Carbenoid reactions of organoelemental compounds containing trifluoromethyl groups: VII. Difluorocyclopropanation of olefins and dienes with a system tris(trifluoromethyl)bismuth-aluminum chloride

Article abstract of DOI:10.1023/A:1012318710556

Tris(trifluoromethyl)bismuth generates difluorocarbene at -30°C in the presence of aluminum chloride. By reaction of the difluorocarbene with isobutylene, styrene, cyclohexene, and 2,3-dimethyl-butadiene the corresponding substituted difluorocyclopropanes were obtained.

Full text of DOI:10.1023/A:1012318710556

Russian Journal of Organic Chemistry, Vol. 37, No. 2, 2001, pp. 207 209. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 2, 2001,
pp. 220 222.
Original Russian Text Copyright
2001 by Kirii, Pazenok, Yagupolskii, Naumann, Turra.
Carbenoid Reactions of Organoelemental Compounds
Containing Trifluoromethyl Groups:
*
VII. Difluorocyclopropanation of Olefins
and Dienes with a System
Tris(trifluoromethyl)bismuth Aluminum Chloride
**
1
1
1
2
1
N. V. Kirii , S. V. Pazenok , Yu. L. Yagupolskii , D. Naumann , and W. Turra
1
Institute of Organic Chemistry, Ukrainian Academy of Sciences, Kiev, 253660 Ukraine
2
Institute of Inorganic Chemistry of Cologne University, Cologne, Germany
Received July 5, 1999
Abstract Tris(trifluoromethyl)bismuth generates difluorocarbene at 30 C in the presence of aluminum
chloride. By reaction of the difluorocarbene with isobutylene, styrene, cyclohexene, and 2,3-dimethyl-
butadiene the corresponding substituted difluorocyclopropanes were obtained.
Quite a few methods of difluorocarbene generation
are known by now [2]. It reacts with olefins to afford
difluorocyclopropanes extensively used as inter-
mediate products in organic synthesis [3]. One among
the principal methods of difluorocarbene generation
is based on the use of organoelemental compounds
containing trifluoromethyl groups, as organocopper,
organotin, organocadmium, organosilicon, and
organophosphorus derivatives. The most often is
applied trifluoromethylphenylmercury that does not
afford difluorocarbene as a result of thermal degrada-
tion but cleanly affords it when treated with sodium
iodide at 80 C [4 6]. Recently an extensive applica-
tion found the preparation of difluorocarbene from
trifluoromethyltin by heating to 150 C [7, 8] or at
lower temperature by treating with sodium iodide [9].
Mild thermal sources of the difluorocarbene among
the organoelemental compounds are trifluormethyl-
trifluorosilane [10] and tris(trifluoromethyl)difluoro-
phosphorane [11 15]. All the procedures for
difluorocarbene generation from organoelemental
compounds mentioned above require high tempera-
ture and cannot be used in reactions with thermally
unstable compounds. Therefore the search for mild
sources of difluorocarbene generation is continued.
We showed before that the tris(trifluoromethyl)-
bismuth in the presence of aluminum chloride
behaved as a selective difluoromethylating agent with
respect to tertiary amines, phosphines, and arsines
[
1, 16]. The target of the present study was to
elucidate whether it was possible to carry out di-
fluorocyclopropanation of olefins and dienes in reac-
tion with tris(trifluoromethyl)bismuth in the presence
of AlCl . We found that with tris(trifluoromethyl)-
3
bismuth (I) in the presence of aluminum chloride
reacted with isobutylene in acetonitrile at 20 C to
afford 2,2-dimethyl-1,1-difluorocyclopropane (II) in
7
5% yield. The monitoring of difluorocyclopropane
II formation in the process of the reaction is easily
performed with the use of 19F NMR spectroscopy by
appearance of the difluoromethylene group triplet in
the region 139 ppm [17].
Reactions of tris(trifluoromethyl)bismuth (I) with
cyclohexene and styrene in the presence of AlCl at
3
20 C result in 7,7-difluoronorcarane (III) and
*
Previous communication see [1].
*
*
The study was carried out under financial support of the
INTAS Foundation (grant no. 95-0005) and DEG (contract
4
36 UKR 113/26/1).
1
070-4280/01/3702-0207$25.00 2001 MAIK Nauka/Interperiodica

