Efficient synthesis of substituted 3-iodofurans by electrophilic cyclization of propargylic oxirane derivatives

Article abstract of DOI:10.1002/ejoc.200700963

The electrophilic cyclization of various propargylic oxirane compounds and I₂ offers an efficient and straightforward route to highly substituted iodofurans under mild reaction conditions. Further functionalization has demonstrated that the iod

Full text of DOI:10.1002/ejoc.200700963

FULL PAPER
DOI: 10.1002/ejoc.200700963
Efficient Synthesis of Substituted 3-Iodofurans by Electrophilic Cyclization of
Propargylic Oxirane Derivatives
Yong-Xin Xie,[a] Xue-Yuan Liu,*[a] Lu-Yong Wu,[a] Yao Han,[a] Lian-Biao Zhao,[a]
Ming-Jin Fan,[a] and Yong-Min Liang[a,b]
Keywords: Electrophilic cyclization / Oxiranes / Furans / Iodine / Alkynes
The electrophilic cyclization of various propargylic oxirane
compounds and I2 offers an efficient and straightforward
route to highly substituted iodofurans under mild reaction
conditions. Further functionalization has demonstrated that
the iodo derivatives obtained are potential synthetic interme-
diates for the amplification of molecular complexity.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
nary range of useful, functionally substituted heterocycles
and carbocycles. Therefore the development of synthetic
routes that allow the facile assembly of substituted furans
or iodofurans under mild conditions from simple readily
available alkynes still remains an important objective.
Electrophile-promoted cyclization has proven to be an
elegant synthetic route to a wide range of halogenated het-
erocyclic compounds.[12,13] Recently, we reported some im-
portant methods for the synthesis of polysubstituted furans
by ammonium ylide and Pd-catalyzed routes.[14,15] On the
basis of this work we considered that propargylic oxiranes
could serve as potential substrates for the synthesis of poly-
substituted furans. An extensive review of the literature
revealed that only a limited number of propargylic oxiranes
had been employed as possible halofuran precursors.[16] Be-
cause propargylic oxirane compounds are more readily
available than the reported unsaturated alcohols or ketones
we envisioned that the utilization of propargylic oxiranes
for electrophilic cyclization could significantly expand the
range of starting materials suitable for the synthesis of func-
tionally substituted furans. Herein, we report an efficient
method for the synthesis of highly substituted furans by
electrophilic cyclization of propargylic oxiranes (Scheme 1).
Introduction
Furans are an important class of heterocyclic com-
pounds which are extensively used as an important reaction
intermediate in organic synthesis.[1] It is also a significant
component of a number of natural products and synthetic
materials, including industrial intermediates and pharma-
ceuticals.[2] Of these, halofurans are important derivatives
that provide an opportunity for further functionalization.
For example, iodofurans are frequently employed as sub-
strates in a variety of C–C, C–N, or C–S bond-forming re-
actions and also serve as building blocks in combinatorial
chemistry.[3–6] Therefore, iodofurans have received much at-
tention because of their potential usefulness in the synthesis
of complex furan derivatives. In general, substituted furans
are accessed by ring derivatization or cyclization of acyclic
precursors. Several interesting approaches to the synthesis
of functionalized furans by the electrophilic cyclization of
3-alkyne-1,2-diols,[7] 2,4-dialkenyl-1,3-dicarbonyls,[8] and 2-
alkynylcarbonyl compounds have been reported.[9] Very re-
cently, similar cyclization reactions were also achieved by
using 2-(1-alkynyl)alk-2-en-1-ones[10] and 1,4-disubstituted
but-3-yn-1-ones.[11]
However, of the above oxygen-containing compounds
that can be subjected to cyclization, unsaturated alcohols or
ketones are the substrates of major interest. The analogous
chemistry of alkynes has been far less studied although it
would appear to be a very promising route to an extraordi-
Scheme 1.
[a] State Key Laboratory of Applied Organic Chemistry, Lanzhou
University,
Lanzhou 730000, P. R. China
Results and Discussion
Fax: +86-931-8912582
E-mail: liuxuey@lzu.edu.cn
Our initial study began with the reaction of propargylic
oxirane 1a and I2 in THF at room temp. in the absence of
base; the desired furan product 2a was isolated in only 37%
yield (Table 1, entry 1). Encouraged by this positive result,
[b] State Key Laboratory of Solid Lubrication, Lanzhou Institute
of Chemical Physics, Chinese Academy of Science,
Lanzhou 730000, P. R. China
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Eur. J. Org. Chem. 2008, 1013–1018
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X.-Y. Liu et al.
FULL PAPER
we optimized the reaction condition by experimenting with Table 2. Iodocyclization of propargylic oxirane compounds.[a]
various bases and solvents. The addition of inorganic bases
such as Na2CO3 and K2CO3 increased the yield of 2a to 45
and 55%, respectively (entries 2 and 3). Interestingly, with
NaHCO3 as the base, product 2a was isolated in 72% yield
in a shorter reaction time (entry 4). When the reaction was
performed with the strong bases tBuOK and NaOMe, no
Entry
1
R2
Time [h]
2
% Yield
product was obtained although the starting material did de-
compose. The organic base Et3N was also evaluated; only
a moderate yield of the product was obtained (entry 7). On
the other hand, the effect of solvent was also very impor-
tant in the electrophilic cyclization. THF proved to be the
optimal medium. Solvents such as CH2Cl2, CH3CN, or
CH3OH did not improve the yield (entries 8–10).
1
2
3
4
5
6
7
1a
1b
1c
1d
1e
1f
Ph
2
5
5
12
10
4
2a
2b
2c
2d
2e
2f
–
72
o-Br-C6H4
m-Br-C6H4
p-Br-C6H4
p-Cl-C6H4
p-CH3–C6H4
n-C5H11
73[b]
83[b]
85[b]
93[b]
90[b]
[c]
1g
2
–
[a] All reactions were run under the following conditions unless
specified: 0.25 mmol of 1, 2 equiv. of I2, 2 equiv. of NaHCO3 in
THF at room temperature. [b] 5 Equiv. of I2 and 5 equiv. of
NaHCO3 were required. [c] The product decomposed as soon as it
was exposed to air.
