Cyclic 1,1-bis(silyl)alkenes-new building blocks for the stereoselective synthesis of unsymmetrical (E)-stilbenes and (E,E)-1,4-diarylbuta-1,3-dienes

Article abstract of DOI:10.1016/j.tet.2009.01.113

A new efficient synthetic protocol for the highly stereoselective synthesis of unsymmetrical (or symmetrical) (E)-stilbenes and (E,E)-1,4-diarylbuta-1,3-dienes based on sequential palladium-catalyzed Heck arylation-Hiyama cross-coupling reactions using cy

Full text of DOI:10.1016/j.tet.2009.01.113

Tetrahedron 65 (2009) 5497–5502
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Tetrahedron
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Cyclic 1,1-bis(silyl)alkenesdnew building blocks for the stereoselective synthesis
of unsymmetrical (E)-stilbenes and (E,E)-1,4-diarylbuta-1,3-dienes
*
*
´
Piotr Pawluc , Grzegorz Hreczycho, Andrzej Suchecki, Maciej Kubicki, Bogdan Marciniec
Department of Organometallic Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
A new efficient synthetic protocol for the highly stereoselective synthesis of unsymmetrical (or sym-
metrical) (E)-stilbenes and (E,E)-1,4-diarylbuta-1,3-dienes based on sequential palladium-catalyzed Heck
arylation–Hiyama cross-coupling reactions using cyclic gem-bis(silyl)ethene as alkenyl building block is
reported.
Received 19 December 2008
Received in revised form 27 January 2009
Accepted 28 January 2009
Available online 14 April 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Bis(silyl)alkene
C–C bond formations
Heck coupling
Hiyama coupling
1. Introduction
1-boryl-4-stannylbuta-1,3-dienes.18 An alternative approach based
on cross-coupling reactions of organometallic reagents with bis-
Highly conjugated
p
-electron compounds such as stilbenes or
electrophilic buta-1,3-dienes has also been reported.19
aryl-substituted polyenes have gained a lot of attention because of
their wide range of biological activities and potential therapeutic
values.1 The conjugated polyenes are essential in functional mate-
rials such as organic fluorescent probes, electroluminescent devices
and nonlinear optical materials.2 Of the available methods for
preparation of stilbenes, the transition metal-catalyzed processes
utilizing the C–C or C]C bond formation reactions are the most
convenient, powerful and selective approaches. Indeed, most
strategies developed so far involve palladium-catalyzed coupling
reactions.3 Among them, protocols based on the Heck,4 Suzuki,5
Stille6 and Negishi7 reactions stand out for their synthetic versatility
and efficiency. Alternative transition metal-catalyzed syntheses
involve the titanium-mediated McMurry coupling of aldehydes8
and ruthenium-catalyzed cross-metathesis of substituted styrenes.9
The palladium-catalyzed and fluoride-promoted cross-coupling
of unsaturated organosilicon compounds with aryl halides (Hiyama
coupling) has been recently employed as a mild and efficient al-
ternative to the well-established Stille and Suzuki reactions due to
commercial availability, high stability and low toxicity of the silicon
derivatives.20 In view of the above advantages, several synthetic
methodologies based on sequential hydrosilylation/Hiyama cou-
pling,21 Heck arylation/Hiyama coupling22 or silylative coupling/
Hiyama coupling23 processes, in which unsaturated organosilicon
precursors or intermediates have been utilized as versatile double
bond equivalents in the iterative construction of
systems, have been reported.
p-conjugated
In the preliminary communication, we have reported that
2,2,4,4-tetramethyl-1,5-dioxa-3-methylene-2,4-disilacycloheptane
A
number of methodologies for the preparation of aryl-
substituted 1,3-butadienes based on palladium-catalyzed cross-
coupling of vinyl halides with alkenyl-substituted organometallic
compounds of boron,10 tin,6a,11 zinc,12 silicon13 or zirconium14 have
been developed over the last two decades. The complementary
synthetic routes involving bis-metallated 1,3-butadienyl building
blocks are represented by palladium-catalyzed cross-coupling of
aryl halides with 1,4-bis(silyl)-,15 2,3-bis(boryl)-,16 2-aryl-3-silyl-17 or
ArI (2 eq.)
[Pd2(dba)3]
Ar
Ar
TBAF, THF, 65 °C, 2h
Me
Me
Me
Si
Si
O
Me
O
X-Ar-X (0.9 eq.)
[Pd2(dba)3]
Ar
1
TBAF, dioxane,
80 °C, 16-48h
n
* Corresponding authors. Fax: þ48 618291508.
E-mail addresses: piotrpaw@amu.edu.pl (P. Pawluc´), marcinb@amu.edu.pl
(B. Marciniec).
Scheme 1. Synthesis of symmetrical (E)-stilbene derivatives using 2,2,4,4-tetramethyl-
1,5-dioxa-3-methylene-2,4-disilacycloheptane 1 as a platform.
