Room temperature preparation of trifluoroethenylzinc reagent by metalation of the readily available halocarbon HFC-134a and an efficient, economically viable synthesis of 1,2,2-trifluorostyrenes

Article abstract of DOI:10.1021/jo049179c

Trifluoroethenylzinc reagent [CF₂=CFZnX] was generated from the readily available halocarbon HFC-134a by an in situ metalation-transmetalation procedure at temperatures near to room temperature (15-20 °C). By systematic standardization of the m

Full text of DOI:10.1021/jo049179c

Room Tem p er a tu r e P r ep a r a tion of Tr iflu or oeth en ylzin c Rea gen t
by Meta la tion of th e Rea d ily Ava ila ble Ha loca r bon HF C-134a a n d
a n Efficien t, Econ om ica lly Via ble Syn th esis of
1,2,2-Tr iflu or ostyr en es
Anilkumar Raghavanpillai and Donald J . Burton*
Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242
donald-burton@uiowa.edu
Received May 15, 2004
Trifluoroethenylzinc reagent [CF2dCFZnX] was generated from the readily available halocarbon
HFC-134a by an in situ metalation-transmetalation procedure at temperatures near to room
temperature (15-20 °C). By systematic standardization of the metalation experiments by
manipulation of solvent, cosolvent, temperature, zinc salt, and the base, the trifluoroethenylzinc
reagent was produced in 73% yield at 20 °C in THF medium. The palladium-catalyzed cross-coupling
reaction of the trifluoroethenylzinc reagent with various aryl iodides was carried out under mild
reaction conditions to produce 1,2,2-trifluorostyrenes in 59-86% isolated yields. The stability of
the intermediate trifluoroethenyllithium reagent was compared at different temperatures and
solvent systems. Experimental evidence for the mono-anion from HFC-134a (CF3CHF-) was obtained
by the trapping of the mono-anion with zinc halide in THF/TMEDA medium. The structure and
complexation of both the mono- and bis-trifluoroethenylzinc reagents with TMEDA and other ligands
are discussed.
In tr od u ction
methodologies have been developed to prepare this
monomer in an efficient and cost-effective manner.1a The
previously reported methods of Cohen6 and Prober7
involved many steps and suffered from low overall yields
(<20%). Pyrolytic methods used for bulk production have
the difficulty of low yield and the formation of many side
products.8 Formation of TFS through organometallic
reagents has been the most impressive route. One of the
earlier methods developed by Dixon9 was promising,
where reaction of an aryllithium reagent with tetrafluo-
roethylene (TFE) generated the 1,2,2-trifluorostyrene in
low yields (30%). 1,2-Difluorostilbene formation was the
major side reaction during this process. With an excess
of the aryllithium, the diaryl- and triaryl-substituted
products were favored.10 Reactions of the phenyl deriva-
tives of the lanthanides (Yb, Sm, Ce) with tetrafluoro-
ethylene produced TFS in poor yield.11 Synthesis of TFS
through trifluoroethenylzinc and trifluoroethenyltin was
developed in the past two decades. Sorokina et al.
developed a palladium-catalyzed cross-coupling reaction
of the trifluoroethenylzinc and trifloroethenyltin reagent
with aryl iodides in DMF, HMPA medium.12 The best
method so far for TFS synthesis was developed from this
1,2,2-Trifluorostyrene (TFS) is one of the important
monomers among the fluorinated monomers capable of
polymerization.1 The polytrifluorostyrene (PTFS) or its
copolymers with various fluorinated monomers have
received recent attention as they are promising proton
exchange membranes for fuel cell separators.1a,2 Polytri-
fluorostyrene-coated silica as a packing material for
column liquid chromatography,3 its derivatized polymers
as optical fibers,4 and 4-chloro bromomethyl derivatives
as an excellent alternative for Merrifield-type resin5 have
been explored in recent years.
A practical synthesis of 1,2,2-trifluorostyrene in good
yield and purity has been a difficult task. Numerous
(1) (a) Nikitina, T. S. Usp. Khim. 1990, 59, 995-1020 (Engl. Transl.
pp 575-589). (b) Narita, T.; Hagiwara, T.; Hamana, H.; Shibasaki,
K.; Hiruta, I. J . Fluorine Chem. 1995, 71, 151-153. (c) Fluoropolymers;
Wall, L. A., Ed.; Wiley-Interscience: New York, 1972. (d) Aoki, T.;
Watanabe, J .; Ishimoto, Y.; Oikawa, E.; Hayakawa, Y.; Nishida, M. J .
Fluorine Chem. 1992, 59, 285-288. (e) Hodgdon, R. B., J r.; Macdonald,
D. I. J . Polym. Sci., Polym. Chem. 1968, 6, 711-717.
(2) (a) Stone. C.; Daynard, T. S.; Hu, L.-Q.; Mah, C.; Steck, A. E. J .
New Mater. Electrochem. Syst. 2000, 3, 43-50. (b) Stone. C.; Steck, A.
E. PCT Int. Appl. WO 2001058576. (c) Steck, A. E.; Stone. C. U.S.
Patent 5,834,523, 1998. (d) Stone. C.; Steck, A. E.; J inzhu, W. U.S.
Patent 5,773,480, 1998. (e) Momose, T.; Kitazumi, T.; Ishigaki, I.;
Okamoto, J . J . Appl. Polym. Sci. 1990, 39, 1221-1230. (f) Wodzki, R.;
Narebska, A.; Ceynowa, J . Angew. Makromol. Chem. 1982, 106, 23-
35.
(6) Cohen, S. G.; Wolosinski, H. T.; Scheuer, P. J . J . Am. Chem. Soc.
1949, 71, 3439-3440.
(7) Prober M. J . Am. Chem. Soc. 1953, 75, 968-973.
(8) Shingu, H.; Hisazumi, M. U.S. Patent 3,489,807, 1970. Chem.
Abstr. 72: 89745d.
(9) Dixon, S. J . Org. Chem. 1956, 21, 400-403.
(10) McGrath, T. F.; Levine, R. J . Am. Chem. Soc. 1955, 77, 4168-
4169.
(3) Saburov, V. V.; Reznikova, O. A.; Kapustin, D. V.; Zubov, V. P.
J . Chromatogr., A 1994, 660, 131-136.
(4) Masayuki, T.; Tsuneaki, M.; Shotaro, Y.; Shoichi, H. JP 63182607,
Chem. Abstr. 110: 25081.
