Thermal cyclopropyl—allyl rearrangement of gem-chlorofluorocyclopropanes under gas-phase pyrolysis conditions. Formation of chlorofluoroalkenes and 2-fluorobuta-1,3-dienes

Article abstract of DOI:10.1007/s11172-019-2567-3

The gas-phase pyrolysis of isomeric 2-chloro-2-fluoro-1-phenylcyclopropanes in a flow reactor at 250–430 °С gives 1-phenyl- and 3-phenyl-3-chloro-2-fluoropropenes. Under similar conditions, methyl-substituted gem-chlorofluorocyclopropanes undergo cyclopropyl—allyl isomerization accompanied by dehydrochlorination to form chlorofluoroalkenes and 2-fluoro-buta-1,3-dienes.

Full text of DOI:10.1007/s11172-019-2567-3

Russian Chemical Bulletin, International Edition, Vol. 68, No. 7, pp. 1391—1401, July, 2019
1391
Thermal cyclopropyl—allyl rearrangement
of gem-chlorofluorocyclopropanes under gas-phase pyrolysis conditions.
Formation of chlorofluoroalkenes and 2-fluorobuta-1,3-dienes
N. V. Volchkov, M. B. Lipkind, and O. M. Nefedov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6390. E-mail: volchkov@ioc.ac.ru
The gas-phase pyrolysis of isomeric 2-chloro-2-fluoro-1-phenylcyclopropanes in a flow
reactor at 250—430 С gives 1-phenyl- and 3-phenyl-3-chloro-2-fluoropropenes. Under simi-
lar conditions, methyl-substituted gem-chlorofluorocyclopropanes undergo cyclopropyl—allyl
isomerization accompanied by dehydrochlorination to form chlorofluoroalkenes and 2-fluoro-
buta-1,3-dienes.
Key words: gem-chlorofluorocyclopropanes, gas-phase pyrolysis, cyclopropyl—allyl rear-
rangement, chlorofluoroalkenes, 2-fluorobuta-1,3-dienes.
Cyclopropane derivatives are intensively studied in the
rational synthesis of new biologically active substances due
to the high pharmacophoric activity of the cyclopropane
fragment.1—3 Since the three-membered carbocycle is
strained, the cyclopropane compounds can undergo spe-
cific rearrangement with ring opening leading to diverse
functionalized acyclic, carbocyclic, and heterocyclic
compounds.4—10 For example, gem-dihalocyclopropanes
are characterized by cyclopropyl—allyl rearrangements
with three-membered ring opening accompanied by the
1,2-migration of one of halogen atoms or dehydrohaloge-
nation and formation of halogen-containing alkenes,6—22
dienes,6—10,23—30 or arenes.6—10,31—34 These reactions are
most interesting from the practical point of view for the
synthesis of fluorine-containing compounds, because
direct fluorination is difficult and the physicochemical and
biological properties of fluorine-containing organic com-
pounds are unique.35—40 Thermal cyclopropyl—allyl
transformations of gem-fluorohalocyclopropanes for the
synthesis of fluoroarenes was shown to be efficient.8,31—34
The ability of gem-fluorohalocyclopropanes to undergo
liquid-phase solvolytic or silver-9,41,42 and copper-cata-
lyzed43,44 cyclopropyl—allyl rearrangements in the pres-
ence of O- or N-nucleophiles giving functional fluoro-
alkenes is known. 2-Fluorobuta-1,3-diene derivatives were
obtained upon thermal transformations of gem-difluoro-
and gem-chlorofluorocyclopropanes23—30 or by liquid-
phase zinc-9,45,46 or tetramethylammonium fluoride-
promoted9,47 rearrangements of halomethyl- and trimeth-
ylsilyl-substituted gem-chlorofluorocyclopropanes. Several
examples of thermal liquid-phase cyclopropyl—allyl isomer-
ization of strained bicyclic derivatives of gem-chlorofluoro-
cyclopropanes are also known.16—20 We have recently
developed an efficient copper(I) chloride-assisted liquid-
phase catalytic isomerization of gem-chlorofluorocyclo-
propanes affording chlorofluoroalkenes and chlorofluoro-
alkadienes.21,22 In this work, we report on specific features
of the thermal cyclopropyl—allyl isomerization of gem-
chlorofluorocyclopropanes under the gas-phase pyrolysis
conditions.
Results and Discussion
In this work, we studied the thermal gas-phase trans-
formations of (1S*,2S*)- and (1S*,2R*)-2-chloro-2-
fluoro-1-phenylcyclopropanes (syn-1 and anti-1, respec-
tively), 2-chloro-2-fluoro-1,1-dimethylcyclopropane (2),
3-chloro-3-fluoro-1,1,2,2-tetramethylcyclopropane (3),
trans-3-chloro-3-fluoro-1,2-dimethylcyclopropane (4),
isomeric (1r*,2R*,3S*)- and (1s*,2R*,3S*)-3-chloro-3-
fluoro-1,2-dimethylcyclopropanes (syn-5 and anti-5, re-
spectively), and (1R*,2S*)- and (1R*,2R*)-1,2-dichloro-2-
fluoro-1-methylcyclopropanes (syn-6 and anti-6, respec-
tively). Cyclopropanes 1—6 were synthesized in 38—94%
yields by addition of chlorofluorocarbene (generated by
the alkaline hydrolysis of dichlorofluoromethane under
the phase-transfer catalysis conditions) to the correspond-
ing alkenes (styrene, isobutylene, tetramethylethylene,
trans-but-2-ene, cis-but-2-ene, and 2-chloropropene)
according to the earlier described procedures.21,22,25 The
purolytic reactions were carried out in a flow tube reactor
under atmospheric pressure in a nitrogen flow at a contact
time of 8—15 s.
Under these conditions, the pyrolysis of a mixture of
stereoisomeric 2-chloro-2-fluoro-1-phenylcyclopropanes
(ratio syn-1 : anti-1 = 58 : 42) in a temperature range of
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1391—1401, July, 2019.
1066-5285/19/6807-1391 © 2019 Springer Science+Business Media, Inc.

1392
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Volchkov et al.
Table 1. Composition of pyrolyzates and the yield of products
obtained by the gas-phase pyrolysis of a mixture of isomeric
2-chloro-2-fluoro-1-phenylcyclopropanes 1* (syn-1 : anti-1 =
= 58 : 42) in a flow reactor at various temperatures
335—450 С affords the expected products of cyclopro-
pyl—allyl isomerization: (Z)- and (E)-3-chloro-2-fluoro-
1-phenylpropenes (Z-7 and E-7, respectively) and 3-chloro-
2-fluoro-3-phenylpropene (8) in an overall yield of
15—85% (NMR spectroscopy data) at the conversion of
Entry Т/С Composition of pyrolyzate** (mol.%) Yield (%)
7 (Z : E)
the starting cyclopropanes of 20—98% (Scheme 1, Table 1).
syn-1 anti-1 Z-7
E-7
8
1
2
3
4
5
6
330
350
375
400
430
450
47
33
17
16
13
11
33
23
11
13
12
11
14
29
51
64
72
75
14
15
11
15
15
14
4
7
8
9
8
6
—
Scheme 1
—
—
—
74 (4.8 : 1)
72 (5.2 : 1)
* A 33% solution of cyclopropanes 1 in СH2Сl2 was used.
