Transformations of perfluorinated 1-alkyl-, 1-phenyl- and 1,2-dialkylbenzocyclobutenes under the action of SiO2/SbF5

Article abstract of DOI:10.1016/j.jfluchem.2012.11.004

Heating of perfluorinated 1-methyl-, 1-ethyl- and 1- isopropylbenzocyclobutenes with SiO₂ in an SbF₅ medium at 75 °C results in perfluoro-2-alkylbenzocyclobutenones or perfluoro-3-alkylphthalides formation. Perfluorinated 1,2-diethyl- and 1-ethyl-2-methylbenzocyclobutenes react with SiO₂/SbF₅ at 75 °C to form, after treatment of the reaction mixture with water, perfluorinated 1,3-diethyl- and 1-ethyl-3-methylphthalan-1,3-diol, respectively. Perfluoro-1,2-diisopropylbenzocyclobutene under the action of SiO ₂/SbF₅ at 95 °C is converted to perfluoro-7,8- diisopropylbicyclo[4.2.0]octa-1,5,7-triene-3,4-dione and perfluoro-1,2- diisobutyrylbenzene. Perfluoro-1-methyl-2-phenylbenzocyclobutene does not react with SiO₂ in an SbF₅ medium at 75 °C, perfluoro-1-phenylbenzocyclobutene in analogous conditions gives a mixture of perfluorinated 2-hydroxy-2-phenylbenzocyclobutenone and 2-benzoylbenzoic acid.

Full text of DOI:10.1016/j.jfluchem.2012.11.004

Journal of Fluorine Chemistry 145 (2013) 41–50
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Transformations of perfluorinated 1-alkyl-, 1-phenyl- and
1,2-dialkylbenzocyclobutenes under the action of SiO2/SbF5
*
Yaroslav V. Zonov, Victor M. Karpov , Vyacheslav E. Platonov, Tatjana V. Rybalova
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:
Heating of perfluorinated 1-methyl-, 1-ethyl- and 1-isopropylbenzocyclobutenes with SiO2 in an SbF5
medium at 75 8C results in perfluoro-2-alkylbenzocyclobutenones or perfluoro-3-alkylphthalides
formation. Perfluorinated 1,2-diethyl- and 1-ethyl-2-methylbenzocyclobutenes react with SiO2/SbF5 at
75 8C to form, after treatment of the reaction mixture with water, perfluorinated 1,3-diethyl- and 1-
ethyl-3-methylphthalan-1,3-diol, respectively. Perfluoro-1,2-diisopropylbenzocyclobutene under the
action of SiO2/SbF5 at 95 8C is converted to perfluoro-7,8-diisopropylbicyclo[4.2.0]octa-1,5,7-triene-3,4-
dione and perfluoro-1,2-diisobutyrylbenzene. Perfluoro-1-methyl-2-phenylbenzocyclobutene does not
react with SiO2 in an SbF5 medium at 75 8C, perfluoro-1-phenylbenzocyclobutene in analogous
conditions gives a mixture of perfluorinated 2-hydroxy-2-phenylbenzocyclobutenone and 2-benzoyl-
benzoic acid.
Received 11 October 2012
Received in revised form 15 November 2012
Accepted 17 November 2012
Available online 30 November 2012
Keywords:
Perfluorinated
Benzocyclobutenes
Phthalides
Phthalanes
ß 2012 Elsevier B.V. All rights reserved.
Silicon dioxide
Antimony pentafluoride
1. Introduction
(Scheme 1) [4]. Thus, the presence of SiO2 induces the four-
membered ring cleavage of the substrate and changes the reaction
It is known that benzylic CF2 groups of perfluorinated
benzocycloalkenes (benzocyclobutene, indan, tetralin), 1,1-diethy-
lindane and 1-alkyltetralins is converted into C55O group under the
action of SiO2/SbF5 to give the corresponding benzocycloalken-1-
ones in good yields [1–3]; one example of such transformations is
illustrated by Scheme 1. Carbonyl derivatives of perfluorobenzo-
cycloalkenes and perfluoroalkylbenzocycloalkenes were found to
undergo carbocationic skeletal rearrangements under the action of
SbF5 leading to contraction, expansion, or cleavage of the aliphatic
ring of the substrate with further formation of oxygen-containing
heterocyclic compounds [3–6].
On the example of the reaction of perfluoro-2-ethylbenzocy-
clobutenone with SiO2, it was shown that SiO2 can influence the
direction of skeletal transformation of polyfluorobenzocyclobu-
ten-1-ones. Thus, heating of perfluoro-2-ethylbenzocyclobute-
none with SiO2 at 75 8C in an antimony pentafluoride medium
leads to the four-membered ring opening with further formation of
perfluoro-3-ethylphthalide. In the absence of SiO2 under similar
conditions the ketone does not change, whereas under more
drastic conditions skeletal transformation of another type is
occurred that results in perfluoro-2-methylindan-1-one formation
route. Other examples of such influence of SiO2 on transformations
of benzocyclobutene derivatives have not been earlier observed.
In this connection in order to establish the regularities of
transformations of perfluorobenzocyclobutene derivatives in
the system SiO2/SbF5 it seemed reasonable to study the
behaviour of a number of perfluoro-1-R-benzocyclobutenes
(R = perfluoroalkyl or perfluoroaryl groups). On the other hand,
it was of interest to investigate the possibility of transformations
of 1,2-disubstituted perfluorobenzocyclobutenes, which do not
contain benzylic CF2 groups, under the action of SiO2/SbF5. This
work describes the reaction of perfluorinated 1-alkyl-, 1-phenyl-
, 1,2-dialkyl-, and 1-methyl-2-phenyl-benzocyclobutenes with
SiO2 in the presence of SbF5.
2. Results and discussion
2.1. Reactions of dialkylbenzocyclobutenes 1, 2, 3 with SiO2/SbF5
Perfluorinated 1,2-diethyl- (1), 1-ethyl-2-methyl- (2) and 1,2-
diisopropyl-benzocyclobutenes (3) react with SiO2/SbF5 to form
products of the four-membered ring cleavage. Thus, heating of
diethylbenzocyclobutene 1 with SiO2/SbF5 at 75 8C and subsequent
hydrolysis
-1,3-diethylphthalan-1,3-diol (4) (Scheme 2). The transformation
of compound is more complicated. This process forms
of
the
reaction
mixture
gives
perfluoro
* Corresponding author. Fax: +7 3832 34 4752.
E-mail address: karpov@nioch.nsc.ru (V.M. Karpov).
2
0022-1139/$ – see front matter ß 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2012.11.004

42
Y.V. Zonov et al. / Journal of Fluorine Chemistry 145 (2013) 41–50
-
SbF5
SiO2
F
F
F
F
F
F
F
F
F
F
F
-[SiOF2]
+
+
OSiO
F
O
F
C2F5
O
C2F5
F
SbF5
SiO2/SbF5
75oC
F
F
CF3
120oC
O
O
O
Scheme 1.
HO CF2CF3
F
O
CF2CF3
CF2CF3
1) SiO2/SbF5 (1:6)
75oC, 10 h
2) H2O
,
,
F
F
F
F
CF2CF3
HO
1
2
4, yield 72%
HO CF2CF3
X
CF2CF3
CF2CF3
CF3
1) SiO2/SbF5 (1:7)
75oC, 5 h
2) H2O
unidentified
impurities
F
F
O
O
+
+
HO CF3
O
X = F 6 (13%)
OH 7 (6%)
5 (content 38%)
Scheme 2.
perfluoro-1-ethyl-3-methylphthalan-1,3-diol (5) along with per-
fluorinated 3-ethylphthalide (6), 3-hydroxy-3-ethylphthalide (7)
and large amounts of unidentified impurities.
reaction mixture. Supposed isomerization of epoxide 10 into
isobenzofuran 11 is analogous to earlier described isomerization of
1,2-diphenyl-1,2-epoxybenzocyclobutene into 1,3-diphenyliso-
benzofuran [8].
