The high-temperature alicyclic ring contraction of 1,1-dichloroperfluorotetralin and the alicyclic ring opening of 1,1-dichloroperfluorobenzocyclobutene

Article abstract of DOI:10.1016/j.jfluchem.2007.02.015

The pyrolysis of 1,1-dichloroperfluorotetralin (4) in a stream of argon gives a mixture contained perfluoro-1-methyleneindan (1), perfluoro-3-methylindene (6), 1,1-dichloroperfluoroindan (2) and perfluoroindene (7), while copyrolysis of tetralin 4 with CH

Full text of DOI:10.1016/j.jfluchem.2007.02.015

Journal of Fluorine Chemistry 128 (2007) 714–717
www.elsevier.com/locate/fluor
The high-temperature alicyclic ring contraction
of 1,1-dichloroperfluorotetralin and the alicyclic ring
opening of 1,1-dichloroperfluorobenzocyclobutene
*
Victor M. Karpov , Tatyana V. Mezhenkova, Vyacheslav E. Platonov
*
N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Novosibirsk 630090, Russia
Received 23 January 2007; received in revised form 21 February 2007; accepted 21 February 2007
Available online 25 February 2007
Dedicated to the Centenary of Academician, Professor I.L. Knunyants.
Abstract
The pyrolysis of 1,1-dichloroperfluorotetralin (4) in a stream of argon gives a mixture contained perfluoro-1-methyleneindan (1), perfluoro-3-
methylindene (6), 1,1-dichloroperfluoroindan (2) and perfluoroindene (7), while copyrolysis of tetralin 4 with CHClF2 gives a mixture of
compounds 1, 6 in the absence of compounds 2 and 7. 1-Chloro-2-(1-chloro-2,2-difluorovinyl)-3,4,5,6-tetrafluorobenzene (12) is formed in the
pyrolysis of 1,1-dichloroperfluorobenzocyclobutene (5) in a stream of argon as well as in a stream of CHClF2.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Fluorinated; Tetralin; Benzocyclobutene; Pyrolysis; Ring contraction; Ring opening
1. Introduction
CHClF2, as well as their high-temperature behaviour in a
stream of argon.
Copyrolysis of a,a-dichloropolyfluoroalkylbenzenes [1,2]
and 1,1-dichloropolyfluoroindans [3] with CHClF2 as a source
of difluorocarbene [4,5] is known to give polyfluorostyrenes
and polyfluoro-1-methyleneindans, respectively. It has been
shown that formation of perfluoro-1-methyleneindan (1) in the
reaction of 1,1-dichloroperfluoroindan (2) with CHClF2 can
proceed by way of difluorocarbene insertion into C–Cl bond of
compound 2, giving 1-chloro-1-(chlorodifluoromethyl)per-
fluoroindan (3), with subsequent dechlorination of the latter
[3] (Scheme 1).
2. Results and discussion
It has been shown that in copyrolysis of tetralin 4 with
CHClF2 the main reaction product is compound 1. The reaction
mixture also contains small amount of perfluoro-3-methylin-
dene (6), which is a product of isomerization of compound 1
under the reaction conditions [3], together with unidentified
impurities (Scheme 2). The formation of compounds 1 and 6
takes place also in the pyrolysis of tetralin 4 in a stream of
argon. But in this case the reaction mixture contains also indan
2 and perfluoroindene (7).
Some possible routes for the transformation of tetralin 4 to
compound 1 can be formulated as shown in Scheme 3. One can
suppose that compound 4 undergoes homolytical transforma-
tions including generation of 1-chloroperfluorotetralin-1-yl
radical (8) with its subsequent b-cleavage similar to [6] and the
formation of 2-[2-(1-chloro-2,2-difluorovinyl)tetrafluorophe-
nyl]tetrafluoroethyl radical (9) (Scheme 3). The latter can
undergo the intramolecular cyclization giving radical 10. A
concert mechanism is also likely. The loss of the chlorine atom
It was interesting to investigate high-temperature reactions
of other polyfluorinated 1,1-dichlorobenzocycloalkenes with
CHClF2 in order to study the effect of the alicyclic ring size on
the route of polyfluorobenzocycloalkenes transformations. This
work describes the copyrolysis of 1,1-dichloroperfluorotetralin
(4) and 1,1-dichloroperfluorobenzocyclobutene (5) with
* Corresponding authors. Tel.: +7 3833 309437; fax: +7 3833 30 9752.
E-mail addresses: karpov@nioch.nsc.ru (V.M. Karpov),
platonov@nioch.nsc.ru (V.E. Platonov).
0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2007.02.015

