Mono- and biscouplings using triarylbismuths for the atom-efficient arylations of functionalized furans under palladium catalysis

Article abstract of DOI:10.1055/s-0032-1316567

Palladium-catalyzed cross-coupling reactions of functionalized bromofurans with triarylbismuths have been described for the atom-economic synthesis of functionalized arylfuran systems. The coupling reactions using triarylbismuths with various 2-bromofurans and 2,5-dibromofuran underwent smoothly to afford the corresponding 2-arylfurans and 2,5-diarylfurans in high yields in a short reaction time (one hour). Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0032-1316567

LETTER
▌1907
lMetteor no- and Biscouplings Using Triarylbismuths for the Atom-Efficient Aryla-
tions of Functionalized Furans under Palladium Catalysis
Arylations of Functionalized Furans
Maddali L. N. Rao,* Dheeraj K. Awasthi, Jalindar B. Talode
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India
Fax +91(512)2597532; E-mail: maddali@iitk.ac.in
Received: 03.04.2012; Accepted after revision: 05.06.2012
We have demonstrated the couplings of aryl halides and
Abstract: Palladium-catalyzed cross-coupling reactions of func-
triflates with triarylbismuths under palladium-catalyzed
tionalized bromofurans with triarylbismuths have been described
conditions.15 The novel coupling ability of triarylbismuths
for the atom-economic synthesis of functionalized arylfuran sys-
tems. The coupling reactions using triarylbismuths with various 2-
with 2-bromothiophenes under palladium catalysis was
bromofurans and 2,5-dibromofuran underwent smoothly to afford also realized very recently.16 These investigations re-
the corresponding 2-arylfurans and 2,5-diarylfurans in high yields
in a short reaction time (one hour).
vealed the high cross-coupling ability of triarylbismuths
with three aryl groups in short reaction times with excel-
Key words: palladium, triarylbismuths, 2-bromofurans, cross-cou-
pling, arylation
lent product yields. This prompted us to expand the scope
of triarylbismuths in couplings with halofurans under pal-
ladium-catalyzed conditions and herein we report this
study as follows.
Heteroaromatic ring systems are important building
blocks for various applications in organic synthesis.1 Fu-
ran systems serve as useful synthons in various synthetic
transformations to generate molecular complexity.2 Sub-
stituted furans are also key intermediates in the synthesis
of various pharmacologically important compounds for
medicinal applications.3 Furan skeletons in particular are
also useful for molecular electronic applications.4 Hence,
the development of new synthetic methodologies for fu-
ran skeletons is of important concern.
5-Bromofurfural is an important substrate for a variety of
coupling reactions.17 So, it was of interest to carry out the
Table 1 Screening Conditionsa–c
[Pd], Ph3P
BiPh3
+
OHC
Ph
OHC
Br
O
O
solvent
temp
(1 equiv)
(3.3 equiv)
(3 equiv)
Entry Catalyst/ligand
Base (equiv) Solvent
Time Yield
(h) (%)
Cross-coupling methodology is widely applied to enhance
the molecular complexity in synthetic organic chemistry
and this led to the development of various viable protocols
to access challenging target structures.5 Furthermore, ar-
ylfuran skeletons have been known for various medicinal
applications. In this context, generation of arylfuran skel-
etons is synthetically important and can be accomplished
through a cross-coupling methodology involving halofu-
rans and organometallic reagents under metal-catalyzed
conditions6,7 in addition to other methods.8 An alternative
strategy also involves metal-catalyzed couplings of fura-
nyl organometallics with aryl halides.9–12 For example, the
cross-couplings of 2-furanyl-boronic acids,9 zinc,10 or
tin11 reagents with aryl halides are reported for the synthe-
sis of 2-arylfurans. The couplings of 2-furanyltellurides
with aryltrifluroborates are also reported.12 The corre-
1
2
PdCl2/2PPh3
Cs2CO3 (6)
DMA
DMF
NMP
NMP
NMP
NMP
DMF
DMA
NMP
NMP
NMP
NMP
2
1
1
1
1
1
1
1
1
1
1
1
62
64
71
87
89
62
62
65
05d
15e
–
Pd(OAc)2/4PPh3 K3PO4 (6)
Pd(OAc)2/4PPh3 K3PO4 (6)
Pd(OAc)2/4PPh3 Cs2CO3 (6)
Pd(OAc)2/4PPh3 Cs2CO3 (3)
Pd(OAc)2/4PPh3 Cs2CO3 (2)
Pd(OAc)2/4PPh3 Cs2CO3 (3)
Pd(OAc)2/4PPh3 Cs2CO3 (3)
Pd(OAc)2/4PPh3 Cs2CO3 (3)
Pd(OAc)2/4PPh3 Cs2CO3 (3)
Pd(OAc)2/4PPh3 no base
3
4
5
6
7
8
9
10
11
12
sponding
biscouplings13
with
2,5-bis(butyltella-
nyl)furan13a or 2,5-bis(tri-n-butylstannyl)furan13b with
aryl halides is an extended strategy for an easy synthesis
of 2,5-diarylfurans. Recently, the regioselective couplings
involving furan systems have also been realized under
metal-catalyzed conditions.14
no catalyst
Cs2CO3 (3)
–
a Reaction conditions: Ph3Bi (0.25 mmol, 1 equiv), bromide (0.825
mmol, 3.3 equiv), base, Pd catalyst (0.025 mmol, 0.1 equiv), Ph3P
(0.2 or 0.4 equiv), solvent (3 mL), 90 °C.