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.01.113

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P. Pawlu´c et al. / Tetrahedron 65 (2009) 5497–5502
Hiyama coupling
Ar2I, Pd cat.
Hiyama coupling
(E)-Ar2CH=CHI
O-silylation/
Silylative coupling
cyclisation
Ar2
Ar1
Ar1
Heck coupling
Me
Me
Me
Me
Me
3
Me
SiMe2Cl
Pd cat.
Si
Si
O
Si
O
Si
Me
Me
+
Ar1I
Pd cat.
OH
O
O
HO
Ar2
Ar1
1
2
4
Scheme 2. Synthetic strategy for unsymmetrical (E)-stilbenes and (E,E)-1,4-diaryl-1,3-dienes.
R
Me
Me
Me
I
Si
Me
Si
O
Pd(OAc)2 (3 mol%)/PPh3 (6 mol%)
AgNO3, Et3N, MeCN
Me
Me
Si
Si
Me
+
R
O
Me
O
O
1
2a-g
Scheme 3. Pd-catalyzed Heck coupling of 1 with aryl iodides.
Table 1
1, in the reaction with 2 equiv of aryl iodides, under standard
cross-coupling conditions forms exclusively (instead of expected
1,1-diarylethenes) cine-substitution products with perfect stereo-
selectivity and almost quantitative yield.24 A double bond of bis-
(silyl)alkene can thus be very efficiently grafted into aromatic
structure, offering the potential of constructing symmetrical (E)-
stilbene derivatives. The extension of this new silicon-assisted
protocol for aryl dihalides has led to stereoselective synthesis of (E)-
poly(arylenevinylene)s (Scheme 1).24
Palladium-catalyzed Heck coupling of 1 with aryl iodides
R
Compound
Yielda (%)
H
4-Ac
2a
2b
2c
2d
2e
2f
82
72
67
88
80
85
90
4-NO2
3-MeO
4-MeO
4-Me
4-Cl
2g
Since the starting compound 1 can be easily prepared with high
yield in a two-step process from inexpensive chlorodimethyl-
vinylsilane and ethylene glycol by silylation–ruthenium-catalyzed
silylative coupling exo-cyclization sequence,25 this novel bis(silyl)-
ethene transformation is expected to be an attractive alternative for
Reaction conditions: 60 ꢀC, [Pd(OAc)2]:[PPh3]:[AgNO3]:[Et3N]:[ArI]:[1]¼0.03:0.06:-
1:1.5:1:1.
a
Isolated yields of chromatographically pure products.
were obtained with electron-rich and electron-poor aryl iodides)
and structurally diverse aryl iodides (Table 1).
the synthesis of unsymmetrically-substituted
p-systems using se-
quential Pd-catalyzed C–H arylation (Heck coupling) and C–Si aryla-
tion (Hiyama coupling).
The 2,2,4,4-tetramethyl-3-(4-acetyl)benzylidene-1,5-dioxa-2,4-
disilacycloheptane 2b proved to be a solid and yielded a crystal
amenable to X-ray structure determination. Thermal-ellipsoid rep-
resentation of molecule 2b is shown in Figure 1. The conformation of
the seven-membered ring in 2b can be described as close to
a ‘pseudo-chair’: five atoms C1, O3, C4, O6 and Si7 make an ap-
proximate plane while the remaining two: C5 and Si2 are signifi-
cantly deviated in two opposite directions. To the best of our
knowledge, this is the first structural characterization of a molecule
containing such a seven-membered ring. In the crystal structure
relatively strong C11–H11/O3(x, yꢁ1, z) hydrogen bond connects
the molecules into infinite chains along the [010] direction.
Therefore, herein we report our results on the use of cyclic 1,1-
bis(silyl)ethene 1 as a new platform for the sequential installation
of aryl groups onto C]C core, which leads to unsymmetrically-
functionalized (E)-stilbenes and (E,E)-1,4-diaryl-substituted buta-
1,3-dienes (Scheme 2).
2. Results and discussion
2.1. Heck coupling of cyclic 1,1-bis(silyl)ethene 1 with aryl
iodides
Since we have recently reported an efficient procedure for the
selective Heck coupling of acyclic 1,1-bis(silyl)ethenes with aryl and
alkenyl iodides,26 the coupling of 1 with aryl iodides was performed
in the presence of palladium(II) acetate/triphenylphosphine as
catalyst, using triethylamine and silver nitrate as iodine abstrac-
tor.27 After several attempts, we found that the reaction of com-
pound 1 (1 equiv) with 1 equiv of aryl iodide, 1 equiv of AgNO3 and
1.5 equiv of Et3N, in the presence of 3 mol % of Pd(OAc)2 and 6 mol %
of PPh3, conducted in acetonitrile at 60 ꢀC for 1 h, afforded exclu-
sively the corresponding 2,2,4,4-tetramethyl-1,5-dioxa-3-benzyli-
dene-2,4-disilacycloheptane derivatives (Scheme 3) in good yield
(compounds 2a–g, Table 1). The noteworthy features of these
processes are that the formation of styrene and symmetrical stil-
bene derivatives (via desilylation) was completely suppressed, and
the formation of biaryls (by homo-coupling of the aryl iodides) was
not observed. Moreover, the Heck coupling occurred under mild
conditions with a wide array of electronically (similar reaction rates
Figure 1. Perspective view of the molecule 2b.33 The anisotropic displacement ellip-
soids were drawn at 50% probability level, hydrogen atoms are depicted as spheres
with arbitrary radii.