Because compounds 1 and 2 practically do not change under the
action of SbF5 at 75 8C in the absence of SiO2 [7], it signifies that
SiO2 plays a key role in these reactions. The transformation of
compound 1 to product 4 can be rationalized by Scheme 3. At first,
compound 1 with SbF5 seems to generate cation 8, which reacts
with SiO2 and then gives cation 9. Intramolecular attack of the
positively charged carbon atom of cation 9 at the oxygen atom and
subsequent elimination of silicon oxofluorides gives epoxide 10.
Isomerization of compound 10 into isobenzofuran 11, subsequent
fluorination and elimination of fluoride anion leads to the
formation of cation 12. Cleavage of the five-membered ring in
cation 12 and reaction of cation 13 with SiO2/SbF5 gives diketone
14, which is transformed to product 4 during hydrolysis of the
Reaction of diisopropylbenzocyclobutene 3 with SiO2/SbF5 at
75 8C and subsequent hydrolysis of the reaction mixture gives
perfluoro-7,8-diisopropylbicyclo[4.2.0]octa-1,4,6-triene-3-one
(15) as a major product together with perfluoro-7,8-diisopropyl-
bicyclo[4.2.0]octa-1,5,7-triene-3,4-dione (16) and perfluoro-1,2-
diisobutyrylbenzene (17) (Scheme 4). Despite the longer reaction
time in comparison with the reactions of compounds 1 and 2,
conversion of initial compound 3 is incomplete. Prolonged heating
of compound 3 with SiO2/SbF5 at 95 8C leads to it complete
conversion to compounds 16 and 17, reaction mixture also
contains small amounts of perfluorinated 3-isopropylphthalide
(18) and 3-hydroxy-3-isopropylphthalide (19).
C2F5
F
F
C2F5
C2F5
+
F
C2F5
C2F5
OSiFO
F
C2F5
C2F5
OSiFO
C2F5
F-
1) SiO2
2) F-
O
F
F
F
F
F
-F-
-F-
+
-[SiOF2]
C2F5
C2F5
1
8
9
10
11
C2F5
C2F5
SiO2/SbF5
C2F5
O
HO C2F5
O
C2F5
F
+
H2O
SbF5
F
O
F
F
O
F
F
F
-F-
+
O
O
-SbF3
C2F5
HO
C2F5
C2F5
C2F5
C2F5
13
12
4
14
Scheme 3.

Y.V. Zonov et al. / Journal of Fluorine Chemistry 145 (2013) 41–50
43
CF(CF3)2
X
CF(CF3)2
1) SiO2/SbF5 (1.5:6),
CF(CF3)2
O
O
95oC, 41 h
2) H2O
O
O
F
F
F
O
+
+
CF(CF3)2
CF(CF3)2
17 (11%)
O
X = F 18 (6%)
16 (81%)
OH 19 (2%)
1) SiO2/SbF5 (1:6),
75oC, 12.5 h
2) H2O
CF(CF3)2
CF(CF3)2
CF(CF3)2
F
F
F
F
16
(17%)
SiO2
17
+
+
O
CF(CF3)2
3
15 (66%)
(8%)
-F-
H2O
SbF5
CF(CF3)2
+
CF(CF3)2
CF(CF3)2
1) SiO2
2) F-
F
F
F
15
F
F
F
F
+
-[SiOF2]
CF(CF3)2
CF(CF3)2
CF(CF3)2
OFSiO
20
20
Scheme 4.
CF(CF3)2
CF(CF3)2
O
CF(CF3)2
F
CF(CF3)2
F-
O
O
O
F
F
F
F
O
-F-
+
O
+
-CF3CF=CF2
CF3CFCF2
CO
CF(CF3)2
O
17
21
22
18
Scheme 5.
It was shown that benzocyclobutene 3 does not undergo
skeletal transformations under the action of SbF5 in the absence of
SiO2, and therefore it seems likely that the mechanism of
compound 17 formation in these reactions is analogous to the
suggested one for the transformation of compound 1 in 4 (Scheme
3), but in contrast to the reaction of compound 1, the ring cleavage
is not the major reaction route for compound 3. Apparently the
proximity of two bulky perfluoroisopropyl groups hinders
interaction of SiO2 with cationic centre in the benzylic position
of cation 20 (Scheme 4), as a result, SiO2 reacts mainly with the
more sterically accessible centre of delocalized cation 20 to
produce ketone 15. Further reaction of the latter with SiO2/SbF5
gives diketone 16. Contribution of cation 20 hydrolysis reaction to
the total yield of ketone 15 also cannot be excluded, because it was
shown that hydrolysis of a SbF5 solution of compound 3 mainly
gives ketone 15.
The formation of phthalide 18 in the reaction of compound 3
with SiO2/SbF5 can be rationalized by Scheme 5. At first, compound
17 with SbF5 seems to generate cation 21 which eliminates of
hexafluoropropene to give benzyl type cation 22 (cf. transforma-
tion of perfluoro-o-isobutyltoluene into perfluoro-o-xylene under
the action of SbF5 [9]). Intramolecular cyclization of cation 22
gives, after addition of fluoride anion, compound 18.
In contrast to dialkylbenzocyclobutenes 1, 2 and 3, the four-
membered ring cleavage in perfluoro-1-methyl-2-phenylbenzo-
cyclobutene (23) does not occur under the action of SiO2/SbF5.
Thus, heating of compound 23 with SiO2/SbF5 at 75 8C and
subsequent hydrolysis of the reaction mixture results in perfluoro-
2-methyl-1-phenylbenzocyclobuten-1-ol (24) formation (Scheme
6). The latter is a product of hydrolysis of stable perfluoro-2-
methyl-1-phenylbenzocyclobuten-1-yl cation (23c) generated
from initial compound 23 under the action of antimony penta-
fluoride [10]. One can assume that stability of cation 23c is the
course of its low reactivity towards SiO2. As a result interaction of
cation 23c with SiO2 is hindered and four-membered ring cleavage
does not occur (cf. Scheme 3). It should be noted that low reactivity
of other stable cations towards SiO2 was earlier observed. For
example, polyfluorinated isochromenium ions practically do not
react with SiO2/SbF5 even at 125 8C to form isochromen-1-one
derivatives [6], whereas less stable perfluorobenzocycloalken-1-yl
cations react with SiO2/SbF5 at 75 8C to give the corresponding
benzocycloalken-1-ones [1–3,6].
2.2. Reactions of alkyl- and phenyl-benzocyclobutenes 25, 26, 27, and
34 with SiO2/SbF5
Reactions of perfluorinated 1-methyl- (25), 1-ethyl- (26) and 1-
isopropyl-benzocyclobutenes (27) with SiO2/SbF5 (molar ratio,
substrate:SiO2:SbF5 = 1:0.5:2) at 75 8C and subsequent hydrolysis
of the reaction mixtures give perfluoro-2-alkylbenzocyclobute-
nones (28), (29) and (30), respectively (Scheme 7). In the case of
compound 25 the reaction mixture also contains perfluoroindan-
1-one, which is a product of ketone 25 isomerization under the
reaction conditions [4].
