The alicyclic ring contraction of perfluoro-1-phenyltetralin in reaction with antimony pentafluoride

Article abstract of DOI:10.1016/j.jfluchem.2003.09.006

Perfluoro-1-phenyltetralin (1) heated with antimony pentafluoride at 130-°C, then treated with water, gave a mixture of perfluorinated 3-methyl-2-phenylindenone (3), 3-methyl-2-phenylindene (4), 3-hydroxy-1-methyl-3-phenylindan (5), 1-methyl-3-phenylindan (6), 9-methyl-1,2,3,4,5,6,7,8-octahydroanthracene (7), and 1,9-dimethyl-5,6,7,8-tetrahydro-β-naphthindan (8). When heated with SbF₅ in the presence of HF, then treated with water, compound 1 is transformed to a mixture of products 3-6. The reaction at 170 and 200 °C forms compounds 3-6 together with perfluoro-2-(cyclohexen-1-yl)-3-methylindene (10).

Full text of DOI:10.1016/j.jfluchem.2003.09.006

Journal of Fluorine Chemistry 125 (2004) 49–53
The alicyclic ring contraction of perfluoro-1-phenyltetralin
in reaction with antimony pentafluoride
Vladimir R. Sinyakov, Tatyana V. Mezhenkova, Victor M. Karpov*, Vyacheslav E. Platonov
N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Novosibirsk 630090, Russia
Received 10 July 2003; received in revised form 24 September 2003; accepted 26 September 2003
Abstract
Perfluoro-1-phenyltetralin (1) heated with antimony pentafluoride at 130 8C, then treated with water, gave a mixture of perfluorinated 3-
methyl-2-phenylindenone (3), 3-methyl-2-phenylindene (4), 3-hydroxy-1-methyl-3-phenylindan (5), 1-methyl-3-phenylindan (6), 9-methyl-
1,2,3,4,5,6,7,8-octahydroanthracene (7), and 1,9-dimethyl-5,6,7,8-tetrahydro-b-naphthindan (8). When heated with SbF5 in the presence of
HF, then treated with water, compound 1 is transformed to a mixture of products 3–6. The reaction at 170 and 200 8C forms compounds 3–6
together with perfluoro-2-(cyclohexen-1-yl)-3-methylindene (10).
# 2003 Elsevier B.V. All rights reserved.
Keywords: Skeletal transformations; Perfluorophenyltetralin; Alicyclic ring contraction; Antimony pentafluoride; NMR spectroscopy
1. Introduction
9,10-dihydroanthracene and perfluoro-6-ethyl-1,2,3,4-tetra-
hydroanthracene [6]. In contrast to this, perfluoro-1-phenyl-
benzocyclobutene does not undergo skeletal transformations
under the same conditions [6].
The aim of this paper is to investigate the behavior of
perfluoro-1-phenyltetralin (1) under the action of antimony
pentafluoride in order to study the effect of the perfluoroaryl
group and the size of the alicycle on the route of the skeletal
transformations of polyfluorobenzocycloalkenes.
Among the chemical transformations of perfluorocarbons
of special interest are the skeletal rearrangements proceeding
under the action of Lewis acids. They are interesting largely
due to the fact that in the hydrocarbon series, cationoid
rearrangements are widespread, whereas in the series of
perfluorinated compounds, they occur very rarely. Thus,
the alicyclic ring contraction of 2-halopolyfluorotetralins in
the reaction with SbF5 [1] and the ring opening of perfluor-
ocyclopropane derivatives under the action of antimony
pentafluoride [2,3] or aluminium chlorofluoride [4] are both
known. Skeletal transformations of the four-, five- and six-
membered alicyclic fragments of perfluorinated benzocyclo-
butene, indan, tetralin, and their perfluoroalkyl derivatives
in an SbF5 medium have been investigated, see for example
[1–7] cited in our previous work [5].
