Direct Radical Polymerization of 4-Styryldiphenylphosphine: Preparation of Cross-Linked and Non-Cross-Linked Triphenylphosphine-Containing Polystyrene Polymers

Article abstract of DOI:10.1021/jo035226+

We report herein a simple synthesis of 4-styryldiphenylphosphine and the radical copolymerization of it with styrene, both with and without a cross-linker, to directly form cross-linked and non-cross-linked polystyrene supported triphenylphosphine in which the level of phosphine incorporation can be easily and accurately controlled. The utility of these polymers is demonstrated by their use in Mitsunobu and alcohol bromination reactions.

Full text of DOI:10.1021/jo035226+

therefore, alternative phosphine reagents that are more
easily separated from the reaction mixture have been
extensively examined.5-8
Dir ect Ra d ica l P olym er iza tion of
4-Styr yld ip h en ylp h osp h in e: P r ep a r a tion of
Cr oss-Lin k ed a n d Non -Cr oss-Lin k ed
Tr ip h en ylp h osp h in e-Con ta in in g
P olystyr en e P olym er s
Despite these innovations, triphenylphosphine remains
the preferred reagent in organic synthesis, and therefore,
many approaches to its immobilization on a polymer
support and applications of such polymer-based reagents
have been reported. Many polymers with different solu-
bility profiles have been used in this regard, including
poly(ethylene glycol),9 a ring-opened norbornene-derived
polymer,10 and most recently a non-cross-linked 4-tert-
butylstyrene polymer.11 However, polystyrene, both cross-
linked and non-cross-linked, has been the polymer most
widely used due to its inertness, low cost, and ease of
preparation, and there are numerous reports regarding
various strategies for the attachment of triphenylphos-
phine equivalents to it. Some of the earliest reports for
the preparation of such polymer-bound phosphine re-
agents involved the radical copolymerization12 and ho-
mopolymerization13 of 4-styryldiphenylphosphine (1) (eq
1). Despite the directness of this method, and for reasons
that are not clear, in recent years the most common
method employed for the preparation of polymer-bound
phosphine reagents involves the sequence of bromination
of preformed polystyrene,14 followed by either lithiation
and subsequent reaction with electrophilic chlorodiphe-
nylphosphine15,16 or reaction with lithium diphenylphos-
phide17 (eq 2). Recently, Charette et al. have reported a
different method for the incorporation of triphenylphos-
phine moieties onto non-cross-linked polystyrene via an
Matthew Kwok Wai Choi, Helen Song He, and
Patrick H. Toy*
Department of Chemistry, The University of Hong Kong,
Pokfulam Road, Hong Kong, People’s Republic of China
phtoy@hkucc.hku.hk
Received August 21, 2003
Abstr a ct: We report herein a simple synthesis of 4-styryl-
diphenylphosphine and the radical copolymerization of it
with styrene, both with and without a cross-linker, to
directly form cross-linked and non-cross-linked polystyrene
supported triphenylphosphine in which the level of phos-
phine incorporation can be easily and accurately controlled.
The utility of these polymers is demonstrated by their use
in Mitsunobu and alcohol bromination reactions.
Recent years have seen a growing use of polymer-
supported reagents by organic chemists in traditional
solution-phase synthesis. These reagents may be used to
either selectively remove impurities from synthetic prod-
ucts or to deliver reagents to dissolved synthesis sub-
strates.1 Ley and co-workers have elegantly shown the
power of this later approach in their syntheses of several
structurally complex natural products using exclusively
polymer-supported reagents.2 However, regardless of how
they are used, all polymer-supported reagents have the
effect of reducing product purification to simple filtration
operations. Of the many reagents supported by polymers
available, variations of triphenylphosphine are among the
most broadly used. This is because triphenylphosphine
is not only a reagent in a wide range of organic reactions,3
but it also serves as a ligand in many organometallic
reagents.4 In the field of organic chemistry, attaching
triphenylphosphine to a polymer has the great advantage
that the byproduct of most reactions involving it, triph-
enylphosphine oxide, can be easily removed. When triph-
enylphosphine is used, the removal of this impurity from
the desired synthesis product is often difficult, and
(5) For applications of phosphines that contain basic functional
groups to aid in chromatographic separation of the phosphine and
phosphine oxide, see: Kiankarimi, M.; Lowe, R.; McCarthy, J . R.;
Whitten, J . P. Tetrahedron Lett. 1999, 40, 4497-4500 and references
therein.
