Skeletal transformations of perfluorinated 2,2-diethyl- and 2-ethyl-2-phenyl-benzocyclobutenones under the action of antimony pentafluoride

Article abstract of DOI:10.1016/j.jfluchem.2008.08.002

Perfluoro-2-ethyl-2-phenylbenzocyclobutenone heated with SbF₅ at 70 °C and then treated with water, forms perfluoro-3-ethyl-3-phenylphthalide. In contrast to this, heating of perfluoro-2,2-diethylbenzo-cyclobutenone with SbF₅ at 70 °C gives, after treatment of the reaction mixture with water, perfluoro-2-(pent-2-en-3-yl)benzoic acid. When the reaction temperature is raised to 125 °C, a solution of a salt of perfluoro-4-ethyl-3-methylisochromenyl cation is obtained. Hydrolysis of the solution of the salt gives perfluoro-4-ethyl-3-methylisochromen-1-one.

Full text of DOI:10.1016/j.jfluchem.2008.08.002

Journal of Fluorine Chemistry 129 (2008) 1206–1208
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Short communication
Skeletal transformations of perfluorinated 2,2-diethyl- and 2-ethyl-2-phenyl-
benzocyclobutenones under the action of antimony pentafluoride
*
Yaroslav V. Zonov, Tatyana V. Mezhenkova, Victor M. Karpov , Vyacheslav E. Platonov
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:
Perfluoro-2-ethyl-2-phenylbenzocyclobutenone heated with SbF5 at 70 8C and then treated with water,
forms perfluoro-3-ethyl-3-phenylphthalide. In contrast to this, heating of perfluoro-2,2-diethylbenzo-
cyclobutenone with SbF5 at 70 8C gives, after treatment of the reaction mixture with water, perfluoro-2-
(pent-2-en-3-yl)benzoic acid. When the reaction temperature is raised to 125 8C, a solution of a salt of
perfluoro-4-ethyl-3-methylisochromenyl cation is obtained. Hydrolysis of the solution of the salt gives
perfluoro-4-ethyl-3-methylisochromen-1-one.
Received 27 June 2008
Received in revised form 5 August 2008
Accepted 10 August 2008
Available online 19 August 2008
Keywords:
ß 2008 Elsevier B.V. All rights reserved.
Skeletal transformations
Perfluoro-2,2-diethyl-benzocyclobutenone
Perfluoro-2-ethyl-2-phenyl-
benzocyclobutenone
Antimony pentafluoride
NMR spectroscopy
1. Introduction
then treated with water, forms perfluorinated 2-ethylbenzoic acid,
indan, 3-methylphthalide and 3-hydroxy-3-methylphthalide [5].
Perfluorinated ketones and vinyl ketones having a CF3 group in
the position to the carbonyl group are known to undergo
Perfluoro-3,4-dimethylisochromenyl cation is obtained in the
reaction of perfluoro-3-ethylindan-1-one with SbF5 at 125 8C.
Hydrolysis of the cation gives perfluoro-3,4-dimethylisochromen-
1-one [7].
In this connection it was worthwhile to study the behaviour of a
number of carbonyl derivatives of perfluoroalkylbenzocycloalk-
enes under the action of antimony pentafluoride with the aim to
study the possibility of their cationoid skeletal transformations.
This work describes the reaction of perfluoro-2,2-diethylbenzo-
cyclobutenone (1) and perfluoro-2-ethyl-2-phenylbenzocyclobu-
tenone (2) with antimony pentafluoride.
b
intramolecular cyclisation on heating with antimony pentafluoride
to give derivatives of oxolane and 2,5-dihydrofuran, respectively
[1–3]. The carbon framework of the compounds in these reactions
does not change. Recently, we have found carbocationoid skeletal
rearrangements of carbonyl derivatives of perfluorinated benzocy-
clobutene [4], indan [5,6], tetralin [4] and 1-ethylindan [7] under the
action of SbF5 [4,5,7] or HF-SbF5 [6], unknown for perfluoroketones.
