Free radical addition of cyclopentane and cyclohexane to halogeno derivatives of 1,2-difluoroethene

Article abstract of DOI:10.1016/S0022-1139(02)00012-X

Free radical addition reactions between cyclopentane and cyclohexane and a range of difluoroalkenes, CF₂=CXY (X, Y = H, F, Cl, Br) gave a series of adducts bearing difluoromethylene substituents, R-CF₂-CXYH (R = c-C₅H₉ or c-C₆H₁₁), in reasonable yield even though telomerisation and halogen transfer (when X, Y = Cl, Br) can compete. Dehydrofluorination of the adducts gave several new polyhalogenated alkenes.

Full text of DOI:10.1016/S0022-1139(02)00012-X

Journal of Fluorine Chemistry 115 (2002) 83–90
Free radical addition of cyclopentane and cyclohexane to
halogeno derivatives of 1,2-difluoroethene
Julian A. Cooper, Elodie Copin, Graham Sandford*
Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Received 8 October 2001; received in revised form 14 January 2002; accepted 15 January 2002
Abstract
Free radical addition reactions between cyclopentane and cyclohexane and a range of difluoroalkenes, CF2=CXY (X, Y ¼ H, F, Cl, Br) gave
a series of adducts bearing difluoromethylene substituents, R-CF2-CXYH (R ¼ c-C5H9 or c-C6H11), in reasonable yield even though
telomerisation and halogen transfer (when X, Y ¼ Cl, Br) can compete. Dehydrofluorination of the adducts gave several new polyhalogenated
alkenes. # 2002 Elsevier Science B.V. All rights reserved.
1. Introduction
homolysis by either g-ray or peroxide initiation, and fluori-
nated alkenes. Free radical addition processes involving
reactions of radicals generated from a variety of alkanes,
[5] alcohols [6] and ethers [7–9] with fluoroalkenes have
been established and, since these processes do not require
the use of highly toxic organo-tin initiators, scale-up is a
realistic possibility. Many fluorinated building blocks have
been accessed by this free radical methodology and some
subsequent chemistry of the free radical adducts has been
explored [10–12]. Largely, however, studies have been
concentrated on reactions involving hexafluoropropene
(HFP) principally because HFP does not homopolymerise
under normal reaction conditions and additions occur regio-
selectively at the difluoromethylene group (Scheme 1)
allowing high yields of adducts to be formed.
Here, we describe our initial studies concerning reactions
of radicals generated from cyclic alkanes with a variety of
difluoroethylene derivatives in order to assess whether free
radical addition methodology could be adapted to the ready
synthesis of numerous fluorine-containing building blocks.
Of course, much related work concerning the synthesis of
high molecular weight telomers from reactions between
various difluoroalkenes (especially, CF2=CH2 and CF2=
CFCl) and a variety of telogens (alcohols, haloalkanes,
etc.) has been published and this area of research has been
reviewed recently [13]. Free radical addition reactions
between carbon-centred radicals generated from, e.g. alco-
hols [14–17] aldehydes [18] and ethers [10,11,19,20] and
some difluoroalkenes giving 1:1 adducts have also been
described. However, we are unaware of any reports detailing
reactions between radicals generated from hydrocarbons and
difluoroalkenes.
The incorporation of fluorine atoms into organic systems
is becoming increasingly important due to the enhanced
chemical and biological activity that selectively fluorinated
systems can have over their non-fluorinated analogues [1].
The commercial availability of many life-science products
that owe their bio-activity to the presence of fluorinated
substituents exemplify these facts [2]. The introduction of
difluoromethylene units into organic molecules is a parti-
cular target because of the ability of this moiety to act as an
ether oxygen mimic [1] and several reagents have been
developed for this purpose. In this context, diethylamino-
sulfur trifluoride (DAST) is widely used for the selective
transformation of carbonyl groups into difluoromethylene
groups [3] and numerous difluoromethylated natural product
analogues have been synthesised [1].
An alternative strategy to the use of fluorinating agents for
introducing fluorine into a target molecule is a ‘building
block’ approach involving the synthetic manipulation of
small molecules that already bear fluorinated groups into
more elaborate systems [4]. This approach is, potentially,
very synthetically versatile providing, of course, that a range
of readily accessible and economically viable functional
fluorine containing building blocks becomes available.
The carbon–hydrogen bond can be used as a functional
group (C–H bond activation) in reactions between carbon-
centred free radicals, derived from carbon–hydrogen bond
* Corresponding author. Tel.: þ44-191-374-4639;
fax: þ44-191-384-4737.
E-mail address: graham.sandford@durham.ac.uk (G. Sandford).
0022-1139/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 0 2 ) 0 0 0 1 2 - X

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J.A. Cooper et al. / Journal of Fluorine Chemistry 115 (2002) 83–90
Scheme 1.
