Building block synthesis of predominantly (E) symmetrical and unsymmetrical 1,2-difluorostilbenes from 1,2-dibromo-1,2-difluoroethene

Article abstract of DOI:10.1016/j.tet.2013.10.067

An efficient synthesis of predominantly (E) symmetrical or unsymmetrical 1,2-difluorostilbenes based on the Suzuki-Miyaura palladium-catalyzed cross-coupling reaction of arylboronic acids with predominantly (E)-1,2-dibromo-1,2-difluoroethene in the presen

Full text of DOI:10.1016/j.tet.2013.10.067

Tetrahedron 69 (2013) 11191e11196
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Building block synthesis of predominantly (E) symmetrical and
unsymmetrical 1,2-difluorostilbenes from 1,2-dibromo-1,2-
difluoroethene
,
,
Said Eddarir a b, Mohammed Kajjout a, Christian Rolando a
*
a
ꢀ
ꢁ
ꢀ
Universite de Lille 1, Sciences et Technologies, Miniaturisation pour la Synthese, l’Analyse & la Proteomique (MSAP), USR CNRS 3290 and Institut
Michel Chevreul FR CNRS 2698, 59655 Villeneuve d’Ascq Cedex, France
b
ꢀ
ꢀ
ꢀ
Universite Cadi Ayyad, Faculte des Sciences et Techniques Gueliz, BP 549 Marrakech, Morocco
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 August 2013
Received in revised form 12 October 2013
Accepted 23 October 2013
Available online 28 October 2013
An efficient synthesis of predominantly (E) symmetrical or unsymmetrical 1,2-difluorostilbenes based on
the SuzukieMiyaura palladium-catalyzed cross-coupling reaction of arylboronic acids with pre-
dominantly (E)-1,2-dibromo-1,2-difluoroethene in the presence of Cs2CO3 in toluene is described. The
reaction preserved the stereochemistry of the building block and performed in good yield independently
of the electron-withdrawing or electron-donating character of the substituents.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
1,2-Difluorostilbenes
Palladium
Cross-coupling
Catalysis
Building block
1. Introduction
the other hand, the photochemistry of 1,2-difluorostilbenes has
received much attention: they isomerize very efficiently in the Z
Introducing a fluorine atom in an organic compound very often
brings different properties either for biological or in material sci-
ence applications. The special properties of fluorine, such as strong
electronegativity, small size (comparable to hydrogen) and low
polarizability of the CeF bond are responsible for these effects.
Indeed, an increasing number of drugs or photoelectronic devices
contain fluorine, the presence of which often is of major impor-
tance to their activity. There are by far fewer reports in the litera-
ture on disubstituted-1,2-difluorinated olefins when compared to
disubstituted monofluorinated olefins, which have found numer-
ous applications, especially in biology. Analogues of combrestatin,
a natural oxygenated stilbene bearing two fluorine-atoms on the
central double bond, have been synthesized as tubulin aggregation
inhibitors. In most of the cases, the difluorinated analogues were
shown to be as efficient for tubulin aggregation inhibition as their
unfluorinated counterpart but proved to be by far less toxic.1a Very
recently, Dalvit and Vulpetti proposed 1,2-difluoroethene as an
amide (O]CeNH) structural analogue for building peptidomi-
metics by a QSAR approach based on 19F NMR displacement.1b On
isomer by photo-irradiation, as their non-fluorinated analogues but
with little halogen elimination, unlike others halogens, especially
Br and I.2a,2b (Z) 1,2-Difluoristilbenes are also less prone under ir-
radiation to phenantrene formation and are thermally more stable
than their non-fluorinated analogues.2c,2d These properties led to
the introduction of difluoroethene bridges in many conjugated
molecules or materials designed to have opto-electronic properties.
Substituted difluorostilbenes resulted in nematic crystals, the
properties of which can be optimized.3a For example, (E)-1-(trans-
4-alkylcyclohexyl)-2-(4-chlorophenyl)-difluoroethylene has been
shown to grow into nematic crystals that show great promise for
super twisted nematic displays due to their high contrast and rapid
response time, but also due to their improved UV stability.3b-e
Substituted 1,4-bis(1,2-difluoro-2-phenylethenyl)-benzene show
electro-optical properties.4a Due to their enhanced stability they
have found applications as sensors.4b Cyanin dyes linked by a per-
fluorinated polymethine chain, which implies the 1,2-difluroethene
bridge, have been synthesized.5 Theoretical calculations have
shown that 1,2-bis-(3-thienyl)-1,2-difluoroethene derivatives ex-
hibit non-linear optical properties and can act as photoswitches
like their non-fluorinated analogues with modulated properties.6
(E)-1,2-Difluoro-1,2-di-2-thienylethene, (E)-1,2-difluoro-1,2-bis(5-
* Corresponding author. E-mail address: christian.rolando@univ-lille1.fr (C.
