Polymer immobilization of bis(oxazoline) ligands using dendrimers as cross-linkers

Article abstract of DOI:10.1016/S0957-4166(03)00074-0

Homopolymers of bis(oxazoline) ligands can be used to prepare efficient catalysts for cyclopropanation reactions. However, the low accessibility to most bis(oxazoline) moieties leads to a low copper loading. As a consequence, the transmission of chiral information from the complexed polymer is not very efficient and only a few chiral cyclopropane molecules are obtained from each molecule of chiral ligand. The use of suitable dendrimers as cross-linkers in the polymerization process allows better copper functionalization. As a consequence the productivity of chiral cyclopropanes per molecule of chiral ligand greatly increases, which improves the ligand economy and the chirality transfer.

Full text of DOI:10.1016/S0957-4166(03)00074-0

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 14 (2003) 773–778
Polymer immobilization of bis(oxazoline) ligands using
dendrimers as cross-linkers
Enrique D´ıez-Barra,a Jose´ M. Fraile,b Jose´ I. Garc´ıa,b Eduardo Garc´ıa-Verdugo,c Clara I. Herrer´ıas,b
Santiago V. Luis,c Jose´ A. Mayoral,b,* Prado Sa´nchez-Verdu´a and Juan Tolosaa
aDep. Qu´ımica Orga´nica, Universidad de Castilla-La Mancha, E-13071 Ciudad Real, Spain
bDep. Qu´ımica Orga´nica, Instituto de Ciencia de Materiales de Arago´n, Universidad de Zaragoza-C.S.I.C.,
E-50009 Zaragoza, Spain
cDep. Qu´ımica Inorga´nica y Orga´nica, E.S.T.C.E., Universidad Jaume I, E-12080 Castello´n, Spain
Received 6 November 2002; accepted 20 December 2002
Abstract—Homopolymers of bis(oxazoline) ligands can be used to prepare efficient catalysts for cyclopropanation reactions.
However, the low accessibility to most bis(oxazoline) moieties leads to a low copper loading. As a consequence, the transmission
of chiral information from the complexed polymer is not very efficient and only a few chiral cyclopropane molecules are obtained
from each molecule of chiral ligand. The use of suitable dendrimers as cross-linkers in the polymerization process allows better
copper functionalization. As a consequence the productivity of chiral cyclopropanes per molecule of chiral ligand greatly
increases, which improves the ligand economy and the chirality transfer. © 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
economy, defined as the number of molecules of
product obtained from each molecule of chiral ligand
immobilized.9 This concept can be considered as a TON
referred to the chiral ligand, and it will have the same
value as the TON only when all the molecules of
immobilized chiral ligand are transformed into catalytic
centers. In an effort to clarify this point we compare the
behavior of the same bis(oxazolines) in homogeneous
phase and immobilized onto different polymers and
show that the use of dendrimers as cross-linkers is an
extremely useful way to improve ligand economy. The
cyclopropanation reaction between equimolecular
amounts of styrene and ethyl diazoacetate10 (Scheme 1)
is used as the test case to measure the efficiency of the
solid-supported catalysts.
Interest in the immobilization of chiral catalysts has
increased over the last few years,1 a situation that is
related to the potential advantages of heterogeneous
catalysts. In this context, several strategies for the
immobilization of bis(oxazoline) metal complexes have
been developed.2 Bis(oxazoline) and azabis(oxazoline)-
copper complexes have been immobilized by electro-
static interaction with anionic supports.3 The same
ligands have been grafted to soluble organic polymers
and recovered by precipitation after the reaction.4
Bis(oxazolines) have been covalently bonded to inor-
ganic supports.5,6 Finally, bis(oxazolines), and the
related pyridine-bis(oxazolines), have been immobilized
onto organic polymers by grafting and polymeriza-
tion.6–9 One of the common features that can be drawn
from these studies is that the support has an enormous
influence on both the catalytic activity and the stereose-
lectivity of the reaction. In particular, in the case of
organic polymers this influence is clearly related to the
morphology of the polymer. In this regard the accessi-
bility of the immobilized chiral ligand is an important
factor and we have introduced the concept of ligand
Scheme 1. Cyclopropanation reaction between styrene 1 and
ethyl diazoacetate 2.
* Corresponding author. Tel./fax: +34-976-762077; e-mail: mayoral@
posta.unizar.es
0957-4166/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0957-4166(03)00074-0