Addition of free radicals to CF2=CXY systems could, in
was used in an attempt to increase hydrogen transfer and
minimise telomer formation, only a very low yield (8%) of a
mixture of two monoaddition products 3 and 4 could be
isolated.
principle, give two intermediate radicals 1a and 1b
(Scheme 1) which could then either abstract a hydrogen
atom from the alkane starting material giving the desired
adducts 2a and 2b or react with a further difluoroethylene
molecule to give higher molecular weight material (telo-
mers) (Scheme 1). The viability of this strategy, therefore,
depends on the regioselectivity of the addition step and
successfully limiting competing telomerisation processes.
Trifluorochloroethene reacted with cyclohexane, present
in large excess to minimise competing telomer formation, to
give preparatively useful quantities of monoadduct 5 and a
small amount of product 6, arising from radical attack at the
CFCl site. Trifluorobromo- and 1,1-difluoro-2-bromoethene
also gave reasonable yields of monoadducts 7 and 9, respec-
tively in reactions with cyclohexane. In each case, the
monoadduct products were accompanied by significant
quantities of bromocyclohexane 8, probably resulting from
bromine atom abstraction by a cyclohexyl radical from
adduct 7 (Scheme 2). Indeed, a small quantity of volatile
trifluoroderivative 9a was observed by GC/MS in support of
this mechanism.
2. Results and discussion
Successful additions of free radicals generated from
cyclopentane and cyclohexane, to various difluoroethylene
derivatives were achieved, by either g-ray or di-tert-butyl
peroxide initiation at room temperature or 140 8C, respec-
tively and the results are collated in Table 1. Structures of
products were determined simply by NMR studies.
Reaction of cyclohexane with 1,1-difluoroethene (ratio
alkane:alkene, 1:1) gave only intractable high molecular
weighttelomersand, even when a large excess of cyclohexane
Difluoromethylene derivatives 10 and 14, prepared in
good yield by reaction of cyclohexane and cyclopentane
with chlorodifluoroethene, respectively were also accompa-
nied by a small quantity of products arising from radical
attack at the CHCl site 11 and 15, chlorocycloalkanes 12 and
Scheme 2.

J.A. Cooper et al. / Journal of Fluorine Chemistry 115 (2002) 83–90
85
Table 1
Free radical additions to difluoroalkenes
Fluoroalkene (CF2=CXY)
CF2=CH2
Conditions (A or B)a
Ratio (RH:alkane)
10:1
Products yield (%)
B
CF2=CFCl
CF2=CFBr
CF2=CHBr
B
A
10:1
2:1
B
A
4:1
4.4:1
B
B
17:1
4:1
CF2=CHCl
CF2=CHCl
B
B
5:1
4:1
CF2=CCl2
CF2=CCl2
A
B
1.5:1
2.5:1
a Conditions: A, g-ray irradiation, room temperature; B, t-BuO2, 140 8C, 24 h.

86
J.A. Cooper et al. / Journal of Fluorine Chemistry 115 (2002) 83–90
Scheme 3.
16 (halogen abstraction analogous to that depicted in
Scheme 2) and various diadducts. In contrast, additions of
cyclopentane and cyclohexane to CF2=CCl2 gave difluor-
odichloro adducts 17 and 19, respectively and only minor
impurities.
Several aspects concerning the mechanism of the free
radical reactions [21] described earlier are of note. The
preferred sites for radical attack are the CF2 groups and
these positions are favoured because they are not only the
most electrophilic sites due to the fluorine substituents, but
are also the least sterically hindered site bearing only small
fluorine atoms rather than larger chlorine and bromine
substituents. These results are consistent with work invol-
ving free radical additions to various halogenated fluoro-
propene derivatives reported by Paleta et al. [22].
synthesis of several novel fluoroalkenes of general formula
R-CF=CXY (X, Y ¼ H, F, Cl).
Dehydrofluorination of several of the adducts prepared
above was achieved by treatment with t-BuOK in THF
(Table 2). In each case, the stereochemistry of the alkene
was deduced by a consideration of either H–F or F–F
coupling constants. On steric grounds, we would expect 5
Table 2
Dehydrofluorination reactions
a
Whilst it is possible to obtain 1:1 adducts from all the
difluoroalkenes used, competing telomerisation processes
affected the yields of the obtained adducts. Many factors
contributing to the degree of telomerisation in various
telomerisation processes have been discussed [21] and here,
a comparison between free radical addition reactions invol-
ving CF2=CH2 and CF2=CCl2 illustrates the effects of the
relative polarities of both the propagating radicals and the
alkenes.