(5) Liu, S.; Akthar, M.; Gani, D. Tetrahedron. Lett. 2000, 41, 4493-
4497.
(11) Sigalov, A. B.; Beletskaya, I. P. Izv. Akad. Nauk SSSR, Ser.
Khim. 1988, 445-450.
10.1021/jo049179c CCC: $27.50 © 2004 American Chemical Society
Published on Web 09/11/2004
J . Org. Chem. 2004, 69, 7083-7091
7083

Raghavanpillai and Burton
SCHEME 1
SCHEME 2
laboratory where the trifluoroethenylzinc reagent was
generated from zinc and bromotrifluoroethylene (BTFE)
in a variety of solvents (DMF, THF, TG).13 The pal-
ladium-catalyzed cross coupling of the zinc reagent with
aryl iodides generated 1,2,2-trifluorostyrenes in very good
yields (Scheme 1). Since this reaction was performed
under mild conditions the usual thermal cyclodimeriza-
tion of TFS was absent. Also the stilbene formation
observed in Dixon’s method was eliminated. But the cost,
the availability, and above all the environmental concern
of BTFE remained as a major problem and thus made it
difficult for commercial applications.
roethylene (HFC-134a) and 1-chloro-2,2,2-trifluoroethane
(HCFC-133a) at low temperature (Scheme 2). The lithium
reagents thus generated were exploited for various
reactions, and with metal halides as the electrophile,
trifluoroethenyllithium was transformed to the trifluo-
roethenylmetal halide at low temperature.18
Recently, we have developed an alternative nonorga-
nometallic route for the synthesis of 1,2,2-trifluoro-
styrenes by dehydrohalogenation of the corresponding
precursors using lithium hexamethyldisilazide base.19
Herein we report a full account of another synthetic
route that we have successfully followed for the synthesis
of 1,2,2-trifluorostyrenes. This route involves the reaction
of LDA with a THF solution of HFC-134a and ZnCl2 at
room temperature followed by Pd(0)-catalyzed cross-
coupling of the transmetalated zinc reagent with aryl
iodides. For a preliminary account of these results see
refs 20a and 20b.
Normant and co-workers14 generated a fluoroethenyl-
zinc reagent via fluoroethenyllithium reagent from a
fluorocarbon of the type CF2dCFY, where Y ) H, Cl, Br,
I. Here the lithium reagent was generated by the reaction
of the fluoroalkene with an alkyllithium at very low
temperature, which was then converted to zinc reagent
by transmetalation with zinc halide. But unlike the
fluoroethenylzinc reagents the corresponding lithium
reagents are thermally unstable. Tarrant15 reported the
potential instability of trifluoroethenyllithium, as they
readily eliminate lithium fluoride leading to an alkyne,
which can undergo further reactions. Also it was very
well established that the stability of the trifluoroethe-
nyllithium reagents is solvent, temperature, and concen-
tration dependent; as ether, THF solutions are stable only
at low temperature15,16 So the Normant method of
generation of the trifluoroethenylzinc reagent from the
lithium reagent suffered from two major difficulties: the
lithium reagent had to be generated at low temperature
and the involvement of CFC type starting materials.
Clearly a challenge has arisen for developing an alterna-
tive route for the synthesis of 1,2,2-trifluorostyrene by
an economically viable route starting from readily avail-
able precursors. The only viable cheap, large volume,
commercially available precursor for the introduction of
the trifluoroethenyl group is 1,1,1,2-tetrafluoroethane
(HFC-134a). Coe and co-workers17 developed an excellent
method for the generation of trifluoroethenyl and chlo-
rodifluoroethenyllithium reagents from 1,1,1,2-tetrafluo-
Resu lts a n d Discu ssion
Gen er a tion of Tr iflu or oeth en ylzin c Rea gen t fr om
HF C-134a a n d Op tim iza tion of Rea ction Con d i-
tion s. The generation of the trifluoroethenylzinc reagent
from halocarbon HFC-134a was attempted under a
variety of reaction conditions by changing the medium,
base, temperature, and the zinc halide used for the
transmetalation. Considering the potential thermal in-
stability of trifluoroethenyllithium our initial experi-
ments were performed at low temperature. Thus, reaction
of HFC-134a with 2 equiv of n-BuLi in THF solvent at
-80 °C generated the trifluoroethenyllithium. Addition
of ZnI2 to the reaction mixture generated the trifluoro-
ethenylzinc reagent in 70% yield with a 90:10 ratio of
mono (CF2dCFZnI) and bis ((CF2dCF)2Zn) zinc reagents
(by 19F NMR analysis of the reaction mixture, vs PhCF3
as internal standard). Palladium-catalyzed coupling of
this zinc reagent with iodobenzene at 65 °C produced a
quantitative yield of the TFS (1) (Scheme 3).
Although the trifluoroethenylzinc reagent and TFS
were successfully generated at low temperature by the
procedure outlined in Scheme 3, the low temperature
utilized was not compatible with industrial production
of TFS. To make this reaction feasible at ambient
temperatures it was rationalized that the metalation-
transmetalation process should be made in situ so that
the trifluoroethenyllithium formed can be trapped before
(12) (a) Sorokina, R. S.; Rybakova, L. F.; Kalinovskii, I. O.; Cher-
noplekova, V. A.; Beletskaya, I. P. Zh. Org. Chim. 1982, 18, 2458-
2459. (b) Sorokina, R. S.; Rybakova, L. F.; Kalinovskii, I. O.; Be-
letskaya, I. P. Izv. Akad. Nauk SSSR, Ser. Khim. 1985, 1647-1649.
(13) (a) Heinze, P. L.; Burton, D. J . J . Fluorine Chem. 1986, 31, 115-
119. (b) Heinze, P. L.; Burton, D. J . J . Org. Chem. 1988, 53, 2714-
2720.
(14) (a) Gillet, J . P.; Sauvetre, R.; Normant, J . F. Synthesis 1986,
538-543. (b) Gillet, J . P.; Sauvetre, R.; Normant, J . F. Synthesis 1986,
355-360.
(15) Tarrant, P.; J ohncock, P.; Savory, J . J . Org. Chem. 1963, 28,
839-843.