Table 1. Electrophile-induced cyclization of propargylic oxirane
1a.[a]
Next we elucidated the scope of the reaction by examin-
ing the effect of various R1 groups on the aliphatic ring. As
can be seen in Table 3 (entries 1 and 2), R1 groups play a
negligible role in the electrophilic cyclization. For example,
furan 2h was generated exclusively in 95% yield from sub-
strate 1h bearing a methyl group (entry 1); the use of 1,3-
Entry
Base
Solvent
Time [h]
% Yield[b]
1
2
3
4
5
6
7
8
9
10
–
THF
THF
THF
THF
THF
THF
THF
CH2Cl2
CH3CN
CH3OH
3
3
3
2
3
3
5
3
3
3
37
45
55
72
0
Na2CO3
K2CO3
NaHCO3
tBuOK
NaOMe
Et3N
NaHCO3
NaHCO3
NaHCO3
Table 3. Iodocyclization of propargylic oxirane compounds.[a]
0
46
58
61
35
[a] Conditions: 0.25 mmol of 1a, 2 equiv. of I2 and 2 equiv. of
NaHCO3 in 3 mL of THF at room temp. [b] Isolated yield.
Thus, we chose the following optimal reaction conditions
for all subsequent experiments: 0.25 mmol of propargylic
oxirane, 2 equiv. of I2, 2 equiv. of NaHCO3 in 5 mL of THF
stirred under argon at room temperature for an appropriate
amount of time (Table 2). First, the effect of a variety of
alkyne substituents R2 on the electrophilic cyclization was
examined. On the whole, both electron-rich and electron-
poor C-aryl-substituted alkynes reacted to form the corre-
sponding products in moderate-to-good yields. The cycliza-
tion of both 2-bromophenyl- 1b and 3-bromophenyl-substi-
tuted propargylic epoxides 1c using I2 generated the corre-
sponding 3-iodofuran in 73 and 83% yields, respectively
(entries 2 and 3). Good results were also obtained with 4-
bromophenyl 1d and 4-chlorophenyl 1e as substituents (en-
tries 4 and 5). The reaction of electron-rich 4-methylphenyl
propargylic oxirane also proceeded smoothly in good yield
(entry 6). Unfortunately, when hept-1-yne group was used,
the expected product was not obtained due to its rapid de-
composition in air to form complex unknown compounds.
However, a single product was observed by TLC under ar-
gon.
[a] All reactions were performed with 0.25 mmol of 1, 2 equiv. of
I2 and 2 equiv. of NaHCO3 in 5 mL of THF at room temp. [b]
5 equiv. of I2 and 5 equiv. of NaHCO3 were required.
1014
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Eur. J. Org. Chem. 2008, 1013–1018

Synthesis of Iodofurans by Electrophilic Cyclization
dioxolane as the R1 moiety in compound 1i did not influ- uct diversity, mild reaction conditions, the simplicity of the
ence the efficiency of this reaction (entry 2) in which the reaction procedure, and good-to-excellent yields. Iodocy-
corresponding product 2i was formed in 90% yield.
clization of propargylic epoxides followed by palladium-cat-
As shown in Table 3, this methodology could also be ex- alyzed coupling afforded products with an increased molec-
tended to other propargylic oxiranes bearing various ali- ular complexity and has provided a powerful tool for the
cyclic substituents, as well as 2-methyl epoxide. The reac- preparation of a wide range of functionalized, polysubsti-
tion of compound 1j with I2 went to completion with quan- tuted furans. Further work to extend this method to the
titative conversion and an excellent yield (entry 3). Chang- synthesis of complex molecular structures is in progress.
ing the substituent R1 to an 8- or 12-membered ring epox-
ide gave 83 and 94% (entries 4 and 5) yields, respectively.
The cyclization of 2-methyl-substituted epoxides (entries 6– Experimental Section
8) also afforded polysubstituted 3-iodofurans in good-to-
General Remarks: Column chromatography was carried out on sil-
excellent yields. For example, the cyclization of epoxide 1m
afforded furan 2m in 85% yield (entry 6). Compared with
the reaction of 1o, epoxide 1n gave a relatively low yield of
75%, probably due to the steric hindrance of the o-bromine
ica gel. 1H NMR spectra were recorded with a 300 or 400 MHz
spectrometer in CDCl3. 13C NMR spectra were recorded with a 75
or 100 MHz spectrometer in CDCl3 by using TMS as the internal
standard. Mass spectra were recorded with a HP5998 MS spec-
atom (entries 7 and 8). In fact, a similar effect is evident in trometer by using the EI method. IR spectra were recorded on a
FT-IR spectrometer and only the major peaks are reported. Melt-
ing points were determined on a microscopic apparatus and are
uncorrected. All new compounds were further characterized by ele-
ment analysis; copies of their 1H and 13C NMR spectra are pro-
vided. Commercially available reagents and solvents were used
without further purification. THF was distilled immediately before
to use from Na/benzophenone.
the data reported in Table 2 (entries 2–4).
As mentioned in the Introduction, the presence of the
iodide functional group on the furan ring provides an op-
portunity for further functionalization. By using the general
conditions for the Suzuki coupling reaction we investigated
the coupling reaction of compound 2l and phenylboronic
acid; the expected tetrasubstituted furan 3l was obtained in
59% yield (Scheme 2).[17]
Preparation of Propargylic Oxiranes
Synthesis of 1-(2-Phenylethynyl)-7-oxabicyclo[4.1.0]heptane (1a):[19]
MCPBA (362 mg, 2.10 mmol) was added to a stirred solution of
(cyclohexenylethynyl)benzene (124 mg, 1.0 mmol) (see the elec-
tronic supporting information) and Na2HPO4 (350 mg, 2.47 mmol)
in DCM (5 mL) at 0 °C. The reaction mixture was stirred at 0 °C
for 3 h and then allowed to warm to room temp., whereupon it was
diluted with diethyl ether and quenched with an aqueous saturated
NaHCO3 solution. The organic layer was washed with 10% NaOH
and brine and finally dried with anhydrous MgSO4. The solvent
was evaporated and column chromatography on basic Al2O3 with
petroleum ether/EtOAc (100:1, v/v) as eluent afforded 1a as a color-
less viscous oil; yield: 178 mg (60%). Compounds 1b–1o were pre-
pared by the same method.