Addition of the nucleophilic radical R to both electro-
philic alkenes occurs rapidly but it is the nature of the
propagating radicals 21a and 21b which lead to differing
product distributions(Scheme 3). Radical 21a is relatively
nucleophilic in character and reacts preferentially with a
further molecule of the electrophilic alkene CF2=CH2 rather
than abstracting a hydrogen atom from the electron rich
alkane. In contrast, radical 21b, which has additional elec-
tron withdrawing chlorine atom attached to the radical
centre is more electrophilic in character than 21a and so
preferentially abstracts a hydrogen atom from the nucleo-
philic alkane to give the 1:1 adduct.
Adduct
Temperature (8C)
Product
20
ꢀ78
ꢀ78
ꢀ78
The experiments described earlier demonstrate that 1:1
adducts derived from difluoroalkenes and alkanes can be
synthesised in preparatively useful amounts providing that
an excess of the alkane is used. The potential use of the
difluorinated adducts as fluorinated building blocks can now
be explored and our initial studies have focussed upon the
ꢀ78
a Conditions: i, KOtBu, THF; 15 h; temperature as in the table.

J.A. Cooper et al. / Journal of Fluorine Chemistry 115 (2002) 83–90
87
4.1. Reactions of cycloalkanes with difluoroethene
derivatives
4.1.1. Di-tert-butyl peroxide initiation—general procedure
An autoclave (ca. 500 ml), fitted with a bursting disc
(maximum working pressure approximately 200 bar) was
charged with the alkane and di-tert-butyl peroxide, evacu-
ated, sealed and degassed by freeze-thawing. The fluoroalk-
ene was degassed separately and transferred to the autoclave
at reduced pressure using vacuum line techniques. The
autoclave was closed while frozen, transferred to a purpose
built chamber and heated at 140 8C for 24 h in a thermo-
statically controlled rocking furnace. The autoclave was
frozen in liquid air and volatile material was collected by
vacuum transfer as the autoclave approached room tempera-
ture. The autoclave was opened and the crude product
mixture was purified by either column chromatography
on silica gel or distillation under reduced pressure.
Scheme 4.
to give the Z-isomer 22, but this is not the case and an
explanation for this result is unclear.
Reduction of adduct 17 to the chlorodifluoro system 14
was accomplished in good yield by reaction with a Grignard
reagent (Scheme 4). This synthesis was adapted from meth-
odology described by Okuhara [23] and is envisaged to
proceed by an SET mechanism.
3. Conclusion
In summary, addition of carbon radicals, generated by C–
H bond homolysis from cycloalkanes, to difluoroethylene
derivatives is possible, but telomerisation and, in cases
where the alkene bears a chlorine or bromine substituent,
halogen atom abstraction compete. Preparatively useful
amounts of products such as 5 and 10 can be isolated and
the chemistry of these adducts as building blocks for the
incorporation of fluorine atoms into organic molecules
presents a useful approach.
4.1.2. 2-Cyclohexyl-1,1-difluoroethane (3) and
1-cyclohexyl-1,1-difluoroethane (4)
Cyclohexane (44.3 g, 530 mmol), 1,1-difluoroethene
(4.2 g, 65 mmol) and DTBP (0.6 g, 4 mmol) after fractional
distillation and preparative scale GLC gave a mixture con-
sisting of 2-cyclohexyl-1,1-difluoroethane (3) and 1-cyclo-
hexyl-1,1-difluoroethane (4) (0.6 g, 8%, 71% conv.) as a
colourless liquid in a ratio of 3:1 by GC; bp 149 8C (found:
C, 65.1; H, 9.6. C8H14F2 requires C, 64.9; H, 9.5%); 2-
cyclohexyl-1,1-difluoroethane (3): dH 0.9–1.2 (m), 1.4–1.8
(m), 5.8 (1H, tt, 2JHꢀF 57, 3JHꢀH 4.8, CF2H); dC 25.7 (s, C-
4), 26.2 (s, C-3), 26.4 (s, C-2), 32.4 (t, 3JCꢀF 5.3, CH), 41.4
4. Experimental
2
1
All solvents were dried before use by literature proce-
dures. NMR spectra were recorded on a Varian VXR 400S
NMR spectrometer with tetramethylsilane and trichloro-
fluoromethane as internal standards and deuteriochloroform
as solvent, unless otherwise stated. In 19F NMR spectra,
upfield shifts are quoted as negative. Coupling constants are
given in Hertz. Mass spectra were recorded on either a VG
7070E spectrometer or a Fisons VG Trio 1000 spectrometer
coupled with a Hewlett Packard 5890 series II gas chroma-
tograph. Accurate mass measurements were performed by
the EPSRC Mass Spectrometry Service, Swansea, UK. IR
spectra were recorded on a Perkin-Elmer 1600 FT-IR spec-
trometer using KBr plates while elemental analyses were
obtained on either a Perkin-Elmer 240 or a Carlo Erba
Elemental Analyser. Melting and boiling points were
recorded at atmospheric pressure and are uncorrected.
