Synthesis of α,α-difluoro-γ-butyrolactones via ethyl iododifluoroacetate

Article abstract of DOI:10.1016/j.jfluchem.2004.10.009

A novel synthesis of α,α-difluoro-γ-butyrolactones was realized by the alkaline hydrolysis of the adducts of ethyl iododifluoroacetate and alkenes. Ethyl iododifluoroacetate reacted with alkenes in the presence of sodium dithionite to give the addition pr

Full text of DOI:10.1016/j.jfluchem.2004.10.009

Journal of Fluorine Chemistry 126 (2005) 63–67
www.elsevier.com/locate/fluor
Synthesis of a,a-difluoro-g-butyrolactones via
ethyl iododifluoroacetate
Fanhua Xiaoa, Fanhong Wua,b,
Yongjia Shena, Lifang Zhoua
*
,
aCollege of Chemistry and Pharmaceutics, East China University of Science and Technology,
Box 422, 130 Meilong Road, Shanghai 200237, China
bKey Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, Shanghai 200032, China
Received 9 June 2004; received in revised form 13 September 2004; accepted 16 October 2004
Available online 2 December 2004
Abstract
A novel synthesis of a,a-difluoro-g-butyrolactones was realized by the alkaline hydrolysis of the adducts of ethyl iododifluoroacetate and
alkenes. Ethyl iododifluoroacetate reacted with alkenes in the presence of sodium dithionite to give the addition products in 62–78% yields.
The products were hydrolyzed in 10% aqueous sodium carbonate solution to give a,a-difluoro-g-butyrolactones in 93–98% yields.
# 2004 Elsevier B.V. All rights reserved.
Keywords: Synthesis; a,a-Difluoro-g-butyrolactone; Ethyl iododifluoroacetate; Sodium dithionite
1. Introduction
a,a-difluoro-g-butyrolactones through the hydrolysis of the
adduct 3 by the reaction of alkenes (1) with ethyl
iododifluoroacetate (2) initiated by sodium dithionite.
Partially fluorinated analogues of biologically important
compounds bring about dramatic changes and distinctive
modifications in their biological activities; this makes it more
necessary to establish the efficient methods for the synthesis
of selectively fluorinated compounds [1]. We are interested in
the synthesis of fluorinated g-lactones, which are important
synthons that display more unique biologically active
properties in organic chemistry [2]. We have reported some
polyfluoroalkyl-g-butyrolactones synthesized by the reaction
of 4-pentenoic acids and polyfluoroalkyl iodides [3]. In
addition, since it is believed that difluoromethylene moiety
acts similar to ether-oxygen in vivo and interesting biological
activity is anticipated for analogues of a,a-difluorinated
biomolecules [4], several works have been reported on the
methods to introduce the CF2 group into organic molecules
[5–7]. In this paper, we wish to report the synthesis of
2. Results and discussion
2.1. The addition reaction between alkenes and ethyl
iododifluoroacetate
The addition reaction between alkenes and ethyl iododi-
fluoroacetate was first reported by copper powder (10–
20 mol%) in 65–83% yield at 50–60 8C [8]. The reaction of
iododifluoroacetates with alkenes and zinc in the presence of
catalytic amounts of nickel dichloride hexahydrate produced
a,a-difluoro functionalized esters in good yields [6,9]. A
single electron transfer initiated radical mechanism was
proposed and confirmed by direct evidence of free radical as
transient intermediates by spin trapping [10].
Studies on the sulfinatodehalogenation reaction showed
that sodium dithionite was able to initiate the addition
of perfluoroalkyl iodides to olefins effectively [11].
* Corresponding author. Fax: +86 21 64253074.
E-mail address: wfh@ecust.edu.cn (F. Wu).
0022-1139/$ – see front matter # 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2004.10.009

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F. Xiao et al. / Journal of Fluorine Chemistry 126 (2005) 63–67
Scheme 1.