** Pyrolyzate composition after distillation off of CH2Cl2.
isomerization of cyclopropane 2, involving three-mem-
bered ring opening at the С(1)—С(3) bond opposite to the
dihalomethylene fragment and migration of the chlorine
atom to the carbon atoms C(1) or C(3) of the cleaved ring
(see Scheme 2). At temperatures higher than 380 С,
fluorodiene 11 becomes the predominant product of
pyrolysis of 2. The content of fluorodiene 11 in the pyrol-
yzate obtained at 415—430 С is 88—93% at the yield in the
mixture equal to 75—77% (19F NMR spectroscopy data with
the internal standard) and a preparative yield of 70—72%
after pyrolyzate distillation. Chlorofluorobutene 10 was
isolated in a yield of 21% by the fractional distillation of
a mixture of products of pyrolysis of cyclopropane 2 ob-
tained at 375 С (see Table 2, entry 7). Chlorofluorobutene
9, the boiling point of which is only by 2—3 С higher than
the boiling point of the starting cyclopropane 2, can be
isolated with the maximum yield 9% and purity 94—96%
by the fractional distillation of the pyrolyzate obtained at
400 С and containing minimum amounts of the unreacted
starting cyclopropane (see Table 2, entry 10).
The major reaction products, chlorofluoro(phenyl)-
propenes 7 (ratio Z : E = 4.8—5.2 : 1), can be isolated in
preparative yields of 72—74% by the distillation of the
pyrolyzates obtained at 430—450 С.
The pyrolytic transformations of methyl-substituted
gem-chlorofluorocyclopropanes had a more complex
character and were accompanied by dehydrochlorination
processes. The gas-phase pyrolysis of 2-chloro-2-fluoro-
1,1-dimethylcyclopropane 2 and its 33% solution in
n-heptane in a flow reactor in the temperature range
330—430 С gave a mixture of 3-chloro-2-fluoro-3-
methylbut-1-ene (9), 1-chloro-2-fluoro-3-methylbut-2-
ene (10), and 2-fluoro-3-methylbuta-1,3-diene (11)
(Scheme 2, Tables 2 and 3). The conversion of cyclopro-
pane 2 and the yield of products 9—11 depend on the
pyrolysis temperature. At 330—375 С (see Table 2, en-
tries 1—7), the major products are isomeric chlorofluoro-
butenes 9 and 10 resulted from the cyclopropyl—allyl
Scheme 2

Pyrolysis of chlorofluorocyclopropanes
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 7, July, 2019
1393
Table 2. Yield of products of the gas-phase pyrolysis of
2-chloro-2-fluoro-1,1-dimethylcyclopropane (2) in a flow
reactor at various temperatures
Table 4. Composition of the pyrolyzates obtained by
the gas-phase pyrolysis of 3-chloro-2-fluoro-3-meth-
ylbut-1-ene (9)* at various temperatures
Entry Т/С Conversion
of 2 (%)
Yield of products* (%)
Entry Т/С Composition of pyrolyzate** (mol.%)
9
10
11
9
10
11
1
2
3
4
5
6
7
8
330
335
340
350
355
365
375
380
390
400
415
430
24
29
15
16
15
17
11
13
1
2
3
4
5
6
7
8
300
320
335
350
365
380
390
405
88
79
71
63
39
27
16
15
17
10
14
16
20
18
13
16
11
18
13
20
40
54
68
87
36
18
18
16
58
25
16
12
64
26
19
16
75
28
24
18
88
26
24 (21)
20
28
92
19
44
9
96
16
16
55
* A mixture containing 32% chlorofluorobutene 9 and
66% n-heptane was used.
10
11
12
99
13 (9)
15
13
58 (54)
75 (70)
77 (73)
100
100
16
** Ignoring heptane, calculated by the 19F NMR and
GC data with the internal standard (fluorobenzene).
12
13
* The yields of compounds 9—11 in the mixtures was cal-
culated from the 19F NMR spectroscopy and GC data with
the internal standard (fluorobenzene). The preparative yield
of the compounds after fractional distillation of the obtained
mixtures is given in parentheses.
a simultaneous increase in the yield of fluorodiene 11,
which can be explained by the reversible isomerization of
chlorofluorobutenes 9 and 10 and different rates of their
dehydrochlorination. This assumption is confirmed by the
results of special studies of the pyrolysis of chlorofluoro-
butenes 9 and 10 (Tables 4 and 5).
As can be seen from the data presented in Tables 4
and 5, diene 11 is formed already at 300—320 С at low con-
versions of chlorofluorobutenes 9 and 10. At 330—350 С,
the dehydrochlorination rates of compounds 9 and 10
turned out to be comparable with the rates of their iso-
merization. At the temperatures higher than 365 C, the
dehydrochlorination rate increases and fluorodiene 11
becomes the major product of pyrolysis of compounds 9
and 10. A comparison of the obtained data with the above
considered results of pyrolysis of cyclopropane 2 under
The pyrolysis of a 33% solution of compound 2 in
n-heptane under comparable conditions gave no appre-
ciable change in the course of the process (see Table 3).
It should be mentioned that a two- to threefold predo-
mination of chlorofluorobutene 9 over isomer 10 is ob-
served in the mixture obtained in the temperature range
330—340 С at relatively low conversions of cyclopropane
2, which is probably due to a more favorable migration of
the negatively charged chlorine atom to the carbon atom,
whose positive charge is stabilized by two methyl groups.
As the pyrolysis temperature increases, the ratio of the
formed isomeric chlorofluorobutenes is equalized with
Table 5. Composition of the pyrolyzates obtained by the
gas-phase pyrolysis of 2-chloro-1-fluoro-3-methylbut-
2-ene (10)* at various temperatures
Table 3. Composition of the pyrolyzates obtained by the
gas-phase pyrolysis of a 33% solution of 2-chloro-2-
fluoro-1,1-dimethylcyclopropane (2) in n-heptane at
various temperatures
Entry Т/С Composition of pyrolyzate** (mol.%)
10
9
11
Entry Т/С
Composition of pyrolyzate* (mol.%)
1
2
3
4
5
6
7
8
300
320
330
350
365
385
395
405
92
86
82
69
47
23
13
15
16
18
19
14
15
10
18
14
12
16
19
17
38
67
79
89
2
9
10
11
1
2
3
4
5
6
7
8
330
340
350
360
370
380
390
400
77
67
47
33
17
11
17
12
16
20
25
28
25
19
16
11
16
19
13
21
25
19
16
12
11
13
14
17
32
49
59
74
* A mixture containing 33% chlorofluorobutene 10 and
67% n-heptane was used.