(6) For application of a phosphine that contains an acid functional
group to aid in the removal of the phosphine and phosphine oxide,
see: Starkey, G. W.; Parlow, J . J .; Flynn, D. L. Bioorg. Med. Chem.
Lett. 1998, 8, 2385-2390.
(7) For applications of phosphines that contain fluorous tags to aid
in the removal of the phosphine and phosphine oxide, see: Dandapani,
S.; Curran, D. P. Tetrahedron 2002, 58, 3855-3864 and references
therein.
(8) For application of a phosphine that contains an anthracene tag
to aid in the removal of the phosphine and phosphine oxide, see: Lan,
P.; Porco, J . A., J r.; South, M. S.; Parlow, J . J . J . Comb. Chem. 2003,
5, 660-669.
(9) (a) Sieber, F.; Wentworth, P. W., J r.; Toker, J . D.; Wentworth,
A. D.; Metz, W. A.; Reed, N. N.; J anda, K. D. J . Org. Chem. 1999, 64,
5188-5192. (b) Kollhofer, A.; Plenio, H. Chem. Eur. J . 2003, 9, 1416-
1425.
* To whom correspondence should be addressed. Tel: (852) 2859-
2167. Fax: (852) 2857-1586.
(1) (a) Ley, S. V.; Baxendale, I. R.; Bream, R. N.; J ackson, P. S.;
Leach, A. G.; Longbottom, D. A.; Nesi, M.; Scott, J . S.; Storer, R. I.;
Taylor, S. J . J . Chem. Soc., Perkin Trans. 1 2000, 3815-4196. (b)
Clapham, B.; Reger, T. S.; J anda, K. D. Tetrahedron 2001, 57, 4637-
4662. (c) Leadbeater, N. E.; Marco, M. Chem. Rev. 2002, 102, 3217-
3274. (d) McNamara, C. A.; Dixon, M. J .; Bradley, M. Chem. Rev. 2002,
102, 3275-3300. (e) Dickerson, T. J .; Reed, N. N.; J anda, K. D. Chem.
Rev. 2002, 102, 3325-3344. (f) Bergbreiter, D. E. Chem. Rev. 2002,
102, 3345-3384. (g) Fan, Q.-H.; Li, Y.-M.; Chan, A. S. C. Chem. Rev.
2002, 102, 3385-3466.
(10) Arstad, E.; Barrett, A. G. M.; Hopkins, B. T.; Kobberling, J .
Org. Lett. 2002, 4, 1975-1977.
(11) Bergbreiter, D. E.; Li, C. Org. Lett. 2003, 5, 2445-2447.
(12) For a report of this approach that contains no experimental
details, see: McKinley, S. V.; Rakshys, J . W. J . Chem. Soc., Chem.
Commun. 1972, 134-135.
(13) Naaktgeboren, A. J .; Nolte, R. J . M.; Drenth, W. J . Am. Chem.
Soc. 1980, 102, 3350-3354.
(14) Camps, F.; Castells, J .; Font, J .; Vela, F. Tetrahedron Lett. 1971,
20, 1715-1716.
(2) Storer, R. I.; Takemoto, T.; J ackson, P. S.; Ley, S. V. Angew.
Chem., Int. Ed. 2003, 42, 2521-2525.
(15) For use of this approach to prepare non-cross-linked polystyrene-
bound triphenylphosphine, see: Harrison, C. R.; Hodge, P.; Hunt, B.
J .; Khoshdel, E.; Richardson, G. J . Org. Chem. 1983, 48, 3721-3728.