Rolando).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.10.067

11192
S. Eddarir et al. / Tetrahedron 69 (2013) 11191e11196
trimethylsilyl-2-thienyl)ethene and (E)-1,2-difluoro-1,2-bis(4-
methoxy-5-trimethylsilyl-2-thienyl)-ethene monomers were pre-
pared and polymerized under controlled oxidation.7a,7b The in-
troduction of fluorine-atoms in the vinylene units yields a blue
optical band gap in the obtained thin films.7c,7d Poly[5,5-(50,60-di-
octy-loxy-40,70-di-2-thienyl-20,10,30-benzothiadiazole)-alt-1,2-
difluorovinylene]polymer have been synthesized and exhibited
also a higher band gap. This material have found applications in
polymer solar cells.8 Difluorinated olefins have also been used as
bridging ligands between organometallic centers.9
catalysis to afford in good yield (Z) difluoroolefins (RCF]CFR) with
a complete retention of the geometry of the double bond. The ob-
tained (E)-1-bromo-1,2-difluoroolefines (RCF]CFBr) could also
been transformed in lithium reagents (RCF]CFLi) by treatment
with butyllithium in THF/Et2O at ꢀ130 ꢁC, then condensed with
electrophiles at the same temperature, with preservation of the
double bond geometry. Recently Giannini et al. used this method to
prepare (Z)-difluorocombretatastin analogues by coupling conve-
niently substituted (E)-b-bromo-a,b-difluorostyrenes with 3,4,5-
trimethoxybenzenboronic acid in presence of palladium.1a
Burton et al. developed several methods for the preparation of
symmetrical or unsymmetrical (E) (and, recently, (Z)) 1,2-
difluorostilbenes. The key compounds in their approach of (E)
isomers are (Z)-(1,2-difluoroethenyl)-tributylstannane (HFC]
These various applications push us to report a novel synthesis of
1,2-difluorostilbenes, symmetrical 3 and unsymmetrical 5 from the
1,2-dibromo-1,2-difluoroethene
1 building block. The cross-
coupling reaction of predominantly (E) 1,2-dibromo-1,2-
difluoroethene with arylboronic acids 2 using palladium(0) as the
catalyst in toluene and cesium carbonate as a base affords, fol-
lowing the protocol established for synthesizing monofluoroolefins
from 1,1-bromofluorolefins by Burton group10 and our group11 (for
reviews see Ref. 12), the expected 1,2-difluorostilbenes either
symmetrical or unsymmetrical in good yield (Scheme 1).
CFSnBu3)
and
(E)-(1,2-difluoro-1,2-ethenediyl)-bis-[tributyl-
stannane], which are obtained in three or four steps. In the first
step chlorotrifluoroethylene (F2C]CFCl) was metalated by n-butyl
lithium in THF at ꢀ80 ꢁC, then reacted with chlorotrimethylsilane
to afford (1,2,2-trifluoroethenyl)-trimethylsilane (F2C]CFSiMe3),
which was not isolated. In the second step (1,2,2-trifluoroethenyl)-
trimethylsilane was reduced in situ by LiAlH4 in THF to afford
a mixture containing predominantly (Z)-(1,2-difluoroethenyl)-tri-
methylsilane (HFC]CFSiMe3) (Z:E, 91:9), which was isolated
by flash distillation. Then (1,2-difluoroethenyl)-trimethylsilane
was reacted in THF with bis(tributyltin)oxide (Bu3SnOSnBu3) in
F
Ar1
F
[Pd]
Ar1
3
Predominantly (E)
OH
OH
F
Br
F
the presence of
a catalytic amount of tetrabutylammonium
Ar1
B
+
fluoride to give the desired, predominantly (Z), (1,2-
difluoroethenyl)-tributylstannane (HFC]CFSnBu3), which could
be further purified by chromatography. Finally (E)-(1,2-difluoro-
1,2-ethenediyl)-bis-[tributylstannane] (Bu3SnFC]CFSnBu3) was
obtained by metalating the monostannane by lithium, 2,2,6,6-
tetramethylpiperidide (LiTMP) in THF at ꢀ90 ꢁC and trapping
the intermediate with tributyltin chloride.18a Symmetrical (E)-1,2-
difluorostilbenes were readily obtained via stereospecific
Pd(0) coupling of (E)-(1,2-difluoro-1,2-ethenediyl)-bis-[tributyl-
stannane] (Bu3SnFC]CFSnBu3) with aryliodides using Pd(PPh3)4/
CuI as a catalyst in StilleeLiebeskind conditions.18b Unfortunately
(Z)-(1,2-difluoro-1,2-ethenediyl)-bis-[tributylstannane] stereoiso-
mers afforded no coupling products in the same conditions.
Nevertheless, unsymmetrical (Z)-1,2-distilbenes were obtained
using a combination of the previously described protocols. First,
(E)-(1,2-difluoroethenyl)-trimethylsilane, obtained by the photo-
isomerization of the (Z) isomer by UV light in presence of a cata-
lytic amount of phenyldisulfide. (E)-(1,2-Difluoroethenyl)-trime-
thylsilane was converted into (E)-1,2-difluorovinyliodide (HFC]
CFI) by iodine at room temperature.18c (E)-1,2-difluorovinyliodide
(HFC]CFI) was treated with zinc and coupled with aryliodide
Br
2
1
OH
OH
F
Br
+
F
F
Ar2
F
Predominantly (E)
[Pd]
Ar
B
2
[Pd]
Ar1
Ar1
4
2
5
Predominantly (E)
Scheme 1. Synthesis of 1,2-difluorostilbenes.
2. Results and discussion
In the literature only a few studies have described the synthesis
of 1,2-difluoroolefins in a simple, versatile, and stereoselective
manner. The most important syntheses are summarized below.
Dixon first reported the preparation of symmetrical (E)-1,2-
difluorostilbenes via the reaction of tetrafluoroethene with phe-
nyllithium in ether at ꢀ60 ꢁC.13 Unsymmetrical (E)-1,2-
difluorostilbenes have been obtained via the reaction of tri-
fluorostyrenes and aryllithiums in hexane at ꢀ80 ꢁC.14 Tri-
fluorostyrene precursors were obtained by treatment of
iodobenzenes with tetrafluoethylene in the presence of n-butyl
lithium in a mixture of n-hexane and diethyl ether at ꢀ80 ꢁC. Re-
cently, trifluorostyrenes have been obtained by the reaction of
phenyl boronic acids with chloro- or bromotrifluoroethylene cat-
alyzed by palladium.15 The Dixon synthesis has been employed for
the synthesis of opto-electronic materials and in the polymer
field.7b,16
using palladium catalysis affording (Z)-
a,b-difluorostyrene
(PhFC]CHF). In turn (Z)- -difluorostyrene was transformed into
a,b
(E)-1,2-difluoro-2-aryl-tributylstannylethenes by metalation by
lithium 2,2,6,6-tetramethylpiperidide (LiTMP) and trapping at
ꢀ78 ꢁC with tributyltin chloride.18d Then (E)-1,2-difluoro-2-aryl-
tributylstannylethenes were coupled with the second aryliodide in
the StilleeLiebeskind conditions described above to afford (Z)-1,2-
difluorostilbenes.18e
Shimizu and Kuroboshi et al. have developed a highly stereo-
selective synthesis of (E) and (Z)
b-bromo-a,b-difluorostyrene
(ArCF]CFBr) from ArCH(OH)CFBr2.17 The treatment of tribromo-
fluoromethane (CBr3F) with BuLi in a mixture of THF and Et2O at
ꢀ130 ꢁC afforded dibromofluoromethyl lithium, which was reacted
with an aldehyde to give the fluorinated alcohol (ArCH(OH)CFBr2).