Recently, we have found that the carbon framework in
perfluoro-1-phenylindan changes under the action of SbF5
to give perfluoro-9-methylfluorene and perfluorinated
di-, tetra- or octa-hydro derivatives of anthracene and b-
naphthindan [5]. When heated with antimony pentafluoride,
perfluoro-1-(2-ethylphenyl)benzocyclobutene is converted
to perfluoro-8,9-dimethyl-1,2,3,4-tetrahydrofluorene while
perfluoro-1-(4-ethylphenyl)benzocyclobutene gives 2-ethyl-
2. Results and discussion
Compound 1 was obtained by electrophilic alkylation of
pentafluorobenzene by perfluorotetralin (2) in the presence of
antimony pentafluoride [7]. It has been shown that compound
1 undergoes skeletal transformations under the action of SbF5
at high temperature. Thus, tetralin 1, heated with antimony
pentafluoride at 130 8C (15 h) and then treated with water,
gives a mixture of perfluoro-3-methyl-2-phenylindenone
(3) and small amounts of perfluoro-3-methyl-2-phenylindene
(4), 3-hydroxy-perfluoro-1-methyl-3-phenylindan (5) in
addition to perfluoro-1-methyl-3-phenylindan (6), perfluoro-
9-methyl-1,2,3,4,5,6,7,8-octahydroanthracene (7), and per-
fluoro-1,9-dimethyl-5,6,7,8-tetrahydro-b-naphthindan (8).
The reaction mixture also contains unchanged compound
1 together with 1-hydroxy-perfluoro-1-phenyltetralin (9)
(Scheme 1).
* Corresponding author. Fax: þ7-3832-34-4752.
E-mail address: karpov@nioch.nsc.ru (V.M. Karpov).
0022-1139/$ – see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2003.09.006

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V.R. Sinyakov et al. / Journal of Fluorine Chemistry 125 (2004) 49–53
Scheme 1.
Heating at 130 8C (15 h) a solution of tetralin 1 (obtained
drous HF and then with water, leads to compounds 3–6 and a
small amount of perfluoro-2-(cyclohexen-1-yl)-3-methylin-
dene (10). The reaction at 170 8C (14.5 h) or at 200 8C (10 h)
forms compounds 3–6, 10, the yield of indene 10 increased
while the yield of compounds 3 and 4 decreased as compared
with the reaction at 130 8C (Scheme 1).
Isomerization of tetralin 1 to indan 6 under the action of
SbF5 possibly, proceeds analogously to the transformations
of perfluoroethyltetralins [8,9] (Scheme 2). At first, the per-
fluoro-4-phenyl-1-tetralinyl cation (11) could be generated
in the reaction of compound 2 with C6F5H in SbF5) and HF
in antimony pentafluoride and subsequent treatment of the
reaction mixture with water, leads to compounds 1, 3–6, and
9 but not compounds 7 and 8 (Scheme 1). It should be noted
that compounds 7 and 8 were obtained in the reaction of
perfluoro-1-phenylindan with SbF5 in the absence of HF [5].
Prolonged heating of equimolar amounts of tetralin 1 and
HF with excess of antimony pentafluoride at 130 8C (60 h),
with further treatment of the reaction mixture with anhy-
Scheme 2.

V.R. Sinyakov et al. / Journal of Fluorine Chemistry 125 (2004) 49–53
51
Scheme 3.
from compound 1. Cation 11 will be transformed, presum-
ably, by the 1,2-shift of the perfluoroalkyl fragment, to
cation 12, which adds the fluoride ion to give indan 6.
Cation 11 is not the most stable one generated from tetralin
1, but its concentration is apparently sufficient for the
reaction.
Intramolecular attack at the ortho-position of the penta-
fluorophenyl ring by the benzyl carbon atom in cation 20
seems to give compound 21 after fluoride ion addition. It
may be suggested thatþin ion 22 generated from compound
21, elimination of CF3 occurs to give perfluoro-9-methyl-
anthracene (23). The latter then undergoes fluorination to
form compound 7, which isomerizes to product 8. Trans-
formation of compound 7 to product 8 was found by us
earlier [5].
The structures of the compounds were established by
HRMS and spectral characteristics. Assignment of signals
in the 19F NMR spectra of compounds was made on the basis
of chemical shifts of the signals, their fine structure and
integral intensities. Patterns observed in the spectra of
compounds 3, 4, and 10 are in agreement with those for
perfluoro-2,3-dimethylindenone, perfluoro-2,3-dimethylin-
dene, and other polyfluoroindenes [10,16]. Compounds 7
and 8 were identified by comparison of the 19F NMR data
with data for authentic samples [5].
