dioxol-5-yl)-5-(4-methoxyphenyl)-
2-oxo-2,3-dihydrofuran-3,4-dicarboxylate (6h, Table 1, entry
12). Yellow oil (64 mg, 92%). Rf (40% EtOAc/hexane): 0.49. IR
(CH2Cl2)
n 3011, 2956, 1813, 1759, 1721, 1605, 1506, 1491, 1180, 1157,
1010, 980, 850 cmꢀ1; 1H NMR (500 MHz, CDCl3)
d
8.04 (d, J¼9.0 Hz,
2H), 7.12 (d, J¼1.9 Hz, 1H), 6.98 (d, J¼9.0 Hz, 2H), 6.91 (dd, J¼8.2,
1.9 Hz, 1H), 6.78 (d, J¼8.3 Hz, 1H), 5.97 (s, 2H), 3.88 (s, 3H), 3.81 (s,
3H), 3.68 (s, 3H); 13C NMR (126 MHz, CDCl3)
d 171.0, 166.8, 162.8,
7. DellaGreca, M.; Iesce, M. R.; Previtera, L.; Purcaro, R.; Rubino, M.; Zarrelli, A.
Photochem. Photobiol. Sci. 2008, 7, 28.
162.7, 161.8, 148.1, 147.8, 131.8, 131.4, 127.1, 121.5, 118.8, 113.8, 109.3,
108.8, 101.4, 63.9, 55.4, 53.6, 51.9; HRMS (ESI) (m/z): found 427.1032
[MþH]þ; calcd for C22H18O9 427.1029.
8. Annangudi, S. P.; Sun, M.; Salomon, R. G. Synlett 2005, 1468.
9. Iesce, M. R.; Cermola, F.; Temussi, F. Curr. Org. Chem. 2005, 9, 109.
10. Merino, P.; Tejero, T.; Delso, J. I.; Matute, R. Curr. Org. Chem. 2007, 11, 1076.
11. Montagnon, T.; Noutsias, D.; Alexopolou, I.; Tofi, M.; Vassilikogiannakis, G. Org.
Biomol. Chem. 2011, 9, 2031.
12. Dimethyl 2-phenylfuran-3,4-dicarboxylate (1a, 70%), dimethyl 2-(4-
bromophenyl)furan-3,4-dicarboxylate (1b, 34%), and dimethyl 2-(4-
methoxyphenyl)furan-3,4-dicarboxylate (1c, 60%) prepared according to a re-
ported procedure: Fan, M.; Yan, Z.; Liu, W.; Liang, Y. J. Org. Chem. 2005, 70, 8204.
13. (a) Kernan, M. R.; Faulkner, D. J. J. Org. Chem. 1988, 53, 2773; (b) Aquino, M.;
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Acknowledgements
We thank the reviewer for his/her thorough review and highly
appreciate the comments and suggestions, which significantly
contributed to improving the quality of the publication. NMR ex-
periments were performed at CIMCF (Centro Interdipartimentale di
Metodologie Chimico-Fisiche) on a 500 MHz spectrometer of Con-
sortium INCA (Interuniversitario Nazionale Consorzio Ambiente).
14. (a) Cauquil, G.; Barrera, H.; Barrera, R. Bull. Soc. Chim. Fr. 1955, 550; (b) Fawcett,
N. C.; Cassidy, P. E.; Lin, J. C. J. Org. Chem. 1977, 42, 2929.
15. Lutz, R. E.; Couper, M. J. Org. Chem. 1941, 6, 77.
16. A 3,5-diaryl furanone has been obtained in the acylation of 1,2-dimethox-
ybenzene with maleic anhydride: Abd El-Fatah, M. E.; Soliman, S. A.; Farahat, S.
M. Indian J. Heterocycl. Chem. 2005, 14, 225.
Supplementary data
17. Gan, L.-S.; Yang, S.-P.; Fan, C.-Q.; Yue, J.-M. J. Nat. Prod. 2005, 68, 221.
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Nat. Prod. 2007, 70, 662; (b) Fiorentino, A.; DellaGreca, M.; D’Abrosca, B.;
Oriano, P.; Golino, A.; Izzo, A.; Zarrelli, A.; Monaco, P. Biochem. Syst. Ecol.
2007, 35, 392.
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2013.03.101.
References and notes
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Please cite this article in press as: DellaGreca, M.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.03.101