This alcohol was stereoselectively converted to pure (E)-1-bromo-
1,2-difluoroolefin via fluorination with Et2NSF3, followed by dehy-
drobromination with lithium 2,2,6,6-tetramethylpiperidide
(LiTMP), in THF at ꢀ98 ꢁC for 10 min. The use of less crowded or-
ganic bases or superbases (DBU, Bu4NþOHꢀ, BEMP) on the same
intermediate led to a mixture that was predominantly (Z). The
obtained (E)-1-bromo-1,2-difluoroolefines (RCF]CFBr) were cou-
pled with silanes, stannanes or boronic acids under palladium
We described here an original method for the stereoselective
synthesis of (E)-1,2-difluorostilbenes in only two steps for un-
symmetrical 1,2-difluorostilbenes and in a single step for sym-
metrical 1,2-difluorostilbenes. The starting reagent 1 1,2-dibromo-
1,2-difluoroethene is a non-volatile liquid product (boiling point
about 85 ꢁC), which is perfectly stable and which is commercially
available as a mixture of stereoisomers (E/Z: 85/15). When 1,2-
dibromo-1,2-difluoroethene 1 was reacted with 2.3 equiv of phe-
nyl boronic acids using tetrakis(triphenylphosphine)palladium(0)
as the catalyst in toluene and cesium carbonate (Cs2CO3) as a base
in ethanol/water at 110 ꢁC during
3 h, symmetrical 1,2-

S. Eddarir et al. / Tetrahedron 69 (2013) 11191e11196
11193
Table 2
difluorostilbenes 3 predominantly (E) were obtained in good yield
(Scheme 2 and Table 1, entries aee).17,19
Synthesis of 1-bromo-1,2-difluorostyrenes 4 from 1,2-dibromo-1,2-difluoroethene 1
(E/Z: 85/15)
Entry
Substituent
4 yield (%)a
4/3
4 (Z/E)b
3 (E/Z)b
X
a
b
c
d
e
p-NMe2
p-Br
3,4-MeO
m-NO2
p-NO2
62
60
58
65
68
79/21
78/22
80/20
83/17
81/19
82/18
87/13
90/10
85/15
84/16
85/15
85/15
88/12
80/20
82/18
B(OH)2
F
Br
F
F
Pd(PPh3)4, Toluene
+
Cs2CO3, Water/EtOH
T = 110 °C
Br
a
F
3
Isolated yield.
X
From 19F NMR.
1
2
b
X
Here also the obtained yields were good (Table 2, entries aee).
Burton and collaborators have shown that the (E)-1,1-
bromofluorostyrene isomer reacts faster than the (Z) isomer in pal-
ladium catalysis.10h,10i We observed the same effect although smaller
Scheme 2. Synthesis of symmetrical 1,2-difluorostilbenes 3 predominantly (E) from
1,2-dibromo-1,2-difluoroethene 1 (E/Z: 85/15).
in the copper stereoselective cyanation of
b-bromo-b-fluorostyr-
enes.11g No such effect is observed here. Despite the excess of 1,2-
dibromo-1,2-difluoroethene 1 the 1-bromo-1,2-difluorostyrenes 4
almost kept the stereochemistry of the starting material (Z/E: 85/15)
indicating that both stereoisomers reacted similarly.
Table 1
Synthesis of symmetrical 1,2-difluorostilbenes
difluoroethene 1 (E/Z: 85/15)
3
from 1,2-dibromo-1,2-
Entry
Substituent
3 Yield (%)a
3 (E/Z)b
The synthesis of unsymmetrical 1,2-difluorostilbenes 5 from 1-
bromo-1,2-difluorostyrenes 4 was straightforward. 1-Bromo-1,2-
difluorostyrenes 4 as E/Z mixture roughly 85/15 obtained in the
previous reaction were heated in presence of phenyl boronic acids 2
with the same catalytic system as previously (tetrakis-(triphenyl-
phosphine)palladium(0) as the catalyst in toluene and cesium
carbonate (Cs2CO3) as a base in ethanol/water) at 110 ꢁC during 3 h
(Scheme 4). Table 3 summarizes the results. Here also the stereo-
chemistry of the starting 1-bromo-1,2-difluorostyrenes 4 is pre-
served. Table 3 shows that the electron-donating or electron-
withdrawing substituents can be introduced in any order. Neither
the yield nor the stereoselectivity are modified.
a
b
c
d
e
p-NMe2
p-Br
3,4-MeO
m-NO2
p-NO2
84
79
68
72
74
83/17
80/20
85/15
79/21
86/14
a
Isolated yield.
b
From 19F NMR.
