Skeletal transformations of perfluoro-1-ethyl-1-phenylbenzocyclobutene in the reaction with antimony pentafluoride

Article abstract of DOI:10.1016/j.jfluchem.2009.07.013

Interaction of perfluoro-1-ethyl-1-phenylbenzocyclobutene with SbF₅ at room temperature gives, after treatment of the reaction mixture with H₂O, perfluoro-4-[1-(2-methylphenyl)propylidene]cyclohexa-2,5-dienone as a main product. The

Full text of DOI:10.1016/j.jfluchem.2009.07.013

Journal of Fluorine Chemistry 130 (2009) 951–958
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Skeletal transformations of perfluoro-1-ethyl-1-phenylbenzocyclobutene in the
reaction with antimony pentafluoride
*
Tatyana V. Mezhenkova, Victor M. Karpov , Vyacheslav E. Platonov, Yuri V. Gatilov
N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Novosibirsk 630090, Russia
A R T I C L E I N F O
A B S T R A C T
Article history:
Interaction of perfluoro-1-ethyl-1-phenylbenzocyclobutene with SbF5 at room temperature gives, after
treatment of the reaction mixture with H2O, perfluoro-4-[1-(2-methylphenyl)propylidene]cyclohexa-
2,5-dienone as a main product. The reaction at 90–95 8C leads, after treatment with H2O, to a mixture of
perfluorinated 9-ethyl-9-methyl-1,2,3,4-tetrahydro-9H-fluorene, 9-ethyl-4a-methyl-4,4a-dihydrofluo-
ren-1-one, 3-ethyl-3-phenylphthalide, 1-hydroxy-2-methyl-1-phenylindan, 3-methyl-2-phenylinde-
none and small amounts of other products.
Received 6 February 2009
Received in revised form 16 April 2009
Accepted 21 July 2009
Available online 28 July 2009
Keywords:
ß 2009 Elsevier B.V. All rights reserved.
Skeletal transformations
Perfluoro-1-ethyl-1-
phenylbenzocyclobutene
Antimony pentafluoride
X-ray structure
NMR spectroscopy
Dedicated to the memory of Professor G.G.
Yakobson on the occasion of his 80th
birthday (1928–1984).
1. Introduction
heated with SbF5 give the products of alicyclic ring opening, which
then convert to polyfluorinated fluorene or anthracene derivatives.
In the hydrocarbon series cationoid rearrangements are wide-
spread, whereas in the series of perfluorinated compounds they
occur very rarely [1,2]. There was reported in the literature the
alicyclic ring contraction of 2-halopolyfluorotetralins in the
reaction with SbF5 [3] and the ring opening of perfluorocyclopro-
pane derivatives under the action of antimony pentafluoride [4] or
aluminium chlorofluoride [5]. Skeletal transformations of per-
fluorobenzocycloalkenes (benzocyclobutene, indan and tetralin)
and their perfluoroalkyl and perfluoroaryl derivatives in the
reactions with antimony pentafluoride have been investigated by
us [6–15]. Thus, perfluoro-1-methyl- and 1-ethylbenzocyclobu-
tenes undergo expansion of the four-membered ring to form
polyfluoroindans [6]. The mechanism of the process differs from
that for the non-fluorinated analogues [16]. The alicyclic ring
cleavage of perfluorodialkylbenzocyclobutenes leads to polyfluor-
ostyrenes, which subsequently undergo cyclization into poly-
fluoroindans or fluorination to perfluoro-ortho-dialkylbenzenes
[9,10]. Perfluoro-1-(2- or 4-ethylphenyl)benzocyclobutenes when
In contrast to this, perfluoro-1-phenylbenzocyclobutene does not
undergo skeletal transformations under the same conditions [13].
Perfluoro-1,2-diethyl-1-phenylbenzocyclobutene in mild condi-
tions undergoes four-membered ring opening along with alicyclic
and pentafluorobenzene rings expansion leading to polyfluoro-
benzoazulene derivatives [15].
In order to establish the common regularities of cationoid
skeletal transformations of polyfluorobenzocyclobutenes, contain-
ing perfluoalkyl group together with perfluoroaryl group in the
alicyclic fragment of the molecule, we have studied the reaction of
perfluoro-1-ethyl-1-phenylbenzocyclobutene (1) with SbF5.
2. Results and discussion
It has been shown that long standing (4 months) of
benzocyclobutene 1 in an excess of SbF5 at 20–25 8C leads, after
treatment of the reaction mixture with H2O, to perfluoro-4-[1-(6-
methylphenyl)propylidene]cyclohexa-2,5-dienone (2) as a main
product. Reaction mixture also contains perfluorinated 3-ethyl-3-
phenylphthalide (3), 9-ethyl-4a-methyl-4,4a-dihydrofluoren-1-
one (4) and a small amount of 9-ethyl-4a-methyl-4,4a-dihydro-
fluoren-3-one (5) (Scheme 1).
* Corresponding author. Fax: +7 3833 30 9752.
E-mail address: karpov@nioch.nsc.ru (V.M. Karpov).
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.07.013

952
T.V. Mezhenkova et al. / Journal of Fluorine Chemistry 130 (2009) 951–958
Scheme 1.
Prolonged heating of benzocyclobutene 1 with SbF5 at 50 8C
methylbenzene (7), 2-methyl-1-phenylindan (8), 3-methyl-2-
phenylindene (9) and compound 2. The reaction at 95 8C (73 h)
leads, after treatment of the reaction mixture with H2O, to
perfluoro-9-ethyl-9-methyl-1,2,3,4-tetrahydro-9H-fluorene (10),
1-hydroxyperfluoro-2-methyl-1-phenylindan (11), perfluoro-3-
(1 month) and further treatment of the reaction mixture
with anhydrous HF and then with water gives predominantly
perfluoro-9-ethyl-4a-methyl-4,4a-dihydro-3H-fluorene (6) along
with perfluorinated 1-[1-(cyclohexa-2,5-dienylidene)propyl]-2-
Scheme 2.

T.V. Mezhenkova et al. / Journal of Fluorine Chemistry 130 (2009) 951–958
953
Scheme 3.
methyl-2-phenylindenone (12), phthalide 3, fluorenone 4 and
small amounts of compounds 5, 6, 8, 9 and perfluoro-9-ethyl-4a-
methyl-4,4a-dihydro-1H-fluorene (13) (Scheme 1).