(18) (a) Coe, P. L. J . Fluorine Chem. 1999, 100, 45-52. (b) Banger,
K. K.; Brisdon, A. K.; Gupta, A. Chem. Commun. 1997, 139-140. (c)
Banger, K. K.; Banham, R. P.; Brisdon, A. K.; Cross, W. I.; Damant,
G.; Parsons, S.; Pritchard, R. G.; Sousa-Pedrares, A. J . Chem. Soc.,
Dalton Trans. 1999, 427-434.
(16) (a) Normant, J . F. J . Organomet. Chem. 1990, 19-34. (b)
Burton, D. J .; Yang, Z. Y.; Morken, P. A. Tetrahedron. 1994, 2993-
3063.
(17) (a) Burdon, J .; Coe, P. L.; Haslock, I. B.; Powell, R. L. Chem.
Commun. 1996, 49-50. (b) Burdon, J .; Coe, P. L.; Haslock, I. B.; Powell,
R. L. J . Fluorine Chem. 1999, 99, 127-131.
(19) Anilkumar, R.; Burton, D. J . Tetrahedron Lett. 2003, 44, 6661-
6664.
7084 J . Org. Chem., Vol. 69, No. 21, 2004

Synthesis of Trifluoroethenylzinc Reagent and 1,2,2-Trifluorostyrenes
SCHEME 3
TABLE 1. In Situ Rea ction s of HF C-134a w ith Va r iou s Alk yllith iu m Ba ses in th e P r esen ce of a Zin c Sa lt
HFC-134a,
equiv
base
(2 equiv)
zinc salt
(1 equiv)
temp,
°C
solvent/
cosolvent
% yield of
% yield of
trial
zinc reagenta
TFSb (1)
1
2
3
1.2
1.2
1.2
1.2
1.2
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
n-BuLi
n-BuLi
n-BuLi
t-BuLi
t-BuLi
t-BuLi
t-BuLi
n-BuLi
t-BuLi
t-BuLi
t-BuLi
t-BuLi
t-BuLi
ZnI2
ZnI2
ZnCl2
ZnI2
ZnCl2
ZnI2
ZnI2
ZnI2
ZnI2
ZnI2
-80
-26
-26
-80
-26
-80
-26
-26
-5
-26
-26
-26
-26
THF
THF
THF
THF
THF
THF
THF
THF
21
10
23
48
40
70
66
21
37
10
57
63
64
4
5c
6
7c
8
59
60
9c
10d
11
12
13
THF
THF/HMPA
THF/DMI
THF/DMPU
THF
ZnI2
ZnI2
ZnCl2‚TMEDA
a
b
Yield from ZnX2 based on 19F NMR analysis of the reaction mixture (vs PhCF3 as internal standard). Overall yield from ZnX2 based
on 19F NMR analysis. c Black decomposition products formed in this reaction. Violent reaction with large amount of black decomposition
d
products.
it undergoes decomposition. Table 1 summarizes the
reactions of HFC-134a with various alkyllithium bases
in the presence of a zinc salt. When such an in situ
reaction was performed with n-BuLi at -80 °C the major
reaction was the reaction of the n-BuLi with the zinc
halide to produce n-butylzinc halide and a poor yield of
the trifluoroethenylzinc reagent (Table 1, entry 1) was
detected. A significantly poorer yield of the zinc reagent
was observed when the reaction was performed at -26
°C, the boiling point of HFC-134a (Table 1, entry 2).
When zinc chloride was used as the zinc salt a slight
improvement in the yield was observed (Table 1, entry
3). It was assumed that more sterically hindered bases
such as s-BuLi or t-BuLi can more effectively metalate
HFC-134a in the presence of the zinc halide. So an in
situ reaction was performed where the metalation reac-
tion was carried out at -80 °C from a solution of HFC-
134a and zinc iodide with t-BuLi as base. But unfortu-
nately this reaction gave only a 48% yield of the zinc
reagent, indicating the partial reaction of zinc halide with
base (Table 1, entry 4). When the reaction was performed
at -26 °C with ZnCl2 a 40% yield of the zinc reagent was
detected (Table 1, entry 5). In another reaction the
amount of HFC-134a was increased 4-fold and the
metalation with t-BuLi was performed at -80 °C to
produce a reasonably good yield of zinc reagent (70%,
Table 1, entry 6). The increase in yield of the zinc reagent
was probably due to the preferential reaction of the base
with the large excess of HFC-134a in the medium. When
the same reaction was performed at -26 °C, a 66% yield
of the zinc reagent was observed along with black
decomposition products resulting from the decomposition
of trifluoroethenyllithium (Table 1, entry 7).
products with 37% yield of the zinc reagent (Table 1,
entry 9). HMPA was tried as a cosolvent along with THF
at -26 °C, but failed to give a clean reaction (Table 1,
entry 10). Cosolvents such as 1,3-dimethyl-3,4,5,6-per-
hydropyrimidin-2-one (DMPU) and 1,3-dimethylimida-
zolidin-2-one (DMI) were reported to be excellent solvents
for dehydrofluorination when used in conjunction with
THF.21 Based on this fact the metalation reaction was
performed with THF-DMI and THF-DMPU mixtures
to obtain 57% and 63% yield of the zinc reagent, respec-
tively (Table 1, entries 11 and 12). Even though the
reaction mixture looked much cleaner in these reactions,
there was no significant improvement in the yield of the
zinc reagent from the reaction where THF alone was
used. We then attempted a simultaneous addition strat-
egy where small portions of the base and electrophile
were successively added to the reaction mixture to avoid
the reaction of base with the electrophile. In fact such a
strategy had been shown to be successful to increase the
yield of the product at a relatively higher temperature,
where small aliquots of the base and electrophile were
added successively to the reaction vessel.15 But unfortu-
nately this method failed in our hands and extensive
decomposition of the trifluoroethenyllithium was noted
in this reaction. Alkali metal analogues of trifluoro-
ethenyllithium like trifluoroethenylsodium or trifluoro-
ethenylpotassium were also considered, but such species
were least studied in the literature except for the patent
literature and their stability seems to be questionable.22
Nonnucleophilic bases such as LDA, lithium-2,2,6,6-
tetramethyl-4-methoxy piperidide (4-OMe-LTMP), and
LHMDS were considered for effecting the metalation.
(20) (a) Anilkumar, R.; Burton, D. J . Tetrahedron Lett. 2002, 43,
2731-2733. (b) Stone, C.; Packham, T. J .; Burton, D. J .; Anilkumar,
R. U.S. Patent 6,653,515, 2003.
(21) Funabiki, K.; Ohtsuki, T.; Ishihara, T.; Yamanaka, H. J . Chem.