Superscript numbers given as part of boiling point data
indicate the pressure (in mmHg) during measurement. Dis-
tillations were carried out using a Fischer Spahltrohr MS200
micro-distillation apparatus. The g-ray irradiations were
performed in a purpose built shielded chamber fitted
with a cobalt-60 source (500 Ci original activity). Column
chromatography was performed on silica gel (Merck no. 1-
09385) and TLC analysis was performed on silica gel TLC
plates (Merck).
(t, JCꢀF 20, CH2CF2H), 116.9 (t, JCꢀF 238, CF2H); dF
ꢀ113.2 (m); m/z (EIþ) 148 (Mþ, 4.9%), 83 (100); 1-cyclo-
hexyl-1,1-difluoroethane (4): dH 0.9–1.2 (m, CH2), 1.6 (m,
CH3), 1.4–1.8 (m, CH2); dC 21.0 (t, 2JCꢀF 28, CH3), 25.7 (s,
C-4), 26.2 (s, C-3), 33.1 (s, C-2), 45.4 (t, 2JCꢀF 24, CHCF2),
125.9 (t, 1JCꢀF 240, CF2); dF ꢀ95.0 (m); m/z (EIþ) 109 (4),
83 (100) The remaining material was attributed to telomer
formation.
4.1.3. 2-Chloro-1-cyclohexyl-1,1,2-trifluoroethane (5)
Cyclohexane (44.7 g, 530 mmol), chlorotrifluoroethene
(6.4 g, 55 mmol) and DTBP (0.6 g, 4 mmol) gave 2-
chloro-1-cyclohexyl-1,1,2-trifluoroethane (5) (3.5 g, 33%,
99% conv.); bp 212 8C (found: C, 47.9; H, 6.1. C8H12ClF3
requires C, 47.9; H, 6.0%); dH 1.1–1.3 (5H, m, CH2 axial),
1.6–1.8 (5H, m, CH2 equatorial), 2.1 (1H, m, CHCF2), 6.2
(1H, ddd, 2JHꢀF 48, 3JHꢀF 8.4, 3JHꢀF 6.4, CFClH); dC 24.8
2
(s, C-4), 25.1 (s, C-3), 25.6 (s, C-2), 40.7 (t, JCꢀF 22,
CHCF2), 97.4 (dt, 1JCꢀF 250, 2JCꢀF 37, CFClH), 119.4 (td,
1JCꢀF 251, 2JCꢀF 24, CF2); dF ꢀ119.7 (2F, m, CF2), ꢀ153.7
(1F, dt, JFꢀH 48, JFꢀF 13, CFHCl); m/z (EIþ) 202 (Mþ,
0.2%), 200 (Mþ, 0.8%), 113 (23), 83 (100). Compound 6
2
3
1
2
was observed by H NMR; dH 5.8 ppm (1H, td, JHꢀF 54,
3JHꢀF 6, CFClCF2H). The remainder of the crude reaction
mixture was attributed to higher-adduct formation.

88
J.A. Cooper et al. / Journal of Fluorine Chemistry 115 (2002) 83–90
4.1.4. 2-Bromo-1-cyclohexyl-1,1,2-trifluoroethane (7)
Cyclohexane (50 g, 585 mmol), bromotrifluoroethene
(23.0 g, 140 mmol) and DTBP (1.0 g, 7 mmol) gave 7
and bromocyclohexane 8 in a ratio of 3:2 by GC/MS.
Fractional distillation gave 2-bromo-1-cyclohexyl-1,1,2-tri-
fluoroethane (7) (12.0 g, 35%, 94% conv.) as a colourless
liquid; bp 218 8C (found: C, 39.2; H, 4.9. C8H12BrF3
requires C, 39.2; H, 4.9%); dH 1.1–1.3 (5H, m, CH2 axial),
1.6–1.8 (5H, m, CH2 equatorial), 2.1 (1H, m, CH), 6.40 (1H,
ddd 2JHꢀF 47, 3JHꢀF 11, 3JHꢀF 11, CHBrF); dC 24.5 (m, C-
4), 25.3 (m, C-3), 25.6 (s, C-2), 40.7 (t, 2JCꢀF 22, CH), 89.8
ꢀ108.9 (dt, 3JHꢀF 14, 3JHꢀF 13); m/z (EIþ) 119 (47), 99 (78),
91 (16), 77 (22), 69 (100). Compound 15 was observed by
2
3
1H NMR; dH 2.3 (1H, td, JHꢀF 14, JHꢀH 6.8, CF2H).