P. Pawlu´c et al. / Tetrahedron 65 (2009) 5497–5502
5499
Table 2
Synthesis of (E)-stilbenes
R1
R2
Product structure
Compound
Yielda (%)
86
Me
H
4-Me
3a
O
Me
4-Ac
H
3b
3c
62
68
Figure 2. Perspective view of the molecule 3e.33 The anisotropic displacement ellip-
soids were drawn at 50% probability level, hydrogen atoms are depicted as spheres
with arbitrary radii. The letter A refers to the symmetry operation ꢁx, 1ꢁy, 1ꢁz.
O
Me
4-Me
4-Ac
Me
NO2
Me
4-NO2
4-Me
2-Me
4-Me
3d
3e
62
78
Me
Me
Figure 3. Perspective view of one of the symmetry-independent molecules of 3f (A).33
The anisotropic displacement ellipsoids were drawn at 50% probability level, hydrogen
atoms are depicted as spheres with arbitrary radii.
OMe
O
4-MeO
3-MeO
3-CN
4-Ac
NC
3f
88
92
productd(E)-4-methylstilbene 3a, as single stereoisomer. Although the
protodesilylation of C–Si bonds mediated by TBAF in THF has been
previously reported,28 the simultaneous ipso-substitution and proto-
desilylation of geminallysilylated alkenes under Hiyama cross-coupling
conditions are unprecedented. To investigate the generality of this re-
action, a series of cyclic 1,1-bis(silyl)-2-arylethenes (Heck coupling
products) bearing various substituents in the aromatic ring were sub-
jected to similar reaction conditions with commercially available
functionalized aryl iodides. For the economical reasons, for further
synthetic investigationwe decided to decrease the necessary amount of
the aryl iodide to 0.9 equiv, which additionally permitted avoiding the
homo-coupling reaction of aryl iodides. In general, the reactions pro-
ceeded smoothly under mild conditions to give the corresponding
unsymmetrical (E)-stilbenes in good yield (Table 2, Scheme 4).
Me
3g
MeO
OMe
4-Cl
4-MeO
3h
90
Cl
[2]:[ArI]:[TBAF]:[Pd]¼1:0.9:2.4:0.01, THF, 60 ꢀC.
a
Isolated yields of products.
Substituted (E)-stilbenes 3e and 3f proved to be solids and yiel-
ded crystals amenable to X-ray structure determination. Perspective
views of these molecules are shown in Figures 2 and 3. The molecule
3e occupies a special position in the space group Pbca: the mid-
dlepoint of the central C–C bond falls at the inversion centre; the
molecule therefore has the Ci symmetry, and the phenyl rings are
coplanar (Table 3). The crystal structure of 3f contains two sym-
metry-independent molecules, of slightly different conformations.
The dihedral angle between the least squares planes of the phenyl
rings is 10.9(4)ꢀ in molecule A and 17.5(3)ꢀ in molecule B (Table 3).
2.2. Synthesis of unsymmetrical (E)-stilbenes
Having established an efficient protocol for the Heck coupling of
1 with aryl iodides, we subsequently investigated the reactivity of
thus-generated b-aryl-substituted cyclic 1,1-bis(silyl)ethenes 2a–g
towards selected aryl iodides under Hiyama cross-coupling condi-
tions. Since trialkyl-substituted alkenylsilanes generally are ex-
tremely stable to chemical manipulation prior to fluoride
activation, cyclic 1,1-bis(silyl)alkenes containing alkoxy groups 2a–
g seem to be essential for efficient reactivity.
Initial studies were carried out using 2,2,4,4-tetramethyl-3-benzy-
lidene-1,5-dioxa-2,4-disilacycloheptane 2a and 4-iodotoluene in the
presence of allylpalladium(II) chloride dimer [Pd(C3H5)Cl]2 catalyst
(2 mol % Pd) and TBAF (2.4 equiv) as an activator. After several attempts,
we found that its reaction with 2 equiv of aryl iodide conducted in THF
at 60 ꢀC for 1 h exclusively afforded the monosubstitution
2.3. Synthesis of unsymmetrical (E,E)-1,4-diarylbuta-1,3-
dienes
A successful, simple and selective method of obtaining un-
symmetrical (E)-stilbenes has prompted us to apply selected b-aryl-
R1
R2
I
Me
Me
Me
[Pd(C3H5)Cl]2 1 mol%
TBAF, THF, 65°C, 1h
R2
Si
Si
O
+
R1
Me
O
Scheme 4. Silicon-assisted synthesis of unsymmetrical (E)-stilbenes.