Compounds 5 and 6 were obtained as E,Z-isomers.
Their 19F NMR spectra are in agreement with those for
other polyfluoroindans [1,8–11]. An E-configuration was
attributed to isomers of compounds 5 and 6, for which
signals of tert-F(1) atoms in 19F NMR spectra are located
at À7.3 and À9.0 ppm, and the Z-configuration, for which
tert-F(1) signals have chemical shifts 5.0 and 2.4 ppm,
respectively.
A possible route for the formation of compound 4 is also
presented in Scheme 2. The perfluoro-1-phenyl-1-tetralinyl
cation (13) generated from compound 1 in an SbF5 medium
is the most stable [7]. Cation 13 apparently undergoes an
intramolecular rearrangement, as a result of which it iso-
merizes into cation 14. The latter is transformed into the
perfluoro-1-benzyl-1-indanyl cation (15) which isomerizes
to the benzyl type ion 16. The double bond in the latter
evidently moves inside the chain. The intramolecular cycli-
zation of the vinylbenzyl cation 17 leads to the perfluoro-1-
methyl-2-phenyl-1-indanyl cation which adds fluoride ion to
produce perfluoro-1-methyl-2-phenylindan (18). A similar
transformation of perfluoro-1-alkyl-1-indanyl cations was
proposed for reactions of perfluoro-1-alkylindans with SbF5
[10,11]. Defluorination and/or disproportionation of com-
pound 18 gives indene 4. It should be noted that the
formation of perfluoro-2,3-dimethylindene from perfluoro-
1,2-dimethylindan [11,12] and disproportionation of poly-
fluorocyclohexadienes in an SbF5 medium are known
[13,14]. Fluorination of compound 4 with SbF5 leads to
indene 10.
It may be suggested that compounds 4 and 6 exist in an
SbF5 medium as salts of perfluoro-1-methyl-2-phenylinde-
nyl and perfluoro-3-methyl-1-phenyl-1-indanyl (19) cations
(cf. [7,10,15]); hydrolysis of these salts leads to the forma-
tion of products 3 and 5, respectively.
Compounds 7 and 8 are possibly formed from indan 6.
The process may be represented, for example, by Scheme 3,
similar to that for skeletal transformations of perfluoro-
1-phenylindan under the action of antimony pentafluoride
[5].
3. Experimental
The 19F NMR spectra of CHCl3 solutions of the reaction
mixtures and individual compounds were recorded on a
Bruker WP-200 SY instrument (188.3 MHz). Chemical
shifts are given in d (ppm) downfield from C6F6
(À162.9 ppm from CCl3F) as internal standard. GC-MS:
Hewlett Packard G1081A, combined with Hewlett Packard
5890 with mass selective detector HP 5971 (EI 70 eV). The
molecular masses of the compounds were determined by
Cation 19, generated from compound 6, possibly under-
goes cleavage of the five-membered ring to give cation 20.

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V.R. Sinyakov et al. / Journal of Fluorine Chemistry 125 (2004) 49–53
high-resolution spectrometry on a Finnigan Mat 8200 instru-
ment. Contents (yields) of products in the reaction mixtures
were established by GLC and GC-MS methods and 19F
NMR spectroscopic data.
4. Analogously to procedure (2), the reaction of C6F5H
(1.24 g), tetralin 2 (2.34 g), and SbF5 (10.22 g) (1.1:1:7)
gave (200 8C, 10 h) a mixture (3.28 g), containing 4%
(yield 4%) of 4, 23% (23%) of 5, 22% (22%) of 6, and
12% (11%) of 10. Compounds 4, 5 (E:Z ꢀ 25:75), 6
(E:Z ꢀ 15:85), and 10 were isolated by preparative GLC
(200 8C, SKTFT-50 on Chromaton N-AW-DMCS, N2)
from the combined products obtained from experiments
(2)–(4). Individual compound Z-5 (m.p. 70–71.5 8C)
was isolated by crystallization of 5 from hexane.