Reaction of alkylbenzocyclobutenes 25, 26 and 27 with the
increasing amount of SiO2 and SbF5 (molar ratio, substrate:-
SiO2:SbF5 = 1:1.5:8) at 75 8C leads to the formation of
C6F5
1) SiO2/SbF5 (1.5:6)
75oC, 10 h
2) H2O
,
C6F5
CF3
F
F
F
OH
CF3
F
23
24 (83%)
Scheme 6.

44
Y.V. Zonov et al. / Journal of Fluorine Chemistry 145 (2013) 41–50
R
R
R
R
OSiFO
O
OSiFO
SbF5
O
F
F
F
O
F
_
+
-[SiOF2]
OSbF5
OSbF4
OSbF4
33
-SbF3
F
SiO2,
SbF5
R
O
HO
F
R
O
R
F
1) SiO2/SbF5 (0.5:2)
75oC, 5 h
2) H2O
,
1) SiO2/SbF5 (1.5:8)
75oC
,
R
F
F
F
F
+
2) H2O
O
O
O
8 h
8 h
R=CF3
25
26
27
31 (36%)
32 (40%)
28 (content 50%)
29, yield 93%
30, 90%
C2F5
6 (26%)
7 (66%)
CF(CF3)2
30 h
18 (51%)
19 (37%)
Scheme 7.
perfluorinated 3-alkylphthalides (31), (6), (18) and perfluoro-3-
hydroxy-3-alkylphthalides (32), (7), (19) respectively (Scheme 7).
Considerable amount of tetrafluorophthalic acid is also formed in
the reaction of compound 25. The reaction of isopropylbenzocy-
clobutene 27 proceeds more slowly as compared with the
reactions of compounds 25 and 26.
Formation of the phthalides in these reactions most probably
proceeds via intermediate generation of ketones 28, 29, and 30.
The transformation of ketone 28 into phthalides 31 and 32 can be
rationalized by its isomerization under the action of SbF5 into
perfluoroindan-1-one, which gives phthalides 31 and 32 in the
reaction with SiO2/SbF5 [4].
On the other hand, transformation of ketones 29 and 30 into the
corresponding phthalides cannot be rationalized in a similar way
since compounds 29 [4] and 30, heated with SbF5 at 75 8C,
practically do not change. This evidence suggests that SiO2 induces
four-membered ring cleavage in compounds 29, 30 and, probably,
in 28. Taking into account that perfluorobenzocyclobutenone with
SbF5 forms cation-like complex with positive charge on the
carbonyl carbon atom [2], the mechanism suggested for the
transformation of compound 1 (Scheme 3) can be used to
rationalize the transformations of alkylbenzocyclobutenones 28,
29, and 30. In this case complex 33 (Scheme 7), apparently, can
play the role similar to that of cation 9.
Reaction of perfluoro-1-phenylbenzocyclobutene (34) with
SiO2/SbF5 at 75 8C gives, after hydrolysis, a mixture of perfluoro-
2-hydroxy-2-phenylbenzocyclobutenone (35) and perfluoro-2-
benzoylbenzoic acid (36) (Scheme 8). Compound 35 apparently
is a product of perfluoro-2-oxo-1-phenylbenzocyclobuten-1-yl
cation (37) hydrolysis. So it seems that the major product of the
reaction, before hydrolysis, is perfluoro-2-phenylbenzocyclobute-
none (38), which transforms to a salt of cation 37 in the reaction
medium. The acid 36 formation probably proceeds via four-
membered ring cleavage in ketone 38 under the action of SiO2/SbF5
with intermediate generation of phthalide 39 (Scheme 8). The
process is analogous to transformation of 2-alkylbenzocyclobute-
nones 29 and 30 into phthalides 6 and 18 (Scheme 7).
Ketone 38 was synthesized by reaction of hydroxyketone 35
with HF/SbF5 (Scheme 8). Dissolving of compound 38 in SbF5/
SO2ClF gives a solution of a salt of cation 37. Heating of compound
38 with SbF5 at 75 8C in the absence of SiO2 and subsequent
hydrolysis of the reaction mixture gives hydroxyketone 35 with
admixture of acid 36. Increasing of the reaction temperature to
130 8C leads to predominant formation of acid 36. Considering
C6F5
C6F5
O
C6F5
F
SiO2/SbF5
SbF5
O
+
38
O
F
F
F
+
CO
O
O
39
H2O
SiO2/SbF5
C6F5
C6F5
1) SiO2/SbF5 (1.5:6)
75oC, 18 h
2) H2O
,
C6F5
F
O
F
F
F
35, 74%
OH
O
F
+
COOH
34
36, 11%
C6F5
OH
C6F5
F
C6F5
O
+
SbF5
SO2ClF
HF/SbF5
20oC
1) SbF5,
2) H2O
Δ
F
F
35
36
+
O
O
35
38, 90%
37
Scheme 8.

Y.V. Zonov et al. / Journal of Fluorine Chemistry 145 (2013) 41–50
45
Fig. 1. Molecular structure of compound 16 (disordered C3F7 major part 62.7(1)% left and minor part 37.3(1)% right). Thermal ellipsoids are drawn at the 30% probability level.
these data it cannot be excluded that in the reaction of
phenylbenzocyclobutene 34 with SiO2/SbF5 giving acid 36, the
four-membered ring cleavage may proceed in two routes: with
participation of SiO2 and without it.
with (CF3CO)2O. The cyclic structures of compounds 4, 5 and 40 are
confirmed by nonequivalence of fluorine atoms of the CF2 groups in
the 19F NMR spectra of compounds 4, 5 and the CF3 groups in the
spectrum of compound 40. In addition, it was shown that reaction
of compound 5 with PCl5 gives 1,3-dichloro-4,5,6,7-tetrafluoro-1-
(pentafluoroethyl)-3-(trifluoromethyl)phthalane (41).
2.3. Structure of compounds
Dialkylphthalanes 4, 5, 40 and 41 are formed as mixtures of cis-
and trans-isomers.Theconfigurationsof isomersof compounds5and
41 were defined on the base of through-space coupling constants
between fluorine atoms of the CF3 and C2F5 groups, which have
appreciable values only in cis-isomers. The configurations of isomers
of diethylphthalane 4 were assigned on the base of fine structure and
chemical shifts of signals of the CF2 groups in the 19F NMR spectrum
by comparison with those for compound 5. On the base of 19F NMR
spectrum it is difficult to define the configuration of isomers of
diisopropylphthalane 17, but it seems reasonable that the major
isomer has more favorable trans-configuration.
Formally, compounds 19 and 36 could exist in cyclic (3-R-
phthalide) or/and open-chain (2-COR-benzoic acid) forms. Com-
pound 36 has the open-chain structure, because the 13C NMR
spectrum contains two signals of carbonyl groups at 178.7 ppm
(RCOAr) and 161.9 ppm (COOH); assignment of the signals was
made by analogy with perfluorinated benzophenone [14] and
phthalic acid [15]. According to the 19F NMR spectrum, CDCl3
solution of compound 19 contains cyclic 19 and open-chain 19a
forms in the ratio 87:13, respectively. The cyclic structure of the
major form is confirmed by nonequivalence of the CF3 groups in
the spectrum. The spectrum of minor form contains one signal of
the CF3 groups.
