Reactions of diazoalkanes with unsaturated compounds 14. Reactions of diazomethane, diazocyclopropane, and methyl diazoacetate with 1,1,2,2-tetrafluoro-3-vinylcyclobutane and 2,3,3-trifluoro-1-vinylcyclobutene to form [3+2] and [1+2] cycloadducts

Article abstract of DOI:10.1023/A:1015049317831

The reactions of diazomethane and diazocyclopropane generated in situ with 1,1,2,2-tetrafluoro-3-vinylcyclobutane (1) and 2,3,3-trifluoro-1-vinylcyclobutene (2) proceeded at the double bond of the substituent as the 1,3-dipolar cycloaddition to form the corresponding 1-pyrazolines. Under the conditions of thermolysis (340 - 400 °C), the resulting cyclobutylpyrazolines 4 and 5 selectively lost the dinitrogen molecule to generate 3-cyclopropyl-1,1,2,2-tetrafluorocyclobutane (6) or 1,1,2,2-tetrafluoro-3-spiropentylcyclobutane (7), respectively, in high yields. In the presence of Pd(acac)₂, the reactions of these fluorine-containing unsaturated compounds and 2-chloro-1,1,2-trifluoro-3-vinylcyclobutane (3) with diazomethane gave rise directly to cyclopropane derivatives 6, 11, and 12, respectively. The reactions of compounds 1 and 2 with methyl diazoacetate in the presence of Rh₂(OAc)₄ proceeded analogously to yield cis- and trans-disubstituted cyclopropanes.

Full text of DOI:10.1023/A:1015049317831

Russian Chemical Bulletin, International Edition, Vol. 50, No. 11, pp. 2113—2120, November, 2001
2113
Reactions of diazoalkanes with unsaturated compounds
14.* Reactions of diazomethane, diazocyclopropane, and methyl diazoacetate
with 1,1,2,2-tetrafluoro-3-vinylcyclobutane and 2,3,3-trifluoro-1-vinylcyclobutene
to form [3+2] and [1+2] cycloadducts**
Yu. V. Tomilov,« E. V. Guseva, N. V. Volchkov, and E. V. Shulishov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. E-mail: tom@ioc.ac.ru
The reactions of diazomethane and diazocyclopropane generated in situ with 1,1,2,2-tetra-
fluoro-3-vinylcyclobutane (1) and 2,3,3-trifluoro-1-vinylcyclobutene (2) proceeded at the
double bond of the substituent as the 1,3-dipolar cycloaddition to form the corresponding
1-pyrazolines. Under the conditions of thermolysis (340—400 °C), the resulting
cyclobutylpyrazolines 4 and 5 selectively lost the dinitrogen molecule to generate 3-cyclo-
propyl-1,1,2,2-tetrafluorocyclobutane (6) or 1,1,2,2-tetrafluoro-3-spiropentylcyclobutane (7),
respectively, in high yields. In the presence of Pd(acac)2, the reactions of these fluorine-
containing unsaturated compounds and 2-chloro-1,1,2-trifluoro-3-vinylcyclobutane (3) with
diazomethane gave rise directly to cyclopropane derivatives 6, 11, and 12, respectively. The
reactions of compounds 1 and 2 with methyl diazoacetate in the presence of Rh2(OAc)4
proceeded analogously to yield cis- and trans-disubstituted cyclopropanes.
Key words: fluorinated vinyl- and cyclopropylcyclobutanes and -cyclobutenes,
tetrafluorocyclobutyl- and trifluorocyclobutenyl-1-pyrazolines, diazo compounds, catalytic
cyclopropanation, 1,3-dipolar cycloaddition, thermal dinitrogen elimination.
The 1,3-dipolar addition to various unsaturated com-
pounds giving rise to nitrogen heterocycles and the
[1+2] cycloaddition of the carbenes, which are derived
from the latter compounds, to form three-membered
rings are typical chemical transformations of diazoalkanes
producing new C—C bonds. The [1+2] cycloaddition
reactions take place due to energetically favorable elimi-
nation of the nitrogen molecule from diazo compounds,
which generally proceeds in the presence of transition
metal complexes. These transformations were examined
for a rich variety of alkenes, cycloalkenes, polyenes, and
acetylenes as unsaturated substrates. However, the reac-
tions of aliphatic diazo compounds with fluorine-con-
taining unsaturated compounds remain poorly studied.
For the most part, studies were devoted to the 1,3-di-
polar cycloaddition involving unsaturated compounds
containing fluorine atoms, which are either directly
bound to the double bond3—6 or are remote from this
bond,7—13 whereas examples of catalytic cyclopro-
panation of double bonds are few in number.14,15 How-
ever, fluorine-containing cyclopropanes and pyrazolines
obtained in these reactions are of interest as new synthons
for preparing biologically active compounds.
2,3,3-trifluoro-1-vinylcyclobutene (2)17,18 with diazo-
methane and methyl diazoacetate (both in the presence
and in the absence of catalysts) as well as with
diazocyclopropane generated in situ. Vinylcyclobutene 2
was synthesized from readily accessible 2-chloro-1,1,2-
trifluoro-3-vinylcyclobutane (3). However, contrary to
procedures described previously,17,18 dehydrochlorina-
tion of the latter compound was carried out under the
action of a 45% aqueous solution (instead of alcoholic
–
solution) of KOH in the presence of PhCH2Et3N+Cl ,
which simplified isolation of the target product. In
addition, we measured the 13C and 19F NMR spectra of
diene 2, which have not been described previously. The
1H NMR spectra, which were recorded on instruments
operating at different frequencies, revealed the equiva-
lence of the methylene protons of the cyclobutene ring
manifested as a doublet of triplets with the spin-spin
coupling constants J = 12.0 and 3.0 Hz. The chemical
shifts of these protons at δ 2.54 and 2.74 (60 MHz),
which have been reported earlier,17 are wrong and are in
reality the manifestation of the spin-spin coupling con-
stant JHF = 12.0 Hz.
The direct reaction of tetrafluorovinylcyclobutane
(1) with diazomethane in an ethereal solution proceeded
rather slowly (20 °C, 3 days) to give a mixture
of diastereomeric 3-(2,2,3,3-tetrafluorocyclobutyl)-1-
pyrazolines (4) in a ratio of ∼1.8 : 1 in a total yield of
∼85%. Both isomers were isolated in the individual form
In the present study, we examined the reactions
of 1,1,2,2-tetrafluoro-3-vinylcyclobutane (1)16 and
* For Part 13, see Ref. 1.
** For the preliminary communication, see Ref. 2.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2019—2025, November, 2001.
1066-5285/01/5011-2113 $25.00 © 2001 Plenum Publishing Corporation

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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 11, November, 2001
Tomilov et al.
1
by preparative TLC and were characterized by the H,
13C, and 19F NMR spectra. The spectra of both isomers
are similar, each being characterized by the presence of
the CH2CH2 fragment in the five-membered hetero-
cycle. This is indicative of the regioselective addition of
diazomethane to the unsymmetrically substituted double
bond in 1, the terminal nitrogen atom of the diazo
compound forming a bond with the substituted C atom
of the vinyl group.
tively, relative to the nitrogen atoms, and signals of the
methylene fragment of the pyrazoline ring with the
geminal spin-spin coupling constant of 12.8 Hz.
