A Convenient Synthesis of 2-Fluoro- and 2-Chloromalonic Esters Mediated by Hypervalent Iodine

Article abstract of DOI:10.1055/s-0034-1378747

Direct fluorination of malonic esters with a reagent system of iodosylbenzene and Et₃N·5HF gave the corresponding 2-fluoromalonic esters in good to high yields. Direct chlorination using iodosylbenzene and hydrochloric acid also provided the 2-chloromalonates in high yields.

Full text of DOI:10.1055/s-0034-1378747

SYNTHESIS
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©
Georg Thieme Verlag Stuttgart · New York
2015, 47, 3241–3245
3241
paper
Synthesis
T. Kitamura et al.
Paper
A Convenient Synthesis of 2-Fluoro- and 2-Chloromalonic Esters
Mediated by Hypervalent Iodine
Tsugio Kitamura*
convenient fluorination and chlorination
Kensuke Muta
Juzo Oyamada
O
O
PhIO, Et3N•5HF
RO
RO
OR
OR
Department of Chemistry of Applied Chemistry, Graduate School
of Science and Engineering, Saga University, Hojo-machi, Saga
5
3% to quant. yield
O
O
F
5
examples
840-8502, Japan
kitamura@cc.saga-u.ac.jp
RO
OR
O
O
PhIO, concd HCl
R = Me, Et, Bu,
Hex, PhCH2
68–83%
examples
Cl
3
Received: 26.05.2015
Accepted after revision: 29.06.2015
Published online: 12.08.2015
Therefore, the development of convenient and effective
methods for preparing 2-fluoromalonic esters is still an im-
portant and challenging subject.
DOI: 10.1055/s-0034-1378747; Art ID: ss-2015-f0334-op
Abstract Direct fluorination of malonic esters with a reagent system
10% F2 in N2
of iodosylbenzene and Et N·5HF gave the corresponding 2-fluoromalo-
3
nic esters in good to high yields. Direct chlorination using iodosylben-
zene and hydrochloric acid also provided the 2-chloromalonates in high
yields.
N-fluoropyridium salts
O
O
O
O
Key words 2-fluoromalonic esters, 2-chloromalonic esters, hydrogen
fluoride, hydrochloric acid, iodosylbenzene
XeF2
EtO
OEt
EtO
OEt
F
Monofluoromalonate derivatives are very attractive
compounds because they are used as synthetic intermedi-
ates for pharmaceuticals and agricultural chemicals con-
taining fluorine atoms. Very recently, Harsanyi and Sandford
emphasized the importance of 2-fluoromalonic acid deriva-
tives, reviewing that they are very versatile building blocks
for introducing fluorine atoms into various aliphatic and
1-fluoro-2-pyridone
Scheme 1 Reported methods for preparing diethyl 2-fluoromalonate
from diethyl malonate
Although stepwise basic alcoholysis of hexafluoropro-
9
10
pene and fluorination of silyl ketene acetals have been
reported as the alternative method of the direct fluorina-
tion, they are not efficient due to the multistep processes
involved. Conveniently, 2-fluoromalonic esters can be pre-
pared from the corresponding 2-chloromalonic esters by
1
heterocyclic compounds. In spite of recognizing that
monofluoromalonic esters are important for synthesis of
fluorine-containing pharmaceuticals, the fluorination reac-
tion of malonic esters is limited to some methods, as shown
in Scheme 1. The fluorination reaction of malonic esters re-
ported so far uses highly electrophilic fluorinating agents
11
exchanging chlorine and fluorine using HF reagents.