b Isolated yields were calculated considering three phenyl couplings
from Ph3Bi. Thus, 0.75 mmol of the product correspond to 100%
yield.
c Homocoupled biphenyl formed in all the reactions in minor
SYNLETT 2012, 23, 1907–1912
Advanced online publication: 23.07.2012
DOI: 10.1055/s-0032-1316567; Art ID: ST-2012-D0300-L
© Georg Thieme Verlag Stuttgart · New York
amounts.
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
d At 40 °C.
e At 60 °C.

1908
M. L. N. Rao et al.
LETTER
Table 2 Cross-Couplings with Different Ar3Bia–d
initial study with 5-bromofurfural in couplings with tri-
arylbismuth reagents. In our earlier couplings with both
aryl and thiophenes, the reactivity of routinely used palla-
dium precursors such as PdCl2 and Pd(OAc)2 demonstrat-
ed excellent reactivity in the presence of Ph3P ligand. This
encouraged us to use this combination in furan couplings.
Pd(OAc)2 (0.1 equiv)
Ph3P (0.4 equiv)
BiAr3
+
Br
OHC
Ar
O
OHC
O
(1 equiv)
Cs2CO3 (3 equiv)
NMP, 90 °C, 1 h
(3.3 equiv)
(3 equiv)
The study was carried out with 3.3 equivalents of 5-bro- Entry Ar3Bi
mofurfural with one equivalent of Ph3Bi under different
5-Aryl-2-furfural
Yield (%)
reaction conditions (Table 1). The study carried out with
OHC
O
Bi
PdCl2 and Pd(OAc)2 provided the desired coupling be-
tween 62–64% isolated yields (Table 1, entries 1 and 2).
Further study using Pd(OAc)2 as a catalyst precursor and
K3PO4 and Cs2CO3 bases revealed higher coupling ability
in N-methylpyrrolidone (NMP) solvent with 71% and
87% yields, respectively (Table 1, entries 3 and 4). This
led us to check the loadings of base amounts (Table 1, en-
tries 5 and 6) and this indicated that three equivalents of
Cs2CO3 is good enough to obtain a high cross-coupling
yield up to 89%, while two equivalents of base afforded
62% yield. The coupling in N,N-dimethylformamide and
N,N-dimethylacetamide solvents furnished 62% and 65%
yields, respectively (Table 1, entries 7 and 8). Investiga-
tions lowering the reaction temperature to 40 °C and 60 °C
provided low yields (Table 1, entries 9 and 10). Expected-
ly, control reactions without base and catalyst–ligand
combination did not furnish the coupling product (Table
1, entries 11 and 12). In these screenings, biphenyl as side
product invariably formed from Ph3Bi, which is a known
process in the presence of palladium catalyst.18 This in-
vestigation unequivocally revealed that Pd(OAc)2/Ph3P in
combination with Cs2CO3 (3 equiv) in NMP at 90 °C as a
suitable combination to obtain high cross-coupling yield
in one hour reaction time (Table 1, entry 5).
1
89
3
2.1
OHC
O
Bi
Bi
Me
2.