It has been shown earlier that perfluoro-1,2-dimethylindan
may transform to perfluoro-2,3-dimethylindene as a result of
defluorination, proceeding with participation of intermediate
double bond containing particles as acceptors of fluorine atoms
[10]. It is believed that in the process of defluorination of indan 21
styrene 16 may act as an acceptor of fluorine atoms (Scheme 2).
Transformation of styrene 16 to compound 17 may also proceed
under the action of SbF5 as fluorination agent (cf. fluorination of
fluoroolefins [17]).
Formation of cation 18 was observed in the reaction of
benzocyclobutene 1 with SbF5 at 20–25 8C. After the treatment
of the solution of a salt of cation 18 with water along with ketone 2
there was obtained phthalide 3 (Scheme 2). It may be supposed
that hydrolysis of cation 18 leads not only to ketone 2 but also to
hydroxyderivative 22, which transforms to phthalide 3 under the
action of antimony pentafluoride and water during the aqueous
treatment of the reaction mixture (cf. the formation of 3-
dichloromethyleneperfluoroindan-1,2-dione together with 3-
dichloromethyleneperfluoroindan-1-one (ratio, 1:1) during the
aqueous treatment of a solution of a salt of 3-dichloromethyle-
neperfluoroindan-1-yl cation in SbF5 [18]).
Transformation of benzocyclobutene 1 to products 2, 3, 7-9 may
be represented by Scheme 2. Thus, reversible elimination of the
fluoride ion from compound 1 under the action of SbF5 possibly
leads to cation 14, which undergoes alicyclic ring opening to give
cation 15 and then compound 16 after the fluoride ion addition.
Subsequent fluorination leads to product 17, which under the
action of SbF5 gives perfluoro-1-(2-methylphenyl)-1-phenylprop-
1-yl cation (18). Addition of the fluoride ion to cation 18 leads to
compound 7. On the other hand cation 15 may undergo
intramolecular cyclization to form perfluoro-2-methyl-1-pheny-
lindan-1-yl cation (19), which adds the fluoride ion to give indan 8.
Opening of the four-membered ring and its expansion to the five-
membered one in compound 1 under the action of SbF5 are similar
to those in perfluoroalkylbenzocyclobutenes [9,10], whereas
formation of indene 9 in this reaction seems to proceed another
way. It may be suggested that intramolecular attack of tetra-
fluorobenzene ring by cationic center in cation 14 leads to indanyl
cation 20, which adds the fluoride ion to form indan 21. The latter
undergoes defluorination to give indene 9 (Scheme 2). Relative
stabilities of cations 14, 15, 19 and 20 will be discussed below.
Cation 19 and perfluoro-1-methyl-2-phenylindenyl cation (23)
have been generated from compounds 8 and 9 in the system SbF5–
Scheme 4.

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T.V. Mezhenkova et al. / Journal of Fluorine Chemistry 130 (2009) 951–958
Scheme 5.
SO2ClF. The treatment of the solutions of the salts of cations 19 and
23 with water leads to products 11 and 12, respectively. In the case
of cation 19 reaction mixture also contained precursor 8 and
perfluoro-8-methyl-7-phenylbicyclo[4.3.0]nona-1,4,6-trien-3-
one (24) (Scheme 3).
Compounds 8, 11 and 24 have been also synthesized in a
separate experiment from perfluoro-2-methylindan (25) and
C6F5H in an SbF5 medium with subsequent hydrolysis of the
reaction mixture (Scheme 3).
DFT calculations of cations 14, 15, 19 and 20 show that cation 19
is more stable by 19.0 and 16.0 kcal molꢀ1 than cations 15 and 20,
respectively. Cation 14 has not local minimum on a potential
energy surface. Therefore we have calculated perfluoro-1-acetyl-1-
phenylbenzocyclobutene. The calculation has showed that this
ketone has two stable conformers. Then C55O groups of both
conformers of the ketone were replaced with C(+)–F and resulted
structures of 14 were optimized. During optimization one
conformer was transformed into cation 15 and the other was
transformed into cation 20.
Formation of fluorene derivatives 6, 10 and 13 may be
represented as a result of transformation of cation 18 in an SbF5
medium (Scheme 4). At first in cation 18 there occurs aromatic ring
attackbyapositivelycharged ortho-carbonofthepentafluorophenyl
group (resonance structure 18a) leading to ion 26, which then
transforms into perfluoro-9-ethyl-4a-methyl-4,4a-dihydro-3H-
fluoren-3-yl cation (27) by the fluoride ion addition–elimination.
Cation27addsthefluorideiontoformcompounds6, 13andpossibly
compound 28. Elimination of the fluoride ion from the latter gives
cation 29. Isomerization of cation 29 to 30 by CF3 group migration
and subsequent addition–elimination of the fluoride ion leads to
cation 31. The latter transforms into cation 32 by 1,2-shift of CF3
group. The possibility of CF3 group migration to cationic centre was
discussed in relation to the route of isomerization of perfluoro-1-
ethylindan to perfluoro-1,1-dimethylindan under the action of SbF5
[8]. Addition of the fluoride ion to cation 32 leads to compound 33,
which then undergoes fluorination and isomerization with removal
of the double bond to give product 10 (Scheme 4). It should be noted
that compound 33 may be also regarded as an acceptor of fluorine
atoms in the process of defluorination of indan 21 to indene 9.
Cation 27 has been generated from compound 6 in the system
SbF5–SO2ClF. The treatment of the solution of the salt of cation 27
with water leads to ketones 4 and 5 (85:15) together with small
amounts of precursor 6 and its isomer 13 (60:40) (Scheme 5).