* Ignoring heptane, calculated by the 19F NMR and GC
data with the internal standard (fluorobenzene).
** Ignoring heptane, calculated by the 19F NMR and
GC data with the internal standard (fluorobenzene).

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Volchkov et al.
Table 6. Composition of the pyrolyzates obtained by the gas-
phase pyrolysis of 3-chloro-3-fluoro-1,1,2,2-tetramethylcyclo-
propane (3) at various temperatures
similar conditions (see Tables 2 and 3) suggests that diene
11 is formed by the pyrolysis of compound 2 mainly due
to the two-step consecutive process involving the pre-
liminary isomerization of cyclopropane 2 to chloro-
fluorobutenes 9 and 10 and their subsequent dehydrochlor-
ination. In this case, the contribution of synchronous ring
opening and dehydrohalogenation processes, which can
occur during pyrolysis of dihalocyclopropanes, is appar-
ently insignificant. The transformations of chlorofluoro-
butene 10 into diene 11 can probably proceed both via its
preliminary isomerization to chlorofluorobutene 9 fol-
lowed by 1,2-dehydrochlorination and due to the possible
1,4-dehydrohlorination through the favorable six-centered
transition state.
Entry
Т/С
Composition of
pyrolyzate (mol.%)
Yield
of 13 (%)
3
13
12
1
2
3
4
5
6
250
260
270
290
305
325
87
77
63
29
17
11
2
4
4
7
3
2
17
17
30
61
87
94
—
—
—
—
78
87
The pyrolysis of 3-chloro-3-fluoro-1,1,2,2-tetrameth-
ylcyclopropane (3) mainly resulted in 3-fluoro-2,4-di-
methylpenta-1,3-diene (12) and minor amounts of
4-chloro-3-fluoro-2,4-dimethylpent-2-ene (13) (Scheme 3).
Appreciable transformations of compound 3 started
already at 250 С, whereas at 325 С its nearly complete
conversion to fluoro diene 12 was achieved with a yield of
87% (Table 6). Product 13 (expected for the cyclopropyl—
allyl isomerization of chlorofluorocyclopropane 3) was
observed in the pyrolyzate obtained in the whole tem-
perature range in amounts not larger than 3—7%. It can
be concluded that, unlike the transformations of 2-chloro-
2-fluoro-1,1-dimethylcyclopropane 2, upon the pyrolysis
of compound 3 the thermal cyclopropyl—allyl transforma-
tion is accompanied by the extremely easy nearly synchro-
nous dehydrochlorination.
at 335—345 С, pyrolysis resulted in isomeric chloro-
fluoropentenes Z-14 and E-14 in comparable amounts
(Z-14 : E-14 = 1.4—1.6). An increase in the pyrolysis
temperature and conversion of 4 was accompanied by
a decrease in the content of isomer E-14 in the pyrolyzate
and an increase in the yields of isomer Z-14 and fluoro-
pentadienes 15.
The maximum overall yield of isomeric chlorofluoro-
pentenes 14 was attained at 380 С (49% in the mixture
according to the NMR spectroscopy data and 33% after
isolation; see Table 7, entry 4). Fluoropentadienes 15
(Z-15 : E-15 = 17 : 1) can be obtained in an overall yield
of 58% by distillation of the pyrolyzate prepared at 425 С
(entry 8).
Stereoisomeric (1r*,2R*,3S*)- and (1s*,2R*,3S*)-3-
chloro-3-fluoro-1,2-dimethylcyclopropanes (5) (syn-5
and anti-5, respectively) under the pyrolysis conditions
undergo similar cyclopropyl—allyl transformations to form
mixtures of the same chlorofluoropentenes 14 and fluo-
ropentadienes 15 (see Scheme 4, Table 8).
Scheme 3
The data presented in Table 8 indicate a significantly
higher rate of transformations of anti-isomer 5 compared
Table 7. Yields of the products of the gas-phase pyrolysis of trans-
3-chloro-3-fluoro-1,2-dimethylcyclopropane (4) in a flow reac-
tor at various temperatures
Entry Т/С Conversion
of 4 (%)
Yield of products* (%)
Z-14 E-14 Z-15 E-15
Interesting stereochemical features were revealed by
the study of the gas-phase pyrolytic transformations of
stereoisomeric 3-chloro-3-fluoro-1,2-dimethylcyclopro-
panes 4 and 5. For example, trans-3-chloro-3-fluoro-1,2-
dimethylcyclopropane (4) at 335—425 С underwent
thermal cyclopropyl—allyl isomerization to (Z)-4-chloro-
3-fluoropent-2-ene (Z-14) and (Е)-4-chloro-3-fluoropent-
2-ene (E-14) accompanied by their dehydrochlorination
to stereoisomeric 3-fluoropenta-1,3-dienes Z-15 and E-15
(Scheme 4, Table 7). At low conversions of compound 4
1
2
3
4
5
6
7
8
335
345
350
360
370
380
390
425
26
37
45
59
72
88
90
97
11
18
26
33
40
44
32
18
8
12
8
11
13
16
10
17
23
38
69
—
—
—
1
6
6
2
5
3
4
3
1
4
* The yield in mixtures was calculated from the 19F NMR spectro-
scopy and GC data with the internal standard (fluorobenzene).

Pyrolysis of chlorofluorocyclopropanes
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 7, July, 2019
1395
Scheme 4
to that of syn-isomer 5. For example, noticeable transfor-
mations of anti-5 are observed already at 305 С, whereas
at 350 С its conversion exceeds 90%, while the conversion
of syn-5 is only 1—16% in this temperature range. Raising
the pyrolysis temperature from 350 С to 385 С leads to
an increase in the conversion of syn-5 to 82%. However,
even at 430 С about 6% of syn-5 remain in the pyrolyzate.
The overall yield of a mixture of isomeric chlorofluoro-
pentenes 14 (Z-14 : E-14 = 15 : 1) obtained by the py-
rolysis of cyclopropane 5 at 385 С does not exceed 48%
in mixture according to the NMR data and 29% after
pyrolyzate separation (see Table 8, entry 10).
Fluoropentadienes 15 (Z-15 : E-15 = 17 : 1) can be ob-
tained by the pyrolysis of compound 5 at 425 С in
a preparative yield of 56%.
The kinetic and stereochemical features observed for
the pyrolytic transformations of isomeric 3-chloro-3-
fluoro-1,2-dimethylcyclopropanes 4 and 5 can be rational-
ized in terms of the known classical electrocyclic mecha-
nism of cyclopropyl—allyl transformation of halocyclo-
propanes6,48—52 that assumes the concerted cleavage of
the halogen—carbon bond and disrotary opening of the
cyclopropane ring with turn of the substituents located in
the syn-position to the leaving halogen atom "inward" the
opened cycle (Scheme 5).
In the case of trans-3-chloro-3-fluoro-1,2-dimethyl-
cyclopropane 4, this mechanism assumes the possibility
of equiprobable formation of chlorofluoropentene Z-14
via transition state G1 and of isomer Е-14 via transition
state G2, which is consistent with the formation of com-
parable amounts of isomers Z-14 and Е-14 during pyroly-
sis of cyclopropane 4 at its low conversions at 335—345 С.