Fig. 1. The reaction mechanism of ethyl iododifluoroacetate with alkenes
initiated by sodium dithionite.
Fig. 2. The reaction of iododifluoroacetic acid with 1-hexene.
2.2. Hydrolysis of the adducts
Scheme 2.
Several examples were reported to provide a,a-difluoro-
g-lactones. Systematic synthesis of multifluorinated-a,a-
difluoro-g-lactones was accomplished through intramole-
cular radical cyclization as a key reaction of O-(trimethyl-
silyl)-a-bromo-a,a-difluoroacetate. The efforts failed to
synthesize the lactones via radical cyclization directly of
allyl-a,a-difluoro-a-iodoacetate [4]. The addition product
of N,N-diethyl iododifluoroacetamide with alkenes could be
converted into a,a-difluoro-g-lactones by column chroma-
tography on silica gel, which was considered that the amide
groups were hydrolyzed on the surface of silica gel and
subsequently cyclized to form g-lactones [7].
Therefore, we tried the reaction of ethyl iododifluoroacetate
(2) with alkenes in the presence of sodium dithionite in
aqueous acetonitrile solution. It showed that the reaction
took place readily at room temperature and completed
within 4 h. The volume ratio of acetonitrile as cosolvents
used to improve the mutual solubility of various reactants to
water was 3:1.
The addition of 2 to terminal alkenes in the presence of
sodium dithionite gave the corresponding products at room
temperature. For example, in the case of the reaction of 2
with 1-hexene and sodium dithionite, ethyl-2,2-difluoro-4-
iodooctanoate (3a) was isolated in 76% yield (Scheme 1).
The addition reaction could be successfully applied to
internal alkenes. Upon reaction of 2 with cyclopentene (1c)
and sodium dithionite, adduct cis-3c was isolated in 75%
yield. The reaction of cyclohexene (1d) gave the corre-
sponding trans- and cis-isomers in a 1.6:1 ratio. In the
reaction with norbornene (1e), trans-3e was separated by
column chromatography eluting with petroleum ether and
ethyl acetate in 67% yield from the mixture of trans/cis-
isomers in a 4:1 ratio. The structures of the isomers were
In order to synthesize the lactones, we tried the reaction
of iododifluoroacetic acid or the sodium salt with alkenes in
the presence of sodium dithionite. However, no desired
product was obtained (Fig. 2).
When the addition product 3a was treated with 3%
aqueous sodium hydroxide solution at room temperature for
1 h, g-lactone (4a) was also obtained in 82% yield. Several
by-products were found in the crude product determined by
GC and GC–MS analysis which were difficult to separate by
column chromatography. When the products 3a–e were
treated with 10% aqueous sodium carbonate solution, a,a-
difluoro-g-butyrolactones 4a–e was produced in 93–98%
yields (Scheme 3). For example, the addition product 3a and
10% aqueous sodium carbonate were refluxed for 4 h to give
the corresponding lactone (4a) in 93% yield after usual
workup. Under similar conditions, the adduct 3c was
hydrolyzed to give the cyclization product 4c in 93% yield.
It was not surprising that the NOESY spectra data of
lactone (4c) suggested the configuration of 4c was cis. The
formation of lactones was supposed to be through the
intramolecular neucleophilic substitution of the hydrolyzed
products of the adducts. May be the cis-isomers of the five or
six membered ring fused lactones were more stable than the
trans-isomers.
1
assigned based on their 19F NMR, H NMR and 13C NMR
data (Scheme 2).
Previous reports by Huang et al. [12–14] documented that
the addition of perfluoroalkyl iodides to alkenes can be
initiated by sodium dithionite. A free radical chain involving
a single electron transfer mechanism has been proposed in
the addition reaction [15]. Accordingly, we propose that
reaction of 2 with alkenes may also involve a single electron
transfer (SET) process for the anion radical (Fig. 1).