When the reaction mixture prepared by heating of benzocy-
clobutene 1 with SbF5 is treated with water, compounds 4–6, 13
are obtained with about the same ratio of isomers. At the same
time, after treatment with anhydrous HF and then with water, the
reaction mixture contains product 6 in the absence of isomer 13. In
addition, after treatment with anhydrous HF or water, the reaction
The structures of compounds 2, 4–8, 10, 11, 13 and 24 were
established by HRMS and 19F NMR spectroscopy. 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 fine structure of signals was interpreted in approximation to
the first order structure. Compounds 8 and 11 are formed as
mixtures of E- and Z-isomers. The configurations of E- and Z-
isomers of compound 8 were defined on the base of JFð1ÞꢀCF
ð2Þ
3
value, which is equal to 19 Hz for E-isomer. For Z-isomer exact
value of JFð1ÞꢀCF ð2Þ cannot be measured but it does not exceed 10 Hz
3
(cf. JFð1ÞꢀCF
and JFð2ÞꢀCF
values in polyfluoromethylindans
ð2Þ
ð1Þ
3
3
[8,20]). The larger value of 4JFð1ÞꢀCF
for E-isomer compared with
ð2Þ
3
Z-isomer of compound 8 indicates that the interacting nuclei in E-
isomer are closely spaced, or, in other words, that F(1) and CF3(2)
are located on one side of the ring plane (see fluorine through-
space coupling constants [21–23]).
The configurations of E-11 and Z-11 were supposed on the base
of tert-F(2) signal chemical shift value by analogy to 8. So, in
spectrum of isomer E-8 the signal of tert-F(2) atom, situated in cis-
position to C6F5-group, is shifed downfield (ꢀ174.1 ppm) as
compared with isomer Z-8 (ꢀ177.5 ppm). In view of this fact E-
configuration was attributed to that isomer of compound 11, for
which the signal of tert-F(2) atom is located at ꢀ171.4 ppm, and Z-
configuration, for which tert-F(2) signal has chemical shift
ꢀ175.8 ppm. Similar regularities were observed for E,Z-2-hydro-
xyperfluoro-1-methyl-2-phenylbenzocyclobutenes with config-
uration of E-isomer defined by X-ray diffraction [24].
Compounds 3, 9 and 12 were identified by comparison of the 19
F
NMR data with data for authentic samples [14,25]. The structures
of cations 18, 19, 23 and 27 were identified by 19F NMR spectra. The
regularities in the spectra of cations 18, 19 and 23 agree with those
for polyfluorodiarylmethyl [13,26], perfluoro-1-phenylindan-1-yl
[12] and polyfluoroindenyl cations [27], respectively.
mixtures contain E-isomer or
a mixture of E,Z-isomers of
compound 8, respectively (Scheme 1).
The formation of product 6 in the absence of isomer 13 and
compound E-8 in the absence of isomer Z-8 after quenching
reaction mixture with HF is apparently a result of a thermo-
dynamic control of the reaction. When the reaction mixture is
treated with water, compounds 6 and 13, E-8 and Z-8 are obtained
because the equilibrium between isomers has no time to attain.
Predominance of ketone 4 as compared with isomer 5 after
hydrolysis of cation 27 is apparently a result of a kinetic control of
the reaction and it is in agreement with MNDO calculated
distribution of positive charge on the carbon atoms (+0.505 and
+0.258, respectively) in this cation.
It should be noted that gas-phase DFT (PBE/TZ2P, PRIRODA
program [19]) calculations show that compound 6 is more stable
by 5.1 kcal molꢀ1 than its isomer 13, ketone 4 is less stable by
3.2 kcal molꢀ1 than its isomer 5, and E-isomer of compound 8 is
more stable by 2.3 kcal molꢀ1 than its Z-isomer.
The structures of compounds 2 and 4 were confirmed by X-ray
crystallography (Figs. 1 and 2).
According to a single crystal X-ray structure determination the
bond lengths in 4-methylenecyclohexa-2,5-dienone fragment of
compound 2 are close to those in perfluoro-8-ethyl-5-phenyl-7,8-
dihydronaphthalen-2(6H)-one [28]. The carbon atoms C3, C5, C7,
C14, attached to the atoms C4 and C13, linked by a double bond, are
located in two planes so that dihedral angle between the
C3C4C5C13 and C4C7C13C14 planes is equal to 11.18. Molecules
of compound 2 form centrosymmetric pairs with C1ꢁ ꢁ ꢁO1 distances
˚
˚
3.043(4) A (the sum of the van der Waals radii is 3.35 A [29]). It
should be also noted reduced intermolecular contacts F1ꢁ ꢁ ꢁF16
˚
2.775(4) and O1ꢁ ꢁ ꢁF17 2.885(4) A (the sums of the van der Waals
˚
radii are 2.92 and 3.04 A, respectively [29]) between pairs.

T.V. Mezhenkova et al. / Journal of Fluorine Chemistry 130 (2009) 951–958
955
determined by high-resolution mass spectrometry on a Finnigan
Mat 8200 instrument (EI 70 eV). GC–MS: Hewlett Packard G1081A,
combined with Hewlett Packard 5890 with mass selective detector
HP 5971 (EI 70 eV). Contents (yields) of products in the reaction
mixtures and the purity of analytical samples (ꢃ97%) were
established by GLC and 19F NMR spectroscopic data. Contents of
products are given in mass percents.
Antimony pentafluoride was distilled at atmospheric pressure
(bp 142–143 8C). Benzocyclobutene 1 was obtained according to
Ref. [31].
3.1. Reaction of perfluoro-1-ethyl-1-phenylbenzocyclobutene (1)
with SbF5
3.1.1. Reaction at room temperature
A mixture of benzocyclobutene 1 (0.98 g) and SbF5 (4.94 g)
(molar ratio, 1:11.5) in a sealed glass ampoule was held at 20–25 8C
for 4 months. According to the 19F NMR spectrum (SO2ClF) the
reaction mixture contained the salts of cations 18 and 27 (80:20).
Then C6F6 (2 ml) was added and the mixture was poured into 5%
hydrochloric acid and extracted with CHCl3. The extract was dried
over MgSO4. The solvent and C6F6 were distilled off to give 0.99 g of
the product, containing 70% (yield 69%) of compound 2, 7% (7%) of
3, 15% (15%) of 4 and 2% (2%) of 5. Compounds 2 (0.55 g), 4 (0.09 g)
and 0.04 g of a mixture of isomers 4 and 5 (88:12) were isolated by
silica gel column chromatography (CCl4 as eluent). Ketones 2 and 4
were then sublimed (50 8C, 2 Torr). By repeated chromatography of
0.04 g of a mixture of isomers 4 and 5 (88:12) on silica gel (hexane
as eluent) a fraction (0.016 g) contained isomers 4 and 5 (66:34)
was isolated.