3
4
5
6
7
Me 84
3
2.2
OHC
O
OMe
OMe
87
84
88
80
84
3
2.3
OMe
OMe
OHC
O
Bi
Bi
3
2.4
OHC
O
Cl
Cl
3
2.5
Cl
Me
F
Cl
Me
F
OHC
O
Bi
Bi
3
3
3
This prompted us to study the general coupling ability of
different Ar3Bi under the established conditions (Table
2).19 The coupling reactions of 5-bromofurfural with dif-
ferent Ar3Bi furnished 5-arylfurfural products in high
yields. It is heartening to see that both electron-rich and
electron-deficient triarylbismuths reacted very well in a
facile manner delivering high product yields in short reac-
tion time. In fact, this is not a common feature with other
organometallic reagents in such couplings. In the litera-
ture, the reactivity of 5-bromofurfural under Suzuki cou-
pling conditions was reported to require longer reaction
times under different conditions even for one C–C cou-
pling using aryl boronic acids or other reagents.3c,7 On the
other hand, the present three C–C couplings using triaryl-
bismuths require only one hour reaction time to obtain
high product yields and is noteworthy. In addition, the
products 5-arylfurfurals obtained in these couplings are
prominent substrates for the synthesis of Dantrolene ana-
logues earlier studied as Ca2+ regulating agents.3d 5-Aryl-
furfurals have also been evaluated for the inhibition
studies of severe acute respiratory syndrome (SARS).3e
These compounds are also useful for the preparation of
new gram-negative antibacterial drugs.3f
2.6
OHC
O
2.7
OHC
O
8
9
87
85
Bi
Bi
2.8
OHC
O
F
F
3
2.9
OHC
O
Bi
OEt
10
85
OEt
3
2.10
a Reaction conditions: Ar3Bi (0.25 mmol, 1 equiv), bromide (0.825
mmol, 3.3 equiv), Cs2CO3 (0.75 mmol, 3 equiv), Pd (OAc)2 (0.025
mmol, 0.1 equiv), Ph3P (0.1 mmol, 0.4 equiv), NMP (3 mL), 90 °C, 1 h.
b Isolated yields were calculated considering three aryl couplings
from Ar3Bi. Thus, 0.75 mmol of the product correspond to 100% yield.
c Homocoupled biaryls were formed in minor amounts.
Further study was continued with substituted and unsub-
stituted furans with Ar3Bi reagents under the established
conditions (Table 3).19 These reactions using unsubstitut-
d All products were characterized by 1H NMR, 13C NMR, and IR spec-
troscopy and ESI-HRMS spectrometry in comparison with literature data.
Synlett 2012, 23, 1907–1912
© Georg Thieme Verlag Stuttgart · New York

LETTER
Arylations of Functionalized Furans
Table 4 Screening with 2,5-Dibromofurana–c
1909
Table 3 Cross-Couplings with Different Furansa–d
Pd(OAc)2 (0.1 equiv)
Ph3P (0.4 equiv)
Pd(OAc)2 (0.1 equiv)
Ph3P (0.4 equiv)
BiAr3
+
Br
R
Ar
R
BiPh3
+
Br
O
O
Ph
Ph
Br
(1 equiv)
Cs2CO3 (3 equiv)
NMP, 90 °C, 1 h
O
O
Cs2CO3 (3 equiv)
NMP, 90 °C
R = H, CO2Et
(3.3 equiv)
(3 equiv)
Entry Ar3Bi
(equiv)
2,5-Dibromofuran Time (h)
(equiv)
Yield (%)
Entry Ar3Bi
2-Arylfuran/ethyl 5-aryl-2-
furancarboxylate
Yield
(%)
1
2
3
4
5
1.0
1.0
1.0
1.0
1.0
1.65
1.37
1.25
1.16
1.16
1
1
1
1
2
53
78
77
80
79
O
Bi
OMe
OEt
1
92
OMe
3
3.1
O
Bi
2.
91
81
OEt
3
a Reaction conditions: Ph3Bi (0.25mmol, 1 equiv,), 2,5-dibromofuran
(1.16–1.65 equiv), Cs2CO3 (0.75 mmol, 3 equiv), Pd(OAc)2 (0.025
mmol, 0.1 equiv), Ph3P (0.1 mmol, 0.4 equiv), NMP (3 mL), 90 °C.
b Isolated yields were based on 2,5-dibromofuran. Thus, 1.16 equiv
(0.29 mmol) of the product correspond to 100% yield.
c Isolated yields.
3.2
EtO2C
O
Bi
3
3
3.3
fact, these products are useful for the preparation of small-
molecule antagonists useful for pharmacological applica-
tions.3g
EtO2C
O
Bi
Me
Cl
4
89
82
80
89
87
Me
3
3.4
This study with differently substituted furans overall dem-
onstrated that a change in the electronics had no bearing
on couplings with Ar3Bi reagents.
