Coupling routes to hexafluoro-1,3-butadiene, substituted-1,3-fluorine-containing butadienes and fluorinated polyenes

Article abstract of DOI:10.1016/j.jfluchem.2007.11.004

Hexafluoro-1,3-butadiene was readily prepared via a variety of self-coupling processes, such as Cu(0) mediated self-coupling of iodotrifluoroethene, Pd(0) catalyzed coupling of iodotrifluoroethene with the trifluorovinylzinc reagent, and CuBr₂ mediated coupling of the trifluorovinylzinc reagent. Perfluoro-2,3-dimethyl-1,3-butadiene was readily synthesized by the reaction of pentafluoropropenyl-2-zinc reagent with either CuBr₂ or FeCl₃. Alternatively, perfluoro-2,3-dimethyl-1,3-butadiene was prepared by oxidation of the pentafluoropropenyl-2-copper reagent with dioxygen. Cu(0) mediated coupling of an (E)-substituted α,β-difluoro-β-iodostyrene provided the first useful route to a (Z)(Z)-1,4-diaryl-1,3-tetrafluorobutadiene. Extension of the Cu(0) mediated coupling methodology to a perfluorodienyl iodide demonstrated a useful stereospecific route to perfluoropolyenes.

Full text of DOI:10.1016/j.jfluchem.2007.11.004

Available online at www.sciencedirect.com
Journal of Fluorine Chemistry 129 (2008) 435–442
www.elsevier.com/locate/fluor
Coupling routes to hexafluoro-1,3-butadiene, substituted-1,
3-fluorine-containing butadienes and fluorinated polyenes
*
Donald J. Burton , Steven W. Hansen, Peter A. Morken,
Kathryn J. MacNeil, Charles R. Davis, Ling Xue
Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA
Received 26 September 2007; received in revised form 2 November 2007; accepted 5 November 2007
Available online 13 November 2007
Abstract
Hexafluoro-1,3-butadiene was readily prepared via a variety of self-coupling processes, such as Cu(0) mediated self-coupling of iodotri-
fluoroethene, Pd(0) catalyzed coupling of iodotrifluoroethene with the trifluorovinylzinc reagent, and CuBr2 mediated coupling of the
trifluorovinylzinc reagent. Perfluoro-2,3-dimethyl-1,3-butadiene was readily synthesized by the reaction of pentafluoropropenyl-2-zinc reagent
with either CuBr2 or FeCl3. Alternatively, perfluoro-2,3-dimethyl-1,3-butadiene was prepared by oxidation of the pentafluoropropenyl-2-copper
reagent with dioxygen. Cu(0) mediated coupling of an (E)-substituted a,b-difluoro-b-iodostyrene provided the first useful route to a (Z)(Z)-1,4-
diaryl-1,3-tetrafluorobutadiene. Extension of the Cu(0) mediated coupling methodology to a perfluorodienyl iodide demonstrated a useful
stereospecific route to perfluoropolyenes.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Hexafluoro-1,3-butadiene; Perfluoro-2,3-dimethyl-1,3-butadiene; (Z)(Z)-1,4-aryl-1,3-tetafluorobutadiene; (2E)(4E)(6E)(8E)-perfluorodecatetraene;
Trifluorovinylzinc reagent; Pentafluoropropenyl-2-zinc reagent; Pentafluoropropenyl-2-copper reagent
1. Introduction
Two perfluorocyclic vinyl bromides, 2-bromononafluoro-
cyclohexene and 1-bromoheptafluorocyclopentene also were
reported to undergo reductive coupling with copper–bronze.
Subsequently in 1978, Yagupol’skii and co-workers demon-
strated that substituted (Z)-1-iodo-a,b-difluorostyrenes could
be prepared stereospecifically by heating the vinyl iodide with
copper in anhydrous DMFA [2] (Eq. (2)). Reiss and co-workers
prepared a series of 1,2,3,4-
Self-coupling of polyfluorinated vinyl iodides with copper–
bronze was first reported by Tatlow and co-workers in 1966 [1]
(Eq. (1).
Cu
FClC ¼ CFI ꢀ! FClC ¼ CFCF ¼ CFCl
(1)
145 ꢁC 24 h
mixture of three isomers
(2)
tetrakis (perfluoroalkyl)-1,3-butadienes via copper coupling of
bis 1,2(perfluoroalkyl)-iodoethenes [3] (Eq. (3)).
* Corresponding author. Tel.: +1 319 335 1363; fax: +1 319 335 1270.
E-mail address: donald-burton@uiowa.edu (D.J. Burton).
0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2007.11.004

436
D.J. Burton et al. / Journal of Fluorine Chemistry 129 (2008) 435–442
2. Results and discussion
(3)
2.1. Preparation of hexafluoro-1,3-butadiene
Hexafluoro-1,3-butadiene (1) is an important industrial gas
and has been of interest to fluorine chemists for several decades.