Tetrafluorocyclopropylcyclobutane (6), which was
obtained in 82—85% yield by passing a mixture of
pyrazolines 4a,b under a stream of argon through a
quartz tube at 340 °C, was virtually free from impurities
of isomerization and dehydrofluorination products, which
indicates that this process is highly selective, unlike, for
example, thermolysis of the products of the 1,3-dipolar
cycloaddition of diazomethane to the strained endocyclic
bond in 3,3-difluoro- and 3,3,4,4-tetrafluorocyclo-
butenes.8
Like the reaction of 1 with diazomethane, the reac-
tion with diazocyclopropane, which was generated in
situ by decomposition of N-cyclopropyl-N-nitrosourea
under the action of MeONa at –20 °C or under the
action of an equimolar mixture of KOH and K2CO3 at
–10 °C, also afforded the corresponding 1,3-dipolar
cycloaddition products, viz., isomeric 5-cyclobutyl-
spiro[1-pyrazoline-3,1´-cyclopropanes] (5) (Scheme 1).
In the former case, isomeric pyrazolines 5 were obtained
in a total yield of up to 48% (the isomer ratio was
ca. 2.3 : 1), whereas the latter reaction gave rise to
isomers of 5 in ∼35% yield in a ratio of ca. 1.4 : 1.
However, the target products obtained in the reaction
with the use of a mixture of KOH and K2CO3 were
more pure because the presence of MeONa led, appar-
ently, to the partial replacement of the fluorine atoms by
the methoxy groups to form the corresponding impuri-
ties. The isomers of 5 were separated by preparative
TLC. The major isomer (5a) was isolated in the indi-
vidual form, whereas isomer 5b was enriched to ∼85%.
Compound 6 can also be prepared in one step by
direct cyclopropanation of unsaturated compound 1 with
diazomethane. The use of palladium compounds, in
particular Pd(acac)2, as catalysts for decomposition of
CH2N2 made it possible to perform the reaction accord-
ing to a one-pot procedure involving simultaneous gen-
eration of CH2N2 (from N-methyl-N-nitrosourea under
the action of KOH) and its catalytic decomposition (see
Ref. 19). The reaction with the use of a threefold molar
excess (with respect to the initial 1) of methylnitrosourea
afforded cyclopropylcyclobutane 6 in ∼90% yield.
Thermolysis of spiro(pyrazolinecyclopropane) 5 pro-
ceeded at higher temperature (400—410 °C) compared
to that of pyrazoline 4 to give (tetrafluorocyclo-
butyl)spiropentane (7) as a mixture of two diastereomers
in 70—75% yield. According to the 13C and 19F NMR
spectra, spiropentanes 7a,b were generated from pyr-
azoline 5a in a ratio of 2.1 : 1, whereas the reaction of
pyrazoline, which was enriched with isomer 5b to 85%,
gave rise to spiropentanes 7a,b in a ratio of 1 : 1.2.
Unlike diazomethane, methyl diazoacetate virtually
did not react with tetrafluorovinylcyclobutane 1 in the
absence of catalysts at 20—25 °C; however, methyl
diazoacetate eliminated the dinitrogen molecule in the
presence of Rh2(OAc)4 (∼1 mol.%) in CH2Cl2 accom-
panied by the addition of the carbene fragment at the
double bond of 1. The latter reaction afforded dimethyl
fumarate and dimethyl maleate along with a mixture of
isomeric methyl 2-(2,2,3,3-tetrafluorocyclobutyl)cyclo-
propanecarboxylates (8) (Scheme 2). These isomers were
isolated by vacuum distillation in a total yield of ∼50%.
The 1H NMR spectrum of the resulting product has four
singlet signals of the methoxy groups at δ 3.69–3.72
with the integral intensity ratio of ∼1.1 : 1 : 1.6 : 1.5,
which is indicative of low selectivity of the addition of
methoxycarbonylcarbene to the double bond of olefin 1.
Preparative TLC of the mixture of isomeric esters 8 on
neutral Al2O3 yielded chromatographic zones en-
riched with the trans (Rf 0.57±0.04) and cis isomers
(Rf 0.65±0.04) to approximately 92 and 80%, respec-
1
The H NMR spectra of both spiro(pyrazolinecyclo-
propanes) 5 have two characteristic groups of signals at
δ ∼1.1 and 1.7–1.8 for the protons of the cyclopropane
ring, which are in the anti and syn orientations, respec-
Scheme 1
F
F
F
F
N
N
CH2N2
340 °C
4a,b
F
F
F
F
F
F
F
CH2N2, Pd(acac)2
F
1
6
N2
F
F
F
F
F
1
tively. The H NMR spectra of compounds from these
F
F
400 °C
zones have two sets of signals each and differ noticeably
from one another in the multiplicities of the signals for
the protons at the C(1) and C(3) atoms of the cyclopro-
pane ring, which corresponds to the different vici-
N
F
N
5a,b
7a,b

Reactions of diazoalkanes
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 11, November, 2001 2115
nal spin-spin coupling constants (Jcis ∼ 8.5 and
Jtrans ∼ 5.0 Hz). Thus, two cisoid spin-spin coupling
constants can appear only for the H(1) and H(3a)
protons in the spectra of the cis isomers; on the con-
trary, two transoid constants should appear in the case
of the H(3b) proton. Actually, the latter constants were
ca. 0 °C, to olefin 1. Vacuum microdistillation (0.1 Torr)
of the reaction mixture afforded 5-(trifluorocyclo-
butenyl)spiro[1-pyrazoline-3,1´-cyclopropane] (10) with
a purity of ca. 92%, which remained unchanged upon
storage in a CDCl3 solution for several days. In the
earlier studies of other spiro[1-pyrazoline-3,1´-cyclo-
propanes],20,21 we have observed the enhancement of
stability of 1-pyrazolines upon the introduction of the
spirocyclopropane fragment.
The catalytic (in the presence of Pd(acac)2) reaction
of diazomethane with unsaturated compound 2 also
proceeded selectively at the vinyl group. However, the
latter reaction, unlike the reaction with 1, afforded
1-cyclopropyl-2,3,3-trifluorocyclobutene (11) in a yield
of at most 40% even with the use of a fivefold excess of
CH2N2. To estimate the reactivities of unsaturated ac-
ceptors 1 and 2, we examined their cyclopropanation in
the competitive reactions with styrene (the molar ratio
CH2N2 : olefin 1 (or diene 2) : styrene = 0.2 : 1 : 1); the
formation of cyclopropylbenzene and cyclopropanes 6
or 11 was judged from the GLC data and the 1H NMR
spectra. All three unsaturated compounds showed ap-
proximately equal reactivities, the relative reactivity of
vinylcyclobutene 2 being even slightly higher (krel ≈ 1.1)
than that of vinylcyclobutane 1 (krel ≈ 0.9).
1
observed in the H NMR spectrum of the compounds
from the upper zone (see the Experimental section).
The NMR spectra of both specimens have two sets of
signals each with the integral intensity ratio of ∼1.5 : 1,
which is attributable to the presence of diastereomers
with respect to the asymmetrical C(2) and C(3´) atoms,
respectively. However, the complexity of the signals for
the corresponding methine protons involved in addi-
tional interactions with the F atoms did not allow us to
assign them to the parf and pref series.