The convenient fluorination reactions of carbonyl com-
pounds mediated by hypervalent iodine compounds have
2
3
such as fluorine gas, N-fluoropyridinium salts, xenon di-
4
5
12
fluoride, and 1-fluoro-2-pyridone. However, fluorine gas
is highly toxic and explosive, and special cautions are re-
quired for the fluorination reactions. In addition, the fluori-
nation reactions under basic conditions give difluorinated
malonic esters as the major product. Although N-fluoropy-
ridinium salts, xenon difluoride, and 1-fluoro-2-pyri-
been recently studied. Since enols of the ketones generat-
ed in situ are fluorinated in these reactions, it is important
for these reactions whether enolization of the carbonyl
compound takes place easily. Generally the degree of eno-
6
13
lization increases as the pK value decreases. Therefore, it
7
8
is expected that the degree of enolization decreases in the
order: 1,3-diketones > β-keto esters > malonic esters. Judg-
ing from this result, the malonic ester is considered to show
the lowest reactivity to the fluorination reaction among
them.
5
done are useful fluorinating reagents, they are expensive.
Since these fluorinating agents are prepared using fluorine
gas, use of dangerous fluorine gas is inevitably needed.
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T. Kitamura et al.
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In the previous fluorination reaction with the reagent
prepared from iodosylbenzene and hydrofluoric acid, 1,3-
dicarbonyl compounds and β-keto esters gave the fluorinat-
ed products in good yields, but this fluorination reaction
could not be applied to monocarbonyl compounds such as
creasing the amount of PhIO to 2 equivalents drastically en-
hanced the yield of 2a (80%) (entry 6). Finally, the use of 2.5
equivalents of PhIO resulted in quantitative formation of 2a
(entry 7). The reaction using pyridine·HF complex de-
creased the yield of 2a (entry 8). Furthermore, we exam-
ined a 10 mmol-scale reaction. When the reaction using 10
mmol of 1a was conducted at 70 °C for 48 hours, 2a was
isolated in 56% yield by column chromatography on silica
gel (entry 9).
With the optimal conditions of fluorination reaction of
diethyl malonate having been determined, the reaction of
other malonate esters was then examined to explore the
scope of the substrate in this fluorination reaction. The
fluorination reaction of other malonate esters such as di-
methyl malonate (1b), dibutyl malonate (1c), dihexyl
malonate (1d), and dibenzyl malonate (1e) was conducted
and the results are given in Table 2. When these malonate
esters were subjected to the fluorination reaction under the
same conditions, the 2-fluoromalonates 2 were formed in
53–85% yields. These results suggest that other malonate
esters also undergo the fluorination reaction efficiently.
However, in the case of a substituted malonate ester, the
present fluorination reaction suffered from steric effect. Ac-
tually, the fluorination of diethyl 2-methylmalonate (1f) de-
creased the yield of the fluorinated product 2f to 18%. The
fluorination of other substrates such as ethyl malonate
monoamide, ethyl cyanoacetate, and ethyl phenylsulfony-
lacetate was attempted, but the fluorinated product was
formed only in a low yield.
1
2a,b
acetophenone.
After screening the fluorine sources, tri-
ethylamine·hydrogen fluoride complexes (Et N·nHF)
3
showed higher reactivity than hydrofluoric acid and en-
abled the fluorination of acetophenone derivatives in the
12c
presence of iodosylbenzene. Encouraged by this finding,
we decided to extend this reaction to malonic esters be-
cause the pK values are lower than those of acetophe-
13
nones. In this paper, we want to report for the first time
the hypervalent iodine-mediated fluorination of malonic
esters.
At the beginning, the reaction of diethyl malonate (1a)
was conducted in order to find the optimal conditions for
the fluorination. The results are given in Table 1. The fluori-
nation of 1a was carried out using 55% hydrofluoric acid as
a fluorine source in the presence of iodosylbenzene (PhIO)
in 1,2-dichloroethane (DCE) at 70 °C for 24 hours, in analo-
gy with the reaction of 1,3-diketones or β-keto esters.1
However, the desired diethyl 2-fluoromalonate (2a) was
formed only in 25% yield (Table 1, entry 1). Increasing the
amount of PhIO to 2.5 equivalents did not improve the yield
2a,b
(entry 2). Although the fluorine source was replaced by
Et N·3HF instead of 55% hydrofluoric acid, the yield of 2a
3
was decreased (entries 3 and 4). The use of Et N·5HF in the
3
fluorination improved the yield of 2a to 41% (entry 5). In-
Table 1 Optimization of Fluorination of Diethyl Malonatea
The fluorination of malonic esters promoted by hyper-
valent iodine is considered to proceed with a mechanism
similar to the proposed one previously in the fluorination
of 1,3-dicarbonyl compounds.1
2a,b
In this fluorination reac-
O
O
tion, iodosylbenzene is transformed into difluoroiodoben-
zene in the presence of HF. Since the reaction is conducted
under acidic conditions, the enolization of malonic esters is
considered to be easier than that under neutral conditions.
