A convenient preparation of octafluoro[2,2]paracyclophane and dodecafluoro[2,2]paracyclophane

Article abstract of DOI:10.1016/S0040-4039(01)02231-6

A new and convenient synthesis of octafluoro[2,2]paracyclophane and dodeca-fluoro[2,2]paracyclophane is reported. It is accomplished by treatment of 1,4-bis(halodifluoromethyl)benzene with PbBr₂/Al in DMF at room temperature via the cyclocoupling of the reactive intermediate α,α,α′α′-tetrafluoro-p-xylylene.

Full text of DOI:10.1016/S0040-4039(01)02231-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 669–671
A convenient preparation of octafluoro[2,2]paracyclophane and
dodecafluoro[2,2]paracyclophane
Shi-zheng Zhu,* Yun-yu Mao, Gui-fang Jin, Chao-yue Qin, Qian-li Chu and Chang-ming Hu
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China
Received 2 October 2001; revised 13 November 2001; accepted 22 November 2001
Abstract—A new and convenient synthesis of octafluoro[2,2]paracyclophane and dodeca-fluoro[2,2]paracyclophane is reported. It
is accomplished by treatment of 1,4-bis(halodifluoromethyl)benzene with PbBr2/Al in DMF at room temperature via the
cyclocoupling of the reactive intermediate a,a,a%a%-tetrafluoro-p-xylylene. © 2002 Elsevier Science Ltd. All rights reserved.
TiCl4 / LiAlH4
32%
CF2Br
CF2Br
F2C
F2C
CF2
CF2
Poly(a,a,a%,a%-tetrafluoro)-p-xylylene (parylene AF4) is
an interesting and a commercially valuable material
which combines a low dielectric constant, high thermal
stability and low moisture absorption.1–3 The precursor
of this polymer is per-a-fluoro-[2,2]paracyclophane
(AF4 2) which was first prepared by Union Carbide
chemists in 1970.4,5
Me3SiSnBu3 / CsF
40%
2
Nevertheless, these two methods required high dilution
technology. In a typical experimental 2.7 L of anhy-
drous THF was used for the preparation of 1.4 g of 21
or 8 L of absolute THF and 2 L of DMSO were used
to prepare 22.7 g of 2.2
F2C
CF2
CF2X
600-800 oC
9-28%
F2C
CF2
CF2X
In our laboratory, a new redox system PbBr2/Al has
been successfully used in the dehaloformylation reac-
tion of perfluoroalkyl halides or a,v-dihaloper-
fluoroalkanes (Scheme 1).6
1
2
In 1993, Dolbier’s research group reported a reductive
method for the synthesis of 2 in which a low valent Ti
complex was used to effect the dehalogenation of 1,4-
It was interesting to note that under the same reaction
conditions 1,4-bis(bromodifluoromethyl)benzene did
not give the expected products OHCCF2-C6H4-
CF2CHO or BrCF2-C6H4-CF2CHO. The product has
been characterized as a mixture of 2 and 3. Here we
report these results.
bis(bromodifluoromethyl)benzene.
This
procedure
allowed relatively easy preparation of gram quantities
of 2 in 32% yield.2 Recently they found that by using an
active species generated (in situ) from the reaction of
(trimethylsilyl)tributyltin with cesium fluoride, the yield
of 2 was improved to 40% and this method can be
carried out on a larger scale.
In a typical reaction, a solution of 1,4-bis(halodi-
fluoromethyl)benzene 1a (50 mmol, 12.35 g) in DMF (10
ml) was added over a period of 2 h to a flask containing
Keywords: poly(a,a,a%a%-tetrafluoro)-p-xylylene (parylene AF4); per-
a-fluoro-[2,2]paracyclophane; AF4; dodecafluoro[2,2]paracyclophane.
* Corresponding author. Fax: +86(21) 64166128; e-mail: zhusz@
pub.sioc.ac.cn
Scheme 1.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)02231-6