4.1.8. 2,2-Dichloro-1-cyclopentyl-1,1-difluoroethane (17)
Cyclopentane (99 g, 1.4 mol), 2,2-dichloro-1,1-difluor-
oethene (46.6 g, 0.35 mol) and DTBP (1.5 g, 0.011 mol),
after distillation under reduced pressure, gave 2,2-dichloro-
1-cyclopentyl-1,1-difluoroethane (17) (34.2 g, 48%) as a
colourless liquid; bp 50 8C (10 mbar) (found: C, 41.1; H,
4.9. C7H10Cl2F2 requires C, 41.4; H, 4.9%); nmax (cmꢀ1
)
1
2
2
(ddd, JCꢀF 259, JCꢀF 40, JCꢀF 35, CHBrF), 119.2 (td,
1JCꢀF 249, 2JCꢀF 24, CF2); dF ꢀ117.3 (2F, m, CF2), ꢀ156.4
2859 and 2937 (C–H); dH 1.6–1.7 (4H, m, CH2 axial), 1.8–
1.9 (4H, m, CH2 equatorial), 2.7 (1H, m, CHCF2), 5.7 (1H, t,
3JHꢀF 8.7, CHCl2); dC 25.6 (s, C-3), 26.0 (t, 3JCꢀF 3.4, C-2),
(1F, dt, JFꢀH 47, JFꢀF 17, CFBrH); m/z (EIþ) 246 (Mþ,
2%), 244 (Mþ, 2%), 133 (36), 113 (37), 93 (12), 83 (100).
2
3
2
2
42.1 (t, JCꢀF 22.3, CHCF2), 70.1 (t, JCꢀF 35.3, CHCl2),
121.0 (t, 1JCꢀF 251, CF2); dF ꢀ113.8 (dd, JHꢀF 8.6, 3JHꢀF
3
4.1.5. 2-Bromo-1-cyclohexyl-1,1-difluoroethane (9)
14.7); m/z (EIþ) 203 (Mþ, 0.27%), 119 (67), 111 (12), 99
(100).
Cyclohexane (250 g, 3 mol), 1-bromo-2,2-difluoroethene
(24 g, 170 mmol) and DTBP (2.5 g, 17 mmol) gave 9 and 8
in a ratio of 5.6:1 by GC/MS. Fractional distillation gave 2-
bromo-1-cyclohexyl-1,1-difluoroethane (9) (7.1 g, 19%) as
a colourless liquid; bp 205 8C (found: C, 42.4; H, 5.8.
C8H13BrF2 requires C, 42.3; H, 5.7%); dH 1.1–1.2 (5H,
m, CH2 axial), 1.7–1.8 (5H, m, CH2 equatorial), 2.0 (1H, m,
CH), 3.47 (1H, t, 3JHꢀF 14, CH2Br); dC 25.3 (t, 3JCꢀF 4.2, C-
4.1.9. 2,2-Dichloro-1-cyclohexyl-1,1-difluoroethane (19)
Cyclohexane (52 g, 620 mmol), 1,1-dichloro-2,2-difluor-
oethene (30 g, 225 mmol) and DTBP (1.0 g, 7 mmol) gave a
mixture of 19 and diadducts 20 in a ratio of 6:1 by GC/MS.
Fractional distillation gave 2,2-dichloro-1-cyclohexyl-1,1-
difluoroethane (19) (19.5 g, 40%); bp 206 8C (found: C,
44.0; H, 5.5. C8H12Cl2F2 requires C, 44.2; H, 5.5%); dH 1.2–
1.3 (5H, m, CH2 axial), 1.8–1.9 (5H, m, CH2 equatorial), 2.2
(1H, m, CH), 5.8 (1H, t, 3JHꢀF 9.2, CHCl); dC 24.9 (t, 3JCꢀF
4.1, C-2), 25.3 (s, C-4), 26.6 (s, C-3), 40.9 (t, 2JCꢀF 23, CH),
2
4), 25.4 (s, C-3), 25.7 (s, C-2), 30.5 (t, JCꢀF 34, CHCF2),
2
1
41.8 (t, JCꢀF 22, CH2Br), 121.9 (t, JCꢀF 245, CF2); dF
ꢀ104.1 (m); m/z (EIþ) 228 (Mþ, 1%), 226 (Mþ, 1%), 147
(8), 83 (100).
2
1
69.4 (t, JCꢀF 35, CHCl2), 120.4 (t, JCꢀF 252, CF2); dF
ꢀ115.9 (dd, 3JHꢀF 9.0, 3JHꢀF 8.7); m/z (EIþ) 133 (87%), 113
(100), 93 (25).