One of the principal synthetic routes to 1 is via the
dehalogenation of 1,2,3,4-tetrahalohexafluorobutanes. The
classical route to the butane precursor was initially reported
by Haszeldine, starting from chlorotrifluoroethene, as outlined
below [8] (Eq. (8)). Similar coupling and dehalogenation were
also reported by Henne and Postelneck [9]. The
Organometallic reagents have also been employed in a
variety of self-coupling processes. For example, Norris and
Finnegan prepared 1,1,1,6,6,6-hexafluorohexa-2,4-diyne via
oxidative coupling of the 3,3,3-trifluoropropyne derivative,
CF3CBBCZnX, with cupric chloride [4] (Eq. (4)). Similarly,
Cairncross and Sheppard, in their pioneering work on the
preparation of pentafluorophenylcopper (I), reported that
C6F5Cu is oxidized cleanly at 0 8C with CuBr2 to
Hg
ICl
CuCl2
Zn
CF3CCl ¼ CCl2ꢀ! ½CF3CBB CZnXꢂꢀ! CF3CBB CꢀCBB CCF3
F2C ¼ CFClꢀ! CF2ClCFClI ꢀ! CF2ClCFClCFClCF2Cl
Zn
hv sealed tube
97%
71-82%
DMF
DMF
46%
ꢀ! F2C ¼ CFCF ¼ CF2
(8)
(4)
EtOH 98%
1
perfluoro biphenyl [5] (Eq. (5)). Similarly, Miller reported that
perfluoro-1-methyl-
low cost of the alkene precursor is an attractive feature of this
method. Other workers have approached the requisite precursor
in other ways. For example, Dedek and Chvatal prepared 1,4-
dibromo-2,3-dichlorohexafluorobutane via photochemical
addition of 1,2-dibromo-1-chlorotrifluoroethane to chlorotri-
fluoroethene [9]; dehalogenation gave 1 [10]. However, the
photochemical addition process gave the butane precursor in
only modest yield (38%), thus the overall yield of 1 is not high.
Haszeldine also prepared the requisite tetrahalohexafluorobu-
tane via a multi-step route from chlorotrifluoroethene via a
cyclobutene intermediate [11] (Eq. (9)).
0 ꢁ
C
C6F5Cu þ CuBr2ꢀ! C6F5ꢀC6F5
(5)
propenylsilver reacted with cupric bromide in CH3CN to
produce the corresponding diene [6]
(6)
(9)
(Eq. (6)). More recently work from our laboratory by
Blumenthal has shown that substituted 1,2-difluorovinylstan-
nanes with anhydrous Cu(OAc)2 in DMF, under an oxygen
atmosphere, at room temperature stereospecifically give the
corresponding symmetrical 1,3-dienes in good to excellent
yield [7] (Eq. (7)). The corresponding cis-vinyl stannane gave
the cis, cis-diene. This
Thermal decomposition of sodium perfluoroadipate has also
been utilized as a route to 1 [12]. However, the low yield (30%)
has limited the application of this process.
In our initial work to prepare trifluorovinylcopper from
iodotrifluoroethene (2), Hansen discovered that direct insertion
of Cu(0) into the carbon–iodine bond did not produce a stable
trifluorovinylcopper reagent [13]. Instead, as found by Tatlow
and Yagupol’skii (see above) copper mediated coupling of the
vinyl iodide occurred to give the symmetrical diene [13–17], 1
(Eq. (10)).
(7)
D
2F2C ¼ CFI þCuð0Þꢀ!1 þ 2CuI
(10)
DMF
2
Similarly (Z)-CF3CF CFI gave only the (E)(E)-homodimer
on reaction with copper–bronze in DMF [13]. Hansen
speculated that the trifluorovinylcopper reagent was most
reaction was proposed to proceed mechanistically via organo-
copper intermediates.

D.J. Burton et al. / Journal of Fluorine Chemistry 129 (2008) 435–442
437
likely formed but reacted rapidly with 2 to give 1 (Eq. (11)).
Indeed, when trifluorovinylcopper
Success was achieved by simultaneous addition of the
DMF
2
(15)
2 þ 2Cuð0Þꢀ!CuI þ ½F2C ¼ CFCuꢂꢀ!1
(11)
D
(prepared by metathesis of F2C CFZnBr with Cu(I)Br) was
treated with 2 at room temperature, 1 was formed in 63% yield
[18]. For this route to be a useful approach to 1, a practical
method to 2 must be available. The literature method for the
preparation of 2 was first reported by Park et al. [19], as
outlined below (Eq. (12)). Hansen demonstrated that 2 could
be more
vinylzinc reagent and CuBr2 at lower temperature (ꢀ25 8C)
(Eq. (15)). This simultaneous addition permitted better tem-
perature control and condensation of 1 [34] (Eq. (15)). The
small amount of F2C CFBr formed could be due to
some residual olefin that was not removed by degassing of
the trifluorovinylzinc reagent solution, but more likely is due to
the known halogenation ability of Cu(I) halides [36,37].
ICl
ꢀ!
F2C ¼ CFH
CF2ClCFHI
72% conversion
autogenous pressure
2.2. Preparation of perfluoro-2,3-dimethyl-1,3-butadiene
powdered
ꢀꢀꢀꢀꢀ!
2
(12)
KOH mineral oil 95 ꢁC
76% conversion
Perfluoro-2,3-dimethyl-1,3-butadiene (3) has been prepared
by pyrolysis (300–350 8C) of perfluoro-2-enylsilver in 56%
yield [38], by pyrolysis (300 8C) of 1,3-bis-(trifluoromethyl)-
2,2,4,4-tetrafluorobicyclobutane [39] and by fragmentation of
C2F5(CF3)C C(CF3)C2F5 (Pt/5308–700 8C) [40]. Low yields,
cyclization by-products and the use of toxic or expensive
reagents plagued these previous reports. In a preliminary report,
Morken described the preparation of 2,2-dibromohexafluor-
opropane and its facile conversion to the perfluoropropenyl-2-
zinc reagent (4) [33,41]. He found that 4 could be readily
converted to 3 via reaction with either CuBr2 or FeCl3
readily prepared via quenching of the trifluorovinylzinc reagent
[20–25] with iodine [20].
Raghavenpillai also discovered that quenching the trifluoro-
vinylzinc reagent (prepared via metallation of CF3CH2F) with
iodine also gave 2 in 61% yield [26]. A large-scale procedure
for the preparation of 2 from F2C CFBr has recently been
published [27] (Eq. (13)).
(13)
(16)
An alternative, mild pathway to 1 mimics the route that we
developed for the preparation of (E)- and (Z)-perfluoro-1,3-
pentadienes [28–30]. Thus, the palladium catalyzed coupling of
the trifluorovinylzinc reagent with 2 readily provides 1 [31]
(Eq. (14)).
