An alternative route for synthesis of o-trifluoroacetylanilines as useful fluorine-containing intermediates

Article abstract of DOI:10.1016/j.jfluchem.2010.04.002

A series of o-trifluoroacetyl aniline derivatives were synthesized in three steps. In this method, we first utilized trifluoroacetic anhydride to introduce trifluoroacetyl group to the ortho position of aniline with higher yield than that of some previously reported methods. In addition, the procedure is shown to be highly regiospecific. This type of compounds can be used as the key intermediates in the preparation of a variety of inhibitors of HIV reverse transcriptase which is an important pharmacological target of many anti-AIDS agents.

Full text of DOI:10.1016/j.jfluchem.2010.04.002

Journal of Fluorine Chemistry 131 (2010) 800–804
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Short communication
An alternative route for synthesis of o-trifluoroacetylanilines as useful
fluorine-containing intermediates
*
*
**
Lingjian Zhu, Zhenyuan Miao , Chunquan Sheng , Jianzhong Yao, Chunlin Zhuang, Wannian Zhang
School of Pharmacy, Second Military Medical University, 325 Guohe Road, Shanghai 200433, People’s Republic of China
A R T I C L E I N F O
A B S T R A C T
Article history:
A series of o-trifluoroacetyl aniline derivatives were synthesized in three steps. In this method, we first
utilized trifluoroacetic anhydride to introduce trifluoroacetyl group to the ortho position of aniline with
higher yield than that of some previously reported methods. In addition, the procedure is shown to be
highly regiospecific. This type of compounds can be used as the key intermediates in the preparation of a
variety of inhibitors of HIV reverse transcriptase which is an important pharmacological target of many
anti-AIDS agents.
Received 22 March 2010
Received in revised form 4 April 2010
Accepted 8 April 2010
Available online 4 May 2010
Keywords:
ß 2010 Elsevier B.V. All rights reserved.
Fluorine-containing compound
o-Trifluoroacetylaniline
Synthesis
Trifluoroacetic anhydride (TFAA)
1. Introduction
group into compounds. In the previous reports, the introduction of
trifluoroacetyl group was mainly described on the basis of four
Nowadays, organic fluorine compounds have attracted much
attention in the materials and pharmaceutical sciences, because
the introduction of fluorine into an organic compound can cause
remarkable changes in the physical, chemical and biological
properties such as the enhanced hydrophobic binding, increased
membrane permeability and stability against metabolic oxidation
[1–3]. The importance of fluorine in medicinal chemistry has been
demonstrated by a large number of fluorinated compounds
approved by the FDA for medical use [4,5].
Among these fluorinated compounds, the trifluoromethyl
group-containing molecules are especially important, and contin-
ue to attract increasing attention from various fields [6,7].
Nowadays, many trifluoromethylated molecules have been
developed as well-known drugs such as prozac (antidepressant),
diflucan (anti-fungal agent), casodex (anti-cancer agent) and
desflurane (inhalation anesthetic) [8]. Accordingly, the develop-
ment of simple and effective methods for the synthesis of
trifluoromethyl-containing molecules has been becoming more
and more meaningful in fluorine chemistry [9–14]. Among these
methods, introducing trifluoroacetyl group into organic molecules
is a convenient measure for the incorporation of trifluoromethyl
methodologies: (1) a route by means of Friedel–Crafts acylation
[15,16], (2) addition of a trifluoromethyl group to the carbonyl
carbon through Ruppert–Prakash reagents [17], Barbier procedure
[18] and electrochemical methods [19], then oxidized by some
oxidants, (3) direct substitution of a hydrogen atom or a halogen
atom [20], and (4) use of some special reagents [21]. However,
these methods generally suffer from the use of toxic and expensive
reagents, severe experimental conditions requirements, low yields
or lack of regioselectivity in the formation of trifluoroacetyl group.