Scheme 2.
Based on previously reported results,[18] a plausible reac-
tion mechanism is shown in Scheme 3 which involves the
cyclic iodonium ion 3 formed by coordination of the pro-
pargylic triple bond to an iodine cation. Subsequent anti
attack by the oxygen on the iodonium ion and elimination
of a hydrogen cation led to the formation of 3-iodofuran 2.
1-(2-Phenylethynyl)-7-oxabicyclo[4.1.0]heptane (1a): Colorless oil.
1H NMR (400 MHz, CDCl3): δ = 1.21–1.43 (m, 2 H), 1.44–1.47
(m, 2 H), 1.91–1.95 (m, 2 H), 2.05–2.12 (m, 1 H), 2.19–2.26 (m, 1
H), 3.42–3.43 (t, J = 2.4 Hz, 1 H), 7.25–7.30 (m, 3 H), 7.41–7.44
(m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 18.8, 19.4, 24.1,
29.6, 50.5, 60.2, 81.8, 89.5, 122.2, 128.1, 128.3, 131.6 ppm. IR
(neat): ν = 2939, 1490, 756 cm–1. C H O (198.2): calcd. C 84.81,
˜
14 14
H 7.12; found C 84.77, H 7.15.
1-[2-(2-Bromophenyl)ethynyl]-7-oxabicyclo[4.1.0]heptane (1b): Col-
orless oil. 1H NMR (400 MHz, CDCl3): δ = 1.17–1.46 (m, 4 H),
1.88–1.93 (m, 2 H), 2.01–2.11 (m, 1 H), 2.16–2.25 (m, 1 H), 3.39
(s, 1 H), 7.09–7.14 (t, J = 10.4 Hz, 1 H), 7.30–7.33 (d, J = 10.8 Hz,
1 H), 7.38–7.41 (m, 1 H),7.54 (s, 1 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 18.4, 19.0, 23.7, 29.2, 49.9, 59.7, 79.9, 90.8, 121.6,
123.9, 129.3, 129.8, 131.2, 134.0 ppm. IR (neat): ν = 2939, 1555,
˜
1473, 783, 679 cm–1. C14H13BrO (276.0): calcd. C 60.67, H 4.73;
found C 60.62, H 4.76.
Scheme 3. Plausible reaction mechanism.
1-[2-(3-Bromophenyl)ethynyl]-7-oxabicyclo[4.1.0]heptane (1c): Col-
orless oil. 1H NMR (400 MHz, CDCl3): δ = 1.36–1.47 (m, 4 H),
1.93–1.97 (m, 2 H), 2.14–2.16 (m, 1 H), 2.25 (s, 1 H), 3.34 (s, 1 H),
7.13–7.17 (m, 1 H), 7.21–7.25 (m, 1 H), 7.43–7.46 (m, 1 H), 7.54–
Conclusions
In summary, we have developed a new approach to the
formation of polysubstituted 3-iodofuran. The process
showed considerable synthetic advantages in terms of prod- 7.57 (m, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 18.7, 19.3,
Eur. J. Org. Chem. 2008, 1013–1018
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1015

X.-Y. Liu et al.
FULL PAPER
24.1, 29.4, 50.5, 60.1, 80.4, 94.1, 124.3, 125.6, 126.8, 129.5, 132.2,
34.5, 54.5, 63.7, 76.8, 77.1, 77.5, 81.4, 90.5, 122.4, 128.2, 128.4,
133.3 ppm. IR (neat): ν = 2942, 1468, 1433, 908, 733 cm–1.
131.8 ppm. IR (neat): ν = 2927, 1724, 1449, 909, 753 cm–1.
˜
˜
C14H13BrO (276.0): calcd. C 60.67, H 4.73; found C 60.58, H 4.71.
C15H16O (212.29): calcd. C 84.87, H 7.60; found C 84.81, H 7.64.
1-[2-(4-Bromophenyl)ethynyl]-7-oxabicyclo[4.1.0]heptane (1d): Col-
orless solid; m.p. 92–93 °C. 1H NMR (400 MHz, CDCl3): δ = 1.23–
1.37 (m, 2 H), 1.40–1.48 (m, 2 H), 1.92–1.96 (m, 2 H), 2.04–2.11
(m, 1 H), 2.18–2.24 (m, 1 H), 3.42–3.43 (t, J = 2.4 Hz, 1 H), 7.26–
1-(2-Phenylethynyl)-9-oxabicyclo[6.1.0]nonane (1k): Colorless oil.
1H NMR (400 MHz, CDCl3): δ = 1.24–1.34 (m, 1 H), 1.39–1.48
(m, 4 H), 1.51–1.60 (m, 4 H), 1.77–1.85 (m, 1 H), 2.17–2.26 (m, 2
H), 3.16–3.19 (t, J = 6.0 Hz, 1 H), 7.25–7.30 (m, 3 H), 7.42–7.45
7.29 (m, 2 H), 7.40–7.44 (m, 2 H) ppm. 13C NMR (100 MHz, (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 25.0, 25.7, 25.9,
CDCl3): δ = 18.7, 19.4, 24.1, 29.6, 50.4, 60.2, 90.9, 90.8, 121.2,
26.3, 26.9, 30.5, 53.9, 63.7, 82.4, 88.6, 122.2, 128.1, 128.3,
122.7, 131.4, 133.1 ppm. IR (KBr): ν = 3438, 2936, 1483, 836 cm–1.
131.7 ppm. IR (neat): ν = 2927, 1491, 1446, 926, 756, 691 cm–1.
˜
˜
C14H13BrO (276.0): calcd. C 60.67, H 4.73; found C 60.62, H 4.79.
C16H18O (226.1): calcd. C 84.91, H 8.02; found C 84.88, H 7.96.