[33] (Eq. (16)). This route provides a convenient useful entry to
this reactive diene under mild conditions [42]. Other workers
have also described the oxidation of organocopper reagents [5]
or copper (I) ate complexes with dioxygen [43]. Similarly,
pyrolysis of organocopper reagents readily yield homodimers
[5,44]. Thus, we investigated the reaction of the pentafluor-
opropenyl-2-copper reagent with dioxygen at room tempera-
ture [45,46] (Eq. (17)). Note (cf. experimental)
Triglyme
ꢀꢀꢀꢀ!
½F2C ¼ CFZnXꢂ þ F2C ¼ CFI
1
(14)
PdðPPh3Þ4 RT to 40 ꢁC ꢃ 1 h 66%
In both the Cu(0) mediated coupling and Pd(0) catalyzed
coupling processes, 2 is required as a reagent. Since 2 is
prepared most conveniently from [F2C CFZnX], a more
simple procedure would involve the preparation of 1 directly
from the vinylzinc reagent. In the introduction section, it was
noted that Norris and Finnegan [4] were successful in coupling
[CF3CBB CZnCl] to the diyne with CuCl2. Thus Hansen
attempted to couple [F2C CFZnX] with CuBr2 as a direct
route to 1 [32]. This reaction was extremely exothermic, and
although 1 was obtained in low yield, the procedure was not
easily scaled up. Later, Morken modified his CuBr2 procedure
for the coupling of the pentafluoropropenyl-2-zinc reagent [33]
to the coupling of the trifluorovinylzinc reagent with CuBr2.
O2
CuBr
CF3CðZnXÞ ¼ CF2 ꢀ! ½CF3CðCuÞ ¼ CF2ꢂꢀ! 3
(17)
DMF RT
RT
62%
4
that 4 does not react with dioxygen. Morken also found that an
(E),(Z) mixture of CF3(C6H5)C CFCu (prepared from a
(E),(Z)- mixture of CF3(C6H5)C CFZnBr) gave a mixture of
the three isomers of [CF3(C6H5)C CF]2 on treatment with
dioxygen at room temperature [47]. The three isomers could
not be separated; the isomers were found in a 1:1.1:1.9 ratio
[(E)(E)/(Z)(Z)/(E)(Z)]- as determined by 19F NMR analysis of
the reaction mixture [48]. The GC/MS of the mixture was in
agreement with the molecular formula of the homodimers.
Similarly, a degassed sample of (E)(Z)-CF3C(C6H5)C CFCu

438
D.J. Burton et al. / Journal of Fluorine Chemistry 129 (2008) 435–442
was heated in an NMR tube at 50–60 8C for 9 days and
monitored by 19F NMR. The major products (as determined
by 19F NMR) were the (E)(E), (Z)(Z) and (E)(Z)-homodimers.
Thus, dioxygen oxidation or pyrolysis of fluorinated vinylcop-
per reagents appears to be an alternative entry to fluorinated
symmetrical dienes [49]. Fluorinated vinylzinc and/or copper
reagents are not the only precursors that can be dimerized by
Cu(II) salts. For example, Muller and Dressler have reported
that K2[F2C CFSiF5] reacts with Cu(II)SO4 to give 1 (14%)
[50].
coupling of iodotrifluoroethene, Pd(0) catalyzed coupling of
iodotrifluoroethene with the trifluorovinylzinc reagent, and
CuBr2 mediated coupling of the trifluorovinylzinc reagent.
Perfluoro-2,3-dimethyl-1,3-butadiene can be readily formed by
treatment of the pentafluoropropenyl-2-zinc reagent with either
CuBr2 or FeCl3. Alternatively, this substituted butadiene can be
prepared by oxidation of the pentafluoropropenyl-2-copper
reagent with dioxygen. Cu(0) mediated coupling of a (E)-
substituted a,b-difluoro-b-iodostyrene provided the first useful
route to (Z)(Z)-1,4-diaryl-1,3-tetrafluorobutadienes. Extension
of the Cu(0) mediated coupling methodology to a perfluor-
odienyliodide demonstrated a useful process for the stereo-
specific preparation of perfluoropolyenes.
2.3. Other Cu(0) mediated symmetrical coupling reactions
Yagupol’skii and co-workers reported that (Z)-1-iodo-2-
aryl-a,b-difluorostyrenes couples with Cu(0) in DMFA to give
the (E)(E)-1,4-diaryl-1,3-tetrafluorobutadienes [2,51–53]. The
corresponding (Z)(Z)-1,4-diaryl-1,3-tetrafluorobutadiene has
only been reported by photoisomerization of the (E)(E)-analog
[56]. Recently, we have reported a stereospecific route to
(E)-a,b-difluoro-b-iodostyrenes [57]. To demonstrate that
the corresponding (Z)(Z)-1,4-diaryl-1,3-tetrafluorobutadienes
could be prepared stereospecifically by Cu(0) mediated
coupling, Davis reacted (E)-p-MeC6H4CF CFI with activated
copper in DMSO [58] (Eq. (18)).
4. Experimental
4.1. General experimental procedures
The 19F NMR spectra were recorded on a JEOL FX90Q
Spectrometer or a Bruker AC-300 Spectrometer. Chemical
shifts have been reported in ppm upfield from CFCl3 and were
generally determined in CDCl3 solvent or d6-acetone (10% by
volume solutions) unless otherwise noted. 19F NMR yields
were determined by integration relative to internal benzotri-
(18)
1
The (Z)(Z)-diene was produced in excellent yield. This
Cu(0) mediated coupling of fluorinated vinyl iodides was
extended by MacNeil to the coupling of perfluorodienyl iodides
[59]. Thus, when 1-iodo-1(Z)(3E)-heptafluoro-1,3-pentadiene
was reacted with Cu(0), a good yield of (2E)(4E)(6E)(8E)-
perfluoro-2,4,6,8-decatetraene was formed (Eq. (19)), as
outlined below. As expected, the increase in the number of
fluorines in the precursor enhanced the reactivity of the vinyl
iodide precursor.
fluoride. Routine H NMR spectra were recorded on a JEOL
FX90Q Spectrometer. High field 1H NMR spectra were
recorded on a Bruker WM 360X or a Bruker AC-300
Spectrometer using CDCl3 as the internal lock solvent.