V.M. Karpov et al. / Journal of Fluorine Chemistry 128 (2007) 714–717
715
Scheme 1.
from radical 10 gives compound 1. One cannot also exclude the
possibility of compound 1 being formed by generation of
carbene 11 with subsequent alicyclic ring contraction of the
latter. It should be noted that migration of perfluoroalkyl group
is known for carbenes [7] as well as for radicals [8].
When the reaction is provided under argon in the absence of
acceptors of chlorine (:CF2, CF2 CF2, which are pyrolysis
products of CHClF2 [4,5]), a chlorination of radical 10 or/and
compound 1 can form product 3. The high-temperature
transformations of the latter apparently give compounds 1, 2,
6, 7.
Scheme 3.
This explanation is in accordance with the fact that mixtures
of compounds 1, 6 and 1, 2, 6, 7, similar to that for tetralin 4, are
formed in the copyrolysis of compound 3 with CHClF2 [3] and
in its high-temperature reaction in a stream of argon,
respectively (Scheme 2).
discussed, for example, in work [9]. In addition, one cannot
also exclude the possibility of compound 1 formation via
intermediate perfluorospiro[benzocyclobutene-1,10-cyclopro-
pane] (14), the product of a cycloaddition of difluorocarbene
to the double bond of compound 13 (Scheme 4). Spiro-
derivative 14 could be further converted into diradical 15,
similar to that discussed for perfluorospiro[indan-1,10-cyclo-
propane] [10]. Four-membered ring opening of diradical 15 and
subsequent cyclization of diradical 16 lead to compound 1. The
formation of compound 13 from benzocyclobutene 5 may be
represented similar to that of compound 1 from indan 2 and
CHClF2 [3].
Copyrolysis of compound 5 with CHClF2 also gives
methyleneindan 1, but the main product of the reaction is 1-
chloro-2-(1-chloro-2,2-difluorovinyl)-3,4,5,6-tetrafluoroben-
zene (12). The latter is also formed in the pyrolysis of
compound 5 in a stream of argon (Scheme 4).
One can assume the possibility of compound 1 being formed
by intermediate formation of indan 2 with subsequent reaction
of the latter with CHClF2. But this route is improbable because
compound 3, which is formed in the reaction of indan 2 with
CHClF2 at 570 8C [3], was not identified in the reaction mixture
obtained in copyrolysis of compound 5 with CHClF2 at this
temperature.
One of possible routes for the transformation of compound 5
to styrene 12 can be formulated as shown in Scheme 5.
One can assume that compound 5 undergoes intramolecular
isomerization into intermediate 17 with subsequent opening of
the four-membered ring of the latter. A concert mechanism is
also likely.
It may be suggested that compound 1 is formed by
intermediate formation of perfluoro-1-methylenebenzocyclo-
butene (13) with subsequent four-membered ring expansion of
the latter under the action of difluorocarbene (Scheme 4). A
possibility of high-temperature expansion of the four-mem-
bered ring of polyfluorinated benzocyclobutenes to the five-
membered one under the action of difluorocarbene was
It should be noted that the reaction inverse to that discussed
above proceeds under photolysis of polyfluorostyrenes giving
polyfluorobenzocyclobutenes (Scheme 5) [11].
Compound 4, required for the investigation of high-
temperature reactions, was synthesized under the heating of
Scheme 2.