1-[2-(4-Chlorophenyl)ethynyl]-7-oxabicyclo[4.1.0]heptane (1e): Col-
orless solid; m.p. 72–73 °C. 1H NMR (400 MHz, CDCl3): δ = 1.24–
1.34 (m, 1 H), 1.36–1.39 (m, 1 H), 1.41–1.50 (m, 2 H), 1.94–1.97
1-(2-Phenylethynyl)-13-oxabicyclo[10.1.0]tridecane (1l): Colorless
oil. H NMR (400 MHz, CDCl3): δ = 1.19–1.85 (m, 18 H), 2.16–
1
2.19 (m, 1 H), 2.39–2.42 (m, 1 H), 3.06 (s, 1 H), 7.26–7.31 (m, 3
(m, 2 H), 2.05–2.12 (m, 1 H), 2.54–2.57 (m, 1 H), 3.43 (s, 1 H), H), 7.41–7.43 (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
7.26–7.29 (m, 2 H), 7.34–7.37 (m, 2 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 18.8, 19.4, 24.1, 29.6, 50.5, 60.3, 80.8, 90.6, 120.8,
23.3, 23.6, 24.2, 24.9, 25.1, 25.6, 26.7, 27.1, 29.6, 35.9, 56.8, 66.2,
85.8, 86.7, 122.5, 128.2, 128.5, 131.7 ppm. IR (neat): ν = 2931,
˜
128.5, 133.0, 134.5 ppm. IR (neat): ν = 3432, 2938, 1485, 1087, 838, 1444, 756, 691 cm–1. C20H26O (282.2): calcd. C 85.06, H 9.28;
˜
755 cm–1. C14H13ClO (232.71): calcd. C 75.26, H 5.63; found C
75.21, H 5.65.
found C 85.10, H 9.32.
2-Methyl-2-(2-phenylethynyl)oxirane (1m): Colorless oil. 1H NMR
(400 MHz, CDCl3): δ = 1.64 (s, 3 H), 2.83–2.84 (d, J = 4.2 Hz, 1
1-[2-(p-Tolyl)ethynyl]-7-oxabicyclo[4.1.0]heptane (1f): Colorless oil.
1H NMR (300 MHz, CDCl3): δ = 1.26–1.40 (m, 1 H), 1.42–1.49 H), 3.11–3.12 (d, J = 5.6 Hz, 1 H), 7.27–7.31 (m, 3 H), 7.42–7.44
(m, 3 H), 1.94–1.96 (d, J = 8.0 Hz, 2 H), 2.08–2.15 (q, J = 8.1, J (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 23.3, 47.9, 55.9,
= 20.1 Hz, 1 H), 2.19–2.27 (m, 1 H), 2.34 (s, 1 H), 2.44 (s, 1 H), 82.3, 88.6, 122.3, 128.5, 128.9, 132.1 ppm. IR (neat): ν = 3396,
˜
7.08–7.11 (d, J = 7.5 Hz, 2 H), 7.31–7.36 (d, J = 7.2 Hz, 2 H) ppm. 2923, 1491, 756, 691 cm–1. C11H10O (158.1): calcd. C 83.51, H 6.37;
13C NMR (75 MHz, CDCl3): δ = 18.9, 19.5, 21.5, 24.2, 29.9, 50.8,
found C 83.47, H 6.42.
60.4, 82.2, 88.9, 119.7, 128.9, 131.7, 138.6 ppm. IR (neat): ν = 3428,
˜
2-[2-(2-Bromophenyl)ethynyl]-2-methyloxirane (1n): Colorless oil.
1H NMR (400 MHz, CDCl3): δ = 1.62 (m, 3 H), 2.80–2.82 (m, 1
H), 3.07–3.09 (d, J = 5.6 Hz 1 H), 7.11–7.15 (m, 1 H), 7.31–7.34
(m, 1 H), 7.40–7.43 (m, 1 H), 7.55–7.56 (q, J = 2.8 Hz, 1 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 22.6, 47.1, 55.2, 80.1, 89.6,
2918, 2850, 1510, 1435, 910, 732 cm–1. C15H16O (212.1): calcd. C
84.87, H 7.60; found C 84.81, H 7.54.
1-(Hept-1-ynyl)-7-oxabicyclo[4.1.0]heptane (1g): Colorless oil. 1H
NMR (400 MHz, CDCl3): δ = 0.88–0.91 (m, 3 H), 1.21–1.47 (m, 8
H), 1.48–1.52 (t, J = 7.0 Hz, 2 H), 1.84–1.88 (m, 2 H), 1.89–2.01 121.7, 123.8, 129.5, 130.0, 131.5, 134.2 ppm. IR (neat): ν = 2984,
˜
(m, 1 H), 2.09–2.16 (m, 1 H), 2.17–2.21 (t, J = 8.0 Hz, 2 H), 3.28
(s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 13.8, 18.5, 18.9,
19.4, 22.0, 24.1, 28.1, 30.0, 30.9, 50.4, 59.9, 76.7, 77.0, 77.3, 80.5,
1590, 1473, 1069, 829, 681 cm–1. C11H9BrO (236.0): calcd. C 55.72,
H 3.83; found C 55.78, H 3.79.
2-[2-(4-Bromophenyl)ethynyl]-2-methyloxirane (1o): Colorless solid;
m.p. 70–71 °C. 1H NMR (400 MHz, CDCl3): δ = 1.64 (s, 3 H),
2.84–2.85 (d, J = 5.6 Hz, 1 H), 3.11–3.12 (d, J = 5.6 Hz, 1 H),
7.28–7.30 (m, 2 H), 7.42–7.45 (m, 1 H) ppm. 13C NMR (100 MHz,
82.9 ppm. IR (neat): ν = 2935, 1460, 844, 759 cm–1. C H O
˜
13 20
(192.2): calcd. C 81.20, H 10.48; found C 81.26, H 10.53.
