The preparation of polymer beads by photocationic suspension co-polymerisation of 2-(arylsilyl)ethyl vinyl ethers

Article abstract of DOI:10.1039/b201520j

Polymer beads have been prepared by photocationic suspension polymerisation of 2-(aryldimethyl)silyl ethers in perfluorooctane in the course of our studies on polymer-supported desymmetrisation of 1-silacyclohexa-2,5-dienes. Good yields of 100-200 μm beads of satisfactory shape have been obtained using a perfluorinated co-polymer as stabilising agent. These beads have no permanent porosity although they have a high nominal cross-linking level. Their swelling in common organic solvents is comparable with those of Merrifield or TentaGel gel-type resins.

Full text of DOI:10.1039/b201520j

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The preparation of polymer beads by photocationic suspension
co-polymerisation of 2-(arylsilyl)ethyl vinyl ethers
Laurent Porres, Hervé Deleuze* and Yannick Landais
1
Laboratoire de Chimie Organique et Organométallique, UMR 5802-CNRS,
Université Bordeaux I, 33405 Talence, France. E-mail: h.deleuze@lcoo.u-bordeaux.fr
Received (in Cambridge, UK) 12th February 2002, Accepted 9th July 2002
First published as an Advance Article on the web 3rd September 2002
Polymer beads have been prepared by photocationic suspension polymerisation of 2-(aryldimethyl)silyl ethers in
perfluorooctane in the course of our studies on polymer-supported desymmetrisation of 1-silacyclohexa-2,5-dienes.
Good yields of 100–200 µm beads of satisfactory shape have been obtained using a perfluorinated co-polymer as
stabilising agent. These beads have no permanent porosity although they have a high nominal cross-linking level.
Their swelling in common organic solvents is comparable with those of Merrifield or TentaGel gel-type resins.
generally easy to synthesise and iii) vinyl ethers, well known to
Introduction
homopolymerise very slowly under radical conditions,5 are
prone to polymerize under cationic conditions.6 It is obvious
that, in this case, the classical aqueous suspension polymeris-
ation cannot be used and therefore an anhydrous system should
be developed in order to obtain the desired poly(vinyl ether)
supports in a bead shape.
Solid-phase chemistry is classically performed using gel-type or
macroporous polystyrene beads.1 The polystyrene backbone is
generally inert for the majority of reactions involved in
polymer-supported synthesis. However, for some applications
including Birch reduction of arenes or Friedel–Crafts reactions,
the presence of aromatic rings on the support might be
troublesome.
We recently reported on the desymmetrisation of 1-silacyclo-
hexa-2,5-dienes as a straightforward route to optically active
sugar mimics having potent glycosidase inhibitory activity.2
Such dienes are easily available through Birch reduction of the
corresponding arylsilanes. In order to simplify the purification
steps in the event of the development of a combinatorial
approach, we envisioned extension of the strategy to solid-
In this paper, we report our preliminary studies on the syn-
thesis of organosilyl-functionalised vinyl ethers and their co-
polymerisation in suspension with divinyl ether cross-linkers in
order to obtain an insoluble polymer support.
Results and discussion
Polymeric supports are generally prepared in bead shapes by
suspension polymerisation.7 This method allows the obtention
of spherical particles in the diameter size range of 100–500 µm,
the most suitable for applications in solid-phase supported
chemistry. In the vast majority of examples of suspension
polymerisation reported in the literature, the suspending
medium is an aqueous solution containing a stabilising agent,8
whereas the dispersed droplets contain a mixture of hydro-
phobic co-monomers and a radical initiator. In the case of the
preparation of polymeric beads from hydrophilic monomers
such as acrylic acid, the so-called inverse suspension polymer-
isation has to be used.9 In this case, the suspending medium is
generally paraffin oil, but low-boiling organic solvents were also
used,10 the hydrophilic co-monomers being then dispersed as an
aqueous solution. Obviously, the presence of water precludes
the use of anionic or cationic polymerisation systems. The sys-
tem must meet with several requirements which are difficult to
combine: i) the two phases involved should be completely
immiscible at the temperature used for the polymerisation, ii)
the monomer has to be liquid in order to form homogeneous
droplets whereas it has to be completely insoluble in the con-
tinuous medium, iii) an efficient stabilising agent has to be
found in order to avoid agglomeration of the polymerising
phase and to allow the obtention of spherical beads and iv) the
polymerisation should initiate only when a stable suspension of
droplets of the right size is obtained. Following the work of
pioneers,11 Meldal and co-workers have developed the concept
of non-aqueous suspension polymerisation using silicone oil as
a continuous medium.12 In order to generalise their approach,
they have synthesised a new kind of surfactant allowing the
preparation of a large range of PEG-based resins by anionic
or cationic ring-opening polymerisation.13 The different beaded
phase chemistry using
hexa-2,5-diene (Scheme 1). We thus initiated a study on the
a polymer supported 1-silacyclo-
Scheme 1 Polymer supported Birch reduction of an arylsilane.
preparation of polymer-supported arylsilanes and their modifi-
cation onto the corresponding diene through Birch reduction.