Cation 37 has a carbonyl group, so formation of cationic
complex 37c cannot be excluded (Scheme 10). Assignment of
signals in the 19F NMR spectrum of cation 37 was made by
analogy with that for perfluoro-1-phenylbenzocyclobuten-1-yl
cation (41) [16], but poor resolution of the signals did not allow
to make full assignment. All signals of cation 37 are shifted
down-field relatively to the corresponding signals of precursor
38 (DdF). The sum of DdF for all fluorine atoms of cation 37 is
equal to 354.5 ppm and it is significantly higher than the sum
of DdF for corresponding fluorine atoms F(3-6), F(20-60) of
cation 41 (267.9 ppm) [16]. The sum of DdF for fluorine atoms
F(3-6) of perfluorobenzocyclobutenone complex with SbF5 is
equal to 72.5 ppm [2]. These data, apparently, testify to
significant contribution of structure 37c. It should be noted,
that the sum of DdF for aromatic fluorine atoms of perfluoro-4-
oxo-1-phenyltetralin-1-yl cation (273.1 ppm [3]) and per-
fluoro-1-phenyltetralin-1-yl cation (265.6 ppm [16]) are close
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. Com-
pounds 6, 7 [2], 23, 24 [11], 28, 29 [12], 31, 32 [1] were identified by
comparison of the 19F NMR data with data for authentic samples.
The structure of compound 16 was confirmed by single crystal
X-ray diffraction (Fig. 1). It should be noted that in the Cambridge
Structural Database (CSD) we have found no data on the structure
of similar compounds with bicyclo[4.2.0]octa-1,5,7-triene-3,4-
dione framework. In the crystal, one of perfluoroisopropyl group
(C12) is disordered over two positions with 62.7(1):37.3(1)% ratio
that testifies to the presence of two conformers in the crystal. In the
major conformer fluorine atoms F3 and F10 (Fig. 1) are in
proximity, atoms C9, C12, F3 lies in the plane of bicyclic fragment
˚
while atom F10 deviates for 0.292(4) A from this plane; in the
minor conformer atoms F3 and F10A are spaced far apart and
atoms C9, C12A, F3, F10A lies in the plane of bicyclic fragment.
Phthalanes 4 and 5 are hydrate forms of the corresponding orto-
diacylbenzenes (Scheme 9). Tendency of such compounds to
formation of stable hydrates was observed earlier [13]. In contrast
to this, compound 17 was isolated from reaction mixture in a non-
hydrated form. Apparently this is caused by a steric influence of the
perfluoroisopropyl groups that decrease stability of hydrate form
40. The latter was prepared from diketon 17 when its solution in
diethyl ether was treated with diluted hydrochloric acid.
Compound 40 loses water by heating in vacuum or by heating
R1
Cl R1
O
HO R1
O
H2O
PCl5
O
O
R2
F
F
F
-H2O
R1
R2
Cl
41 (63:37)
HO
R1, R2= CF3, C2F5
R1 = R2= C2F5
5 (cis:trans=48:52)
4 (39:61)
R1 = R2= CF(CF3)2
17
40 (10:90)
Scheme 9.

46
Y.V. Zonov et al. / Journal of Fluorine Chemistry 145 (2013) 41–50
5'
4'
2'
6'
F
3'
F
F
6
5
4
SbF5
+
+
+
+
F
F
F
_
_
+
O
O SbF5
37c
O SbF5
3
37
Scheme 10.
to each other, that indicates small contribution of complexa-
tion in this case.
Centre as supplementary publication no. CCDC 904148. Copy of the
data can be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB21EZ, UK (fax: +44 122 3336033 or
deposit@ccdc.cam.ac.uk; internet: www.ccdc.cam.ac.uk).
Antimony pentafluoride was distilled at atmospheric pressure
(bp 142–143 8C); SiO2 was prepared by heating of silica gel at 400–
450 8C. The starting compounds were obtained according to Refs.:
25 and perfluorobenzocyclobutene [18]; 1, 26 [19]; 2, 3, 27 [20];
1,2-dialkyl isomers of 1 and 2 were separated from 1,1-dialkyl
isomers as described in Ref. [12]. The reactions were carried out in
glassware.
3. Conclusion
The behaviour of a number of perfluorinated benzocyclobu-
tenes with alkyl and phenyl substituents in four-membered ring
under the action of SiO2 in the presence of SbF5 was investigated, as
a result new reactions of the four-membered ring cleavage were
found. In these reactions 1,2-dialkylbenzocyclobutenes 1–3 give
perfluorinated 1,2-diacylbenzenes or their hydrated forms –
phthalan-1,3-diols; 1-alkylbenzocyclobutenes 25–27 give 3-
alkylphthalides; 1-phenylbenzocyclobutene 34 forms 2-benzoyl-
benzoic acid 36. The reactions of 1-R-benzocyclobutenes proceed
via intermediate formation of the corresponding 2-R-benzocyclo-
butenones.
4.1. Reaction of perfluoro-1,2-diethylbenzocyclobutene (1) with
SiO2–SbF5
A mixture of compound 1 (0.505 g), SiO2 (0.067 g) and SbF5
(1.465 g) (molar ratio, 1:1:6) was stirred at 75 8C for 10 h. The
mixture was treated with 5% hydrochloric acid and extracted with
CH2Cl2. The extract was dried over MgSO4. The solvent was
distilled off to give 0.373 g (yield 72%) of compound 4 (mixture of
isomers, trans:cis = 61:39).
Bulky perfluoroisopropyl groups hinder the transformations of
benzocyclobutenes as compared with the less sterically hindered
perfluoroethyl derivatives. In diisopropylbenzocyclobutene
3
steric influence of two perfluoroisopropyl groups leads to the fact
that the process of the ring cleavage in the reaction with SiO2/SbF5
becomes a minor reaction route. The main one is reaction of SiO2
with the more sterically accessible positions in the benzene ring
that results in diketone 16 formation. The presence of penta-
fluorophenyl group in the four-membered rings of compounds 23
and 34 also hinders the ring cleavage as compared with the similar
perfluoroethyl derivatives, presumably, due to formation in the
reaction media of stable phenylbenzocyclobutenyl cations, which
have low reactivity in respect to SiO2.
4.1.1. Perfluoro-1,3-diethylphthalan-1,3-diol (4)
Mixture of two isomers, ratio trans:cis = 61:39; liquid. IR (CCl4)
n
, cmꢀ1: 3582 (OH); 1513 [fluorinated aromatic ring (FAR)]. 1H
NMR (CDCl3):
d 4.4 (bs, OH).
Trans-4a: 19F NMR (CDCl3):
d
ꢀ79.8 (s, 6F, CF3), ꢀ122.6 (dd, 2FA,
CF2), ꢀ125.5 (dd, 2FB, CF2), ꢀ136.8 (m, 2F, F-4, F-7), ꢀ146.1 (m, 2F,
F-5, F-6); JA,B = 277, JA,4 = 12.5, JB,4 = 38.
Cis-4b: 19F NMR (CDCl3):
d
ꢀ80.1 (s, 6F, CF3), ꢀ122.8 (m, 4F, CF2),
ꢀ136.5 (m, 2F, F-4, F-7), ꢀ146.6 (m, 2F, F-5, F-6). HRMS (mixture of
4. Experimental
two isomers) m/z, 459.9780 (M+). Calcd. for C12H2F14O3 = 459.9784.