4-Methyl-1-(2-phenylethynyl)-7-oxabicyclo[4.1.0]heptane (1h, mix-
ture): Colorless oil. 1H NMR (400 MHz, CDCl3): δ = 0.86–0.90 (t, CDCl3): δ = 22.9, 47.5, 55.7, 80.9, 89.6, 121.1, 122.9, 131.6,
J = 7.6 Hz, 3 H), 0.96–1.25 (m, 1 H), 1.32–1.38 (m, 3 H), 1.97–
2.02 (m, 2 H), 2.24–2.42 (m, 1 H), 3.40 (s, 0.36 H), 3.46 (s, 0.60 H),
7.25–7.40 (m, 3 H), 7.41–7.45 (m, 2 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 21.3, 21.9, 23.5, 26.9, 27.2, 28.7, 30.1, 32.3, 33.3, 50.0,
50.9, 59.9, 61.5, 76.5, 77.0, 77.4, 82.0, 89.2, 89.7, 122.2, 128.2,
133.3 ppm. IR (neat): ν = 2972, 1483, 1067, 821 cm–1. C H BrO
˜
11 9
(236.0): calcd. C 55.72, H 3.83; found C 55.68, H 3.88.
General Procedure for the Synthesis of Propargylic Oxiranes 2a–2n
by Electrophilic Cyclization: Iodine (2.0 equiv.) dissolved in THF
(1.5 mL) was gradually added to a solution of propargylic oxirane
(0.25 mmol), NaHCO3 (2.0 equiv.) and THF (1.5 mL). The reac-
tion mixture was flushed with argon and allowed to stir at room
temp. for the desired time. The excess I2 was removed by washing
with a saturated solution of Na2S2O3. The aqueous solution was
then extracted with diethyl ether (2ϫ10 mL). The combined ether
128.4, 131.7, 131.7 ppm. IR (neat): ν = 2950, 2926, 1490, 756,
˜
691 cm–1. C15H16O (212.1): calcd. C 84.87, H 7.60; found C 84.91,
H 7.63.
4,4-Ethylenedioxy-1-(2-phenylethynyl)-7-oxabicyclo[4.1.0]heptane
1
(1i): Colorless solid; m.p. 95–96 °C. H NMR (400 MHz, CDCl3):
δ = 1.46–1.53 (m, 1 H), 1.65–1.73 (m, 1 H), 2.11–2.17 (m, 2 H), layers were dried with anhydrous Na2SO4 and concentrated under
2.37–2.41 (m, 2 H), 3.46–3.47 (d, J = 4 Hz, 1 H), 3.87–3.99 (m, 4 vacuum to yield the crude product which was purified by flash
H), 7.27–7.33 (m, 3 H), 7.42–7.44 (m, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 27.4, 27.7, 50.7, 59.1, 64.1, 64.5, 82.6, 88.2,
chromatography on alkali alumina using pure petroleum as the elu-
ent.
105.9, 122.1, 128.2, 128.5, 131.8 ppm. IR (KBr): ν = 2927, 1365,
˜
4,5,6,7-Tetrahydro-3-iodo-2-phenylbenzofuran (2a): Colorless oil. 1H
NMR (400 MHz, CDCl3): δ = 1.76–1.80 (m, 2 H), 1.83–1.88 (m, 2
H), 2.29–2.33 (m, 2 H), 2.62–2.66 (m, 2 H), 7.24–7.30 (m, 1 H),
7.37–7.41 (m, 2 H), 7.95–7.97 (m, 2 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 22.9, 23.2, 23.3, 23.3, 66.6, 123.2, 125.8, 127.5, 128.3,
1118, 757 cm–1. C16H16O3 (256.1): calcd. C 74.98, H 6.29; found C
74.90, H 6.33.
1
1-(2-Phenylethynyl)-8-oxabicyclo[5.1.0]octane (1j): Colorless oil. H
NMR (400 MHz, CDCl3): δ = 1.31–1.42 (m, 1 H), 1.49–1.61 (m, 5
H), 1.64–1.75 (m, 1 H), 1.78–2.12 (m, 2 H), 2.22–2.27 (m, 1 H), 130.8, 148.9, 151.2 ppm. IR (neat): ν = 3335, 2973, 2884, 1452,
˜
3.36–3.38 (m, J = 7.2 Hz, 1 H), 7.27–7.37 (m, 3 H), 7.42–7.50 (m, 1090, 1049 cm–1. C14H13IO (324.0): calcd. C 51.87, H 4.04; found
2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 24.2, 24.7, 29.1, 31.1,
C 51.92, H 3.96.
1016
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 1013–1018

Synthesis of Iodofurans by Electrophilic Cyclization
2-(2-Bromophenyl)-4,5,6,7-tetrahydro-3-iodobenzofuran (2b): Color-
less oil. 1H NMR (300 MHz, CDCl3): δ = 1.75–1.88 (m, 4 H), 2.29–
2.32 (t, J = 4.5 Hz, 2 H), 2.61–2.65 (t, J = 6.0 Hz, 2 H), 7.22–7.24
2.45–2.47 (t, J = 6.4 Hz, 2 H), 2.82–2.85 (t, J = 5.6 Hz, 1 H), 7.27–
7.29 (d, J = 7.2 Hz, 1 H), 7.36–7.40 (m, 2 H), 7.93–7.95 (t, J =
1.6 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 26.2, 27.3,
(d, J = 5.7 Hz, 1 H), 7.38–7.40 (t, J = 6.9 Hz, 1 H), 7.92–7.94 (d, 27.9, 28.9, 30.3, 70.3, 125.4, 125.9, 127.5, 128.2, 130.8, 148.2,
J = 5.7 Hz, 1 H), 8.10 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 22.8, 23.1, 23.2, 67.9, 122.5, 123.6, 124.0, 128.3, 129.8, 130.2,
152.7 ppm. IR (neat): ν = 2928, 2253, 1480, 908, 734, 650 cm–1.
C15H15IO (338.0): calcd. C 53.27, H 4.47; found C 53.31, H 4.54.
˜
132.7, 147.2, 151.8 ppm. IR (neat): ν = 2936, 1593, 909, 737 cm–1.