The yields are largely independent of the electron-acceptor or
electron-donor character of the substituents. The stereochemistry
of the starting material was always preserved in the obtained
symmetrical 1,2-difluorostilbenes 3. These results prove that the
starting reagent 1 did not isomerize under our coupling conditions,
contrary to the results we found in the stereoconvergent for-
Y
B(OH)2
F
F
Br
Pd(PPh3)4, Toluene
mylation of (E/Z)-
b-bromo-b-fluorostyrenes mixture to (Z)-a-fluo-
rocinnamic aldehydes.11f
+
Cs2CO3, Water/EtOH
T = 110 °C
F
F
In order to prepare asymmetrical 1,2-difluorostilbenes using the
same methodology we needed to stop the reaction after the sub-
stitution of only one bromine. We studied the preparation of 1-
bromo-1,2-difluorostyrenes 4 by varying the ratio of the reagents.
When phenyl boronic acids 2 were reacted with 1,2-dibromo-1,2-
difluoroethene 1 in excess in the same catalysis conditions as be-
fore, but at lower temperature we formed the expected 1-bromo-
1,2-difluorostyrenes 4 but also the disubstituted product 3. After
careful optimization, in the best conditions (3 equiv of 1, 40 ꢁC, 4 h)
the monosubstituted product 4 was formed predominantly, but the
disubstituted product 3 could not be totally avoided (Scheme 3).
Both products 3 and 4 were separated by chromatography on silica
using ethyl acetate/petroleum ether (5/95) as an eluent. Table 2
summarizes the results for various substituents. The reaction con-
ditions are robust and do not need optimization in function of the
electron-withdrawing or electron-donating character of the
substituents.
Y
4
5
2
X
X
Scheme 4. Synthesis of unsymmetrical 1,2-difluorostilbenes 5 predominantly (E) from
1-bromo-1,2-difluorostyrenes 4.
Table 3
Synthesis of unsymmetrical 1,2-difluorostilbenes
difluorostyrenes 4 (Z/E w 85/15)
5
from 1-bromo-1,2-
Entry
4
X
Y
5 yield (%)a
5 (E/Z)b
a
b
c
a
b
e
p-NMe2
p-Br
p-NO2
p-NO2
p-CHO
p-NMe2
85
79
78
81/19
85/15
83/17
a
Isolated yield.
From 19F NMR.
b
We demonstrated in a previous paper that a phenyl bearing
a phenol function protected by a methoxymethyl (MOM) ether group
behaves similarly to methoxy groups during SuzukieMiyaura
palladium-catalyzed cross-coupling reaction with arylboronic acids
and may be deprotected without loss of a fluorine atom in the vinylic
position in the resveratrol series.11d Therefore, this synthesis paves
the way to the synthesis of difluorinated resveratrol, pterostilbene
and more complex structures, such as viniferin.
X
B(OH)2
F
Br
F
F
Br
F
Pd(PPh3)4, Toluene
+
+
Cs2CO3, Water/EtOH
T = 40 °C
Br
F
F
3
X
1
2
4
3. Conclusion
X
X
In conclusion, the cross-coupling reaction of arylboronic
acids with predominantly (E)-1,2-dibromo-1,2-difluoroethene,
Scheme 3. Synthesis of 1-bromo-1,2-difluorostyrenes 4 predominantly (Z) from 1,2-
dibromo-1,2-difluoroethene 1 (E/Z: 85/15).

11194
S. Eddarir et al. / Tetrahedron 69 (2013) 11191e11196
which is commercially available, was achieved using tetrakis-
(triphenylphosphine)palladium(0) as the catalyst in toluene and
JCF¼8.5 Hz), 147.6. Isomer Z 19F NMR (300 MHz, CDCl3): ꢀ127.5
3
(s, 2F). 1H NMR (CDCl3):
d
¼7.6 (d, JHH¼8.2 Hz, 4H), 7.80 (d,
cesium carbonate as
a
base to afford symmetrical or un-
3JHH¼8.2 Hz, 4H).
symmetrical difluorostilbenes in good yields with the same ge-
ometry as the starting building block. The method was applied to
a variety of boronic acids, which opens the route to a general
synthesis of 1,2-diflurostilbenes bearing reactive substituents
like phenol groups. The 1-bromo-1,2-difluorostilbene in-
4.2.3. 1,10-(1,2-Difluoro-1,2-ethenediyl)bis[3,4-dimethoxy-benzene]
3c. Isomer E 19F NMR (CDCl3):
d
¼ꢀ138.3 (s, 2F). 1H NMR (CDCl3):
3
d
¼3.96 (s, 3H, OMe), 3.98 (s, 3H, OMe), 6.95 (d, JHH¼8.1 Hz, 2H),
3
7.10 (s, 2H), 7.23 (d, JHH¼8.2 Hz, 2H). 13C NMR (CDCl3):
¼123.4,
d
termediate may be potentially transformed into (E)-
a
,
b
-difluor-
124.9 (t, JCF¼8.0 Hz), 126.4 (t, JCF¼9.2 Hz), 125.4 (t, JCF¼8.4 Hz),
ocinnamaldehydes by formylation with carbon monoxide and
sodium formate catalyzed by palladium, or with cyanide to afford
146.7, 146.9, 156.4, 159.3. Isomer Z 19F NMR (300 MHz, CDCl3):
ꢀ124.3 (s, 2F). 1H NMR (CDCl3):
d
¼3.94 (s, 3H, OMe), 3.97 (s, 3H,
3
3
(E)-
a
,
b
-difluorocinnamonitrile or coupled with itself to give
OMe), 7.02 (d, JHH¼8.3 Hz, 2H), 7.18 (s, 2H), 7.36 (d, JHH¼8.2 Hz,
(1E,3E)-1,2,3,4-tetrafluoro-1,4-diphenyl-buta-1,3-dienes.11g,11e
Therefore, this general synthesis of (E)-difluorostilbenes opens
the way to access new families of potentially active compounds.