Chemical shifts are reported in ppm downfield from internal
TMS. The 13C NMR spectra were obtained on a Brucker AC-
300 Spectrometer with CDCl3 as the internal lock solvent.
Chemical shifts are reported in ppm downfield from internal
TMS. Infrared absorbance spectra were obtained using a
(19)
3. Conclusions
Mattson Cygnus 100 FTIR Spectrophotometer from solutions
in CCl4. The sample solutions were prepared from 10 ml of
sample in 1 ml of CCl4. All IR values have been reported in
units of reciprocal centimeters. Low-resolution spectra
Hexafluoro-1,3-butadiene can be readily prepared via a
variety of self-coupling processes, such as Cu(0) mediated

D.J. Burton et al. / Journal of Fluorine Chemistry 129 (2008) 435–442
439
(LRMS) were obtained using a TRIO-1 GC Mass spectrometer
operated at 70 eV in the electron impact mode, using a DB-1
column (0.25 mm ID ꢄ 15 m). High-resolution mass spectra
(HRMS) were performed by the University of Iowa High
Resolution Mass Spectroscopy Facility. The data were
collected on a VG Analytical ZAB-HF mass spectrometer
operated at 70 eV in the electron impact mode. Analytical
GLPC were performed on a Hewlett-Packard Model 5890
equipped with a TCD detector and 3393A integrator. The
column was packed with 5% OV101 on Chromosorb B.
Capillary GLPC were performed using a FID. All boiling points
were determined during fractional distillation and are
uncorrected. Melting points were determined in a Thomas-
Hoover Unimelt apparatus and are uncorrected. Starting
materials were obtained from commercial vendors and/or
prepared by literature procedures. DMSO was dried over CaH2
overnight and distilled at ꢃ70 8C/0.5 mm Hg prior to use. THF
was distilled from sodium benzephenone ketyl at atmospheric
pressure. DMF was dried by stirring overnight over CaH2, then
distilled at reduced pressure (bp ꢃ 65 8C/5 mmHg) prior to use.
Copper–bronze powder was obtained from Aldrich and
activated as described below. FeCl3 (Aldrich, anhydrous,
98%) was dried in a Kugelrohr oven apparatus at 80 8C/5 mm
Hg for 30 h. P2O5 was used in the cold receptacle of the
apparatus. CuBr2 (Aldrich) was used as received.
The flask was charged with 50 ml of dry triglyme (via syringe)
followed by the addition of 5.0 g (0.070 mol) of acid-washed
zinc and 10.4 g (0.050 mol) of iodotrifluoroethene. After
stirring for ꢃ30 min, the flask became warm and the reaction
mixture turned green. After the contents of the flask returned to
room temperature, the stirring was stopped and the excess zinc
allowed to settle. The supernatant solution was transferred (via
syringe) into another 100 ml flask, which was connected to a
trap cooled in a dry ice/isopropyl alcohol bath. Then, 3.00 g
(0.0025 mol) Pd(PPh3)4 and 9.7 g (0.0467 mol) of F2C CFI
were added to the trifluorovinylzinc reagent solution, and the
reaction mixture heated to 40 8C for 40 h. The contents of the
reaction mixture were dark-brown and 2–3 ml of colorless
liquid had collected in the trap. The reaction mixture was flash
distilled at 40 mm/Hg, the volatiles transferred to Rotoflo tube
to obtain 5.3 g (66%) of hexafluoro-1,3-butadiene. The 19F
NMR spectrum was identical to the reported literature [61–63]
and to the butadiene prepared by alternative routes by
co-workers (cf. above).
4.5. Preparation of hexafluoro-1,3-butadiene via oxidation
of the trifluorovinylziinc reagent with cupric bromide
Trifluorovinylzinc reagent was prepared in 72% 19F NMR
yield from F2C CFBr (34.2 g, 0.213 mol) and activated zinc
(10.7 g, 0.164 mol) in DMF via the literature procedure [21,22].
Then, a 3-necked 250 ml flask, equipped with a stir bar, rubber
septum, and a solids addition tube containing CuBr2 (40.1 g,
0.157 mol) was connected to two ꢀ196 8C traps linked to a
vacuum manifold. The flask was charged with 10 ml of dry
DMF, cooled to ꢀ25 8C, and degassed at 0.5–1.0 mm Hg for
several minutes. The previously prepared trifluorovinylzinc
reagent (76 ml, 0.119 mol) was then syringed (slowly) into the
flask with concomitant slow addition of CuBr2 from the solids
addition tube. Immediate boiling of hexafluoro-1,3-butadiene
was observed in the flask. After complete addition of the zinc
reagent and CuBr2, the reaction mixture was stirred for 1.5 h
with slow warming to ꢀ15 8C. At this time, trap #1 contained
the bulk of the product and a small amount of DMF, while trap
#2 contained small amounts of product—but no DMF. The
volatile contents of trap #1 were allowed to distill into trap #2
by slowly warming trap #1 to room temperature. After 30 min,
9.32 g (0.0575 mol, 97% based on the amount of zinc reagent
used) of product was isolated in trap #2. 19F NMR analysis of
the contents of trap #2 indicated a ratio of C4F6:F2C CFBr of
4.2. Activation of copper–bronze
Copper–bronze powder (Aldrich) was activated by the
addition of 100 g to a solution made up of 200 ml CCl4 and 30 g
I2. The mixture was stirred until the iodine color was no longer
evident. The metal was filtered, washed with a solution of 20 ml
conc. HCl in 200 ml acetone, followed by a washing with
acetone. The copper metal was dried under full vacuum
overnight.