The silicon atom, located between the support and the aromatic
ring, would be used both as an orientating group for the Birch
reduction3 and as a ’traceless linker’.4a The silylethoxy group
frequently used in silicon protective groups4b (i.e. SEM group)
would constitute a suitable and robust linker, which should be
easily removed through a fluoride mediated β-elimination. The
resulting fluorosilane would then be further oxidised into the
corresponding hydroxy group through the Tamao–Kumada–
Fleming oxidation. As we needed a non-styrenic polymer
support for our purpose, we reasoned that vinyl ether would be
an attractive monomer because: i) a poly(vinyl ether) is quite
stable towards chemical reaction, ii) functional vinyl ethers are
2198
J. Chem. Soc., Perkin Trans. 1, 2002, 2198–2203
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b201520j

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supports thus obtained were successfully used in solid-phase
synthesis.14 However, even if silicone oil is a good suspend-
ing medium for hydrophilic PEG-containing monomers, the
solubility of other kinds of compounds in low-viscosity silicone
oil is not always negligible.15 In these cases, a truly non-
solubilising medium is required. Perfluorocarbon solvents are
a very attractive alternative for this purpose. The use of a per-
fluorocarbon solvent as the suspending medium in suspension
polymerisations was proposed by Zhu16 and Mosbach and co-
workers17 in their pioneering works. This approach appeared
attractive since perfluorocarbons are highly insoluble with
non-fluorinated organic compounds near or below ambient
temperature.18 The perfluorocarbon used in this study was the
perfluorooctane.
Scheme 3 Synthesis of the perfluorinated emulsifying agents S1 and
S2.
radical polymerisation using two different molar ratios (Scheme
3). The results of the polymerisation have been summarized in
Table 1. The co-polymer composition is very similar to that of
the monomer feed. This behavior is in good agreement with
previously published results with closely related systems.24
1. Optimisation of the suspension polymerisation conditions
We started our study by searching for the optimal conditions
needed to obtain regular spherical beads with the 2-chloroethyl
vinyl ether 1–tri(ethylene glycol) divinyl ether 2 system (Scheme
2). Our first attempt was realised with BF3ؒEt2O as a polymer-
1.2 Test of the efficiency of the stabilisers. The ability of the
two co-polymers obtained above to act as stabilising agents of
an organic–perfluorocarbon suspension was tested with our
system. Our results are reported in Table 2. While aggregation
still appears with the weakly fluorinated stabiliser S1, the use of
the more highly fluorinated S2 at its higher possible concen-
tration allows the obtention of satisfactory yields of spherical
beads. Therefore, S2 at a concentration of 0.15% (w/v) was used
for all the following experiments.
2. Synthesis of the organosilyl vinyl ethers
Different synthetic routes may be envisioned to obtain
these compounds. However, in each case the key intermediate is
the 2-(aryldimethylsilyl)ethanol which will give access to the
desired product by transetherification.
2.1 Preparation of 2-(dimethylphenylsilyl)ethanol 5. 2-
(Dimethylphenylsilyl)ethanol 5 was obtained through reduction
of an α-silyl ester prepared in one step by Rh2(OAc)4 catalyzed
insertion of ethyl diazoacetate into the Si–H bond of
PhMe2SiH.25 The fragile α-silyl ester was not isolated but
directly reduced into the desired alcohol 5 in 70% overall yield
(Scheme 4). In parallel, we developed an alternative procedure
Scheme 2 Photocationic suspension co-polymerisation of 2-chloro-
ethyl vinyl ether with tri(ethylene glycol) divinyl ether.
isation catalyst19 and sodium dodecylsulfonate as a stabiliser.
The suspension polymerisation device which we used has previ-
ously been described.20 The polymerisation was very rapid, even
at Ϫ70 ЊC, and the polymer was collected as a black powder on
the walls of the reactor without formation of beads. Obviously,
we had to find a more efficient stabiliser as well as more
practical polymerisation conditions.
Crivello et al.21 have described a photoinitiated cationic
polymerisation of vinyl ethers. In our case, such an approach
would allow us to set up good suspension conditions at
room temperature before the initation of the polymerisation
by irradiation. The exothermicity developed by the reaction
should be absorbed by the large excess of continuous phase.
Commercially available triaryl sulfonium hexafluorophosphon-
ate was chosen as the catalyst and perylene was added to initiate
the photolysis of the triarylsulfonium salt in the visible region.22
In order to avoid aggregation of the forming beads, the
stabiliser should be soluble in the continuous phase (i.e. the
perfluorooctane) but still be able to interact with the dispersed
droplets of monomer. In our case, the ideal stabiliser
should constitute a convenient balance of a perfluoro-alkylated
component and a perhydro-alkylated part. Having failed to
obtain satisfactory results with the commercially available
perfluorohexyldecene, we decided to synthesise our own
stabiliser.