Soc., Perkin Trans. 1 1998, 2413-2423.
(22) Delavarenne, S. Y. U.S. Patent 3,751,492, 1973; Chem. Abstr.
79: P 91561d.
When n-BuLi was substituted for t-BuLi in this reac-
tion under similar reaction conditions a much lower yield
of the zinc reagent was detected (Table 1, entry 8).
Further increase in the temperature to -5 °C with t-BuLi
as base produced a large amount of decomposition
J . Org. Chem, Vol. 69, No. 21, 2004 7085

Raghavanpillai and Burton
TABLE 2. In Situ Rea ction s of HF C-134a w ith Va r iou s Lith iu m Am id e Ba ses in th e P r esen ce of a Zin c Sa lt
HFC-134a,
equiv
base
(2 equiv)
zinc salt
(1 equiv)
temp,
°C
solvent/
cosolvent
% yield of
% yield of
trial
the zinc reagenta
TFSb(1)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
4.0
4.0
4.0
4.0
1.5
1.5
1.5
1.5
1.3
1.2
1.2
1.2
1.2
1.2
4-OMe-LTMP
LHMDS
4-OMe-LTMP
LDA
LDA
LDA
LDA
LDA
LDA
LDA
ZnI2
ZnI2
ZnCl2‚TMEDA
ZnCl2‚TMEDA
ZnCl2‚TMEDA
ZnCl2
ZnCl2
ZnCl2
ZnCl2
ZnCl2
-26
THF
THF
THF
THF
THF
THF/TMEDA
THF
THF/TMEDA
THF/TMEDA
THF/TMEDA
THF
76
0
82
-26
-26
-26
-26
-26
-26
-10
0
75
79
71
48d
86 (5)c
84 (4)c
80 (9)c
70
79 (9)c
82 (6)c
78
76
81
73
60
67
70
70
22
0
15-20
0
0
LDA
LDA
LDA
LDA
ZnCl2
ZnCl2
ZnCl2
ZnCl2
71
73
77
79
THF
THF/iPr2NH
THF/2,2′-bipiridyl
a
b
Yield from ZnX2 based on 19F NMR analysis of the reaction mixture (vs PhCF3 as internal standard). Overall yield from ZnX2 based
on 19F NMR analysis. c Yields of the saturated zinc reagent (CF3CHFZnCl). Coupling reaction with C6H5Br (65 °C, 36 h).
d
Results of these experiments are summarized in Table
2. Reaction of HFC-134a with 4-OMe-LTMP, performed
in the presence of ZnI2 at -26 °C, produced 76% yield of
the zinc reagent (Table 2, entry 1). The metalation
reaction was then performed with LHMDS, but unfor-
tunately no zinc reagent formation was detected, prob-
ably due to the poor basicity of LHMDS (pKa ) 29.5)
compared to other lithium amide bases (Table 2, entry
2).23 Addition of 2 equiv of t-BuLi to the LHMDS reaction
mixture produced the zinc reagent in 63% yield and
confirmed the inefficiency of LHMDS to deprotonate
HFC-134a. We thought it was worthwhile to try a
reaction with completely anhydrous zinc chloride as the
zinc salts used herein are extremely hygroscopic even
though zinc iodide was generated just before the reaction
from zinc and iodine in THF. Zinc chloride forms a
crystalline complex with TMEDA, which is stable to air
and moisture.24 Also it was thought that the TMEDA
could act as an additive in this metalation reaction thus
facilitating the zinc reagent formation.25 A search for the
zinc reagent-TMEDA complexes revealed that dialkyl-
zinc compounds are capable of forming stable coordina-
tion complexes having well-defined stoichiometry with a
variety of oxygen, nitrogen, and phosphorus and arsenic
ligands.26 A chelate structure (tetracoordinated zinc) was
assumed for these 1:1 complexes with the sp3 hybridized
zinc atom. Highly unstable trifluoroisopropenylzinc re-
agent recently was generated in a solution of THF-
TMEDA medium, where the stability of this reagent was
attributed to the possible 1:1 complexation of the tri-
fluoroisopropenylzinc reagent with TMEDA.27 A meta-
lation reaction performed with the ZnCl2‚TMEDA com-
plex and t-BuLi at -26 °C produced a 64% yield of the
zinc reagent (Table 1, entry 13). The zinc reagent formed
was essentially mono (CF2dCFZnCl) with traces of bis
((CF2dCF)2Zn) reagent appearing as shoulders in the
upfield direction. We then performed this reaction using
4-OMe-LTMP. This reaction produced 82% yield of the
zinc reagent (Table 2, entry 3). The success of 4-OMe-
LTMP prompted us to consider a relatively inexpensive
base like lithiumdiisopropylamide (LDA) for effecting this
transformation. This reaction produced a clean reaction
mixture (yellowish rather than the usual dark brown)
with an 86% yield of the zinc reagent (Table 2, entry 4).
As a next step we reduced the concentration of HFC-134a
from 4 equiv to 1.5 equiv, and the reaction was performed
at -26 °C with LDA as base and the ZnCl2‚TMEDA
complex as the zinc salt. This reaction produced an 84%
yield of the zinc reagent (Table 2, entry 5). Another
consideration at this point was whether preformation of
the complex is required or TMEDA can be added to a
zinc chloride solution in THF. Thus, by using fresh solid
commercial zinc chloride, a reaction was performed
without preforming the complex in THF-TMEDA me-
dium, and resulted in an excellent yield of the zinc
reagent indicating preformation of complex is not re-
quired (Table 2, entry 6). Another noteworthy observation
in the TMEDA-mediated reaction was the formation of
traces of the saturated zinc reagent (∼10%) (CF3-
CHFZnCl) along with the trifluoroethenylzinc reagent,
which gradually transformed to the trifluoroethenylzinc
reagent. The presence of this species was rather surpris-
ing and is believed to be formed by the reaction of the
mono anion (CF3CHF-) generated from HFC-134a with
zinc halide before elimination of the fluoride (Scheme 4).
In fact, a trace amount of such a species (CF3CHFSnBu3)
was detected in the metalation reaction of HFC-134a with
LDA and Bu3SnCl.17a
(23) Fraser, R. R.; Mansour, S. T. J . Org. Chem. 1984, 49, 3442-
3443.
Evidence for the formation of CF3CHFZnCl was ob-
tained from the 19F NMR and 19F-1H decoupled spectra.