Analytical and spectral measurements were carried out in the
Collective Chemical Service Center of SB RAS. IR spectra were taken
on a Bruker Vector 22 IR spectrophotometer. 19F, 1H and 13C NMR
spectra were recorded on a Bruker AV 300 instrument (282.4 MHz,
300 MHz and 75.5 MHz, respectively). Chemical shifts are given in
4.2. Reaction of perfluoro-1-ethyl-2-methylbenzocyclobutene (2)
with SiO2–SbF5
A mixture of compound 2 (1.454 g), SiO2 (0.222 g) and SbF5
(5.65 g) (molar ratio, 1:1:7.1) was stirred at 75 8C for 5 h. The
mixture was treated with 5% hydrochloric acid and extracted with
mixture CH2Cl2–Et2O (3:1). The extract was dried over MgSO4. The
solvent was distilled off and the residue was sublimed (100 8C, 30–
3 Torr) to give 0.85 g of a mixture containing (estimated by using
internal standard) 38% of 5, 13% of 6 and 6% of 7 together with
unidentified impurities. The mixture was dissolved in CH2Cl2 and
extracted with aqueous solution of NaHCO3. The aqueous extract
was acidified with HCl and extracted with mixture CH2Cl2–Et2O
(3:1). The extract was dried over MgSO4. The solvent was distilled
off to give 0.536 g of a mixture containing ꢁ60% compound 5
together with compound 7 and unidentified impurities. PCl5
(0.894 g) and CH2Cl2 (5 ml) were added, the resulting mixture was
heated at 40 8C for 5 h and treated with water. Organic layer was
separated and washed three times with aqueous solution of
NaHCO3. The aqueous fractions were combined, acidified with HCl
and extracted with mixture CH2Cl2–Et2O (3:1). The extract was
d
ppm from CCl3F (19F) and TMS (1H, 13C), J values in Hz; C6F6 and
SO2ClF (ꢀ162.9 and 99.9 ppm from CCl3F), CHCl3 (7.24 ppm from
TMS), CDCl3 and CO(CD3)2 (76.9 ppm and 29.8 ppm from TMS)
were used as internal standards. The molecular masses of the
compounds were determined by high-resolution mass-spectrom-
etry on a Thermo Electron Corporation DFS instrument (EI 70 eV).
Contents of products in the reaction mixtures were established by
19F NMR spectroscopic data.
The X-ray diffraction experiment was carried out on a Bruker
KAPPA APEX II diffractometer (graphite-monochromated Mo
K(radiation) at 150 K. Intensity data were collected using
w,v-
scan, 2 < 56.88. Reflection intensities were corrected for absorp-
u
tion by SADABS program. The structure was solved by direct
methods and refined by anisotropic full-matrix least-squares
against F2 of all reflections using SHELX-97 program suite [17].
Crystallographic data for the structure of compound 16 in this
paper have been deposited at the Cambridge Crystallographic Data

Y.V. Zonov et al. / Journal of Fluorine Chemistry 145 (2013) 41–50
47
dried over MgSO4. The solvent was distilled off to give compound 5
(0.137 g, mixture of isomers, trans:cis = 52:48). Compound 41
(0.15 g, mixture of isomers, trans:cis = 37:63) was obtained from
CH2Cl2 fraction (the rest after NaHCO3 treatment) by column
chromatography (hexane as eluent).
MgSO4. The solvent was distilled off in vacuum (30 8C, 30 Torr)
to give 0.032 g of a mixture containing 86% of phthalane 40
(mixture of isomers, 40a:40b = 90:10), 7% of diketone 17 and 7%
of phthalide 19.
4.2.1. Perfluoro-1-ethyl-3-methylphthalan-1,3-diol (5)
4.3.1. Perfluoro-7,8-diisopropylbicyclo[4.2.0]octa-1,4,6-triene-3-one
Mixture of two isomers, ratio trans:cis = 52:48; liquid. IR (CCl4)
(15)
n
, cmꢀ1: 3572 (OH); 1514 (FAR). 1H NMR (CDCl3):
d 4.7 (bs, OH).
7'
Trans-5: 19F NMR (CDCl3):
CF3-3), ꢀ122.5 (dd, 1FA, CF2), ꢀ125.7 (dd, 1FB, CF2), ꢀ136.8 (m, 1F,
F-4 or F-7), ꢀ137.9 (m, 1F, F-7 or F-4), ꢀ146.3 (m, 2F, F-5, F-6);
JCF3(3)–F(4) = 16, JA,B = 277.5, JA,7 = 15, JB,7 = 36.
d
ꢀ79.8 (s, 3F, CF3-1), ꢀ84.0 (d, 3F,
5
CF(CF3)2
6
1
7
4
3
F
F
8
O
CF(CF3)2
2
Cis-5: 19F NMR (CDCl3):
d
ꢀ80.2 (s, 3F, CF3-1), ꢀ82.7 (dddq, 3F,
8'
CF3-3), ꢀ122.2 (ddq, 1FA, CF2), ꢀ123.2 (ddq, 1FB, CF2), ꢀ137.0 (m,
1F, F-4 or F-7), ꢀ138.1 (m, 1F, F-7 or F-4), ꢀ146.6 (m, 1F, F-5 or F-6),
ꢀ146.8 (m, 1F, F-6 or F-5); JCF3(3)–F(4) = 17, JCF3(3)–F(A) = 11, JCF3(3)–
F(B) = 2.5, JCF3(3)–CF3(1) = 1.5, JA,B = 277.5, JA,7 = 14, JB,7 = 39.5. HRMS
(mixture of two isomers) m/z, 409.9798 (M+). Calcd. for
Yellow crystals, mp 36–38.5 8C. IR (CCl4)
1634 (C55O, C55C). 19F NMR (CDCl3):
n
, cmꢀ1: 1719, 1656,
ꢀ72.9 (m, 3F, CF3), ꢀ74.0 (m,
d
3F, CF3), ꢀ75.1 (m, 3F, CF3), ꢀ76.3 (m, 3F, CF3), ꢀ124.3 (dt, J = 9,
J = 6, 1F, F-4), ꢀ126.5 (m, 1F, F-5 or F-2), ꢀ133.6 (m, 1F, F-2 or F-5),
0
ꢀ142.6 (m, 1F, F-8), ꢀ180.9 (dm, J7 ,8 = 47.5, 1F, F-8 or F-70),
0
0
C
11H2F12O3 = 409.9807.
+
0
0
0
0
ꢀ182.0 (dm, J7 ,8 = 47.5, 1F, F-7 or F-8 ). HRMS m/z, 525.9658 (M ).
4.2.2. 1,3-dichloro-4,5,6,7-tetrafluoro-1-(pentafluoroethyl)-3-
(trifluoromethyl)phthalane (41)
Calcd. for C14F18O = 525.9656.
Mixture of two isomers, ratio trans:cis = 37:63; liquid.
4.3.2. Perfluoro-7,8-diisopropylbicyclo[4.2.0]octa-1,5,7-triene-3,4-
Trans-41: 19F NMR (CDCl3):
d
ꢀ78.6 (s, 3F, CF3-1), ꢀ80.5 (d, 3F,
dione (16)
CF3-3), ꢀ117.4 (dd, 1FA, CF2), ꢀ120.0 (dd, 1FB, CF2), ꢀ134.7 (m, 1F,
F-7), ꢀ136.0 (m, 1F, F-4), ꢀ144.5 (m, 2F, F-5, F-6); JCF3(3)–F(4) = 16,
JA,B = 273, JA,7 = 18, JB,7 = 33.5.
Yellow crystals, mp 139–141 8C (CCl4). IR (CCl4) n
, cmꢀ1: 1724,
1704 (C55O, C55C). 19F NMR (CDCl3):
d
ꢀ73.7 (bd, 12F, J = 13, CF3),
ꢀ124.5 (bm, 2F, F-2, F-5), ꢀ178.1 (bm, 2F, CF(CF3)2). 13C NMR
Cis-41: 19F NMR (CDCl3):
d
ꢀ79.2 (q, 3F, CF3-1), ꢀ82.7 (dm, 3F,
[CO(CD3)2]: d
172.4 (d, 2JCF = 24, CO), 142.5 (m, C-1, C-6 or C-7, C-8),
CF3-3), ꢀ117.9 (ddq, 1FA, CF2), ꢀ118.3 (ddq, 1FB, CF2), ꢀ134.4 (m,
1F, F-7), ꢀ135.4 (m, 1F, F-4), ꢀ144.5 (m, 2F, F-5, F-6); JCF3(3)–
F(4) = 17.5, JCF3(3)–F(A) = 5, JCF3(3)–F(B) = 2, JCF3(3)–CF3(1) = 2.5, JA,B = 274,
JA,7 = 23.5, JB,4 = 31.5. HRMS (mixture of two isomers) m/z,
445.9125 (M+). Calcd. for C11Cl2F12O1 = 445.9129.