4.3. Preparation of hexafluoro-1,3-butadiene via the
reaction of F2C CFCu and F2C CFI
The olefin, F2C CFI (30 ml), was added to an NMR tube
containing F2C CFCu in DMF (0.6 ml of a 0.7 M solution—
prepared from F2C CFZnBr + CuBr). 19F NMR analysis
showed no reaction after 5 min, but after 24 h at RT, F2C
CFCu had completely disappeared and hexafluorobutadiene was
present in 63% 19F NMR yield. The mixture was flash distilled
and the distillate analyzed by GC–MS and 19F NMR. GC-MS, m/
z (relative intensity): 162 (42.5, M+), 93 (100, M-CF3). 19F NMR
(triglyme) (ppm): d – 93.1 (dm, 2JFF = 48 Hz, 1F), ꢀ107.1 (ddm,
1
97:3. The H NMR of this mixture was silent. No F2C CFH
was observed by either 19F or 1H NMR or FTIR. The 19F NMR
data was in good agreement with literature values [61–63].
2
3
3JFF = 105 Hz, JFF = 48 Hz), ꢀ180.4 (ddm, JFF = 105 Hz,
3JFF = 27 Hz), in good agreement with literature data [60–63].
4.6. Preparation of pentafluoropropenyl-2-zinc reagent
4.4. Preparation of hexafluoro-1,3-butadiene via palladium
coupling of the trifluorovinylzinc reagent and
iodotrifluoroethene
A 4-neck 2 l flask was equipped with a pressure equalizing
dropping funnel, immersion thermometer, stir bar, and a dry
ice/isopropyl alcohol condenser attached to a nitrogen source.
The apparatus was purged with N2 then charged with activated
zinc (155 g, 2.37 mol) and 600 ml of dry DMF. A solution of
CF3CBr2CF3 [41] (300 g, 0.968 mol) in DMF (300 ml) was
A 100 ml flask was fitted with a dry ice/isopropyl alcohol
condenser (with a nitrogen inlet, stir bar, septum and N2 tee.

440
D.J. Burton et al. / Journal of Fluorine Chemistry 129 (2008) 435–442
then added dropwise to the well-stirred reaction mixture over a
3–4 h period at a rate that maintained the internal temperature at
70–80 8C. After completion of the reaction, the excess zinc was
removed by filtration through a medium frit Schlenk funnel
under positive N2 pressure. The yield of the pentafluoropro-
penyl-2-zinc reagent was determined by 19F NMR integration
vs. internal hexafluorobenzene; yields ranged from 90 to 95%.
flask was charged with 10 ml of a 0.57 M pentafluoropropenyl-
2-zinc reagent solution (0.0057 mol); then an O2 source was
attached to the needle and dioxygen bubbled into the mixture at
a rate sufficient to insure agitation and to keep the ꢀ78 8C trap
under positive pressure. No reaction or distillate was observed
after 1 h and 19F NMR analysis of the reaction mixture
indicated only CF3(ZnX)C CF2. Then CuBr (1.34 g,
0.00934 mol) was added to the reaction mixture and the
dioxygen flow resumed. After 15 min, the flask was warm to the
touch and liquid had condensed in the trap. After an additional
30 min stirring, the ꢀ78 8C trap was found to contain 0.42 g
(62% yield) of perfluoro-2,3-dimethyl-1,3-butadiene and a
trace of DMF, as determined by 19F and 1H NMR, respectively.
4
4
19F NMR (DMF) (ppm): d-49.0 (dd, JFF = 18 Hz, JFF
=
13 Hz, 3F), ꢀ60.9 (dq, 2JFF = 37 Hz, 4JFF = 18 Hz, 1F), ꢀ72.5
2
(dq, JFF = 37 Hz, JFF = 13 Hz, 1F).
4
4.7. Preparation of perfluoro-2,3-dimethyl-1,3-butadiene
via cupric bromide oxidation of pentafluoropropenyl-2-zinc
reagent
4.10. Copper (0)-mediated-coupling of (Z)-p-nitro-b-iodo-
a,b-difluorostyrene
A 100 ml flask was equipped with a Teflon coated stir bar
and a solids addition tube containing 11.6 g (0.052 mol) of
CuBr2. The flask was cooled to 0 8C and charged with
0.042 mol of the pentafluoropropenyl-2-zinc reagent (prepared
as described above). A ꢀ196 8C trap was connected to the
apparatus and to a vacuum source (0.5–1 mm Hg). Then, with
stirring, the CuBr2 was added slowly via the solids addition
tube at a rate to keep the reaction mixture from foaming into the
trap. The lower layer of the distillate was removed by pipette to
afford 4.4l g (80% yield) of perfluoro-2,3-dimethyl-1,3-
A 25 ml flask equipped with a nitrogen tee, stir bar, septum
port and condenser was charged with 0.05 g (0.00079 mol) of
activated copper metal, 0.12 g (0.00038 mol) of (Z)-p-nitro-b-
iodo-a,b-difluorostyrene and 5 ml of dry DMSO. The reaction
mixture was stirred at 120 8C overnight. 19F NMR analysis of the
reaction mixture indicted total consumption of the starting
material. After cooling, the reaction mixture was separated by
flash column chromatography on silica gel using hexane/CH2Cl2
as eluant to give 0.05 g (71%) of a mixture of (1E), (3E)-1,4-
di( p-nitrophenyl)-1,3-tetrafluorobutadiene and (1E), (3Z)-1,4-
di( p-nitrophenyl)-1,3-tetrafluoro-butadiene in a ratio of 10:3.