Therefore, HF is not only essential for generation of PhIF2,
but also promotes the enolization of malonic esters. The
enols of malonic esters react with difluoroiodobenzene to
give the corresponding 2-fluoromalonic esters 2. Under the
present reaction conditions, monofluorinated malonic es-
ters 2 were selectively formed. The 19F NMR of the reaction
mixture obtained from the reaction of 1a showed a tiny
peak at –112.4 ppm, which might be assignable to diethyl
O
O
PhIO
fluorine source
EtO
OEt
EtO
OEt
F
DCE, 70 °C, 24 h
1a
2a
Entry
PhIO (mmol) Fluorine source (mmol)
Yield (%)b
1
2
3
4
5
6
7
1.2
2.5
1.2
2
55% aq HF (20 mmol HF)
55% aq HF (20 mmol HF)
25
24
Et
Et
Et
Et
Et
3
3
3
3
3
N·3HF (6.67 mmol)
N·3HF (6.67 mmol)
N·5HF (4 mmol)
N·5HF (4 mmol)
N·5HF (4 mmol)
9
11
1.2
2
41
2
,2-difluoromalonate.10 However, the integral was only 3%
81
as compared with that of 2a. Probably, the yield is 1–2% at
most, even if diethyl difluoromalonate had formed.
2.5
2.5
25
100 (85)
49
8
pyridine·(HF)
x
(20 mmol HF)
As an alternative method for direct fluorination, 2-fluo-
romalonic esters were prepared from 2-chloromalonic es-
ters using HF reagents in high yields.11 Therefore, it is im-
portant to study the synthesis of 2-chloromalonic esters
since the chlorination using hypervalent iodine reagents
has not been applied to malonic esters.14 Thus, a convenient
9c
Et N·5HF (40 mmol)
3
(56)
a
Conditions: 1a (1 mmol), PhIO, a fluorine source (20 equiv HF), DCE (2
mL), 70 °C, 24 h.
b
1
Yields were determined by H NMR spectroscopy using an internal stan-
dard. Isolated yield is given in parenthesis.
c
The reaction was conducted using 1a (10 mmol) and DCE (20 mL) for 48
h.
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T. Kitamura et al.
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Table 2 Fluorination of Malonic Estersa
to 50% (entry 2). Similarly, the chlorination reaction of 1b
and 1c gave the corresponding 2-chloromalonates 3b and
O
O
O
O
F
3c in 83 and 80% isolated yield, respectively (entries 3 and
PhIO, Et3N•5HF
1
OR1
1
OR1
4). Thus, the present chlorination method was helpful in
supplying the starting materials for the alternative fluori-
nation method using the chloride exchange.
R O
R O
DCE, 70 °C, 24 h
R2
R2
1
2
R1
R2
Yield (%)b
53 (45)
Table 3 Chlorination of Malonic Estersa
Entry
1
Product 2
O
O
O
O
O
O
O
PhIO, concd HCl
DCE, 70 °C, 2 h
Me
Bu
H
MeO
OMe
RO
OR
RO
OR
F
F
Cl
3
2
b
1
O
Entry
R
Product 3
Yield (%)b
2
3
4
H
H
BuO
OBu
OHex
OBn
OEt
85 (74)
61 (51)
O
O
2
c
1
2
68
50
Et
EtO
OEt
c
O
O
Cl
3
a
Hex
HexO
O
O
F
2
d
3
Bu
BuO
OBu
83
80
O
O
Cl
3
b
Bn
Et
H
BnO
58 (33)
O
O
F
2
e
4
Hex
HexO
OHex
O
O
Cl
3
c
5
Me
18
EtO
a
Conditions: 1 (0.5 mmol), PhIO (1.25 mmol), concd HCl (5 mmol), DCE
7.5 mL), 70 °C, 2 h.