In our present work, we first make use of trifluoroacetic
anhydride to introduce trifluoroacetyl group to the ortho position
of aniline with high regiospecificity in excellent yield, and the
reaction condition is not severe (Scheme 1). Although the o-
trifluoroacetylanilines do not possess direct biological activities,
they are highly valuable synthetic intermediates in the preparation
of many trifluoromethylated drugs such as HIV reverse transcrip-
tase inhibitor efavirenz (DMP 266) [22], antiprotozomal drug
mefloquine [23] and some antileishmanial compounds [24,25].
Therefore, this class of compounds has highly synthetic value in
medicinal chemistry.
2. Results and discussion
2.1. Synthesis
* Corresponding author. Tel.: +86 21 81871233; fax: +86 21 81871233.
** Corresponding author. Tel.: +86 21 81871243; fax: +86 21 81871243.
E-mail addresses: miaozhenyuan@hotmail.com (Z. Miao),
To verify the practicality and reaction regiospecificity of this
shengcq@hotmail.com (C. Sheng), zhangwnk@hotmail.com (W. Zhang).
method, we had designed and synthesized
a series of o-
0022-1139/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2010.04.002

L. Zhu et al. / Journal of Fluorine Chemistry 131 (2010) 800–804
801
Scheme 1. The synthetic route of compounds 4a–4j.
trifluoroacetylaniline derivatives. The reactions are shown in
Scheme 1, and the results are summarized in Table 1. We can
obviously see from Table 1 that a wide range of substituted N-
pivaloylanilines can react smoothly with trifluoroacetic anhydride
under the condition of n-butyllithium to give various o-trifluor-
oacetylanilines in reasonably high yields.
Scheme 1 shows its synthetic route from the easily available
materials of substituted anilines and trifluoroacetic anhydride
(TFAA) in three steps: reaction of anilines 1 with pivaloyl chloride
in a two-phase mixture of diethyl ether and aqueous sodium
hydroxide afforded pivaloylamides 2 in high yields. Directed
orthometalation of 2 (2.2 equiv. of n-BuLi, 1.0 equiv. of TMEDA)
generated the corresponding dilithio intermediate [26]. Reaction
of the dilithio species with trifluoroacetic anhydride results in the
formation of ketoamides 3 which can be isolated by crystallization.
Hydrolysis of the amide in situ (conc. HCl) provided the
hydrochloride of 4. Treatment of the salt with aqueous Na2CO3
in water provided the corresponding free base 4.
Table 1 (Continued )
Compound
R in anilines
p-MeO
Product
Yielda (%)
4c
85
84
95
4d
4e
p-Br
p-CF3
2.2. The role of protective group of anilines and the reaction
mechanism
4f
p-CN
90
91
82
In spite of the versatility of o-trifluoroacetylanilines as reactive
intermediates, a simple preparative route to them from anilines
has not been known to date, because the Friedel–Crafts trifluor-
oacetylation of anilines is usually unsuccessful and the formation
of isomers and the marginal yields are synthetically unattractive.
Herein, we wish to report on the facile and regiospecific synthetic
route to get the target molecules.
The presence of two active hydrogens in primary anilines is a
formidable obstacle to nuclear metalation and is presumably the
reason for the lack of reports on the successful synthesis of o-
trifluoroacetylanilines. Therefore, control experiments were con-
ducted to study the role of suitable protecting groups. As a part of
4g
4h
m-MeO
o-MeO
Table 1
Structures of the compounds 4a–4j.
Compound
R in anilines
H
Product
Yielda (%)
4i
4j
p-OH
75
80
4a
m-OH
4b
p-Cl
80
a
Isolated yields.

802
L. Zhu et al. / Journal of Fluorine Chemistry 131 (2010) 800–804
should be exploited for the synthesis of various other useful
trifluoromethylated compounds.