Scheme 2
N2CHCOOMe
1
Rh2(OAc)4, CH2Cl2
F
F
F
F
F
F
F
F
+
Scheme 3
3´
H
COOMe
Hb
Hb
1
2
F
F
COOMe
H
H
H
3
F
F
F
F
Ha
trans-8a,b
Ha
cis-8a,b
N
N
N
N
Unlike the reaction of diazomethane with vinyl-
cyclobutane 1, the reaction with trifluorovinylcyclobutene
2 proceeded much more rapidly (during 0.5 h at 20 °C)
and, in spite of the presence of the strained endocyclic
double bond and the use of an excess of CH2N2, gave
rise to the product of the 1,3-dipolar cycloaddition at
the vinyl group, viz., to 1-pyrazoline 9, in ≥90% yield
(Scheme 3). The fact that the reaction proceeded selec-
tively at the vinyl group seems to be reasonable because
it is known3,7 that the presence of the fluorine atoms at
the double bond leads to weakening of its dipolarophilic
properties. The 1H NMR spectrum of the resulting
compound has one set of signals corresponding to the
five-spin system of the α-substituted pyrazoline ring, the
spin-spin coupling constants of the CH2CH2 fragment
being in good agreement with those for isomeric
pyrazolines 4a,b. However, 1-pyrazoline 9 is unstable.
Thus, it turned red and underwent rapid resinification
even in attempting to concentrate its solutions at
5—10 °C. Interestingly, related spirocyclopropane-con-
taining 1-pyrazoline 10 is more stable. The latter com-
pound was obtained in 40—45% yield (according to the
1H NMR spectroscopic data) by the addition of
diazocyclopropane, which was generated by decomposi-
tion of N-cyclopropyl-N-nitrosourea with K2CO3 at
9
10
N2
CH2N2
F
F
F
F
F
CH2N2, Pd(acac)2
F
11
2
KOH, cat.
KOH, cat.
85 °C
95 °C
Cl
F
F
F
F
F
CH2N2
Cl
F
Pd(acac)2
3
12
The relatively low yield of cyclopropylcyclobutene
11 (<40%) observed in catalytic cyclopropanation of
diene 2 with diazomethane is, apparently, associated
with a decrease in the catalytic activity of the Pd catalyst
due to its transformation into an inactive complex with

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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 11, November, 2001
Tomilov et al.
pyrazoline 9, which was concurrently formed through
the 1,3-dipolar cycloaddition of CH2N2 to unsaturated
compound 2 (see above).
shifts (∆δ ≈ 2.5) and are split into a doublet with the
2
spin-spin coupling constants JFF = 203—205 Hz. An
analogous situation was observed in the 19F NMR spec-
tra of pyrazolines 9 and 10 containing the asymmetrical
C atom adjacent to the cyclobutene fragment; however,
the difference between the chemical shifts of the gemi-
nal fluorine atoms in these cases is only 0.4—0.5 ppm
(see the Experimental section).
Yet another procedure for the synthesis of compound
11 involves cyclopropanation by chlorotrifluorovinyl-
cyclobutane (3) instead of rather labile trifluorovinyl-
cyclobutene (2) followed by dehydrochlorination of the
cyclopropanation product. The reaction of compound 3
(a mixture of two isomers) with diazomethane catalyzed
by Pd compounds proceeded readily under the condi-
tions of the simultaneous generation and catalytic de-
composition of the latter19 to form a mixture of isomeric
2-chloro-3-cyclopropyl-1,1,2-trifluorocyclobutanes (12)
in a total yield of ca. 90%. These compounds are much
more stable compared with 2. Subsequent dehydrochlo-
rination of a mixture of two isomers 12 with a 45%
To summarize, the 1,3-dipolar cycloaddition of
diazomethane and diazocyclopropane generated in situ
can proceed regioselectively at the vinyl group of com-
pounds 1 and 2 and elimination of the dinitrogen mol-
ecule from 1-pyrazolines derived from vinylcyclobutane
1 can proceed selectively as exemplified by the reac-
tions of 1,1,2,2-tetrafluoro-3-vinylcyclobutane (1) and
2,3,3-trifluoro-1-vinylcyclobutene (2) with diazo com-
pounds. Catalytic cyclopropanation of the above-men-
tioned olefins with diazomethane in the presence of
Pd(acac)2 or with methyl diazoacetate in the presence of
Rh2(OAc)4 made it possible to obtain the corresponding
cyclopropylcyclobutanes or -cyclobutenes in rather high
yields. The most convenient procedure for the prepara-
tive synthesis of 1-cyclopropyl-2,3,3-trifluorocyclobutene
(11) involves cyclopropanation of 2-chloro-1,1,2-tri-
fluoro-3-vinylcyclobutane (3) with diazomethane in the
presence of Pd(acac)2 followed by dehydrochlorination
of the resulting 2-chloro-3-cyclopropyl-1,1,2-trifluoro-
cyclobutane (12). The 1H, 13C, and 19F NMR spectra of
all the compounds synthesized were interpreted in detail.
–
solution of KOH in the presence of PhCH2Et3N+Cl
afforded cyclopropylcyclobutene 11 in 92% yield.
Cyclopropanation of diene 2 under the action of
methyl diazoacetate in the presence of Rh2(OAc)4 also
proceeded at the exocyclic double bond. The reaction
with the use of the diene and methyl diazoacetate taken
in a molar ratio of 2.2 : 1 gave rise to isomeric methyl
2-(trifluorocyclobutenyl)cyclopropanecarboxylates (13) in
58% yield in the ratio trans-13 : cis-13 of approxi-
mately 1.4 : 1.
