Sodium dithionite initiated addition of 1-bromo-1-chloro-2,2,2-trifluoroethane to allylaromatics. Facile synthesis of conjugated dienes substituted with terminal CF3 group

Article abstract of DOI:10.1016/j.jfluchem.2006.01.007

Sodium dithionite effectively promotes the addition of 1-bromo-1-chloro-2,2,2-trifluoroethane to the terminal double bond of allylbenzenes 1. The reactions proceeded in MeCN/H₂O to give a 3:1 mole ratio of diastereoisomers of 1-(2-bromo-4-chloro-5,5,5-trifluoropentyl)benzenes 2 as the main products together with small amounts of its reductive debromination products 3. Total yields of 2 and 3 were dependent on the nature of the aromatic ring substituents in 1. Treatment of adducts 2 with DBU in refluxing hexanes resulted in double dehydrohalogenation affording, in good yields, conjugated dienes 4 (1,1,1-trifluoro-5-phenyl-2,4-pentadienes) terminated with the CF₃ group at the one end and the phenyl group at the opposite end. These dienes were found to be sufficiently reactive to undergo Diels-Alder condensation with active dienophiles to give trifluoromethylated carbocycles. The reactions of CF₃CHClBr with allylheterocycles were less successful and lead to low yields of mixtures of hardly separable compounds or to polymeric resins.

Full text of DOI:10.1016/j.jfluchem.2006.01.007

Journal of Fluorine Chemistry 127 (2006) 720–729
www.elsevier.com/locate/fluor
Sodium dithionite initiated addition of 1-bromo-1-chloro-
2,2,2-trifluoroethane to allylaromatics
Facile synthesis of conjugated dienes substituted
with terminal CF3 group
*
Jolanta Ignatowska, Wojciech Dmowski
Institute of Organic Chemistry, Polish Academy of Sciences, 01-224 Warsaw, Poland
Received 22 December 2005; received in revised form 25 January 2006; accepted 31 January 2006
Available online 23 February 2006
Abstract
Sodium dithionite effectively promotes the addition of 1-bromo-1-chloro-2,2,2-trifluoroethane to the terminal double bond of allylbenzenes 1.
The reactions proceeded in MeCN/H2O to give a 3:1 mole ratio of diastereoisomers of 1-(2-bromo-4-chloro-5,5,5-trifluoropentyl)benzenes 2 as the
main products together with small amounts of its reductive debromination products 3. Total yields of 2 and 3 were dependent on the nature of the
aromatic ring substituents in 1. Treatment of adducts 2 with DBU in refluxing hexanes resulted in double dehydrohalogenation affording, in good
yields, conjugated dienes 4 (1,1,1-trifluoro-5-phenyl-2,4-pentadienes) terminated with the CF3 group at the one end and the phenyl group at the
opposite end. These dienes were found to be sufficiently reactive to undergo Diels-Alder condensation with active dienophiles to give
trifluoromethylated carbocycles. The reactions of CF3CHClBr with allylheterocycles were less successful and lead to low yields of mixtures
of hardly separable compounds or to polymeric resins.
# 2006 Elsevier B.V. All rights reserved.
Keywords: 1-Bromo-1-chloro-2,2,2-trifluoroethane; Radical addition; Sodium dithionite; Allylaromatics; Trifluoromethyl dienes
1. Introduction
We have found that sodium dithionite is also effective in
generating CF3CHClꢁ radicals from 1-bromo-1-chloro-2,2,2-
trifluoroethane (CF3CHClBr), inexpensive and commercially
available reagent known as an inhalation anaesthetic
(Halothane1). In preceding papers we reported addition of
1-bromo-1-chloro-2,2,2-trifluoroethane to a number of vinyl
ethers leading, after dehydrohalogenation, to valuable a,b-
unsaturated carbonyl compounds substituted with the trifluor-
omethyl group [6,7]. The addition of CF3CHClBr to b-pinene
occurred almost quantitatively and dehalogenation and reduc-
tion of the adduct gave a number of trifluoromethyl substituted
terpenoids [8]. As an extension of these investigations, we
studied the sodium dithionite initiated reactions of CF3CHClBr
with a number of linear, branched and cyclic alkenes and in
most cases good yields of the addition products were obtained
[9]. However, the attempted reactions with styrene and other
alkenes, in which the double bond is conjugated with an
aromatic ring, totally failed. In contrast to the latter,
allylbenzene and ring substituted allylbenzenes were found
to be particularly reactive.
The sodium dithionite initiated addition of perfluoroalkyl
halides to the electron rich substrates like alkenes and alkynes,
developed a long time ago by Huang [1,2], is a well-known
procedure with numerous applications. Recently, this procedure
has been successfully applied to the perfluoroalkylation of
steroids [3], glycosides [4] and thioles [5]. This is a free radical
process in which radical anions SO2ꢀ, existing in an equilibrium
withdithioniteanionsS2O42ꢀ, abstracthalogenfromRFX (X = I,
Br) molecules to generate highly electrophilic perfluoroalkyl
radicals. This method of generating perfluoroalkyl radicals
posseses a number of advantages, i.e. aqueous medium (H2O–
CH3CN mixture is usually used), very mild reaction conditions,
simplicity and low cost of the initiator and the solvents.
* Corresponding author. Fax: +48 22 632 66 81.
E-mail address: dmowski@icho.edu.pl (W. Dmowski).
0022-1139/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2006.01.007

J. Ignatowska, W. Dmowski / Journal of Fluorine Chemistry 127 (2006) 720–729
721
In the present paper, we report the results of our studies on
the addition of CF3CHClBr to numerous allylaromatics and
allylheterocycles and dehydrohalogention reactions of the
adducts, which lead to interesting conjugated dienes terminally
substituted with the trifluoromethyl group.
aromatic system and therefore decreased electron density at the
allylic double bond.
Compounds 2 and 3 were isolated by column chromato-
graphy as inseparable mixtures (oils) and their ratios were
1
determined from the integrated H and 19F NMR spectra and
GC–MS analyses. In all cases, adducts 2 were found to be
approximately 3:1 mixtures of two diastereoisomers. Two
NMR signals for the CF3 and CHCl groups appear in all spectra
but, because of overlapping, it was not possible in every case to
2. Results and discussion
The reactions of 1-bromo-1-chloro-2,2,2-trifluoroethane
with allylbenzenes 1 were carried out under typical conditions
in a water–acetonitrile solution (1:1, v/v) in which sodium
dithionite and sodium hydrogen carbonate (HBr scavanger)
were suspended (the salts are only partially soluble in the
reaction mixture). The reaction mixture was vigorously stirred
at ambient temperature and organic substrates (CF3CHClBr
and 1) were added one by one. The reactions proceeded within
the temperature range of 20–25 8C with evolution of carbon
dioxide (formed by the reaction of SO2 with NaHCO3). In most
cases, gas evolution ceased after 1 h but, to complete the
reactions, stirring was continued overnight. The crude mixtures
of products (after extraction with Et2O) consisted of adducts 2
(4-bromo-2-chloro-1,1,1-trifluoro-5-phenylpentanes) as the
main components together with small amounts of reductively
debrominated compounds 3 and traces of unreacted alkenes 1
(Scheme 1). A 1:1 mole ratio of Na2S2O4 to alkenes 1 was
found to be necessary for the reactions to afford good yields of
the products. Decreased Na2S2O4/1 ratio does not diminish
formation of compounds 3 but resulted in lower total yields. As
shown in Table 1, there is no clear evidence for the influence of
electron donating substituents (Me, OMe, OH) on the total
yields of compounds 2 and 3 and on their ratio. It may be,
however, that the yields are increased by the presence of
methoxy groups in the aromatic ring of 1f (Table 1, entry 7).