In the addition to bicyclo-alkene norbornene (1e), the
initial attack by free radical RF could be from both the endo
side and the exo side. Since the attack from the endo side
was less-hindered, so the RF-endo products were the only
products.

F. Xiao et al. / Journal of Fluorine Chemistry 126 (2005) 63–67
65
Table 2
Synthesis of a,a-difluoro-g-butyrolactones
Entry
Adducts
Lactones
Isolated yield (%)
Configuration
1
2
3
4
5
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
93
96
93
98
96
–
–
Cis
Cis
Cis
added to the solution. The mixture was stirred at ambient
temperature for 6 h. When the reaction accomplished, the
reactant was treated with water (ca. 50 ml). The mixture was
extracted with ether of 3Â 20 ml. The combined organic
layer was washed with saturated brine and dried over
anhydrous sodium sulfate. After the evaporation of ether, the
crude product was purified by column chromatography or
distillation under reduced pressure to give 3a–e.
Scheme 3.
In summary, a novel and efficient synthesis method
of a,a-difluoro-g-butyrolactones was realized by the
hydrolysis of the addition products of alkenes with ethyl
iododifluoroacetate initiated by sodium dithionite in
aqueous sodium carbonate solution under mild conditions
in high yields (Tables 1 and 2).
3.1.1. Ethyl-2,2-difluoro-4-iodooctanoate (3a)
The product was isolated in 76% yield by distillation at
1
reduced pressure, bp 103–105 8C, 3–4 mmHg; H NMR
(500 MHz, CDCl3), d: 0.93 (3H, t, H-8), 1.38 (3H, t,
J = 7.1 Hz, CH3CH2O), 1.38 (2H, m, H-7), 146 (2H, m, H-
6), 1.80 (2H, m, H-5), 2.87 (2H, m, H-3), 4.22 (1H, m, H-4),
4.35 (2H, q, J = 7.1 Hz, CH2O); 19F NMR (470 MHz,
CDCl3), d: 107.90 (dt, 1F, JF,F = 258.5 Hz, JF,H = 18.8 Hz),
3. Experimental
À103.18 (ddd, 1F,
JF,F = 263.2 Hz, JF,H = 18.8 Hz,
1H NMR and 13C NMR spectra were recorded with
Bruker AC-500 (500 MHz) spectrometer with CDCl3 as
the solvent and TMS as the internal standard. 19F NMR
spectra were recorded with Bruker AC-500 (500 MHz)
spectrometer with CDCl3 as the solvent and TFA as the
external standard. Infrared spectra were measured using a
Nicolet Magna IR-550 instrument. High-resolution mass
spectra were obtained on Finnigan GC-MS-4021 spectro-
meters. GC was measured by using Shimadzu GC-14B
instrument. The configurations of 3c–e and 4c–e were
confirmed by two-dimensional NMR (COSY, NOESY,
HMQC and HMBC).
JF,H = 9.4 Hz); in accordance with Ref. [6].