Scheme 4
N2CHCOOMe
Experimental
2
Rh2(OAc)4, CH2Cl2
1
The H and 13C NMR spectra were recorded on Bruker
AC-200 (200.13 and 50.3 MHz), Bruker AM-300 (300.13 and
75.5 MHz), and Bruker DRX-500 (500.13 MHz) spectrom-
eters for solutions in CDCl3 containing 0.05% of Me4Si as the
internal standard. The 19F NMR spectra were measured
on Bruker AC-200 (188.3 MHz) and Bruker DRX-500
(470.8 MHz) spectrometers; the chemical shifts are given
relative to CCl3F. The mass spectra were obtained on a Finnigan
MAT INCOS-50 instrument (EI, 70 eV, a 30-m RSL-200
capillary column or a direct inlet system). 1,1,2,2-Tetrafluoro-
3-vinylcyclobutane (1), 2-chloro-1,1,2-trifluoro-3-vinylcyclo-
butane (3),16—18 N-cyclopropyl-N-nitrosourea,22 palladium
acetylacetonate,23 and dirhodium tetraacetate24 were prepared
according to known procedures. The solvents were distilled
before use. Preparative TLC was carried out on plates
(20½20 cm) with a nonfixed layer of an adsorbent (silica gel
L 40/100 (Chemapol), unless otherwise indicated); the thick-
ness of the layer was 2 mm. The competitive reactions
of diazomethane with the unsaturated compounds (ole-
fin 1—styrene and diene 2—styrene) were carried out accord-
ing to a procedure described previously.25
2,3,3-Trifluoro-1-vinylcyclobutene (2). 2-Chloro-2,3,3-tri-
fluoro-1-vinylcyclobutane (3) (34.2 g, 0.2 mol) and benzyl-
triethylammonium chloride (0.8 g, 3.5 mmol) were placed in a
flask equipped with a stirrer, a dropping funnel, and a system
for purging with argon. Then a 45% aqueous solution of KOH
(20 mL) was added dropwise with intense stirring at 85 °C for
30 min, the product that formed with a small amount of water
being collected (argon was fed at a rate of ∼3 mL•min–1) in a
F
F
F
F
F
F
+
1
´
COOMe
1
2
COOMe
trans-13
cis-13
The structures of the resulting compounds were es-
tablished by 1H, 13C, and 19F NMR spectroscopy. Un-
like the H NMR spectra of vinyl- and cyclopropyl-
1
substituted cyclobutenes 2 and 11, the NMR spectra of
isomeric esters 13 reveal the nonequivalence of the
methylene protons of the four-membered ring due to the
presence of the additional substituent in the cyclopro-
pane fragment, this effect being more pronounced for
the cis isomer (∆δ ≈ 0.13) than for the trans isomer
(∆δ ≈ 0.02). Analogously, the 19F NMR spectrum has a
signal of the CF2 group of the trans isomer as a multiplet
with small spin-spin coupling constants (J < 10 Hz)
resulting from coupling with the adjacent H and F
atoms, whereas the signals for the fluorine atoms of the
CF2 group in the cis isomer have different chemical

Reactions of diazoalkanes
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 11, November, 2001 2117
trap cooled to –20 °C. The liquid phase was decanted from
ice, dried with anhydrous Na2SO4, and distilled under reduced
pressure. Trifluorovinylcyclobutene 2 was obtained as a color-
less liquid in a yield of 22.8 g (83%), b.p. 49—50 °C (200 Torr)
(cf. lit.17,18). 1H NMR (CDCl3), δ: 2.70 (dt, 2 H, CH2,
JHF = 12.0 and 3.0 Hz); 5.40 (d, 1 H, =CH2, Jtrans = 17.2 Hz);
5.51 (d, 1 H, =CH2, Jcis = 10.6 Hz); 6.54 (dd, 1 H, =CH,
CH2Cl2 (4 mL). The solvent and an excess of the olefin were
distilled off on a rotary evaporator. A yellowish oil was ob-
tained in a yield of 0.32 g (48%). According to the H and
13C NMR spectra, the liquid was a mixture of two isomeric
pyrazolines 5 in the ratio 5a : 5b = 2.3 : 1. Found (%):
C, 49.18; H, 4.95. C9H10F4N2. Calculated (%): C, 48.65;
H, 4.54. The isomers were separated by preparative TLC
(Al2O3; ether—heptane as the eluent, 5 : 4). Isomer 5a was
1
Jtrans = 17.2 Hz, Jcis = 10.6 Hz). 13C NMR (CDCl3), δ: 36.2
1
(dt, C(4), JCF ≈ 19 and 22 Hz); 118.3 (td, CF2, JCF
=
isolated in the individual form, whereas isomer 5b was isolated
with an impurity of isomer 5a (∼6 : 1).
272 Hz, 2JCF = 25 Hz); 122.9 (d, =CH2, 4JCF = 7 Hz); 123.4
3
2
(td, C(1), JCF = 17 Hz, JCF = 5 Hz); 124.1 (br.d, =CH,
JCF = 3 Hz); 138.2 (dt, =CF, 1JCF = 350 Hz, 2JCF = 26 Hz).
19F NMR (CDCl3), δ: –110.3 (br.s, CF2), –112.2 (br.t, =CF,
4JHF = 12.0 Hz).
Method B. A powdered mixture of K2CO3 (0.66 g,
4.8 mmol) and KOH (0.27 g, 4.8 mmol) was added with
intense stirring to a solution of 1,1,2,2-tetrafluoro-3-vinyl-
cyclobutane (1) (3.70 g, 24 mmol) and N-cyclopropyl-N-
nitrosourea (0.48 g, 3.7 mmol) in CH2Cl2 (10 mL) at –10 °C.
Then the reaction mixture was stirred for 30 min and the
temperature was raised to 20 °C during 30 min. Subsequent
treatment was carried analogously to the method A. A yellow-
ish oil was obtained in a yield of 0.29 g (35%). According to
the 1H and 13C NMR spectra, the liquid was a mixture of two
isomeric pyrazolines 5a,b in a ratio of 1.4 : 1.
3-(2,2,3,3-Tetrafluorocyclobutyl)-1-pyrazolines (4). A so-
lution of 1,1,2,2-tetrafluoro-3-vinylcyclobutane (1) (6.94 g,
0.045 mol) and an ethereal solution (200 mL) of diazomethane
(∼7.6 g, 0.18 mol) were kept at 20 °C for 3 days and then
passed through a layer of Al2O3 (1 cm). The solvent and the
unconsumed starting compounds were removed at 20 Torr. A
yellowish liquid was obtained in a yield 7.52 g (85%). Accord-
ing to the 1H and 13C NMR spectra, the liquid was a mixture
of parf- and pref-cyclobutylpyrazolines 4 (the isomer ratio
4a : 4b ≈ 1.8 : 1). Found (%): C, 42.89; H, 4.20; N, 14.34.
C7H8F4N2. Calculated (%): C, 42.86; H, 4.11; N, 14.28.
The isomers were separated by preparative TLC (Al2O3;
ether–heptane–methanol as the eluent, 1 : 6 : 1) and charac-
terized by NMR spectroscopy.
Isomer 5a, Rf = 0.50, m.p. 39—41 °C. 1H NMR (CDCl3),
δ: 1.12 (m, 2 H, H(1´) and H(2´), directed away from the
N atom of the heterocycle); 1.55 (dd, 1 H, H(4b), 2J = 12.8 Hz,
J4b,5 = 7.0 Hz); 1.68 and 1.81 (both m, 1 H each, H(1´) and
H(2´), directed toward the N atom of the heterocycle); 2.06
(dd, 1 H, H(4a), 2J = 12.8 Hz, J4a,5 = 9.4 Hz); 2.63 (m, 1 H,
C(3″)H); 2.91 (m, 2 H, C(4″)H2); 4.70 (ddd, 1 H, H(5),
J5,3″ = 10.2 Hz, J4a,5 = 9.4 Hz, J4b,5 = 7.0 Hz). 13C NMR
(CD2Cl2), δ: 14.1 (s, CH2CH2); 30.0 (s, C(4)); 34.0 (tdd,
1
Isomer 4a. Rf = 0.50. H NMR (CDCl3), δ: 1.25 (ddt,
2
3
3
1 H, H(4a), Jab = 13.0 Hz, J = 9.5 Hz, J ≈ 8.3 Hz); 2.00
2
3
3
2
3
(ddt, 1 H, H(4b), Jab = 13.0 Hz, J ≈ 9.0 Hz, J = 4.4 Hz);
2.57 (m, 1 H, H(3´)); 2.93 (m, 2 H, H(4´)); 4.34 (dddd, 1 H,
H(5b), 2Jab = 17.2 Hz, 3J = 9.3 Hz, 3J = 8.2 Hz, 4J = 2.4 Hz);
4.45 (m, 1 H, H(3)); 4.76 (dddd, 1 H, H(5a), 2Jab = 17.2 Hz,
C(4″)H2, JCF = 21 Hz, JCF = 9.9 and 3.0 Hz); 43.8 (tdd,
C(3″)H, 2JCF = 21 Hz, 3JCF = 9.8 and 4.2 Hz); 70.1 (s, C(5));
1
84.1 (s, C(3)); 118.1 (ddt, CF2, JCF = 290 and 268 Hz,
2JCF = 28 Hz); 118.5 (ddt, CF2, JCF = 287 and 272 Hz,
1
3
4
3J = 9.5 Hz, J = 4.4 Hz, J = 2.4 Hz). 13C NMR (CDCl3),
2JCF = 27 Hz). 19F NMR (CDCl3), δ: –109.4 and –127.9
(both d, CF2, JFF = 209 Hz), –110.3 and –117.1 (both d,
CF2, JFF = 208 Hz).