Scheme
4
Synthesis of 2-(dimethylphenylsilyl)ethanol 5 through
rhodium–carbene insertion.
allowing the large scale preparation of our precursors and
the possible extension to the synthesis of diversely substituted
analogues. Compound 5 was thus available starting from
PhMe2SiCl (Scheme 5) using a Reformatski reaction, followed
by reduction of the ester function of the α-silyl ester with
LiAlH4 (Scheme 6). It is noteworthy that the use of ether as a
co-solvent in the Reformatski reaction was essential in order to
Based on the pioneering work of Mosbach and co-workers17
we reasoned that a co-polymer of perfluoroacrylate and a
methacrylate would lead to an efficient stabilising agent.
1.1 Synthesis of the stabilising agent. Co-polymers of
2-ethylhexyl methacrylate 3 and 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,
10,10-heptadecafluorodecyl acrylate 423 were synthesised by
Scheme 5 Synthesis of aryldimethylchlorosilanes.
J. Chem. Soc., Perkin Trans. 1, 2002, 2198–2203
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Table 1 Synthesis of the stabilizers
Monomer feed
composition
(mol%)
Co-polymer
compositiona
(mol%)
Resulting stabiliser
3
4
3
4
Yield of co-polymer(%)
Fluorine loadinga (%, w/w)
S1
S2
0.7
0.5
0.3
0.5
0.75
0.54
0.25
0.46
83
78
33
44
a Estimated from elemental analysis (F).
Table 2 Efficiency of the stabiliser in the photocationic suspension co-polymerisation
Monomer feed
composition (mol%)
Chlorine loading of the
co-polymer/mmol gϪ1
Yield of polymer
in satisfactory
bead shape (%)
Stabiliser used
(%, w/v)
Co-polymer
aspect
Entry
1
2
Expecteda
Obtainedb
1
2
3
0.5
0.5
0.5
0.5
0.5
0.5
6.5
6.5
6.5
5.7
5.6
5.2
S1 (0.1)
S2 (0.1)
S2 (0.15)c
Aggregation
Aggregation ϩ some beads
Beads ϩ some aggregation
—
15
85
a Calculated from the monomer feed composition. b Estimated from elemental analysis (Cl). c Maximum apparent solubility.
Scheme 6 Synthesis of 2-(aryldimethylsilyl)ethanols 5 and 6 via the
Reformatski reaction.
obtain acceptable yields of α-silyl esters.26 The use of benzene
alone led to poor results due to the aggregation and thus to
Scheme 7 Synthesis of 2-(aryldimethylsilyl)ethyl vinyl ethers 7 and 8.
the low reactivity of the zinc reagent in this solvent. Accord-
ingly, analogue 6 was prepared using the same route, start-
ing from 4-methoxyphenyldimethylchlorosilane, available from
the corresponding aryl bromide27 as depicted in Scheme 5.
Analogue 6 was prepared since it was envisioned that such
arylsilanes could be versatile precursors for other supported
organosilanes. A 4-methoxyphenyl group on silicon can be
readily cleaved under electrophilic conditions since electron-
donating groups on the aromatic ring are known to dramatic-
ally increase the rate of ipso substitution of arylsilanes.28
For instance, ipso substitution with HCl would afford the
corresponding chlorosilane which would constitute a valuable
precursor for various types of supported organosilanes.
2.2 Transetherification. The introduction of the vinyl ether
function was carried out by transetherification of the silyl
alcohol with ethyl vinyl ether using a catalytic amount of
Hg(OOCF3)2 (Scheme 7).29
Scheme
8
Preparation of supports P1 to P3 by photocationic
suspension co-polymerisation.
Having our organosilyl vinyl ether monomers in hand, we
then studied their photocationic polymerisation in suspension.
used in this case were those established previously for the 1–2
system. Our results are summarized in Table 3.
Good yields of beads having a spherical shape were obtained
using both cross-linkers. The resulting polymers P1–3 are soft
light-orange colored beads in the diameter range 800–200 µm
(Fig. 1).
3. Photocationic suspension polymerisation of the
(aryldimethylsilyl)ethyl vinyl ethers
Polymer beads were prepared using 7 and 8 as monomers
and tri(ethylene glycol)divinyl ether 2, or cyclohexane-1,4-
dimethanol divinyl ether 9 as cross-linking agents (Scheme 8).
Compound 9 was employed in order to increase the rigidity of
the resulting beads. The suspension polymerisation conditions
4. Structural characterisation of supports P1–3
4.1 Specific surface area. Specific surface areas of our dif-
ferent supports were measured using the nitrogen adsorption
2200
J. Chem. Soc., Perkin Trans. 1, 2002, 2198–2203

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Table 3 Photocationic suspension co-polymerisation of the organosilyl monomers
Silicon co-polymer loading/mmol gϪ1
Monomer feed
composition (mol%)
Yield of polymer in
satisfactory bead shape (%)
Entry
Expecteda
Obtainedb
Beads aspect
P1
P2
P3
7 (0.5)
7 (0.5)
8 (0.5)
2 (0.5)
9 (0.5)
2 (0.5)
4.6
4.9
4.6
3.7
4.8
3.5
Some aggregation
Beads ϩ little aggregation
Beads ϩ little aggregation
75
82
85
a Calculated from monomer feed composition. b Estimated from elemental analysis (Si).