A decrease in the content of isomer Е-14 in the pyrolyzate
observed at higher temperatures can be explained by its
isomerization to more thermodynamically stable isomer
Z-14 or by the possibility of easy transformation of com-
pound Е-14 into fluoropentadiene Z-15 due to 1,4-de-
hydrochlorination via six-centered transition state G5.
In the case of cyclopropane anti-5, the mechanism of
cyclopropyl—allyl transformation assumes its skeletal
rearrangement via transition state G3 followed by chlorine
atom migration to give stereoselectively chlorofluoro-
pentene Z-14. A similar mechanism for isomer syn-5 in-
cludes sterically hindered (because of approaching methyl
groups) transition state G4 and subsequent chlorine atom
migration to afford chlorofluoropentene E-14.
Table 8. Yields of the products of the gas-phase pyrolysis of
a mixture of (1r*,2R*,3S*)- and (1s*,2R*,3S*)-3-chloro-3-flu-
oro-1,2-dimethylcyclopropanes 5 (syn-5- and anti-5)* in a flow
reactor at various temperatures
Entry Т/С Conversion of 5 (%) Yield of products** (%)
anti-5
syn-5
Z-14 E-14 Z-15 E-15
1
2
3
4
5
6
7
8
305
310
315
325
340
350
360
370
375
385
395
410
430
18
42
10
10
11
13
10
16
28
48
62
82
86
91
94
15
12
16
21
27
28
34
41
43
45
32
20
8
—
—
1
—
—
—
—
12
16
19
15
18
22
41
57
69
—
—
—
—
—
—
1
52
70
1
88
2
94
2
100
100
100
100
100
100
100
2
2
1
The assumed mechanism well explains the observed
differences in reactivity of syn- and anti-isomers 5, which
are caused by the indicated above steric factor. However,
it contradicts following from it requirement of stereoselec-
tive occurrence of isomerization of syn-5 to Е-14, which
is a minor product of the pyrolysis of compound 5 in the
whole temperature range studied. It should be mentioned
that similar deviations from stereoselective cyclopropyl—
allyl transformations postulated for the electrocyclic
mechanism have previously been observed9,21,22 for the
9
3
2
10
11
12
13
3
2
2
2
2
3
1
4
* A mixture containing 67% syn-5 and 33% anti-5 was used.
** The yields of the individual compounds in the mixtures based
on the starting compound 5 were determined from the 19F NMR
spectroscopy and GC data with the internal standard (fluoro-
benzene).

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Volchkov et al.
Scheme 5
similar liquid-phase processes of CuCl-promoted iso-
merization of gem-chlorofluorocyclopropanes and solvo-
lytic transformations of gem-chlorofluorocyclopropanes
in the presence of Ag salts and were explained by the pos-
sibility of the isomerization of cis-haloallyl products or
intermediate cis-haloallyl cations to the thermodynami-
cally more stable trans-isomers.9,21,22,53 Similarly, the
observed stereochemical features of the occurrence of the
gas-phase transformations of chlorofluorocyclopropanes
4 and 5 can be explained by the isomerization of Е-14 to
Z-14 and the possibility of easy dehydrochlorination of
Е-14 to fluoropentadiene Z-15.
It is known that the direction of cyclopropyl—allyl
transformations with the cleavage of the bond opposite to
the dihalomethylene fragment, which is characteristic of
gem-dihalocyclopropanes, changes upon the introduc-
tion of additional halogen atoms into the cyclopropane
cycle.13—15 For example, the pyrolytic transformations of
1,2,2-trichloro-, 1,2,3,3-tetrachloro-, and 1,2,2,3,3-penta-
chlorocyclopropanes proceed predominantly or exclu-
sively via ring opening at the С—С bond lying oppositely
to the monochloromethylene fragment, and the reaction
products expected for similar transformations with the
cleavage of the С—С bonds opposite to the ССl2 fragment
are absent or formed in minor amounts.13—15 We studied
the possibility of a similar change in the regioselectiv-
ity of the cyclopropyl—allyl transformation of gem-chloro-
fluorocyclopropanes using as an example the pyro-
lytic transformations of stereoisomeric (1R*,2S*)- and
(1R*,2R*)-1,2-dichloro-2-fluoro-1-methylcyclopropanes
(syn-6 and anti-6, respectively).
It is found that the gas-phase pyrolysis of a mixture of
syn-6 and anti-6 in the flow reactor at 360—405 С leads
mainly to 3,3-dichloro-2-fluorobut-1-ene (16), Z- and
E-isomeric 1,3-dichloro-2-fluorobut-2-enes (17а,b), and
3-chloro-2-fluorobuta-1,3-diene (18) (Scheme 6, Table 9).
Evidently, they are formed via ring opening at the
С(1)—С(3) bond lying oppositely to the chlorofluoro-
methylene fragment. The expected products of isomeriza-
tion of dichlorofluorocyclopropane 6 with the ring open-
ing at the С(2)—С(3) bond opposite to the monochloro-
substituted fragment, namely, dichlorofluoropropenes 19
and 20а,b, are observed in the pyrolyzates in the amounts
that totally do not exceed 4—9%.
1,2,2-Trichloro-1-methylcyclopropane (21) studied
for comparison under similar conditions turned out to be
noticeably less reactive and underwent no substantial
transformations at the temperatures below 400 C. The

Pyrolysis of chlorofluorocyclopropanes
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 7, July, 2019
1397
Scheme 6
Scheme 7
pyrolysis of trichlorocyclopropane 21 at 450 C led to
a mixture containing, according to the GC and NMR
spectroscopy data, 45% of the starting cyclopropane 21,
17% of stereoisomeric 1,2,3-trichlorobut-2-enes (22а,b)
(ratio 22а : 22b = 4 : 1), 10% of 2,3-dichlorobuta-1,3-
diene (23), 26% of 1,1,3-trichloro-2-methylprop-1-ene
(24), and two minor unidentified products in an amount
of 0.5—1.5% (Scheme 7).
The obtained data are consistent with proceeding of
cyclopropyl—allyl transformations of trichlorocyclo-
propane 21 via two comparable in rates competitive
routes involving three-membered ring opening with the
С(1)—С(3) bond cleavage to form trichlorobutenes 22
and dichlorobutadiene 23 or with the С(2)—С(3) bond
cleavage to form trichloroisobutylene (24).