Work is in progress in our laboratory to produce (Z)-1,2-dibromo-
1,2-difluoroethene in order to obtain compounds with opposite
stereochemistry by the same method.
2H).
4.2.4. 1,10-(1,2-Difluoro-1,2-ethenediyl)bis[3-nitro-benzene]
3d. Isomer E 19F NMR (CDCl3): ꢀ149.6 (s, 2F). 1H NMR (CDCl3): 7.63
(m, 1H), 8.05 (d, 3JHH¼7.9 Hz, 1H), 8.23 (d, 3JHH¼8.2 Hz, 1H), 8.60 (s,
1H). 13C NMR (CDCl3): 115.0, 118.2 (t, JCF¼8.3 Hz), 123.2 (t,
JCF¼9.2 Hz), 128.3, 132.2 (t, J¼8.5 Hz), 145.7, 147.5. Isomer Z 19F NMR
(CDCl3): ꢀ128.3 (s, 2F). 1H NMR (CDCl3): 7.72 (m, 1H), 8.12 (d,
4. Experimental
4.1. General
3
3JHH¼8.0 Hz, 1H), 8.40 (d, JHH¼8.1 Hz, 1H), 8.60 (s, 1H).
4.2.5. 1,10-(1,2-Difluoro-1,2-ethenediyl)bis[4-nitro-benzene]
3e. Isomer E 19F NMR (CDCl3):
d
d
¼ꢀ155.6 (s, 2F). 1H NMR (CDCl3):
1,2-Dibromo-1,2-difluoroethene was obtained from ABCR
(Karlsruhe, Germany) as as a mixture of stereoisomers (E/Z: 85/15).
All other commercially available products were purchased from
Aldrich (Saint-Quentin Fallavier, France) and used as received.
Deuterated solvents (99.9% or better) were purchased from Euriso-
Top (Saint-Aubin, France). For flash chromatography, Merck silica
gel 60 (230e400 mesh ASTM) was used. NMR spectra were recor-
ded on a Bruker (Wissembourg, France) AM 300 spectrometer (300,
282, and 75 MHz, for 1H, 19F, and 13C, respectively) using CDCl3 as
solvent and TMS as internal standard; chemical shifts and J values
are given in parts per million and Hertz, respectively.
3
3
¼7.55 (d, JHH¼8.7 Hz, 4H), 8.21 (d, JHH¼8.3 Hz, 4H). 13C NMR
(CDCl3):
d
¼125.4 (t, JCF¼9.2 Hz), 125.1, 129.2 (t, JCF¼8.4 Hz), 146.9,
147.8. Isomer Z 19F NMR (300 MHz, CDCl3): ꢀ124.0 (s, 2F). 1H NMR
(300 MHz, CDCl3):
4H).
d
¼7.71 (d, 3JHH¼8.5 Hz, 4H), 8.30 (d, 3JHH¼8.4 Hz,
4.3. General procedure for the preparation of 1-bromo-1,2-
difluorostyrenes
A 50 mL two neck flask equipped with a stir bar, water condenser,
rubber septum, and argon inlet adapter was charged sequentially
with (1 equiv, 0.5 mmol) of arylboronic acid (3 equiv, 1.5 mmol) of
dibromodifluoroethene (3 equiv, 1.5 mmol) of anhydrous cesium
carbonate, 6 mL of toluene, 2 mL of water and 2 mL of ethanol. The
mixture was treated with 5% of tetrakis(triphenylphosphine) palla-
dium (0). The solution was heated at 40 ꢁC for 4 h. The reaction
mixture was transferred to a 50 mL separatory funnel and parti-
tioned between 20 mL of diethyl ether and 10 mL H2O. The aqueous
layer was extracted with 10 mL of diethyl ether. The organic layer
combined dried over MgSO4 and concentrated by rotary evaporation.
The residue was purified by flash column chromatography on silica
gel using a mixture of ethyl acetate/petroleum ether (5/95) as eluent,
to give the desired product.
4.2. General procedure for the preparation of symmetrical
1,2-difluorostilbenes
A 50 mL two neck flask equipped with a stir bar, water con-
denser, rubber septum, and argon inlet adapter was charged se-
quentially with (2.3 equiv, 1.2 mmol) of arylboronic acid, (1 equiv,
0.5 mmol) of dibromodifluoroethene, (3 equiv, 1.5 mmol) of anhy-
drous cesium carbonate, 6 mL of toluene, 2 mL of water and 2 mL of
ethanol. The mixture was treated with 5% of tetrakis-(triphenyl-
phosphine) palladium (0). The solution was heated at 110 ꢁC for 3 h.
The reaction mixture was transferred to a 50 mL separatory funnel
and partitioned between 20 mL of diethyl ether and 10 mL H2O. The
aqueous layer was extracted with 10 mL of diethyl ether. The or-
ganic layer combined dried over MgSO4 and concentrated by rotary
evaporation. The solvent was evaporated and the residue was pu-
rified by flash column chromatography on silica gel using a mixture
of ethyl acetate/petroleum ether (5/95) as eluent, to give the de-
sired product.