4.1.6. 2-Chloro-1-cyclohexyl-1,1-difluoroethane (10)
Cyclohexane (85 g, 1020 mmol), 1-chloro-2,2-difluor-
oethene (24.2 g, 246 mmol) and DTBP (1.0 g, 7 mmol) gave
a mixture of 10, 11, chlorocyclohexane 12 and isomers of
diadduct 13 in a ratio of 45:3:1:5 by GC/MS. Fractional
distillation gave 2-chloro-1-cyclohexyl-1,1-difluoroethane
(10) (11.9 g, 49%) as a colourless liquid; bp 184 8C (found:
C, 52.3; H, 7.2. C8H13ClF3 requires C, 52.6; H, 7.1%); dH
1.0–1.3 (5H, m, CH2 axial), 1.6–1.8 (5H, m, CH2 equator-
4.2. g-Ray initiation—general procedure
A Pyrex Carius tube (ca. 60 ml) was charged with the
alkane and degassed three times by freeze-thawing. The
fluoroalkene was degassed separately by the same procedure
and transferred to the tube, which was cooled in liquid air, at
reduced pressure using vacuum line techniques. The tube
was sealed under vacuum while frozen and allowed to reach
room temperature in a metal sheath. The tube was housed in
a purpose built irradiation chamber and irradiated with g-
rays for a period of 10 days to give a total dose of ca.
10 Mrad. The tube was then removed from the chamber,
frozen in liquid air and opened. Volatile material was
collected via vacuum transfer as the tube approached room
temperature and the product mixture was collected and
purified by either fractional distillation at reduced pressure
(Spaltrohr) or column chromatography on silica gel.
3
ial), 1.97 (1H, m, CH), 3.60 (2H, t, JHꢀF 13, CH2Cl); dC
3
25.1 (t, JCꢀF 4, C-2), 25.5 (s, C-4), 25.8 (s, C-3), 41.1 (t,
2
2JCꢀF 22.4, CHCF2), 43.0 (t, JCꢀF 34.7, CH2Cl), 122.5 (t,
1JCꢀF 245, CF2); dF ꢀ109.4 (m); m/z (EIþ) 184 (Mþ,
0.57%), 182 (Mþ, 2%), 133 (10), 113 (13), 83 (100).
4.1.7. 2-Chloro-1-cyclopentyl-1,1-difluoroethane (14)
Cyclopentane (33 g, 484 mmol), 1-chloro-2,2-difluor-
oethene (9.5 g, 97 mmol) and DTBP (1.0 g, 7 mmol) gave
a mixture of 14, 15 and diadducts 16 in a ratio of 50:1:5 by
GC/MS. Fractional distillation gave 2-chloro-1-cyclopentyl-
1,1-difluoroethane (14) (4.0 g, 24%) as a colourless liquid;
bp 197 8C (dec) (found: C, 49.7; H, 6.55. C7H11ClF2
requires C, 49.85; H, 6.5%); dH 1.6–1.8 (8H, m, CH2),
4.2.1. 2-Bromo-1-cyclohexyl-1,1,2-trifluoroethane (7)
Cyclohexane (8.0 g, 95 mmol) and bromotrifluoroethene
(7.7 g, 48 mmol) gave 7 and 8 in a ratio of 1:2 by GLC/MS.
Fractional distillation gave 2-bromo-1-cyclohexyl-1,1,2-tri-
fluoroethane (7) (2.6 g, 22%, 86% conv.); physical and
3
2.6 (1H, m, CH), 3.7 (2H, t, JHꢀF 13, CH2Cl); dC 26.0
(s, C-3), 26.2 (t, 3JCꢀF 3.8, C-2), 42.6 (t, 2JCꢀF 23, CHCF2),
2
1
44.4 (t, JCꢀF 34, CH2Cl), 122.7 (t, JCꢀF 245, CF2); dF

J.A. Cooper et al. / Journal of Fluorine Chemistry 115 (2002) 83–90
89
spectral data as earlier. Two more by-products with higher
retention times were also detected (9 and 15%), but could
not be identified.
45.9; H, 4.9%); nmax (cmꢀ1) 1656 (C=C); dH 1.4–1.6
(4H, m, CH2 axial), 1.7–1.9 (4H, m, CH2 equatorial),
3
3
3
3.1 (1H, dtt, JHꢀF 30.4, JHꢀH 8.4, JHꢀH 8.4, CHCF);
2
dC 25.9 (s, C-3), 29.3 (s, C-2), 38.8 (d, JCꢀF 24, CH),
1
4.2.2. 2-Bromo-1-cyclohexyl-1,1-difluoroethane (9)
Cyclohexane (11.5 g, 137 mmol) and 1-bromo-2,2-
difluoroethene (4.5 g, 31.5 mmol) gave 9 and 8 in a ratio
of 4:1 by GLC/MS. Fractional distillation gave 2-bromo-1-
cyclohexyl-1,1-difluoroethane (9) (2.6 g, 36%); physical
and spectral data as earlier.