The relatively low yield of the reaction with 2-methoxyallyl-
benzene 1d (entry 4) may be caused by steric reason. Electron
withdrawing substituents, like halogens (entries 10–12)
definitely decrease the reactivity of allylbenzenes 1j–1l with
increased formation of debrominated products. No reaction
occurred with 4-nitroallylbenzene 1m (entry 13) under any
conditions. 1-Allylnaphthalene 1n (entry 14) gave low yields of
the adducts with increased amount of the debrominated
compound 3n. In this last case, decreased reactivity may be
attributed to delocalisation of the electrons around large
1
resolve all H signals of the minor isomers (Table 2). The
identity of minor compound 3 was confirmed by comparison of
weak signals appearing in the NMR spectra of mixtures of
products 2 + 3 with the spectra of pure compounds 3a, 3k and 3l
(see Section 3), which were obtained by treatment of the
selected mixtures (2a + 3a, 2k + 3k and 2l + 3l) with zinc metal
in ethanol (Scheme 2). Not high yields of 3k and 3l may be
attributed to a tar formation; no C–Cl bond reduction was
observed.
Compounds 2 were found to be resistant to medium strong
bases like pyridine and triethylamine but on treatment with
DBU (1,8-diazabicyclo[5.4.0]undece-7-ene) they undergo
double dehydrohalogenation (–HBr and –HCl) to give
conjugated dienes 4 (1,1,1-trifluoro-5-phenyl-2,4-pentadienes)
in high yields (Scheme 3 and Table 1). Thus, heating mixtures
of 2 and 3 and DBU in refluxing hexanes resulted in mixtures of
4 and 3 from which, pure dienes 4 were easily separated by
simple crystallisation; in only few cases additional purification
was required. The 1H NMR spectra of dienes 4 (Table 3)
revealed that they are formed exclusively as the trans,trans-
form (transJHH = ca. 15 Hz).
Compound 2g substituted with the hydroxy group in the
ortho-position in the aromatic ring, unlike all other adducts 2,
did not undergo dehydrohalogenation under basic condition
but, instead, intermolecular nucleophilic substitution occured
to give 2,3-dihydrobenzofuran derivative 5 (Table 1, entry 7).
Reactions of 1-bromo-1-chloro-2,2,2-trifluoroethane with
allylheterocycles were much less successful. The reactions with
2-allylpyridine (6) and 3-allylpyridine (10), even with an excess
of CF3CHClBr and prolonged reaction time, gave only low
yields of products. In case of 6 (Scheme 4), a mixture of three
compounds was obtained which were tentatively identified as 7,
8 and 9 (GC–MS analysis only). In case of 10, a 4:1 mixture of
compounds 11 and 12 (Scheme 5) was obtained with total yield
Scheme 1.

722
J. Ignatowska, W. Dmowski / Journal of Fluorine Chemistry 127 (2006) 720–729
Table 1
Na2S2O4 initiated addition of CF3CHClBr to allylaromatics and dehydrohalogenation of the adducts with DBU
Entry
1
Substrate
Addition of CF3CHClBra
Product
Dehydrohalogenationb
Product
Yield (%)c
Yield (%)c
73
77 (incl. 13% 3a)d
2
3
65 (incl. 8.5% 3b)d
89
98
58 (incl. 9% 3c)d
4
5
52 (incl. 6% 3d)d
71 (incl. 8% 3e)d
80 (incl. 13% 3f)d
63 (incl. 14% 3g)d
64 (incl. 12% 3h)d
67 (incl. 10% 3i)d
59 (incl. 8% 3j)d
44 (incl. 10% 3k)d
50 (incl. 28% 3l)d
50
80
70
52
6
7
e
8
9
91
94
44
10
11
12
13
No reaction
0

J. Ignatowska, W. Dmowski / Journal of Fluorine Chemistry 127 (2006) 720–729
723
Table 1 (Continued )
Entry
Substrate
Addition of CF3CHClBra
Product
Dehydrohalogenationb
Product
Yield (%)c
Yield (%)c
53
14
30 (incl. 16% 3n)d
a
Reaction conditions: CF3CHClBr/allylAr/Na2S2O4/Na2HCO3 ratio = 2:1:1:3; solvents: H2O/MeCN = 1:1; temperature: 20–25 8C; time: 24 h.
Reaction conditions: DBU/2 ratio = 3:1; solvent: hexanes; temperature: reflux; time: 12–18 h.
Isolated total yields of 2 and 3.
GLC estimate.
b
c
d
e
Reaction conditions: EtONa/EtOH, r.t.: 12 h.
Table 2
NMR data of compounds 2
Compound, R Chemical shift (d, ppm)a,b
Coupling constants (J, Hz)
HaHb HaHx HbHx HcHd HcHx HcHy HdHx HdHy HyF
Ha
Hb
Hx
Hc
Hd
Hy
CF3
2a, H
3.20 dd 3.32 dd 4.43 dtd 2.19 ddd 2.32 ddd 4.54 dqd ꢀ75.0 d 14.3 6.9
3.20c 3.20c
4.35 dtd 2.44 dt 2.60 dt n.f.
ꢀ74.0 d 14.3 n.f.
7.3
n.f.
15.0 2.4
15.2 n.f.
11.4 11.4
7.6 6.3
2.4
n.f.
6.6
6.1
2b, 2-CH3
2c, 4-CH3
2d, 2-CH3O
2e, 4-CH3O
3.19 dd 3.38 dd 4.43 dtd 2.20 ddd 2.38 ddd 4.55 dqd ꢀ75.0 d 14.4 7.3
7.3
n.f.
15.0 2.2
15.1 n.f.
11.5 11.3
7.5 6.2
2.2
n.f.
6.6
6.5
n.f. n.f. 4.31 dtd 2.50 dt 2.63 dt n.f. ꢀ74.5 d n.f. n.f.