5500
P. Pawlu´c et al. / Tetrahedron 65 (2009) 5497–5502
Table 3
containing (E,E)-dienes as predominant products, however, trace
amounts of the respective (E,Z) isomers (4–5%) were also detected
using the GC–MS method. Although the stereochemistry of dienes
4a–c cannot be directly derived from the 1H NMR spectra on the basis
of the protons of the diene moiety, the analysis of spin systems by
means of MestReC NMR software19a as well as comparison with lit-
erature data15a,19a allowed us to define a diene structure (Scheme 5).
Crystal data, data collection and structure refinement for 2b, 3e and 3f
2b
3e
3f
Formula
C16H24O3Si2
320.53
Monoclinic
P21/c
13.752(2)
9.083(1)
14.571(1)
92.41(1)
1818.4(4)
4
1.171
688
0.202
2.64–25.00
ꢁ14ꢂhꢂ16
ꢁ10ꢂkꢂ9
ꢁ17ꢂlꢂ17
C16H16
C16H13NO
235.27
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
208.28
Orthorhombic
Pbca
7.521(3)
6.016(3)
27.090(5)
90
1225.7(8)
4
1.13
448
0.063
4.40–25.00
ꢁ8ꢂhꢂ7
ꢁ7ꢂkꢂ7
ꢁ31ꢂlꢂ32
Orthorhombic
P212121
7.1105(11)
11.1854(13)
30.944(3)
90
2461.1(6)
8
1.27
992
0.079
1.94–25.00
ꢁ8ꢂhꢂ7
ꢁ13ꢂkꢂ13
ꢁ36ꢂlꢂ36
3. Conclusions
b
(ꢀ)
V (Å3)
Z
In conclusion, a new application of cyclic 1,1-bis(silyl)ethene for the
highly stereoselective construction of unsymmetrical (E)-stilbenes and
(E,E)-1,4-diarylbuta-1,3-dienes based on sequential palladium-cata-
lyzed Heck and Hiyama cross-coupling reactions is described. Further
results on the application of this strategy to the synthesis of highly
Dx (g cmꢁ3
F (000)
)
m
(mmꢁ1
range (ꢀ)
)
Q
hkl range
p-conjugated triene systems will be reported in due course.
Reflections
Collected
Unique (Rint
4. Experimental
4.1. General
8080
3195 (0.020)
0.041
3225
1060 (0.037)
0.072
14,786
4307 (0.118)
0.114
)
R(F) [I>2
s
(I)]
wR(F2) [I>2
s
(I)]
0.114
0.120
0.272
1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were
recorded on a Varian XL 300 spectrometer using CDCl3 or as a sol-
vent. GC analyses were performed on a Varian 3400 with a Mega-
bore column (30 m) and TCD. Mass spectra of the products were
determined by GC–MS analysis on a Varian Saturn 2100T, equipped
with a BD-5 capillary column (30 m) and a Finnigan Mat 800 ion
trap detector. The Hiyama coupling reactions were performed un-
der an atmosphere of deoxygenated and dried argon. Triethylamine
was dried over CaH2, distilled under argon and stored over mo-
lecular sieves type 4A. THF and acetonitrile as well as all the
commercial materials were purchased from Aldrich and used
without further purification. 2,2,4,4-Tetramethyl-1,5-dioxa-3-
methylene-2,4-disilacycloheptane 1 was prepared using procedure
described in literature.25
Goodness of fit
1.08
0.27/ꢁ0.22
1.07
0.32/ꢁ0.13
1.06
0.47/ꢁ0/39
max/min Dr (e Åꢁ3
)
Table 4
Synthesis of unsymmetrical (E,E)-1,4-diarylbuta-1,3-dienes
R1
R2
Product structure
(E,E)/(Z,E) Yielda (%)
4-Me
H
4a 95/5
86
80
68
Me
Br
H
4-Br
4b 96/4
4c 96/4
Me
Me
4.2. Representative procedure for Heck coupling of 1 with
aryl iodides
4-MeO 4-Me
MeO
A mixture consisting of 33.5 mg (0.15 mmol) of palladium(II)
acetate, 78.6 mg (0.3 mmol) of triphenylphosphine, 0.85 g of silver
nitrate (5 mmol), 5 mmol of aryl iodide, 5 mmol of cyclic 1,1-bis-
(silyl)ethene 1, 1.05 mL (7.5 mmol) of triethylamine and 10 mL of
acetonitrile was placed in 50 mL, two-necked, round-bottomed flask
equipped with a magnetic stirring bar and reflux condenser. The
suspension was heated in an oil bath at 60 ꢀC for 1 h. After cooling to
room temperature, the solvent was evaporated and reaction mixture
was extracted twice with 30 mL of hexane. The combined organic
layers were dried (MgSO4) and the crude product obtained was then
purified by column chromatography (deactivated silica gel (5% Et3N)/
eluentdhexane) to give corresponding compounds 2a–g.