EtO2C
O
O
O
O
Bi
5
Cl
3
2,5-Dibromofurans are important substrates to enhance
the molecular complexity and are important synthons for
the synthesis of molecular targets valuable for variety of
applications.20 Furthermore, bisarylations of 2,5-dibro-
mofurans under metal-catalyzed conditions are also use-
ful methodology for this purpose.13
3.5
EtO2C
Bi
F
6
F
3
3.6
Hence, to demonstrate the scope of this study, coupling
reactions were performed with 2,5-dibromofurans with
Ar3Bi reagents. Initial study under the established stoi-
chiometric conditions provided 2,5-diphenylfuran in 53%
yield (Table 4, entry 1). This was due to the formation of
the homocoupling product from Ph3Bi as a side product.
In general, formation of the homocoupled product from
triarylbismuths in the presence of palladium catalyst is a
competitive reaction. This will be predominant or in mi-
nor amounts depending on the relative cross-coupling re-
activity. So, further screening was carried out by changing
the stoichiometric equivalents of coupling reagents to ob-
tain the optimum conditions required (Table 4, entries 2–
4). From this study, it was revealed that the biscoupling is
effective within a range of 1.16–1.37 equivalents with
only marginal change in overall yields. Notably, by in-
creasing the reaction time to two hours, there was no fur-
ther improvement in the biscoupling yield (Table 4, entry
5). Hence, it was decided to further elaborate this study
using 1.16 equivalents of 2,5-dibromofuran with one
equivalent of Ar3Bi as a preferred combination.
EtO2C
Bi
OMe
7
OMe
OEt
3
3.7
EtO2C
Bi
OEt
8
3
3.8
a Reaction conditions: Ar3Bi (0.25 mmol, 1 equiv), bromide (0.825
mmol, 3.3 equiv), Cs2CO3 (0.75 mmol, 3 equiv), Pd(OAc)2 (0.025
mmol, 0.1 equiv), Ph3P (0.1 mmol, 0.4 equiv), NMP (3 mL), 90 °C, 1 h.
b Isolated yields were calculated considering three aryl couplings
from Ar3Bi. Thus, 0.75 mmol of the product correspond to 100%
yield.
c Homocoupled biaryls were formed in minor amounts as side products.
d All products were characterized by 1H NMR, 13C NMR, and IR spectros-
copy and ESI-HRMS spectrometry in comparison with literature data.
ed 2-bromofuran furnished 91–92% yields efficiently
with Ar3Bi reagents (Table 3, entries 1 and 2). Similarly,
the couplings of ethyl 5-bromo-2-furancarboxylate also
produced good to excellent yields of the corresponding
cross-coupled products, ethyl 5-aryl-2-furancarboxylate
with different Ar3Bi reagents (Table 3, entries 3–8). In
Hence, these conditions were applied to the coupling re-
action of 2,5-dibromofuran with different Ar3Bi reagents
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 1907–1912

1910
M. L. N. Rao et al.
LETTER
(Table 5).21 All the coupling reactions carried out with means, for example, the cross-coupling reaction of palla-
electronically different Ar3Bi furnished 2,5-diarylfurans dium-catalyzed cross-couplings of 2,5-bis(butyltella-
in 76–83% yields in short reaction time.
nyl)furan13a with aryltrifluoroborate salts or through Stille
couplings involving 2,5-bis(tri-n-butylstannyl)furan3b,13b
with aryl bromides. The cross-coupling reactions of 2-
There are a few methods known for the synthesis of 2,5-
diarylfurans by cross-coupling and by various other
Table 5 Biscouplings with Different Triarylbismuthsa–d
Pd(OAc)2 (0.1 equiv)
Ph3P (0.4 equiv)
+
BiAr3
Br
(1.16 equiv)
Br
Ar
(1.16 equiv)
Ar
O
O
Cs2CO3 (3 equiv)
NMP, 90 °C, 1 h
(1 equiv)
Entry
Ar3Bi
2,5-Diarylfuran
Yield (%)
80
O
Bi
1
3
5.1
O
Bi
Bi
Bi
Me
2.
3
4
5
6
7
83
79
76
80
79
77
Me
Me
3
5.2
O
Cl
Cl
Cl
3
5.3
O
OMe
OMe
MeO
3
5.4
O
Bi
F
F
F
3
5.5
Me
Me
Me
Cl
O
Bi
Bi
3
5.6
Cl
Cl
O
3
5.7
OMe
MeO
OMe
O
O
8
78
83
Bi
Bi
3
5.8
OEt
9.