3.14 dd 3.29 dd 4.38 dtd 2.19 ddd 2.30 ddd 4.53 dqd ꢀ75.0 d 14.3 7.1
3.14 3.14 4.33 dtd 2.43 dt 2.59 dt n.f. n.f.
ꢀ74.4 d n.f.
7.2
n.f.
15.0 2.4
15.1 n.f.
11.5 11.3
7.5 6.3
2.4
n.f.
6.6
6.4
3.23 dd 3.32 dd 4.52 dtd 2.18 ddd 2.33 ddd 4.56 dqd ꢀ75.0 d 13.9 7.1
7.1
5.7
15.0 2.3
15.0 n.f.
11.5 11.5
7.5
2.3
6.6
6.5
3.14 dd 3.27 dd 4.36c
2.43 dt 2.57 ddd n.f.
ꢀ74.7 d 14.0 7.7
7.01 n.f.
2.5
3.13 dd 3.32 dd 4.38 dtd 2.18 ddd 2.29 ddd 4.54 dqd ꢀ75.0 d 14.4 7.1
3.13 3.13 4.31 dtd 2.41 dt 2.59 dt n.f. n.f.
ꢀ74.4 d n.f.
7.1
n.f.
15.0 2.5
15.2 n.f.
11.4 11.1
7.6 6.25 n.f.
6.6
6.4
2f, 3,4-CH3O 3.13 dd 3.29 dd 4.40 dtd 2.20 ddd 2.30 ddd 4.54 dqd ꢀ75.0 d 14.3 7.1
7.01 15.0 2.4
11.3 11.2
7.6 6.3
2.5
n.f.
6.6
6.5
n.f. n.f. 4.34 dt 2.42 dt 2.59 dt n.f. ꢀ74.4 d n.f. n.f.
n.f.
15.1 n.f.
2g, 2-OH
3.26 dd 3.32 dd 4.53 dtd 2.24 ddd 2.36 ddd 4.60 dqd ꢀ75.0 d 14.0 7.1
3.18 dd 3.26 4.43 dt 2.43 dt 2.61 dt n.f.
ꢀ74.6 d 14.2 7.7
7.2
n.f.
15.0 2.4
15.1 n.f.
11.4 11.4
7.5 6.3
2.4
n.f.
7.6
6.1
2h, 3-CH3OH 3.11 dd 3.27 dd 4.36 dtd 2.19 ddd 2.29 ddd 4.53 dqd ꢀ75.0 d 14.3 7.3
7.1
n.f.
15.0 2.5
15.1 n.f.
11.4 11.2
7.6 6.3
2.6
n.f.
6.6
6.5
4-OH
n.f.
3.18 dd 3.26 dd 4.38 dtd 2.18 ddd 2.32 ddd 4.53 dqd ꢀ75.0 d 14.4 6.6
3.08 dd 3.20 4.30 dt 2.44 dt 2.59 dt n.f.
ꢀ74.4 d 14.5 8.5
3.18 dd 3.27 dd 4.38 dtd 2.19 ddd 2.32 ddd 4.53 dqd ꢀ75.0 d 14.4 6.6
3.10 dd 3.20 4.30 dt 2.44 dt 2.59 dt n.f.
ꢀ74.4 d 14.4 8.2
2l, 1,2,3,4,5-F 3.30 dd 3.38 dd 4.41 dtd 2.24 ddd 2.44 ddd 4.51 dqd ꢀ75.0 d 14.9 5.8
n.f. n.f. 4.34 2.54 dt 2.65 dt n.f. n.f.
ꢀ74.6 d n.f.
3.62 dd 3.82 dd 4.54 dtd 2.24 ddd 2.46 ddd 4.62 dqd ꢀ75.0 d 14.5 7.5
n.f.
4.32 dt
2.41 dt
2.59 dt
n.f.
ꢀ74.0 d n.f.
n.f.
2j, 4-Cl
7.5
n.f.
15.0 2.3
15.1 n.f.
11.4 11.4
7.6 6.3
2.3
n.f.
6.8
6.3
2k, 4-F
7.4
n.f.
15.0 2.4
15.1 n.f.
11.5 11.4
7.5 6.3
2.3
n.f.
6.4
6.5
8.6
n.f.
14.8 2.3
15.1 n.f.
11.4 11.5
7.6 6.3
2.5
n.f.
6.2
6.2
2n, 1-Naftyl
7.1
n.f.
15.0 2.3
15.3 n.f.
11.6 11.4
7.6 6.2
2.2
n.f.
6.6
6.4
c
3.68 dd n.f.
4.36c dt 2.56 dt
2.68 dt
ꢀ74.5 d 14.5 6.5
n.f.: not found.
a
Spectra of all compounds 2 exhibit the expected signals of the aromatic ring protons and the substituents R protons.
For each compound, the upper row contains NMR data for the major diastereoisomer and the lower row for the minor diastereoisomer.
The signal is overlapped by the signal of the major diastereoisomer.
b
c

724
J. Ignatowska, W. Dmowski / Journal of Fluorine Chemistry 127 (2006) 720–729
Scheme 2.
Scheme 3.
of 28%. The reactions of CF3CHClBr with 2-allylfuran and 2-
allylthiofuran resulted in a polymeric tar.
with maleic anhydride gave adduct 13 as the only product
in 33% yield, while from the dimethoxy substituted diene
4f, a 46% yield of a mixture of the expected adduct 14
and aromatized compound 15 was obtained (Scheme 6).
Similarly, cycloaddition of methoxy substituted diene 4e with
diethyl acetylenedicarboxylate resulted in a mixture of normal
and aromatized adducts 16 and 17 in over 80% total yield
(Scheme 7). These results confirm the effectiveness of
trifluoromethyl substituted dienes 4 as components of the
2 + 4 cycloaddition reactions. The presence of electron
donating substituents in the aromatic ring of these dienes
enhances their reactivity.
Dienes, terminally substituted with the trifluoromethyl
group have been previously synthesized by the ene reactions of
trifluoromethyl carbonyl compounds followed by dehydration
of the resultant homoallylic alcohols [10,11]. Such dienes
were reported to be sufficiently reactive to undergo Diels-
Alder condensation with active dienophiles to give trifluor-
omethylated cyclohexenes, albeit the reaction of 4a with
maleic anhydride gave only 23% yield of the cycloadduct [11].