The 19F NMR spectra showed two distinct peaks at δ
-70.3 (3F, dd, 3J FH ) 15.0 Hz, 3J FF ) 15.0 Hz) and -245.1
(24) (a) Isobe, M.; Kondo, S.; Nagasawa, N.; Goto, T. Chem. Lett.
1977, 679-682. (b) Watson, R. A.; Kjonass, R. A. Tetrahedron Lett.
1986, 27, 1437-1440.
(25) Collum, D. B. Acc. Chem. Res. 1992, 25, 448-454.
(26) (a) Notels, J . G.; Van Den Hurk, J . W. G. J . Organomet. Chem.
1964, 1, 377-383. (b) Notels, J . G.; Van Den Hurk, J . W. G. J .
Organomet. Chem. 1965, 3, 222-228. (c) Inoque, S.; Yamada, T. J .
Organomet. Chem. 1970, 25, 1-9.
2
3
(1F, dq, J FH ) 48.0, J FF ) 16.0 Hz). The 19F-1H
decoupled spectra showed the collapse of the dd at -70.3
to a doublet (3J FF ) 15.0 Hz) and the dq at -245.1 to a
(27) J iang, B.; Xu, Y. J . Org. Chem. 1991, 56, 7336-7340.
7086 J . Org. Chem., Vol. 69, No. 21, 2004

Synthesis of Trifluoroethenylzinc Reagent and 1,2,2-Trifluorostyrenes
SCHEME 4
SCHEME 5
at -26 °C and higher temperatures (0 and 20 °C) also
produced a reasonably good yield of the trifluoroethe-
nylzinc reagent (>75%) (Table 2, entry 13). Reactions
performed with 2,2′-bipyridyl at different temperatures
(-80, -26, 0, 20 °C) produced a good yield of the
trifluoroethenylzinc reagent (Table 2, entry 14). Yields
of the zinc reagent dropped from 92% to 72% when the
temperatures were increased from -80 to 20 °C. There
was not much loss in yield of the zinc reagent when the
reaction was performed at 0 or 20 °C. Change of cosolvent
to triethylamine did not significantly improve the yield
of the trifluoroethenylzinc reagent.
quartet (3J FF ) 15.0 Hz). Also, the saturated zinc reagent
was generated in much higher ratio (40%) when the
metalation reaction was performed at lower temperatures
(-80 °C) in THF-TMEDA medium. Stepwise hydrolysis
of this zinc reagent mixture with a calculated amount
(equivalent to the amount of trifluoroethenylzinc reagent)
of concentrated HCl preferentially hydrolyzed the trif-
luoroethenylzinc reagent to trifluoroethylene (CF2dCFH),
which was pumped out from the reaction mixture leaving
the saturated zinc reagent intact. The residual saturated
zinc reagent liberated CF3CH2F when treated with excess
concentrated HCl. The CF3CH2F thus generated was
isolated and confirmed the presence of the saturated zinc
reagent in this metalation reaction. Also quenching of
the saturated zinc reagent with deuterated solvents such
as D2O, CD3CO2D, or DCl produced CF3CHFD thus
confirming the formation of the saturated zinc reagent.
Treatment of the zinc reagent mixture with an excess of
iodine at 0 °C produced only CF2dCFI leaving the
saturated zinc reagent intact. Formation of CF3CH2I was
not detected. But upon warming the reaction mixture to
50 °C, decomposition of the saturated zinc reagent was
noted. Palladium(0)-catalyzed coupling reactions per-
formed with zinc reagent mixtures produced a quantita-
tive yield of the 1,2,2-trifluorostyrene (derived from
trifluoroethenylzinc reagent) and again decomposition of
the saturated zinc reagent was noticed under this condi-
tion. To understand the role of TMEDA in this metalation
reaction, a control experiment was performed at -26 °C
without the addition of a cosolvent, TMEDA, to obtain a
70% yield of the trifluoroethenylzinc reagent (Table 2,
entry 7). This experiment suggested that TMEDA plays
a role for obtaining a better yield of the zinc reagent by
one or more of the following reasons: stabilizing the
trifluoroethenyllithium at higher temperature or increas-
ing the reactivity of zinc halide toward trifluoroethenyl-
lithium or reducing the reactivity of the base toward the
zinc halide.
The success of the transmetalation reaction in TMEDA-
THF at -26 °C prompted us to try this reaction at higher
temperatures. The reaction performed at -10 and 0 °C
gave good yield (>80%) of the trifluoroethenylzinc re-
agent (Table 2, entries 8 and 9). When the reaction was
performed at room temperature (22 °C), 78% yield of the
trifluoroethenylzinc reagent with a clean reaction mix-
ture (Table 2, entry 10) was produced. Reactions without
TMEDA at 0 and 20 °C also produced reasonably good
yields of the zinc reagent (Table 2, entries 11 and 12),
which could be due to the presence of diisopropylamine
liberated in the medium acting as an amine cosolvent
instead of TMEDA. We then tried other ligands similar
to TMEDA which can complex with ZnCl2: 2,2′-bipyridyl,
diisopropylamine, and triethylamine. Reactions per-
formed with an excess of diisopropylamine as cosolvent
St a b ilit y of [CF 2dCF Li] a n d Na t u r e of t h e Tr i-
flu or oeth en ylzin c Rea gen t. We next investigated the
stability of the trifluoroethenyllithium in TMEDA-THF
medium and also the nature of the zinc reagent formed
in this metalation reaction. The excellent formation of
the zinc reagent at temperatures close to room temper-
ature made us believe that the intermediate trifluoro-
ethenyllithium species is stable in the TMEDA medium.
To test this hypothesis we have generated trifluoro-
ethenyllithium by the metalation of HFC-134a using LDA
at -78 °C in THF-TMEDA medium and the clear
solution obtained was slowly warmed to room tempera-
ture. The color of the solution slowly turned slightly
brown when the temperature of the reaction mixture
reached -25 °C and black solid decomposition products
formed at -20 to -15 °C, and addition of a solution of
ZnCl2 in THF to this medium produced only 5% of the
zinc reagent with traces of reduced product. In another
reaction the clear solution of trifluoroethenyllithium
generated in THF-TMEDA at -78 °C was warmed to
-30 °C (no significant color change noticed) and slowly
transmetalated with a solution of ZnCl2 in THF. 19F NMR
analysis of this mixture showed an 86% yield of the
trifluoroethenylzinc reagent (Scheme 5). This experiment
demonstrated that the trifluoroethenyllithium generated
is stable even at -30 °C in the THF-TMEDA medium.