105.5 (d,2JCꢀF 46.5, CCl2), 159.5 (d, JCꢀF 263, CF); dF
ꢀ113.4 (d, JHꢀF 30.5); m/z (EIþ) 182 (Mþ, 46%), 142
3
(24), 141 (20), 140 (36), 105 (28).
4.2.7. 1,1-Dichloro-2-cyclohexyl-2-fluoroethene (24)
Potassium tert-butoxide (0.85 g, 7.6 mmol) and 19 (1.5 g,
6.9 mmol) in THF (15 ml) at ꢀ78 8C gave1,1-dichloro-2-
cyclohexyl-2-fluoroethene (24) (1.1 g, 81%) as a colourless
liquid; bp 199 8C (found: C, 48.8; H, 5.7. C8H11Cl2F
requires C, 48.7; H, 5.6%); dH 1.0–1.6 (5H, m, CH2 axial),
4.2.3. 2,2-Dichloro-1-cyclohexyl-1,1-difluoroethane (19)
Cyclohexane (10.0 g, 119 mmol) and 1,1-dichloro-2,2-
difluoroethene (12.7 g, 105 mmol) gave a mixture of 2,2-
dichloro-1-cyclohexyl-1,1-difluoroethane (19) and dia-
dducts 20 in a ratio of 1:1 by GC/MS. Fractional distillation
gave 2,2-dichloro-1-cyclohexyl-1,1-difluoroethane (19)
(5.1 g, 24%, 100% conv.); physical and spectral data as
earlier.
3
1.6–1.9 (5H, m, CH2 equatorial), 2.7 (1H, dtt, JHꢀF 28,
3
3JHꢀH axial 12, JHꢀH equatorial 3.6, CHCF); dC 25.4 (s, C-4),
25.7 (s, C-3), 28.2 (s, C-2), 38.5 (d, 2JCꢀF 22, CHCF), 105.7
(d, 2JCꢀF 46, CCl2), 160.6 (d, 1JCꢀF 264, CF); dF ꢀ111.6 (d,
3JHꢀF 28); m/z (EIþ) 200 (Mþ, 2%), 198 (Mþ, 14%), 196
(Mþ, 20%), 142 (22), 140 (33), 105 (18), 67 (100).
4.2.4. Dehydrofluorination—general procedure
A mixture of dry potassium tert-butoxide and THF was
cooled to the required temperature under nitrogen. The
perfluoroalkyl derivative was added dropwise and stirred
for 3 h before being allowed to warm up slowly to room
temperature. The reaction mixture was poured into water
and neutralised with 10% hydrochloric acid, extracted into
dichloromethane, dried (MgSO4) and distilled to give the
desired fluoroalkene.
4.2.8. (Z)-1-chloro-2-cyclohexyl-2-fluoroethene (25)
Potassium tert-butoxide (4.97 g, 44 mmol) and 10 (5.4 g,
30 mmol) in THF (25 ml) at ꢀ78 8C gave (Z)-1-chloro-2-
cyclohexyl-2-fluoroethene (25) (3.0 g, 62%) as a colourless
liquid; bp 180 8C (found: C, 59.0; H, 7.5. C8H12ClF requires
C, 59.1; H, 7.4%); dH 1.1–1.2 (5H, m, CH2 axial), 1.7–1.8
(5H, m, CH2 equatorial), 2.1 (1H, m, CHCF), 5.23 (1H, d,
3JHꢀF 26, CHCl); dC 25.6 (s, C-4), 25.7 (s, C-3), 29.3 (d,
3JCꢀF 1.5, C-2), 40.1 (d, 2JCꢀF 23, CHCF), 94.9 (d, 2JCꢀF 19,
CHCl), 164.8 (d, 1JCꢀF 263, CF); dF ꢀ108.5 (dd, 3JHꢀF trans
26, 3JHꢀF 24); m/z (EIþ) 164 (Mþ, 4%), 162 (Mþ, 10%), 127
(32), 82 (32), 67 (100).