Isolated yields.
Me
F
(
2
f
b
c
a
The reaction was conducted for 24 h.
3
Conditions: 1 (1 mmol), PhIO (2.5 mmol), Et N·5HF (4 mmol), DCE (2
mL), 70 °C, 24 h.
b
1
Yields were determined by H NMR spectroscopy using an internal stan-
dard. Values in parentheses refer to the isolated yields.
In summary, we have demonstrated that malonic esters
could be efficiently fluorinated with a convenient fluorinat-
ing reagent composed of PhIO and Et N·5HF to form the cor-
3
chlorination of malonic esters was explored with PhIO and
a commercially available hydrochloric acid, as shown in
Scheme 2.
responding 2-fluoromalonic esters. This method has been
applied to the chlorination reaction because 2-chloromalo-
nic esters are useful as the starting materials for the alter-
native fluorination reaction. Due to increasing the impor-
tance of fluoromalonic esters as a building block, this con-
venient procedure is useful in synthesis of pharmaceuticals
and agricultural chemicals containing fluorine atoms.
PhIO
concd HCl
F–
O
O
O
O
O
O
EtO
OEt
EtO
OEt
EtO
OEt
(
this work)
Cl
(ref. 11)
F
Scheme 2 Chlorination of diethyl malonate for diethyl 2-fluorom-
alonate
All solvents and starting materials were used during the research
work as received without further purification unless otherwise indi-
1
13
19
cated. H NMR (400 MHz), C NMR (100 MHz), and F NMR (376
MHz) were recorded on an Agilent 400-MR NMR spectrometer in
Using the optimized conditions obtained by the fluori-
nation reaction, the reaction of 1a with concentrated hy-
drochloric acid was examined. When the reaction of 1a
with concentrated HCl was conducted in the presence of
PhIO at 70 °C for two hours, diethyl 2-chloromalonate (3a)
was obtained in 68% isolated yield (Table 3, entry 1). In-
creasing the reaction time to 24 hours decreased the yield
19
CDCl solution. The chemical shifts for F NMR were determined us-
3
ing hexafluorobenzene as an internal standard. High-resolution mass
spectra were measured by the Analytical Center, Institute for Materi-
als Chemistry and Engineering, Kyushu University. Column chro-
matographic separation was carried out using Silica Gel 60, spherical
(Kanto Chemical Co.). Pre-coated plates (silica gel 60 F254, Merck)
were used for TLC examination.
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T. Kitamura et al.
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Fluorination of Malonic Esters 1; General Procedure
Diethyl 2-Fluoro-2-methylmalonate (2f)10
PhIO (550 mg, 2.5 mmol), Et N·5HF (800 mg, 4 mmol), and DCE (1 mL)
Yield: 18%; colorless oil. This compound could not be isolated purely
and the yield was determined by H NMR spectroscopy using 1,4-di-
methoxybenzene as an internal standard.
3
1
were placed in a Teflon test tube. After stirring at r.t. for 15 min, the
appropriate malonic ester 1 (1 mmol) and DCE (1 mL) were added.
The test tube was sealed with a septum rubber and heated at 70 °C for
1
H NMR (400 MHz, CDCl ): δ = 1.31 (t, J = 7 Hz, 6 H, 2 × CH CH ), 1.76
3
2
3
24 h with stirring. The reaction mixture was neutralized with aq
(
d, J = 22 Hz, 3 H, CH ), 4.27 (q, J = 7 Hz, 4 H, 2 × CH ).