Fig. 1. Molecular structure of 2. Thermal ellipsoids are drown at the 30% probability
˚
level. Selected bond lengths (A) and torsion angles (8): O1–C1 1.217(4), C1–C2
1.449(5), C1–C6 1.459(5), C2–C3 1.327(4), C3–C4 1.467(4), C4–C13 1.360(3), C4–C5
1.461(4), C5–C6 1.331(4), C4–C13–C7–C12 84.1(3), C4–C13–C14–C15–90.8(3), and
C3–C4–C13–C7 11.6(4).
3.1.1.1. Perfluoro-4-[1-(6-methylphenyl)propylidene]cyclohexa-2,5-
dienone (2).
Fig. 2. Molecular structure of 4. Thermal ellipsoids are drown at the 30% probability
mp 57.5–59 8C. NMR 19F (282.4 MHz, (CH3)2CO):
d
ꢀ55.3 (3F,
˚
level. Selected bond lengths (A) and torsion angles (8): O1–C1 1.211(5), C1–C2
1.475(6), C1–C9A 1.487(5), C2–C3 1.326(6), C3–C4 1.492(6), C4A–C9A 1.529(4),
C4A–C4 1.547(5), C9–C9A 1.347(5), C3–C4–C4A–C9A ꢀ41.2(4), and C9A–C9–C11–
C12 96.8(4).
CF3-11), ꢀ77.7 (3F, CF3-10), ꢀ99.86 (1F, F-9), ꢀ99.92 (1F, F-90),
ꢀ130.7 (1F, F-5), ꢀ132.1 (1F, F-8), ꢀ134.4 (1F, F-4), ꢀ135.9 (1F, F-
1), ꢀ146.3 (1F, F-3), ꢀ146.6 (1F, F-6), ꢀ147.0 (1F, F-7), ꢀ147.3 (1F,
In a molecule 4, indene fragment is planar within the limits of
F-2). J1,2 = J2,3 = J3,4 = 21, J1,3 = 9, J1,4 = 10, J2,4 = 7, JFð1ÞꢀCF ð11Þ ¼ 16,
3
˚
0
ꢂ0.064 A, and the cyclohexene moiety has a sofa conformation with
JFð4ÞꢀCF
¼ 9,
J5,6 ꢄ 5,
J5,8 ꢄ J7,8 ꢄ 7,
J5,9 = 54,
J5,9 = 83,
ð10Þ
ð10Þ
3
the C4a atom deviation of 0.571(5) A from the plane of other atoms. In
JFð5ÞꢀCF
¼ 29. HRMS m/z, 511.9684 (M+). Calcd for
˚
3
the Cambridge structural database [30] there are no structures
containing a 2,3-difluoro-6-methylenecyclohex-2-enone fragment. It
is necessary to note syn-orientation of the C(12)F3 group relative to
the C(10)F3 group; according to gas phase DFT/PBE/TZ2P calculations
anti-orientation is less stable by 1.5 kcal molꢀ1 than syn-orientation.
It is interesting to note that in compound 4, unlike compound 2, the
O1 atom has no short intermolecular contacts. Contacts F5ꢁ ꢁ ꢁF14
C
16F16O = 511.9688.
3.1.1.2. Perfluoro-9-ethyl-4a-methyl-4,4a-dihydrofluoren-1-one
(4). mp 71–72.5 8C. NMR 19F (188.3 MHz, CHCl3):
d
ꢀ65.8 (3F, CF3-
4a), ꢀ83.7 (3F, CF3CF2-9), ꢀ93.0 (1F, FA) and ꢀ110.3 (1F, FB, F-4),
ꢀ110.7 (1F, FA1 ) and ꢀ111.5 (1F, FB1 , CF3CF2-9), ꢀ129.7 (1F, F-8),
ꢀ132.6 (1F, F-5), ꢀ135.1 (1F, F-3), ꢀ141.4 (1F, F-2), ꢀ146.0 (1F, F-
˚
2.830(4) and F7ꢁ ꢁ ꢁF9 2.831(3) A can be marked out.
7), ꢀ146.4 (1F, F-6). JA,B = 285, JA
¼ 279, J2,3 ꢄ 2, J2,A = 11,
1
1
;B
J2,B = 15, J3,A = 29, J3,B = 15, JFðBÞꢀCF
¼ 14, JFð5ÞꢀCF
¼ 19,
ð4aÞ
ð4aÞ
3
3
J5,B = 32, J5,6 = 20, J5,7 = 7, J5,8 = 15, J6,7 = 19, J6,8 = 8, J7,8 = 19,
3. Experimental
JFð8ÞꢀCF
¼ 14; J
¼ 67; J8;B ¼ 34. HRMS m/z, 511.9688 (M+).
1
1
ð9Þ
8;A
3
19F NMR spectra were recorded on a Bruker AV 300 instrument
(282.4 MHz) and on a Bruker AC 200 instrument (188.3 MHz).
Calcd for C16F16O = 511.9688.
Chemical shifts are given in
d
ppm from CCl3F, J values in Hz; C6F6
3.1.1.3. Perfluoro-9-ethyl-4a-methyl-4,4a-dihydrofluoren-3-one
and SO2ClF (ꢀ162.9 and 99.9 ppm from CCl3F) were used as
(5). Mixture with isomer 4 (4:5 = 66:34). Compound 5: NMR 19F
internal standards. The molecular masses of the compounds were
(282.4 MHz, CHCl3):
d
ꢀ66.8 (3F, CF3-4a), ꢀ84.3 (3F, CF3CF2-9),

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T.V. Mezhenkova et al. / Journal of Fluorine Chemistry 130 (2009) 951–958
ꢀ105.2 (1F, FA) and ꢀ116.2 (1F, FB, F-4), ꢄꢀ111 (2F, F-1, CF3CF2-9),
ꢀ130.2 (1F, F-8), ꢀ131.6 (1F, F-5), ꢀ141.1 (1F, F-2), ꢀ146.0 and
Mixture with isomer 6 (6:7 = 41:59). Compound 7. NMR 19F
(282.4 MHz, CHCl3):
d
ꢀ57.5 (3F, CF3-12), ꢀ80.2 (3F, CF3-11),
ꢀ147.1 (2F, F-6,7). NMR 19F (282.4 MHz, CHCl3 + (CH3)2CO):
d
ꢀ102.51 (1F, F-10), ꢀ102.55 (1F, F-100), ꢀ109.0 (1F, F-7), ꢀ109.2 (1F,
F-70), ꢀ135.5 (1F, F-4), ꢀ136.1 (1F, F-1), ꢀ137.6 (1F, F-5), ꢀ141.0 (1F,
F-9), ꢀ147.5 (1F, F-3), ꢀ148.6 (1F, F-2), ꢀ150.3 (1F, F-8), ꢀ150.6 (1F,
ꢀ65.9 (3F, CF3-4a), ꢀ83.4 (3F, CF3CF2-9), ꢀ103.9 (1F, FA) and
ꢀ115.0 (1F, FB, F-4), ꢄꢀ110 (2F, CF3CF2-9), ꢀ111.3 (1F, F-1), ꢀ130.4
(1F, F-8), ꢀ132.0 (1F, F-5), ꢀ140.7 (1F, F-2), ꢀ146.2 and ꢀ147.3 (2F,
F-6,7). JA,B = 286. GC–MS m/z, 512 (M+) for 4 and for 5.