(16) For use of this approach to prepare divinylbenzene cross-linked
polystyrene-bound triphenylphosphine, see: (a) Farrall, M. J .; Frechet,
J . M. J . J . Org. Chem. 1976, 41, 3877-3882. (b) Bernard, M.; Ford,
W. T. J . Org. Chem. 1983, 48, 326-332.
(3) (a) Cobb, J . E.; Cribbs, C. M.; Henke, B. R.; Uehling, D. E.
Polystyrene. In Encyclopedia of Reagents for Organic Synthesis;
Paquette, L. A., Ed.; Wiley: 1995; pp 5357-5363. (b) Valentine, D.
H., J r.; Hillhouse, J . H. Synthesis 2003, 317-334.
(4) For a review of polymer-supported triphenylphosphine organo-
metallic complexes, see: Leadbeater, N. E. Curr. Med. Chem. 2002, 9,
2147-2171.
(17) Relles, H. M.; Schluenz, R. W. J . Am. Chem. Soc. 1974, 96,
6469-6475.
10.1021/jo035226+ CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/12/2003
J . Org. Chem. 2003, 68, 9831-9834
9831

ether linkage.18 This process is also indirect and involves
the sequence of chloromethylation of preformed polysty-
rene followed by etherification with 4-hydroxyphenyl-
diphenylphosphine oxide and subsequent reduction to the
phosphine.
SCHEME 1a
Our interest in developing both soluble19 and in-
soluble20 polystyrene-based reagents led us to require a
reliable method to prepare polystyrene polymers with
varying concentrations of triphenylphosphine moieties in
order to determine effects of functional group concentra-
tion on reagent utility and resin performance. The
indirectness of the last two routes mentioned above made
them unattractive for our use since they involve multiple
reactions that need to proceed predictably and reliably
in order to accurately incorporate the desired amount of
phosphine groups. Therefore, we chose to examine the
route shown in eq 1 that involves the direct radical
copolymerization of 1. Herein we report our results for
preparing such soluble and insoluble reagents with
varying but predictable loading levels by this method.
For the first time, full experimental detail is provided
for the one-step synthesis of 1 together with its radical
copolymerization with styrene. Furthermore, we show the
synthetic utility of the resulting polymer-bound tri-
phenylphosphine reagents by applying them in Mit-
sunobu and alcohol bromination reactions.
To study the polymerization of 1, we first examined
several routes to prepare it on a 100 mmol scale.
Recently, the synthesis of 1 in 89% yield using a modified
Grignard reaction that involves potassium, magnesium
chloride, potassium iodide, and 4-chlorostyrene has been
reported.21 A different synthesis of 1 that involves 4 steps
in 52% overall yield has also been reported.22 For con-
venience, we examined the simple Grignard reaction of
4-bromostyrene using magnesium (Scheme 1).23 To our
satisfaction, this method reproducibly produced 1 in over
50% yield on a 30 g scale.
a
Reaction conditions: (a) Mg, THF, 0 °C; (b) ClPPh2, 0 °C to
rt; (c) PhMe, AIBN, 85 °C; (d) PhCl, water, acacia gum, NaCl,
AIBN, 85 °C.
TABLE 1. Syn th esis of J J -P P h 3 (3)
P content (%)
loading (mmol/g)
1
styrene
yield
(%)
(mmol) (mmol) theor
obsd
theor
obsd
3a
3b
3c
3d
3e
3f
35
25
16
10
5
1
80
0
27
52
65
82
93
259
10.85
7.75
4.96
3.10
1.55
0.31 <0.5
4.96 4.59
9.85
7.25
4.80
3.15
1.57
3.5
2.5
1.6
1.0
0.5
0.1
1.6
3.2
2.3
1.5
1.0
0.5
0.1
1.5
96
90
84
82
75
70
98
3g
With access to adequate quantities of 1 available, we
next examined conditions for the copolymerization of 1
with styrene to prepare a soluble reagent (2) and with
styrene and the cross-linker 1,4-bis(4-vinylphenoxy)-
butane, to form insoluble J andaJ el-PPh3 (J J -PPh3, 3)
(Scheme 1).24 We found that AIBN induced radical
copolymerization of 4:1 and 8:1 mixtures of styrene/1
afforded 2 that had loadings of 1.5 and 1.2 mmol PPh3/g,
2a and 2b, respectively.25 Suspension polymerization of
various molar ratios of styrene and 1, ranging from 93:1
to 0:35, with 2 mol % of the cross-linker initiated by
AIBN26
afforded 3a -f with the predicted loading levels
(Table 1).27 This procedure was used to prepare either
10 or 50 g of polymer 3 per batch. Importantly this
procedure works at both extremes in terms of ratio
between styrene and 1, and allows for the production of
3a , with the theoretical maximum possible loading level
of 3.5 mmol PPh3/g and 3f, that contains minimal loading
of approximately 0.1 mmol PPh3/g.