3
2
NaHCO and the product was extracted with CH Cl (3 × 10 mL). The
3
2
2
19
F NMR (376 MHz, CDCl ): δ = –157.53 (d, J = 22 Hz).
3
combined organic layers were washed with brine (20 mL), dried
Na SO ), and concentrated under reduced pressure. The product was
(
2
4
Chlorination of Malonic Esters 1; General Procedure
purified by column chromatography on silica gel with hexane–CH Cl2
2
as eluent.
PhIO (275 mg, 1.25 mmol) and DCE (1.5 mL) were placed in a 15 mL
test tube. After adding concd HCl (5 mmol), additional DCE (2 mL)
was introduced. After stirring at r.t. for 15 min, the appropriate malo-
nic ester 1 (0.5 mmol) and DCE (4 mL) were added. The test tube was
sealed with a septum rubber and heated at 70 °C for 2 h with stirring.
Diethyl 2-Fluoromalonate (2a)2a
Yield: 151 mg (85%); colorless oil.
1
H NMR (400 MHz, CDCl ): δ = 1.34 (t, J = 7 Hz, 6 H, CH ), 4.33 (q, J = 7
3
3
The reaction mixture was neutralized with aq NaHCO and the prod-
3
Hz, 4 H, CH ), 5.28 (d, J = 48 Hz, 1 H, CHF).
2
uct was extracted with CH Cl (3 × 5 mL). The combined organic lay-
2
2
13
C NMR (100 MHz, CDCl ): δ = 13.9, 62.6, 85.2 (d, J = 195 Hz), 163.9
ers were washed with brine (20 mL), dried (Na SO ), and concentrat-
3
2 4
(d, J = 24 Hz).
ed under reduced pressure. The product was purified by column chro-
19
matography on silica gel with hexane–CH Cl as eluent.
2 2
F NMR (376 MHz, CDCl ): δ = –195.19 (d, J = 48 Hz).
3
Diethyl 2-Chloromalonate (3a)18
Dimethyl 2-Fluoromalonate (2b)15
Yield: 66.2 mg (68%); colorless oil.
Yield: 67.5 mg (45%); colorless oil.
1H NMR (400 MHz, CDCl
Hz, 4 H, CH ), 4.85 (s, 1 H, CH).
): δ = 1.32 (t, J = 7 Hz, 6 H, CH ), 4.31 (q, J = 7
3
1
3
H NMR (400 MHz, CDCl ): δ = 3.88 (s, 6 H, CH ), 5.34 (d, J = 49 Hz, 1
3
3
H, CHF).
2
13C NMR (100 MHz, CDCl
): δ = 13.8, 55.4, 63.1, 164.5.
13
3
C NMR (100 MHz, CDCl ): δ = 53.3, 85.0 (d, J = 196 Hz), 164.2 (d, J =
3
2
4 Hz).
19
Dibutyl 2-Chloromalonate (3b)
F NMR (376 MHz, CDCl ): δ = –195.47 (d, J = 49 Hz).
3
Yield: 104 mg (83%); colorless oil.
Dibutyl 2-Fluoromalonate (2c)16
1H NMR (400 MHz, CDCl
): δ = 0.94 (t, J = 7 Hz, 6 H, 2 × CH
), 1.36–
3
3
1
2
.42 (m, 4 H, 2 × CH ), 1.63–1.70 (m, 4 H, 2 × CH ), 4.22–4.26 (m, 4 H,
Yield: 173 mg (74%); colorless oil.
2
2
× CH ), 4.85 (s, 1 H, CH).
2
1
H NMR (400 MHz, CDCl ): δ = 0.94 (t, J = 7 Hz, 6 H, CH ), 1.35–1.42
3
3
13
C NMR (100 MHz, CDCl ): δ = 13.5, 18.9, 30.3, 55.5, 66.9, 164.6.
(
m, 4 H, CH ), 1.64–1.71 (m, 4 H, CH ), 4.28 (dt, J = 4, 6 Hz, 4 H, CH ),
3
2
2
2
5.29 (d, J = 48 Hz, 1 H, CHF).