4.3.1. 4-(2-Bromo-1,2-difluoroethenyl)-N,N-dimethylbenzenamine
3
4a. Isomer E: 19F NMR (CDCl3):
d
¼ꢀ104.4 (d, JFF¼8.2 Hz, 1F),
ꢀ120.2 (d, JFF¼8.6 Hz, 1F). 1H NMR (CDCl3):
d
¼2.87 (s, 6H,
3
N(CH3)2), 6.67 (d, JHH¼8.1 Hz, 2H), 7.17 (d, JHH¼8.2 Hz, 2H). 13C
3
3
NMR (CDCl3):
d
¼44.4, 112.7, 116.7, 124.3 (dd, 3JCF¼4.0, 4JCF¼3.4 Hz),
2
1
2
126.8 (d, JCF¼25.4 Hz), 135.9 (dd, JCF¼312.4 Hz, JCF¼28.5 Hz),
4.2.1. 4-(1,2-Difluoroethenediyl)bis-N,N-dimethylbenzenamine
146.2 (dd, 1JCF¼257.6 Hz, 2JCF¼14.5 Hz). Isomer Z: 19F NMR (CDCl3):
3a. Isomer E 19F NMR (CDCl3):
d
¼ꢀ141.7 (s, 2F). 1H NMR (CDCl3):
d
¼ꢀ121.9 (d, JFF¼132.6 Hz, 1F), ꢀ141.4 (d, JFF¼132.6 Hz, 1F). 1H
3
3
3
3
d
¼2.95 (s, 6H, N(CH3)2), 7.41 (d, JHH¼8.2 Hz, 4 H), 7.53 (d,
NMR (CDCl3):
d
¼2.93 (s, 6H, N(CH3)2), 7.24 (d, JHH¼7.16 Hz, 2H),
3JHH¼8.4 Hz, 4 H). 13C NMR (CDCl3):
d¼42.8, 115.6, 121.8 (t,
7.38 (d, 3JHH¼8.4 Hz, 2H).
JCF¼9.4 Hz), 125.5 (t, JCF¼8.1 Hz), 146.5. Isomer Z 19F NMR (CDCl3):
ꢀ130.6 (s, 2F). 1H NMR (CDCl3):
d
¼3.02 (s, 6H, N(CH3)2), 7.56 (d,
4.3.2. 4-(2-Bromo-1,2-difluoroethenyl)-1-bromo-benzene
3
3
3JHH¼8.3 Hz, 4H), 7.82 (d, JHH¼8.4 Hz, 4H).
4b. Isomer E: 19F NMR (CDCl3):
d
¼ꢀ98.8 (d, JFF¼11.1 Hz, 1F),
ꢀ122.6 (d, JFF¼11.1 Hz, 1F). 1H NMR (CDCl3):
d
¼7.32 (d,
3
3
4.2.2. 1,10-(1,2-Difluoro-1,2-ethenediyl)bis[4-bromo-benzene
3JHH¼8.2 Hz, 2H), 7.61 (d, JHH¼8.3 Hz, 2H). 13C NMR (CDCl3):
3b. Isomer
(CDCl3):
13C NMR (CDCl3):
E
19F NMR (CDCl3):
d
¼ꢀ151.0 (s, 2F). 1H NMR
d
¼128.3 (dd, 3JCF¼4JCF¼3.8 Hz), 130.7 (d, 2JCF¼25.4 Hz), 131.8, 132.2,
3
3
1
2
1
d
¼7.51 (d, JHH¼8.3 Hz, 4H), 7.65 (d, JHH¼8.4 Hz, 4H).
137.9 (dd, JCF¼315.3 Hz, JCF¼26.8 Hz), 147.6 (dd, JCF¼263.4 Hz,
d
¼121.8, 122.8, 123.2 (t, JCF¼9.2 Hz), 127.2 (t,
2JCF¼15.4 Hz). Isomer Z: 19F NMR (CDCl3):
d¼ꢀ114.4 (d,

S. Eddarir et al. / Tetrahedron 69 (2013) 11191e11196
11195
3
3
3
3JFF¼133.4 Hz, 1F), ꢀ142.2 (d, JFF¼133.4 Hz, 1F). 1H NMR (CDCl3):
(d, JHH¼8.8 Hz, 2H), 7.44 (d, JHH¼8.7 Hz, 2H), 8.02 (d,
3JHH¼8.3 Hz, 2H) ppm.
3
3
d
¼7.41 (d, JHH¼8.7 Hz, 2H), 7.53 (d, JHH¼8.5 Hz, 2H).
4.3.3. 4-(2-Bromo-1,2-difluoroethenyl)-1,2-dimethoxy-benzene
4.4.2. 4-[1,2-Difluoro-2-(4-bromophenyl)ethenyl]benzaldehyde
3
3
4c. Isomer E: 19F NMR (CDCl3):
d
¼ꢀ106.1 (d, JFF¼6.3 Hz, 1F),
5b. Isomer E: 19F NMR (CDCl3):
d
¼ꢀ114.4 (d, JFF¼133.4 Hz, 1F),
3
3
ꢀ116.9 (d, JFF¼6.3 Hz, 1F). 1H NMR (CDCl3):
d
¼3.89 (s, 3H, OMe),
ꢀ142.2 (d, JFF¼133.4 Hz, 1F). 1H NMR (CDCl3):
d
¼7.30 (d,
3
3
3
3.85 (s, 3H, OMe), 6.90 (d, JHH¼7.4 Hz, 1H), 6.97 (s, 1H), 7.0 (d,
3JHH¼8.4 Hz, 2H), 7.45 (d, JHH¼8.3 Hz, 2H), 7.82 (d, JHH¼8.4 Hz,
3JHH¼7.3 Hz, 1H). 13C NMR (CDCl3):
d
¼110.8, 112.3, 126.5, 128.8
2H), 7.95 (d, JHH¼8.3 Hz, 2H), 9.98 (s, 1H, CHO) ppm. 13C NMR:
3
2
1
2
(d, JCF¼25.2 Hz), 137.3 (dd, JCF¼318.5 Hz, JCF¼24.1 Hz), 147.3
d
¼123.42, 125.4, 126.8 (d, 2JCF¼23.1 Hz), 130.2 (dd,
(dd, 1JCF¼284.5 Hz, JCF¼16.5 Hz), 156.4, 157.8. Isomer Z: 19F NMR
3JCF¼4JCF¼4.0 Hz), 131.5 (dd, JCF¼4JCF¼2.8 Hz), 132.7, 134.7 (d,
2
3
1
2
(CDCl3):
d
¼ꢀ121.1 (d, 3JFF¼139.8 Hz, 1F), ꢀ132.3 (d,
2JCF¼24.5 Hz), 149.7 (dd, JCF¼247.3 Hz, JCF¼22.3 Hz), 152.3 (dd,
3JFF¼139.8 Hz, 1F). 1H NMR (CDCl3):
d
¼3.89 (s, 3H, OMe), 3.85 (s,
1JCF¼252.8 Hz, JCF¼22.1 Hz), 164.5. Isomer Z: 19F NMR (CDCl3):
2
3
3
3
3H, OMe), 6.92 (d, JHH¼7.4 Hz, 1H), 6.94 (s, 1H), 7.23 (d,
d
¼ꢀ98.8 (d, JFF¼11.1 Hz, 1F), ꢀ122.6 (d, JCF¼11.1 Hz, 1F). 1H NMR
3JHH¼8.1 Hz, 1H).