The success of this experiment prompted us to generate
the trifluoroethenyllithium at -30 °C and then trans-
metalate it with zinc chloride at that temperature in the
THF-TMEDA medium. This experiment when per-
formed produced a clear solution of the trifluoroethenyl-
lithium and the trifluoroethenylzinc reagent in 81% yield
(Scheme 5). A similar reaction performed without TME-
DA showed much less stability for the trifluoroethenyl-
lithium as the decomposition was noticed at -45 °C with
formation of a black reaction mixture even in the pres-
ence of diisopropylamine in the medium. But the thermal
stability expressed by trifluoroethenyllithium in this
reaction (THF/iPr2NH) was better than that generated
in THF medium by metalation with use of alkyllithium
bases (THF solutions of trifluoroethenyllithium are known
to decompose at temperatures higher than -78 °C).16 We
have cross checked the thermal stability of trifluoro-
ethenyllithium in THF by performing the metalation of
HFC-134a with n-BuLi at -80 °C in THF medium and
J . Org. Chem, Vol. 69, No. 21, 2004 7087

Raghavanpillai and Burton
F IGURE 1. 19F NMR spectrum of the bis-trifluoroethenylzinc reagent in THF-TMEDA medium.
F IGURE 2. 19F NMR spectrum of the mono- and bis-trifluoroethenylzinc reagents in THF-TMEDA (mono/bis ) 75:25) medium.
warming the resulting trifluoroethenyllithium solution
to higher temperatures. At -70 °C the clear solution
turned to black and at -50 °C complete decomposition
was the result with no trifluoroethenylzinc reagent
formation upon transmetalation with zinc chloride. In
another experiment the trifluoroethenyllithium gener-
ated at -80 °C was warmed to -60 °C and when the dark
reaction mixture was quenched at -60 to -55 °C
produced 78% yield of the zinc reagent, which shows
there is trifluoroethenyllithium present even at -55 °C.
On the basis of these experiments we have concluded that
amines in the medium enhance stability for the trifluo-
roethenyllithium, especially TMEDA, and the decomposi-
tion temperature of trifluoroethenyllithium in TMEDA-
THF solution lies somewhere around -25 °C.
We have also performed experiments to test the nature
of the zinc reagents formed in this metalation reaction.
During our experiments (Table 2) it was noticed that the
zinc reagent was obtained as a mixture of mono and bis
species in varying ratio from 60:40 to 85:15. The 19F
chemical shifts of the mono and bis zinc reagent varied
slightly depending on the cosolvent (THF or THF/
TMEDA or THF/diisopropylamine, THF/2,2′-bipyridyl)
and the counterion (Cl, Br, I). The zinc reagent generated
in THF/diisopropylamine medium showed spectral pat-
terns corresponding to both mono and bis zinc reagents
complexed to THF and diisopropylamine with a slight
difference in the chemical shift in the upfield direction.
Addition of TMEDA to the medium produced one set of
peaks resulting from the preferential complexation of the
mono and bis zinc reagent to TMEDA over diisopropyl-
amine or THF. An interesting complex splitting pattern
was noticed for the 19F NMR spectra of the bis zinc
reagent generated in the TMEDA medium. The complex
splitting pattern observed for the bis reagent in TMEDA
medium was absent in the case of both the mono and bis
zinc reagents generated in THF/ iPr2NH medium and for
the mono zinc reagent in TMEDA. To unequivocally
confirm the mono and bis zinc reagent assignments, we
have performed a series of experiments (Scheme 6). At
first we attempted to generate only the bis zinc reagent
by using 0.5 equiv of zinc chloride rather than the usual
1 equiv. To our joy this experiment exclusively produced
only the bis zinc reagent (Figure 1) whose chemical shifts
and splitting pattern matched exactly for the minor
component of the usual reaction, thus demonstrating that
the major zinc reagent in the usual reaction is the mono
reagent. We have added a slight excess of ZnCl2 (1.0
equiv) to this reaction mixture to shift the equilibrium
(Scheme 6) to the mono side and obtained a 75:25 mixture
of mono and bis zinc reagents (Figure 2) proving that our
assignments of mono and bis zinc reagents are correct.
In another experiment we have increased the concentra-
tion of ZnCl2 from 0.5 to 0.75 equiv and this reaction
produced a 40:60 mixture of mono and bis zinc reagent
and the ratio changed to 75:25 when excess ZnCl2 was
7088 J . Org. Chem., Vol. 69, No. 21, 2004

Synthesis of Trifluoroethenylzinc Reagent and 1,2,2-Trifluorostyrenes
F IGURE 3. Mono- and bis-trifluoroethenylzinc reagents complexed to TMEDA and their 19F NMR chemical shifts.
SCHEME 6
SCHEME 7
SCHEME 8
the same RF and close boiling points) we elected to
perform the coupling reaction with iodide as the limiting
reagent. When the reaction was performed with a 1:0.8
ratio of zinc reagent and aryl iodide in THF-TMEDA
medium, the corresponding 4-fluoro-substituted styrene
2 (87% by 19F NMR) was produced along with a small
amount of an addition-elimination product (0.5:1 cis/
trans, p-FC6H4CFdCFOBu). But the coupling reaction
in the absence of TMEDA (from the zinc reagent gener-
ated in THF medium) produced exclusively (99% by 19F
NMR) the styrene 2 with no addition-elimination prod-
uct formation (Table 3). Isolation of the product by
column chromatography produced 64% yield of pure 2.28
Even though the presence of TMEDA was important for
obtaining a better yield of the trifluoroethenylzinc re-
agent, formation of side products during the Pd(0)-
catalyzed coupling process and the additional cost of
another reagent and its removal from the reaction
mixture were disadvantageous.
Finally the best conditions for the generation of the
trifluoroethenylzinc reagent and for the coupling reaction
were chosen as follows: addition of LDA (50.0 mmol, ∼1.0
M) to a medium of zinc chloride (25.0 mmol) and HFC-
134a (30.0 mmol) in THF (15.0 mL) and heating of the
concentrated solution of zinc reagent in THF with the
aryl iodide (1:0.8 ratio) with 1.5 mol % of Pd(PPh3)4.