4-Ac
4-Me
4d 95/5
80
Me
O
[2]:[ArCH]CHI]:[TBAF]:[Pd]¼1:0.9:2.4:0.01, THF, 60 ꢀC.
a
Isolated yields of products.
substituted derivatives 2a, 2b, 2e and 2f in the synthesis of stereo-
defined (E,E)-1,4-diaryl-1,3-butadienes by their palladium-catalyzed
Hiyama cross-coupling with (E)-styryl iodides. The optimal condi-
tions established for the reactions of compounds 2a–g with aryl
iodides were applied to (E)-styryl iodides providing good yields (68–
86%) of the desired unsymmetrical 1,4-diaryl-substituted buta-1,3-
dienes (4a–d, Table 4). Thus, the coupling reactions were performed
in THF using [Pd(C3H5)Cl]2 (2 mol % Pd) as catalyst, in the presence of
tetrabutylammonium fluoride (20% excess per silyl group) as the
activator at 60 ꢀC. It is worth noting that the Hiyama coupling pro-
cesses proceeded in highly stereoselective manner to yield products
4.2.1. 2,2,4,4-Tetramethyl-3-benzylidene-1,5-dioxa-2,4-
disilacycloheptane (2a) (yield 82%)
1H NMR (CDCl3)
d
(ppm): 0.12 (s, 6H, SiCH3), 0.36 (s, 6H, SiCH3),
3.75–3.78 (m, 2H, CH2O), 3.87–3.89 (m, 2H, CH2O), 7.20–7.35 (m, 5H,
Ph), 7.68 (s,1H, –CH]). 13C NMR (CDCl3)
d
(ppm): ꢁ1.3, 0.5, 65.8, 65.9,
127.7,127.8,128.6,141.6,148.8,154.6. MS (EI) m/z (%): 278 (Mþ 1%), 263
R1
R2
Me
Me
Me
I
[Pd(C3H5)Cl]2 0.5mol%
TBAF, THF, 65 °C, 1h
Si
Si
O
+
Me
R2
R1
O
Scheme 5. Silicon-assisted synthesis of unsymmetrical (E,E)-1,4-diarylbuta-1,3-dienes.

P. Pawlu´c et al. / Tetrahedron 65 (2009) 5497–5502
5501
(100), 250 (18), 219 (20), 193 (16), 159 (10), 145 (24), 133 (65), 115 (14),
73 (20), 45 (15). HRMScalcdfor C14H22O2Si2: 278.1158, found: 278.1161.
bubbling tube and thermostated heating oil bath) was evacuated and
flushed with argon. Respective compounds 2a–g (5 mmol) and THF
(20 mL) were added to the reactor. At room temperature 12 mmol of
TBAF (1 M solution inTHF) was added and the mixture was stirred for
10 min. After this time, 4.55 mmol of the respective aryl iodide and
18.3 mg (0.05 mmol) of [Pd(C3H5)Cl]2 were added and the reaction
mixture was stirred under argon for 1 h at 65 ꢀC. After the reaction
wascompleted (GC–MSanalysis)the volatileswere evaporated under
vacuum and the crude product was chromatographed on silica gel
(eluentdhexane/ethyl acetate 10:1 for compounds 3a–f or hexane/
CH2Cl2 10:1 for 3g–h) to afford the analytically pure products. The
structuresofsynthesized (E)-stilbenes wereconfirmed byGC–MSand
NMR spectroscopy matching data reported in the literature: (E)-4-
methylstilbene (3a),4g (E)-4-acetylstilbene (3b),4g (E)-4-acetyl-40-
methylstilbene (3c),5c (E)-4,40-dimethylstilbene (3e),29a (E)-4-acetyl-
30-methoxystilbene (3g)9b and 4-chloro-40-methoxystilbene (3h).29b
4.2.2. 2,2,4,4-Tetramethyl-3-(4-acetyl)benzylidene-1,5-dioxa-2,4-
disilacycloheptane (2b) (yield 72%)
1H NMR (CDCl3)
d (ppm): 0.11 (s, 6H, SiCH3), 0.36 (s, 6H, SiCH3),
2.61 (s, 3H, CH3CO), 3.78–3.82 (m, 2H, CH2O), 3.86–3.89 (m, 2H,
CH2O), 7.31 (d, 2H, Ar), 7.91 (d, 2H, Ar), 7.66 (s, 1H, –CH]). 13C NMR
(CDCl3)
d
(ppm): ꢁ1.54, 0.48, 26.6, 65.9, 127.9, 128.2, 136.3, 152.3,
145.9, 153.0, 197.6. MS (EI) m/z (%): 320 (Mþ 10%), 305 (100), 262
(17), 201 (15), 187 (13), 151 (13), 141 (76), 133 (80), 115 (15), 75 (22),
73 (34). HRMS calcd for C16H24O3Si2: 320.1264, found: 320.1273.