OEt
EtO
3
5.9
a Reaction conditions: 2,5-dibromofuran (0.29 mmol, 1.16 equiv), Ar3Bi (0.25 mmol, 1 equiv), Cs2CO3 (0.75 mmol, 3 equiv), Pd(OAc)2 (0.025
mmol, 0.1 equiv), Ph3P (0.1 mmol. 0.4 equiv), NMP (3 mL), 90 °C, 1 h.
b Isolated yields were calculated considering 2,5-dibromofuran for coupling. Thus, 0.29 mmol of the product correspond to 100% yield.
c Homocoupled biaryls were formed in minor amounts as side products.
d All products were characterized by 1H NMR, 13C NMR, and IR spectroscopy and ESI-HRMS spectrometry in comparison with literature data.
Synlett 2012, 23, 1907–1912
© Georg Thieme Verlag Stuttgart · New York

LETTER
Arylations of Functionalized Furans
1911
R.; Bur, S. K.; Straub, C. S.; Padwa, A. Org. Lett. 2003, 5,
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bromo-5-arylfurans with arylboronic acids under palladi-
um catalysis also provide 2,5-diarylfurans.22 Some of the
other methods reported for the synthesis of 2,5-diarylfu-
rans include (i) rhodium-catalyzed isomerization of pro-
tected 2-butyne-1,4-diols,23 (ii) Au(I)-catalyzed hydration
of 1,3-diynes,24 (iii) Ru(II)- and Cu(II)-catalyzed sequen-
tial synthesis from alkynes,25 (iv) Au(I)-catalyzed intra-
molecular cyclization of 3-alkyne-1,2-diols,26 (v) Pt-
catalyzed cyclization of propargylic oxiranes,27 (vi)
ZnCl2-catalyzed cycloisomerization of alk-3-yn-1-ones,28
(vii) Heck arylation–oxidation process catalyzed by Ru
and Pd catalysts,29 and (viii) transformation of 2-butene-
1,4-diones catalyzed by Pd catalysts.30
Importantly, 2,5-dibromofuran couplings with organome-
tallic reagents is a useful strategy for the synthesis of 2,5-
diarylfurans, which are useful for photophysical applica-
tions,20d in the preparation of ligands that are useful for
catalytic polymerization reactions,20e and also in medici-
nal applications.31 Hence, despite the availability of many
methods as described above, the cross-coupling reaction
of 2,5-dibromofuran with organometallic reagents is still
a favorite route for its simplicity and ease of preparation
of starting materials and associated high coupling reactiv-
ity. It is a surprise to see that there are not many methods
reported so far for this purpose. In that context, the present
method involving cross-couplings of triarylbismuths with
2,5-dibromofuran under palladium-catalyzed conditions
is high-yielding and involves three aryl couplings from
Ar3Bi in a one-pot operation and is hence atom-economic
and requires only a short reaction time. Overall, this meth-
odology is useful for the synthesis of substituted furans
such as 2-arylfurans and 2,5-diarylfurans known to be
useful for various medicinal applications.31
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In conclusion, the efficient coupling reactions of triaryl-
bismuths with various 2-bromofuran compounds and 2,5-
dibromofuran have been demonstrated under palladium-
catalyzed conditions in a short reaction time. This phe-
nomenal reactivity of Ar3Bi compounds as aryl coupling
partners is expected to show high utility for applications
in organic synthesis under metal-catalyzed conditions.
Acknowledgment
We acknowledge the financial support received from the Depart-
ment of Science and Technology (DST), New Delhi under the
Green Chemistry Program (SR/S5/GC-11/2008). D.K.A. and J.B.T.
thank UGC, New Delhi for research fellowships.
(9) (a) Parry, P. R.; Bryce, M. R.; Tarbit, B. Org. Biomol. Chem.
2003, 1, 1447. (b) McClure, M. S.; Roschangar, F.; Hodson,
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Tetrahedron Lett. 1995, 36, 8055. (b) Kim, S.-H.; Rieke, R.
D. Tetrahedron Lett. 2010, 51, 2657. (c) Rieke, R. D.; Kim,
S.-H. Tetrahedron Lett. 2011, 52, 1128. (d) Gauthier, D. R.