2
3
δ: 22.2 (s, C(4)); 34.0 (tdd, C(4´), JCF = 21 Hz, JCF = 9.1
and 3.6 Hz); 43.1 (tdd, C(3´), 2JCF = 22 Hz, 3JCF = 10.1 and
3.5 Hz); 76.9 (s, C(5)); 85.2 (s, C(3)); 117.7 (ddt, CF2,
1JCF = 295 and 282 Hz, JCF = 27 Hz); 118.1 (ddt, CF2,
1JCF = 300 and 286 Hz, JCF = 25 Hz). 19F NMR (CDCl3),
Isomer 5b, Rf = 0.38. 1H NMR (CDCl3), δ: 1.11 (m, 2 H,
H(1´) and H(2´), directed away from the N atom of
the heterocycle); 1.54 (dd, 1 H, H(4b), 2J = 12.8 Hz,
J4b,5 = 7.4 Hz); 1.69 and 1.82 (both m, 1 H each, H(1´) and
H(2´), directed toward the N atom of the heterocycle); 1.96
(dd, 1 H, H(4a), 2J = 12.8 Hz, J4a,5 = 9.4 Hz); 2.46 and 3.20
(both m, 1 H each, C(4″)H2); 2.62 (m, 1 H, C(3″)H); 4.87
(br.dt, 1 H, H(5), J4a,5 = 9.4 Hz, J5,3″ ≈ J4b,5 ≈ 7.4 Hz).
13C NMR (CD2Cl2), δ: 14.2 (s, CH2CH2); 28.3 (s, C(4)); 32.1
2
2
δ: –108.8 and –127.6 (both d, CF2, JFF = 209 Hz), –109.6
and –116.7 (both d, CF2, JFF = 208 Hz). The partial mass
spectrum, m/z (Irel (%)): 196 (1.5) [M]+, 114 (7), 104 (100),
103 (46), 77 (40), 68 (97), 67 (68).
Isomer 4b. Rf = 0.34. 1H NMR (CDCl3), δ: 1.22 and 1.92
(both m, 1+1 H, C(4)H2, 2Jab ≈ 13.0 Hz); 2.53 and 2.65 (both
m, 1+1 H, C(4´)H2); 3.08 (m, 1 H, H(3´)); 4.28 (dtd, 1 H,
2
3
(tdd, C(4″)H2, JCF = 21 Hz, JCF = 11 and 2.5 Hz); 42.6
2
3
4
2
3
H(5b), J = 17.5 Hz, J ≈ 8.7 Hz, J = 2.5 Hz); 4.56 (br.qt,
1 H, H(3), 3J ≈ 8.5 Hz, 4J ≈ 2.5 Hz); 4.76 (dddd, 1 H, H(5a),
2Jab = 17.5 Hz, 3J = 9.7 Hz, 3J = 4.0 Hz, 4J = 2.4 Hz).
13C NMR (CDCl3), δ: 20.7 (s, C(4)); 31.7 (td, C(4´),
2JCF = 22 Hz, 3JCF = 9.5 Hz); 41.9 (tdd, C(3´), 2JCF = 23 Hz,
3JCF = 9.9 and 3.3 Hz); 76.1 (s, C(5)); 83.9 (s, C(3)); 117.1
(ddt, CF2, 1JCF = 296 and 284 Hz, 2JCF = 26 Hz); 118.2 (ddt,
CF2, 1JCF = 299 and 288 Hz, 2JCF = 26 Hz). The partial mass
spectrum, m/z (Irel (%)):196 (9) [M]+, 114 (10), 104 (100),
103 (53), 77 (45), 68 (99), 67 (70).
(tdd, C(3″)H, JCF = 21 Hz, JCF = 9.9 and 3.1 Hz); 69.5
1
(s, C(5)); 83.1 (s, C(3)); 117.6 (ddt, CF2, JCF = 289 and
2
1
267 Hz, JCF = 28 Hz); 118.0 (ddt, CF2, JCF = 286 and
272 Hz, JCF = 26 Hz). 19F NMR (CDCl3), δ: –107.6 and
2
–129.3 (both d, CF2, JFF = 210 Hz), –110.4 and –118.5
(both d, CF2, JFF = 209 Hz).
3-Cyclopropyl-1,1,2,2-tetrafluorocyclobutane (6). Cyclo-
propanation of olefin 1 with diazomethane. The reaction was
carried out under the conditions of the simultaneous genera-
tion and catalytic decomposition of CH2N2.19 A solution of
Pd(acac)2 (0.015 g, 0.05 mmol) in CH2Cl2 (1 mL) was added
to a stirred mixture of tetrafluorovinylcyclobutane 1 (0.77 g,
5 mmol) in CH2Cl2 (6 mL) and a 45% aqueous solution of
KOH (5 mL) at 5 °C and then N-methyl-N-nitrosourea
(1.54 g, 15 mmol) was added portionwise. The reaction mix-
ture was stirred at 5—8 °C until liberation of nitrogen ceased.
Then the organic layer was separated, passed through a thin
layer of Al2O3, and fractionated under atmospheric pressure.
Compound 6 was obtained as a colorless liquid in a yield of
5-(2,2,3,3-Tetrafluorocyclobutyl)spiro(1-pyrazoline-3,1´-
cyclopropanes) (5). Method A. A solution of MeONa (0.22 g,
4 mmol) in methanol (1 mL) was added with intense stirring to
a solution of tetrafluorovinylcyclobutane (1) (5.0 g, 32 mmol)
and N-cyclopropyl-N-nitrosourea (0.39 g, 3 mmol) in CH2Cl2
(15 mL) at –20 °C for 15 min. Then the reaction mixture was
stirred for 10 min and the temperature was raised to 20 °C
during 30 min. The resulting straw-yellow turbid solution was
passed through a layer of Al2O3 (∼1 cm) and washed with

2118
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 11, November, 2001
Tomilov et al.
1
0.75 g (89%), b.p. 113—115 °C. H NMR (CDCl3), δ: 0.25
and 0.61 (both m, 2 H each, CH2CH2); 0.82 (m, 1 H, CH in
cyclo-C3H5); 2.13 (m, 2 H, H(4)); 2.55 (m, 1 H, H(3)).