(18) Charette, A. B.; Boezio, A. A.; J anes, M. K. Org. Lett. 2000, 2,
3777-3779.
(19) (a) Toy, P. H.; J anda, K. D. Acc. Chem. Res. 2000, 33, 546-
554. (b) Toy, P. H.; Reger, T. S.; J anda, K. D. Org. Lett. 2000, 2, 2205-
2207. (c) Choi, M. K. W.; Toy, P. H. Tetrahedron 2003, 59, 7171-7176.
(20) (a) Toy, P. H.; J anda, K. D. Tetrahedron Lett. 1999, 40, 6329-
6332. (b) Toy, P. H.; Reger, T. S.; J anda, K. D. Aldrichimica Acta 2000,
33, 87-93. (c) Toy, P. H.; Reger, T. S.; Garibay, P.; Garno, J . C.;
Malikayil, J . A.; Liu, G.-Y.; J anda, K. D. J . Comb. Chem. 2001, 3, 117-
124.
To assess the synthetic utility of our polymers we chose
to apply them in reactions in which commercially avail-
(24) J andaJ el is a registered trademark of the Aldrich Chemical
Co.
(25) The loading levels of 2a and 2b were determined by elemental
analysis. The homogeneity of the phosphine groups was determined
by 31P NMR spectroscopy.
(26) Attempts to use benzoyl peroxide as the initiator failed to
produce any filterable polymer beads.
(27) A polystyrene supported ferrocene-based triarylphosphine re-
agent has been prepared by this method. Stille, J . K.; Su, H.; Hill, D.
H.; Schneider, P.; Tanaka, M.; Morrison, D. L.; Hegedus, L. S.
Organometallics 1991, 10, 1993-2000.
(21) Borner, H. G.; Heitz, W. Macromol. Chem. Phys. 2000, 201,
740-746.
(22) Hon, Y. S.; Lee, C. F.; Chen, R. J .; Szu, P. H. Tetrahedron 2001,
57, 5991-6001.
(23) For an early synthesis of 1 from the simple Grignard reagent
of 4-chlorostyrene in comparable yield, see: Rabinowitz, R.; Marcus,
R. J . Org. Chem. 1961, 26, 4157-4158.
9832 J . Org. Chem., Vol. 68, No. 25, 2003

TABLE 2. Mitsu n obu Rea ction s Usin g 2a
TABLE 3. Br om in a tion of Alcoh ols Usin g 3g
able polystyrene-bound triphenylphosphine28 has been
successfully applied in, namely Mitsunobu and alcohol
bromination reactions.29,30 The Mitsunobu reactions were
performed using 2a in a 1.5-fold molar excess. The results
are summarized in Table 2. As can be seen, reagent 2a
affords good isolated yields of the expected esters (entries
1-6, 9, and 10) and ethers (entries 7 and 8). Additionally,
even secondary alcohols perform reasonably well with
this crystalline reagent (entries 5 and 6). In these
reactions, it was necessary to precipitate the polymer
using diethyl ether in order to get a crystalline form of
the polymer that was easy to remove by filtration.31 After
removal of the polymer, the crude material was filtered
through a plug of silica gel to afford the pure product,
with no trace of phosphine or phosphine oxide contami-
nants.