3.1. Reaction of perfluoro-1-phenyltetralin (1) with
antimony pentafluoride
Phenyltetralin 1 (1.44 g) and SbF5 (3.78 g) (molar ratio,
1:6) were heated in a nickel bomb (10 ml) for 15 h at 130 8C.
The mixture was poured into an ice-water and extracted with
CHCl3. The extract was dried over MgSO4. The solvent was
distilled off to give 1.24 g of the product, containing 17%
(yield 15%) of 1, 25% (25%) of 3, 2% (2%) of 4, 6% (5%) of
5, 6% (5%) of 6, 5% (4%) of 7, 5% (4%) of 8, and 16%
(14%) of 9. The yields of compounds 3–8 for converted
phenyltetralin 1 are 34, 3, 7, 7, 5, and 5%, respectively. The
individual compound 3 (0.17 g) was isolated by silica gel
column chromatography (CCl4 as eluent).
Perfluoro-3-methyl-2-phenylindene (4) (contaminated
with about 10% of 6): HRMS m/z, 457.9757 (Mþ). Calcd.
for C16F14 ¼ 457:9776. 19F NMR d: 96.9 (d, 3F,
JCF -Fð4Þ ¼ 21 Hz, CF3); 43.0 (2F, F-1); 26.6 (1F, F-4);
3
23.9 (1F, F-7); 16.2 (1F) and 13.3 (1F, F-5, F-6); 24.7
(2F, F-o); 13.3 (1F, F-p); 2.0 (2F, F-m) ppm.
3-Hydroxy-perfluoro-1-methyl-3-phenylindan (5): HRMS
m/z, 493.9774 (Mþ). Calcd. for C16HF15O ¼ 493:9788. GC-
MS m/z, 494 (Mþ) for Z-5 and for E-5 as well. Compound
Z-5: 19F NMR d: 88.0 (3F, CF3); 46.4 (1FA) and 38.7 (1FB,
JA;B ¼ 250 Hz, CF2-2); 28.5 (1F, F-7); 22.3 (1F, F-4), 18.0
(1F, F-5); 14.8 (1F, F-6); 24.0 (1F, F-o); 20.2 (1F, F-o); 12.7
(1F, F-p); 2.5 (1F, F-m); 2.0 (1F, F-m); 5.0 (1F, F-1) ppm.
Compound E-5: 19F NMR d: 86.8 (3F, CF3); 51.0 (1FA) and
38.2 (1FB, JA;B ¼ 245 Hz, CF2-2); 27.4 (1F, F-7); 21.9 (1F,
F-4), 17.7 (1F, F-5); 14.9 (1F, F-6); 24.1 (1F, F-o); 20.2 (1F,
F-o); 12.6 (1F, F-p); 2.6-1.9 (2F, F-m); À7.3 (1F, F-1) ppm.
Perfluoro-1-methyl-3-phenylindan (6): HRMS m/z,
495.9718 (Mþ). Calcd. for C16F16 ¼ 495:9744. GC-MS
m/z, 496 (Mþ) for Z-6 and for E-6. Compound Z-6: 19F
NMR d: 87.7 (3F, CF3); 46.0 (1FA) and 40.6 (1FB,
JA;B ¼ 255 Hz, CF2-2); 29.2 (1F, F-7); 24.2 (1F, F-4),
19.0 (1F, F-5); 18.3 (1F, F-6); 26.3 (dm, 1F,
JFðoÞ-Fð3Þ ¼ 60 Hz, F-o); 22.5 (1F, F-o); 14.6 (1F, F-p); 3.2
(1F, F-m); 1.6 (1F, F-m); 24.0 (dm, 1F, JFð3Þ-FðoÞ ¼ 60 Hz, F-
3); 2.4 (1F, F-1) ppm. Compound E-6: 19F NMR d: 86.4 (3F,
CF3); 49.5 (1FA) and 38.1 (1FB, JA;B ¼ 250 Hz, CF2-2); 28.4
(1F, F-7); 26.4–22.5 (4F, F-3, F-4, 2F-o), 19.0 (1F, F-5); 18.3
(1F, F-6); 14.4 (1F, F-p); 3.2–1.6 (2F, F-m); À9.0(1F, F-
1) ppm. Exact identification of some E-6 signals was diffi-
cult since they overlap with signals of the isomer Z-6.