˜
4,5,6,7,8,9-Hexahydro-3-iodo-2-phenylcycloocta[b]furan (2k): Color-
less oil. 1H NMR (400 MHz, CDCl3): δ = 1.47–1.54 (m, 4 H), 1.65–
1.76 (m, 4 H), 2.52–2.55 (t, J = 6.4 Hz, 2 H), 2.83–2.86 (t, J =
6.4 Hz, 2 H), 7.25–7.29 (t, J = 7.2 Hz, 1 H), 7.37–7.41 (m, 2 H),
7.96–7.99 (t, J = 1.2 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 24.7, 25.4, 25.7, 26.4, 27.7, 27.9, 69.1, 123.3, 125.8, 127.4, 128.2,
C14H12BrIO (401.9): calcd. C 41.72, H 3.00; found C 41.79, H 2.94.
2-(3-Bromophenyl)-4,5,6,7-tetrahydro-3-iodobenzofuran (2c): Color-
less oil. 1H NMR (300 MHz, CDCl3): δ = 1.76–1.91 (m, 4 H), 2.32–
2.36 (m, 2 H), 2.62–2.66 (m, 2 H), 7.21–7.26 (m, 1 H), 7.23–7.37
(m, 1 H), 7.45–7.48 (q, J = 1.8, J = 7.8 Hz, 1 H), 7.64–7.67 (q, J
= 0.9, J = 7.8 Hz, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
22.8, 22.9, 23.2, 23.3, 70.9, 121.8, 123.8, 126.9, 130.3, 131.9, 132.7,
130.8, 148.6, 151.4 ppm. IR (neat): ν = 2926, 1602, 1447, 1072, 908,
˜
733 cm–1. C16H17IO (352.0): calcd. C 54.56, H 4.86; found C 54.58,
H 4.82.
133.2, 150.0, 151.8 ppm. IR (neat): ν = 3346, 2974, 1452, 1049,
˜
881 cm–1. C14H12BrIO (401.9): calcd. C 41.72, H 3.00; found C
41.77, H 3.03.
4,5,6,7,8,9,10,11,12,13-Decahydro-3-iodo-2-phenylcyclododeca[b]-
furan (2l): Colorless oil. 1H NMR (400 MHz, CDCl3): δ = 1.26–
1.43 (m, 12 H), 1.72–1.79 (m, 4 H), 2.38–2.42 (t, J = 6.4 Hz, 2 H),
2.63–2.67 (t, J = 6.8 Hz, 2 H), 7.28–7.30 (q, J = 5.2, J = 2.4 Hz 1
H), 7.37–7.41 (m, 2 H), 7.96–7.98 (m, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 22.2, 22.8, 23.0, 23.5, 24.0, 24.8, 24.9, 26.1,
26.9, 67.9, 123.8, 126.0, 127.5, 128.2, 130.8, 149.5, 151.9 ppm. IR
2-(4-Bromophenyl)-4,5,6,7-tetrahydro-3-iodobenzofuran (2d): Color-
1
less solid; m.p. 82–83 °C. H NMR (400 MHz, CDCl3): δ = 1.75–
1.89 (m, 4 H), 2.29–2.33 (t, J = 7.6 Hz, 2 H), 2.61–2.65 (t, J =
6.8 Hz, 2 H), 7.49–7.52 (d, J = 8.8 Hz, 2 H), 7.84–7.86 (d, J =
11.6 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 22.8, 23.1,
23.2, 29.7, 67.2, 121.2, 123.5, 127.1, 129.7, 131.4, 147.9, 151.6 ppm.
(neat): ν = 2934, 2253, 1472, 908, 737, 651 cm–1. C H IO (408.1):
˜
20 25
IR (KBr): ν = 3334, 2973, 1380, 1090, 1049, 881 cm–1. C H BrIO
˜
calcd. C 58.83, H 6.17; found C 58.78, H 6.22.
14 12
(401.9): calcd. C 41.72, H 3.00; found C 41.66, H 3.05.
3-Iodo-4-methyl-2-phenylfuran (2m): Colorless oil. 1H NMR
(400 MHz, CDCl3): δ = 1.83–1.84 (d, J = 1.0 Hz, 3 H), 7.14–7.16
(t, J = 1.2 Hz, 2 H), 7.24–7.28 (q, J = 6.8, J = 8.4 Hz, 2 H), 7.84–
7.86 (t, J = 1.2 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
11.8, 68.9, 125.7, 126.0, 127.9, 128.3, 130.4, 138.1, 151.5 ppm. IR
2-(4-Chlorophenyl)-4,5,6,7-tetrahydro-3-iodobenzofuran (2e): Color-
1
less viscous oil. H NMR (400 MHz, CDCl3): δ = 1.67–1.70 (m, 4
H), 1.77–1.79 (m, 2 H), 2.21–2.24 (m, 2 H), 2.53–2.56 (m, 2 H),
7.26–7.28 (q, J = 1.2, J = 6.4 Hz, 2 H), 7.81–7.83 (q, J = 2, J =
6.8 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 23.1, 23.4,
23.5, 29.9, 67.4, 123.7, 127.1, 128.7, 129.5, 133.3, 148.2, 151.8 ppm.
(neat): ν = 2920, 1765, 1481, 1024, 764, 690 cm–1. C H IO (284.0):
˜
11
9
calcd. C 46.51, H 3.19; found C 46.47, H 3.25.
IR (KBr): ν = 3334, 2973, 1453, 1090, 881, 667 cm–1. C H ClIO
˜
14 12
2-(2-Bromophenyl)-3-iodo-4-methylfuran (2n): Colorless oil. 1H
NMR (400 MHz, CDCl3): δ = 1.98 (s, 3 H), 7.22–7.30 (m, 2 H),
7.40–7.44 (m, 1 H), 7.91–8.10 (m, 1 H), 8.11 (s, 1 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 11.7, 70.1, 122.5, 124.4, 126.0, 128.7,
(358.0): calcd. C 46.89, H 3.37; found C 46.84, H 3.44.
4,5,6,7-Tetrahydro-3-iodo-2-(p-tolyl)benzofuran (2f): Colorless oil.
1H NMR (400 MHz, CDCl3): δ = 1.76–1.88 (m, 4 H), 2.29–2.37
(m, 2 H), 2.41 (s, 1 H), 2.62–2.65 (m, 2 H), 7.19–7.22 (t, J = 8.0 Hz,
2 H), 7.83–7.85 (d, J = 8.0 Hz, 2 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 21.3, 22.9, 23.3, 29.7, 65.8, 123.0, 125.8, 128.1, 128.9,
129.8, 130.8, 132.3, 138.6, 149.9 ppm. IR (neat): ν = 2924, 1769,
˜
1467, 908, 733 cm–1. C11H8BrIO (361.9): calcd. C 36.40, H 2.22;
found C 36.45, H 2.27.