The differences observed in activity and regioselectiv-
ity of thermal skeletal transformations of dichlorofluoro-
cyclopropane 6 and trichlorocyclopropane 21 are prob-
ably caused by the known ability of the fluorine atom to
induce a significantly higher (compared to that of the
chlorine atom) structural and kinetic destabilization of
the cyclopropane cycle and substantial weakening and
elongation of the С—С cyclopropane bond lying oppo-
sitely to the fluoromethylene fragment.8,54
Table 9. Yields of the products of the gas-phase pyrolysis of
isomeric 1,2-dichloro-2-fluoro-1-methylcyclopropanes 6*
Entry Т/С Conversion of 6 (%) Yield of products** (%)
anti-6
syn-6
16 17а 17b 18 19 20
On the whole, it can be concluded that the gas-phase
pyrolysis in a flow reactor provides easy thermal cyclo-
propyl—allyl transformations of methyl- and phenyl-
substituted gem-chlorofluorocyclopropanes. The stereo-
chemical and kinetic regularities of the studied gas-phase
thermal transformations are similar to those observed for
processes of liquid-phase isomerization of these com-
pounds5 catalyzed by the copper salts and agree, as a whole,
with the classical electrocyclic mechanism of cyclopro-
pyl—allyl transformation. In the case of 2-chloro-2-fluoro-
1
2
3
4
5
6
360
380
390
405
425
450
42
68
85
93
95
97
30
65
82
90
93
96
13
6
9
3
7
1
2
3
3
3
3
2
3
4
4
4
4
19 11 17
21 12 22 12
22
18
6
8
6
2
23 23
24 32
6
64
* A mixture containing 55% anti-6 and 45% syn-6 was used.
** The yields of the individual compounds in the mixtures were
calculated from the 19F NMR spectroscopy and GC data with
the internal standard (fluorobenzene).

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Russ. Chem. Bull., Int. Ed., Vol. 68, No. 7, July, 2019
Volchkov et al.
(mixture of 45% syn-6 and 55% anti-6; 38% yield). The spectral
characteristics of the obtained compounds coincide with pub-
lished ones.21,22,25
1-phenylcyclopropane 1, the yields of the isomerization
products are close to those observed for similar liquid-
phase transformations catalyzed by the copper salts. For
methyl-substituted gem-chlorofluorocyclopropanes, ther-
mal isomerization processes are accompanied by dehydro-
chlorination reactions, which provides low or moderate
yields of chlorofluoroalkenes but reasonable yields of
2-fluorobuta-1,3-dienes. The latter can be formed both at
the stage of cyclopropyl—allyl opening of the chlorofluoro-
cyclopropane cycle due to the competitive reactions of
the chlorine atom migration and dehydrochlorination and
as a result of secondary processes of dehydrochlorination
of the chlorofluoroalkene isomerization products.
1,2,2-Trichloro-1-methylcyclopropane (21). A solution of
KOH (24 g, 0.36 mol) in water (18 mL) was added dropwise to
a mixture of 2-chloropropene (7.65 g, 0.10 mol), CHCl3 (30.0 g,
0.25 mol), TEBAC (0.5 g, 2 mmol), and CH2Cl2 (50 mL) on
cooling with ice and vigorous stirring (about 800 rpm) over 1 h,
after which the mixture was stirred at 20—25 C for additional
5 h monitoring conversion by GC. The reaction mixture was
diluted with water (100 mL), and the organic layer was washed
with water (250 mL) and dried with CaCl2. The drying agent
was filtered off, CH2Cl2 was distilled off under atmospheric
pressure, the residue was distilled, and the fraction with b.p.
79—80 C (90 Torr) was collected. Compound 21 as a colorless
liquid was obtained in a yield of 10.83 g (68%). 1H NMR, : 1.70
(d, 1 H, J = 8.8 Hz); 1.84 (d, 1 H, J = 8.8 Hz); 1.89 (s, 3 H,
CH3). MS (EI, 70 eV), m/z (Irel (%)): 127, 125, 123 [M – Cl]+
(8, 64, 100), 89, 87 [M – Cl]+ (16, 55), 51 (19).
Pyrolysis of gem-chlorofluorocyclopropanes 1—6 was carried
out in a tube quartz reactor (length 350 mm, internal diameter
22 mm) in the flow mode under atmospheric pressure in a nitro-
gen flow (100 mL min–1). The starting cyclopropanes or their
solutions in inert solvents were fed with a constant rate using
a pumping microdrive to the reactor heated to a specified tem-
perature. The pyrolysis products coming out from the reactor
were collected into a trap cooled with a СО2—acetone mixture.
The obtained pyrolyzate was washed with water and a 10% aque-
ous solution of Na2CO3, and dried with Na2SO4. After separat-
ing the drying agent, the obtained mixtures of the products were
analyzed by GC, NMR spectroscopy, and chromatography
coupled with mass spectrometry (GC-MS). Preparative synthe-
ses with the duration of the processes 60—120 min and frac-
tional distillation of the obtained pyrolyzates were also used for
the isolation and identification of the products of pyrolysis of
gem-chlorofluorocyclopropanes.
Experimental
Commercially available dichlorofluoromethane (99.9%)
(LLC Poly-Trade, Russia), styrene (99%), isobutylene (99%),
cis-but-2-ene (99%), trans-but-2-ene (99%), 2-chloropropene
(98%), potassium hydroxide (85%), triethylbenzylammonium
chloride (TEBAC) (99%), CHCl3 (99%), CH2Cl2 (99%), and
n-heptane (99%) (all Aldrich) were used as purchased. GC
analysis was carried out on a Kristall 2000M chromatograph
(Macherey-Nagel OPTIMA-1 capillary column, 30 m0.25 mm,
1
helium as carrier gas, flame-ionization detector). H and 19F
NMR spectra were recorded on a Bruker AС-200 spectrometer
(working frequencies 200.1 (1H) and 188.3 MHz (19F)) for solu-
tions in CDCl3 containing 0.05% Me4Si (internal standard).
Chemical shifts in 19F NMR spectra are presented relative to
CCl3F (external standard). Mass spectra were recorded on
a Finnigan MAT INCOS-50 instrument (EI, 70 eV, direct
injection) or on a Trace GC Ultra instrument equipped with
a Finnigan MAT DSQII mass detector (EI, 70 eV, temperature
of the ion source—ion trap system 200 C) and a Thermo TR-5ms
SQC capillary chromatographic column (15 m×0.25 mm).
3-Chloro-3-fluoro-1,1,2,2-tetramethylcyclopropane (3).55
A solution of KOH (60 g, 0.91 mol) in water (46 mL) was added
dropwise with vigorous stirring and cooling with ice over 1 h to
a mixture of 2,3-dimethylbut-2-ene (28.5 g, 0.34 mol), CHCl2F
(45.0 g, 0.44 mol), TEBAC (1.0 g, 5 mmol), and CH2Cl2
(120 mL), and the resulting mixture was stirred at 0 C for 3 h.
The reaction mixture was diluted with water (500 mL), and the
organic layer was washed with water (2×200 mL) and dried with
CaCl2. The drying agent was filtered off, the solvent was distilled
off under atmospheric pressure, the residue was distilled under
reduced pressure, and the fraction with b.p. 67—68 C (112 Torr)
was collected. Compound 3 was obtained as a colorless liquid in
a yield of 48.2 g (94%). 1H NMR, : 1.13 (d, 6 H, 2 CH3,
J = 8.5 Hz); 1.14 (d, 6 H, 2 CH3, J = 8.5 Hz). 19F NMR, :
–146.8 (m, 1 F, CFCl3). MS (EI, 70 eV), m/z (Irel (%)): 137,
135 [M – CH3]+ (1, 4), 115 [M – Сl]+ (100), 73 (19), 61 (29).