142.2 (d, 1JCF = 295, C-2, C-5), 123.1 (m, C-7, C-8 or C-1, C-6), 120.0
1
2
1
2
(qd, JCF = 288, JCF = 27, CF3), 90.3 (dqq, JCF = 213, JCF = 36,
2JCF = 36, CF(CF3)2). HRMS m/z, 503.9633 (M+). Calcd. for
C14F16O2 = 503.9637. Single crystals of compound 16 were grown
by slow evaporation of solvent from CCl4 solution.
Crystallographic data and refinement parameters:
Formula C14F16O2, M = 504.14, crystal size 0.12 mm ꢂ
4.3. Reaction of perfluoro-1,2-diisopropylbenzocyclobutene (3) with
SiO2–SbF5
0.18 mm ꢂ 0.43 mm,
monoclinic,
space
group
= 111.919(1)8,
= 0.254 mmꢀ1
,
P21/n,
˚
a = 15.2303(7), b = 6.5079(2), c = 17.9829(7) A,
b
m
3
V = 1653.6(1) A , Z = 4, Dcalc = 2.025 g cmꢀ3
,
˚
1. A mixture of compound 3 (0.526 g), SiO2 (0.058 g) and SbF5
(1.533 g) (molar ratio, 1:1:6) was stirred at 75 8C for 12.5 h. The
mixture was treated with 5% hydrochloric acid and extracted
with CH2Cl2. The extract was dried over MgSO4. The solvent was
distilled off to give 0.435 g of a mixture of compounds 3, 15, 16
and 17 in the ratio 9:66:17:8. Column chromatography (CCl4 as
eluent) of the mixture gave 0.206 g of compound 15.
53,685 total reflexions, 4151 unique reflexions (Rint = 0.0337),
R = 0.0559 for 3229 I > 2 (I), 389 parameters, wR2 = 0.1778 and
s
GOF = 1.047 for all data, max/min Dr 0.56/ꢀ0.38.
4.3.3. Perfluoro-1,2-diisobutyrylbenzene (17)
Mixture with phthalide 19, ratio 17:19 = 92:8, liquid. IR (CCl4) n,
cmꢀ1: 1746 (C55O); 1518, 1475 (FAR). 19F NMR (CDCl3):
d
ꢀ73.5 (m,
2. A mixture of compound 3 (0.785 g), SiO2 (0.132 g) and SbF5
(1.863 g) (molar ratio, 1:1.5:6) was heated at 95 8C for 41 h. The
mixture was treated with 5% hydrochloric acid and extracted
with CH2Cl2. The extract was dried over MgSO4. The solvent was
distilled off to give 0.646 g of a mixture of compounds 16, 17, 18
and 19 in the ratio 81:11:6:2. Filtration of the mixture gave
0.419 g of crystals of compound 16. Filtrate was sublimed
(100 8C, 30 Torr) to give 0.122 g of a mixture of compounds 16,
17, 18 and 19 in the ratio 22:48:26:4. The mixture was dissolved
in Et2O (2 ml) and stirred with 10% hydrochloric acid (3 ml) for 7
days. Ether solution was separated and dried over MgSO4. The
solvent was distilled off. Sublimation (90 8C, 30 Torr) of the
residue gave a fraction (0.04 g), which contained compounds 17,
19 and 40 in the ratio 80:8:12. This fraction was dissolved in
CHCl3 (1 ml), (CF2CO)2O (0.09 g) was added and resulting
mixture was heated in a sealed ampoule at 80 8C for 16 h. Then
the mixture was washed with water and dried over MgSO4. The
solvent was distilled off to give 0.035 g of a mixture containing
92% of diketone 17 and 8% of phthalide 19. This mixture was
dissolved in Et2O (3 ml) and stirred with 5% hydrochloric acid
(3 ml) for 5 days. Ether solution was separated and dried over
12F, CF3), ꢀ129.5 (dm, 2F, F-3, F-6), ꢀ143.7 (m, 2F, F-4, F-5), ꢀ184.6
(dm, 2F, F-10, F-20); J1 ,6 = J2 ,3 = 57. 13C NMR (CDCl3):
2JCF = 31, CO), 147.3 (dd, 1JCF = 264, 2JCF = 10, C-3, C-6), 143.5 (ddd,
d
183.7 (d,
0
0
2
2
1JCF = 267, JCF = 17, JCF = 13, C-4, C-5), 119.5 (m, C-1, C-2), 118.5
1
2
1
2
(qd, JCF = 289, JCF = 27, CF3), 91.6 (dqq, JCF = 223, JCF = 33,
2JCF = 33, CF(CF3)2).
4.3.4. Perfluoro-1,3-diisopropylphthalan-1,3-diol (40)
1'a CF3
1'b
HO
7
CF-CF3
1'
6
5
1
3
F
O
3'b
3'
4
CF-CF3
3'a CF3
HO
Mixture of two isomers 40 (trans:cis = 90:10) with diketone 17
and phthalide 19, ratio 40:17:19 = 86:7:7; liquid. 1H NMR (CDCl3):
4.7 (bs, OH).
d

48
Y.V. Zonov et al. / Journal of Fluorine Chemistry 145 (2013) 41–50
Trans-40: 19F NMR (CDCl3):
d
ꢀ71.8 (qdd, 6F, CF3-10a, CF3-30a),
mixture of compounds 6, 7, 29 and tetrafluorophtalic acid in the
ratio 26:66:4:4.
ꢀ72.5 (qdd, 6F, CF3-10b, CF3-30b), ꢀ135.9 (m, 2F, F-4, F-7), ꢀ147.0
(m, 2F, F-5, F-6), ꢀ177.3 (dqq, 2F, F-10, F-30); JCF3(1 a)–CF3(1 b) = 9.5,
0
0
0
0
0
0
0
0
JCF3(1 a)–F(1 ) = 5.5, JCF3(1 a)–F(7) = 7, JCF3(1 b)–F(1 ) = 5.5, JCF3(1 b)–
4.8. Reaction of perfluoro-1-isopropylbenzocyclobutene (27) with
SiO2–SbF5
0
F(7) = 2.5, J1 ,7 = 35.
Cis-40: 19F NMR (CDCl3):
d
ꢀ71.9 (bs, 6F, CF3-10a, CF3-30a), ꢀ73.1
(bs, 6F, CF3-10b, CF3-30b), ꢀ133.9 (dm, 2F, F-4, F-7), ꢀ147.8 (m, 2F,
1. A mixture of compound 27 (0.2 g), SiO2 (0.015 g) and SbF5
(0.22 g) (molar ratio, 1:0.5:2) was stirred at 75 8C for 5 h. The
mixture was treated with 5% hydrochloric acid and extracted
with CH2Cl2. The extract was dried over MgSO4. The solvent was
distilled off to give 0.17 g (yield 90%) of ketone 30.
F-5, F-6), ꢀ178.8 (bd, 2F, F-10, F-30); J1 ,7 ꢁ 47. HRMS (mixture of
0
two isomers) m/z, 559.9711 (M+). Calcd. for C14H2F18O3 =
559.9706.