In the reactions of perfluorobenzocyclo-alken-1-ones with SbF5
there occur skeletal transformations of ketones along with their
disproportionation to benzocycloalkenes and benzocycloalkene-
diones. The latters undergo skeletal transformations under the
reaction conditions [4,5]. Thus, perfluorobenzocyclobutenone
heated with SbF5 and then treated with water, gives perfluor-
obenzocyclobutene, perfluoro-2-methylbenzoic and tetrafluoroph-
talic acids as well as the products containing more complicated
carbon frame [4]. Analogous reaction of perfluorotetralin-1-one
leads tothe mixtureof perfluorinated tetralin, benzocondensed five-
and six-membered oxygen-containing heterocyclic compounds and
alkylbenzoic acids [4]. Perfluoroindan-1-one heated with SbF5 and
2. Results and discussion
It has been shown that heating of ketone 1 with SbF5 at 70 8C
gives, after treatment of the reaction mixture with water,
perfluoro-2-(pent-2-en-3-yl)benzoic acid (3) as a mixture of E-
and Z-isomers. When the reaction temperature is raised to 125 8C,
a solution of a salt of perfluoro-4-ethyl-3-methylisochromenyl
cation (4) is obtained. Hydrolysis of the solution of the salt gives
perfluoro-4-ethyl-3-methylisochromen-1-one (5) (Scheme 1).
The probable mechanism for the transformations of ketone 1 in
the presence of SbF5 can be formulated as shown in Scheme 1. At
first compound 1 with SbF5 seems to generate cation 6, which
undergoes four-membered ring opening, analogously to that for
* Corresponding author. Fax: +7 3833 30 9752.
E-mail address: karpov@nioch.nsc.ru (V.M. Karpov).
0022-1139/$ – see front matter ß 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2008.08.002

Y.V. Zonov et al. / Journal of Fluorine Chemistry 129 (2008) 1206–1208
1207
Scheme 2.
integral intensities. The configurations of E- and Z-isomers of acid
3 were defined on the basis of through–space coupling constants
of the – C(CF2CF3) = CFCF3 group, similarly to that for E- and Z-
isomers of perfluoro-2-(but-2-en-2-yl)benzoic acid [7] and
(perfluorobut-2-en-2-yl)benzene [9]. The J , J ,A, J
g
values
,B
,
a g
g
Scheme 1.
are equal to 7, 12 and 23 Hz for E-3 and less than 2 Hz for Z-3
isomers. It should be noted nonequivalence of the CF2-group
fluorine atoms of acid 3, which can be a result of restricted rotation
of the group ortho-C6F4COOH around C–C-bond. Similar phenom-
enon was observed for perfluoro-2-(pent-2-en-3-yl)benzophe-
none [10].
the reaction of perfluoro-1,1-diethylbenzocylobutene with SbF5
[8], to give the benzoyl type ion 7. Hydrolysis of the latter gives acid
3. Cation 7 may isomerise to allyl type cation 8 by way of the
fluoride anion addition–elimination (the lower row of the Scheme
1). An intramolecular attack of positively charged carbon atom of
the allyl system of cation 8 at the fluorocarbonyl oxygen atom
gives cation 9. This ion undergoes isomerisation with a double
bond migration to the thermodynamically more stable isomer 4.
The mechanism of the formation of isochromenyl cation 4 by
cyclisation of ion 7 is similar to that for the formation of perfluoro-
3,4-dimethylisochromenyl cation in the reaction of perfluoro-3-
ethylindan-1-one with antimony pentafluoride [7].
3. Experimental
IR spectra were taken on a Bruker Vector 22 IR spectro-
photometer. UV spectra were measured on a Hewlett Packard 8453
UV spectrophotometer. 19F and 1H NMR spectra were recorded
on a Bruker AC 200 instrument (188.3 and 200 MHz, respectively),
19F NMR spectrum of cation 10 – on a Bruker AV 300 instrument
In contrast to diethylbutenone 1, heating ketone 2 with SbF5 at
70 8C gives a salt of perfluoro-3-ethyl-3-phenylphthalan-1-yl
cation (10). Hydrolysis of the salt leads to perfluoro-3-ethyl-3-
phenylphthalide (11) (Scheme 2).
(282.4 MHz). Chemical shifts are given in d ppm from CCl3F
(
and 99.9 ppm from CCl3F) and (Me3Si)2O (0.04 ppm from TMS)
were used as internal standards. The molecular masses of the
compounds were determined by high-resolution spectrometry on
a Finnigan Mat 8200 instrument (EI 70 eV).
19F) and TMS (1H), J values in Hz; C6F6 and SO2ClF (ꢀ162.9
Transformation of ketone 2 to cation 10 in the presence of
antimony pentafluoride possibly proceeds in the following way
(Scheme 2). At first cation 12 is formed from ketone 2 and SbF5.
The four-membered cycle of the cation 12 may undergo ring
opening to produce the intermediate 13. The latter adds fluoride
anion and the product obtained is further fluorinated to yield
compound 14, which seems to generate cation 15 under the action
of SbF5. Intramolecular cyclisation of ion 15 gives cation 10. In
addition, the possibility of transformation of cation 13 to 16 with
further cyclisation and fluorination yielding cation 10 cannot be
excluded.