F-6). J1,2 = J2,3 = J3,4 = 21, J1,3 = 8, J1,4 = 10, JFð1ÞꢀCF ð12Þ ¼ 16, J2,4 = 6,
3
0
0
0
JFð4ÞꢀCF
¼ 9, J5,7 ꢄ J5,7 ꢄ J7,9 ꢄ J7 ,9 ꢄ 10, J5,10 = 81, J5,10 = 57,
ð11Þ
ð11Þ
3
0
0
JFð5ÞꢀCF
¼ 28, J6,7 ꢄ J6,7 ꢄ J7,8 ꢄ J7 ,8 ꢄ 22. HRMS (mixture of
3
3.1.1.4. Perfluoro-1-(2-methylphenyl)-1-phenylprop-1-yl
isomers
6:7 = 41:59) m/z, 533.9712 Calcd for
(M+).
cation (18).
C
16F18 = 533.9707. GC–MS m/z, 534 (M+) for 6 and for 7.
3.1.3. Reaction at 95 8C
A mixture of benzocyclobutene 1 (0.9 g) and SbF5 (2.3 g) (molar
ratio, 1:5.8) in a nickel bomb (10 ml) was heated at 95 8C for 72 h.
Then C6F6 (1.5 ml) was added and the mixture was poured into 5%
hydrochloric acid and extracted with CH2Cl2. The extract was dried
over MgSO4. The solvent and C6F6 were distilled off to give 0.88 g of
the product, containing (GLC, 19F NMR spectrum) 9% (yield 9%) of
compound 3, 15% (14%) of 4, 2% (2%) of 5, 5% (5%) of 6, 7% (7%) of 8
(E:Z = 63:37), 3% (3%) of 9, 12% (10%) of 10, 22% (22%) of 11
(E:Z = 60:40), 11% (12%) of 12 and 3% (3%) of 13. Compound 3
(0.064 g) and 0.1 g of a mixture, containing 61% of compound 10
and 27% of isomers 6 and 13 (60:40) were isolated by silica gel
column chromatography (CCl4 as eluent). By repeated chromato-
graphy of this mixture on silica gel (hexane as eluent) product 10
(0.02 g) and a fraction (0.011 g), containing compounds 6, 10 and
13 (37:34:29), were isolated.
NMR 19F (282.4 MHz, SbF5–SO2ClF): ꢀ40.5 (1F, F-7), ꢀ54.4 (3F,
CF3-12), ꢀ72.1 (1F, F-5), ꢀ74.7 (3F, CF3-11), ꢀ83.7 (1F, F-9), ꢀ102.3
(1F, FA) and ꢀ103.7 (1F, FB, CF2-10), ꢀ127.5 (1F, F-1 or F-4), ꢀ129.0
(1F, F-1 or F-4), ꢀ134.4 (1F, F-2), ꢀ140.1 (2F, F-3,8), ꢀ140.5 (1F, F-
6). JA,B = 265, J5,A = 95, J5,7 ꢄ J7,9 ꢄ 65, J6,7 ꢄ J7,8 ꢄ 25.
3.1.2. Reaction at 50 8C
A mixture of benzocyclobutene 1 (0.92 g) and SbF5 (2.32 g)
(molar ratio, 1:5.8) in a sealed glass ampoule was heated at 50 8C
for 1 month. The reaction mixture and C6F6 (3 ml) was placed in a
Teflon container, and then anhydrous HF (7.5 ml) was added. The
mixture was kept at 25 8C for 5 h, then poured onto ice and
extracted with CHCl3. The extract was dried over MgSO4. The
solvent and C6F6 were distilled off to give 0.91 g of the product,
containing 4% (yield 4%) of compound 2, 52% (48%) of 6, 12% (11%)
of 7, 14% (14%) of E-8 and 8% (9%) of 9. Compound 6 (0.21 g) and
0.15 g of a mixture of isomers 6 and 7 (75:25) were isolated by
silica gel column chromatography (hexane as eluent). By repeated
chromatography of 0.15 g of a mixture of isomers 6 and 7 (75:25)
on silica gel (hexane as eluent) a fraction (0.03 g) contained
isomers 6 and 7 (41:59) was isolated.
3.1.3.1. Perfluoro-9-ethyl-9-methyl-1,2,3,4-tetrahydro-9H-fluorene
(10). NMR 19F (282.4 MHz, CHCl3):
d
ꢀ63.8 (3F, CF3-9), ꢀ82.6 (3F,
CF2CF3), ꢀ104.6 (1F, FA) and ꢀ105.6 (1F, FB, CF2CF3), ꢀ104.4, ꢀ108.8
(2F, FA1 , FA2 ) and ꢀ120.4, ꢀ124.2 (2F, FB1 , FB2 , F-1,4), ꢀ123.3 (1F, FA
)
,
3
and ꢀ138.9 (1F, FB3 , F-2 or F-3), ꢀ124.6 (1F, FA4 ) and ꢀ142.8 (1F, FB
4
F-3 or F-2), ꢀ128.3 (1F, F-8), ꢀ131.1 (1F, F-5), ꢀ146.3 and ꢀ146.7
(2F, F-6,7). JA,B = 285, JA 1 ꢄ JA 2 ꢄ 280; JA ¼ 280; JA ¼ 277.