4. Experimental
4.1. General
All reagents and solvents were reagent grade or were purified
by standard methods before use. The melting points were
determined using an electrothermal apparatus and are uncorrect-
ed. 1H and 13C NMR spectra were recorded at either 400 MHz or
500 MHz with a Bruker instrument, and reported with TMS as
internal standard and CDCl3 as solvent. 19F NMR spectra were
obtained either on a Bruker instrument using CF3COOH (TFA) as an
external standard. Chemical shifts
(d values) and coupling
constants (J values) are given in ppm and Hz respectively. TLC
analysis was carried out on silica gel plates GF254 (Qindao Haiyang
Chemical, China). Anhydrous solvent and reagents were all
analytically pure and dried through routine protocols. All reactions
requiring anhydrous conditions were performed under a positive
nitrogen flow, and all glassware was oven-dried before using.
Scheme 2. The proposed mechanism.
Table 2
The comparison of different protecting groups.
4.2. Typical experimental procedure for the synthesis of 2
Anilines (1, 50 mmol) were charged into a mixture of diethyl
ether (60 ml) and 40% aqueous sodium hydroxide (5.5 g, 55 mmol),
and the mixture was cooled to 0 8C. To the resulting slurry,
trimethylacetyl chloride (PVCL) (6.6 g, 55 mmol) was added over
0.5 h, keeping the temperature below 15 8C. After being stirred for
2.5 h at 25 8C, the slurry was cooled to 0 8C and held for 1.5 h. The
product was collected by filtration, washed with a solution of 9/1
water/methanol (150 ml) and water (100 ml), and dried in vacuo to
give pivaloylamide 2 as white solid.
.
R
Yielda (%)
-CO(CH3)3
-COPh
88
0
-COCH3
-COC2H5
-Boc
5
18
20
a
Isolated yields.
4.3. General procedure for the preparation of compounds 4a–4h
the systematic research work, we investigated the suitability of
several ortho-directing groups (Table 2). According to the
experimental results, it can be revealed that the protective group
could not be aryl [27] and most alkyl groups had to be excluded as
well, based on the acidic character of their a proton [28]. However,
Under an atmosphere of nitrogen, compound 2 (0.1 mol) was
charged to a solution of TMEDA (1.1 g, 0.1 mol) in anhydrous
diethyl ether (50 ml), and the mixture was cooled to 0 8C. The n-
butyllithium solution (88 ml of a 2.5 M solution in hexane,
0.22 mol) was added dropwise to the cold amide solution slowly
over 2.5 h, while the temperature was kept below 15 8C. The
mixture was aged at 10–15 8C for 4 h and cooled below À25 8C. To
this mixture trifluoroacetic anhydride (32.0 ml, 0.25 mol) was
added rapidly. After 5 h, the resulting clear solution was quenched
with 15% aqueous HCl, keeping the temperature below 10 8C. The
mixture was diluted with 50 ml diethyl ether and the layers were
separated. The organic phase was washed with brine, dried, filed
and concentrated in vacuo, to give a yellow oil. This material was
cooled to 25 8C, 12N HCl (10 ml, 0.12 mol) was added, and the
mixture was heated to 80–85 8C and held for 6 h. The cooled
solution was diluted with 100 ml of EtOAc and the mixture was
made basic with a solution of sodium carbonate in water. Then the
mixture was extracted with ethyl acetate (50 ml, 3Â). The
combined organic phase was washed with brine and dried over
anhydrous Na2SO4. After the removal of solvent, the residue was
purified by flash chromatography on silica gel (petroleum ether/
ethyl acetate = 20/1) or by crystallization to afford 4a–4h.
a
bulky tert-butyl group (R = t-C4H9) which could prevent
unwanted side reactions turned out to be ideal, and the desired
reaction could occur readily and under relatively mild conditions.
A mechanistic pathway can be suggested (Scheme 2). Fundamen-
tally, it could be assumed that by analogy with other ortho
metalations [29], the oxygen atom in the deprotonated species II
should serve as a ligand for a second equivalent of lithiating
agent, thus facilitating a regiospecific protophilic attack on the
o-hydrogen and the formation of the dilithio intermediate III.
Reaction of the dilithio species with trifluoroacetic anhydride
results in the formation of o-trifluoroacetyl N-pivaloylaniline
IV which can be isolated by crystallization. Finally, IV was
deprotected by concentrated hydrochloride to give the target
compound V.