4.2.3. 2,2,4,4-Tetramethyl-3-(4-nitro)benzylidene-1,5-dioxa-2,4-
disilacycloheptane (2c) (yield 67%)
1H NMR (CDCl3)
d (ppm): 0.11 (s, 6H, SiCH3), 0.37 (s, 6H, SiCH3),
3.76–3.78 (m, 2H, CH2O), 3.87–3.89 (m, 2H, CH2O), 7.36 (dd, 2H,
J¼8.8 Hz, Ar), 7.92–7.94 (m, 2H, Ar), 8.18 (s, 1H, –CH]). 13C NMR
4.3.1. (E)-2-Methyl-40-nitrostilbene (3d) (yield 62%)
(CDCl3)
d
(ppm): ꢁ1.4, 0.7, 65.9, 66.0, 123.3, 124.8, 128.4, 138.6,
1H NMR (CDCl3)
d
(ppm): 2.46 (s, 3H, CH3), 7.03 (d,1H, J¼16.1 Hz,
147.6, 151.2. MS (EI) m/z (%): 323 (Mþ 2%), 308 (75), 293 (12), 264
(80), 218 (15), 203 (18), 148 (50), 133 (100), 115 (48), 101 (30), 73
(20). HRMS calcd for C14H21O4Si2N: 323.1009, found: 323.0997.
CH]CH), 7.08 (d, 1H, J¼16.1 Hz, CH]CH), 7.20–7.25 (m, 2H), 7.49–
7.54 (m, 2H), 7.60–7.66 (m, 2H), 8.21–8.25 (m, 2H). 13C NMR (CDCl3)
d
(ppm): 19.9, 124.1, 125.5, 126.3, 126.8, 127.5, 128.6, 130.6, 130.9,
135.2, 136.3, 144.0, 146.7. MS (EI) m/z (%): 239 (Mþ, 100%), 223 (12),
207 (8), 192 (25), 178 (62), 165 (18), 115 (20), 63 (5). HRMS calcd for
C15H13NO2: 239.0946, found: 239.0969.
4.2.4. 2,2,4,4-Tetramethyl-3-(3-methoxy)benzylidene-1,5-dioxa-
2,4-disilacycloheptane (2d) (yield 88%)
1H NMR (CDCl3)
d
(ppm): 0.10 (s, 6H, SiCH3), 0.38 (s, 6H, SiCH3),
3.83 (s, 3H CH3O), 3.86 (t, 2H, CH2O), 7.22–7.30 (m, 4H, Ar), 7.67 (s,
1H, –CH]). 13C NMR (CDCl3)
4.3.2. (E)-3-Cyano-40-methoxystilbene (3f) (yield 88%)
d
(ppm): ꢁ6.6, ꢁ4.1, 50.0, 60.6, 60.7,
1H NMR (CDCl3)
d (ppm): 3.84 (s, 3H, OCH3), 6.89–6.94 (m, 2H,
107.7, 108.0, 108.4, 115.0, 123.7, 137.3, 143.6, 149.2. MS (EI) m/z (%):
308 (Mþ 3), 293 (92), 265 (30), 249 (25), 193 (17), 175 (37), 133
(100), 115 (30), 73 (28), 59 (25), 45 (23). HRMS calcd for
C15H24O3Si2: 308.1264, found: 308.1256.
Ar), 7.08 (d, 1H, J¼16.2 Hz, CH]CH), 7.13 (d, 1H, J¼16.2 Hz,
CH]CH), 7.43–7.48 (m, 4H, Ar), 7.68–7.75 (m, 2H, Ar). 13C NMR
(CDCl3)
d (ppm): 55.4, 112.8, 114.2, 118.8, 123.9, 127.9, 129.0, 129.3,
129.5, 129.9, 130.2, 130.7, 138.8, 159.2. MS (EI) m/z (%): 235 (Mþ,
100%), 219 (17), 204 (25), 190 (25), 165 (30), 152 (10), 140 (6), 89
(12), 63 (15). HRMS calcd for C16H13NO: 235.0997, found: 235.1006.
4.2.5. 2,2,4,4-Tetramethyl-3-(4-methoxy)benzylidene-1,5-dioxa-
2,4-disilacycloheptane (2e) (yield 80%)
1H NMR (CDCl3)
d
(ppm): 0.24 (s, 6H, SiCH3), 0.41 (s, 6H, SiCH3),
4.4. Representative procedure for the synthesis of (E,E)-1,4-
3.83 (s, 3H, CH3O), 3.86–3.89 (m, 4H, CH2O), 6.87–6.92 (dd, 2H,
diarylbuta-1,3-dienes
J¼8.5 Hz), 7.09–7.12 (d, 2H, J¼8.6), 7.67 (s, 1H, –CH]). 13C NMR
(CDCl3)
d
(ppm): ꢁ1.4, 1.2, 55.2, 65.8, 65.8, 112.9, 113.3, 129.4, 130.5,
The glass reactor (100 mL, two-necked, round-bottomed flask
equipped with a magnetic stirring bar, reflux condenser, argon
bubbling tube and thermostated heating oil bath) was evacuated and
flushed with argon. Compound 2 (5 mmol) and THF (20 mL) were
added to the reactor. At room temperature 12 mmol of TBAF (1 M
solution in THF) was added and the mixture was stirred for 10 min.