HRMS (FAB): m/z [M + H]+ calcd for C11H20ClO : 251.1050; found:
4
13
251.1050.
C NMR (100 MHz, CDCl ): δ = 13.5, 18.8, 30.3, 66.4, 85.2 (d, J = 195
3
Hz), 164.0 (d, J = 24 Hz).
19
Dihexyl 2-Chloromalonate (3c)
F NMR (376 MHz, CDCl ): δ = –195.48 (d, J = 48 Hz).
3
Yield: 123 mg (80%); colorless oil.
1H NMR (400 MHz, CDCl
.37 (m, 12 H, 6 × CH ), 1.64–1.71 (m, 4 H, 2 × CH ), 4.23 (t, J = 7 Hz, 4
): δ = 0.88 (t, J = 7 Hz, 6 H, 2 × CH ), 1.31–
3
Dihexyl 2-Fluoromalonate (2d)
3
1
Yield: 148 mg (51%); colorless oil.
2
2
H, 2 × CH ), 4.85 (s, 1 H, CH).
2
1
H NMR (400 MHz, CDCl ): δ = 0.89 (t, J = 7 Hz, 6 H, CH ), 1.31–1.38
3
3
13
C NMR (100 MHz, CDCl ): δ = 13.9, 22.4, 25.2, 28.2, 31.2, 55.5, 67.2,
(
m, 12 H, CH ), 1.65–1.72 (m, 4 H, CH ), 4.26 (dt, J = 4, 7 Hz, 4 H, CH ),
3
2
2
2
164.5.
5.28 (d, J = 48 Hz, 1 H, CHF).
HRMS (FAB): m/z [M + H]+ calcd for C15
07.1674.
H28ClO : 307.1676; found:
4
13
C NMR (100 MHz, CDCl ): δ = 13.8, 22.4, 25.2, 28.2, 31.2, 66.6, 85.2
3
3
(d, J = 195 Hz), 164.0 (d, J = 24 Hz).
19
F NMR (376 MHz, CDCl ): δ = –195.14 (d, J = 48 Hz).
3
HRMS (FAB): m/z [M + H]+ calcd for C15H28FO : 291.1972; found:
4
Acknowledgment
291.1972.
This work was partly supported by a Grant-in-Aid for Scientific Re-
search from the Ministry of Education, Culture, Sports, Science and
Technology of Japan (25410048).
Dibenzyl 2-Fluoromalonate (2e)17
Yield: 100 mg (33%); colorless oil.
1
H NMR (400 MHz, CDCl ): δ = 5.24 (s, 4 H, CH ), 5.36 (d, J = 48 Hz, 1
3
2
H, CHF), 7.29–7.35 (m, 10 H, 2 × C H ).
6
5
Supporting Information
13
C NMR (100 MHz, CDCl ): δ = 68.2, 85.2 (d, J = 196 Hz), 128.4,
3
128.65, 128.7, 134.2, 163.6 (d, J = 24 Hz).
Supporting information for this article is available online at
19
http://dx.doi.org/10.1055/s-0034-1378747.
S
u
p
p
ortioIgnfmr oaitn
S
u
p
p
o
nrtogI
i
f
rm oaitn
F NMR (376 MHz, CDCl ): δ = –195.32 (d, J = 48 Hz).
3
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References
(11) (a) Guenther, A.; Weintritt, H.; Boehm, S. PCT Int. Appl WO
2
2
005019154, 2005. (b) Braun, M.; Brosch, C. PCT Int. Appl WO
002060838, 2002. (c) Mueh, T.; Fiedler, P.; Weintritt, H.;
(
(
1) Harsanyi, A.; Sandford, G. Org. Process Res. Dev. 2014, 18, 981.
2) (a) Chambers, R. D.; Hutchinson, J. J. Fluorine Chem. 1998, 92, 45.
b) Chambers, R. D.; Hutchinson, J.; Moilliet, J. S. PCT Int. Appl
Westerkamp, W.; Reinecke, A. PCT Int. Appl WO 2002016304,
002.