Experimental
1. Materials
Triarylsulfonium hexafluorophosphonate (50% solution in
propylene carbonate) (Aldrich), perylene (Aldrich), and tri-
(ethylene glycol) divinyl ether (Aldrich) were used without
purification. Perfluorooctane (P.M. fluorochemicals, Moscow,
Russia) was distilled (bp760 = 103–104 ЊC) before use. The
remaining solvents and chemicals were general purpose
reagents. All reactions were performed under a flow of N2.
2. Synthesis of the stabiliser S2
Perfluorooctylethyl acrylate 4 (2 mmol, 1.12 g), 2-ethylhexyl
methacrylate 3 (2 mmol, 0.396 g) and AIBN (0.04 mmol,
6.6 mg) were placed in a 25 mL Schlenk tube. The system was
degassed three times then heated at 80 ЊC under stirring for
15 h. The resulting gel was then redissoved in ether (100 mL),
concentrated under vacuum then precipitated in methanol. A
white powder was collected under filtration (1.1 g, yield = 78%).
Elemental analysis F: 32.9%.
Fig. 1 Optical microscope photography of P1 beads.
method through a BET (Brunauer–Emmett–Teller) treat-
ment. The results are as follows: P1 = 0.08 m2 gϪ1, P2 = 1.1 m2
g
Ϫ1, P3 = 1.3 m2 Ϫ1. Therefore, it appears that in the dry
g
state, our poly(vinyl ether) polymers have no permanent
porosity.
The same procedure was employed for the synthesis of S1.
3. Synthesis of 2-(dimethylphenylsilyl)ethanol with ethyl
diazoacetate
4.2 Swelling of the supports in solvents. The degree of
swelling of a polymeric support is a good indication of its
compatibility with the solvent and therefore, of the ability of
small molecules to diffuse towards the polymeric moieties
grafted onto the chains.30 This parameter is even more import-
ant for supports having no permanent porosity such as
Dimethylphenylsilane (7.14 g, 52.4 mmol) was dissolved in
dichloromethane (20 mL) in a 100 mL two-neck round bottom
flask. Rh2(OAc)4 (0.88 g, 2 mmol) was then added. A solution
of ethyl diazoacetate (5.74 g, 50.3 mmol) in dichloromethane
(40 mL) was then added slowly to the stirred solution at room
P1–3
.
temperature using a syringe pump at a rate of 1.2 mL hϪ1
.
We have mesured the swelling of support P1 in some common
organic solvents and compared them with those reported in the
literature for Merrifield gel-type resin and TentaGel S RAM
(both 1% DVB cross-liked).31 The results are summarised in
Fig. 2. The range of solvents compatible with supports P1 is
comparable with that of Merrifield resins, but is less extended
than for TentaGel. The swelling values are of the same order of
magnitude.
When the addition was complete, dichloromethane was evapor-
ated under vacuum and anhydrous ether (50 mL) was added to
the residue. A solution of LiAlH4 (1.9 g, 50 mmol) in ether
(30 mL) was then added dropwise at 0 ЊC, over a period of
15 min. The reaction was heated under reflux for 1.5 h, then
cooled down to 0 ЊC in an ice bath and water (30 mL) was
added. The organic layer was decanted and the aqueous phase
extracted with ether (2 × 50 mL). The combined organic layers
were collected, dried over MgSO4, and the solvent evaporated
under vacuum. Compound 5 was obtained as an oil (5 g, yield =
70%). 1H-NMR δ (CDCl3) 0.3 (6H, s, (CH3)2Si), 1.25 (2H,
CH2Si), 1.8 (1H, s, OH), 3.7 (2H, m, CH2OH), 7.2–7.45 (5H,
Ar). 13C-NMR δ (CDCl3) Ϫ2.8 ((CH3)2Si), 21.1 (CH3Si), 59.9
(OCH2), 127.8 (CH–CH–CH), 129.0 (CH–CH–CH), 133.4
(Si–C–CH), 138.5 ((CH3)2Si–C). IR (cmϪ1) 3362 (OH), 2956
(C–H), 1425, 1251 (Si–CH3), 1119 (SiAr), 1038, 825, 738 (Ar),
700 (Ar).
4. Synthesis of chlorodimethyl(4-methoxyphenyl)silane
In a 100 mL two-neck round bottom flask, magnesium turnings
(5.24 g, 222 mmol) were placed in anhydrous ether (30 mL). A
solution of 4-bromoanisole (31.8 g, 170 mmol) in ether (75 mL)
was added dropwise to the suspension, over a period of 1 h. The
reaction mixture was then heated under reflux for 6 h, and then
cooled in an ice bath. A solution of dichlorodimethylsilane
(25.8 g, 200 mmol) in ether (40 mL) was added dropwise over a
Fig.
2
Solvent swelling of support P1 compared with some
commercial beads.