To test the performance of J J -PPh3, 3g was used to
convert alcohols to alkyl bromides (Table 3). This polymer
was chosen since the 1.5 mmol/g loading level afforded
reasonable resin swelling and it seemed likely to allow
for efficient substrate diffusion through it. Thus, it was
first reacted with bromine to form the phosphine-halogen
complex in situ that converted the alcohol substrates into
their corresponding alkyl bromides in quantitative yield
in less than 10 min. In these reactions, the pure products
were isolated in essentially quantitative yield after
filtration to remove the polymer and concentration in
vacuo to remove the solvent.
In summary, we have developed a facile synthesis of 1
and used this monomer to directly prepare both non-
cross-linked and cross-linked triphenylphosphine con-
taining polystyrene polymers using homogeneous and
suspension polymerization processes. It is noteworthy
that monomer 1 can be incorporated into the polymers
at predictable levels, depending upon the ratio of mono-
mers used in the polymerization reaction. This allows for
the facile variation of the loading levels of the polymers
and thereby facilitates the study of the effects of func-
tional group density and polymer microenvironment in
polymer-assisted organic synthesis.32 In a pioneering
report by Alexandratos,32c it was observed that for a
different polymer-bound phosphine in Mitsunobu reac-
tions, having maximally loaded polymer is not optimal
(28) Polystyrene-bound PPh3 is available from many suppliers with
loading ranging from 1.0 to approximately 3.0 mmol PPh3/g. J anda-
J el-PPh3 is also commercially available with a loading of approximately
3.0 mmol PPh3/g.
(29) Barrett, A. G. M.; Roberts, R. S.; Schroder, J . Org. Lett. 2000,
2, 2999-3001 and references therein.
(30) Hodge, P.; Khoshdel, E. J . Chem. Soc., Perkin Trans. 1 1984,
195-198.
(31) When either methanol or hexanes was used as the precipitation
solvent, the polymer formed a sticky and intractable residue that was
difficult to filter.
J . Org. Chem, Vol. 68, No. 25, 2003 9833

monomers), and AIBN (0.2 g, 1.3 mmol) in chlorobenzene (10
mL) was injected into the rapidly stirred aqueous solution. The
resulting suspension was heated at 85 °C for 20 h. At this time,
the crude polymer was collected and washed with hot water (3
× 100 mL) and then placed in a Soxhlet extractor and washed
with THF for 24 h. The beads were then washed sequentially
with methanol (250 mL), diethyl ether (250 mL), and hexanes
(250 mL) and then dried in vacuo for 24 h to afford 3a -f (Table
1). Polymer 3g was prepared using an analogous procedure in
which a total of 50 g of the monomer mixture was suspended in
750 mL of the aqueous phase. Elemental analysis was used to
determine the phosphorus content and thus the loading level of
PPh3/g for 3a -g.
Gen er a l P r oced u r e for Ester -F or m in g Mitsu n obu Rea c-
tion s. To a solution of 2a (1.0 g, 1.5 mmol, 1.5 equiv) in
anhydrous THF (30 mL) was added benzoic acid (0.1 g, 1.0 mmol,
1.0 equiv) and the alcohol (1.2 mmol, 1.2 equiv). This was then
cooled to 0 °C and DEAD (0.3 g, 1.5 mmol, 1.5 equiv) was added
dropwise. The mixture was stirred at rt for 30 min more and
then concentrated in vacuo. The resulting crude product mixture
was redissolved in THF (10-15 mL) and then poured slowly into
cold diethyl ether (100 mL, 0 °C). After filtration to remove the
precipitated polymer, the filtrate was concentrated in vacuo and
the crude residue was filtered through a plug of silica gel to
provide the essentially pure product (Table 2).