After this time, 4.55 mmol of the respective (E)-styryl iodide and
18.3 mg (0.05 mmol) of [Pd(C3H5)Cl]2 were added and the reaction
mixture was stirred under argon for 1 h at 65 ꢀC. After the reaction
was completed (GC–MS analysis) the volatiles were evaporated
under vacuum and the crude product was chromatographed on silica
gel (eluentdtoluene) to afford the analytically pure products.
133.6, 154.5, 159.5. MS (EI) m/z (%): 308 (Mþ 1%), 293 (100), 250 (8),
266 (20), 191 (5), 159 (10), 133 (24), 115 (5), 73 (12). HRMS calcd for
C15H24O3Si2: 308.1264, found: 308.1252.
4.2.6. 2,2,4,4-Tetramethyl-3-(4-methyl)benzylidene-1,5-dioxa-2,4-
disilacycloheptane (2f) (yield 85%)
1H NMR (CDCl3)
d
(ppm): 0.22 (s, 6H, SiCH3), 0.42 (s, 6H, SiCH3),
2.42 (s, 3H, CH3), 3.82–3.85 (m, 2H, CH2O), 3.91–3.96 (m, 2H, CH2O),
7.19 (s, 4H, Ar), 7.72 (s,1H, –CH]).13C NMR (CDCl3)
d
(ppm): ꢁ1.5, 0.4,
21.2, 65.8, 65.9, 127.8, 128.6, 137.2, 138.2, 147.5, 154.9. MS (EI) m/z (%):
277 (Mþꢁ15,100%), 234 (20), 208 (12),160 (20),133 (56),115 (20), 73
(15). HRMS calcd for C15H24O2Si2, [Mꢁ15]: 277.1080, found: 277.1069.
4.4.1. (E,E)-1-(4-Methylphenyl)-4-phenylbuta-1,3-diene (4a)
4.2.7. 2,2,4,4-Tetramethyl-3-(4-chloro)benzylidene-1,5-dioxa-2,4-
(yield 86%)
disilacycloheptane (2g) (yield 90%)
1H NMR (CDCl3)
d
(ppm): 2.35 (s, 3H, CH3), 6.62–6.69 (m, 2H,
ArCH]CH), 6.87–6.95 (m, 2H, ArCH]CH), 7.13–7.22 (m, 2H), 7.30–
7.36 (m, 3H), 7.42–7.45 (m, 4H). 13C NMR (CDCl3)
(ppm): 21.3,
126.2, 127.3, 128.2, 128.5, 129.3, 129.3, 132.1, 132.7, 134.5, 137.6,
137.4. MS (EI) m/z (%): 220 (Mþ, 100%), 205 (96), 190 (20), 178 (10),
165 (8), 128 (32), 115 (24), 105 (35), 91 (30), 77 (20), 63 (18), 51 (22).
HRMS calcd for C17H16: 220.1252, found: 220.1262.
1H NMR (CDCl3)
d (ppm): 0.12 (s, 6H, SiCH3), 0.34 (s, 6H, SiCH3),
3.82–3.86 (dt, 4H, CH2O), 7.15 (d, 2H, J¼8.1 Hz), 7.29 (d, 2H,
d
J¼8.5 Hz), 7.59 (s, 1H, –CH]). 13C NMR (CDCl3)
d
(ppm): ꢁ1.4, 0.6,
65.9, 128.1,129.0,133.7,139.5, 150.2, 153.0. MS (EI) m/z (%): 297 (Mþ,
75%), 253 (55), 133 (35), 73 (25). HRMS calcd for C14H21ClO2Si2,
[Mꢁ15]: 297.0534, found: 297.0537.
4.3. Representative procedure for the synthesis
4.4.2. (E,E)-1-(4-Bromophenyl)-4-phenylbuta-1,3-diene (4b)
of (E)-stilbenes
(yield 80%)
1H NMR (CDCl3)
d
(ppm): 6.57–6.67 (m, 2H, ArCH]CH), 6.88–
6.96 (m, 2H, ArCH]CH), 7.22–7.28 (m, 3H), 7.31–7.36 (m, 2H), 7.43–
7.46 (m, 4H). 13C NMR (CDCl3)
(ppm): 121.2, 126.3, 126.4, 127.7,
The glass reactor (100 mL, two-necked, round-bottomed flask
equipped with a magnetic stirring bar, reflux condenser, argon
d

5502
P. Pawlu´c et al. / Tetrahedron 65 (2009) 5497–5502
Lim, E.; Tak, J.; Sim, M.; Lee, D.; Park, N.; Oh, W. K.; Hur, K. Y.; Kang, E. S.; Lee,
H.-C. Bioorg. Med. Chem. Lett. 2007, 17, 4481–4486.