A similar procedure was used to synthesize (1S*,2S*)- and
(1S*,2R*)-2-chloro-2-fluoro-1-phenylcyclopropanes (mixture
of 58% syn-1 and 42% anti-1; 81% yield), 2-chloro-2-fluoro-
1,1-dimethylcyclopropane (2) (87% yield), trans-3-chloro-3-
fluoro-1,2-dimethylcyclopropane (4) (73% yield), (1r*,2R*,3S*)-
and (1s*,2R*,3S*)-3-chloro-3-fluoro-1,2-dimethylcyclopropanes
(mixture of 67% syn-5 and 33% anti-5; 74% yield), and (1R*,2S*)-
and (1R*,2R*)-1,2-dichloro-2-fluoro-1-methylcyclopropanes 6
Pyrolysis of (trichloro)(methyl)cyclopropane 21 and chlo-
rofluorobutenes 9 and 10 was conducted similarly.
Pyrolysis of 2-chloro-2-fluoro-1-phenylcyclopropanes 1.
A solution of cyclopropane 1 (mixture of 58% syn-1 and 42%
anti-1; 17.05 g, 100 mmol) in CH2Cl2 (34.0 g) was fed using
a pumping microdrive with a constant rate of 0.43 g min–1 for
120 min to a tube reactor heated to 430 C under atmospheric
pressure in a nitrogen flow (100 mL min–1). The obtained pyrol-
yzate was washed with water and a 10% aqueous solution of
Na2CO3 and dried with Na2SO4. After separating the drying agent
and distilling off CH2Cl2, the residue (16.52 g) obtained was
analyzed by GC, NMR spectroscopy, and GC-MS. The residue
was distilled in vacuo to obtain a mixture of (Z)- and (E)-3-
chloro-2-fluoro-1-phenylpropenes 7 in a yield of 12.61 g (74%;
Z-7 : E-7 = 5 : 1) with b.p. 93—96 C (6 Torr).
Pyrolysis of compound 1 at other temperatures and analysis
of the pyrolyzate composition were carried out similarly.
(Z)-3-Chloro-2-fluoro-1-phenylpropene (Z-7).21,22 1H NMR,
: 4.29 (d, 2 H, CH2Cl, J = 18.7 Hz); 5.92 (d, 1 H, CH=,
J = 36.4 Hz); 7.25—7.75 (m, 5 H, arom.). 19F NMR, : –109.5
(dt, J = 36.4 Hz, J = 18.7 Hz). MS (EI, 70 eV), m/z (Irel (%)):
170, 172 [M]+ (40, 14), 135 [M+ – Cl] (100), 133 (31), 115 (55).
(E)-3-Chloro-2-fluoro-1-phenylpropene (E-7).21,22 1H NMR,
: 4.38 (d, 2 H, CH2Cl, J = 21.8 Hz); 6.58 (d, 1 H, CH=,
J = 18.7 Hz); 7.25—7.75 (m, 5 H, arom.). 19F NMR, : –105.1

Pyrolysis of chlorofluorocyclopropanes
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 7, July, 2019
1399
(td, J = 21.8 Hz, J = 18.7 Hz). MS (EI, 70 eV), m/z (Irel (%)):
170, 172 [M]+ (41, 14), 135 [M – Cl]+ (100), 133 (34), 115 (58).
3-Chloro-2-fluoro-3-phenylpropene (8).21,22 1H NMR: 4.81
(dd, 1 H, CH2, J = 46.6 Hz, J = 3.6 Hz); 4.97 (dd, 1 H, CH2,
J = 16.0 Hz, J = 3.6 Hz); 5.58 (d, 1 H, CHCl3, J = 13.3 Hz);
7.25—7.75 (m, 5 H, arom.). 19F NMR, : –103.8 (ddd, J = 46.6 Hz,
J = 16.0 Hz, J = 13.3 Hz). MS (EI, 70 eV), m/z (Irel (%)): 170,
172 [M]+ (15, 5), 135 [M – Cl]+ (100), 133 (32), 115 (58).
Pyrolysis of 2-chloro-2-fluoro-1,1-dimethylcyclopropane (2).
Compound 2 (32.40 g, 0.264 mol) was fed into a tube reactor
heated to 375 C under atmospheric pressure in a nitrogen flow
(100 mL min–1) using a pumping microdrive for 90 min with a
constant rate of 0.36 g min–1 (2.94 mmol min–1). The obtained
pyrolyzate was washed with water and a 10% aqueous solution
of Na2CO3 and dried with Na2SO4. After separating the drying
agent, a mixture of products (26.48 g) containing, according to
the GC, NMR spectroscopy, and GC-MS data, 15.0% of the
starting cyclopropane 2, 31.8% of 3-chloro-2-fluoro-3-methyl-
but-1-ene (9), 29.4% of 1-chloro-2-fluoro-3-methylbut-2-ene
(10), and 24.1% of 2-fluoro-3-methylbuta-1,3-diene (11) was
obtained. Fractional distillation gave compound 10 with b.p.
66—67 C (112 Torr) in a yield of 6.89 g (21%).
Similarly, pyrolysis of compound 2 (32.40 g, 0.264 mol) at
400 C for 90 min gave the pyrolyzate (22.03 g) containing 0.4%
of the starting cyclopropane 2, 18.7% of butene 9, 18.5% of
butene 10, and 68.1% of diene 11. Fractional distillation
gave fluorodiene 11 (12.73 g, 58%) with b.p. 46—47 C and 2.82 g
of a mixture with b.p. 85—88 C containing 95% of chloro-
fluorobutene 9, 4% of cyclopropane 2, and 1% of chlorofluoro-
butene 10.
Similarly, pyrolysis of compound 2 (32.40 g, 0.264 mol) at
430 C for 90 min gave the pyrolyzate (20.73 g) containing 7.8%
of chlorofluorobutene 9, 9.3% of chlorofluorobutene 10, and
82.7% of fluorodiene 11. The distillation of the mixture gave
fluorodiene 11 (15.9 g, 70%).
2,4-dimethylpent-2-ene (13). Fluoropentadiene 12 with b.p.
96—98 C was obtained in a yield of 12.93 g (87%) by distillation
of the mixture.
3-Fluoro-2,4-dimethylpenta-1,3-diene (12). 1H NMR, :
1.76 (m, 6 H, 2 CH3); 1.90 (m, 3 H, CH3); 5.05 (m, 1 H, =CH2);
5.15 (m, 1 H, =CH2). 19F NMR, : –112.9 (m, 1 F). MS (EI,
70 eV), m/z (Irel (%)): 114 [M]+ (100), 99 [M – CH3]+ (59), 85
(10), 79 (33), 77 (24).