19F NMR (CDCl3) (ppm): (1E), 3(E) isomer: d ꢀ141.6 (d,
butadiene, GLPC purity, 100%. 19F NMR (CDCl3) (ppm): d
4
ꢀ61.2 (dd, JFF = 20 Hz, 4JFF = 14 Hz, 3F); ꢀ67.8 (qd, 4JFF
=
2
20 Hz, JFF = 8 Hz, 1F); ꢀ69.6 (m, 1F).
3
1
4.8. Preparation of perfluoro-2,3-dimethyl-1,3-butadiene
via ferric chloride oxidation of pentafluoropropenyl-2-zinc
reagent
3JFF = 130 Hz, 2F), ꢀ151.6 (d, JFF = 130 Hz, 2F); H NMR
3
(CDCl3) (ppm): d 8.35 (d, JHH = 9.0 Hz, 4H), 8.00 (d,
3JHH = 9.0 Hz, 4H): For the (1E), (3Z) isomer: 19F NMR
3
5
(CDCl3) (ppm): d ꢀ120.6 (ddd, JFF = 13.6 Hz, JFF = 7.9 Hz,
4JFF = 5.7 Hz, 1F), ꢀ138.3 (ddd, 3JFF = 40.7 Hz, 4JFF = 15.3 Hz,
3JFF = 14.0 Hz), ꢀ141.5 (ddd, 3JFF = 131.6 Hz, 4JFF = 15.9 Hz,
A 100 ml flask equipped with a septum, solids addition tube
containing anhydrous FeCl3 (4.36 g, 0.0269 mol) and stir bar
was charged with 10 ml of dry DMF. The flask was cooled to
ꢀ15 8C, then the FeCl3 was added slowly to control the
exothermic reaction between the Lewis acid (FeCl3) and the
Lewis base (DMF). The apparatus was connected to a ꢀ196 8C
trap linked to a vacuum system (0.5–1 mm Hg) and the FeCl3/
DMF solution degassed at ꢀ15 8C for several minutes. Then,
0.020 mol of a pentafluoropropenyl-2-zinc reagent was slowly
added (via syringe) to the FeCl3/DMF solution at a rate to keep
the reaction mixture from foaming into the trap. The lower
layer of the distillate was removed by pipette to afford 1.79 g
(68%) perfluoro-2,3-dimethyl-1,3-butadiene, GLPC purity
100%. The 19F NMR spectrum was identical to that reported
above.
3
3
5JFF = 8.2 Hz, 1F), ꢀ151.2 (ddd, JFF = 131.6 Hz, JFF
=
4
1
40.7 Hz, JFF = 5.7 Hz, 1F); H NMR (CDCl3) (ppm): d 8.31
3
3
(d, JHH = 8.7 Hz, 2H), 8.26 (d, JHH = 8.5 Hz, 2H), 7.82 (d,
3JHH = 8.8 Hz, 2H), 7.72 (d, 3JHH = 8.9 Hz, 2H).
4.11. Preparation of (Z,Z)-1.4-bis( p-tolyl)-1,3-
tetrafluorobutadiene
A 25 ml flask equipped with a stir bar, N2 tee, condenser, and
septum port was charged with 0.25 g (0.004 mol) of activated
Cu(0) powder, 8–10 ml of dry DMSO, and 0.95 g (0.0034 mol)
of (E)-p-MeC6H4CF CFI [57]. The mixture was heated in an
oil bath with stirring for 5 h at 110–120 8C. After cooling, the
mixture was poured into 50 ml H2O and extracted with Et2O
(3 ml ꢄ 75 ml). The ether layer was dried (MgSO4) filtered,
and the solvent removed by rotary evaporation. The product,
1.67 g (98%) was purified by column chromatography (Rf 0.3,
hexane) to obtain a white solid: mp 71–72 8C. 19F NMR
4.9. Preparation of perfluoro-2,3-dimethyl-1,3-butadiene
via dioxygen oxidation of pentafluoropropenyl-2-copper
reagent
3
A 2-necked 25 ml flask equipped with a septum and a glass
stopcock was connected to a ꢀ78 8C trap, which was vented to
a N2 source. A 6 in. needle attached to the N2 source was
inserted into the septum and the apparatus purged with N2. The
(CDCl3)(ppm): d ꢀ119.1 (d, JFF = 9.5 Hz, 1F), ꢀ139.3 (d,
3JFF = 9.5 Hz, 1F); 13C NMR (CDCl3) (ppm): 136.4 (dddd,
vinyl carbon, 1JCF = 252.7 Hz, 2JCF = 32.1 Hz, 3JCF = 24.4 Hz,
1
4JCF = 6.1 Hz), 151.5 (dm, vinyl carbon, JCF = 257.6 Hz),

D.J. Burton et al. / Journal of Fluorine Chemistry 129 (2008) 435–442
441
2
125.2 (dd, JCF = 24.4 Hz, JCF = 1.8 Hz, quaternary ring
3
[11] R.N. Haszeldine, J.E. Osborne, J. Chem. Soc. (1955) 3880–3888.
[12] R.N. Haszeldine, J. Chem. Soc. (1954) 4026–4027.
carbon), 126.8 (m, ring carbon), 129.0 (m, ring carbon),
1
140.7 (quaternary ring carbon), 21.9 (CH3 carbon); H NMR
[13] S.W. Hansen, Ph.D. Thesis, University of Iowa, 1984, cf. also [14–17].
[14] G.A. Olah, R.D. Chambers, S. Prakash (Eds.), Synthetic Fluorine Chem-
istry, Wiley-Interscience, 1992, p. 218 (Chapter 9).
(CDCl3) (ppm): 2.30 (s, 3H), 7.03 (d, 3JHH = 8.3 Hz, 2H), 7.08
(d, 3JHH = 8.3 Hz, 2H): FTIR (CCl4): 3038 (w), 2925 (w), 1680
(m), 1613 (w), 1515 (w), 1284 (s), 1125 (m), 1018 (s), 956 (m),
862 (m). HRMS: calculated for C18H14F4; 306.1032, observed
306.1028.
