Testing the 1,1,3,3-tetramethyldisiloxane linker in olefin metathesis

Article abstract of DOI:10.1016/j.crci.2013.01.017

Compounds 12-15, possessing two styrenes connected by a silicon linker [1,1,3,3 tetramethyl-di-siloxane], were synthesized, characterized and used as model compounds for the ring-closing metathesis (RCM) catalyzed by commercially available ruthenium catalysts 1, 2 and 3. The RCM reactions of 12 and 15 in the presence of catalysts 1 or 2 resulted exclusively in the formation of (E)-stilbenes. The RCM reactions of 13 and 14, compounds possessing alkoxide substituents in the ortho position to styrene functionality, were not observed in the presence of 2, presumably due to the formation of inactive Hoveyda type ruthenium complexes. The RCM of mixture of 12 and 15, with 2, was used for the detailed examination of the mechanism of metathesis reactions investigated in this work. They revealed that both inter- and intramolecular metathesis is possible, in this case, despite the use of siloxane linker.

Full text of DOI:10.1016/j.crci.2013.01.017

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Full paper/Memoire
Testing the 1,1,3,3-tetramethyldisiloxane linker in olefin metathesis
Ewa Jabłonka-Gronowska, Bartłomiej Witkowski, Paweł Horeglad,
*
Tomasz Gierczak, Karol Grela
Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
A B S T R A C T
A R T I C L E I N F O
Compounds 12-15, possessing two styrenes connected by a silicon linker [1,1,3,3
Article history:
tetramethyl-di-siloxane], were synthesized, characterized and used as model compounds
for the ring-closing metathesis (RCM) catalyzed by commercially available ruthenium
catalysts 1, 2 and 3. The RCM reactions of 12 and 15 in the presence of catalysts 1 or 2
resulted exclusively in the formation of (E)-stilbenes. The RCM reactions of 13 and 14,
compounds possessing alkoxide substituents in the ortho position to styrene functionality,
were not observed in the presence of 2, presumably due to the formation of inactive
Hoveyda type ruthenium complexes. The RCM of mixture of 12 and 15, with 2, was used
for the detailed examination of the mechanism of metathesis reactions investigated in this
work. They revealed that both inter- and intramolecular metathesis is possible, in this
case, despite the use of siloxane linker.
Received 30 October 2012
Accepted after revision 24 January 2013
Available online xxx
Keywords:
Catalysis
Olefin metathesis
Ruthenium
Stilbenes
´
ß 2013 Published by Elsevier Masson SAS on behalf of Academie des sciences.
1. Introduction
often examined for their utility as drugs components. For
example, they can be isolated from grapes and combre-
Stilbenoids are well-known compounds applied in the
pharmaceutical industry. Some stilbenoids occur in nature,
but their synthetic analogs are also known [1,2]. Naturally
occurring stilbenoids are prominent building blocks in
organic synthesis. Both (E)- and (Z)-stilbenoids have
important biological activities [3,4]. They possess anti-
oxidative, anti-microbial and anti-tumor properties [5],
induce apoptosis (programmed cell death) [6], cause
vascular disruption in tumors [7] or inhibit tubulin
polymerization [8]. Among (E)-stilbenoids, resveratrol
and its derivatives play a crucial role in cancer therapy
due to their physiological and therapeutic properties [9].
Among (Z)-stilbenoids combretastatins possess the most
interesting properties for pharmaceutical industry, due to
their ability to inhibit tubulin polymerization [8].
tastatins from the willow bush. Stilbenoids can also be
modified to enhance their medicinal properties [10].
However, currently known synthetic methods for obtain-
ing stilbenoids are frequently complex and not efficient
enough. Therefore, it is important to find novel and simple
methods to synthesize stilbenoid derivatives [11,12].
Stilbenes were initially obtained in Wittig [13] and
Horner–Wadsworth–Emmons reactions [14]. Unfortu-
nately, these reactions have led to the formation of
carbon–carbon double bonds, providing unsatisfactory
(E)/(Z) selectivity. To enhance the (E)/(Z) selectivity a
number of transition metal-based catalysts were later
used, such as palladium complexes in Heck [15], Negishi–
Stille [16], Suzuki [17] and tandem [18] processes.