3.1.2. Ethyl-2,2-difluoro-4-iododecanoate (3b)
The product was isolated in 76% yield by distillation at
1
reduced pressure; bp 108–110 8C, 2–3 mmHg; H NMR
(500 MHz, CDCl3), d: 0.89 (3H, t, H-10), 1.29 (6H, m, H-7,
8, 9), 1.38 (3H, t, J = 7.1, CH3CH2O), 1.50 (2H, m, H-6),
1.81 (2H, m, H-5), 2.86 (2H, m, H-3), 4.22 (1H, m, H-4),
4.35 (2H, q, J = 7.1 Hz, CH2O); 19F NMR (470 MHz,
CDCl3), d: 107.91 (dt, JF,F = 258.5 Hz, JF,H = 18.8 Hz, 1F),
À103.16 (ddd,
JF,F = 263.2 Hz, JF,H = 18.8 Hz, JF,H =
14.1 Hz, 1F); in accordance with Ref. [6].
3.1.3. Ethyl-a,a-difluoro-(2-iodocyclopentanyl)acetate
(trans-3c)
3.1. General method for the synthesis of adduct 3
The product was isolated in 75% yield by column
chromatography eluting with petroleum ether and ethyl
acetate (10:1). IR (film), n (cmÀ1): 2980, 1780 (g-lactone),
1300, 1220, 720; 1H NMR (500 MHz, CDCl3), d: 1.39 (3H, t,
J = 7.1 Hz, CH3CH2O, H-10), 1.73 (2H, m, H-4), 1.89 (2H,
m, H-5), 2.17 (2H, m, H-3), 3.13 (1H, m, H-1), 4.31 (1H, m,
H-2), 4.37 (2H, q, J = 7.1 Hz, CH2O); 19F NMR (470 MHz,
CDCl3), d: 114.21 (dd, JF,F = 258.5 Hz, JF,H = 14.1 Hz, 1F),
À111.95 (dd, JF,F = 258.5 Hz, JF,H = 14.1 Hz, 1F); 13C NMR
(125.8 MHz, CDCl3): 14.7 (s, CH3), 20.2 (s, C-5), 26.2 (s,
C-2), 26.0 (S, C-4), 41.9 (s, C-3), 55.9 (t, C-1), 63.8
(s, CH2O), 116.7 (t, CF2), 164.2 (s, C=O); HRMS calcd. for
C9H13O2F2I 318.1012, found 318.1015.
In a typical experiment, alkene (10 mmol) and ethyl
iododifluoroacetate (12 mmol) were dissolved in the
solution of water (10 ml) and acetonitrile (10 ml). Sodium
dithionite (3.7 g) and sodium bicarbonate (1.85 g) was
Table 1
The addition reaction between alkenes and ethyl iododifluoroacetate
Entry
Alkenes
Products
Isolated yield (%)
Cis
Trans
1
2
3
4
5
1a
1b
1c
1d
1e
3a
3b
3c
3d
3e
76
78
75
62
67
–
–
–
–
Trace
100
1.6
4
1
1

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F. Xiao et al. / Journal of Fluorine Chemistry 126 (2005) 63–67
3.1.4. Ethyl-a,a-difluoro-(2-iodocyclohexanyl)acetate
(trans-3d)
(ddd, JF,F = 277.3 Hz, JF,H = 23.5 Hz, JF,H = 18.8 Hz, 1F);
13C NMR (125.8 MHz, CDCl3), d: 13.8 (s, C-9), 22.3 (s, C-
8), 26.8 (s, C-7), 34.9 (s, C-6), 37.6 (t, C-4), 115.7 (t, C-3),
76.8 (s, C-5), 165.2 (t, C-2); HRMS calcd. for C8H11O2F2
(M À 1) 177.0727, found 177.0732.
The pure trans-isomer was isolated from a mixture of
trans- and cis-isomers by column chromatography eluting
with petroleum ether and ethyl acetate (100:1). Trans-isomer:
IR (film), n (cmÀ1): 2980, 1780 (g-lactone), 1300, 1220, 720;
1H NMR (500 MHz, CDCl3), d: 1.38 (3H, t, J = 7.1,
CH3CH2O), 1.45 (3H, m, H-4,5,6), 1.63 (1H, m, H-4), 1.80
(1H, m, H-5), 2.06 (2H, m, H-3 and H-6), 2.35 (1H, m, H-3),
2.73 (1H, m, H-1), 4.35 (1H, m, H-2), 4.36 (2H, q, J = 7.1 Hz,
CH2O); 19F NMR (470 MHz, CDCl3), d: À112.37 (dd,
3.2.2. 3,3-Difluoro-5-hexyldihydrofuran-2-one (4b)
The product was isolated in 96% yield by column
chromatography eluting with petroleum ether and ethyl
acetate (10:1). IR (film), n (cmÀ1): 2960, 2900, 1810 (g-
lactone), 1480, 1420, 1320, 1260, 1100, 760; 1H NMR
(500 MHz, CDCl3), d: 0.89 (3H, t, J = 7.1 Hz, H-11), 1.45
(8H, m, H-7,8,9,10), 1.71 (1H, m, H-6), 1.81 (1H, m, H-6),
J
F,F = 258.5 Hz, JF,H = 14.1 Hz, 1F), À106.67 (dd, JF,F
=
258.5 Hz, JF,H = 14.1 Hz, 1F); 13C NMR (125.8 MHz,
CDCl3), d: 13.8 (s, CH3), 24.0 (s, C-5), 25.0 (s, C-6), 26.0
(s, C-2), 27.0 (s, C-4), 39.7 (s, C-3), 48.8 (t, C-1), 63.8 (s,
OCH2), 164.5–163.9 (t, C=O), 117.0 (t, CF2); HRMS calcd.