1
2
3
3
4
4
;B
;B
;B
;B
HRMS m/z, 571.9682 (M+). Calcd for C16F20 = 571.9680.
3.1.3.2. Perfluoro-9-ethyl-4a-methyl-4,4a-dihydro-1H-fluorene
(13). Mixture with isomer and compound 10 (6:10:13 =
37:34:29). GC–MS m/z, 534 (M+) for 6 and for 13; 572 (M+) for
10. Compound 13: NMR 19F (282.4 MHz, CHCl3):
6
d
ꢀ65.9 (3F, CF3-
4a), ꢀ82.2 (3F, CF2CF3), ꢀ92.4 (1F, FA) and ꢀ101.3 (1F, FB, F-1),
ꢀ94.5 (1F, FA1 ) and ꢀ112.6 (1F, FB1 , F-4), ꢀ106.6 (1F, FA2 ) and
ꢀ108.1 (1F, FB2 , CF2CF3), ꢀ130.3 (1F, F-8), ꢀ132.0 (1F, F-5), ꢀ146.2
and ꢀ147.3 (2F, F-6,7), ꢀ149.0 and ꢀ150.3 (2F, F-2,3). JA,B = 300,
3.1.2.1. Perfluoro-9-ethyl-4a-methyl-4,4a-dihydro-3H-fluorene
(6). Liquid NMR 19F (282.4 MHz, CHCl3):
d
ꢀ66.2 (3F, CF3-4a),
ꢀ84.4 (3F, CF3CF2-9), ꢀ110.8 (1F, FA) and ꢀ112.0 (1F, FB, CF3CF2-9),
ꢀ111.3 (1F, FA1 ) and ꢀ119.2 (1F, FB1 , F-4), ꢀ111.6 (1F, FA2 ) and
ꢀ118.6 (1F, FB2 , F-3), ꢀ128.2 (1F, F-1), ꢀ131.2 (1F, F-8), ꢀ132.8 (1F,
F-5), ꢀ146.7 (1F, F-6), ꢀ147.4 (1F, F-2), ꢀ148.2 (1F, F-7). JA,B = 281,
JA
1
¼ 282; JA
¼ 283.
1
2
2
;B
;B
3.2. Reaction of perfluoro-2-methylindan (25) with C6F5H in the
presence of SbF5
JA
¼ 266; JA
¼ 282, J1,2 ꢄ 8, J1,A ꢄ J8,B ꢄ 77, J1,B ꢄ J8,A ꢄ 30,
1
2
2
J1;A 1ꢄ J1;B ꢄ 10; JFð1ÞꢀCF
¼ 10; J2;A ꢄ J2;B ꢄ 23; J2;B ꢄ 9;
;B
;B
2
2
2
2
1
ð9Þ
3
JFðA
¼ 15; JA
¼ 7; JA
¼ JB
¼ 10; JFðA
¼ 6;
A mixture of indan 25 and SbF5 was prepared by heating of
perfluoro-1-ethylbenzocyclobutene (1.7 g, 4.89 mmol) with SbF5
(5.95 g, 27.44 mmol) in a nickel bomb (10 ml) at 130 8C for 12 h [3].
Then pentafluorobenzene (0.95 g, 5.65 mmol) and C6F6 (3 ml) were
added to the mixture. The resulting mixture was held at 25 8C for
48 h, then poured into 5% hydrochloric acid and extracted with
CH2Cl2. The extract was dried over MgSO4. The solvent and C6F6
were distilled off to give 2.2 g of the product, containing 11% of
compound 8 (E:Z = 50:50), 66% of 11 (E:Z = 57:43) and 5% of 24. By
silica gel column chromatography (CCl4, then CHCl3 as eluents)
there were isolated compounds 8 (0.2 g, E:Z = 50:50), 24 (0.03 g)
and 11 (0.06 g, E:Z = 20:80; 0.9 g, E:Z = 54:46; 0.05 g, E:Z = 88:12).
By repeated chromatography of 0.2 g of the mixture of isomers 8
(E:Z = 50:50) on silica gel (hexane as eluent) there were isolated
fractions, containing compound 8 with a predominance of one or
another isomer (0.04 g, E:Z = 80:20; 0.012 g, E:Z = 18:82).
2
2
1
1
2
1
1
2
ÞꢀCF ð4aÞ
ÞꢀCF ð4aÞ
;B
;B
;B
ÞꢀCF ð4aÞ
3
3
JFðB
¼ 10; J5;B ¼ 54; JFð5ÞꢀCF
¼ 17, J5,6 = 20, J5,7 = 8,
ð4aÞ
1
1
3
3
J5,8 = 15, J6,7 = 18, J6,8 = 7, J7,8 = 21. HRMS m/z, 533.9706 (M+). Calcd
for C16F18 = 533.9707.
3.1.2.2. Perfluoro-1-(1-cyclohexa-2,5-dienylidene)propyl-2-methyl-
benzene (7).

T.V. Mezhenkova et al. / Journal of Fluorine Chemistry 130 (2009) 951–958
957
3.2.1. Perfluoro-2-methyl-1-phenylindan (8)
The solution was poured into water and extracted with CH2Cl2. The
extract was dried over MgSO4, and CH2Cl2 was distilled off to give
0.065 g of the product, containing 10% of compound
8
(E:Z = 67:33), 60% of 11 (E:Z = 38:62) and 22% of 24.
3.3.1. Cation (19)
NMR 19F (282.4 MHz, SbF5–SO2ClF):
d
ꢀ66.8 (3F, CF3), ꢄ–88 (2F,
F-40,5), ꢀ91.8 (1F, FA) and ꢀ102.8 (1F, FB, F-3), ꢀ96.6 (1F, F-20),
ꢀ99.9 (1F, F-60), ꢀ111.0 (1F, F-7), ꢀ127.6 (1F, F-4), ꢀ133.0 (1F, F-6),
ꢀ148.0 (2F, F-30,50), ꢀ163.1 (1F, F-2). JA,B = 255, J2 ,2 = 67.
0
3.4. Perfluoro-1-methyl-2-phenylindenyl cation (23)
mixture of E- and Z-isomers (E:Z = 80:20, E:Z = 18:82).