J. Chem. Soc., Perkin Trans. 1, 2002, 2198–2203
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period of 30 min. The reaction mixture was then heated under
reflux for 80 h. After cooling, the resulting thick suspension was
filtered over Celite under vacuum and the solid washed with
petroleum ether (2 × 50 mL). The organic layers were collected
and concentrated under vacuum. The resulting viscous oil was
distilled under reduced pressure in a Kugelrohr apparatus (bp0.6
= 82 ЊC), to give a light-orange oil (13.6 g, yield = 40%).
1H-NMR δ (CDCl3) 0.6 (6H, s, (CH3)2Si), 3.7 (3H, s, CH3O),
6.75–6.9 (2H, Ar), 7.2–7.5 (2H, Ar). 13C-NMR δ (CDCl3) 2.3
((CH3)2Si), 55.1 (OCH3), 113.9 (CH3O–C–CH), 121.1 (Si–C–
CH), 124.9 ((CH3)2Si–C), 134.8 (CH3–O–C). IR (cmϪ1) 2963
(C–H), 1599 (Ar), 1498 (Ar), 1248 (Si–CH3), 1114 (Si–Ar),
1077, 1041, 808, 767 (Ar).
8. Synthesis of 2-(dimethylphenylsilyl)ethanol 5
The title compound was obtained from ethyl 2-dimethylphenyl-
silyl ethanoate using the same procedure as for 2-[dimethyl-
(4-methoxyphenyl)silyl]ethanol (yield = 96%).
9. Synthesis of 2-(dimethylphenylsilyl)ethylvinyl ether 7
In a 500 mL three-necked round bottom flask equipped with a
thermometer, a dropping funnel and a septum, was placed a
solution of 2-(dimethylphenylsilyl)ethanol 5 (6.6 g, 40 mmol) in
ethyl vinyl ether (200 mL). Triethylamine (0.56 mL, 4 mmol),
then mercury trifluoroacetate (0.856 g, 2 mmol) in ethyl vinyl
ether (5 mL) were then sucessively added to the stirred suspen-
sion. The reaction mixture was heated under reflux for 60 h.
After cooling to room temperature, a 2 M solution of NaOH
(50 mL) was added dropwise with stirring. The organic layer
was decanted and the aqueous phase extracted with ether
(3 × 50 mL). The combined organic layers were collected and
successively washed with saturated solutions of NaHCO3 (50
mL), NH4Cl (50 mL) and NaCl (50 mL). After drying over
MgSO4, the solution was concentrated under vacuum to give a
viscous oil. Kugelrhor apparatus distillation under reduced
pressure (bp0.8 = 70 ЊC), gave compound 7 as a yellow oil
5. Synthesis of ethyl 2-[dimethyl(4-methoxyphenyl)silyl]-
ethanoate
Zinc powder (acid-washed) (3.5 g, 50 mmol), was suspended in
dry benzene (55 mL) in a 250 mL three-necked round bottom
flask equiped with a magnetic stirrer, a condenser and an inlet
for nitrogen. An iodine crystal was then added and the suspen-
sion gently heated at 40–50 ЊC under stirring while a solution of
chlorodimethyl(4-methoxyphenyl)silane (8.5 g, 42.4 mmol) and
ethyl bromoacetate (8.81 g, 52.7 mmol) in a mixture of benzene
(12 mL) and ether (12 mL) was added dropwise over a period of
1 h. The reaction mixture was then heated under reflux for 2.5
h. After cooling the flask in an ice bath, a solution of hydro-
chloric acid (1 mol LϪ1, 50 mL) was added dropwise. The
organic layer was decanted and the organic phase washed
sucessively with HCl (1 mol LϪ1, 50 mL), saturated Na2CO3
(2 × 50 mL) then water (2 × 50 mL). After drying over MgSO4
and elimination of the solvent under vacuum, a light-yellow oil
1
(5.1 g, yield = 62%). H-NMR δ (250 MHz, CDCl3) 0.35 (6H,
s, (CH3)2Si), 1.10 (2H, t, J = 8.1 Hz, CH2Si), 3.70 (2H, t,
J = 8.1 Hz, CH2CH2O), 3.80 (2H, t, J = 8.1 Hz, OCH2CH), 4.05
(1H, dd, J = 6.8, 1.8 Hz, OCH᎐CH ), 4.20 (1H, dd, J = 14.4, 1.8
᎐
2
Hz, OCH᎐CH ), 6.5 (1H, dd, J = 14.4, 6.8 Hz, OCH᎐CH ),
᎐
᎐
2
2
7.55–7.65 (5H, Ar). 13C-NMR δ (90 MHZ, CDCl3) Ϫ02.5
((CH ) Si), 16.9 (Si–CH ), 65.3 (Si–CH –CH O), 86.8 (O–CH᎐
᎐
3
2
2
2
2
CH ), 114.5 (–C–CH), 121.0 (Si–C–CH), 152.1 (CH ᎐CH–O).