4.4. Reaction of perfluoro-1,2-diisopropylbenzocyclobutene (3) with
2. A mixture of compound 27 (0.392 g), SiO2 (0.091 g) and SbF5
(1.769 g) (molar ratio, 1:1.5:8.3) was stirred at 75 8C for 30 h.
The mixture was treated with 5% hydrochloric acid and
extracted with mixture CH2Cl2–Et2O (3:1). The extract was
dried over MgSO4. The solvent was distilled off and the residue
was sublimed (from 80 8C, 30 Torr to 130 8C, 3 Torr) to give
0.245 g of a mixture of compounds 18, 19 and 30 in the ratio
51:37:12. The mixture was dissolved in CH2Cl2, washed with
aqueous solution of NaHCO3 and dried over MgSO4. The solvent
was distilled off, the residue was sublimed (85 8C, 30 Torr) and
crystallized from hexane to give 0.057 g of phthalide 18.
SbF5
A solution of compound 3 (0.4 g) in SbF5 (1.582 g) (molar ratio,
1:10) was heated at 95 8C for 40 h in a nickel bomb (V = 10 ml). The
mixture was treated with 5% hydrochloric acid and extracted with
CH2Cl2. The solvent was distilled off to give 0.343 g of a mixture of
compounds 3 and 15 in the ratio 6:94.
4.5. Reaction of perfluoro-1-methyl-2-phenylbenzocyclobutene (23)
with SiO2–SbF5
A solution of compound 23 and perfluoro-1-methyl-1-phenyl-
benzocyclobutene (ratio 91:9) in SbF5 was prepared by the
reaction of metylbenzocyclobutene 25 (0.69 g) with C6F5H
(0.4 g) and SbF5 (3.015 g) (molar ratio 25: C6F5H:SbF5 = 1:1:6).
Then SiO2 (0.209 g) was added and the resulting mixture was
stirred at 75 8C for 10 h. The mixture was treated with 5%
hydrochloric acid and extracted with CH2Cl2. The extract was dried
over MgSO4. The solvent was distilled off to give 0.98 g of a mixture
containing ꢁ95% of compounds 23, 24 and perfluoro-1-pheny-
lindan-1-ol [10] in the ratio 4:87:9.
4.8.1. Perfluoro-2-isopropylbenzocyclobutenone (30)
Liquid. IR (CCl4)
n
, cmꢀ1: 1824 (C55O); 1522, 1484 (FAR). 19F
NMR (CDCl3):
d
ꢀ73.1 (dqdd, 3F, CF3-20a), ꢀ74.8 (ddqd, 3F, CF3-
20b), ꢀ126.5 (dddd, 1F, F-6), ꢀ130.9 (ddqddqd, 1F, F-3), ꢀ133.2
(dddd, 1F, F-4), ꢀ140.4 (dddd, 1F, F-5), ꢀ149.5 (dqqdddd, 1F, F-2),
ꢀ181.0 (dqqd, 1F, F-20); JCF3(2 a)–CF3(2 b) = 9, JCF3(2 a)–F(2 ) = 7, JCF3(2 a)–
0
0
0
0
0
0
0
0
0
F(2) = 11.5, JCF3(2 a)–F(3) = 2.5, JCF3(2 b)–F(2 ) = 8, JCF3(2 b)–F(2) = 9.5,
0
0
0
JCF3(2 b)–F(3) = 15, J2 ,2 = 13.5, J2 ,3 = 1.5, J2,3 = 4.5, J2,4 = 2, J2,5 = 5,
J2,6 = 2.5, J3,4 = 19, J3,5 = 9.5, J3,6 = 24.5, J4,5 = 17.5, J4,6 = 12,
J5,6 = 20. HRMS m/z, 375.9743 (M+). Calcd. for C11F12O1 = 375.9752.
4.6. Reaction of perfluoro-1-methylbenzocyclobutene (25) with SiO2–
SbF5
4.8.2. Perfluoro-3-isopropylphthalide (18)
Mp 36.5–37.5 8C. IR (CCl4) n
, cmꢀ1: 1846 (C55O); 1522, 1507
1. A mixture of compound 25 (0.857 g), SiO2 (0.088 g) and SbF5
(1.24 g) (molar ratio, 1:0.5:2) was stirred at 75 8C for 5 h. The
mixture was treated with 5% hydrochloric acid and extracted
with CH2Cl2. The extract was dried over MgSO4. The solvent was
distilled off to give 0.748 g of a mixture of compounds 28, 31,
perfluoroindan-1-one and perfluoroindane in the ratio
50:3:44:3.
2. A mixture of compound 25 (0.267 g), SiO2 (0.079 g) and SbF5
(1.526 g) (molar ratio, 1:1.5:7.9) was stirred at 75 8C for 8 h. The
mixture was treated with 5% hydrochloric acid and extracted
with mixture CH2Cl2–Et2O (4:1). The extract was dried over
MgSO4. The solvent was distilled off to give 0.242 g of a mixture
of compounds 31, 32, perfluoroindan-1-one and tetrafluoroph-
talic acid in the ratio 36:40:5:19.
(FAR). 19F NMR (CDCl3):
d
ꢀ72.6 (dqd, 3F, CF3-30a), ꢀ74.1 (qddd, 3F,
CF3-30b), ꢀ112.6 (qdqdd, 1F, F-3), ꢀ132.0 (dddddq, 1F, F-4), ꢀ133.9
(ddd, 1F, F-7), ꢀ137.9 (ddd, 1F, F-5), ꢀ143.0 (dddd, 1F, F-6), ꢀ183.1
(ddqq, 1F, F-30); JCF3(3 a)–CF3(3 b) = 9, JCF3(3 a)–F(3 ) = 6, JCF3(3 a)–
0
0
0
0
0
0
0
0
0
JCF3(3 b)–F(3) = 5,
F(3) = 17,
JCF3(3 a)–F(4) = 1.5,
JCF3(3 b)–F(3 ) = 6,
0
0
J3 ,3 = 14.5, J3 ,4 = 52, J3,4 = 4, J3,6 = 4, J4,5 = 20.5, J4,6 = 9, J4,7 = 18.5,
J5,6 = 17.5, J5,7 = 11.5, J6,7 = 20.5. HRMS m/z, 391.9710 (M+). Calcd.
for C11F12O2 = 391.9701.
4.9. Perfluoro-3-hydroxy-3-isopropylphthalide (19)
A mixture of compound 18 (0.04 g), ether (0.5 ml) and 10%
hydrochloric acid (1 ml) was stirred at 20 8C for 8 days. Ether
solution was separated and dried over MgSO4. The solvent was
distilled off to give 0.036 g (yield 90%) of compound 19.
4.7. Reaction of perfluoro-1-ethylbenzocyclobutene (26) with SiO2–
SbF5
4.9.1. Perfluoro-3-hydroxy-3-isopropylphthalide (19)
1. A mixture of compound 26 (0.395 g), SiO2 (0.034 g) and SbF5
(0.491 g) (molar ratio, 1:0.5:2) was stirred at 75 8C for 5 h. The
mixture was treated with 5% hydrochloric acid and extracted
with CH2Cl2. The extract was dried over MgSO4. The solvent was
distilled off to give 0.347 g (yield 93%) of ketone 29.