3. Conclusion
In summary, based on some previously reported results, we
have developed a simple and efficient method to introduce
trifluoroacetyl group to the ortho position of anilines in higher
yield. Some of these compounds were firstly reported to be novel
trifluoromethylated molecules to the best of our knowledge. The
results obtained in this paper indicated that our strategies for the
synthesis of some trifluoromethylated molecules are commercially
important in both organofluorine and organic synthetic area, and
4.4. Procedure for the demethylation of 4c and 4g
To a solution of acetic acid (25 ml) and aqueous hydrobromic
acid (48%, 25 ml) heated at 80 8C (oil bath) 4c or 4g (0.3 g,
1.3 mmol) was added. The mixture was heated at 80 8C for 2 h.
After cooling, the mixture was diluted with cold water (150 ml)
and extracted with ethyl acetate. The organic layer was washed

L. Zhu et al. / Journal of Fluorine Chemistry 131 (2010) 800–804
803
with water and brine, dried over MgSO4. On evaporation of the
solvent, the product solidified.
109.76, 118.38, 121.26, 136.54, 152.31, 161.81, 183.77; MS (ESI):
220 (M+H); Anal. calcd. for C9H8F3NO2: C, 49.32; H, 3.68; N, 6.39.
Found: C, 49.29; H, 3.67; N, 6.37.
4.5. Spectral data
4.5.8. 1-(2-Amino-3-methoxyphenyl)-2,2,2-trifluoroethanone (4h)
A yellow solid; yield (82%); mp 67–68 8C; 1H NMR (500 MHz,
4.5.1. 1-(2-Aminophenyl)-2,2,2-trifluoroethanone (4a)
A bright yellow needles; yield (88%); mp 51–52 8C; 1H NMR
CDCl3):
(d, 1H, J = 8.2 Hz), 7.21 (t, 1H, J = 8.2 Hz); 19F NMR (CDCl3, TFA):
= 2.25; 13C NMR (400 MHz, CDCl3):
= 55.81, 101.11, 110.76,
d = 3.86 (s, 3H), 6.07 (br s, 2H), 6.25 (d, 1H, J = 8.3 Hz), 6.43
(500 MHz, CDCl3):
(dd, 1H, J = 1.8 Hz, 3.9 Hz), 7.38 (dd, 1H, J = 1.2 Hz, J = 3.9 Hz), 6.67
(d, 1H, J = 1.8 Hz); 19F NMR (CDCl3, TFA): = 6.42; 13C NMR
(400 MHz, CDCl3): = 111.32, 115.84, 117.70, 118.74, 131.55,
d = 6.24 (br s, 2H), 6.67 (d, 1H, J = 1.2 Hz), 6.73
d
d
d
117.89, 120.56, 132.45, 140.68, 150.55, 181.48; MS (ESI): 220
(M+H); Anal. calcd. for C9H8F3NO2: C, 49.32; H, 3.68; N, 6.39.
Found: C, 49.29; H, 3.67; N, 6.37.
d
136.85, 153.40, 180.01; MS (ESI): 188 (MÀH); Anal. calcd. for
C8H6F3NO: C, 50.80; H, 3.20; N, 7.41. Found: C, 50.87; H, 3.21; N,
7.39.