(CDCl3):
d
¼7.23 (d, 3JHH¼8.2 Hz, 2H), 7.50 (d, 3JHH¼8.3 Hz, 2H), 7.74
3
3
(d, JHH¼8.4 Hz, 2H), 7.92 (d, JHH¼8.3 Hz, 2H), 9.92 (s, 1H,
4.3.4. 4-(2-Bromo-1,2-difluoroethenyl)-2-nitro-benzene 4d. Isomer
CHO) ppm.
3
E: 19F NMR (CDCl3):
d
¼ꢀ95.3 (d, JFF¼11.3 Hz, 1F), ꢀ123.8 (d,
3JFF¼11.4Hz,1F).1HNMR(CDCl3):
d
¼7.34(m, 2H), 8.12 (d,3JHH¼8.1 Hz,
Acknowledgements
1H), 8.33 (d, 3JHH¼7.9 Hz,1H), 8.74 (s, 1H). 13C NMR (CDCl3):
d¼124.3,
126.9, 127.4, 128.5, 131.8 (d, JCF¼24.6 Hz), 138.7 (dd, 1JCF¼320.8 Hz,
2
ꢀ
This work was supported by the Conseil Regional Nord, Pas-de-
2JCF¼25.3 Hz),145.8,148.9 (dd,1JCF¼272.5 Hz, 2JCF¼16.2 Hz). Isomer Z:
Calais, France. The NMR and Mass Spectrometry facilities used in
this study were funded by the European Community (FEDER), the
19F NMR (CDCl3):
d
¼ꢀ112.2 (d, JFF¼133.7 Hz, 1F), ꢀ142.6 (d;
3
3JFF¼133.6 Hz, 1F). 1H NMR (CDCl3):
d¼7.21 (m, 2H), 8.05 (d,
ꢀ
ꢀ
Region Nord-Pas de Calais (France), the CNRS, and the Universite de
3JHH¼7.9 Hz, 1H), 8.23 (d, 3JHH¼8.5 Hz, 1H), 8.60 (s, 1H).
ꢀ
Lille 1, Sciences et Technologies. S.E. thanks the Universite Cadi
ꢀ
ꢀ
Ayyad, Faculte des Sciences et Techniques Gueliz, Marrakech, Mo-
rocco, for a sabbatical leave funded by the Erasmus Mundus Al Fihri
program. This work was performed in the frame of the CNRST-CNRS
4.3.5. 4-(2-Bromo-1,2-difluoroethenyl)-1-nitro-benzene 4e. Isomer
3
E: 19F NMR (CDCl3):
d
¼ꢀ109.5 (d, JFF¼8.6 Hz, 1F), ꢀ124.5 (d,
3JFF¼8.7 Hz, 1F). 1H NMR (CDCl3):
d
¼7.85 (d, 3JHH¼8.3 Hz, 2H), 8.04
ꢀ
ꢁ
Action Concertee Chimie 08/09 ‘Synthese de sondes fluorescentes
(d, JHH¼8.2 Hz, 2H). 13C NMR (CDCl3):
d
¼126.4, 127.2 (dd,
3
ꢀ
specifiques des glyco et phopshopeptides pour l’analyse
3JCF¼4JCF¼3.4 Hz), 128.3 (d, 2JCF¼25.4 Hz), 138.6 (dd, 1JCF¼314.6 Hz,
ꢀ
proteomique’. The authors thank Tarik Legdali, Abdelhamid Iuiry
2JCF¼27.6 Hz), 147.0 (dd, 1JCF¼259.6 Hz, 2JCF¼15.5 Hz), 147.8. Isomer
and Rachid Chbelti for performing some of the experiments during
Z: 19F NMR (CDCl3):
d
¼ꢀ109.85 (d, JFF¼131.8 Hz, 1F), ꢀ142.30 (d,
3
ꢀ
their Master’s degree from Universite Cadi Ayyad. The authors
3JFF¼131.8 Hz, 1F). 1H NMR (CDCl3):
d
¼7.63 (d, JHH¼8.1 Hz, 4H),
3
thank Dr. Maria van Agthoven for correcting the manuscript and
the Referees for their careful reading.
8.02 (d, 3JHH¼8.4 Hz, 4H).
References and notes
4.4. General procedure for the preparation of unsymmetrical
1. (a) Alloatti, D.; Giannini, G.; Cabri, W.; Lustrati, I.; Marzi, M.; Ciacci, A.; Gallo, G.;
Tinti, M. O.; Marcellini, M.; Riccioni, T.; Guglielmi, M. B.; Carminati, P.; Pisano, C.
J. Med. Chem. 2008, 51, 2708e2721; (b) Dalvit, C.; Ko, S. Y.; Vulpetti, A. J. Fluorine
Chem. 2013, 152, 129e135.