Antimony pentafluoride was obtained commercially; ketones 1
and
2 were synthesized according to Refs. [11] and [10],
respectively.
3.1. Reaction of perfluoro-2,2-diethylbenzocyclobutenone (1) with
SbF5
A mixture of compound 1 (0.54 g) and SbF5 (3.06 g) (molar ratio,
1:11) in a nickel bomb (10 ml) was heated at 70 8C for 26 h. The
mixture was treated with 5% hydrochloric acid and extracted with
CH2Cl2. The extract was dried over MgSO4. The solvent was
distilled off and the residue was sublimed (90 8C, 5 Torr) to give
0.42 g (yield 78%) of acid 3.
The structures of the compounds were established by HRMS
and spectral characteristics. Assignment of signals in the 19F NMR
spectra of the compounds and cations 4 and 10 was made on the
basis of chemical shifts of the signals, their fine structure and

1208
Y.V. Zonov et al. / Journal of Fluorine Chemistry 129 (2008) 1206–1208
3.1.1. Perfluoro-2-(pent-2-en-3-yl)benzoic acid (3)
3.2. Reaction of perfluoro-2-ethyl-2-phenylbenzocyclobutenone (2)
with SbF5
1. Mixture of two isomers, ratio E:Z = 13:87. IR (CCl4)
n :
, cmꢀ1
3516, 3024 (OH), 1753, 1718 (C O); 1524, 1481 [fluorinated
aromatic ring (FAR)]. 1H NMR (CCl4):
11.20 (s, OH).
Analogously to the previous experiment, the reaction of
compound 2 (0.08 g) and SbF5 (1.86 g) (molar ratio, 1:48) gave
(70 8C, 14 h) a solution of a salt of cation 10 in SbF5, which was
diluted with SO2ClF and 19F NMR spectrum of the solution was
measured at ꢁ20 8C. The spectrum contained bad-resolved signals
of cation 10. Hydrolysis of the solution gave 0.06 g of a mixture
contained (GLC) 87% (yield 63%) of compound 11. An analytical
sample of compound 11 was prepared by crystallization.
d
E-isomer: 19F NMR (CH2Cl2):
CF3- ), ꢀ109.4 (1FA) and ꢀ110.5 (1FB, CF2),
), ꢀ95.8 (1F, F-
ꢀ131.6 (1F, F-6), ꢀ134.5 (1F, F-3), ꢀ146.1 (1F, F-4), ꢀ148.9 (1F,
F-5); = 7, ,A = 12, ,B = 23, JA,B = 284, J3,4 = 22, J3,5 = 6,
J3,6 = 11, J4,5 = 20, J4,6 = 10, J5,6 = 21.
d
ꢀ67.3 (3F, CF3-
g
), ꢀ83.9 (3F,
3.2.1. Perfluoro-3-ethyl-3-phenylphthalan-1-yl cation (10)
a
b
19F NMR (SbF5–SO2ClF):
d
ꢀ0.1 (1F, F-1), ꢀ77.6 (3F, CF3), ꢀ100.9
(1F) and ꢀ105.5 (1F, F-5, F-7), ꢀ111.2 (1FA) and ꢀ111.8 (1FB, EF2,
J!,% = 291), ꢀ112.7 (1F, F-4), ꢀ132.0 (2F, F-ortho), ꢀ133.4 (1F, F-6),
ꢀ138.8 (1F, F-para), ꢀ155.3 (2F, F-meta).
J
J
g
J
g
,
a g
3.2.2. Perfluoro-3-ethyl-3-phenylphthalide (11)
mp 110–111 8C (hexane). UV (hexane)
(3.45). IR (CCl4)
, cmꢀ1: 1831 (C O); 1518, 1505 (FAR).19F NMR
(CHCl3):
lmax, nm (lg e): 272
n
d
ꢀ78.5 (3F, s, CF3), ꢀ115.5 (1FA) and ꢀ116.7 (1FB, CF2),
ꢀ134.2 (1F, F-4), ꢀ135.2 (2F, F-ortho), ꢀ136.1 (1F, F-7), _139.7 (1F,
F-5), ꢀ145.5 (1F, F-6), ꢀ148.0 (1F, F-para), ꢀ159.5 (2F, F-meta);
JA,B = 280, JA,4 = 28, JA,ortho = 21, JB,4 = 18, JB,ortho = 35, Jortho,para = 6,
Z-isomer: 19F NMR (CH2Cl2):
CF3- ), ꢀ112.4 (1FA) and ꢀ112.6 (1FB, CF2),
), ꢀ105.4 (1F, F-
ꢀ130.9 (1F, F-6), ꢀ133.7 (1F, F-3), ꢀ145.8 (1F, F-4), ꢀ148.3 (1F,
F-5); J = 14, J ,3 = 9, J ,! = 2, J ,B = 2, J = 7, J ,A = 26, J ,B = 18,
d
ꢀ69.7 (3F, CF3-
g
), ꢀ84.6 (3F,
a
b
J
ortho,4 = 18, Jmeta,para = 22, J4,5 = 20, J4,6 = 8, J4,7 = 18, J5,6 = 18,
J5,7 = 11, J6,7 = 21, J6,7 = 21. HRMS m/z, 489.9671 (M+). Calcd for
16F14O2 = 489.9675.