127.8, 128.7, 128.9, 129.9, 131.4, 131.7, 131.8, 133.5. MS (EI) m/z (%):
286 (Mþ, 60%), 285 (58), 269 (8), 205 (100), 190 (25), 169 (22), 152
(8), 128 (25), 115 (15), 101 (22), 63 (20), 50 (20). HRMS calcd for
C16H13Br (79Br): 284.0201, found: 284.0212.
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4.4.3. (E,E)-1-(4-Methoxyphenyl)-4-(4-methylphenyl)buta-1,3-
3. For excellent review on the catalytic methods for the synthesis of stilbenes, see:
Ferre´-Filmon, K.; Delaude, L.; Demonceau, A.; Noels, A. F. Coord. Chem. Rev.
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diene (4c) (yield 68%)
1H NMR (CDCl3)
d (ppm): 2.35 (s, 3H, CH3), 3.82 (s, 3H, OCH3),
6.58–6.62 (m, 2H), 6.76–6.80 (m,1H), 6.84(d,1H,15.6 Hz), 6.88(d, 2H,
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J¼8.1 Hz), 7.14(m, 2H), 7.34(d, 2H, J¼8.1 Hz), 7.38(d, 2H,J¼8.1 Hz).13C
NMR (CDCl3) d (ppm): 21.2, 55.3,114.2,126.2,127.4,127.6,128.2,129.4,
129.5, 120.3, 131.6, 131.8, 134.7, 137.2, 159.2. MS (EI) m/z (%): 250 (Mþ,
100%), 235 (30), 220 (22),192 (10),165 (8),159 (10),121 (10),105 (15).
4.4.4. (E,E)-1-(4-Acetylphenyl)-4-(4-methylphenyl)buta-1,3-diene
(4d) (yield 80%)
1H NMR (CDCl3)
d (ppm): 2.36 (s, 3H, CH3), 2.60 (s, 3H, COCH3),
6.48–6.62 (m, 2H), 6.90–7.02 (m, 2H), 7.12 (d, 2H, 7.6 Hz), 7.36 (d,
2H, J¼8.0 Hz), 7.54 (m, 2H), 7.92 (d, 2H, J¼8.0 Hz). 13C NMR (CDCl3)
d
(ppm): 21.2, 26.3, 126.2, 126.8, 127.8, 128.8, 129.4, 130.6, 132.3,
134.1, 134.8, 135.6, 138.2, 143.0, 197.8. MS (EI) m/z (%): 262 (Mþ, 40),
247 (100), 219 (62), 204 (30), 143 (10), 129 (12), 101 (10). HRMS
calcd for C19H18O: 262.1357, found: 262.1366.
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4.5. X-ray crystal structure analysis
Crystals of approximate dimensions 0.3ꢃ0.3ꢃ0.4 mm3 (2b),
0.02ꢃ0.1ꢃ0.4 mm3 (3e) and 0.02ꢃ0.4ꢃ0.4 mm3 (3f) were grown
from the hexane solution. The crystals of 3e and 3f were obtained as
very thin plates, this caused the relatively poor quality of the
datadhowever the data are good enough for the structure analysis.
The X-ray diffraction data were collected on Oxford Diffraction four-
circle diffractometer equipped with CCD detector30 at room tem-
perature. The data were corrected for Lp and absorption effects.31
The crystal data together with some experimental and refinement
details are given in Table 3. The structures were solved by direct
methods with SHELXS9732 and refined by full-matrix least squares
with SHELXL97.32 Non-hydrogen atoms were refined anisotropi-
cally, hydrogen atoms were located from the ideal geometry32 and
refined as ‘riding model’. The isotropic displacement parameters of
hydrogen atoms were set at 1.2 (1.4 for methyl groups) times the
equivalent displacement parameters of appropriate carrier atoms.
Crystallographic data (excluding structure factors) for the struc-
tural analysis has been deposited with the Cambridge Crystallo-
graphic Data Centre, No. CCDC-648155 (2b), CCDC-713055 (3f) and
CCDC-713056 (3e). Copies of this information may be obtained free
of charge from: The Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK. Fax: þ44(1223)336-033, e-mail: deposit@ccdc.cam.ac.uk,
or www: www.ccdc.cam.ac.uk.
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Acknowledgements
25. Pawluc, P.; Marciniec, B.; Hreczycho, G.; Gaczewska, B.; Itami, Y. J. Org. Chem.
2005, 70, 370–372.
26. Pawluc, P.; Hreczycho, G.; Marciniec, B. J. Org. Chem. 2006, 71, 8676–8679.
27. For application of silver nitrate to palladium-catalyzed arylation of vinylsilanes
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30. Oxford Diffraction Version 1.171.31.8; CrysAlis CCD, Oxford Diffraction Ltd: 2007.
31. Oxford Diffraction Version 1.171.31.8; CrysAlis RED, Oxford Diffraction Ltd: 2007.
32. Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
Financial support from the Ministry of Science and Higher Ed-
ucation (Poland); Grant NN 204 238734 and PBZ KBN 118/T09/17 is
gratefully acknowledged.
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