2. A mixture of compound 26 (0.31 g), SiO2 (0.08 g) and SbF5
(1.531 g) (molar ratio, 1:1.5:7.9) was stirred at 75 8C for 8 h. The
mixture was treated with 5% hydrochloric acid and extracted
with mixture CH2Cl2–Et2O (3:1). The extract was dried over
MgSO4. The solvent was distilled off and the residue was
sublimed (from 90 8C, 30 Torr to 140 8C, 3 Torr) to give 0.27 g of a
Mp 95–97 8C (CCl4). IR (KBr)
1524, 1506 (FAR). 1H NMR (CDCl3):
mixture with acyclic form 19a, ratio 19:19a = 87:13:
n
, cmꢀ1: 3252 (OH); 1773 (C55O);
d
4.5 (bs, OH). 19F NMR (CDCl3),
d
ꢀ71.9 (bs,
3F, CF3-30a), ꢀ73.8 (bs, 3F, CF3-30b), ꢀ134.6 (m, 1F, F-4), ꢀ136.1 (bs,
1F, F-7), ꢀ139.7 (bs, 1F, F-5), ꢀ145.6 (bs, 1F, F-6), ꢀ180.3 (bd, 1F,
J3 ,4 = 36, F-30). HRMS m/z, 389.9741 (M+). Calcd. for
0
C11H1F11O3 = 389.9745.
4.9.2. Perfluoro-2-isobutyrylbenzoic acid (19a)
19F NMR (CDCl3), mixture with cyclic form 19, ratio
19a:19 = 13:87:
d
ꢀ73.6 (bs, 6F, CF3), ꢀ131.1 (bs, 1F, F-3 or F-6),

Y.V. Zonov et al. / Journal of Fluorine Chemistry 145 (2013) 41–50
49
ꢀ136.5 (bs, 1F, F-6 or F-3), ꢀ144.3 (bs, 1F, F-4 or F-5), ꢀ146.7 (bs,
1F, F-5 or F-4), ꢀ181.1 (bs, 1F, CF(CF3)2).
75 8C for 18 h. The mixture was treated with 5% hydrochloric
acid and extracted with CH2Cl2. The extract was dried over
MgSO4. The solvent was distilled off to give 0.045 g of a mixture
of compounds 35 and 36 in the ratio 92:8.
4.10. Reaction of perfluoro-2-isopropylbenzocyclobutenone (30) with
SbF5
2. A solution of compound 38 (0.21 g) in SbF5 (3.875 g) (molar
ratio, 1:32) and SO2ClF (1 ml) was prepared and then heated at
130 8C for 9 h in a nickel bomb (V = 10 ml). The mixture was
treated with 5% hydrochloric acid and extracted with Et2O. The
solvent was distilled off and the residue was sublimed (150 8C,
3 Torr) to give 0.18 g of a mixture of compounds 35 and 36 in the
ratio 20:80. Crystallization from CCl4 gave 0.095 g of acid 36.
A solution of compound 30 (0.177 g) in SbF5 (1.088 g) (molar
ratio, 1:10.7) was heated at 75 8C for 37 h. The mixture was treated
with 5% hydrochloric acid and extracted with CH2Cl2. The extract
was dried over MgSO4. The solvent was distilled off to give 0.165 g
of product containing ꢁ90% of unchanged ketone 30.
4.11. Reaction of perfluoro-1-phenylbenzocyclobutene (34) with
SiO2–SbF5
4.13.1. Perfluoro-2-oxo-1-phenylbenzocyclobuten-1-yl cation (37)
19F NMR (SbF5–SO2ClF):
d
ꢀ74.3 (bs, 1F, F-4); ꢀ84.6 (bs, 1F),
ꢀ92.9 (bs, 1F), ꢀ95.7 (bs, 1F) and ꢀ100.0 (bs, 1F, F-3, F-5, F-20, F-40);
A solution of compound 34 in SbF5 was prepared by the reaction
of perfluorobenzocyclobutene (1 g) with C6F5H (0.682 g) and SbF5
(5.144 g) (molar ratio, 1:1:5.9) [16]. Then SiO2 (0.363 g) (molar
ratio 34:SiO2 = 1:1.5) was added and the resulting mixture was
stirred at 75 8C for 18 h. After 2 h of heating the mixture became
very viscous, therefore C6F6 (2 ml) was added as a solvent. The
mixture was treated with 5% hydrochloric acid and extracted with
CH2Cl2. The extract was dried over MgSO4. The solvent was
distilled off to give 1.42 g of a mixture containing ꢁ85% of
compounds 35 and 36 in the ratio 87:13 together with unidentified
impurities. The mixture was sublimated (130 8C, 3 Torr), crystal-
lized from hexane, dissolved in CH2Cl2, washed with aqueous
solution of NaHCO3 and dried over MgSO4. The solvent was
distilled off to give 0.677 g of compound 35 (yield 45%).
0
0
0
ꢀ93.3 (dm, 1F, J6,6 = 165, F-6); ꢀ99.1 (dm, 1F, J6,6 = 165, F-6 );
ꢀ145.8 (bs, 1F) and ꢀ146.1 (bs, 1F, F-30, F-50).
4.13.2. Perfluoro-2-benzoylbenzoic acid (36)
Mp 167–168 8C (CCl4). IR (CCl4)
1627 (C55O);1523, 1506, 1475, 1442 (FAR). 1H NMR (20% of
dioxane in CDCl3):
10.4 (bs, OH). 19F NMR (20% of dioxane in
CDCl3):
n
, cmꢀ1: 3435 (OH); 1711,1650,
d
d
ꢀ134.2 (ddd, 1F, F-6), ꢀ140.9 (m, 2F, F-ortho), ꢀ141.9
(dddt, 1F, F-3), ꢀ146.9 (tt, 1F, F-para), ꢀ148.5 (ddd, 1F, F-4), ꢀ150.0
(ddd, 1F, F-5), ꢀ161.3 (m, 2F, F-meta); Jpara,meta = 21, Jpara,ortho = 6,
J
orto,3 = 1.5, J3,4 = 22, J3,5 = 5.5, J3,6 = 12.5, J4,5 = 19.5, J4,6 = 8.5,
J5,6 = 21.5. 13C NMR (20% of dioxane in CDCl3):
d 178.7 (s,
Ar1Ar2CO), 161.9 (s, COOH), 146.5–137.2 (C–F), 125.2 (d,
2JCF = 16, C-1 or C-2), 115.1 (d, JCF = 13, C-2 or C-1), 113.0 (m,
2
C-ipso in C6F5). HRMS m/z, 387.9787 (M+). Calcd. for
4.11.1. Perfluoro-2-hydroxy-2-phenylbenzocyclobutenone (35)
C14H1F9O3 = 387.9777.
Mp 81–82 8C (hexane). IR (CCl4)
(C55O);1516, 1501, 1481 (FAR). 1H NMR (CDCl3):
NMR (CDCl3):
ꢀ136.2 (ddd, 1F, F-4), ꢀ140.2 (m, 2F, F-ortho), ꢀ145.9 (ddd, 1F, F-
5), ꢀ151.4 (tt, 1F, F-para), ꢀ160.9 (m, 2F, F-meta); Jpara,meta = 21,
Jpara,ortho = 3.5, Jorto,3 = 15.5, J3,4 = 20, J3,5 = 7, J3,6 = 25, J4,5 = 18,
J4,6 = 10.5, J5,6 = 20.5. HRMS m/z, 371.9830 (M+). Calcd. for
n
, cmꢀ1: 3582 (OH); 1811,1782
d
4.0 (bs, OH). 19
F
Acknowledgement
d
ꢀ127.9 (ddd, 1F, F-6), ꢀ134.9 (ddtd, 1F, F-3),
We gratefully acknowledge the Russian Foundation for Basic
Researches (project no. 10-03-00120) for financial support.
References
C14H1F9O2 = 371.9827.
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spectrum of the solution was recorded at 20 8C. The spectrum
contained signals of cation 37. Then the solution was heated at

50
Y.V. Zonov et al. / Journal of Fluorine Chemistry 145 (2013) 41–50
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