When iodobenzene was used for the coupling reaction
with the trifluoroethenylzinc reagent, a 95% yield (19F
NMR) of TFS (1) was produced. Isolation of the product
by column chromatography resulted in a 69% yield of
pure 1.6
added to this reaction mixture. It was not possible to
generate exclusively the mono zinc reagent even with a
large excess of ZnCl2 (3.0 equiv). The Schlenk equilibrium
for the TMEDA complexes of mono and bis zinc reagents
is shown in Scheme 7.
The 19F NMR chemical shifts for the TMEDA com-
plexes of mono and bis trifluoroethenylzinc reagents are
represented in Figure 3.
We have also applied the metalation strategy for the
synthesis of the trifluoroethenyltin reagent (CF2d
CFSnBu3). Metalation of HFC-134a in the presence of
Bu3SnCl produced the trifluroethenyltin reagent in a 69%
NMR yield. From this reaction mixture trifluoroethenyl-
tin was isolated in 64% yield by column chromatography
(Scheme 8).
Cou p lin g Rea ction of Tr iflu or oeth en ylzin c Re-
a gen t w ith Ar yl iod id es. After standardizing the
conditions of the metalation reaction at 15-20 °C in the
THF-TMEDA medium, we have attempted the pal-
ladium-catalyzed cross-coupling reaction of the zinc
reagent with aryl iodides. In fact during our optimization
experiments in most cases the coupling reactions were
performed with Pd(PPh3)4 and aryl iodide resulted in a
quantitative yield of the TFS (1) (Tables 1 and 2). To
standardize conditions for the coupling reaction, 1-fluoro-
4-iodobenzene was chosen, since it can be easily moni-
tored through 19F NMR analysis of the reaction mixture.
Reactions were performed with a 1:1 and 1:0.9 zinc
reagent:iodide ratio produced a reaction mixture with
traces of unreacted iodide. Since the unreacted iodide
cannot be easily removed from the product (both have
We then carried out this synthesis for a series of aryl
iodides with various substituents in the aromatic ring
(Table 3). Generally the reaction was complete when
(28) Sergeev, N. M.; Shapet’ko, N. N.; Timofeyuk, G. V. Zh. Strukt.
Khim. 1965, 6, 300-302 (Engl. Transl. pp 276-278).
J . Org. Chem, Vol. 69, No. 21, 2004 7089

Raghavanpillai and Burton
TABLE 3. Syn th esis of 1,2,2-Tr iflu or ostyr en es
henylzinc reagent at 60 °C for 1 h to produce the
corresponding styrenes 10 and 11 in 85% and 82%
isolated yields, respectively.13b,29 Reaction with 2-iodo-
isopropylbenzene was performed to test the effect of the
bulky isopropyl group at the ortho position for this cross-
coupling reaction. This reaction proceeded smoothly
under normal coupling reaction conditions to produce the
corresponding styrene 12 in 86% yield.13b We then
compared the reactivity of other aryl halides such as
bromides and chlorides in this coupling reaction. Thus,
a reaction of 1-chloro-3-iodobenzene was treated with
trifluoroethenylzinc reagent and palladium under normal
coupling reaction conditions and complete conversion of
the iodide to styrene 13 was noted keeping the ring
chlorine intact. The isolated yield of 13 was 78%.32
1-Chloro-4-iodobenzene was also tried and resulted in the
corresponding styrene 14 in 82% yield under similar
conditions.13b The coupling reaction of bromobenzene with
the trifluoroethenylzinc reagent was also attempted,
where the bromobenzene was heated with the zinc
reagent at 65 °C for 36 h to produce a 48% overall yield
(19F NMR) of 1 (Table 2, entry 6). Reaction of 1-bromo-
4-iodobenzene with the trifluoroethenylzinc reagent pro-
duced the corresponding bromo-substituted mono styrene
15 along with traces of the bis styrene 16 (mono/bis
1:0.03) when treated with palladium catalyst at room
temperature for 18 h.20a The isolated yield of the product
was 75%. The bis styrene 16 was produced exclusively
from 1,4-diiodobenzene by treating it with the zinc
reagent and palladium catalyst at room temperature for
12 h.13b The isolated yield of 16 was 71%. 1-Iodonaph-
thalene coupled with the trifluoroethenylzinc reagent
under normal coupling reaction conditions to produce the
corresponding styrene 17 in 83% isolated yield.33 The
heterocyclic iodide, 2-iodothiophene, reacted with the
trifluoroethenylzinc reagent within 1 h under normal
coupling reaction conditions to produce a mixture of
products from which the product styrene 18 was isolated
in 59% yield.13a
product
(1-18)
temp, °C;
time, h
NMR
yield
isolated
Ar
yield,a
%
C6H5-
1
2
3
65; 3
65; 4
65; 2
65; 2
60; 1
rt; 15
65; 1.5
65; 1
65; 48
60; 1
65; 1
65; 2
60; 2
60; 2
rt; 18
rt; 12
60; 2
60; 1
99
95
99
98
50
84
86
95
93
94
99
96
97
96
95
90
98
84
69
64
63
74
37
61
66
67
61
82
85
86
78
82
75
71
83
59
p-FC6H4-
m-FC6H4-
o-FC6H4-
4
p-NO2C6H4-
m-NO2C6H4-
p-CF3C6H4-
m-CF3C6H4-
o-CF3C6H4-
p-OMeC6H4-
m-OMeC6H4-
o-(CH3)2CHC6H4-
m-ClC6H4-
p-ClC6H4-
5b
6
7
8
9
10
11
12
13
14
15c
16
17
18d
p-BrC6H4-
p-IC6H4-
1-naphthyl
2-thienyl
a
Yield of styrene after column chromatography of the reaction
mixture; all products gave satisfactory 19F, 1H, 13C NMR (>95%
b
purity) and GC-MS data. A mixture of unidentified products
formed in this reaction. c No bis-styrene was detected after 12 h
at room temperature; ∼3% of bis-styrene was formed after 24 h
d
at room temperature. A better NMR yield (95%) was noticed with
stirring at rt for 24 h.
heated at 65 °C for 1-3 h for most of the substrates. Most
of these coupling reactions were also feasible even at
room temperature with stirring for a prolonged time.