13C NMR (CDCl3), δ: 2.5 and 3.5 (both s, CH2CH2); 7.6 (dd,
analysis was carried out for a specimen, which was obtained by
purification of the reaction product by TLC (Al2O3 5–40µ,
heptane—ether, 1 : 1) and vacuum microdistillation of the
chromatographic zone with Rf 0.60±0.05. Found (%): C, 47.95;
H, 4.91. C9H10F4O2. Calculated (%): C, 47.80; H, 4.46. The
partial mass spectrum of the major isomer, m/z (Irel (%)):
226 (28) [M]+, 195 (52), 127 (35), 111 (20), 103 (32), 59
(100). The mass spectra of the other isomers are characterized
by very similar fragmentations and intensities of the peaks. To
3
CH in cyclo-C3H5, JCF = 6.3 and 3.2 Hz); 34.1 (tdd, C(4),
2JCF = 21 Hz, JCF = 12 and 2.2 Hz); 45.0 (tdd, C(3),
3
2JCF = 21 Hz, JCF = 9.4 and 3.4 Hz); 117.7 (ddt, CF2,
3
1JCF = 295 and 283 Hz, JCF = 27 Hz); 118.7 (ddt, CF2,
2
1JCF = 299 and 288 Hz, JCF = 25 Hz). 19F NMR (CDCl3),
2
1
δ: –111.2 and –130.3 (both d, CF2, JFF = 207 Hz), –111.4
and –118.6 (both d, CF2, JFF = 210 Hz). The partial mass
spectrum, m/z (Irel (%)): 168 (1) [M]+, 153 (6), 117 (7), 104
(100), 103 (42), 99 (12), 84 (25), 77 (35), 68 (27), 67 (66).
Found (%): C, 50.18; H, 5.00. C7H8F4. Calculated (%):
C, 50.01; H, 4.80.
Thermolysis of pyrazoline 4. Pyrazoline 4 (2.4 g, 12 mmol)
as a mixture of isomers (1.8 : 1) was passed through a quartz
tube (the inner diameter was 0.6 cm and the length was
18 cm), which was filled with small-sized quartz grains (by 2/3
of the volume) and purged with argon (4—5 mL•min–1) at
340 °C for 1 h, the reaction products being collected in a trap
cooled to –60 °C. The pyrolyzate was distilled and a colorless
liquid was obtained in a yield of 1.66 g (82%), b.p. 113–114 °C.
According to the GLC data and the 1H and 13C NMR spectra,
the liquid was identical with compound 6 prepared as de-
scribed above.
(2,2,3,3-Tetrafluorocyclobutyl)spiropentane (7) (a mixture
of isomers). Pyrazoline 5a (0.10 g, 0.45 mmol) was added
microportionwise into a vertical pyrolyzer at 400 °C, the
pyrolyzate was recondensed at 50 Torr into a cooled microtrap,
and a mixture of diastereomeric spiropentanes 7 was obtained
in a yield of 0.062 g (71%) (according to the 13C NMR
spectral data, 7a : 7b ≈ 2.1 : 1). 1H NMR (CDCl3), δ: 0.79 (m,
CH2CH2 in both isomers); 0.67 and 1.10 (both m, 2 H(2) in
both isomers); 1.31 (m, H(1) in both isomers); 2.11 and 2.50
(both m, C(4´)H2 in isomer b); 2.23 and 2.59 (both m,
C(4´)H2 in isomer a); 2.30 and 2.47 (both m, C(3´)H in
isomers a and b, respectively). 13C NMR (CDCl3), δ: 4.1 and
5.7 (both s, C(4,5) in isomer a); 4.3 and 5.5 (both s, C(4,5) in
isomer b); 11.0 and 11.2 (both s, C(2) in isomers a and b,
respectively); 12.7 and 13.6 (both s, C(3) in isomers a and b,
make the assignment of the signals in the H NMR spectra,
two chromatographic zones, which were enriched with
the diastereomeric trans (Rf 0.57±0.04) and cis isomers
(Rf 0.65±0.04) to ∼92 and 80%, respectively, were isolated by
preparative TLC under the same conditions. 1H NMR (CDCl3),
δ: for trans-8, 0.84 (ddd, H(3a) in isomer a, 2J = 4.7 Hz,
Jcis = 8.3 Hz, Jtrans = 6.5 Hz); 0.90 (ddd, H(3a) in isomer b,
2J = 4.8 Hz, Jcis = 8.5 Hz, Jtrans = 6.3 Hz); 1.29 (ddd, H(3b)
in isomer a, 2J = 4.7 Hz, Jcis = 8.4 Hz, Jtrans = 6.0 Hz); 1.33
(dt, H(3b) in isomer b, 2J ≈ Jtrans = 4.7 Hz, Jcis = 8.5 Hz); 1.55
(dt, H(1) in isomer b, Jcis = 8.5 Hz, Jtrans ≈ 4.7 Hz); 1.60 (m,
H(1) in isomer a and H(2) in both isomers); 2.22 (m, CH2CF2);
2.61 (m, CHCF2); for cis-8, 1.03 (dt, H(3a) in isomer a,
2J ≈ J1,2 = 5.1 Hz, J2,3 = 6.8 Hz); 1.12 (dt, H(3a) in isomer b,
2J ≈ J1,2 = 5.1 Hz, J2,3 = 6.7 Hz); 1.16 (dt, H(3b) in isomer a,
2J = 4.8 Hz, Jcis = 8.4 Hz); 1.26 (dt, H(3b) in isomer b,
2J = 4.8 Hz, Jcis = 8.4 Hz); 1.43 (m, H(2) in both isomers);
1.81 (dt, H(1) in isomer b, Jtrans = 5.5 Hz, Jcis = 8.4 Hz); 1.91
(dt, H(1) in isomer a, Jtrans = 5.5 Hz, Jcis = 8.4 Hz); 2.16, 2.51
and 2.90 (all m, CHCH2CF2 in isomer b), 2.19, 2.69 and 2.91
(all m, CHCH2CF2 in isomer a). 19F NMR (CDCl3), δ: from
–110.2 to –111.6 (overlapping doublets of the C(1)F2 group of
all four isomers); –118.0 and –129.4 (both d, C(2)F2 in
isomer trans-8a, JFF = 207 Hz); –118.2 and –129.6 (both d,
C(2)F2 in isomer trans-8b, JFF = 207 Hz); –118.3 and –130.2
(both d, C(2)F2 in isomer cis-8a, JFF = 207 Hz); –118.4 and
–130.5 (both d, C(2)F2 in isomer cis-8b, JFF = 207 Hz).
3-(2,3,3-Trifluorocyclobuten-1-yl)-1-pyrazoline (9). Tri-
fluorovinylcyclobutene (2) (0.11 g, 0.8 mmol) was added to an
ethereal solution (5 mL) of diazomethane (∼3 mmol) at 20 °C
and the reaction mixture was kept for 0.5 h. Then a portion
(1/10) of the reaction solution was withdrawn, CDCl3 (0.5 mL)
was added at –10 °C, and the ether was distilled off in vacuo.