᎐
2
2
IR (cmϪ1) 2956 (C–H), 1636 (OCH᎐CH ), 1614 (OC᎐CH ),
᎐
᎐
2
2
1
was obtained (10.7 g, yield = 99%). H-NMR δ (CDCl3) 0.2
1596 (Ar), 1504 (Ar), 1318 (Si–C), 1248 (Si–CH ), 1182 (OCH ᎐
᎐
2
3
(6H, s, (CH3)2Si), 1.2 (2H, t, O–CH2–CH3), 2.0 (2H, s, CH2Si),
3.65 (3H, s, CH3O), 3.9 (2H, t, O–CH2–CH3), 6.7–6.9 (2H, Ar),
7.0–7.3 (2H, Ar). 13C-NMR δ (CDCl3) Ϫ2.4 ((CH3)2Si), 14.8
(CH3–CH2), 25.1 (Si–CH2), 52.0 (O–CH2–CH3), 55.1 (O–CH3),
114.1 (CH3O–C–CH), 122.0 (Si–C–CH), 128.9 ((CH3)2Si–C),
134.8 (CH O–C), 172.1 (C᎐O). IR (cmϪ1) 2959 (Si–C), 1720
CH2), 1112 (Si–Ar), 823, 778 (Ar). Found C 64.8; H 8.2; Si 12.3.
C12H18OSi requires C 64.9; H 8.1; Si 12.6%.
10. Synthesis of 2-[dimethyl(4-methoxyphenyl)silyl]ethyl vinyl
ether 8
᎐
3
The title compound was obtained from 2-[dimethyl-
(4-methoxyphenyl)silyl]ethanol 6 using the same procedure as
for 2-(dimethylphenylsilyl)ethyl vinyl ether 7 (yield = 75%).
1H-NMR δ (CDCl3) 0.35 (6H, s, (CH3)2Si), 1.25 (2H, t,
J = 8.0 Hz, CH2Si), 3.70 (2H, t, J = 8.1 Hz, CH2CH2O), 3.80
(2H, t, J = 8.0 Hz, OCH2CH), 3.85 (3H, s, CH3O), 3.95 (1H, dd,
(COOEt), 1596 (Ar), 1504 (Ar), 1464, 1279 (Si–C), 1248
(Si–CH3), 1183, 1114 (Si–Ar), 824, 776 (Ar).
6. Synthesis of ethyl [2-(dimethylphenyl)silyl]ethanoate
The title compound was obtained from chlorodimethyl-
phenylsilane according to the same procedure as for ethyl
2-[dimethyl(4-methoxyphenyl)silyl]ethanoate, (yield = 98%).
Spectroscopic data were identical in many respects with those
described in the literature.25b
J = 6.5, 2.1 Hz, OCH᎐CH ),.4.15 (1H, dd, J = 14.2, 1.7 Hz,
᎐
2
OCH᎐CH ), 6.45 (1H, dd, J = 14.2, 6.5 Hz, OCH᎐CH ), 6.9–7.0
᎐
᎐
2
2
(2H, Ar), 7.45–7.55 (2H, Ar). 13C-NMR δ (90 MHZ, CDCl3)
Ϫ0.25 (CH3)2Si), 17.1 (Si–CH2), 55.0 (OCH3), 65.5 (Si–CH2–
CH O), 86.5 (O–CH᎐CH ), 113.8 (CH O–C–CH), 121.0
᎐
2
2
3
7. Synthesis of 2-[dimethyl(4-methoxyphenyl)silyl]ethanol 6
(Si–C–CH), 129.1 (CH ) Si–C), 135.0 (CH O–C), 151.7 (CH ᎐
᎐
3 2 3 2
CH–O). IR (cmϪ1) 2956 (C–H), 1636 (OCH᎐CH ), 1614 (OC᎐
᎐
᎐
2
In a 100 mL two-necked round bottom flask equiped with a
magnetic stirrer, a condenser and an inlet for nitrogen, a solu-
tion of ethyl 2-[dimethyl(4-methoxyphenyl)silyl]ethanoate (10.7
g, 42 mmol) in ether (100 mL) was added dropwise to a stirred
suspension of LiAlH4 (1.7 g, 45 mmol) in anhydrous ether
(55 mL). The reaction mixture was then heated under reflux for
1.5 h. After cooling in an ice bath, water (50 mL) was added
dropwise and the layers were decanted. The aqueous phase was
washed with ether (2 × 50 mL). The organic phases were
collected, dried under MgSO4, and the solvent evaporated
under vacuum. Compound 6 was obtained as an oil (8.55 g,
yield = 96%). 1H-NMR δ (CDCl3) 0.2 (6H, s, (CH3)2Si), 1.2 (2H,
CH2Si), 1.8 (1H, s, OH), 3.45 (2H, CH2O), 3.6 (3H, s, CH3O),
6.5–6.8 (2H, Ar), 7.0–7.3 (2H, Ar). 13C-NMR δ (CDCl3) Ϫ2.4
((CH3)2Si), 21.2 (CH3Si), 59.7 (OCH2), 127.5 (CH–CH–CH),
134.2 (Si–C–CH), 135.1 (CH3O–Si), 138.1 ((CH3)2Si–C). IR
(cmϪ1) 3363 (OH), 2958 (C–H), 1595 (Ar), 1503 (Ar),
1463, 1277 (Si–C), 1250 (Si–CH3), 1112 (Si–Ar), 1033, 823, 780
(Ar).