Iodides with electron withdrawing groups in the benzene
ring coupled smoothly at 65 °C in 2-4 h to produce the
corresponding styrenes in reasonably good yield. From
1-fluoro-3-iodobenzene the corresponding styrene 3 was
isolated in 63% yield.29 1-Fluoro-2-iodobenzene was also
converted to the corresponding styrene 4 in 74% yield.30
The coupling reaction with 1-iodo-4-nitrobenzene pro-
duced a complex red reaction mixture from which the
corresponding styrene 5 was isolated in 37% yield.11a The
coupling reaction with 1-iodo-3-nitrobenzene performed
at room temperature for 15 h produced the corresponding
styrene 6 in 61% isolated yield.13b
4-Iodobenzotrifluoride was transformed to the corre-
sponding styrene 7 in 66% yield when heated with
trifluoroethenylzinc reagent and Pd(PPh3)4 at 65 °C for
1 h.31 Similarly from 3-iodobenzotrifluoride, the product
styrene 8 was isolated in 67% yield.13a Reaction of
2-iodobenzotrifluoride with trifluoroethenylzinc reagent
was sluggish under the usual reaction conditions and the
complete conversion was observed when the reaction
mixture was heated at 65 °C for 48 h with a slight excess
of the palladium catalyst (2.0 mol %). Column chromato-
graphic isolation produced the corresponding styrene 9
in 61% yield.13b Iodides with electron donating groups
reacted very smoothly under the coupling reaction condi-
tions to produce the corresponding styrenes in excellent
yield. 3- and 4-iodoanisoles reacted with the trifluoroet-
Con clu sion s
In summary, a novel strategy was developed for the
formation of the trifluoroethenylzinc reagent from the
readily available, economically viable, halocarbon HFC-
134a. Operating this methodology at 0 °C or at room
temperature was a challenge due to the potential insta-
bility of the trifluoroethenyllithium. By systematic stan-
dardization of the metalation experiments by manipu-
lating solvent, cosolvent, temperature, zinc salt, and the
base, trifluoroethenylzinc reagent generation was achieved
in good yields near room temperature. The palladium-
catalyzed coupling reaction of the trifluoroethenylzinc
reagent with aryl iodides was carried out under mild
conditions to produce TFS and substituted trifluoro-
styrenes in essentially quantitative yields. Trifluoro-
ethenyllithium showed exceptional thermal stability in
THF-TMEDA medium. Experimental evidence for the
mono anion of HFC-134a was obtained by the trapping
(32) Stepanov, M. V.; Panov, E. M.; Kocheshkov, K. A. Izv. Akad.
Nauk SSSR, Ser. Khim. 1975, 11, 2544-2547 (Engl. Transl. pp 2430-
2433).
(33) Kazennnikova, G. V.; Talalaeva, T. V.; Zimin, A. V.; Simonov,
A. P.; Kocheshkov, K. A. Izv. Akad. Nauk SSSR, Ser. Khim. 1961, 835-
838 (Engl. Transl. pp 772-774).
(29) J i, G.; J iang, X.; Zhang, Y.; Yuan, S.; Yu, C.; Shi, W. J . Phys.
Org. Chem. 1990, 3, 643-650.
(30) Simmons, H. E. J . Am. Chem. Soc. 1961, 83, 1657-1664.
(31) J iang, X. K.; J i, G. Z.; Wang, D. Z. J . Phys. Org. Chem. 1995,
8, 143-148.
7090 J . Org. Chem., Vol. 69, No. 21, 2004

Synthesis of Trifluoroethenylzinc Reagent and 1,2,2-Trifluorostyrenes
Gen er a l P r oced u r e for th e P r ep a r a tion of 1,2,2-Tr i-
of the mono anion with zinc halide in TMEDA medium.
The mono and bis nature of the zinc reagent was
unequivocally demonstrated by complexation experi-
ments with TMEDA. The in situ metalation strategy was
successfully applied for the synthesis of the trifluoro-
ethenyltin reagent (CF2dCFSnBu3) by performing the
metalation in the presence of Bu3SnCl.
flu or ostyr en es. C6H5CF dCF 2 (1): The zinc reagent was
concentrated to about half its volume (40.0 mL; 17.5 mmol)
then 2.85 g (14.0 mmol) of iodobenzene and 0.28 g (1.5 mol %)
of Pd(PPh3)4 were added to the solution of the zinc reagent.
The reaction mixture was heated at 65 °C for 3 h, and complete
conversion of the zinc reagent to TFS was detected (99% by
19F NMR analysis). The mixture was cooled and triturated
several times with pentane, and the solvent removed by careful
rotoevaporation (the distillate collected in the receiver showed
traces of TFS). Silica gel column chromatography (elution with
pentane) gave 1.52 g (9.6 mmol, 69%) of pure C6H5CFdCF2
as a colorless liquid. The spectroscopic data were in agreement
with a sample prepared previously in this laboratory.13b
Exp er im en ta l Section
Gen er a l P r oced u r e for t h e P r ep a r a t ion of t h e Tr i-
flu or oeth en ylzin c Rea gen t fr om HF C-134a . A 250-mL
three-necked flask fitted with a dry ice/2-propanol condenser,
septum, and low-temperature thermometer was charged with
anhydrous ZnCl2 (3.42 g, 25.0 mmol) and THF (15.0 mL) under
a N2 atmosphere. The suspension was cooled to 15 °C and
HFC-134a (2.5 mL, 30.0 mmol) was condensed into the slurry.
Then an LDA solution [generated from diisopropylamine (7
mL, 50.0 mmol) and n-BuLi (20.0 mL, 2.5 M, 50.0 mmol) in
THF (25.0 mL) at 0 °C] solution was slowly added (35 min)
through a cannula to the HFC-134a/ZnCl2 slurry while keeping
the temperature at 15-20 °C (the tip of the cannula was
dipped into the THF to avoid decomposition of the trifluoro-
ethenyllithium, formed by the reaction of gaseous HFC-134a
with LDA, at the tip). The pale yellow reaction mixture was
stirred for 1 h and allowed to warm to room temperature. The
19F NMR analysis of the zinc reagent indicated a 73% (18.3
mmol) yield.
Ack n ow led gm en t. The authors greatly acknowl-
edge Dr. Charles Stone for insight into this project and
thank Ballard Power Systems Inc. BC, Canada and NSF
for financial support.
Su p p or tin g In for m a tion Ava ila ble: Experimental and
characterization data for all the 1,2,2-trifluorostyrenes (1-
18) prepared by this methodology. This material is available
free of charge via the Internet at http://pubs.acs.org.
J O049179C
J . Org. Chem, Vol. 69, No. 21, 2004 7091