With the aim to check the reactivity of dienes 4, cycloaddition
reactions of 4a, 4e and 4f were carried out. The reaction of 4a
Table 3
NMR data of compounds 4
Compound, R
Chemical shift (d, ppm)a,b
Coupling constants (J, Hz)
Ha
Hb
Hc
Hd
CF3
HaHb
HbHc
HcHd
HdF
4a, H
6.75 dd
6.68 dd
6.81 d
7.06 d
6.90 ddq
6.94 ddq
6.89 ddq
6.96 ddq
6.86c
5.79 dq
5.79 dq
5.76 dq
6.03 dq
5.72 dq
5.76 dq
5.82 dq
6.10 dq
6.00 dq
6.16 dq
ꢀ63.7 d
ꢀ63.7 d
ꢀ63.6 d
ꢀ62.7 d
ꢀ63.5 d
ꢀ63.5 d
ꢀ63.7 d
ꢀ62.9 d
ꢀ62.9 d
ꢀ62.8 d
15.6
15.4
15.5
10.0
10.8
10.0
10.6
10.6
10.5
10.2
15.3
15.4
15.3
15.3
15.3
15.4
15.3
15.3
15.5
15.3
7.0
7.1
7.0
7.4
7.0
7.0
7.0
7.3
7.3
7.3
4b, 2-CH3
4c, 4-CH3
4d, 2-CH3O
4e, 4-CH3O
4f, 3,4-CH3O
4i, 4-Br
4j, 4-Cl
4k, 4-F
4e, Ar = 1-naphtyl
6.72 dd
e
6.79 d
e
6.74 dd
6.74 d
15.6
15.6
15.3
6.64 dd
d
6.76 d
d
6.89c
6.88 ddq
e
e
e
e
e
e
7.57c
7.13 dd
7.29 ddq
15.3
10.7
a
Spectra of all compounds 4 exhibit the expected signals of the aromatic ring protons and the substituents R protons.
Signals of Ha, Hb and Hc protons appear as the ABX system.
b
c
Overlapped by signals of the phenyl ring protons.

J. Ignatowska, W. Dmowski / Journal of Fluorine Chemistry 127 (2006) 720–729
725
Scheme 4.
Scheme 5.
In conclusion, sodium dithionite initiated addition of
CF3CHClBr to allylaromatics, followed by dehydrohalogena-
tion of the adducts, provides an easy and effective way to dienes
with terminal CF3 groups. These dienes were found to be
sufficiently reactive to undergo Diels-Alder condensation with
active dienophiles to give trifluoromethylated carbocycles. The
reaction is, however, less or not applicable for the addition of
CF3CHClBr to allylheterocycles.
Scheme 6.

726
J. Ignatowska, W. Dmowski / Journal of Fluorine Chemistry 127 (2006) 720–729
Scheme 7.
PhCH2CH CH+); 91 (100, PhCH2 ).
+
3. Experimental
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-2-methylben-
zene (2b): 332, 330, 328 (2, 8, 6, M+); 249, 251 [6, 2 (M-
Melting points were determined in capillaries and boiling
points were measured during distillation; both are uncorrected.
1H NMR and 19F NMR spectra were recorded with a Varian 400
spectrometer, both in CDCl3 or C2D6CO (compounds 4)
solutions. Chemical shifts are quoted in ppm from internal TMS
Br)+]; 131 (4); 117 (5); 105 [100 (C8H9)+]; 91 (5, PhCH2 ).
+
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-4-methylben-
zene (2c): 332, 330, 328 (2, 7, 5, M+); 249, 251 [4, 2 (M-
+
Br)+]; 131 (6); 117 (5); 105 [100 (C8H9)+]; 91 (4, PhCH2 ).
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-2-methoxyben-
1
for H nuclei and from internal CFCl3 for 19F nuclei. GLC
analyses were performed with a Shimadzu GC-14A Chroma-
tograph using a 3.5 m ꢂ 2 mm column packed with 5% silicone
oil SE-52 on Chromosorb. GC–MS analyses were performed
with a Hewlett-Packard 5890 apparatus (30 m capillary
column, HP-5 oil). Mass spectra of pure compounds were
obtained with an AMD-604 spectrometer and IR spectra with a
Perkin-Elmer Spectrum 2000 instrument.
zene (2d): 348, 346, 344 (3, 14, 11, M+); 267, 265 [3, 8 (M-
Br)+]; 229 (4); 121 [100 (C8H9O)+]; 91 (34, PhCH2 ).
+
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-4-methoxyben-
zene (2e): 348, 346, 344 (7, 29, 22, M+); 267, 265 [7, 19 (M-
Br)+]; 147 (4); 121 [100 (C8H9O)+].
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-3,4-dimethoxy-
benzene (2f): 378, 376, 374 (5, 20, 16, M+); 297, 295 [8, 4
(M-Br)+]; 178 (3); 151 [100 (C9H11O2)+].
1-Bromo-1-chloro-2,2,2-trifluoroethane was a commercial
reagent (FLUKA). Allylbenzenes 1a–1l, allylnaphthalene 1n
and allylpyridines 1o–1p were prepared by allylation of the
adequate magnesium aryl bromides with allylbromide [12–15].
2-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-phenol
(2g):
334, 332, 330 (1, 6, 4, M+); 252, 250 [6, 4 (M-HBr)+];
133 (12); 119 (8); 107 [100 (C6H7O)+].
4-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-2-methoxyphe-
nol (2h): 364, 362, 360 (2, 8, 6, M+); 283, 281 [3, 8 (M-Br)+];
164 (4); 137 [100 (C8H9O2)+].
3.1. General procedure for the reactions of CF3CHClBr
with allylbenzenes
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-4-bromoben-
zene (2i): 396, 394, 392 (16, 35, 18, M+); 315, 313 [8, 6 (M-
Br)+]; 171 (99); 169 [100 (C7H6Br)+]; 116 (4).
Sodium dithionite (2.1 g, 10 mmol [85%]) and sodium
hydrogen carbonate (2.52 g, 30 mmol) were suspended in a
water–acetonitrile solution (1:1, 40 ml). The reaction mixture
was stirredvigorouslyat ambient temperatureandallylbenzene 1
(10 mol) and 1-bromo-1-chloro-2,2,2-trifluoroethene (3.95 g,
20 mol) were added one by one. Gas evolution (CO2) occurred
which ceased after about 1 h. Stirring was continued for 24 h at
ambient temperature then water (30 ml) was added, the reaction
mixture was extracted with diethyl ether (3 ꢂ 40 ml) and the
combinedextractsweredriedoverMgSO4.Thecrudemixturesof
products obtained after removal of the solvent were purified by
column chromatography (silica gel, hexanes or hexanes–ethanol,
4:1)togivemixturesof2and3ascolorlessoils.Totalyieldsofthe
productsareshowninTable1andtheNMRdataforcompounds2
(two diastereoisomers in a 3:1–4:1 ratio) are collected in Table 2.
The MS data for compounds 2 are given below.
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-4-chloroben-
zene (2j): 352, 350, 348 (4, 9, 5, M+); 269, 271 [4, 2 (M-
Br)+]; 181 (3); 131 (16); 127 (32); 125 [100 (C7H6Cl)+].