Alternatively, low-valent titanium complexes were in a
stoichiometric manner used for coupling two aldehydes or
ketones in a McMurry reaction [19]. Moreover, in the
presence of molybdenum [20] or ruthenium [21] com-
plexes, a new carbon–carbon double bond can be directly
formed in the olefin metathesis reaction between two
styrenes. This method is very promising as it allows the use
For economic reasons, stable stilbenoids that can be
isolated in large quantities from natural sources are most
* Corresponding author.
E-mail address: klgrela@gmail.com (K. Grela).
1631-0748/$ – see front matter ß 2013 Published by Elsevier Masson SAS on behalf of Acade´mie des sciences.
http://dx.doi.org/10.1016/j.crci.2013.01.017
Please cite this article in press as: Jabłonka-Gronowska E, et al. Testing the 1,1,3,3-tetramethyldisiloxane linker in olefin
metathesis. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.017

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Fig. 1. Substrates used in the present study.
of a broad range of substrates and requires only a small
amount of catalyst under relatively mild experimental
conditions. However, problems with (E)/(Z) stereoselec-
tivity and the tendency for the formation of the mixture of
products due to cross-metathesis (CM) or homo-dimeriza-
tion (HD) are the main drawbacks of this approach.
Fig. 2. Structures of the ruthenium catalysts 1, 2 and 3 used in this study.
reagents 8–11, respectively. The completeness of the
metalation step was guaranteed by rising the temperature
from
0 to 25 8C. The reaction of cinammyllithium
Therefore, according to our knowledge, only
examples of stilbene formation using alkene metathesis
are reported in the literature [20–22].
a
few
derivatives 8–11 with 0.6 equiv. of 1,3-dichloro-1,1,3,3-
tetramethyldisiloxane afforded exclusively compounds
12–15. We obtained the products with (E)-isomer excess
of 88–92%.
In order to eliminate the drawbacks of the stilbenoid
synthesis via metathesis, which are indicated above, we
have investigated the system where two styrenes are
connected by silicon linker [1,1,3,3-tetramethyldisilox-
ane], as shown in Fig. 1. Here, we describe the effect of the
use of such linker in the stilbenoid synthesis on the
selectivity of metathesis reaction using standard metathe-
sis condition (dichloromethane [DCM] at 40 8C and toluene
at 80 8C) and commercially available catalysts 1–3 (Fig. 2).
Initially, we have examined the reactivity of compound
12 in olefin metathesis using complexes 1–3 (Fig. 1) at 40 8C
in DCM and 80 8C in toluene (Table 1). The reaction did not
proceed in the presence of the first-generation Grubbs
catalyst 3 (5 mol%) in DCM at 40 8C (Table 1, entry 3), and 12
was still present in the reaction mixture, indicating no
degradation of the substrate under the reaction conditions.
Even an increase of temperature had no effect on the
reaction performed with catalyst 3 (5 mol/%) in toluene at
80 8C (Table 1, entry 5). The use of catalysts 1 and 2 at 40 8C
(Table1, entry1and2)led totheformationofstilbenein44%
and 91% yields, respectively. At high temperature (80 8C),
catalyst 2 promoted the reaction very effectively, resulting
in 90% of yield (Table 1, entry 4). In all cases the formation of
stilbene has been proven by GC–MS analysis (Tab. I). In the
case of reactions catalyzed by 1 and 2, we compared the
retention times of the reaction product and the (Z)- and (E)-
stilbene standards, and found that only (E)-isomer was
formed.