2
08
KIRII et al.
1,1-Difluoro-2,2-dimethylcyclopropane
2
6
-phenyl-1,1-difluorocyclopropane (IV) in 40 and
0% yield respectively.
(II).
To a solution of 0.82 g (1.97 mmol) of tris(trifluoro-
methyl)bismuth (I) in 5 ml of anhydrous acetonitrile
at 20 C at vigorous stirring was added 0.166 g
(
2.96 mmol) of isobutylene and 0.376 g (2.78 mmol)
of fine powder of aluminum chloride. The mixture
was stirred at this temperature for 1 h, and then
gradually warmed to room temperature. The reaction
mixture was poured into water, the precipitate was
filtered off, the reaction products were trice extracted
into benzene, and the benzene extract was dried with
magnesium sulfate. On distilling off benzene the
fractional distillation afforded 0.16 g of 1,1-difluoro-
cyclopropane (II), yield 75%, bp 41 42 C. The
boiling point and spectral characteristics of compound
II are consistent with the published data [17].
2
,3-Dimethylbutadiene reacts with the tris(tri-
fluoromethyl)bismuth in the presence of AlCl at
3
2
0 C to provide a product of difluorocarbene addi-
tion only across one double bond, 2-isopropenyl-2-
methyl-1,1-difluorocyclopropane V in 75% yield.
7
,7-Difluoronorcarane (III) was similarly pre-
pared from 0.92 g (2.21 mmol) of tris(trifluoro-
methyl)bismuth (I), 0.182 g (2.21 mmol) of cyclo-
hexene, and 0.306 g (2.26 mmol) of aluminum
chloride. Yield 0.12 g (40%), bp 122 C. The boiling
point and spectral characteristics of compound III are
consistent with the published data [19].
2
-Phenyl-1,1-difluorocyclopropane (IV) was
prepared in the same way as compound II from
.649 g (1.56 mmol) of tris(trifluoromethyl)bismuth
(I), 0.162 g (1.56 mmol) of styrene, and 0.223 g
1.65 mmol) of aluminum chloride. Yield of com-
pound IV 0.14 g (60%), bp 64 65 C (25 mm) [17].
Compound V is a colorless fluid; its composition
and structure are confirmed by H, F, and NMR
spectra, mass spectrum, and elemental analysis. In the
1
19
13
0
1
9
F NMR spectrum appears a single resonance of the
fluorine atoms of the difluoromethylene group in
37.75 ppm region in the form of triplet of quartets
(
1
3
4
2
-Isopropenyl-2-methyl-1, 1-difluorocyclo-
propane (V) was prepared as compound II from
.84 g (2.02 mmol) of tris(trifluoromethyl)bismuth
I), 0.166 g (2.02 mmol) of 2,3-dimethylbutadiene,
with the coupling constants J 8.8 and J 2.3 Hz.
FH
FH
1
9
F NMR spectrum of compound V at 55 C contains
two signals of fluorine atoms from the CF group at
0
(
2
1
35.62 ppm and 136.58 ppm respectively with a
2
and 0.47 g (3.47 mmol) of aluminum chloride. Yield
of compound V 0.2 g (75%), bp 58 C. H NMR
spectrum (CDCl , , ppm), at 30 C: 4.88 d (2H,
geminal coupling constant J 158 Hz.
FF
1
This the tris(trifluoromethyl)bismuth in the
presence of aluminum chloride can be applied to
difluorocyclopropanation of olefins and dienes. The
mild conditions of the reaction are favorable for
preparation of thermally unstable compounds.
3
2
CH = , J 9 Hz), 1.76 s (3H, CH -vinyl), 1.25 m
2
HH
3
4
(
3H, CH -cycle, J 2.3 Hz), 1.44 d.m (1H cycle,
JHH 10, J 8.8 Hz), 1.12 d.m (1H cycle, J 10,
JHF 8.8 Hz). F NMR spectra: (1) (CDCl , , ppm),
at 20 C: 137.75 t.q (2F, CF2, JFH 8.8, JFH
.3 Hz); 2) (CDCl , F, ppm), at 55 C: 135.62
d.m (1F, CF , J 158 Hz), 136.58 d.m (1F, CF2,
JFF 158 Hz). C NMR spectrum (CD CN, C, ppm):
7.55 t (CH -cycle, J 2 Hz), 20.34 (CH -vinyl),
1.56 t (CH , J 10 Hz), 32.03 t (C cycle, J
CF
3 HF
2
3
2
HF
HH
3
19
3
F
3
4
EXPERIMENTAL
2
3
2
1H, 13C, and 19F NMR spectra were recorded on
spectrometer Bruker AC 200 at operating frequencies
2
FF
2
13
3
3
1
2
1
1
3 CF 3
2
00, 50.3, and 188.3 MHz respectively, internal
2
2
1
13
19
2
CH
references TMS ( H, C) and CCl F ( F). The mass
1
3
0 Hz), 113.41 (CH =), 114.94 t (CF , J 288 Hz),
2
2
CF
spectrum was measured on Varian CH-5 instrument
at 180 C.
42.26 (C vinyl). Mass spectrum (180 C), m/z: 132
+
[
M] .
All reactions were carried out in argon atmo-
sphere. Acetonitrile was distilled over P O . The tris-
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