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-4-fluoroben-
zene (2k): 336, 334, 332 (2, 8, 6, M+); 255, 253 [1, 4 (M-
Br)+]; 147 (1); 135 (8); 109 [100 (C7H6F)+].
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)-2,3,4,5,6-penta-
fluorobenzene (2l): 408, 406, 404 (3, 11, 9, M+); 327, 325 [7,
21 (M-Br)+]; 207 (5); 181 [100 (C7H2F5)+].
1-(2-Bromo-4-chloro-5,5,5-trifluoropentyl)naphthalene
(2n): 368, 366, 364 (5, 18, 14, M+); 287, 285 [3, 5 (M-Br)+];
249 (2); 153 (6); 141 [100 (C11H9)+].
3.2. Reductive debromination of selected compounds 2
MS (EI, 70 eV): m/z (rel. int., ion):
Zinc powder (1.2 g, 18 mmol) was added to a solution of a
mixture of compounds 2 and 3 (6.4 mmol, 2/3 ratio as in
Table 1) in ethanol (50 ml) and the reaction mixture was
(2-Bromo-4-chloro-5,5,5-trifluoropentyl)benzene (2a): 318,
316, 314 (5, 22, 17, M+); 237, 235 [9, 24 (M-Br)+]; 117 (13,

J. Ignatowska, W. Dmowski / Journal of Fluorine Chemistry 127 (2006) 720–729
727
refluxed for 12 h. After cooling to ambient temperature, brine
(100 ml) was added, organic oil was extracted with diethyl
ether (4 ꢂ 40 ml) and the combined extracts were dried over
MgSO4. The crude product obtained after removal of the
solvent was purified by column chromatography (silica gel,
hexanes or hexanes–ethanol) to give compounds 3 as colorless
oils (GLC purity 91–94%).
(E,E-5,5,5-Trifluoropenta-1,3-dienyl)benzene (4a): mp 32–
33 8C. MS (EI, 70 eV): m/z (rel. int., ion): 198 (99, M+); 179 [10
(M-F)+]; 177 (21); 129 [100 (M-CF3)+]. Analysis—found: C,
66.8%, H, 4.4%, F, 28.2%. Calculated for C11H9F3 (198.18): C,
66.7; H, 4.6; F, 28.7%.
1-Methyl-2-(E,E-5,5,5-trifluoropenta-1,3-dienyl)benzene
(4b): colorless liquid, GLC purity 90% (7% of 3b). MS (EI,
70 eV): m/z (rel. int., ion): 212 (84, M+); 197 [19 (M-CH3)+];
193 [6 (M-F)+]; 177 [32 (M-CH3-HF)+]; 143 [62 (M-CF3)+];
128 [35 (M-CF3-CH3)+]; 115 (9). HRMS—found: 212.08089.
Calculated for C12H11F3: 212.08129.
(4-Chloro-5,5,5-trifluoropentyl)benzene (3a)—yield: 83%.
1H NMR d: 1.7–1.9 (complex AB system, CH2); 2.00 (m, CH2);
3
3
2.66 (m, PhCH2); 4.06 (dqd, JHH = 10.1 Hz, JHF = 6.6 Hz,
3JHH = 3.0 Hz, CHClCF3); 7.18 (m, 1H, Ph); 7.21 (m, 2H, Ph);
3
7.30 (m, 2H, Ph); 19F NMR d: ꢀ75.2 (d, JHF = 6.6 Hz,
1-Methyl-4-(E,E-5,5,5-trifluoropenta-1,3-dienyl)benzene
(4c): mp 80–83 8C. MS (EI, 70 eV): m/z (rel. int., ion): 212 (96,
M+); 197 [24 (M-CH3)+]; 193 [7 (M-F)+]; 177 [42 (M-CH3-
HF)+]; 143 [100 (M-CF3)+]; 128 [68 (M-CF3-CH3)+]; 115 (13).
Analysis—found: C, 67.7; H, 4.95; F, 26.6%. Calculated for
C12H11F3 (212, 21): C, 67.9; H, 5.2; F, 26.9%.
CF3); MS (EI, 70 eV): m/z (rel. int., ion): 238, 236 (7, 22, M+);
+
+
+
117 (3, C9H9 ); 105 (5, PhCH2CH2 ); 91 (100, PhCH2 ).
HRMS—found: 236.05783. Calculated for C11H12ClF3:
236.05796.
1-(4-Chloro-5,5,5-trifluoropentyl)-4-fluorobenzene (3k)—
yield: 42%. 1H NMR d: 1.6–1.85 (complex AB system,
CH2); 1.98 (m, CH2); 2.64 (m, PhCH2); 4.07 (dqd,
1-Methoxy-2-(E,E-5,5,5-trifluoropenta-1,3-dienyl)benzene
(4d): colorless liquid, GLC purity 94% (3% of 3d). MS (EI,
70 eV): m/z (rel. int., ion): 228 (100, M+); 209 [8 (M-F)+]; 177
[9 (M-OCH3-HF)+]; 159 [55 (M-CF3)+]. HRMS—found:
228.07610. Calculated for C12H11F3O: 228.07620.
3
3
3JHH = 9.9 Hz, JHF = 6.5 Hz, JHH = 3.1 Hz, CHClCF3); 6.98
(tm, 3JHF = 3JHH = 8.8 Hz, 2H, Ph); 7.10 (ddm, 3JHH = 8.8. Hz,
4JHF = 5.5 Hz, 2H, Ph); 19F NMR d: ꢀ75.1 (d, JHF = 6.5 Hz,
3
3
4
CF3); ꢀ117.6 (tt, JHF = 8.8 Hz, JHF = 5.5 Hz, 1Farom); MS
(EI, 70 eV): m/z (rel. int., ion): 256, 254 (5, 15, M+); 218 [1 (M-
HCl)+]; 135 (4, C9H8F+); 109 [100 (C7H6F)+]. HRMS—found:
254.04759. Calculated for C11H11ClF4: 254.04854.
1-Methoxy-4-(E,E-5,5,5-trifluoropenta-1,3-dienyl)ben-
zene (4e): mp 76–78 8C. MS (EI, 70 eV): m/z (rel. int., ion):
228 (100, M+); 209 [8 (M-F)+]; 159 [59 (M-CF3)+]; 144 [29,
M-CF3-CH3)+]. Analysis—found: C, 63.2: H, 4.7; F,
24.9%. Calculated for C12H11F3O (228.21): C, 63.2; H, 4.9;
F, 25.0%.