2. Results and discussion
2.1. Preparation of 1,3-dicinnamyl-1,1,3,3-
tetramethyldisiloxane derivatives
For our studies, we have chosen 1,3-dicinnamyl-
1,1,3,3-tetramethyldisiloxane derivatives (Fig. 3) as model
compounds as in this case two styrenes are connected by
silicon linker. Following the synthetic route presented in
Fig. 3, desired lithium reagents were obtained by metala-
tion of allyl-substituted arenes 4-7 by n-buthyllithium–
tetramethylethylenediamine (n-BuLi–TMEDA) in tetrahy-
drofuran (THF) at 0 8C, resulting in the formation of lithium
On the basis of initial results presented above, catalyst 2
(UmicoreTM M2) was chosen for further examination of the
metathesis reactions of compounds 13–15 (Figs. 4 and 5).
Fig. 3. Synthetic route of 1,3-dicinnamyl-1,1,3,3-tetramethyldisiloxane derivatives.
Please cite this article in press as: Jabłonka-Gronowska E, et al. Testing the 1,1,3,3-tetramethyldisiloxane linker in olefin
metathesis. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.017

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Table 1
Metathesis of substrate 12 witch catalysts 1–3.
Catalyst
Solvent
Temperature (8C)
Yeld (%)a
1
2
3
4
5
1
2
3
2
3
DCM
40
40
40
80
80
44
91
0
DCM
DCM
Toluene
Toluene
90
0
Conditions: catalyst (5 mol%), t = 12 h, c = 0.1 mol/L.
a
Yields determined by GC–MS analysis of the reaction mixture.
The reactivity of substrate 15 was found to be similar to the
reactivity of 12. Despite noticeable (E)/(Z) isomerisation of
substrate 15 resulting in (E)/(Z) of 88/12, we observed that
metathesis of 15 led exclusively to the (E)-stilbene and was
also fast and efficient, and no other products were formed.
However, both 13 and 14 were inactive towards metathe-
sis and the formation of stilbene 17 and 18, respectively,
was not observed (Table 1).
Fig. 5. Metathesis reaction promoted by catalyst 2.
1. For the latter the lack of RCM of 13 is in line with our
earlier observations.
In the next step, we performed the metathesis reaction
using the mixture of compounds 12 and 15 in order to
show whether inter- or intramolecular process operate in
that case (Fig. 7). The metathesis of 12:15 (1:1) was
catalyzed by 2 (5 mol%, c = 0.02 mol/L). We monitored the
reaction progress by the GC–MS and observed that initially
(after 15 min), only compound 23 was formed. After
prolonged reaction time, the formation of compounds 16,
19 and 22 was observed. After 5 h, the products 16, 19 and
22 were present in 26:17:49 molar ratios, respectively.
Noteworthy, the metathesis reaction of 12 + 15 (mixed in
molar ratio 1:1) proceeded more slowly in comparison
with the metathesis reaction performed separately for
compound 12 or 15. This experiment indicates that both
CM and RCM may operate in the investigated system. The
control CM reaction with styrene and 3,4 dimethoxystyr-
In order to explain the lack of metathesis activity of 13
and 14 catalyzed by 2, we performed the equimolar
reaction between 13 and catalyst 2, obtaining compound
20 (Fig. 6). Compound 20 was isolated as green crystals in
49% yield. Noteworthy, the formation of the new catalyst
inactive in the metathesis of 13, explains the lack of
formation of 17. It should be noted that complex 20 [23] is
a methyl analog of Hoveyda–Grubbs catalyst (21), which
apparently exhibits low activity in olefin metathesis with
this specific substrate. As 21 is expected to be formed in the
case of an equimolar reaction between 14 and 2, the lack of
formation of 18 should be explained by low catalytic
activity of 21 in the metathesis of 14. In order to check the
stability of substrates under the reaction conditions, we
performed the stability tests in the absence of Ru catalysts
by heating compounds 12–15 at 80 8C for 3 h. It was
confirmed that the substrates are stable under these
conditions. To support our findings discussed above, the
formation of the catalyst 20 in the RCM of 13 prevents
further metathesis reaction, we performed RCM of 13 with
ene promoted with catalyst
2 (the experiment was
performed analogously to the one with 12 and 15) shows
Fig. 4. Reaction profiles of the compounds 12–15 with catalyst
2 (5 mol/%).