4.5.9. 1-(2-Amino-5-hydroxyphenyl)-2,2,2-trifluoroethanone (4i)
A bright yellow solid; yield (75%); mp 108–109 8C; 1H NMR
4.5.2. 1-(2-Amino-5-chlorophenyl)-2,2,2-trifluoroethanone (4b)
A bright yellow solid; yield (80%); mp 90–91 8C; 1H NMR
(500 MHz, CDCl3):
J = 9.0 Hz), 7.05 (dd, 1H, J = 2.8 Hz, 9.0 Hz), 7.17 (d, 1H, J = 2.8 Hz);
19F NMR (CDCl3, TFA): = 6.17; 13C NMR (400 MHz, CDCl3):
= 110.79, 115.75, 118.65, 119.18, 127.46, 145.71, 148.68, 180.35;
d = 4.46 (s, 1H), 6.19 (br s, 2H), 6.67 (d, 1H,
(500 MHz, CDCl3):
(dd, 1H, J = 2.1 Hz, 9.0 Hz), 7.71 (d, 1H, J = 2.1 Hz); 19F NMR (CDCl3,
TFA): = 111.62, 115.52,
= 6.19; 13C NMR (400 MHz, CDCl3):
d
= 6.46 (br s, 2H), 6.70 (d, 1H, J = 9.0 Hz), 7.32
d
d
d
d
MS (ESI): 204 (MÀH); Anal. calcd. for C8H6F3NO2: C, 46.84; H, 2.95;
118.42, 119.24, 130.25, 137.09, 151.82, 180.31; MS (ESI):
222(MÀH)À; Anal. calcd. for C8H5ClF3NO: C, 42.98; H, 2.25; N,
6.26. Found: C, 42.96; H, 2.24; N, 6.27.
N, 6.83. Found: C, 46.79; H, 2.96; N, 6.82.
4.5.10. 1-(2-Amino-6-hydroxyphenyl)-2,2,2-trifluoroethanone (4j)
A lemon-yellow solid; yield (80%); mp 98–99 8C; 1H NMR
4.5.3. 1-(2-Amino-5-methoxyphenyl)-2,2,2-trifluoroethanone (4c)
An orange solid; yield (85%); mp 105–106 8C; 1H NMR
(500 MHz, CDCl3):
J = 8.0 Hz), 6.45 (d, 1H, J = 8.2 Hz), 7.11 (t, 1H, J = 8.3 Hz); 19F NMR
(CDCl3, TFA): = 3.25; MS (ESI): 206 (M+H); Anal. calcd. for
d = 4.75 (s, 1H), 6.01 (br s, 2H), 6.18 (d, 1H,
(500 MHz, CDCl3):
J = 9.0 Hz), 7.11 (dd, 1H, J = 2.1 Hz, 9.0 Hz), 7.15 (d, 1H, J = 2.1 Hz);
19F NMR (CDCl3, TFA): = 4.35; 13C NMR (400 MHz, CDCl3):
= 56.77, 101.88, 110.96, 119.45, 121.44, 134.78, 148.69, 159.44,
d
= 3.78 (s, 3H), 6.25 (br s, 2H), 6.69 (d, 1H,
d
C8H6F3NO2:C,46.84;H,2.95;N,6.83.Found:C,46.80;H,2.96;N,6.84.
d
d
Acknowledgments
183.43; MS (ESI): 218 (MÀH); Anal. calcd. for C9H8F3NO2: C, 49.32;
H, 3.68; N, 6.39. Found: C, 49.28; H, 3.69; N, 6.38.
This research was supported in part by the Key Project of
Science and Technology of Shanghai (No. 09431901700), Major
Special Project for the Creation of New Drugs (Grant No.
2009ZX09301-011) and Shanghai Leading Academic Discipline
Project (Project No. B906).
4.5.4. 1-(2-Amino-5-bromophenyl)-2,2,2-trifluoroethanone (4d)
An orange solid; yield (84%); mp 100–101 8C; 1H NMR
(500 MHz, CDCl3):
(dd, 1H, J = 2.0 Hz, 8.9 Hz), 7.84 (d, 1H, J = 2.0 Hz); 19F NMR (CDCl3,
TFA): = 112.35, 115.53,
= 6.26; 13C NMR (400 MHz, CDCl3):
d = 6.42 (br s, 2H), 6.64(d, 1H, J = 8.9 Hz), 7.44
d
d
References
117.44, 119.51, 133.33, 139.63, 152.10, 180.26; MS (ESI): 266
(MÀH); Anal. calcd. for C8H5BrF3NO: C, 35.85; H, 1.88; N, 5.23.
Found: C, 35.90; H, 1.88; N, 5.24.