for C10H15O2F2I 332.0085, found 332.0078.
2.33 (1H, m, H-4), 2.84 (1H, m, H-4), 4.62 (1H, m, H-5); 19
NMR (470 MHz, CDCl3), d: 108.78 (ddd, JF,F = 277.3 Hz,
F
JF,H = 14.1 Hz, JF,H = 4.7 Hz, 1F), À107.44 (ddd, JF,F
=
282 Hz, JF,H = 21.2 Hz, JF,H = 16.5 Hz, 1F); 13C NMR
(125.8 MHz, CDCl3), d: 13.9 (s, C-11), 22.4 (s, C-10),
24.5 (s, C-9), 28.6 (s, C-8), 31.4 (s, C-7), 35.1 (s, C-6), 37.4
(t, C-4), 76.8 (s, C-5), 115.6 (t, C-3), 165.2 (t, C-2); HRMS
calcd. for C10H16O2F2 206.1118, found 206.1114.
3.1.5. Ethyl-a,a-difluoro-(3-iodobicyclo[2,2,1]hept-2-
yl)acetate (3e)
The product was isolated in 67% yield by column
chromatography eluting with petroleum ether and ethyl
acetate (80:1). IR (film), n (cmÀ1): 2980, 2900, 1770 (g-
3.2.3. 3,3-Difluorohexahydrocyclopenta[b]furan-2-one (4c)
The product was isolated in 93% yield by column
chromatography eluting with petroleum ether and ethyl
acetate (10:1). IR (film), n (cmÀ1): 2990, 1810 (g-lactone),
1
lactone), 1450, 1310, 1080, 850, 780; H NMR (500 MHz,
CDCl3), d: 1.27 (1H, m, H-7), 1.31 (1H, m, H-6), 1.38 (3H, t,
J = 7.1 Hz, CH3), 1.61 (1H, m, H-6), 1.64 (1H, m, H-5), 1.69
(1H, m, H-7), 1.83 (1H, m, H-5), 2.29 (1H, m, H-2), 2.35 (1H,
s, H-1), 2.47 (1H, s, H-4), 4.22 (IH, m, H-3), 4.37 (2H, q,
J = 7.1 Hz, OCH2); 19F NMR (470 MHz, CDCl3), d: 116.22
1
1460, 1340, 1260, 1220, 1160, 760; H NMR (500 MHz,
CDCl3), d: 1.65 (1H, m, H-7), 1.86 (3H, m, H-7 and H-8),
2.00 (1H, m, H-6), 2.17 (1H, m, H-6), 3.09 (1H, m, H-5),
5.13 (1H, t, JF,H = 5.1 Hz, H-1); 19F NMR (470 MHz,
CDCl3), d: À116.76 (d, JF,F = 282 Hz, 1F), À99.73 (dd,
(dd, JF,F = 253.8 Hz, JF,H = 18.8 Hz, 1F), À110.14 (dd, JF,F
=
253.8 Hz, JF,H = 14.1 Hz, 1F); 13C NMR (125.8 MHz,
CDCl3), d: 14.6 (s, CH3), 27.9 (s, C-5), 27.9 (s, C-3), 30.6
(s, C-6), 35.6 (s, C-7), 38.0 (s, C-1), 456 (s, C-4), 58.3 (t, C-2),
63.9 (s, OCH2), 116.2 (t, CF2), 164.3 (t, C=O); HRMS calcd.
for C11H15O2F2I 344.0085, found 344.0080.