Fig. 6. Formation of Hoveyda–Grubbs catalysts in reaction of 13 and 14.
Please cite this article in press as: Jabłonka-Gronowska E, et al. Testing the 1,1,3,3-tetramethyldisiloxane linker in olefin
metathesis. C. R. Chimie (2013), http://dx.doi.org/10.1016/j.crci.2013.01.017

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Fig. 8. Possible structures for the silane by-product.
was detected by GC–MS. For the concentration of 0.02 mol/
L, we observed the same stilbene derivatives, in 14:16:35
molar ratio, respectively. The above study showed that
concentration of 12 and 15 influences the composition of
the products formed only slightly (Table 2).
After characterization of the styrene derivatives formed
in metathesis of 12–15, we have focused on the fate of the
disiloxane part. The GC–MS analysis of the reaction
mixtures revealed the presence of only one silane-
containing product for both 12 and 15. The GC–MS peak,
representing this product had a retention time of 7.67 min.
This retention time and the mass spectrum shown on
(Fig. 9) indicate the presence of divinyldisiloxane 24,
according to the mass spectra library. However, unambig-
uous identification was not possible due to some
differences between the spectrum shown in Fig. 9 and
the mass spectrum of compound 24 in the NIST library.
Fragmentation process of both compounds (showed in
Supplementary data, Figs. S3 and S4), most likely begins
with the elimination of methyl radical leading to the
formation of the ion m/z = 171.
Fig. 7. Structures of the possible products formed in the metathesis of
12+15 mixture.
The most significant difference between the spectrum
of the compounds is the absence of the ion m/z = 159 for the
silane obtained in this work. For the divinyldisiloxane 24,
this ion is most likely produced by the silicon–carbon bond
cleavage and the elimination of the ethene radical from the
ion m/z = 186.
that simple CM of these substrates leads to the formation
of 16, 19 and 22 in 32:26:48 molar ratios, respectively. It
shows that the presence of siloxane linker influences the
distribution of products.
In order to investigate the concentration effect on the
product distribution, we also performed the experiment
described above using two different concentrations,
0.1 mol/L or 0.02 mol/L, of both 12 and 15. After 2 h for
the reaction in concentration 0.1 mol/L, we obtained
stilbene derivatives 16,19 and 22 in 12:17:30 molar ratio,
respectively. In the reaction mixture, a small amount of 23
However, on account of the cyclic nature of the
compound 25 showed on Fig. 8, such a bond cleavage
will not lead to the formation of the ion m/z = 159. Cyclic
structure of the silane present in the reaction mixture is
supported by the higher intensity of the molecular ion
m/z = 186 compared with the mass spectrum of the
divinyldisiloxane 24. As it is showed on Fig. 9, the
remaining peaks in the mass spectrum can be formed
from both silanes. Therefore, the cyclic silane 25 showed
on Fig. 8 is most likely present in the reaction mixture. Due
to the short retention time of the investigated compound,
it was reasonable to assume that the silane had relatively
small molecular weight, and thus, we did not consider
aggregates. The formation of both 24 and 25 in the
presence of ruthenium catalysts can be explained.
A vinylsilane derivative 24 can be formed if the double
bond isomerisation and subsequent metathesis reaction
occurred. Both reactions could be catalyzed by ruthenium
species. Compound 25 is expected to be formed in
the metathesis reaction of 12–15 in two subsequent
metathesis processes. The first is the formation of
ruthenium complex with silane chain and styrene
derivative abstraction. The second includes intramolecular
cyclization, which leads to the oxadisilepine derivatives
and benzylidene ruthenium catalyst. Noteworthy the
Table 2
Products formed in the metathesis of 12+15 mixture.
Time (min)
Concentration (mol/L)
Yield (%)a
16
19
22
5
0.1
0
0
0
0
0
0
0.02
0.1
15
30
60
120
300
0
0
0
0.02
0.1
0
3
0
0
5
7
0.02
0.1
1
4
4
6
12
11
16
16
17
23
17
30
35
49
0.02
0.1
6
11
14
26
0.02
0.02
Conditions: catalyst 2 (5 mol%).
a
Yields determined by GC–MS analysis of the reaction mixture.