[1] L. Kuznetsova, M.I. Ungureanu, A. Pepe, I. Zanardi, X. Wu, I. Ojima, J. Fluorine
Chem. 125 (2004) 415–419.
[2] R.D. Chambers, D. Holling, G. Sandforda, A.S. Batsanov, J.A.K. Howard, J. Fluorine
Chem. 125 (2004) 661–671.
4.5.5. 1-(2-Amino-5-(trifluoromethyl)phenyl)-2,2,2-
trifluoroethanone (4e)
[3] (a) S. Large, N. Roques, B.R. Langlois, J. Org. Chem. 65 (2000) 8848–8856;
(b) R.P. Singh, G.F. Cao, R.L. Kirchmeier, J.M. Shreeve, J. Org. Chem. 64 (1999)
2873–2876.
[4] J.P. Begue, D. Bonnet-Delpon, J. Fluorine Chem. 127 (2006) 992–1012.
[5] C. Isanbor, D. O’Hagan, J. Fluorine Chem. 127 (2006) 303–319.
[6] O.G. Khudina, E.V. Shchegol’kov, Ya.V. Burgart, M.I. Kodess, O.N. Kazheva, A.N.
Chekhlov, G.V. Shilov, O.A. Dyachenko, V.I. Saloutin, O.N. Chupakhin, J. Fluorine
Chem. 126 (2005) 1230–1238.
A bright yellow needles; yield (95%); mp 270–271 8C; 1H NMR
(500 MHz, CDCl3)
1H, J = 1.2 Hz), 7.57 (dd, 1H, J = 1.2 Hz, 8.9 Hz); 19F NMR (CDCl3,
TFA): = 110.04,
= 6.21, 13.72; 13C NMR (400 MHz, CDCl3):
d: 6.66 (br s, 2H), 6.81 (d, 1H, J = 8.9 Hz), 7.15 (d,
d
d
115.46, 118.35, 125.33, 128.02, 129.37, 132.81, 154.92, 180.54; MS
(ESI): 256 (MÀH); Anal. calcd. for C9H5F6NO: C, 42.04; H, 1.96; N,
5.45. Found: C, 42.09; H, 1.96; N, 5.46.
[7] M.L. Quan, P.Y.S. Lam, Q. Han, D.J.P. Pinto, M.Y. He, R.H. Li, C.D. Ellis, C.A. Clark, J.H.
Sun, R.S. Alexander, S. Bai, J.M. Luettgen, R.M. Knabb, P.C. Wong, R.R. Wexler, J.
Med. Chem. 48 (2005) 1729–1744.
[8] M. Abid, B. To¨ro¨k, Adv. Synth. Catal. 347 (2005) 1797–1803.
[9] K. Mikami, Y. Itoh, M. Yamanaka, Chem. Rev. 104 (2004) 1–16.
[10] R.P. Singh, J.M. Shreeve, Tetrahedron 56 (2000) 7613–7632.
[11] G.K.S. Prakash, A.K. Yudin, Chem. Rev. 97 (1997) 757–786.
[12] J.H. Steenis, A. Gen, J. Chem. Soc., Perkin Trans. 1 (2002) 2117–2133.
[13] I. Ojima, Chem. Rev. 88 (1988) 1011–1030.
[14] K. Uneyama, Organofluorine Chemistry, Blackwell, Oxford, UK, 2006.
[15] W.E. Hull, K. Seeholzer, M. Baumeister, I. Ugi, Tetrahedron 42 (1986) 547–552.
[16] Y. Izawa, K. Ishiguro, H. Tomioka, Bull. Chem. Soc. Jpn. 56 (1983) 1490–1496.
[17] (a) R. Krishnamurti, D.R. Bellew, G.K.S. Prakash, J. Org. Chem. 56 (1991) 984–989;
(b) S.P. Kotun, J.O. Anderson, D.D. DesMarteau, J. Org. Chem. 57 (1992) 1124–
1131.