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V.M. Karpov et al. / Journal of Fluorine Chemistry 128 (2007) 714–717
The structures of the compounds were established by
elemental analysis, HRMS and spectral characteristics.
Assignment of signals in the 19F NMR spectra was made on
the basis of chemical shifts of the signals, their fine structure
and integral intensities. The spectrum of compound 11 is in
agreement with spectra of others polyfluorostyrenes [2,12,13].
Compounds 1 [3], 2 [14], 6 [3], 7 [3,15] were identified by
comparison of the 19F NMR data with those for authentic
samples.
3.1. Reaction of perfluoro-3,4-dihydronaphthalen-1(2H)-
one (18) with PCl5
A mixture of 5.9 g (18.1 mmol) of compound 18 with
12.8 g (61.3 mmol) of PCl5 was heated in a sealed ampoule
at 190 8C for 7 h. The contents were transferred into water.
The organic layer was dried over MgSO4 to give a mixture
(7 g), which contained (GLC and 19F NMR) 72% (yield
73%) of compound 4 and 10% (10%) of 19 together with
unidentified impurities. Chlorotetralins 4 and 19 were
isolated by preparative GLC (170 8C, SKTFT-50 on
chromaton N, N2).
Scheme 4.
1,1-Dichloroperfluorotetralin (4): liquid. NMR 19F
(CHCl3): d ꢀ106.5 (2F, F-4), ꢀ119.7 (2F, F-2), ꢀ127.5
(1F, F-8), ꢀ131.5 (2F, F-3), ꢀ136.7 (1F, F-5), ꢀ144.7 (1F, F-
7), ꢀ147.0 (1F, F-6); J4,5 = 21 Hz, J4,6 = 1 Hz, J4,7 = 2 Hz,
J
J
4,8 = 1 Hz,
J5,6 = 21 Hz,
J5,7 = 9 Hz,
J5,8 = 11 Hz,
6,7 = 21 Hz, J6,8 = 10 Hz, J7,8 = 21 Hz. Anal. Calcd for
C10Cl2F10: M 379.9217; C, 31.5; Cl, 18.6; F, 49.9%. Found:
HRMS m/z, 379.9214 (M+); C, 31.5; Cl, 18.6; F, 50.4%.
1,1,6-Trichloroperfluorotetralin(19): liquid. NMR 19F
(CHCl3): d ꢀ106.8 (2F, F-4), ꢀ114.3 (1F, F-5), ꢀ119.7
(2F, F-2), ꢀ123.9 (1F, F-7), ꢀ129.1 (1F, F-8), ꢀ131.3 (2F, F-
Scheme 5.
perfluoro-3,4-dihydronaphthalen-1(2H)-one (18) with PCl5
(Scheme 6). Other reaction product was 1,1,6-trichloroper-
fluorotetralin (19) together with unidentified impurities.
3);
J4,5 = 22 Hz, J4,7 = 2 Hz, J4,8 = 1 Hz, J5,7 = 5 Hz,
J5,8 = 13 Hz, J7,8 = 20 Hz. Anal. Calcd for C10Cl3F9: M
395.8922; C, 30.2; Cl, 26.8; F, 43.0%. Found: HRMS m/z,
395.8919 (M+); C, 30.5; Cl, 26.6; F, 43.0%.
3. Experimental
3.2. Copyrolysis of compound 4 with CHClF2
IR spectrum of styrene 12 was taken on a Bruker Vector 22
IR spectrophotometer. 19F NMR spectra of compounds were
recorded on a Bruker WP-200 SY instrument (188.3 MHz).
Chemical shifts are given in d (ppm) from CCl3F; C6F6
(ꢀ162.9 ppm from CCl3F) was used as internal standard. The
molecular masses of the compounds were determined by high-
resolution mass spectrometry on a Finnigan Mat 8200
instrument (EI 70 eV). Contents of products in the reaction
mixtures were established by GLC-method and 19F NMR
spectroscopic data.
Compound 4 (8.61 g) was passed through quartz tube
(400 mm ꢁ 20 mm) at 640–645 8C in a stream of CHClF2
(15 l/h) for 45 min. Distillation with steam gave 6.2 g of a
mixture (dried over MgSO4), which contained 57% of
methyleneindan 1 and 9% of methylindene 6.
3.3. Pyrolysis of compounds 3 and 4
1. By following a similar procedure, from 1.3 g of compound 4
in a stream of argon (15 l/h) at 640–645 8C (7 min) 0.85 g of
a mixture were obtained, which contained compounds 1
(16%), 2 (12%), 6 (29%) and 7 (5%).
2. Analogously to procedure (1), from 2 g of compound 3 in a
stream of argon (15 l/h) at 640–645 8C (10 min) 1.26 g of a
mixture were obtained, which contained compounds 1
(17%), 2 (19%), 6 (18%), 7 (13%).
Scheme 6.