1
4-Chloro-3-fluoro-2,4-dimethylpent-2-ene (13). H NMR,
: 1.73 (m, 3 H, CH3); 1.86 (m, 6 H, 2 CH3); 1.89 (m, 3 H,
CH3). 19F NMR, : –109.0 (m, 1 F). MS (EI, 70 eV), m/z
(Irel (%)): 152 and 150 [M]+ (4 and 15), 115 [M – Cl]+ (100 ),
73 (22), 61 (38), 55 (15).
Pyrolysis of trans-3-chloro-3-fluoro-1,2-dimethylcyclopro-
pane (4) and cis-3-chloro-3-fluoro-1,2-dimethylcyclopropanes
(5) was carried out using a procedure described above. Pyrolysis
of compound 4 (32.40 g, 0.264 mol; flow rate 0.36 g min–1) at
380 C for 90 min gave the pyrolyzate (25.40 g) containing 13.9%
of the starting cyclopropane 4, 56.1% of chlorofluoropentene
Z-14, 6.3% of chlorofluoropentene E-14, 20.1% of pentadiene
Z-15, and 2.9% of isomer E-15. The distillation of the mixture
gave fluoropentadienes 15 (4.63 g, 20%; Z-15 : E-15 = 8 : 1) with
b.p. 48—52 C and chlorofluoropentenes 14 (10.66 g, 33%;
Z-14 : E-14 = 8.2 : 1) with b.p. 104—107 C.
Similarly, pyrolysis of compound 4 (32.40 g, 0.264 mol) at
425 C for 90 min gave the pyrolyzate (20.15 g) containing 3.1%
of the starting compound 4, 12.8% of isomer Z-14, 1.6% of
isomer E-14, 76.9% of compound Z-15, and 4.7% of compounds
Е-15. The distillation of the mixture gave fluoropentadienes 15
(Z-15 : E-15 = 17 : 1) with b.p. 48—52 C in a yield of 13.11 g
(58%).
Similarly, pyrolysis of compound 5 (32.40 g, 0.264 mol; 67%
syn-5 and 33% anti-5) at 385 C for 90 min gave the pyrolyzate
(25.78 g) containing 18.8% of anti-5, 56.4% of Z-14, 3.8% of
E-14, 19.1% of Z-15, and 1.76% of Е-15. After distillation,
fluoropentadienes 15 (4.73 g, 30%; Z-15 : E-15 = 11 : 1) with
b.p. 48—52 C and chlorofluoropentadienes 14 (9.71 g, 29%;
Z-14 : E-14 = 15 : 1) with b.p. 104—107 C were isolated.
Similarly, pyrolysis of compound 5 (32.40 g, 0.264 mol; 67%
syn-5 and 33% anti-5) at 430 C for 90 min gave after treatment
the pyrolyzate (21.15 g), from which fluoropentadienes 15 (12.75
g, 56%; Z-15 : E-15 = 17 : 1) with b.p. 48—52 C were isolated
by distillation.
3-Chloro-2-fluoro-3-methylbut-1-ene (9).21,22 1H NMR, :
1.75 (d, 6 H, 2 CH3, J = 1.0 Hz); 4.65 (dd, 1 H, =CH2, J = 48.2 Hz,
J = 3.3 Hz); 4.66 (dd, 1 H, =CH2, J = 16.3 Hz, J = 3.3 Hz).
19F NMR, : –105.6 (br.dd, 1 F, J = 48.2 Hz, J = 16.3 Hz). MS
(EI, 70 eV), m/z (Irel (%)): 122, 124 [M]+ (14, 4), 109, 107
[M – CH3]+ (8, 22), 87 [M – Cl]+ (100), 59 (39), 41 (46).
1-Chloro-2-fluoro-3-methylbut-2-ene (10).21,22 1H NMR,
: 1.70 (s, 3 H, CH3); 1.72 (s, 3 H, CH3); 4.20 (d, 2 H, CH2Cl,
J = 22.4 Hz). 19F NMR, : –117.2 (t, J = 22.4 Hz). MS (EI,
70 eV), m/z (Irel (%)): 122, 124 [M]+ (32, 12), 87 [M – Cl]+ (100),
59 (50), 41 (49).
(Z)-4-Chloro-3-fluoropent-2-ene (Z-14).21,22 1H NMR, :
1.64 (d, 6 H, 2 CH3, J = 6.8 Hz); 4.51 (dq, 1 H, CHCl3, J = 18.5 Hz,
J = 6.8 Hz); 4.95 (dq, 1 H, CH, J = 35.1 Hz, J = 6.9 Hz).
19F NMR, : –123.2 (ddq, 1 F, J = 35.1 Hz, J = 18.5 Hz,
J = 2.5 Hz). MS (EI, 70 eV), m/z (Irel (%)): 124, 122 [M]+ (7, 24),
109, 107 [M – CH3]+ (2, 6), 87 [M – Cl]+ (100), 59 (49).
(E)-4-Chloro-3-fluoropent-2-ene (E-14).21,22 1H NMR, :
1.63 (d, 6 H, 2 CH3, J = 7.0 Hz); 4.91 (dq, 1 H, J = 27.2 Hz,
J = 7.0 Hz); 5.17 (dq, 1 H, J = 19.5 Hz, J = 7.5 Hz). 19F NMR,
: –123.6 (ddq, J = 27.4 Hz, J = 19.5 Hz, J = 2.8 Hz). MS (EI,
70 eV), m/z (Irel (%)): 124, 122 [M]+ (12, 34), 109 , 107 [M – CH3 ]+
(2, 6), 87 [M – Cl]+ (100), 59 (39).
2-Fluoro-3-methylbuta-1,3-diene (11).25 1H NMR, : 1.90
(m, 3 H, CH3); 4.55 (d, 1 H, CF=CH2, J = 49.3 Hz); 4.71
(d, 1 H, CF=CH2, J = 15.8 Hz); 5.10 (m, 1 H, =CH2); 5.46
(m, 1 H, =CH2). 19F NMR, : –109.7 (dd, 1 F, J = 49.3 Hz,
J = 15.8 Hz). MS (EI, 70 eV), m/z (Irel (%)): 86 [M]+ (100),
85 (80), 71 (21), 65 (31), 51 (49).
Pyrolysis of solutions of compounds 2, 9, and 10 in n-heptane
at flow rates of the solutions of 0.40 g min–1 was conducted
similarly.
Pyrolysis of 3-chloro-3-fluoro-1,1,2,2-tetramethylcyclopro-
pane (3) was carried out according to a procedure described above.