Please cite this article in press as: Jabłonka-Gronowska E, et al. Testing the 1,1,3,3-tetramethyldisiloxane linker in olefin
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Fig. 9. Comparison of mass spectra of the vinylsilane derivative 24 and the obtained compound 25.
presence of 25 supports the intramolecular process
operating in the investigated system.
min to 300 8C, maintained for 10 min; analysis was
completed in 33.7 min. MS was equipped with electron
impact (EI) ion source (70 eV) and the spectrum was
acquired in the total ion current (TIC) mode in the mass
range of 35–500 m/z, solvent cut was 5 min. GC–MS
solution 2.53 (Shimadzu) software was used to process
the data.
To check the linearity of the MS detector response, a
linear regression analysis of the peaks areas versus
concentration of the studied compounds was carried
out. The linearity was determined by the square correla-
tion coefficients of the calibration curves that were
generated by injections of the standard solutions at
concentration levels between 0.1 and 0.5 mg/mL. The
straight lines with the regression coefficients ꢀ 0.99 were
obtained.
3. Conclusions
A series of compounds including two styrenes con-
nected by a siloxane linker (12–15) were synthesized and
investigated in metathesis reactions catalyzed by selected
ruthenium catalysts 1–3. Indenylidene ruthenium catalyst
2 (UmicoreTM M2) was the most efficient in the metathesis
of 12 and 15 and as a result (E)-stilbene derivatives were
formed. In the case of 13 and 14, the presence of the ortho-
alkoxide substituents in the aromatic ring led to the
formation of Hoveyda–Grubbs type catalysts, which were
essentially inactive in the studied process. Therefore no
metathesis product could be obtained in this case. Finally,
despite the presence of the linker both inter- or
intramolecular metathesis processes operate for the
studied substrates.
4.1.1. Starting materials
Catalyst [1,3-bis(2,4,6-trimethylphenyl)-2-imidazoli-
dinylidene]dichloro-(3-phenyl-1H-inden-1-ylidene)
(tricyclohexylphosphine)rutchenium 2 was purchased
from UMICORE and used without purification. Catalyst
4. Experimental
bis(tricycylohexylphosphine)benzylidene
rutchenium
4.1. General information
dichloride 3 was purchased from Aldrich and used
without purification. Catalyst 1 was synthesized accord-
ing literature [24].
All reactions were performed under argon using
standard Schlenk techniques. Solvents were distilled from
standard drying agents and kept under argon. NMR spectra
were recorded with a Varian 500. 1H and 13C NMR chemical
shifts are listed in ppm using CDCl3 as a standard. Column
chromatography: Merck silica gel (230–400 mesh).
Gas chromatography (GC) was performed using GC–
MS-QP2010 Ultra gas chromatograph coupled to QP-5000
(Shimadzu) quadrupole mass spectrometer (MS); GC–MS
was equipped with an AOC-5000 auto-sampler (Shi-
madzu). Separation of the studied compounds was carried
out with HP-5ms (Agilent) chemically bonded fused silica
4.2. Typical procedure for synthesis of 12–15 derivatives
A Schlenk tube was charged with an allylbenzene
(1 mmol), TMEDA (1.2 mmol) and THF (10 mL) under an
argon atmosphere. The solution was cooled to 0 8C. n-
Buthyllithium (1.2 mmol; 2.5 mol/L solution in n-Hexane)
was slowly added. Next, a cooling bath was removed and
the reaction mixture was stirred at 25 8C for 1 h. Then, after
cooling the reaction mixture to À40 8C, 1,3-dichloro-
1,1,3,3-tetramethyldisiloxane (0.6 mmol) was added. Re-
action proceeded at À40 8C for 30 min and then the
reaction mixture was allowed to reach room temperature.