J
F,F = 282 Hz, JF,H = 18.8 Hz, 1F); 13C NMR (125.8 MHz,
CDCl3), d: 23.5 (s, C-7), 24.9–24.8 (t, C-6), 33.4 (s, C-8),
45.9 (t, C-5), 83.9 (d, C-1), 116.5 (dd, C-4), 165.9 (dd, C-3),
HRMS calcd. for C7H8O2F2 162.0492, found 162.0500.
3.2. General method for the synthesis of
a,a-difluoro-g-lactones (4)
3.2.4. 3,3-Difluorohexahydrocyclohexyl[b]furan-2-one
(4d)
The product was isolated in 98% yield by column
chromatography eluting with petroleum ether and ethyl
acetate (10:1). IR (film), n (cmÀ1): 2990, 1810 (g-lactone),
A mixture of the adduct 3a–e (1 g) and 10% Na2CO3
aqueous solution (10 ml) was refluxed for 4 h. The mixture
was acidified and extracted with ether, washed with
saturated brine and dried over anhydrous sodium sulfate.
After concentrated, the crude product was purified by
column chromatography to give lactones 4a–e.
1
1460, 1340, 1260, 1220, 1160, 760; H NMR (500 MHz,
CDCl3), d: 1.30 (1H, m, H-8), 1.35 (1H, m, H-6), 1.44 (1H,
m, H-8), 1.56 (1H, m, H-7), 1.76 (2H, m, H-7 and H-9), 1.85
(1H, m, H-6), 2.15 (1H, m, H-9), 2.66 (1H, m, H-5), 4.73
(1H, q, J = 4.1 Hz, H-1); 19F NMR (470 MHz, CDCl3), d:
3.2.1. 3,3-Difluoro-5-butyldihydrofuran-2-one (4a)
125.26 (d, JF,F = 267.9 Hz, 1F), À111.87 (dd, JF,F
=
The product was isolated in 93% yield by column
chromatography eluting with petroleum ether and ethyl
acetate (10:1). IR (film), n (cmÀ1): 2980, 1810 (g-lactone),
1480, 1420, 1320, 1260, 1100, 1000, 740; 1H NMR
(500 MHz, CDCl3), d: 0.93 (3H, t, J = 7.1 Hz, H-9), 1.83–
1.81 (m, 1H), 1.44 (m, 4H, m, H-7 and H-8), 1.76 (2H, m, C-
6), 2.32 (1H, m, H-4), 2.83 (1H, m, H-4), 4.62 (1H, m, H-5);
19F NMR (470 MHz, CDCl3), d: 108.75 (ddd, JF,F
277.3 Hz, JF,H = 14.1 Hz, JF,H = 4.7 Hz, 1F), À107.35
272.6 Hz, JF,H = 14.1 Hz, 1F); 13C NMR (125.8 MHz,
CDCl3), d: 19.8 (s, C-7), 20.7 (s, C-8), 22.7 (s, C-6), 28.1
(s, C-9), 41.8 (t, C-5), 76.1 (d, C-1), 118.1 (dd, C-4), 166.7 (t,
C-3); HRMS calcd. for C8H10O2F2 176.1618, found
176.1621.