1-(4-Chloro-5,5,5-trifluoropentyl)-2,3,4,5,6-pentafluoro-
benzene (3l)—yield: 50%. 1H NMR d: 1.7–1.9 (m, CH2); 2.00
(m, CH2); 2.02 (m, 2H, CH2); 2.77 (m, PhCH2); 4.10 (dqd,
1,2-Dimethoxy-4-(E,E-5,5,5-trifluoropenta-1,3-dienyl)-
benzene (4f): mp 79–80 8C. MS (EI, 70 eV): m/z (rel. int., ion):
258 (100, M+); 239[10 (M-F)+]; 227 [16 (M-OCH3)+]; 189 [75
(M-CF3)+]; 174 [13 (M-CF3-CH3)+]; 158 [13 (M-CF3-
OCH3)+]. Analysis—found: C, 60.5; H, 4.8; F, 22.2%.
Calculated for C13H13F3O2 (258): C, 60.5; H, 5.1; F, 22.1%.
1-Bromo-4-(E,E-5,5,5-trifluoropenta-1,3-dienyl)benzene
(4i): mp 43–45 8C. MS (EI, 70 eV): m/z (rel. int., ion): 278, 276
(65, M+); 209 [3 (M-CF3)+]; 197 [40 (M-Br)+]; 177 [100 (M-Br-
HF)+]; 171 [22]; 169 [22]; 128 [76 (M-CF3-Br)+]. Analysis—
found: C, 47.5; H, 2.7; F, 20.2%. Calculated for C11H8F3Br
(277.08): C, 47.7; H, 2.9; F, 20.6%.
3
3
3JHH = 10.0 Hz, JHF = 6.6 Hz, JHH = 3.2 Hz, CHClCF3); 19F
3
NMR d: ꢀ75.2 (d, JHF = 6.6 Hz, CF3); ꢀ144.6 (dd,
4
3
3JFF = 21.9 Hz, JFF = 8.6 Hz, 2Farom); ꢀ157.3 (t, JFF
=
3
20.7 Hz, 1Farom); ꢀ162.7 (td, JFF = average 21.3 Hz,
4JFF = 8.6 Hz, 2F). MS (EI, 70 eV): m/z (rel. int., ion): 328,
326 (4, 13, M+); 290 [2 (M-HCl)+]; 207 (6, C9H4F5 ); 181 [100
+
(C7H2F5)+]; HRMS—found: 326.01058. Calculated for
C11H7F8Cl: 326.01085.
3.3. General procedure for dehydrohalogenation of
compounds 2
1-Chloro-4-(E,E-5,5,5-trifluoropenta-1,3-dienyl)benzene
(4j): mp 43–44 8C. MS (EI, 70 eV): m/z (rel. int., ion): 232, 234
(61, M+); 197 [54 (M-Cl)+]; 177 [100 (M-HF-Cl)+]; 163 [26 (M-
CF3)+]; 128 [84 (M-CF3-Cl)+]; 127 [54 (M-CF3-HCl)+].
Analysis—found: C, 56.3; H, 3.2; F, 24.0%. Calculated for
C11H8F3Cl (232.63): C, 56.8; H, 3.5; F, 24.5%.
A mixture of compounds 2 and 3 (12–25 mmol, 2/3 ratio as
in Table 1) was dissolved in hexane (50–100 ml) and
3 equivalents of DBU was added dropwised. A precipitate
was immediately formed. After refluxing for 12–18 h, the
mixture was cooled to ambient temperature and 5% hydro-
chloric acid (20 ml) was added. The hexane layer was
separated, washed with 5% HCl followed by brine and dried
over MgSO4. Evaporation of the solvent gave solid (in most
cases) or oily (4b, 4d and 4k) material. Recrystallization of
solid products from hexane or hexane–ethanol gave pure
compounds 4a–4c, 4e, 4f, 4i, 4j and 4n as white crystals. Liquid
compounds 4b, 4d and 4k were purified by column
chromatography (silica gel, hexane or hexane–ethanol).
Isolated yields and melting points of compounds 4 are collected
in Table 1. The MS data and elemental analyses are given
below.
1-Fluoro-4-(E,E-5,5,5-trifluoropenta-1,3-dienyl)benzene
(4k): colorless liquid, GLC purity 80% (15% of 3k). MS (EI,
70 eV): m/z (rel. int., ion): 216 (50, M+); 197 [7 (M-F)+]; 147
[100 (M-CF3)+]; 127 [26 (M-CF3-HF)+]; [109 (96, C7H6F)+,
3k]. HRMS—found: 216.05656. Calculated for C11H8F4:
216.05621.
1-(E,E-5,5,5-Trifluoropenta-1,3-dienyl)naphthalene (4n):
mp 50–52 8C. MS (EI, 70 eV): m/z (rel. int., ion): 248 (74,
M+); 229 [4 (M-F)+]; 179 [100 (M-CF3)+]. Analysis—found: C,
72.1; H, 4.2; F, 22.6%. Calculated for C15H11F3 (248.24): C,
72.6; H, 4.5; F, 23.0%.

728
J. Ignatowska, W. Dmowski / Journal of Fluorine Chemistry 127 (2006) 720–729
3.4. Preparation of 2-(2-chloro-3,3,3-trifluoropropyl)-2,3-
dihydrobenzofuran (5)
in hexanes as described in Section 3.3 and purified by column
chromatography (silica gel, hexanes–AcOEt, 5:1) to give a
yellowish oil (0.36 g, total yield 28%) consisted of inseparable
compounds 11 and 12 in a 4:1 ratio (19F NMR estimate).
3-(4-Chloro-5,5,5-trifluoropentyl)pyridine (11): H NMR:
1.80 (m, 2H); 2.02 (m, 2H); 2.67 (m, 2H); 4.10 (dqd,
Compound 2g (1.5 g, 4.5 mmol) was added to ethanolic
sodium ethoxide (4.6 mmol) solution and the reaction mixture
was stirred at ambient temperature for 24 h. The reaction was
quenched with 5% hydrochloric acid (15 ml) and the organic
material was extracted with ether (2 ꢂ 30 ml), the extract was
washed with 5% hydrochloric acid followed by water and dried
over Na2SO4. The crude product obtained after evaporation of
the solvent was purified by column chromatography (silica gel,
hexanes–ethanol, 4:1) to give 5 as colorless oil (0.6 g, two
diastereoisomers in a 3.8:1 ratio). Yield: 52%, GLC purity:
90%. Major isomer: 1H NMR: 2.38 (narrow AB system,
1
3JHH = 10.0 Hz, 3JHF = 6.6 Hz, 3JHH = 3.0 Hz, 1H, CHCl). 19
F
3
NMR: ꢀ75.2 (d, JHF = 6.6 Hz, CF3). GC–MS: m/z (rel. int.,
ion): 239, 237 (10, 30, M+); 106 [6 (C7H8N)+]; 92 [100
(C6H6N)+].