137.4, 149.3, 150.9 ppm. IR (neat): ν = 3334, 2973, 1452, 1379,
˜
1090, 1049, 881 cm–1. C15H15IO (338.0): calcd. C 53.27, H 4.47;
found C 53.33, H 4.41.
2-(4-Bromophenyl)-3-iodo-4-methylfuran (2o): Colorless viscous oil.
1H NMR (400 MHz, CDCl3): δ = 1.99–1.20 (d, J = 1.2 Hz, 3 H),
7.31–7.32 (d, J = 1.2 Hz, 1 H), 7.51–7.54 (d, J = 8.8 Hz, 2 H),
7.84–7.86 (t, J = 2.0 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 11.7, 69.6, 121.9, 126.0, 127.5, 129.4, 131.5, 138.4, 150.7 ppm.
4,5,6,7-Tetrahydro-3-iodo-5-methyl-2-phenylbenzofuran (2h): Color-
less oil. 1H NMR (400 MHz, CDCl3): δ = 1.06–1.08 (d, J = 8.8 Hz,
3 H), 1.24–1.42 (m, 1 H), 1.81–1.93 (m, 2 H), 2.19–2.32 (m, 3 H),
2.67–2.74 (d, J = 20.8, J = 6.0 Hz, 1 H), 7.23–7.28 (t, J = 10.0 Hz,
1 H), 7.35–7.40 (t, J = 10.0 Hz, 2 H), 7.94–7.96 (d, J = 10.0 Hz, 2
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.3, 22.5, 29.9, 31.1,
31.3, 66.3, 122.8, 125.7, 127.4, 128.2, 130.8, 149.1, 150.9 ppm. IR
IR (neat): ν = 3340, 2973, 2885, 1452, 1089, 1049, 881 cm–1
.
˜
C11H8BrIO (361.9): calcd. C 36.40, H 2.22; found C 36.37, H 2.18.
4,5,6,7,8,9,10,11,12,13-Decahydro-2,3-diphenylcyclododeca[b]furan
(3l): Pd(OAc)2 (0.92 mg, 2 mol-%) was added to a solution of 2l
(81.60 mg, 0.20 mmol) and K2CO3 (55 mg, 0.40 mmol) in DMF
(2.0 mL). The mixture was stirred for 5 min and phenylboronic acid
(29.3 g, 0.24 mmol) was added. The resulting mixture was then
stirred under argon at 80 °C for 6 h and then diluted with aqueous
saturated ammonium chloride and extracted with EtOAc. The
combined extracts were washed with water four times. The solvent
was removed under reduced pressure and the residue upon work-
up was purified by chromatography on basic Al2O3 with petroleum
ether/EtOAc (100:1, v/v) as eluent to give 3l as a colorless viscous
oil (39.1 mg, 59%). 1H NMR (400 MHz, CDCl3): δ = 1.16–1.92 (t,
J = 5.2 Hz, 4 H), 1.25–1.45 (m, 10 H), 1.86–1.88 (t, J = 4.8 Hz, 2
H), 2.34–2.37 (t, J = 6.8 Hz, 2 H), 2.69–2.72 (t, J = 6.4 Hz, 2 H),
7.10–7.19 (m, 3 H), 7.31–7.41 (m, 7 H) ppm. 13C NMR (100 MHz,
(neat): ν = 3374, 2974, 1452, 1088, 1048, 881 cm–1. C H IO
˜
15 15
(338.0): calcd. C 53.27, H 4.47; found C 53.32, H 4.39.
5,5-Ethylenedioxy-4,5,6,7-tetrahydro-3-iodo-2-phenylbenzofuran
1
(2i): Colorless solid; m.p. 79–80 °C. H NMR (400 MHz, CDCl3):
δ = 1.91–1.96 (t, J = 8.8 Hz, 2 H), 2.44–2.48 (t, J = 8.0 Hz, 2 H),
2.93 (s, 1 H), 7.23–7.31 (m, 1 H), 7.36–7.41 (t, J = 9.2 Hz, 2 H),
7.91–7.94 (m, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 20.5,
29.9, 31.9, 34.6, 64.7, 65.7, 109.1, 122.3, 125.8, 127.7, 128.3, 130.6,
147.8, 150.5 ppm. IR (neat): ν = 3333, 2973, 1452, 1090, 881,
˜
662 cm–1. C16H15IO3 (382.0): calcd. C 50.28, H 3.96; found C
50.33, H 3.92.
5,6,7,8-Tetrahydro-3-iodo-2-phenyl-4H-cyclohepta[b]furan (2j): Col-
orless oil. 1H NMR (400 MHz, CDCl3): δ = 1.70–1.78 (m, 7 H), CDCl3): δ = 20.7, 22.4, 22.7, 23.3, 24.4, 24.7, 25.2, 26.4, 26.8, 122.1,
Eur. J. Org. Chem. 2008, 1013–1018
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1017

X.-Y. Liu et al.
FULL PAPER
[10]
A. Sniady, K. A. Wheeler, R. Dembinski, Org. Lett. 2005, 7,
1769–1772.
Y. H. Liu, S. B. Zhou, Org. Lett. 2005, 7, 4609–4611.
a) K. E. Harding, T. H. Tinger in Comprehensive Organic Syn-
thesis (Eds.: B. M. Trost, I. Fleming), Pergamon, Oxford, 1991,
vol. 4, p. 463; b) J. Mulzer, in Organic Synthesis Highlights,
VCH, Weinheim, 1991, 157; c) G. Rousseau, S. Robin, Tetrahe-
dron 1998, 54, 13681–13736.
a) Q. Huang, J. A. Hunter, R. C. Larock, J. Org. Chem. 2002,
67, 3437–3444; b) X. Zhang, A. C. Marino, T. Yao, R. C. Lar-
ock, Org. Lett. 2005, 7, 763–766; c) J. Barluenga, H. Vazquez-
Villa, A. Ballesteros, J. M. Gonzalez, J. Am. Chem. Soc. 2003,
125, 9028–9029; d) D. Yue, C. N. Della, R. C. Larock, Org.