12) (a) Kitamura, T.; Kuriki, S.; Morshed, M. H.; Hori, Y. Org. Lett.
011, 13, 2392. (b) Kitamura, T.; Kuriki, S.; Muta, K.; Morshed,
M. H.; Muta, K.; Gondo, K.; Hori, Y.; Miyazaki, M. Synthesis 2013,
(
2
WO 9903802 A1 19990128, 1999. (c) Chambers, R. D.;
Hutchinson, J.; Thomson, J. PCT Int. Appl WO 9700848 A1
(
2
19970109, 1997.
(3) Umemoto, T.; Fukami, S.; Tomizawa, G.; Harasawa, K.; Kawada,
K.; Tomita, K. J. Am. Chem. Soc. 1990, 112, 8563.
4
7
5, 3125. (c) Kitamura, T.; Muta, K.; Muta, K. J. Org. Chem. 2014,
9, 5842. (d) Hara, S.; Sekiguchi, M.; Ohmori, A.; Fukuhara, T.;
(
(
(
4) Patrick, T. B.; Nadji, S. J. Fluorine Chem. 1988, 39, 415.
5) Purrington, S. T.; Jones, W. A. J. Org. Chem. 1983, 48, 761.
6) Chambers, R. D.; Hutchinson, J.; Thomson, J. J. Fluorine Chem.
Yoneda, N. Chem. Commun. 1996, 1899. (e) Yoshida, M.;
Fujikawa, K.; Sato, S.; Hara, S. ARKIVOC 2003, (vi), 36. (f) Geary,
G. C.; Hope, E. G.; Singh, K.; Stuart, A. M. Chem. Commun. 2013,
1
996, 78, 165.
7) (a) Umemoto, T.; Tomita, K. Tetrahedron Lett. 1986, 27, 3271.
b) Umemoto, T.; Tomita, K.; Kawada, K. Org. Synth. 1990, 69,
29.
4
9, 9263. (g) Suzuki, S.; Kamo, T.; Fukushi, K.; Hiramatsu, T.;
Tokunaga, E.; Dohi, T.; Kita, Y.; Shibata, N. Chem. Sci. 2014, 5,
754.
(
(
1
2
(
13) Carey, F. A.; Sundberg, R. J. Advanced Organic Chemistry, 4th ed.;
Kluwer Academic/Plenum Publishers: New York, 2000.
14) (a) Kitamura, T.; Tazawa, Y.; Morshed, M. H.; Kobayashi, S. Syn-
thesis 2012, 44, 1159. (b) Duan, X.; Zhou, H.; Tian, X.; Liu, J.; Ma,
J. Synthesis 2015, 47, 777.
15) Lerman, O.; Rozen, S. J. Org. Chem. 1983, 48, 724.
16) Bergmann, F. D.; Shahak, I. Chem. Ind. (London) 1961, 591.
17) Dubois, J.; Foures, C.; Bory, S.; Falcou, S.; Gaudry, M.; Marquet,
A. Tetrahedron 1991, 47, 1001.
(
8) (a) Hoppe, R.; Dähne, W.; Mattauch, H.; Rödder, K. Angew.
Chem., Int. Ed. Engl. 1962, 1, 599. (b) Weeks, J. L.; Matheson, M.;
Chernick, C. J. Am. Chem. Soc. 1962, 84, 4612. (c) Šmalc, A.; Lutar,
K.; Kinkead, S. A. Inorg. Synth. 1992, 29, 1.
(
(9) Ishikawa, N.; Takaoka, A. Chem. Lett. 1981, 107.
(
(
(
(
10) Purrington, S. T.; Woodard, D. L. J. Org. Chem. 1990, 55, 3423.
(18) Zheng, Z.; Han, B.; Cheng, P.; Niu, J.; Wang, A. Tetrahedron 2014,
70, 9814.
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Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 3241–3245