Then CDCl3 (0.3 mL) was added and the reaction mixture was
3
respectively); 14.2 and 14.9 (both br.d, JCF ≈ 6, C(1) in
isomers a and b, respectively); 33.1 and 33.8 (both m, C(4´)H2
in isomers b and a, respectively); 43.3 (m, C(3´)H in
both isomers); 118.0–118.9 (m, CF2CF2 in both isomers,
1
concentrated in vacuo to 0.4 mL. According to the H NMR
spectrum, the resulting compound was pyrazoline 9 with the
purity of 93–95%. 1H NMR (CDCl3), δ: 1.59 (ddt, 1 H,
1JCF = 290–299 Hz, JCF ≈ 27 Hz). 19F NMR (CDCl3),
2
2
3
3
δ: –109.2 and –129.7 (both d, CF2 in isomer a, JFF = 206 Hz);
–109.3 and –118.1 (both d, CF2 in isomer a, JFF = 207 Hz);
–109.7 and –128.3 (both d, CF2 in isomer b, JFF = 206 Hz);
–110.7 and –117.3 (both d, CF2 in isomer b, JFF = 208 Hz).
Methyl 2-(2,2,3,3-tetrafluorocyclobutyl)cyclopropane-
carboxylate (8). A solution of methyl diazoacetate (0.75 g,
7.5 mmol) in CH2Cl2 (2 mL) was added to a stirred solution of
tetrafluorovinylcyclobutane (1) (3.08 g, 20 mmol) and
Rh2(OAc)4 (0.031 g, 0.07 mmol) in CH2Cl2 (7 mL) at 20 °C
for 4 h. After completion of the reaction, an excess of the
olefin and the solvent were distilled off in vacuo. The residue
(∼1.2 g) was dissolved in ether (20 mL) and passed through a
layer of Al2O3 (∼1.5 cm) to remove the catalyst and the major
portion of dimethyl fumarate and dimethyl maleate. After
removal of the solvent and vacuum distillation, a colorless
liquid with the b.p. 91—95 °C (24 Torr) was obtained in a yield
of 0.84 g (49%), which contained no less than 95% (GLC,
1H NMR spectrum) of the target product 8 as a mixture of
four isomers (the ratio of the trans- and cis-esters was ∼1.1 : 1,
the ratio of the epimers in each ester a : b ≈ 1.6 : 1). Elemental
H(4a), Jab = 12.5 Hz, J = 9.5 Hz, J ≈ 8.0 Hz); 2.02 (dtd,
2 3 3
1 H, H(4b), Jab = 12.5 Hz, J ≈ 9.3 Hz, J = 4.7 Hz); 2.78
(m, 2 H, C(4´)H2, 4JHF = 12.1 Hz); 4.42 (dddd, 1 H, H(5b),
2Jab = 17.5 Hz, 3J = 9.3 Hz, J = 8.0 Hz, J = 2.2 Hz); 4.79
(dddd, 1 H, H(5a), 2Jab = 17.5 Hz, 3J = 9.5 Hz, 3J = 4.7 Hz,
4J = 2.3 Hz); 5.09 (m, 1 H, H(3)). 19F NMR (CDCl3),
3
4
δ: –111.3 (ttd, =CF, 4JFH = 12.1 Hz, 3JFF ≈ JFH = 4.0 Hz);
–112.2 and –112.7 (both br.d, CF2, JFF ≈ 202 Hz). The
4
2
remaining portion of the reaction mixture was concentrated in
vacuo and a reddish liquid, which underwent rapid resinification
at room temperature, was obtained in a yield of 0.13 g.
5-(2,3,3-Trifluorocyclobuten-1-yl)spiro[1-pyrazoline-3,1´-
cyclopropane] (10). A powdered mixture of K2CO3 (0.66 g,
4.8 mmol) and KOH (0.30 g, 4.8 mmol) was added with
intense stirring to a solution of trifluorovinylcyclobutene (2)
(1.34 g, 10 mmol) and N-cyclopropyl-N-nitrosourea (0.48 g,
3.7 mmol) in CH2Cl2 (5 mL) at –5 °C. The reaction mixture
was stirred for 30 min, filtered through a dense filter, and
washed with CH2Cl2. The filtrate was concentrated in vacuo
without heating. Then the residue was treated with ether

Reactions of diazoalkanes
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 11, November, 2001 2119
2
(3 mL) and passed through a thin layer of neutral Al2O3. After
removal of the solvents, a viscous liquid was obtained in a yield
of 0.43 g. The major signals in the H NMR spectrum of this
(both br.d, CF2, JFF = 198 Hz); –111.2 (br.s, CClF). The
partial mass spectrum, m/z (Irel (%)): 169 and 171 (2 and 0.7)
[M–Me]+, 149 (21) [M–Cl]+, 120 and 122 (37 and 13)
[M–(CF2=CH2)]+, 85 (80) [C5H6F]+, 67 (100) [C5H7]+.
Step 2. A 45% aqueous solution of KOH (7 mL, 0.09 mmol)
was added dropwise with intense stirring to a mixture of isomers
of chlorocyclopropyltrifluorocyclobutane 12 (8.3 g, 0.045 mol)
and PhCH2Et3N+Cl (0.2 g) under an atmosphere of argon at
95 °C during 0.5 h. Cyclopropyltrifluorocyclobutene 11 that
formed was blew off with a stream of argon (3–4 mL•min
1
liquid corresponded to compound 10. Taking into account the
integral intensity of the signals and the amount of the com-
pound obtained, the yield of the target product was 40–45%.
Microdistillation of the residue in vacuo (0.1 Torr) afforded
pyrazoline 10 in a yield of 0.19 g (24%) with the purity of
–
1
∼90% (Òbath 90–95 °C). H NMR (CDCl3), δ: 1.16 (m, 2 H,
–1
H(1´) and H(2´), directed away from the N atom of the
heterocycle); 1.79 (m, 2 H, H(1´) and H(2´), oriented toward
the N atom of the heterocycle); 1.82 (dd, 1 H, H(4b),
2J = 12.6 Hz, J4b,5 = 7.2 Hz); 2.09 (dd, 1 H, H(4a),
2J = 12.6 Hz, J4a,5 = 9.7 Hz); 2.73 (m, 2 H, C(4″)H2); 5.32
(m, 1 H, H(5)). 19F NMR (CDCl3), δ: –111.7 (=CF); –112.4
)
into a trap cooled to –20 °C. The product was dried with
anhydrous Na2SO4 and distilled under atmospheric pressure.
1-Cyclopropyl-2,3,3-trifluorocyclobutene (11) was obtained in
a yield of 6.1 g (92%) with the purity of ca. 98%, b.p.
110–111 °C. The spectral characteristics corresponded to the
compound obtained according to the method A. Found (%):
C, 56.48; H, 4.51. C7H7F3. Calculated (%): C, 56.76; H, 4.76.
Methyl cis-/trans-2-(2,3,3-trifluorocyclobuten-1-yl)cyclo-
propanecarboxylate (13). Dirhodium tetraacetate Rh2(OAc)4
(0.057 g, 0.15 mmol) was added to a stirred solution of
trifluorovinylcyclobutene (2) (5.36 g, 0.04 mol) in CH2Cl2
(10 mL) and then a solution of methyl diazoacetate (1.80 g,
0.018 mol) in CH2Cl2 (2 mL) was added at 20 °C for 4 h. The
reaction mixture was concentrated and the residue was dis-
solved in ether and passed through a layer of Al2O3. After
removal of the solvents and vacuum distillation, ether 13 was
obtained as a mixture of trans and cis isomers in a yield of
2.15 g (58%) in a ratio of 1.4 : 1, b.p. 60–62 °C (10 Torr).