The pyrolysis of compound 3 (19.80 g, 0.131 mol; flow rate
0.33 g min–1) at 325 C for 60 min gave the pyrolyzate (14.55 g)
containing 1% of the starting cyclopropane 3, 95% of 3-fluoro-
2,4-dimethylpenta-1,3-diene (12), and 2% of 4-chloro-3-fluoro-
(Z)-3-Fluoropenta-1,3-diene (Z-15).25 1H NMR, : 1.72 (dd,
3 H, CH3, J = 6.9 Hz, J = 1.5 Hz); 4.83 (dq, 1 H, CH=CF,
J =37.0 Hz, J = 6.9 Hz); 5.09 (d, 1 H, =CH2, J1 = 11.8 Hz); 5.43
(d, 1 H, =CH2, J =17.4 Hz); 6.09 (ddd, 1 H, CH=, J = 27.8 Hz,
J = 17.4 Hz, J = 11.8 Hz). 19F NMR, : –127.1 (dd, 1 F, J = 37.0 Hz,
J = 27.8 Hz). Mass spectrum of isomers Z-15 and E-15 (EI,

1400
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 7, July, 2019
Volchkov et al.
70 eV), m/z (Irel (%)): 86 [M]+ (100), 85 (65), 71 (15), 66 (60),
65 (40).
Pyrolysis of 1,2,2-trichloro-1-methylcyclopropane (21) was
carried out using the procedure described above. The pyrolysis
of compound 21 (3.60 g, 22.57 mol) at 450 C for 10 min gave
the pyrolyzate (3.14 g) containing (according to the GC and
NMR spectroscopy data) 45% of the starting cyclopropane 21,
17% of a mixture of stereoisomeric 1,2,3-dichlorobut-2-enes 22а
and 22b (ratio 4 : 1), 10% of 2,3-dichlorobuta-1,3-diene (23),
26% of 1,1,3-trichloro-2-methylprop-1-ene (24), and two minor
unidentified products in an amount of 0.5—1.5%.
(Е)-3-Fluoropenta-1,3-diene (E-15).25 1H NMR, : 1.70
(m, 3 H, CH3); 5.20 (m, 1 H, CH=CF); 5.22 (d, 1 H, =CH2,
J = 12.0 Hz); 5.55 (d, 1 H, =CH2, J = 16.5 Hz); 6.44 (ddd, 1 H,
CH=, J = 26.5 Hz, J = 16.5 Hz, J = 12.0 Hz). 19F NMR, :
–120.8 (dd, 1 F, J = 26.5 Hz, J = 23.0 Hz).
Pyrolysis of 1,2-dichloro-2-fluoro-1-methylcyclopropane (6)
was carried out using a procedure described above. Pyrolysis of
compound 6 (33.60 g, 0.235 mol; 45% syn-6 and 54% anti-6) at
405 C for 120 min gave the pyrolyzate (28.40 g) containing 4%
of syn-6, 4% of anti-6, 26% of 3,3-dichloro-2-fluorobut-1-ene (16),
36% of compound 17, 20% of diene 18, 3% of compound 19,
and 5% of a mixture of isomers 20а,b. The distillation of the
mixture gave 3-chloro-2-fluorobuta-1,3-diene (18) (4.61 g, 18%)
with b.p. 52—53 C, the fraction (9.61 g) with b.p. 101—106 C
containing 71% of butene 16, 9% of syn-6, 9% of anti-6, 6% of
propene 19, and 5% of butenes 17а,b, and the fraction (10.8 g) with
b.p. 110—117 C containing 80% of butenes 17а,b, 13% of propenes
20а,b, and 5% of butene 16. The obtained pyrolyzate and frac-
tions were analyzed using GC, NMR spectroscopy, and GC-MS.
Similarly, pyrolysis of compound 6 (33.60 g, 0.235 mol; 45%
syn-6 and 55% anti-6) at 450 C for 120 min gave the pyrolyzate
(22.80 g) containing 2% of syn-6, 2% of anti-6, 9% of 3,3-di-
chloro-2-fluorobut-1-ene (16), 14% of a mixture of stereoiso-
meric 1,3-dichloro-2-fluorobut-2-enes 17а and 17b, 71% of
3-chloro-2-fluorobuta-1,3-diene (18), 3% of propene 19, and
6% of a mixture of compounds 20а,b. 3-Chloro-2-fluorobuta-
1,3-diene (18) with m.p. 52—53 C was isolated by distillation
of the mixture in a yield of 12.54 g (50%).
1,2,3-Trichlorobut-2-ene (22а,b). 1H NMR of mixture of
isomers, : 2.30 (s, 3 H, CH3 of both isomers); 4.34 and 4.45
(both s, 2 H, CH2Cl, ratio of integral intensities 4 : 1). Mass
spectrum of major isomer (EI, 70 eV), m/z (Irel (%)): 162, 160,
158 [M]+ (8, 26, 28), 127, 125, 123 [M – Cl]+ (10, 64, 100), 89,
87 [M – 71]+ (20, 62), 51 (27). Mass spectrum of minor isomer
(EI, 70 eV), m/z (Irel (%)): 162, 160, 158 [M]+ (8, 25, 26), 127,
125, 123 [M – Cl] (9, 63, 100), 89, 87 [M+ – 71] (17, 51), 51 (19).
2,3-Dichlorobuta-1,3-diene (23).27 1H NMR, : 5.62 (br.s,
2 H, =CH2); 6.02 (br.s, 2 H, =CH2). MS (EI, 70 eV), m/z
(Irel (%)): 126, 124, 122 [M]+ (9, 52, 79), 89, 87 [M – Cl]+ (34,
100), 51 (95), 50 (37).
1,1,3-Trichloro-2-methylprop-1-ene (24).56 1H NMR, :
2.03 (s, 3 H, CH3); 4.23 (s, 2 H, CH2Cl). MS (EI, 70 eV), m/z
(Irel (%)): 162, 160, 158 [M]+ (7, 24, 25), 127, 125, 123 [M – Cl]+
(9, 61, 100), 89, 87 [M – 71]+ (18, 57), 51 (23).
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 16-03-
01098a) and the Presidium of the Russian Academy of
Sciences (Program for Basic Research No. 38; theme
0080-2018-0007).
3,3-Dichloro-2-fluorobut-1-ene (16).22 1H NMR, : 2.30
(d, 3 H, CH3, J = 0.5 Hz); 4.86 (dd, 1 H, J = 15.0 Hz, J = 4.0 Hz);
5.05 (dd, 1 H, J = 45.0 Hz, J = 4.0 Hz). 19F NMR, : –113.7
(dd, 1 F, J = 45.0 Hz, J = 15.0 Hz). MS (EI, 70 eV), m/z (Irel (%)):
142 [M]+ (1), 131, 129, 127 [M – CH3]+ (1, 3, 4), 109, 107
[M – Cl]+(30, 100), 71 (30), 51 (36).
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isomer). 1H NMR, : 2.03 (d, 3 H, CH3, J = 4.2 Hz); 4.21 (d, 2 H,
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1,3-Dichloro-1-fluoro-2-methylprop-1-ene (20а,b)22
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isomers). MS (EI, 70 eV), m/z (Irel (%)): 146, 144, 142 [M]+
(2, 13, 21), 109, 107 [M – Cl]+ (33, 100), 87 (17), 71 (75), 51 (83).

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Received December 20, 2018;
in revised form March 29, 2019;
accepted April 10, 2019