Gen er a l P r oced u r e for Eth er -F or m in g Mitsu n obu Re-
a ction s. To a solution of 2a (1.0 g, 1.5 mmol, 1.5 equiv) in
anhydrous THF (30 mL) were added benzyl alcohol (0.1 g, 1
mmol, 1 equiv) and the phenol (1.0 mmol, 1 equiv). This was
then cooled to 0 °C, and DEAD (0.3 g, 1.5 mmol, 1.5 equiv) was
added dropwise. The mixture was stirred at rt for 30 min more
and then concentrated in vacuo. The resulting crude product
mixture was redissolved in THF (10-15 mL) and then poured
slowly into cold diethyl ether (100 mL, 0 °C). After filtration to
remove the precipiated polymer, the filtrate was concentrated
in vacuo and the crude residue was filtered through a plug of
silica gel to provide the essentially pure product (Table 2).
Gen er a l P r oced u r e for th e Br om in a tion of Alcoh ols
Usin g J a n d a J el-P P h 3 (3g). To a magnetically stirred suspen-
sion of 3g (1.2 g, 1.5 mmol PPh3/g) in anhydrous CH2Cl2 (15 mL)
at rt and under a nitrogen atmosphere was added bromine (0.3
g, 1.8 mmol, 1 equiv). The color from the bromine dissipated
almost immediately. After the addition was complete, the alcohol
substrate (0.6 mmol, 0.3 equiv) was added. The reactions,
monitored by thin-layer chromatography, were complete within
10 min. The suspension was then filtered, and the resin was
washed with additional CH2Cl2 (3 × 10 mL). The combined
filtrate was concentrated in vacuo to afford the pure alkyl
bromide product that was determined to be essentially pure by
1H NMR analysis (Table 3). Since all of the products, except for
entry 6, are commercially available, they were only characterized
by 1H NMR analysis. Our recorded 1H NMR spectra matched
those available from the various suppliers of authentic samples.
The product from entry 6 (4-bromophenethyl bromide) was
further characterized by 13C NMR analysis: 1H NMR (300 MHz,
CDCl3) δ 2.01-2.02 (m, 3H), 5.12-5.17 (m, 1H), 7.28 (d, 2H, J
) 8.3 Hz), 7.46 (d, 2H, J ) 8.2 Hz); 13C NMR (100 MHz, CDCl3)
δ 26.6, 48.1, 122.1, 128.4 (2C), 131.7 (2C), 142.2.
and that resin with approximately half of the styrene
monomers functionalized afforded better results. Our
preparation of 3a -f allows for a similar systematic
examination of the effects that triarylphosphine group
concentration has on resin performance.
The utility of these polymers has been demonstrated
in Mitsunobu reactions and in the conversion of alcohols
to alkyl bromides. While various syntheses of 1 and
methods for its polymerization have been previously
reported, we present here the first detailed procedures
for the direct medium-scale synthesis of reagents 2 and
3 with variable and predictable loading levels. Prepara-
tion of other polymer-bound phosphine reagents using
the methodology presented here is currently being in-
vestigated.
Exp er im en ta l Section
4-Styr yld ip h en ylp h osp h in e (1). Chlorodiphenylphosphine
(30 mL, 164 mmol) was added slowly at 0 °C to a solution of the
Grignard reagent prepared from 4-bromostyrene (30.0 g, 164
mmol) and Mg (4.8 g, 197 mmol) in dry THF (300 mL). After
the addition was complete, the reaction mixture was stirred at
rt for 3 h. At this time, the reaction mixture was diluted with
diethyl ether (1 L) and then washed sequentially with water (2
× 250 mL), 10% aqueous HCl (2 × 250 mL), saturated aqueous
NaHCO3 (2 × 250 mL), and brine (2 × 250 mL). The organic
layer was dried over MgSO4, filtered, and concentrated in vacuo.
The crude product was purified by silica gel chromatography
(5% EtOAc/hexanes) to afford 1 as a white solid (25.0 g, 87 mmol,
53%): 1H NMR (300 MHz, CDCl3) δ 5.27 (dd, 1H, J ) 10.9, 0.6
Hz), 5.77 (dd, 1H, J ) 17.6, 0.6 Hz), 6.70 (dd, 1H, J ) 17.6, 10.9
Hz), 7.25-7.44 (m, 14H); 13C NMR (75 MHz, CDCl3) δ 114.4,
126.3 (2C), 128.5 (2C), 128.7 (4C), 133.6 (4C), 133.8 (2C), 134.0
(2C), 136.4, 137.2, 137.9; 31P NMR (162 MHz, CDCl3) δ -5.12;
HR EI-MS calcd for C20H17P 288.1068, found 288.1066.