4.2.5. (Z)- and (E)-1-chloro-2-cyclohexyl-1,2-
difluoroethene (22)
Potassium tert-butoxide (2.8 g, 25 mmol) and 5 (2.0 g,
10 mmol) in THF (25 ml) at 0 8C gave a mixture of (Z)- and
(E)-1-chloro-2-cyclohexyl-1,2-difluoroethene (22) (1.0 g,
55%, Z:E 4:1 by NMR) as a colourless liquid; bp 190 8C
(found: C, 53.4; H, 6.25. C8H11ClF2 requires C, 53.2; H,
6.1%); Z isomer: dH 1.0–1.4 (5H, m, CH2 axial), 1.5–1.8
(5H, m, CH2 equatorial), 2.3 (1H, dtm, 3JHꢀF 30, 3JHꢀH 12,
CH); dC 25.4 (s, C-4), 25.9 (s, C-3), 28.3 (d, 3JCꢀF 2.7, C-2),
4.2.9. (Z)-1-chloro-2-cyclopentyl-2-fluoroethene (26)
Potassium tert-butoxide (5.3 g, 47 mmol) and 14 (4 g,
24 mmol) in THF overnight gave (Z)-1-chloro-2-cyclopen-
tyl-2-fluoroethene (26) (0.9 g, 25%) as a yellow oil; bp 90 8C
(10 mbar); (Mþ, 148.046. C7H10ClF requires: Mþ, 148.046);
dH 1.4–1.6 (4H, m, CH2 axial), 1.7–1.9 (4H, m, CH2 equatorial),
5.3 (1H, dd, 3JHꢀF trans 24.8, 4JHꢀH 0.8, CH); dC 25.5 (s, C-3),
2
3
1
36.8 (dd, JCꢀF 21, JCꢀF 2.4, C-1), 134.8 (dd, JCꢀF 296,
2JCꢀF 39, CHCF), 146.8 (dd, JCꢀF 255, CFCl); dF ꢀ112.1
26 (s, C-2), 41.4 (d, JCꢀF 23.6, CH), 94.9 (d, JCꢀF 19.4,
CHCl), 160 (d, 1JCꢀF 262, CF); dF ꢀ109.8 (2d, 3JFꢀH 24.4,
3JFꢀH trans 24.8).
1
2
2
(1F, s, CFCl), ꢀ144.4 (1F, m, CHCF); E-isomer: dH 1.0–1.4
(5H, m, CH2 axial), 1.5–1.8 (5H, m, CH2 equatorial), 2.5
(1H, dtm, 3JHꢀF 28, 3JHꢀH 12, CH); dC 25.5 (s, C-4), 26.0 (s,
C-3), 28.8 (d, 3JCꢀF 2.3, C-2), 36.8 (dd, 2JCꢀF 21, 3JCꢀF 2.4,
4.2.10. Reduction of 2,2-dichloro-1-cyclopentyl-1,1-
difluoroethane (17)
1
2
CH), 135.6 (dd, JCꢀF 282, JCꢀF 57, CHCF), 151.4 (dd,
1JCꢀF 248, CFCl); dF ꢀ128.7 (1F, d, JFꢀF 126, CFCl),
Compound 16 (2.5 g, 12 mmol) was added dropwise to a
cooled, stirred solution of C2H5MgBr (12 ml, 36 mmol) in
THF (25 ml). The reaction mixture was heated at reflux for
24 h and then poured into 10% aqueous sodium hydrogen
carbonate. The organic product was extracted with dichlor-
omethane and dried (MgSO4) and solvents were removed
under vacuum. Further distillation under reduced pressure
gave 2-chloro-1-cyclopentyl-1,1-difluoroethane (14) (1.1 g,
54%); spectral and physical data as earlier.
3
ꢀ153.8 (1F, dd, 3JFꢀF 126, 3JFꢀH 29, CHCF); m/z (EIþ) 182
(Mþ, 8%), 180 (23), 126 (19), 124 (56), 81 (28).
4.2.6. 1,1-Dichloro-2-cyclopentyl-2-fluoroethene (23)
Potassium tert-butoxide (6 g, 54 mmol) and 17 (10 g,
49 mmol) and in THF gave 1,1-dichloro-2-cyclopentyl-2-
fluoroethene (23) (5.8 g, 63%) as a yellow liquid; bp
185 8C (found: C, 45.6; H, 4.9. C7H9Cl2F requires C,

90
J.A. Cooper et al. / Journal of Fluorine Chemistry 115 (2002) 83–90
[7] R.D. Chambers, B. Grievson, J. Chem. Soc., Perkin Trans. 1 (1985)
Acknowledgements
2215.
[8] R.D. Chambers, B. Grievson, J. Fluorine Chem. 29 (1985) 323.
[9] R.D. Chambers, B. Grievson, N.M. Kelly, J. Chem. Soc., Perkin
Trans. 1 (1985) 2209.
We thank the EPSRC (Quota Studentship to JAC), the
University of Durham (Studentship to EC) and the Royal
Society (University Research Fellowship to GS).
[10] V. Cirkva, O. Paleta, J. Fluorine Chem. 94 (1999) 141.
[11] V. Cirkva, S. Bohm, O. Paleta, J. Fluorine Chem. 102 (2000) 159.
[12] J.A. Cooper, C.M. Olivares, G. Sandford, J. Org. Chem. 66 (2001)
4887.
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