The mixture was stirred at room temperature for 15 h,
while the reaction progress was checked by TLC analysis.
After that time, the solvent was removed from the reaction
mixture by evaporation. Oily residue was purified by
column chromatography (n-Hexane/Et2O 97:3). The (E)/(Z)
ratio was determined by 1H NMR.
capillary column (30 m  0.25 mm, 0.25
mm). Carrier gas
(He) was delivered at a flow rate of 36.8 mL/min, split ratio
was 50:1 and the pressure was maintained constantly.
Chromatographic conditions were as follows: injector
temperature 300 8C; temperatures of the MS transfer line
and ion source were set to 300 8C and 320 8C, respectively.
The following temperature program of the column oven
was used: initially 40 8C maintained for 2 min, then 12 8C/
Please cite this article in press as: Jabłonka-Gronowska E, et al. Testing the 1,1,3,3-tetramethyldisiloxane linker in olefin
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4.2.1. Compound 12: 1,3-dicinnamylo-1,1,3,3-
tetramethyldisiloxane
respectively). Reaction progress was checked by GC–MS
analysis. Next, the solvent was removed on a rotary
evaporator. Oily residue was purified by column chroma-
tography (n-Hexane/Et2O 97:3), and the product was
obtained as white crystals. The crude product was
crystallized from toluene at À20 8C.
Colorless oil, mixture of (E)- and (Z)-isomers, 92% yield,
1H NMR (500 MHz, CDCl3, 25 8C)
d = 0.12 (s, 6H), 1.71 (bd,
2H, J = 6.79 Hz); 6.16–6.28 (m, 2H); 7.12–7.18 (m, 2H),
7.22–7.32 (m, 3H) ppm; 13C NMR (125 MHz, CDCl3, 25 8C)
d
= 0.2; 25.6; 125.5; 126.3; 126.7; 128.4; 129.0;
138.4 ppm; HRMS (ESI) calcd for [M+Na+] (C22H30OSi2Na):
389.1750; found: 389.1733; IR (film): 3024, 2956, 1253
Metathesis of compound 12 yields product 16 as white
crystals (67% yield). 1H, 13C NMR spectra were according to
the literature [25].
n
(stretching Si–O–Si), 1064, 961, 851, 831, 799, 748,
692 cmÀ1
Metathesis of compound 13 gives the product as white
crystals of compound 19. 60% yield. 1H, 13C spectra were
according to the literature [26].
4.2.2. Compound 13: 1,3-di[3-(2-methoxyphenyl)allyl]-
1,1,3,3-tetramethyldisiloxane
4.4. Typical procedure for a stability test
Colorless oil, mixture of (E) and (Z) isomer 91:9; 86%
yield, 1H NMR (500 MHz, CDCl3, 25 8C)
d=0.21 (s, 6H); 1.83
A Schlenk tube was charged with disiloxane derivatives
(dd, 2H, J = 1.29 Hz, J = 8.25 Hz); 3.87 (s, 3H); 6.30 (dt, 1H,
J = 15.84, J = 8.25 Hz); 6.66 (d, 1H, J = 15.84 Hz); 6.89 (dd,
1H, J = 0.8, J = 8.25 Hz); 6.95 (ddd, 1H, J = 0.65, J = 7.43,
J = 7.6 Hz); 7.21 (ddd, 1H, J = 1.78, J = 7.43, J = 8.25 Hz); 7.43
(dd, 1H, J = 1.78, J = 7.6 Hz) ppm; 13C NMR (125 MHz, CDCl3,
12–15 (0.25 mmol) and dry toluene (2.5 mL) was added
under an argon atmosphere. Next, a 10 mL sample of this
solution was taken and diluted to 1 mL with the same
solvent and analysed by GC–MS. The mixture was then
stirred in an oil bath at 80 8C for 3 h. Next, the second GC–
MS analysis was made in the same manner. No change was
observed.