[15] Inorganic Fluorine Chemistry, in: J.S. Thrasher, S.H. Strauss (Eds.), ACS
Symposium #555, 1994, p. 298 (Chapter 18).
[16] Tetrahedron 50 (1994) 2993–3063; D.J. Burton, Z.Y. Yang, P.A. Morken,
Tetrahedron Report #351, p. 3024.
[17] D.J. Burton, S.W. Hansen, J. Fluorine Chem. 31 (1986) 461–465.
[18] S.W. Hansen, Ph.D. Thesis, University of Iowa, 1984, p. 239.
[19] J.D. Park, R.J. Steffl, J.R. Lacher, J. Am. Chem. Soc. 78 (1956) 59–62.
[20] S.W. Hansen, Ph.D. Thesis, pp. 178–179; for detailed experimental
directions to the preparation of [F2C CFZnBr] from F2C CFBr, cf.
[21,22].
4.12. Preparation of (2E,4E,6E,8E)-perfluoro-2,4,6,8-
decatetraene
A 25 ml flask with a septum port was fitted with a stir bar and
N2 tee. Then 5 ml of dry DMSO was syringed into the flask
followed by the addition of activated copper metal (1.0 g,
0.015 mol) and 1.45 g (0.0045 mol) of 1-iodo-1(E),3(E)-
heptafluoropentadiene. The mixture was stirred overnight at
room temperature; then the contents of the flask were flash
distilled. The distillate contained the product as a small bottom
layer, which was pipetted from the distillate to give 0.6 g (69%)
of the tetraene: GLPC purity, 98%; bp 42–43 8C (15 mm/Hg).
[21] P.L. Heinze, D.J. Burton, J. Org. Chem. 53 (1988) 2714–2720.
[22] P. Knochel, P. Jones (Eds.), Organozinc Reagents, Oxford University
Press, NY, 1999, pp. 58–60 (Chapter 4).
[23] The trifluorovinyl reagent can also be prepared from CF3CH2F, cf. [24,25].
[24] R. Anilkumar, D.J. Burton, Tetrahedron Lett. 43 (2002) 2731–2733.
[25] A. Raghavenpillai, D.J. Burton, J. Org. Chem. 69 (2004) 7083–7091.
[26] A. Raghavenpillai, University of Iowa, unpublished results.
[27] C. Lim, D.J. Burton, C.A. Wesolowski, J. Fluorine Chem. 119 (2003) 21–
26.
[28] W.R. Dolbier Jr., H. Koroniak, D.J. Burton, P.L. Heinze, Tetrahedron Lett.
27 (1986) 4387–4390.
3
19F NMR (CDCl3) (ppm): d ꢀ68.0 (dd, CF3, JFF = 8 Hz,
[29] W.R. Dolbier Jr., H. Koroniak, D.J. Burton, P.L. Heinze, A.R. Bailey, G.S.
Shaw, S.W. Hansen, J. Am. Chem. Soc. 109 (1987) 219–225.
[30] P.L. Heinze, Ph.D. Thesis, University of Iowa, 1986.
[31] K. MacNeil, Ph.D. Thesis, University of Iowa, 1991, pp. 250–251.
[32] S.W. Hansen, Ph.D. Thesis, University of Iowa, 1984, p. 180.
[33] P.A. Morken, H. Lu, A. Nakamura, D.J. Burton, Tetrahedron Lett. 32
(1991) 4271–4274.
3
4JFF = 20 Hz); ꢀ155.0 (bd, vinyl F, JFF = 136 Hz), ꢀ155.9
(dq, vinyl F, 3JFF = 136 Hz, 4JFF = 20 Hz), ꢀ150.9 (AB pattern,
middle vinyl F’s); 13C NMR (CDCl3) (ppm): 118.3 (qdd, CF3,
3
4
1JCF = 270 Hz, JCF = 35 Hz, JCF = 4 Hz), vinyl F’s 139.4–
144.6. GCMS; m/z (relative intensity): 386 (M+, 11.8), 317
(85.2), 267 (86.8), 248 (41.1), 229 (28.3), 217 (100.0), 205
(21.0), 198 (20.9), 186 (24.2), 181 (22.6), 179 (51.4), 155
(33.0), 131 (45.6), 117 (34.9), 93 (35.0), 69 (87.8). HRMS:
calculated for C10F14 385.9776, observed 385.9748. FTIR
(CCl4): 700 (m), 912 (m), 920 (m), 1012 (w), 1026 (w), 1146
(s), 1161 (s), 1169 (s), 1180 (s), 1186 (s), 1190 (s), 1201 (s),
1213 (s), 1226 (s), 1234 (s), 1290 (s), 1298 (s), 1304 (s), 1329
(m), 1337 (m), 1362 (s), 1380 (s), 1392 (s), 1425 (w), 1688 (w),
1715 (w).
[34] P.A. Morken, Ph.D. Thesis, University of Iowa, 1992, pp. 55–56; see also
[35] for another citation to this work.
[35] Ref. 16, p. 3020.
[36] Norris and Finnegan [4] reported the formation of CF3CBB CCl when
[CF3CBB CZnCl] was coupled with CuCl2.
[37] C.E. Castro, E.J. Gaughan, D.C. Owsley, J. Org. Chem. 30 (1965) 587–
592.
[38] R.E. Banks, R.N. Haszeldine, D.R. Taylor, G. Webb, Tetrahedron Lett. 60
(1970) 5215–5216.
[39] W. Mahler, J. Am. Chem. Soc. 84 (1962) 4600–4601.
[40] R.D. Chambers, A. Lindley, J. Chem. Soc. Chem. Commun. (1978) 475–
476.
Acknowledgement
[41] P.A. Morken, D.J. Burton, J. Org. Chem. 58 (1993) 1167–1172.