Gen er a l P r oced u r e for P r ep a r in g Non -Cr oss-Lin k ed
P olystyr en e Rea gen ts 2. To a solution of styrene (28.9 g, 278
mmol) and 1 (20.0 g, 69 mmol) in toluene (300 mL) was added
AIBN (0.5 g, 3 mmol). The mixture was purged with N2 for 30
min, and the solution was stirred at 90 °C for 24 h. The solution
was concentrated in vacuo, and the residue was taken up in 40
mL of THF. This solution was added dropwise to a vigorously
stirred cold methanol (0 °C, 1 L). The white precipitate was
filtered and dried to afford 2a as a white powder (23.4 g, 53%):
1H NMR (300 MHz, CDCl3) δ 1.01-2.36 (bm, 15 H) and 6.23-
7.78 (bm, 24 H); 31P NMR (162 MHz, CDCl3) δ -6.22. The ratio
of monomer 1 to styrene in 2a was determined by elemental
analysis to be 1:3.4 based on 4.7% P. This corresponds to a
loading level of 1.5 mmol PPh3/g of 2a . Polymer 2b was prepared
by an analogous procedure in which the ratio of styrene to 1
was 8:1 (47%): 1H NMR (300 MHz, CDCl3) δ 1.01-2.36 (bm,
18H) and 6.23-7.78 (bm, 29H); 31P NMR (162 MHz, CDCl3) δ
-6.22. The ratio of monomer 1 to styrene in 2b was determined
by elemental analysis to be 1:5.1 based on 3.8% P. This
corresponds to a loading level of 1.2 mmol PPh3/g of 2b.
Ack n ow led gm en t. This research was supported
financially by the University of Hong Kong, the Hung
Hing Ying Physical Sciences Research Fund, and the
Research Grants Council of the Hong Kong Special
Administrative Region, P. R. of China (Project No. HKU
7112/02P). We would also like to thank Mr. Bob Wan-
dler and the Aldrich Chemical Co. for their gift of many
of the reagents used in this project.
Gen er a l P r oced u r e for P r ep a r in g Cr oss-Lin k ed P oly-
st yr en e R ea gen t s 3 (J a n d a J el-P P h 3). A solution of acacia
gum (6.0 g) and NaCl (3.8 g) in warm deionized water (45 °C,
150 mL) was placed in a 150 mL flanged reaction vessel equipped
with a mechanical stirrer and deoxygenated by purging with N2
for 2 h. A solution of approximately 10 g in total of 1, styrene,
1,4-bis(4-vinylphenoxy)butane (2 mol % compared to the other
(32) (a) Yaroslavsky, C.; Patchornik, A.; Katchalski, E. Tetrahedron
Lett. 1970, 11, 3629-3632. (b) Morawetz, H. J . Macromol. Sci. Chem.
1979, 3, 311-320. (c) Alexandratos, S. D.; Miller, D. H. J . Macromol-
ecules 1996, 29, 8025-8029. (d) Deratani, A.; Darling, G. D.; Horak,
D.; Frechet, J . M. J . Macromolecules 1987, 20, 767-772. (e) Alexan-
dratos, S. D.; Miller, D. H. J . Macromolecules 2000, 33, 2011-2015.
(f) Vaino, A. R.; J anda, K. D. J . Comb. Chem. 2000, 2, 579-596.
Su p p or tin g In for m a tion Ava ila ble: NMR spectra of
monomer 1, polymers 2a and 2b, and the Mitsunobu and
bromination reaction products. This material is available free
of charge via the Internet at http://pubs.acs.org.
J O035226+
9834 J . Org. Chem., Vol. 68, No. 25, 2003