V.M. Karpov et al. / Journal of Fluorine Chemistry 128 (2007) 714–717
717
3. Copyrolysis of compound 3 with CHClF2 gave a mixture,
which contained compounds 1 (69%) and 6 (4%) [3].
References
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(1975) 2383–2387;
3.4. Pyrolysis of 1,1-dichloroperfluorobenzocyclobutene
(5)
K.V. Dvornikova, V.E. Platonov, G.G. Yakobson, J. Org. Chem. USSR 11
(1975) 2430–2434 (English Translation).
[2] K.V. Dvornikova, V.E. Platonov, G.G. Yakobson, J. Fluorine Chem. 28
(1985) 99–113.
By following a procedure similar to that described above,
from 2 g of compound 5 [9] in a stream of argon at 630–635 8C
(10 min) 1.46 g of a mixture were obtained, which contained
81% of compound 12. Analytical sample of compound 12 was
isolated by preparative GLC (140 8C, SKTFT-50 on chromaton
N, N2).
[3] V.M. Karpov, V.E. Platonov, I.P. Chuikov, G.G. Yakobson, J. Fluorine
Chem. 22 (1983) 459–473.
[4] Yu.A. Panshin, Zh. Fiz. Khim. (Russ.) 40 (1966) 2226–2230;
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New York, 1964 (Chapter 5).
[7] R. Fields, R.N. Haszeldine, J. Chem. Soc. (1964) 1881–1889.
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816–821;
1-Chloro-2-(1-chloro-2,2-difluorovinyl)-3,4,5,6-tetrafluoro-
benzene (12): liquid. IR (CCl4) n, cmꢀ1: 1745 (CCl = CF2);
1630, 1514, 1477 (fluorinated aromatic ring). NMR 19F
(CHCl3): d ꢀ83.0 (1F, F-Y), ꢀ83.9 (1F, F-Z), ꢀ135.5 (1F, F-
3), ꢀ137.0 (1F, F-6), ꢀ150.5 (1F, F-5), ꢀ156.1 (1F, F-4);
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Nauk SSSR Ser. Khim. (1988) 1839–1845;
J
Y,Z = 21 Hz, JY,3 = 2 Hz, JZ,3 = 3 Hz, J3,4 = 22 Hz, J3,5 =
5 Hz, J3,6 = 10 Hz, J4,5 = 20 Hz, J4,6 = 3 Hz, J5,6 = 21 Hz.
Anal. Calcd for C8Cl2F6: M 279.9281; C, 34.2; Cl, 25.2; F,
40.6%. Found: HRMS m/z, 279.9286 (M+); C, 34.6; Cl, 25.4;
F, 40.4%.
I.P. Chuikov, V.M. Karpov, V.E. Platonov, G.G. Yakobson, Bull. Acad. Sci.
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2385–2390;
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(1974) 2396–2401 (English Translation).
3.5. Copyrolysis of compound 5 with CHClF2
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19 (1983) 2164–2173;
1. By following a procedure similar to that described above,
from 1.5 g of compound 5 and CHClF2 at 620 8C (8 min)
0.91 g of a mixture were obtained, which contained
compounds 1 (9%) and 12 (70%).
2. Analogously to procedure (1), from 1.1 g of compound 5
and CHClF2 at 570 8C (6 min) 0.6 g of a mixture were
obtained, which contained compounds 1 (11%), 5 (27%) and
12 (45%).
V.M. Karpov, V.E. Platonov, I.P. Chuikov, G.G. Yakobson, J. Org. Chem.
USSR 19 (1983) 1880–1888 (English Translation).
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(1974) 663–664;
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133094g.