[42] S.W. Hansen, Ph.D. Thesis, University of Iowa. 1984, p. 228 also noted
that trans-(CF3CF CFCu) with FeCl3 gave a modest yield (37%) of the
trans, trans-perfluoro-2,4-hexadiene.
We gratefully appreciate the financial support from the Air
Force Office of Scientific Research and the National Science
Foundation.
[43] G.M. Whitesides, J. San Fillippo Jr., C.P. Casey, E.J. Panek, J. Am. Chem.
Soc. 89 (1967) 5302–5304.
[44] G.M. Whitesides, C.P. Casey, J.K. Krieger, J. Am. Chem. Soc. 92 (1970)
1379–1389.
References
[45] P.A. Morken, Ph.D. Thesis, University of Iowa, 1992, pp. 54–55.
[46] A sample of CF3C(Cu) CF2 prepared from 4 and one equivalent of CuBr
[1] G. Camaggi, S.F. Campbell, D.R.A. Perry, R. Stephens, J.C. Tatlow,
Tetrahedron 22 (1966) 1755–1763.
4
exhibited the following 19F NMR spectrum: d – 47.1 (dd, JFF = 18 Hz,
4JFF = 12 Hz, 3F), ꢀ63.7 (dq, 2JFF = 51 Hz, 4JFF = 18 Hz, 1F), ꢀ72.4. (dq,
[2] A.P. Sevast’yan, Y.A. Fialkov, V.A. Khranovskii, L.M. Yagupol’skii, Zh.
Org. Khim 14 (1978) 204.
4
2JFF = 51 Hz, JFF = 12 Hz, 1F).
[47] P.A. Morken, Ph.D. Thesis, University of Iowa, 1992, pp. 104–105.
[48] 19F NMR of he homodimers of [CF3(C6H5)C CF]2: 19F NMR (CDCl3)
[3] F. Jeanneaux, G. Santini, M. LeBlanc, A. Cambon, J.G. Reiss, Tetrahedron
30 (1974) 4197–4200.
4
(ppm): (E)(E)-isomer: d – 61.3 (t, JFF = 7–8 Hz, 3F), ꢀ95.4 (m, 1F);
[4] W.P. Norris, W.G. Finnegan, J. Org. Chem. 31 (1966) 3292–3295.
[5] A. Cairncross, W.A. Sheppard, J. Am. Chem. Soc. 90 (1968) 2186–2187.
[6] W.T. Miller, R.H. Snider, R.J. Hummel, J. Am. Chem. Soc. 91 (1969)
6532–6534.
(Z)(Z)-isomer: d – 60.3 (dm, 4JFF = 20–25 Hz, 3F), ꢀ99.6 (m, 1F): (E)(Z)-
4
isomer: d – 60.7 (dm, JFF = 22 Hz, 3F), ꢀ96.9 (m, 1F), ꢀ94.3 (dq,
4
3JFF = 40 Hz, JFF = 10 Hz, 1F), ꢀ62.0.(m, 3F).
[49] S.W. Hansen, Ph.D. Thesis, University of Iowa, 1984, p. 204 also noted
qualitatively that trans-CF3CF CFCu on exposure to atmospheric oxy-
gen gave the trans,trans-perfluoro-2,4-hexadiene.
[7] E.J. Blumenthal, D.J. Burton, Israel J. Chem. 39 (1999) 109–115.
[8] R.N. Haszeldine, J. Chem. Soc. (1952) 4423–4431.
[9] A.L. Henne, W. Postelneck, J. Am. Chem. Soc. 77 (1955) 2334–2335.
[10] V. Dedek, Z. Chvatal, J. Fluorine Chem. 31 (1986) 363–379.
[50] V.R. Muller, M. Dressler, C. Dathe, J. Prakt. Chem. (1970) 150.

442
D.J. Burton et al. / Journal of Fluorine Chemistry 129 (2008) 435–442
[51] In our hands, coupling of (Z)-p-nitro-b-iodo-a,b-difluorostyrene with
activated Cu(0) in DMSO at 120 8C afforded a mixture of the (E)(E)-
and (Z)(Z)-1,4-bis(p-nitrophenyl)-tetrafluoro-1,3-butadienes in a 10:3
ratio [52,53], cf. experimental section.
[55] R.D. Chambers, A.A. Lindley, H.C. Fielding, J. Chem. Soc. Perkin I
(1981) 939–942.
[56] V. Khramovskii, Y. Egerov, A. Sevest’lyan, L. Yagupol’skii, Zh. Prikl.
Spektrosk 14 (1971), 688; CA75:55792p.
[52] Ling Xue, Ph.D. Thesis, University of Iowa, 1996, p. 95.
[53] It’s not clear how isomerization occurred here, either thermally or
catalyzed by fluoride ion (from decomposition of an intermediate copper
reagent). The p-nitro diene would be the analog most prone to react with
fluoride ion and isomerize. Fluoride ion isomerizations of fluorinated
dienes are well known [54,55].
[57] C.R. Davis, D.J. Burton, J. Org. Chem. 62 (1997) 9217–9222.
[58] C.R. Davis, Ph.D. Thesis, University of Iowa, 1993, p. 122.
[59] K. MacNeil, Ph.D. Thesis, University of Iowa, 1991, p. 261.
[60] For literature reports of 19F NMR data for 1, see [61–63].
[61] V. Dedek, M. Kovac, Coll. Czech. Chem. Commun. 44 (1979) 2660.
[62] S.S. Dubov, B.I. Ketel’baum, R.N. Sterlin, Zh. Khim. Obshch 7 (1962) 691.
[63] S.L. Manatt, M.T. Bowers, J. Am. Chem. Soc. 91 (1969) 4381.
[54] K.J. MacNeil, D.J. Burton, J. Org. Chem. 60 (1995) 4085–4089.