Lett. 2004, 6, 1581–1584; e) A. Arcadi, S. Cacchi, S. D. Giu-
seppe, G. Fabrizi, F. Marinelli, Org. Lett. 2002, 4, 2409–2412;
f) D. Yue, R. C. Larock, Org. Lett. 2004, 6, 1037–1040; g) J.
Barluenga, M. Trincado, E. Rubio, J. M. Gonzalez, Angew.
Chem. Int. Ed. 2003, 42, 2406–2409; h) T. Yao, R. C. Larock,
J. Org. Chem. 2005, 70, 1432–1437; i) D. W. Knight, A. L.
Redfern, J. J. Gilmore, J. Chem. Soc. Perkin Trans. 1 2002, 622–
628; j) M. Nishizawa, H. Takao, V. K. Yadav, H. Imagawa, T.
Sugihara, Org. Lett. 2003, 5, 4563–4565.
123.7, 124.9, 126.3, 127.1, 128.2, 128.7, 129.9, 131.6, 135.2 ppm.
IR (neat): ν = 3409, 2929, 1444, 1026, 763, 696 cm–1. C26H30
O
˜
[11]
[12]
(358.2): calcd. C 87.10, H 8.43; found C 87.16, H 8.49.
Supporting Information (see also the footnote on the first page of
this article): Experimental characterization for all products.
Acknowledgments
[13]
We thank the Chinese National Science Foundation (NSF) (NSF-
20021001, NSF-20672049) and the “Hundred Scientist Program”
of the Chinese Academy of Sciences for financial support.
[1] D. M. X. Donnelly, M. J. Meegan in Comprehensive Heterocy-
clic Chemistry (Eds.: A. R. Katritzky, C. W. Rees), Pergamon
Press, New York, 1984, vol. 4, pp. 657–712.
[2] a) A. R. Katritzky, Advances in Heterocyclic Chemistry, Aca-
demic Press, New York, 1982; b) M. V. Sargent, F. M. Dean in
Comprehensive Heterocyclic Chemistry (Eds.: A. R. Katritzky,
C. W. Rees), Pergamon Press, New York, 1984, vol. 4, pp. 599–
656; c) K. Nakanishi, Natural Products Chemistry, Kodansha,
Tokyo, 1974; d) C. W. Bird, G. W. H. Cheeseman, Comprehen-
sive Organic Chemistry, Pergamon Press, New York, 1984; e)
G. Vernin, The Chemistry of Heterocyclic Flavouring and Aroma
Compounds, Ellis Harwood, Chichester, 1982.
[3] a) Y. Tanabe, K. Wakimura, Y. Nishii, Y. Muroya, Synthesis
1996, 388–392; b) R. Chinchilla, C. Najera, M. Yus, Chem.
Rev. 2004, 104, 2667–2722.
[4] a) S.-Y. Lin, C.-L. Chen, Y.-J. Lee, J. Org. Chem. 2003, 68,
2968–2971; b) T. Bach, L. Krüger, Eur. J. Org. Chem. 1999,
2045–2057; c) C. Alvarez-Ibarra, M. L. Quiroga, E. Toledano,
Tetrahedron 1996, 52, 4065–4078.
[5] a) M. W. Hooper, M. Utsunomiya, J. F. Hartwig, J. Org. Chem.
2003, 68, 2861–2873; b) A. Padwa, K. R. Crawford, P. Rashata-
sakhon, M. Rose, J. Org. Chem. 2003, 68, 2609–2617; c) K. R.
Crawford, A. Padwa, Tetrahedron Lett. 2002, 43, 7365–7368.
[6] Y. Arroyo, J. F. Rodriguez, M. A. Sanz-Tejedor, M. Santos, Tet-
rahedron Lett. 2002, 43, 9129–9132.
[7] S. P. Bew, D. W. Knight, Chem. Commun. 1996, 1007–1008.
[8] H. A. Stefani, N. Petragnani, C. J. Valduga, C. A. Brandt, Tet-
rahedron Lett. 1997, 38, 4977–4980.
[14]
a) Z. J. Yang, M. J. Fan, R. Z. Mu, W. M. Liu, Y. M. Liang,
Tetrahedron 2005, 61, 9140–9146; b) M. J. Fan, Z. Y. Yan,
W. M. Liu, Y. M. Liang, J. Org. Chem. 2005, 70, 8204–8207.
X. H. Duan, X. Y. Liu, L. N. Guo, M. C. Liao, W. M. Liu,
Y. M. Liang, J. Org. Chem. 2005, 70, 6980–6983.
[15]
[16]
a) J. A. Marshall, W. J. DuBay, J. Org. Chem. 1991, 56, 1685–
1687; b) J. A. Marshall, W. J. DuBay, J. Am. Chem. Soc. 1992,
114, 1450–1456; c) A. S. K. Hashmi, P. Sinha, Adv. Synth. Ca-
tal. 2004, 346, 432–438.
a) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–2483; b)
A. Suzuki, J. Organomet. Chem. 1999, 576, 147–168; c) A. Su-
zuki in Metal-Catalyzed Cross-Coupling Reactions (Eds.: F.
Diederich, P. J. Stang), Wiley-VCH, New York, 1998, chapter
2.
a) Y. H. Liu, F. J. Song, L. Q. Cong, J. Org. Chem. 2005, 70,
6999–7002; b) M. S. Rao, N. Esho, C. Sergeant, R. Dembinski,
J. Org. Chem. 2003, 68, 6788–6790.
A. S. K. Hashmi, P. Sinha, Adv. Synth. Catal. 2004, 346, 432–
438.
[17]
[18]
[19]
[9] M. S. Rao, N. Esho, C. Sergeant, R. Dembinski, J. Org. Chem.
2003, 68, 6788–6790.
Received: October 12, 2007
Published Online: December 17, 2007
1018
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Eur. J. Org. Chem. 2008, 1013–1018