An analogous procedure was used to generate cation 23 from
indene 9 (0.06 g) and SbF5 (1.14 g) (molar ratio, 1:40) in SO2ClF
(0.21 g). Hydrolysis of the salt of cation 23 yielded 0.055 g of the
product, containing (GLC, 19F NMR spectrum) 95% of compound 12.
3.2.1.1. E-isomer. NMR 19F (282.4 MHz, CHCl3):
d–73.2 (3F, CF3),
ꢀ96.4 (1F, FA) and ꢀ104.3 (1F, FB, F-3), ꢀ137.2 (1F, F-20), ꢀ138.6 (1F,
F-60), ꢀ139.2 (1F, F-4), ꢀ140.2 (1F, F-7), ꢀ143.8 (1F, F-6), ꢀ144.5
(1F, F-5), ꢀ146.3 (1F, F-1), ꢀ148.3 (1F, F-40), ꢀ159.8 and ꢀ161.2 (2F,
F-30,50), ꢀ174.1 (1F, F-2). JA,B = 273, J1,2 ꢄ70, JFð1ÞꢀCF ꢄ 19, J1,5 = 7,
3.4.1. Cation (23)
0
3
JFðAÞꢀCF ꢄ 16, J4,5 = 20, J4,6 = 6, J4,7 = 17, J5,6 = 20, J5,7 = 7, J6,7 = 21,
NMR 19F (282.4 MHz, SbF5–SO2ClF):
d
18.3 (1F, F-1), ꢀ57.9 (1F,
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
J2 ,3 ꢄ J3 ,4 ꢄ J4 ,5 ꢄ J5 ,6 ꢄ 22, J2 ,4 ꢄ J4 ,6 ꢄ 5, J3 ,5 ꢄ 7.
F-7), ꢀ67.7 (3F, CF3), ꢀ89.3 (1F, F-4 or F-5), ꢀ91.0 (1F, F-4 or F-5),
ꢀ131.7 (2F, F-20,60), ꢀ137.8 (1F, F-6 or F-40), ꢀ142.2 (1F, F-6 or F-
40), ꢀ157.4 (2F, F-30,50). J1,4 ꢄ J5,7 ꢄ 55, J1,7 ꢄ 90.
3.2.1.2. Z-isomer. NMR 19F (282.4 MHz, CHCl3):
d
ꢀ74.3 (3F, CF3),
ꢀ100.0 (2F, F-3), ꢀ135.0 (1F, F-20), ꢀ139.3 (1F, F-60), ꢀ139.5 (1F, F-
4), ꢀ139.9 (1F, F-7), ꢀ143.7 (1F, F-6), ꢀ144.7 (1F, F-5), ꢀ145.5 (1F,
F-1), ꢀ148.0 (1F, F-40), ꢀ159.3 and ꢀ160.9 (2F, F-30,50), ꢀ177.5 (1F,
3.5. Perfluoro-9-ethyl-4a-methyl-4,4a-dihydro-3H-fluoren-3-yl
cation (27)
0
F-2). J1,2 = 72, J1,5 = 6, J4,5 = J5,6 = J6,7 = 20, J4,6 = J5,7 = 7, J4,7 = 17,
0
0
0
0
0
0
0
0
0
0
0
0
0
0
J2 ,3 ꢄ J3 ,4 ꢄ J4 ,5 ꢄ J5 ,6 ꢄ 22, J2 ,4 ꢄ J4 ,6 ꢄ 5, J3 ,5 ꢄ 7. HRMS
(E:Z = 50:50) m/z, 495.9744 (M+). Calcd for C16F16 = 495.9744.
GC–MS m/z, 496 (M+) for E-8 and for Z-8.
Cation (27) was generated by the analogous procedure from
compound 6 (0.085 g) and SbF5 (1.29 g) (molar ratio, 1:37) in
SO2ClF (0.17 g). Hydrolysis of the salt of cation 27 yielded 0.05 g of
the product, containing 75% of compound 4, 12% of 5, 4% of 6 and
2% of 13.
3.2.2. 1-Hydroxyperfluoro-2-methyl-1-phenylindan (11)
Mixture of E- and Z-isomers (E:Z = 88:12, E:Z = 20:80).
3.5.1. Cation (27)
3.2.2.1. E-isomer. NMR 19F (282.4 MHz, CHCl3):
d
ꢀ72.4 (3F, CF3),
NMR 19F (282.4 MHz, SbF5–SO2ClF):
d
ꢀ17.7 (1F, F-1), ꢀ64.1 (3F,
ꢀ94.4 (1F, FA) and ꢀ107.0 (1F, FB, F-3), ꢀ136.6 and ꢀ141.3 (2F, F-
20,60), ꢀ140.5 (1F, F-4), ꢀ142.4 (1F, F-7), ꢀ145.5 (1F, F-6), ꢀ148.5
(1F, F-5), ꢀ150.4 (1F, F-40), ꢀ161.0 and ꢀ161.4 (2F, F-30,50), ꢀ171.4
(1F, F-2). JA,B = 271, JFð2ÞꢀCF ¼ 7, JFðAÞꢀCF ¼ 15, J4,5 = 21, J4,6 = 7,
CF3-4a), ꢀ69.5 (1F, F-3), ꢀ79.5 (3F, CF2CF3), ꢀ85.6 (1F, FA) and
ꢀ112.6 (1F, FB, F-4), ꢀ94.1 (1F, F-8), ꢀ98.2 (1F, F-6), ꢀ105.0 (1F,
FA1 ) and ꢀ106.1 (1F, FB1 , CF2CF3), 41.5 (1F, F-5), ꢄ29.3 (2F, F-2,7).
JA,B = 301, JA
¼ 287.
1
1
;B
3
3
0
0
0
0
0
0
0
0
J4,7 = 17, J5,6 = 19, J5,7 = 6, J6,7 = 21, J2 ,4 ꢄ J4 ,6 ꢄ 5, J3 ,4 ꢄ J4 ,5 ꢄ 22.