670
S. Zhu et al. / Tetrahedron Letters 43 (2002) 669–671
Table 1. Preparation of 2 under different reaction conditions
Entry
Reactant p-R-C6H4-R
Reagents
Solvents
Temperature (°C)
Time (h)
Products and yield (%)a
1
2
3
4
5
6
7
8
9
1a
1b
1b
1a
1a
1a
1a
1b
1b
CuI/Zn
TiCl2Cp2/Zn
InI3/Al
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
THF
80
90
80
80
6
6
8
2 (8)
2 (12)
2 (10)
2 (8)
2 (10), 3 (7)
2 (19), 3 (18)
2 (22), 3 (20)
2 (22), 3 (19)
2 (9), 3 (4)
InI3/Al
8
PbBr2/Al
PbBr2/Al
PbBr2/Al
PbBr2/Al
PbBr2/Al
80
20
24
50
30
30
0-Rt
0-Rt
0-Rt
0-Rt
a Isolated yields based on 1.
PbBr2 (2 mmol, 0.734 g), aluminum powder (66 mmol,
1.78 g) and DMF (90 ml) at 0°C under a nitrogen
atmosphere. After the addition, the reaction mixture
was stirred for 24 h at room temperature. General
work-up gave a mixture of the dimer 2 and trimer 3 in
a combined yield of 37%.7
which was formed from the intermediates of radical
[CF2CF2Y].
Elemental analysis of the inorganic salt which was
filtered out from the reaction mixture indicated a high
concentration of fluoride. It might be formed by the
decomposition of the intermediate a,a,a%,a%-tetrafluoro-
p-xylylene and results in a decrease in the yield of
cyclocoupled products.
The above described reaction conditions have been
optimized with respect to choice of redox system, sol-
vent and reaction temperature. Several other redox
systems such as CuI/Zn, TiCl2Cp2/Zn and InI3/Al were
tried. They were all workable and gave the dimer 2 as
the only product but in low yield (8–11%). These
reactions could also be carried out in dioxane or THF,
however, DMF was the most suitable solvent. These
results are summarized in Table 1.
The mixture of dimer and trimer can be separated by
recrystallization from benzene or CHCl3. The solubility
of the trimer in CHCl3 is very low. It was noticed that
there was one peak in the 19F NMR spectrum of 2 or 3,
which indicated that all the fluorine atoms were chemi-
cally equivalent in these two compounds. The 19F and
1H NMR spectra of 3 [lF(CF2)=−112.8 lH(C6H4)=
7.35] are at a lower field compared with compound 2
[lF(CF2)=−118.8 ppm lH(C6H4)=7.17]. Recrystalliza-
tion of 3 from benzene gave fine crystals,9 the molecular
structure of which is shown in Fig. 1.
It is believed that a single electron transfer (SET)
process could be involved in the dehalocyclocoupling
reaction of 1, using the redox PbBr2/Al system. A
possible reaction mechanism is proposed as shown
below.
In conclusion, octafluoro[2,2]paracyclophane and dode-
cafluoro[2,2]paracyclophane have been prepared by
dehalocyclocoupling of 1,4-bis(halodifluoromethyl)-
benzene using several redox systems, among which the
PbBr2/Al system gave the best result.
In our previous work, we also found that 1,2-dihalotet-
rafluoroethane XCF2CF2Y reacted with PbBr2/Al in
DMF not to give the dehaloformylation product
XCF2CF2CHO,8 but in fact decomposed to CF2ꢀCF2

S. Zhu et al. / Tetrahedron Letters 43 (2002) 669–671
671
References
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CF2C6H4CF2, 5.92), 176 (M+−CF2C6H4CF2, 100.00); IR
(wmax, cm−1): 3100 (w, C–H), 1402 (s, CꢀC), 1002–1264 (s,
C–F). Anal. calcd for 3 C, 36.36; H, 1.52; F, 28.79%.
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NMR lH (C6H4)=7.17 ppm, 19F NMR (CDCl3) lF=
−118.8 ppm; MS (m/z, %): 352 (M+, 6.32), 176 (M+−
CF2C6H4CF2, 100.00).
Figure 1. X-Ray structure of compound 3.
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9. X-Ray diffraction analysis data for compound 3.
C24H12F12, M=528.34, a=15.340(2), b=10.339(2), c=
Acknowledgements
3
,
,
17.173(2) A, i=94.69 (1)°, V=2708.1(6) A , Z=4, Dc=
1.487 g/cm3, F(000)=1224.00 v(Mo Ka)=1.44 cm−1
,
Rw=0.065, Rf=0.073. Crystal dimensions: 0.20×0.20×0.30
mm. Data were measured at 293 K on a Rigaku AFC7 R
diffractometer with graphite-monochromated Mo Ka radi-
ation and a 12 kW rotating anode generator.
This work was supported by the National Natural
Science Foundation of China (NNSFC) (No. 20032010,
20072049) and the Innovation Foundation of Chinese
Academy of Sciences for financial support.