Jr.; Szumigala, R. H.; Dormer, P. G.; Armstrong, J. D. III.;
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Lett. 1999, 40, 4769.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnoIufproig
m
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ungIifoop
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References and Notes
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© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 1907–1912

1912
M. L. N. Rao et al.
LETTER
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Analytical data of all the products with spectra for 2.1–2.10
and 3.1–3.8 are given in the Supporting Information.
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(21) Biscouplings of 2,5-dibromofuran were performed in a hot
oven-dried Schlenk tube with the reaction conditions: 2,5-
dibromofuran (0.29 mmol, 1.16 equiv), Ar3Bi (0.25 mmol,
1 equiv), Cs2CO3 (0.75 mmol, 3 equiv), Pd(OAc)2 (0.025
mmol, 0.1 equiv), Ph3 P (0.1 mmol. 0.4 equiv), dry NMP
(3 mL), 90 °C, 1 h. The workup procedure was followed as
given in ref. 16 to obtain 2,5-diphenylfuran (5.1).25
Analytical Data
(16) Rao, M. L. N.; Banerjee, D.; Dhanorkar, R. J. Synlett 2011,
1324.
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J. J. J. Org. Chem. 2003, 68, 1503.
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1988, 44, 5661.
(19) Representative Procedure for the Cross-Coupling
Reaction of 5-Bromofurfural with Ph3Bi
White solid (0.051 g, 80%), mp 67–69 °C. 1H NMR (500
MHz, CDCl3): δ = 7.76 (d, 4 H, J = 8.3 Hz, CHar), 7.42 (t, 4
H, J = 7.8 Hz, CHar), 7.26–7.30 (m, 2 H, CHar), 6.75 (s, 2 H,
CHar) ppm. 13C NMR (125 MHz, CDCl3): δ = 153.3, 130.8,
128.7, 127.3, 123.7, 107.2 ppm. IR (KBr): ν = 1597, 1473,
1020, 914, 796, 757, 686 cm–1. ESI-HRMS: m/z calcd for
C16H12O [M]+: 220.0888; found: 220.0885. Analytical data
of all the products with spectra for 5.1–5.9 are given in the
Supporting Information.
The reaction was performed in a hot oven-dried Schlenk tube
with the following reaction conditions: 5-bromofurfural
(0.825 mmol, 144 mg, 3.3 equiv), Ph3Bi (0.25 mmol, 110
mg, 1.0 equiv), Pd(OAc)2 (0.025 mmol, 5.6 mg, 0.1 equiv),
Cs2CO3 (0.75 mmol, 244 mg, 3.0 equiv), Ph3P (0.1 mmol, 26
mg, 0.4 equiv), dry NMP (3 mL), 90 °C, 1 h. After the
reaction, it was worked up following the procedure given in
ref. 16 to obtain the product 2.1.3d
(22) Vachal, P.; Toth, L. M. Tetrahedron Lett. 2004, 45, 7157.
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2687.
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Org. Lett. 2010, 12, 2758.
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P. H. Angew. Chem. Int. Ed. 2009, 48, 1681.
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2454.
Analytical Data
Orange liquid (0.115 g, 89%). 1H NMR (500 MHz, CDCl3):
δ = 9.63 (1 H, s, CHO), 7.80–7.82 (m, 2 H, CHar), 7.30–7.44
(28) Sniady, A.; Durham, A.; Morreale, M. S.; Wheeler, K. A.;
Dembinski, R. Org. Lett. 2007, 9, 1175.
(m, 4 H, CHar), 6.83 (d, 1 H, J = 3.7 Hz, CHar) ppm. 13
C
NMR (125 MHz, CDCl3): δ = 177.2, 159.4, 152.0, 129.7,
128.9, 125.3, 123.6, 107.7 ppm. IR (KBr): ν = 1671, 1435,
1210, 1040, 971, 933, 887, 784, 671 cm–1. ESI-HRMS: m/z
calcd for C11H9O2 [MH]+: 173.0603; found: 173.0606.
(29) Schmidt, B.; Geibler, D. Eur. J. Org. Chem. 2011, 4814.
(30) Rao, H. S. P.; Jothilingam, S. J. Org. Chem. 2003, 68, 5392.
(31) De Oliveira, R. B.; De Souza-Fagundes, E. M.; Siqueira, H.
A. J.; Leite, R. S.; Donnici, C. L.; Zani, C. L. Eur. J. Med.
Chem. 2006, 41, 756.
Synlett 2012, 23, 1907–1912
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