1
3-(5,5,5-Trifluoropenta-1,3-dienyl)pyridine (12): H NMR:
3
3
5.68 (dq, JHH = 15.2 Hz, JHF = 6.9 Hz, 1H, H4); 6.91 (ddq,
4
3JHH = 15.2 and 10.6 Hz, JHF = 2.1 Hz, 1H, H3). 19F NMR:
3
4
ꢀ64.0 (dd, JHF = 6.9 Hz, JHF = 2.1 Hz, CF3). GC–MS: m/z
(rel. int., ion): 199 (60, M+); 180 [6 (M-F)+]; 130 [100 (M-
CF3)+]; 103 (15, C7H5N+); 77 [12 (C5H3N)+].
2
2JHH = 14.5 Hz, 2H, CH2CHCl); 2.90 (dd, JHH = 15.4 Hz,
2
3
3JHH = 7.0 Hz, 1H); 3.38 (dd, JHH = 15.4 Hz, JHH = 9.0 Hz,
3
3
1H); 4.36 (dq, JHH = 7.8 Hz, JHF = 6.5 Hz, 1H, CHCl); 5.00
(dq, 3JHH = 9.0 and 7.0 Hz, 1H); 6.79 (m, 1H, arom.); 6.87 (m,
1H, arom.); 7.15 (m, 2H, arom.). 19F NMR: ꢀ74.65 (d,
The 1H NMR signals of the pyridine ring protons of both 11
and 12 and of two vinylic protons of 12 appeared within the
range of 6.8–8.7 ppm and overlapped each other.
1
3JHF = 6.5 Hz, CF3). Minor isomer: H NMR: ca. 2.4 (over-
lapped by signal of the major isomer, 2H), ca. 2.9 (overlapped,
2
3.7. Reactions of compounds 4 with dienophiles
3
1H); 3.34 (dd, JHH = 15.6 Hz, JHH = 9.0 Hz, 1H); 4.54 (dqd,
3JHH = 11.8 Hz, 3JHF = 6.5 Hz, 3JHH = 2.1 Hz, 1H, CHCl); 5.07
3.7.1. Reaction of 4a with maleic anhydride
3
(m, 1H). 19F NMR: ꢀ75.5 (d, JHF = 6.5 Hz, CF3). HRMS—
Diene 4a (1.48 g, 7.5 mmol), maleic anhydride (0.78 g,
8 mmol) and mesitylene (1 ml) were heated at reflux for 48 h.
After cooling to ambient temperature, the reaction mixture was
dissolved in ethyl acetate, the solution was washed with water
(removal of maleic anhydride), dried over MgSO4. A solid
material obtained after removal of the solvents was purified by
column chromatography (silica gel, hexanes–ethanol, 4:1) to
give compound 13 as brownish solid (0.74 g, yield: 33%).
4-Phenyl-7-trifluoromethyl-3a,4,7,7a-tetrahydroisobenzo-
found: 250.03628. Calculated for C11H10ClF3O: 250.03723.
3.5. Reaction of CF3CHClBr with 2-allylpyridine
2-Allylpyridine (6) (0.23 g, 2.3 mmol), CF3CHClBr (0.92 g,
4.7 mmol), Na2S2O4 (0.5 g, 2.3 mmol) and NaHCO3 (0.57 g,
6.9 mmol) were reacted in a MeCN–H2O solution as in Section
3.1. GLC analysis of an aliquot taken after 24 h showed only
partial conversion of 6. Additional portion of Na2S2O4 (0.25 g)
and CF3CHClBr (0.46 g) were added and the reaction was
continued for another 24 h and worked up. An oily product
obtained after column chromatography (0.23 g, total yield
22%) consisted of compounds 7–9 in a 1:2:2 ratio (GC–MS
identification only).
1
furan-1,3-dione (13): mp 165–168 8C. H NMR (in acetone-
3
d6): 3.72 (m, 1H); 4.02 (m, 1H); 4.14 (dd, JHH = 9.2, 6.8 Hz,
1H); 4.24 (dd, 3JHH = 9.2, 6.2 Hz, 1H); 6.30 (m, 1H); 6.72 (m,
1H); 7.32 (m, 2H, arom.); 7.40 (m, 3H, arom.). 19F NMR (in
acetone-d6): ꢀ61.9 (3JHF = 10.3 Hz, CF3). MS (EI): m/z (rel.
int., ion): 296 (35, M+); 268 [10 (M-CO)+]; 224 [18 (M-
C2O3)+]; 223 [26 (M-C2HO3)+]; 198 [75 (M-C4H2O3)+]; 183
GC–MS: m/z (rel. int., ion):
+
(12); 155 (30); 129 (100, C10H9 ). Analysis—found: C, 60.9;
H, 3.7; F, 19.2%. Calculated for C15H11F3O3 (296.24): C, 60.8;
H, 3.7; F, 19.4%.
2-(4-Chloro-5,5,5-trifluoropentyl)pyridine (7): 202 [100 (M-
Cl)+]; 182 [30 (M-Cl-HF)+]; 120 [60 (C8H10N)+]; 106 [20
(C7H8N)+]; 93 [50 (C6H7N)+]; 78 [15 (C5H4N)+].
2-(5,5,5-Trifluoropenta-1,3-dienyl)pyridine (8): 199 (40,
M+); 180 [8 (M-F)+]; 130 [100 (M-CF3)+]; 78 [10 (C5H4N)+].
2-(4-Chloro-5,5,5-trifluoropent-1-enyl)pyridine (9): 237,
235 (7, 20, M+); 200 [33 (M-Cl)+]; 180 [10 (M-Cl-HF)+];
130 [25 (M-Cl-CF3)+]; 118 [100 (C8H8N+]; 78 [12
(C5H4N)+].
3.7.2. Reaction of 4f with maleic anhydride
Compound 4f (0.52 g, 2 mmol), maleic anhydride (0.25 g,
2.5 mmol) and CHCl2CHCl2 (1 ml) were heated at reflux for
48 h and worked up as above. Purification of the crude product
by column chromatography (silica gel, hexanes–ethyl acetate,
3:2) gave a 2:1 mixture of compounds 14 and 15 (19F NMR
estimate) as yellowish solid (mp 134–138 8C, 0.33 g, total
yield: 46%).