CH2), 1596 (Ar), 1504 (Ar), 1318 (Si–C), 1248 (Si–CH3), 1182
(OCH ᎐CH ), 1112 (Si–Ar), 823, 778 (Ar). Found C 66.2; H
8.3; Si 11.6. C13H20OSi requires C 66.1; H 8.5; Si 11.9%.
᎐
2
2
11. Suspension polymerisation
The supports were prepared using a non-aqueous suspension
polymerisation using a parallel-side flanged glass reactor
specially designed according to the literature.7
In a typical experiment, the suspension medium was pre-
pared by dissolving the stabiliser S2 (330 mg) in perfluorooctane
(200 mL) under mechanical stirring (500 rpm) over 1 h. The
speed was then reduced to 250 rpm, and a mixture of tri(ethyl-
ene glycol) divinyl ether 2 (0.92 g, 4.55 mmol), 2-(dimethyl-
phenylsilyl)ethyl vinyl ether 7 (0.83 g, 4.55 mmol), hexafluoro-
phosphonium triarylsulfonium (140 µL) and perylene (10 mg,
0.4 mmol) in dichloromethane (1.8 mL) was added rapidly. The
stirring speed was adjusted (usually between 200–250 rpm)
at room temperature in order to obtain, visually, droplets of
2202
J. Chem. Soc., Perkin Trans. 1, 2002, 2198–2203

View Article Online
6 J. V. Crivello, Adv. Polym. Sci., 1984, 62, 3.
satisfactory size. A day-light tungsten lamp was then placed at
about 5 cm from the wall of the reactor and the suspension
irradiated under mechanical stirring for 30 min. The result-
ing beads were filtered under vacuum, washed with dichloro-
methane (2 × 100 mL) then continuously extracted for 48 h with
THF in a Soxhlet apparatus. After filtration, the beads were
sieved manually (0.17 g > 800; 800 < 0.18 g > 500; 500 < 0.37 g
> 315; 315 < 0.75 g > 200; 0.28 g < 200 µm) The beads in the
diameter range 800–200 µm were collected (1.3 g, 75%), and
both the very small and large particles were discarded. Per-
fluorooctane was regenerated by distillation (190 mL, yield =
90%).
7 D. C. Sherrington, in Polymer-Supported Reactions in Organic
Synthesis, eds.D. C. Sherrington and P. Hodge, Wiley, New York,
1980.
8 (a) P. D. Dowding and B. Vincent, Colloids Surf., A, 2000, 161, 259;
(b) B. Borham, J. A. Wilson, M. J. Gasch, Y. Ko, D. M. Kurth and
M. J. Kurth, J. Org. Chem., 1995, 60, 7375.
9 (a) Z. Lui and B. W. Brooks, Polymer, 1999, 40, 2181; (b) H. G.
Yuan, G. Kalfas and W. H. Ray, J. Macromol. Sci., Rev. Macromol.
Chem. Phys., 1991, C31,(2–3), 215.
10 J. Buchardt and M. Meldal, Tetrahedron Lett., 1998, 39, 8695.
11 (a) R. Arshady, Colloid Polym. Sci., 1992, 270, 717; (b) T. Brock and
D. C. Sherrington, Polymer, 1992, 33, 1773.
12 (a) J. Rademann, M. Grotli, M. Meldal and K. Block, J. Am. Chem.
Soc., 1999, 121, 5459; (b) M. Grotli, C. H. Gotfedsen, J. Rademann,
J. Buchardt, A. J. Clark, J. O. Duus and M. Meldal, J. Comb. Chem.,
2000, 2, 108.
12. Solvent swelling determination
13 (a) M. Grotli, J. Rademan, T. Groth, W. D. Lubell, L. P. Miranda
and M. Meldal, J. Comb. Chem., 2001, 3, 28.
14 (a) A. Craven Sams, M. Grotli and M. Meldal, J. Chem. Soc., Perkin
Trans 1, 2000, 955; (b) J. Rademann, M. Meldal and K. Block,
Chem. Eur. J., 1999, 5, 1218; (c) A. Schleyer, M. Meldal, R. Manat,
H. Paulsen and K. Block, Angew. Chem., Int. Ed. Engl., 1997, 36,
1976.
15 Siloxane Polymers, eds. S. J. Clarson, J. A. Semlyen, PTR Prentice
Hall, Englewood Cliffs, 1993.
16 D. W. Zhu, Macromolecules, 1996, 29, 2813.
The swelling ratio of beads was obtained as follows: about 0.5 g
of dry spherical beads (range size 800–200 µm) were accurately
weighed into a graduated cylinder (id 10 mm). The apparent
volume of the dry material was measured (Vd). Solvent was
added to the cylinder with gentle shaking to remove every
entrapped air. The beads were then allowed to swell without
entrapping air bubbles at room temperature for 48 hours and
the apparent swollen volume mesured (Vs). The swelling volume
was given by: Vs Ϫ Vd.
17 (a) A. G. Mayes and K. Mosbach, Anal. Chem., 1996, 68, 3769;
(b) R. J. Ansell and K. Mosbach, J. Chromatogr. A, 1997, 787, 55.