3.6. X-ray crystallography
3.2.2.2. Z-isomer. NMR 19F (282.4 MHz, CHCl3):
d–73.9 (3F, CF3),
ꢀ99.3 (1F, FA) and ꢀ100.1 (1F, FB, F-3), ꢀ137.1 and ꢀ138.9 (2F, F-
20,60), ꢀ141.0 (1F, F-4), ꢀ141.4 (1F, F-7), ꢀ145.2 (1F, F-6), ꢀ148.2
(1F, F-5), ꢀ150.3 (1F, F-40), ꢀ160.5 and ꢀ161.3 (2F, F-30,50), ꢀ175.8
(1F, F-2). JA,B = 273, J4,5 = 20, J4,6 = 7, J4,7 = 17, J5,6 = J6,7 = 19, J5,7 = 6,
A powder of compound 2 or 4 was placed in an ampoule. Then
the ampoule was evacuated (2 Torr), sealed and heated at 50 8C
during 2 weeks. Single crystals of compounds 2 and 4 were grown.
The X-ray diffraction experiments were carried out on a Bruker
0
0
0
0
0
0
0
0
0
0
0
0
0
0
J2 ,3 ꢄ J3 ,4 ꢄ J4 ,5 ꢄ J5 ,6 ꢄ 22, J2 ,4 ꢄ J4 ,6 ꢄ 5, J3 ,5 ꢄ 7. HRMS
(E:Z = 88:12) m/z, 493.9785 (M+), (E:Z = 20:80) m/z, 493.9784
(M+). Calcd for C16F16 = 495.9744.
P4 diffractometer (graphite monochromated Mo K
a radiation, u/
2u
-scan, 2 < 548) at room temperature. Reflection intensities of 2
u
and 4 were corrected for evaporation and absorption (2) by
empirical method. The structures were solved by direct methods
and refined by anisotropic full-matrix least squares against F2 of all
reflections using SHELX-97 programs [32]. Crystallographic data
for the structures 2 and 4 in this paper have been deposited at the
Cambridge Crystallographic Data Centre as supplement publica-
tion no. CCDC 698633 and 698634. Copy of the data can be
obtained, free of charge, on application to CCDC (e-mail:
deposit@ccdc.cam.ac.uk, internet: http://www.ccdc.cam.ac.uk/
deposit).
3.2.3. Perfluoro-8-methyl-7-phenylbicyclo[4.3.0]nona-1,4,6-trien-3-
one (24)
NMR 19F (282.4 MHz, CHCl3):
d
ꢀ75.8 (3F, CF3), ꢀ105.9 (1F, FA)
and ꢀ110.4 (1F, FB, F-6), ꢀ122.5 (1F, F-4), ꢀ135.5 (1F, F-20), ꢀ137.0
(1F, F-1), ꢀ138.6 (1F, F-60), ꢀ138.9 (1F, F-2), ꢀ147.0 (1F, F-40),
ꢀ159.8 and ꢀ160.0 (2F, F-30,50), ꢀ168.2 (1F, F-7). JA,B = 277, J1,2 = 9,
0
0
J1,2 ꢄ J1,6 ꢄ 7, J2,4 = 7, J4,A = 7, J4,B = 8, JFðBÞꢀCF ¼ 17, JFð7ÞꢀCF ¼ 12,
3
3
J7,2 ꢄ 36. HRMS m/z, 473.9730 (M+). Calcd for C16F14O =
0
473.9725.
3.6.1. Crystallographic data and refinement parameters for 2
3.3. Perfluoro-2-methyl-1-phenylindan-1-yl cation (19)
C16F16O, M = 512.16, orthorhombic, space group Pbca,
˚
a = 9.9571(15), b = 18.010(2), c = 19.140(2) A, V = 3432.3(8), Z = 8,
Dcalc = 1.982 g cmꢀ3
= 0.243, 6412 total reflexions, 3751 unique
reflexions (Rint = 0.1066), R = 0.0477 for 2142 I > 2 (I), 298
Indan 8 (0.07 g) was dissolved in SbF5 (1.22 g) (molar ratio,
1:40), then SO2ClF (0.1 g) was added at 0 8C and NMR 19F spectrum
of the solution was measured at 20 8C. The spectrum contained the
signals of cation 19 in the absence of the signals of the precursor 8.
, m
s
parameters, wR2 ¼ 0:1533 and GOF = 1.022 for all data, max/min
Dr 0.28/ꢀ0.23.

958
T.V. Mezhenkova et al. / Journal of Fluorine Chemistry 130 (2009) 951–958
[13] V.M. Karpov, T.V. Mezhenkova, V.E. Platonov, V.R. Sinyakov, J. Fluorine Chem. 117
(2002) 73–81.
[14] V.R. Sinyakov, T.V. Mezhenkova, V.M. Karpov, V.E. Platonov, J. Fluorine Chem. 125
(2004) 49–53.
[15] T.V. Mezhenkova, V.R. Sinyakov, V.M. Karpov, V.E. Platonov, T.V. Rybalova, Y.V.
Gatilov, J. Fluorine Chem. 129 (2008) 64–67.
[16] H.W. Whitlock, P. Fuchs, Tetrahedron Lett. (1968) 1453–1456.
[17] G.G. Belen’kii, Y.L. Kopaevich, L.S. German, I.L. Knunyants, Izv. Akad. Nauk SSSR,
Ser. Khim. (1972) 983;
3.6.2. Crystallographic data and refinement parameters for 4
16F16O, M = 512.16, monoclinic, space group Cc, a = 9.3786(5),
C
˚
b = 16.2874(9), c = 10.7469(6) A, V = 1641.4(2), Z = 4, Dcalc
2.073 g cmꢀ3
= 0.254, 1893 total unique reflexions, R = 0.0286
for 1531 I > 2
=
,
m
s
(I), 298 parameters, wR2 ¼ 0:0843 and GOF = 1.091
for all data, max/min Dr 0.19/ꢀ0.19.
G.G. Belen’kii, Y.L. Kopaevich, L.S. German, I.L. Knunyants, Bull. Acad. Sci. USSR
Div. Chem. Sci. 21 (1972) 950 (English translation).
Acknowledgement
[18] V.M. Karpov, V.E. Platonov, Zh. Org. Khim. 37 (2001) 1033–1039;
V.M. Karpov, V.E. Platonov, Russ. J. Org. Chem. 37 (2001) 981–987 (English
translation).
[19] D.N. Laikov, Chem. Phys. Lett. 281 (1997) 151–156.
[20] I.P. Chuikov, V.M. Karpov, V.E. Platonov, Izv. Akad. Nauk SSSR Ser. Khim. (1990)
837–845;
We gratefully acknowledge the Russian Foundation for Basic
Researches (project no. 06-03-32170) for financial support.
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