3.2.5. 5,5-Difluoro-3-oxatricyclo[5.2.1.02,6]decanone (4e)
The product was isolated in 96% yield by column
chromatography eluting with petroleum ether and ethyl
=

F. Xiao et al. / Journal of Fluorine Chemistry 126 (2005) 63–67
67
acetate (10:1). IR (film), n (cmÀ1): 2980, 2900, 1810 (g-
References
lactone), 1470, 1300, 1250, 1100, 810, 780; 1H NMR
(500 MHz, CDCl3), d: 1.20 (1H, m, H-9), 1.26 (1H, m, H-8),
1.35(2H, m, H-10), 1.65(1H, m, H-8), 1.71(1H, m, H-9), 2.57
(1H, dd, JF,H = 24.7 Hz, JH,H = 6.3 Hz, H-6), 2.62 (2H, s, H-1
and H-7), 4.65 (1H, dd, JF,H = 6.2 Hz, JH,H = 1.2 Hz, H-2);
19F NMR (470 MHz, CDCl3), d: À117.37 (d, JF,F = 286.7 Hz,
1F), À95.80 (dd, JF,F = 286.7 Hz, JF,H = 23.5 Hz, 1F); 13C
NMR (125.8 MHz, CDCl3), d: 22.6 (s, C-9), 27.4 (s, C-8),
32.8 (s, C-10), 36.1 (t, C-7), 40.6 (s, C-1), 48.9 (t, C-6), 83.1 (s,
C-2), 115.1 (dd, C-5), 166.4 (t, C-4); HRMS calcd. for
C9H10O2F2 188.0649, found 188.0627. HRMS calcd. for
C8H10F2 (M À CO2) 144.0751, found 144.0747. Anal. calcd.
for C9H10O2F2: C, 57.45; H, 5.36; F, 20.19. Found C, 57.03;
H, 5.33; F, 20.26.
[1] P.V. Ramachandran, K.J. Padiya, V. Rauniyar, M.V.R. Reddy, H.C.
Rrown, Tetrahedron Lett. 45 (2004) 1015–1017.
[2] Y. Komatsu, F. Sasaki, S. Takei, T. Kitazume, J. Org. Chem. 63 (1998)
8058–8061.
[3] X.W. Zou, F.H. Wu, Chin. Chem. Lett. 13 (2002) 410–411.
[4] T. Itoh, K. Sakabe, K. Kudo, H. Ohara, Y. Tagagi, H. Kihara, P. Zagatti,
M. Renou, J. Org. Chem. 64 (1999) 252–265.
[5] K. Sato, S. Nakazato, H. Enko, H. Tsujita, K. Fujita, T. Yamamoto, M.
Omote, A. Ando, I. Kumadaki, J. Fluorine Chem. 121 (2003) 105–107.
[6] Z.Y. Yang, D.J. Burton, J. Org. Chem. 56 (1991) 5125–5132.
[7] W.Y. Huang, L. Lu, Y.F. Zhang, Chin. J. Chem. 8 (1990) 68–74.
[8] Z.Y. Yang, D.J. Burton, J. Fluorine Chem. 45 (1989) 435–439.
[9] Z.Y. Yang, D.J. Burton, J. Chem. Soc., Chem. Commun. 57 (1992)
233–234.
[10] L. Julia, M.P. Bosch, S. Rodriguez, A. Guerrero, J. Org. Chem. 65
(2000) 5098–5103.
[11] W.Y. Huang, W. Wang, B.N. Huang, Acta Chim. Sinica (Chin. Ed.) 43
(1985) 409–410.
Acknowledgments
[12] W.Y. Huang, W. Wang, B.N. Huang, Acta Chim. Sinica (1986) 178–
184.
This research work was supported by the National Natural
Science Foundation of China (Grant No. 29902001) and
Shanghai Science and Technology Committee (03QB14012).
[13] F.H. Wu, W.Y. Huang, Youji Huaxue 17 (1997) 106–125.
[14] W.Y. Huang, F.H. Wu, Israel J. Chem. 39 (1999) 167–170.
[15] B.N. Huang, F.H. Wu, C.M. Zhou, J. Fluorine Chem. 75 (1995) 1–5.