3.6. Reaction of CF3CHClBr with 3-allylpyridine
4-(3,4-Dimethoxyphenyl)-7-trifluoromethyl-3a,4,7,7a-tet-
rahydroisobenzofuran-1,3-dione (14): 1H NMR: 3.26 (m, 1H);
3.69 (m, 2H); 3.81 (dd, 3JHH = 8.6, 6.8 Hz, 1H); 3.87 (s, CH3);
3.89 (s, CH3); 6.21 (ddd, 3JHH = 9.4, 3.3, 2.2 Hz, 1H, vinylic);
3-Allylpyridine (10) (0.74 g, 6.2 mmol), CF3CHClBr
(2.45 g, 12 mol), Na2S2O4 (1.3 g, 6.2 mmol) and NaHCO3
(1.56 g, 18.6 mmol) were reacted as in Section 3.5. The crude
mixture of products, obtained after extraction with Et2O and
removal of the solvent, was treated with DBU (2.8 g, 18 mmol)
3
6.48 (dm, 3JHH = 9.4 Hz, 1H, vinylic); 6.75 (d, JHH = 2.2 Hz,
3
1H, arom.); 6.82 (dd, JHH = 8.2, 2.0 Hz, 1H, arom.); 6.88 (d,

J. Ignatowska, W. Dmowski / Journal of Fluorine Chemistry 127 (2006) 720–729
729
3JHH = 8.2 Hz, 1H, arom.). 19F NMR: ꢀ66.5 (d, 3JHF = 9.7 Hz,
CF3). GC–MS: m/z (rel. int., ion): 356 (100, M+); 328 [25 (M-
CO)+]; 297 [12 (M-CO-OCH3)+]; 283 [58 (M-CO3H)+]; 189
C2H5OH)+]; 283 [67 (C17H15O4)+]; 255 [100 (C16H15O3)+];
237 (12); 209 (8); 168 (8); 139 (12); 108 (12). HRMS—found:
398.13434. Calculated for C20H21F3O5: 398.13411.
+
+
(62, C12H13O2 ); 128 (23, C10H8 ). HRMS—found:
356.08805. Calculated for C17H15F3O5: 356.08716.
40-Methoxy-4-trifluoromethylbiphenyl-2,3-dicarboxylic
acid diethyl ester (17): 1H NMR: 1.03 (t, 3JHH = 7.15 Hz, CH3);
3
1.38 (t, JHH = 7.15 Hz, CH3); 3.85 (s, OCH3); 4.09 (q,
4-(3,4-Dimethoxyphenyl)-7-trifluoromethyl-isobenzofuran-
1,3-dione (15): 1H NMR: 3.94 (s, CH3); 3.97 (s, CH3); 7.02 (d,
3JHH = 7.15 Hz, CH2); 4.39 (q, 3JHH = 7.15 Hz, CH2); 6.95 (d,
3
3
3JHH = 8.3 Hz, 1H, arom.); 7.12 (d, JHH = 2.06 Hz, 1H,
3JHH = 8.8 Hz, 2H); 7.27 (d, JHH = 8.8 Hz, 2H); 7.78 (d,
3
arom.); 7.16 (dd, JHH = 8.3, 2.06 Hz, 1H, arom.); 7.96 (d,
3
3JHH = 8.6 Hz, 1H); 7.85 (d, JHH = 8.6 Hz, 1H). 19F NMR:
3
3JHH = 8.1 Hz, 1H, vinylic); 8.14 (d, JHH = 8.1 Hz, 1H,
ꢀ59.8 (s, CF3). GC–MS: m/z (rel. int., ion): 396 (100, M+); 368
[4 (M-CO)+]; 351 (12); 303 (33); 283 (17); 207 (12). HRMS—
found: 396.12013. Calculated for C20H19F3O5: 396.11846.
vinylic). 19F NMR: ꢀ61.92 (s, CF3). GC–MS: m/z (rel. int.,
ion): 352 (100, M+); 280 (8); 237 (6); 193 (12). HRMS—found:
352.05671. Calculated for C17H11F3O5: 352.05586.
References
3.7.3. Reaction of 4e with acetylenedicarboxylic acid
diethyl ester
[1] W.Y. Huang, J. Fluorine Chem. 58 (1992) 1–8.
[2] W.Y. Huang, F.H. Wu, Isr. J. Chem. 39 (1999) 167–170.
[3] Y. Shen, J. Wen, J. Fluorine Chem. 113 (2002) 13–15.
[4] A. Wegert, R. Miethchen, H. Hein, H. Reinke, Synthesis (2005) 1850–
1858.
Compound 4e (1.14 g, 5 mmol), diethyl acetylenedicarbox-
ylate (0.89 g, 5 mmol) and catalytic amount of iodine (1–2 mg)
were heated and stirred at 170–180 8C for 48 h. Purification of
the crude product by column chromatography (silica gel,
hexanes–ethanol, 4:1) gave a 3.5:1 mixture of compounds 16
and 17 (19F NMR estimate) as yellow oil (1.62 g, total yield:
82%).
[5] D. Schwa¯bish, R. Miethchen, J. Fluorine Chem. 120 (2003) 85–91.
´
[6] H. Plenkiewicz, W. Dmowski, M. Lipinski, J. Fluorine Chem. 111 (2001)
227–232.
[7] W. Dmowski, J. Ignatowska, J. Fluorine Chem. 123 (2003) 37–42.
[8] W. Dmowski, J. Ignatowska, K. Piasecka-Maciejewska, J. Fluorine Chem.
125 (2004) 1147–1151.
3-(4-Methoxyphenyl)-6-trifluoromethylcyclohexa-1,4-
diene-1,2-dicarboxylic acid diethyl ester (16): 1H NMR: 1.07 (t,
3
3JHH = 7.15 Hz, CH3); 1.28 (t, JHH = 7.15 Hz, CH3); 3.79 (s,
[9] J. Ignatowska, W. Dmowski, unpublished results.
[10] T. Nagai, G. Nishioka, M. Koyama, A. Ando, T. Miki, I. Kumadaki, J.
Fluorine Chem. 57 (1992) 229–237.
OCH3); 4.05 (q, 3JHH = 7.15 Hz, CH2); 4.09 (q,
3JHH = 7.15 Hz, CH2); 4.26 (qd, 3JHF = 7.2 Hz, 3JHH = 3.3 Hz,
1H, CHCF3); ca. 4.3 (1H, overlapped by the signal at 4.26);
5.80 (ddd, 3JHH = 10.0 and 3.9 Hz, 4JHH = 1.3 Hz, 1H, vinylic);
[11] T. Nagai, Y. Nasu, T. Shimada, H. Shoda, M. Koyama, A. Ando, T. Miki, I.
Kumadaki, J. Fluorine Chem. 57 (1992) 245–249.
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34 (1991) 2638–2643.
3
4
6.04 (ddd, JHH = 10.0 and ca. 4 Hz, JHH = ca. 1 Hz, 1H,
3
vinylic); 6.85 (d, JHH = 8.8 Hz, 2H, arom.); 7.16 (d,
[14] J.P. Wibaut, H. Bloemendal, Recl. Trav. Chim. 77 (1958) 123–128.
[15] J.P. Wibaut, H.G.P. van der Voort, Recl. Trav. Chim. 71 (1952) 798–
803.
3JHH = 8.8 Hz, 2H, arom.).19F NMR: ꢀ68.6 (d, 3JHF = 7.2 Hz,
CF3). GC–MS: m/z (rel. int., ion): 398 (8, M+); 352 [14 (M-