18 I. T. Howath, Acc. Chem. Res., 1998, 31, 641.
19 S. Murahashi, S. Nozakura and K. Matsumura, J. Polym. Sci.,
Polym. Phys. Ed., 1965, 4, 59.
Conclusion
20 (a) H. Deleuze and D. C. Sherrington, J. Chem. Soc., Perkin Trans. 2,
1995, 12, 2217; (b) A. Chemin, H. Deleuze and B. Maillard,
Eur. Polym. J., 1998, 34, 1395; (c) A. Chemin, H. Deleuze and
B. Maillard, J. Chem. Soc., Perkin Trans. 1, 1999, 2, 137;
(d ) X. Schultze, H. Deleuze and D. C. Sherrington, J. Mol. Cat. A:
Chem., 2000, 159, 257; (e) H. Deleuze, A. Chemin and B. Maillard,
J. Appl. Polym. Sci., 2001, 79, 1297.
21 (a) J. V. Crivello, J. L. Lee and D. A. Conlon, J. Rad. Cur., 1983, 1, 6;
(b) J. V. Crivello, J. Polym. Sci. Chem. Ed., 1999, 37, 4241.
22 J. V. Crivello and J. H. W. Lam, J. Polym. Sci. Chem. Ed., 1979, 17,
1059.
23 Perfluorooctylethyl acrylate 4 was kindly supplied by Dr. B.
Améduri (ENSCM, France). It can also be synthesized according to:
B. Guyot, B. Améduri, B. Boutevin, M. Melas, M. Viguier and
A. Collet, Macromol. Chem. Phys., 1998, 199, 1879.
24 B. Guyot, B. Boutevin and B. Améduri, Macromol. Chem. Phys.,
1996, 197, 937.
This paper describes the efficient preparation of beads by photo-
cationic suspension polymerisation of 2-(aryldimethylsilyl)ethyl
vinyl ethers with perfluorooctane as the dispersing medium.
Even with a nominal cross-linking level of 50%, the resulting
supports have no permanent porosity. In terms of swelling in
solvents, these new poly(vinyl ether) supports behave some-
where between Merrifield and TentaGel resins.
Applications of these new supports to solid-phase organic
synthesis via the Birch reduction of the aryl moiety are
currently under investigation.
References
1 D. C. Sherrington, Chem. Commun., 1998, 2275.
2 (a) R. Angelaud and Y. Landais, J. Org. Chem., 1996, 61, 5202;
(b) R. Angelaud, Y. Landais and K. Schenk, Tetrahedron Lett., 1997,
38, 1407; (c) R. Angelaud and Y. Landais, Tetrahedron Lett., 1997,
38, 8841; (d ) R. Angelaud, Y. Landais and L. Parra-Rapado,
Tetrahedron Lett., 1997, 38, 8845; (e) Y. Landais, Chimia, 1998,
52, 104; ( f ) R. Angelaud, O. Babot, T. Charvat and Y. Landais,
J. Org. Chem., 1999, 64, 9613; (g) Y. Landais and E. Zekri,
Tetrahedron Lett., 2001, 42, 37, 6547.
3 C. Eaborn, R. A. Jackson and R. Pearce, J. Chem. Soc.,
Perkin Trans. 1, 1974, 2055.
4 (a) Solid Phase Synthesis, eds. S. A. Kates, F. Albericio, Marcel
Dekker, New York, 2000; (b) For the use of β-silylethylalcohols as
protective groups in organic synthesis, see: P. J. Kocienski, Protective
Groups, Georg Thieme, New York, 1994.
25 (a) Y. Landais and D. Planchenault, Tetrahedron Lett., 1997, 53,
2855; (b) O. Andrey, Y. Landais, D. Planchenault and V. Weber,
Tetrahedron, 1995, 51, 12083.
26 (a) N. Fotouhi and D. S. Kemp, Int. J. Pept. Protein Res., 1993, 41,
153; (b) J. S. Fessenden and R. J. Fessenden, J. Org. Chem., 1967, 32,
3535.
27 P. G. Gray, R. K. Norris and T. A. Wright, J. Chem. Soc.,
Chem Commun., 1979, 6, 259.
28 (a) F. X. Wooland, J. Paetsch and J. A. Ellman, J. Org. Chem., 1997,
62, 6102; (b) F. B. Dean and C. J. Eaborn, J. Chem. Soc., 1959, 2299.
29 (a) J. Wu, B. K. Shull and M. Korreda, Tetrahedron Lett., 1996, 37,
3647; (b) L. E. Colon and W. H. Watanabe, J. Am. Chem. Soc., 1957,
79, 2828.
30 A. R. Vairo, D. B. Gooding and K. D. Janda, J. Comb. Chem., 2000,
2, 330.
31 R. Santini, M. C. Griffith and M. Qi, Tetrahedron Lett., 1998, 39,
8951.
5 O. Nuyken, J. V. Crivello, Poly(vinylether)s in Handbook of Polymer
Synthesis, Part 1, ed.H. R. Kricheldorf, M. Dekker, NY, 1992, Vol 3,
145.
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