Perfluoro-2-(cyclohexen-1-yl)-3-methylindene(10):HRMS
m/z, 533.9717(Mþ). Calcd. forC16F18 ¼ 533:9712. 19F NMR
Perfluoro-3-methyl-2-phenylindenone (3): m.p. 79.5–
81 8C (from hexane). HRMS m/z, 435.9769 (Mþ). Calcd.
for C16F12O ¼ 435:9757. 19F NMR d: 96.1 (3F, CF3); 29.7
(1F, F-7); 28.6 (1F, F-4); 20.8 (1F, F-5); 13.1 (1F, F-6); 25.5
(2F, F-o); 14.7 (1F, F-p); 1.6 (2F, F-m) ppm; JCF -Fð4Þ
¼
3
21 Hz, J4;5 ¼ 20 Hz, J4;6 ¼ 6:5 Hz, J4;7 ¼ 14 Hz, J5;6
¼
16 Hz, J5;7 ¼ 11 Hz, and J6;7 ¼ 21 Hz.
3.2. Reaction of perfluoro-1-phenyltetralin (1) þ HF
with antimony pentafluoride
1. Pentafluorobenzene (0.78 g) was added at room tem-
perature to a solution of 1.47 g of perfluorotetralin (2) in
6.4 g of SbF5 (molar ratio, 1.1:1:7) in a nickel bomb
(10 ml). The mixture was heated at 50 8C for 5 h
(preparation of 1 þ HF), then at 130 8C for 15 h and
treated as in the previous experiment to give 1.89 g of
the product, containing 14% (yield 13%) of 1, 16%
(16%) of 3, 2% (2%) of 4, 19% (17%) of 5, 10% (9%) of
6, and 20% (18%) of 9. The yields of compounds 3–6
for converted phenyltetralin 1 are 24, 3, 25, and 13%,
respectively. In this and the previous experiment, the
ratio of E:Z isomers is ꢀ15:85 for 5 and ꢀ40:60 for 6.
2. A mixture of phenyltetralin 1 þ HF and SbF5 prepared
from 0.87 g of C6F5H, 1.63 g of tetralin 2, and 7.11 g of
SbF5 (molar ratio, 1.1:1:7) was heated at 130 8C for
59.5 h. The mixture was diluted with anhydrous HF
(2.5–3 ml), poured onto ice and extracted with CHCl3.
The extract was dried over MgSO4. The solvent was
distilled off to give a product (2.2 g), containing 4%
(yield 4%) of 3, 13% (13%) of 4, 22% (21%) of 5, 27%
(26%) of 6, and 3% (3%) of 10.
d:96.6(d,3F,JCF -Fð4Þ ¼ 21 Hz,CF3);48.2(2F,F-1);27.7(1F,
3
F-4); 24.4 (1F, F-7); 16.3 (1F) and 14.7 (1F, F-5, F-6); 46.6
(1F, F-20); 43.7 (dm, 2F, JFð3 Þ-Fð2 Þ ¼ 20 Hz, F-30); 34.2 (1FA)
and 22.3 (1FB, JA;B ¼ 280 Hz), 32.7 (1FA) and 22.3 (1FB,
JA;B ¼ 280 Hz, CF2-40, CF2-50); 60.9 (1FA) and 37.1 (1FB,
JA;B ¼ 290 Hz, CF2-60) ppm.
0
0
3. Analogously to the previous procedure, the reaction of
C6F5H (0.82 g), tetralin 2 (1.54 g) and SbF5 (7.26 g)
(molar ratio, 1.1:1:7.6) gave (170 8C, 14.5 h) a mixture
(1.94 g), containing 3% (yield 3%) of 3, 8% (8%) of 4,
23% (20%) of 5, 28% (25%) of 6, and 10% (8%) of 10.
Acknowledgements
We gratefully acknowledge the Russian Foundation for
Basic Researches (project no. 99-03-32876a) for financial
support.

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