2. (a) Gegiou, D.; Muszkat, K. A.; Fischer, E. J. Am. Chem. Soc. 1968, 90, 3907e3918;
(b) Goerner, H. J. Photochem. Photobiol., A 1995, 90, 57e63; (c) Muszkat, K. A.;
Fischer, E. J. Chem. Soc. B 1967, 662e678; (d) Fischer, G.; Muszkat, K. A.; Fischer,
E. J. Chem. Soc. B 1968, 1156e1158.
3. (a) Goodby, J. W.; Hindmarsh, P.; Hird, M.; Lewis, R. A.; Toyne, K. J. Mol. Cryst.
Liq. Cryst. A 2001, 364, 889e898; (b) Roussel, F.; Bayle, J.-P.; Khan, M. A.; Fung,
B. M.; Yokokohji, O.; Shimizu, T.; Koh, H.; Kumai, S. Liq. Cryst. 1999, 26,
251e260; (c) Araya, K.; Dunmur, D. A.; Grossel, M. C.; Luckhurst, G. R.;
Marchant-Lane, S. E.; Sugimura, A. J. Mater. Chem. 2006, 16, 4675e4689; (d)
Yokokoji, O.; Miyajima, T.; Irisawa, J.; Shimizu, T.; Inoue, S. Liq. Cryst. 2009, 36,
799e807; (e) Hird, M. Chem. Soc. Rev. 2007, 36, 2070e2095.
4. (a) Martinelli, C.; Farinola, G. M.; Pinto, V.; Cardone, A. Materials 2013, 6,
1205e1236; (b) Bettini, S.; Valli, L.; Santino, A.; Martinelli, C.; Farinola, G. M.;
Cardone, A.; Sgobba, V.; Giancane, G. Dyes Pigm. 2012, 94, 156e162.
5. Yagupolskii, L. M.; Kondratenko, N. V.; Chernega, O. I.; Chernega, A. N.; Buth, S.
A.; Yagupolskii, Y. L. Dyes Pigm. 2008, 79, 242e246.
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Miceli, G.; Fichera, A. M. J. Mater. Chem. 2002, 12, 2202e2207; (b) Albertin, L.;
Bertarelli, C.; Gallazzi, M. C.; Meille, S. V.; Capelli, S. C. J. Chem. Soc., Perkin Trans.
2 2002, 1752e1759; (c) Losurdo, M.; Giangregorio, M. M.; Capezzuto, P.; Bruno,
G.; Babudri, F.; Cardone, A.; Martinelli, C.; Farinola, G. M.; Naso, F.; Buechel, M.
Polymer 2008, 49, 4133e4140; (d) Losurdo, M.; Giangregorio, M. M.; Capezzuto,
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1,2-difluorostilbenes
A 50 mL two neck flask equipped with a stir bar, water con-
denser, rubber septum, and argon inlet adapter was charged se-
quentially with 1.2 equiv of arylboronic acid, 1 equiv of 1-bromo-
1,2-difluorostyrene, 3 equiv of anhydrous cesium carbonate, 4 mL of
toluene,1 mL of water and 1 mL of ethanol. The mixture was treated
with 5% of tetrakis(triphenylphosphine)palladium(0). The solution
was heated at 110 ꢁC for 3 h. The reaction mixture was transferred
to a 50 mL separatory funnel and partitioned between 15 mL of
diethyl ether and 10 mL of H2O. The aqueous layer was extracted
with 10 mL of diethyl ether. The combined organic layer dried over
MgSO4 and concentrated by rotary evaporation. The residue was
purified by flash column chromatography on silica gel using
a mixture of ethyl acetate/petroleum ether (5/95) as eluent, to give
the desired product.
4.4.1. 4-[1,2-Difluoro-2-(4-nitrophenyl)ethenyl]-N,N-dime-
thylbenzenamine 5a (identical with 5c). Isomer E: 19F NMR
(CDCl3):
d
¼ꢀ157.9 (d, 3JFF¼136.4 Hz, 1F), ꢀ144.1 (d, 3JFF¼136.4 Hz,
1F) ppm. 1H NMR (CDCl3):
d
¼3.02 (s, 6H, N(CH3)2), 6.70 (d,
3JHH¼8.5 Hz, 2H), 7.63 (d, JHH¼8.8 Hz, 2H), 7.78 (d, JHH¼8.6 Hz,
3
3
2H), 8.24 (d, 3JHH¼8.2 Hz, 2H) ppm. 13C NMR:
¼43.7, 115.8, 116.2,
d
120.4 (d, JCF¼23.1 Hz), 127.3 (dd, JCF¼4JCF¼3.9 Hz), 129.5 (dd,
2
3
3JCF¼4JCF¼2.6 Hz), 130.7, 134.7 (d, JCF¼24.5 Hz), 148.2 (dd,
2
1JCF¼246.5 Hz, JCF¼22.8 Hz), 150.3, 151.4 (dd, JCF¼253.7 Hz,
2
1
8. Cardone, A.; Martinelli, C.; Losurdo, M.; Dilonardo, E.; Bruno, G.; Scavia, G.;
Destri, S.; Cosma, P.; Salamandra, L.; Reale, A.; Di Carlo, A.; Aguirre, A.; Milian-
Medina, B.; Gierschner, J.; Farinola, G. M. J. Mater. Chem. A 2013, 1, 715e727.
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Bull. 1998, 47, 1532e1536; (b) Farrugia, L. J.; Evans, C.; Lentz, D.; Roemer, M. J.
2JCF¼21.2 Hz). Isomer Z: 19F NMR (CDCl3):
d
¼ꢀ138.1 (d,
3JFF¼17.1 Hz, 1F), ꢀ114.3 (d, JFF¼17.1 Hz, 1F) ppm. 1H NMR
3
3
(CDCl3):
d
¼3.08 (s, 6H, N(CH3)2), 6.62 (d, JHH¼8.6 Hz, 2H), 7.23

11196
S. Eddarir et al. / Tetrahedron 69 (2013) 11191e11196
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