,
,
a b
a
a
a
b g
b
b
J
b
,3 = 3, JA,B = 278, J3,4 = 22, J3,5 = 7, J3,6 = 11, J4,5 = 20, J4,6 = 10,
C
J5,6 = 21. HRMS (mixture of E- and Z-isomers) m/z, 423.9765
(M+). Calcd for C12HF13O2 = 423.9769.
Acknowledgements
2. A mixture of compound 1 (0.17 g) and SbF5 (1.04 g) (molar ratio,
1:12) in an ampoule with FEP inliner for recording of NMR
spectra was heated at 70 8C for 17 h and then at 125 8C for 84 h.
SO2ClF (ꢁ0.2 g) was added to the resulting mixture and 19F NMR
spectrum of the solution was measured at ꢁ20 8C. The spectrum
contained signals of cation 4.The solution was poured into 5%
hydrochloric acid and extracted with CH2Cl2. The extract was
dried over MgSO4. The solvent was evaporated to give a mixture
contained (19F NMR) 83% (yield 67%) of compound 5. An
analytical sample of compound 5 was prepared by crystal-
lization.
We gratefully acknowledge the Russian Foundation for Basic
Researches (project no. 06-03-32170) for financial support.
References
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Chem. 127 (2006) 1574–1583.
3.1.2. Perfluoro-4-ethyl-3-methylisochromenyl cation (4)
19F NMR (SbF5–SO2ClF):
d
ꢀ9.5 (1F, F-1), ꢀ59.4 (3F, CF3-3),
ꢀ75.2 (3F, CF3-4), ꢀ96.0 (2F, CF2), ꢀ98.5 (1F, F-6), ꢀ107.4 (1F, F-8),
ꢀ113.4 (1F, F-5), ꢀ130.8 (1F, F-7); J1,5 = 4, J1,6 = 9, J1,8 = 96,
JCF
¼ 8, JCF
¼ 20, J ¼ 29, JCF
¼ ꢁ 60, J5,6 = 18,
ꢀFð5Þ
ð3ÞꢀCF ð4Þ
ð3ÞꢀCF
3
3
3
2
2
J5,7 = 16, J5,8 = 11, J6,7 = 19, J6,8 = 32, J7,8 = 20.
[7] Ya.V. Zonov, V.M. Karpov, V.E. Platonov, J. Fluorine Chem. 128 (2007) 1065–1073.
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Div. Chem. Sci. 39 (1990) 1000–1004.
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(2007) 1678–1686;
3.1.3. Perfluoro-4-ethyl-3-methylisochromen-1-one (5)
mp 75.5–76.5 8C (hexane). UV (hexane) max, nm (lg
(4.36), 308 (3.59). IR (CCl4)
, cmꢀ1: 1795 (C O); 1518, 1483 (FAR).
19F NMR (CH2Cl2):
ꢀ64.7 (3F, CF3-3), ꢀ75.1 (3F, CF3-4), ꢀ96.0 (3F,
CF2), ꢀ128.2 (1F, F-5), ꢀ130.6 (1F, F-8), ꢀ139.4 (1F, F-6), ꢀ147.3
(1F, F-7); JCF ¼ 18, JCF ¼ 31,
¼ 8, JCF
l
e): 224
n
d
ð3ÞꢀCF ð4Þ
ꢀCF
ð4ÞꢀFð5Þ
3
3
3
3
2
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(2007) 1677–1685.
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JCF
¼ 52, J5,6 = 19, J5,7 = 8, J5,8 = 13, J6,7 = 21, J6,8 = 13, J7,8 = 21.
ꢀFð5Þ
2
HRMS m/z, 403.9712 (M+). Calcd for C12F12O2 = 403.9707.