25 8C)
d = 0.2; 26.1; 55.4; 110.8; 120.6; 123.6; 126.0;
127.2; 127.4; 127.6; 156.0 ppm; HRMS (ESI) calcd for
[M+Na+] (C24H34O3Si2Na): 449.1944; found: 449.1935; IR
(film):
n
2956, 1488, 1242 (stretching Si–O–Si), 1052, 1031,
4.5. Catalyst 20 formation
806, 748 cmÀ1
Disiloxane derivative 12 (0.156 mmol), catalyst
2
4.2.3. Compound 14: 1,3-di[3-(2-isopropoxyphenyl)allyl]-
1,1,3,3-tetramethyldisiloxane
(0.13 mmol) and copper(I) chloride (0.13 mmol) were
added to the Schlenck flask in dry toluene (1.5 mL) under
argon atmosphere. The mixture was stirred in an oil bath at
80 8C; progress of the reaction was controlled by TLC. Full
conversion was observed after 15 min. The reaction
mixture was cooled to room temperature, the solvent
was removed in vacuo, and the product was purified by
column chromatography (c-Hexane/Ethyl Acetate 4:1).
Removal of the solvent, washing with a small amount of n-
pentane and drying under vacuum afforded the product as
a green solid in 49% yield. 1H and 13C NMR spectra were
according to the literature [24].
Colorless oil, mixture of (E) and (Z) isomers 92: 8; 92%
yield, 1H NMR (500 MHz, CDCl3, 25 8C)
d = 0.13 (s, 6H); 1.34
(d, 6H J = 6.15 Hz); 1.75 (dd, 2H J = 1.29, J = 8.24 Hz); 4.51
(Sept, 1H, J = 6.15); 6.22 (dt, 1H, J = 15.85, J = 8.24 Hz); 6.57
(d, 1H, J = 15.85 Hz); 6.83–6.91 (m, 2H); 7.11 (m, 1H); 7.37
(dd, 1H, J = 7.60, J = 1.61 Hz) ppm; 13C NMR (125 MHz,
CDCl3, 25 8C)
d = 0.2; 22.3; 26.1; 70.7; 114.4; 120.7; 124.1;
126.2; 126.9; 127.0; 128.9; 154.4 ppm; HRMS (ESI) calcd
for [M+Na+] (C28H42O3Si2Na): 505.2570; found: 505.2575;
IR (film):
n 2976, 1484, 1238 (stretching Si–O–Si), 1119,
1062, 844, 803, 747 cmÀ1
Acknowledgements
4.2.4. Compound 15: 1,3-di[3-(3,4-dimethoxyphenyl)allyl]-
1,1,3,3-tetramethyldisiloxane
Financial support was provided by the University of
Warsaw (Grant No. 501/86-DSM-100100 and No. 501/86-
DSM-102400). We wish to thank Dr. Hanna Majewska-
Elz˙ anowska for proof reading the manuscript.
Pale yellow oil, mixture of (E) and (Z) isomers 88:12;
90% yield. 1H NMR (500 MHz, CDCl3, 25 8C)
d = 0.13 (s, 6H);
1.69 (dd, 2H J = 0.97, J = 8.08); 3.86 (s, 3H); 3.87 (s, 3H); 6.08
(dt, 1H, J = 7.92, J = 8.09, J = 15.68), 6.19 (d, 1H, J = 15.67);
6.78 (d, 1H, J = 8.25); 6.82 (dd, 1H, J = 1.78, J = 8.91); 6.85 (d,
1H, J = 1.78) ppm; 13C NMR (125 MHz, CDCl3, 25 8C)
d = 0.2;
Appendix A. Supplementary data
25.4; 55.8; 55.9; 108.4; 111.3; 118.2; 124.7; 128.6; 131.7;
147.9; 149.0 ppm; HRMS (ESI) calcd for [M + Na+]
(C26H38O5Si2Na): 509.2155; found: 509.2138; IR (film):
2955, 1514, 1256 (stretching Si–O–Si), 1234, 1158, 1139,
1059, 1028, 836, 802 cmÀ1
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.crci.2013.01.017.
n
4.3. Typical procedure for metathesis reaction
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