4.5.6. 1-(2-Amino-5-cyanphenyl)-2,2,2-trifluoroethanone (4f)
An orange solid; yield (90%); mp 131–132 8C; 1H NMR
(500 MHz, CDCl3):
7.74 (dd, 1H, J = 2.1 Hz, 8.5 Hz), 7.84 (d, 1H, J = 2.1 Hz); 19F NMR
(CDCl3, TFA): = 112.36,
= 6.27; 13C NMR (400 MHz, CDCl3):
d = 6.57 (br s, 2H), 6.75 (d, 1H, J = 8.5 Hz),
d
d
115.88, 118.01, 118.56, 119.87, 134.35, 140.12, 155.23, 180.05; MS
(ESI): 213 (MÀH); Anal. calcd. for C9H5F3N2O: C, 50.48; H, 2.35; N,
13.08. Found: C, 50.45; H, 2.36; N, 13.09.
[18] (a) M. Tordeux, C. Francese, C. Wakselman, J. Chem. Soc., Perkin Trans. 1 (1990)
1951;
4.5.7. 1-(2-Amino-6-methoxyphenyl)-2,2,2-trifluoroethanone (4g)
A lemon-yellow solid; yield (91%); mp 49–50 8C; 1H NMR
´
(b) C. Francese, M. Tordeux, C. Wakselman, Tetrahedron Lett. 29 (1988) 1029–
1030.
[19] (a) T. Shono, M. Ishifune, T. Okada, S. Kashimura, J. Org. Chem. 56 (1991) 2–4;
(b) T. Kitazume, T. Ikeya, J. Org. Chem. 53 (1988) 2349–2350.
[20] I.N. Houpis, A. Molina, A.W. Douglas, L. Xavier, J. Lynch, R.P. Volante, P.J. Reider,
Tetrahedron Lett. 35 (1994) 6811–6814.
(500 MHz, CDCl3):
J = 8.1 Hz), 6.31 (d, 1H, J = 8.3 Hz), 7.25 (t, 1H, J = 8.2 Hz); 19F NMR
(CDCl3, TFA): = 55.79, 98.95,
= 2.14; 13C NMR (400 MHz, CDCl3):
d = 3.84 (s, 3H), 6.05 (br s, 2H), 6.20 (d, 1H,
d
d

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L. Zhu et al. / Journal of Fluorine Chemistry 131 (2010) 800–804
[21] (a) Y. Gong, K. Kato, H. Kimoto, Synlett 9 (1999) 1403–1404;
(b) Y. Gong, K. Kato, H. Kimoto, Bull. Chem. Soc. Jpn. 74 (2001) 377–383.
[22] M.E. Pierce, R.L. Parsons Jr., L.A. Radesca, Y.S. Lo, S. Silverman, J.R. Moore, Q. Islam,
A. Choudhury, J.M.D. Fortunak, D. Nguyen, C. Luo, S.J. Morgan, W.P. Davis, P.N.
Confalone, J. Org. Chem. 63 (1998) 8536–8543.
[24] T. Hiyama (Ed.), Organofluorine Compounds: Chemistry and Applications, Spring-
er-Verlag, Berlin, Germany, 2000, p. 137.
[25] J. Dade, O. Provot, H. Moskowitz, J. Mayrargue, E. Prina, Chem. Pharm. Bull. 49
(2001) 480–483.
[26] W. Fuhrer, J. Org. Chem. 44 (1979) 1133–1136.
[23] R.D. Chambers, in: R.D. Chambers (Ed.), Organofluorine Chemistry Techniques
and Synthons, Topics in Current Chemistry, vol. 193, Springer-Verlag, Berlin,
Heidelberg, Germany, 1997, p. 3.
[27] G.-L. Mao, I.T. Barnish, C.R. Hauser, J. Heterocycl. Chem. 6 (1969) 475–482.
[28] R.P. Woodbury, M.W. Rathke, J. Org. Chem. 42 (1977) 1688–1690.
[29] H.W. Gschwend, H.R. Rodriguez, Org. React. 26 (1979) 13–19.