1H NMR (CDCl3), δ: for trans-13: 1.20 (ddd, H(3a),
2J = 4.8 Hz, Jcis = 8.5, Jtrans = 6.1 Hz); 1.50 (m, H(3b)); 1.94
(ddd, H(1), Jcis = 8.6 Hz, Jtrans = 4.5 and 5.6 Hz); 2.19 (m,
H(2)); 2.45 (m, CH2CF2); 3.72 (s, OMe), for cis-13: 1.34 (dt,
H(3b), 2J = 5.0 Hz, Jcis = 8.5 Hz); 1.50 (m, H(3a)); 1.98 (m,
H(2)); 2.55 (dt, H(1), Jtrans = 6.0 Hz, Jcis = 8.4 Hz); 2.53 and
2.66 (both m, CH2CF2); 3.70 (s, OMe). 13C NMR (CDCl3),
δ: for trans-13: 13.9 (s, C(3)); 17.0 (q, C(2), JCF ≈ 4 Hz); 20.2
(s, C(1)); 36.8 (dt, C(4´), JCF ≈ 18 and 23 Hz); 52.3 (s, OMe);
117.6 (td, CF2, 1JCF = 275 Hz, 2JCF = 26 Hz); 125.5 (C(1´));
2
and –112.8 (AB spectrum, CF2, JFF ≈ 203 Hz). Attempts to
purify the resulting pyrazoline by TLC (on SiO2 or Al2O3) led
to its transformation into unidentified compounds.
1-Cyclopropyl-2,3,3-trifluorocyclobut-1-ene
(11).
Method A. An excess of diazomethane, which was generated in
an individual reactor by decomposition of N-methyl-N-
nitrosourea (8.2 g, 0.08 mol) and then was blew off with a
stream of argon, was passed through a solution of trifluorovinyl-
cyclobutene 2 (2.15 g, 0.016 mol) and Pd(acac)2 (0.05 g,
0.16 mmol) in a mixture of pentane (2 mL) and CH2Cl2
(3 mL) at 0–5 °C for ∼2 h (see Refs. 26 and 27). After
completion of the reaction, the mixture was filtered through a
layer of Al2O3 (∼1 cm) and fractionated in the presence of
hydroquinone. The fractions contained the initial diene 2 and
cyclopropylcyclobutene 11 in different ratios. According to the
GLC data and the 1H NMR spectrum, the last fraction
(0.42 g) with the b.p. 72–73 °C (200 Torr) contained 95—96%
of compound 11. The total yield of cyclopropyltrifluoro-
cyclobutene (taking into account all fractions) was 38—40%.
1H NMR (CDCl3), δ: 0.71 and 0.89 (both m, 2 H each,
CH2CH2); 1.62 (m, 1 H, CH), 2.36 (dt, 2 H, CH2, JHF = 12.0
and 2.6 Hz). 13C NMR (CDCl3), δ: 5.5 (s, CH2CH2); 6.9 (q,
CH, JCF ≈ 4 Hz); 36.3 (dt, C(4), JCF ≈ 19 and 22 Hz); 118.0
1
2
1
2
(td, CF2, JCF = 275 Hz, JCF = 26 Hz); 129.5 (td, C(1),
139.6 (dt, CF, JCF = 340 Hz, JCF = 25 Hz); 172.5 (C=O),
for cis-13: 12.4 (s, C(3)); 15.5 (q, C(2), JCF ≈ 4 Hz); 20.8 (s,
C(1)); 38.8 (dt, C(4´), JCF ≈ 18 and 23 Hz); 52.1 (s, OMe);
117.7 (td, CF2, 1JCF = 275 Hz, 2JCF = 26 Hz); 125.3 (C(1´));
140.0 (dt, CF, JCF = 340 Hz, JCF = 25 Hz); 171.4 (C=O).
19F NMR (CDCl3), δ: for trans-13: –112.1 (CF2); –116.0
(=CF); for cis-13: –111.6 and –114.1 (both br.d, CF2,
2JFF ≈ 204 Hz); –113.6 (=CF). The partial mass spectrum,
m/z (Irel (%)): 206 (26) [M]+, 186 (9), 175 (20), 127 (75), 59
(100). Found (%): C, 52.16; H, 4.49. C9H9F3O2. Calcu-
lated (%): C, 52.43; H, 4.40.
1
JCF ≈ 17 and 6 Hz); 138.4 (dt, CF, JCF = 336 Hz,
2JCF = 26 Hz). 19F NMR (CDCl3), δ: –111.6 (br.s, CF2),
–120.6 (br.t, =CF, 4JHF = 12 Hz). The partial mass spectrum,
m/z (Irel (%)): 148 (61) [M]+, 147 (16), 133 (100), 127 (38).
Method B. Step 1. 2-Chloro-3-cyclopropyl-1,1,2-trifluoro-
cyclobutanes (12). The reaction was carried out analogously to
the synthesis of compound 6 under the conditions of the
simultaneous generation and catalytic decomposition of
CH2N2.19 A solution of 2-chloro-1,1,2-trifluoro-3-vinylcyclo-
butane (3) (12.0 g, 0.07 mol) in a mixture of pentane (30 mL)
and CH2Cl2 (20 mL) was added to a 45% aqueos solution of
KOH (50 mL) at 5 °C. Then a solution of Pd(acac)2 (0.15 g,
0.5 mmol) in CH2Cl2 (2 mL) was added and N-methyl-N-
nitrosourea (12.4 g, 0.12 mol) was added portionwise (0.5–0.8 g
per portion, during 12–15 min) with stirring, the temperature
being maintained at 5–8 °C. After completion of gas evolu-
tion, the organic layer was separated and passed through a thin
layer of Al2O3. The adsorbent was washed with pentane (3 mL)
and the solution was dried with anhydrous CaCl2 and fraction-
ated under atmospheric pressure. Chlorocyclopropyltrifluoro-
cyclobutane 12 was obtained as a mixture of two isomers in a
ratio of ∼1 : 1 in a yield of 11.5 g (89%); colorless liquid, b.p.
137—140 °C. 1H NMR (200 MHz, CDCl3), δ: 0.12—0.45 and
0.53—0.79 (both m, 2 H each, CH2CH2); 0.87–1.10 (m, 1 H,
CH); 1.95—2.80 (m, 3 H, CHCH2). 19F NMR (CDCl3), δ; for
isomer 12a: –98.2 and –117.6 (both br.d, CF2, 2JFF = 197 Hz),
–135.5 (br.s, CClF), for isomer 12b: –105.9 and –108.4
1
2
We thank G. V. Zatonskii (the N. D. Zelinsky
Institute of Organic Chemistry of the Russian Academy
of Sciences) for methodological help in the measure-
ments of the H and 19F NMR spectra on a Bruker
1
DRX-500 spectrometer (500 and 470.8 MHz).
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos. 99-03-
32980 and 00-15-97387).
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Received March 26, 2001