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E. D´ıez-Barra et al. / Tetrahedron: Asymmetry 14 (2003) 773–778
ing. Copper contents were determined by plasma emis-
sion spectroscopy. Table shows the monomer
2. Results and discussion
1
Methylenebis[(S)-4-phenyl-2-oxazoline]
methylenebis[(S)-4-tert-butyl-2-oxazoline]
5a
5b
and
were
compositions of the polymers 8–10 together with the
bis(oxazoline) contents of these polymers and the cop-
per contents of the catalysts obtained from them. The
results of these analyses clearly indicate that the degree
of copper functionalization depends on both the poly-
mer morphology and the nature of the chiral ligand.
dibenzylated at the central methylene bridge to yield
the soluble ligands 6. The alkylation with p-vinylbenzyl
chloride led to the chiral monomers 7. These monomers
were used to prepare the different polymers following
the general protocol for the preparation of monolithic
resins (Scheme 2).7–9,11
The next question concerns how these parameters can
influence the catalytic behavior of these systems.
Although better yields can be obtained by using an
excess of styrene,7 the use of equimolecular amounts of
both reagents allows an easier comparison of the TON
based on both copper and the chiral ligand. These
values, together with the different selectivities, are gath-
ered in Table 2 for both homogeneous and polymeric
catalysts. With the homopolymers 8a and 8b the TON
based on copper is improved with regard to the
analogous homogeneous ligands 6a and 6b, without a
decrease in the enantioselectivity. However, the low
copper functionalization makes the TON based on
bis(oxazoline) similar with both homogeneous and het-
erogeneous catalysts. As this parameter is really impor-
tant for efficient transmission of the chiral information,
we tried to improve it by using dendrimers as cross-
linkers, leading to a significant modification in polymer
morphology. The use of dendrimer 11 leads to different
results as a function of the chiral ligand. The polymer
with the phenyl bis(oxazoline) 9a shows a spectacular
improvement in the TON wrt both copper and chiral
ligand, reaching a cyclopropanes/box ratio of 101, with
the same enantioselectivity. However, with the tert-
butyl substituted polymer 9b low TON and enantiose-
lectivity are obtained. The nature of the dendrimeric
cross-linker has an important effect, as shown by the
results with polymers containing the dendrimer 12. The
cyclopropanes/box ratio increases to 141 with 10a and
132 with 10b, with no decrease in enantioselectivity
compared to the analogous homogeneous catalysts 6a
and 6b. Although recovered catalysts are less active and
longer reaction times are needed, re-use allows a further
improvement of both TON, up to 242 cyclopropanes/
box with 10a. Given that leaching of copper is not
detected, deactivation may be due to deposition of
by-products that reduces accessibility to the catalytic
centers. New dendrimers are being designed with the
aim of solving this problem.
Dendrimers 11 and 12 were used as cross-linkers. These
dendrimers were obtained by reacting 1,3,5-trischloro-
carbonylbenzene with two different dendrons following
a standard procedure (Scheme 3).12 The dendrons have
a hydroxymethyl group as the focal point and were
prepared by reaction of 3,5-dihydroxybenzyl alcohol
with the appropriate vinyl end-capped bromides follow-
ing Fre´chet’s procedure.
The polymers were characterized by IR spectroscopy
and the spectra show bands corresponding to the chiral
ligand. Nitrogen analysis was used to determine the
amount of bis(oxazoline) incorporated into the poly-
meric network. Catalysts were obtained by treatment
with Cu(OTf)2 followed by filtration, washing and dry-
It can be concluded that the use of suitable dendrimers
as cross-linkers allows a better use of the chiral ligand
and hence a better transmission of chiral information,
with up to 140 new chiral molecules produced per
ligand molecule. The structure of both the dendrimer
and the chiral monomer is important to optimize the
results. In fact, it is known that the selection of the
cross-linker is a key point for the enantioselective reac-
tions promoted by chiral copolymers. These parameters
are related with the copper functionalization of the
chiral ligand and the accessibility of the catalytic
centers.
Scheme 2. Preparation of homopolymers 8 and copolymers
with different cross-linkers.

E. D´ıez-Barra et al. / Tetrahedron: Asymmetry 14 (2003) 773–778
775
Scheme 3. Preparation of dendron precursors for dendrimeric cross-linkers.
a
Table 1. Immobilized catalysts prepared from polymers 8–10 and Cu(OTf)2
Polymer
Composition of the monomers mixture
Functionalization
Cu (mmol g−1
Box 7
Styrene
Cross-linker
Box (mmol g−1
)
)
Box/Cu
8ab
8bb
9ac
100
100
9
11
5
–
–
77
74
85
73
–
–
14
15
10
18
1.74
2.01
0.15
0.19
0.21
0.28
0.140
0.070
0.015
0.004
0.080
0.043
12.4
28.8
10.0
47.5
2.6
9bc
10ac
10bc
9
6.5
a Polymerization conditions: 80°C, monomer mixture/porogen=40/60, 1% AIBN.
b Porogen: mixture toluene/1-dodecanol (1/5 w/w).
c Porogen: mixture toluene/1-dodecanol/DMF (1/4/1).
3. Experimental
emission spectroscopy on a Perkin–Elmer Plasma 40
emission spectrometer. Transmission FTIR spectra of
self supported wafers evacuated (<10−4 Torr) at 50°C
were obtained with a Mattson Genesis series FTIR
spectrophotometer. Gas chromatography was carried
out on two Hewlett-Packard 5890 chromatographs
equipped with FID detectors.
3.1. General
1H and 13C NMR spectra (CDCl3, l ppm, J Hz) were
obtained using a Varian FT-300 or Gemini FT-200
instrument with TMS as standard. MS spectra were
obtained by the Universidad Auto´noma de Madrid
(Servicio Interdepartamental de Investigacio´n, S.I.D.I.)
mass spectroscopy facility. Spectra matrix: dithranol
(MALDI-TOF). Quantitative elemental analyses were
performed in duplicate on a Perkin–Elmer 2400 instru-
ment. Copper analyses were carried out by plasma
3.2. Preparation of dendrimers
3.2.1. General procedure for 3,5-bis(p-vinylphenylmethyl
oxy)phenylmethyl 1,3,5-benzenetricarboxylate, 11 and
3,5-bis(p-vinylphenylmethyloxy-p-phenyloxyethylenoxy

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E. D´ıez-Barra et al. / Tetrahedron: Asymmetry 14 (2003) 773–778
Table 2. Results obtained from the cyclopropanation reaction between styrene 1 and ethyl diazoacetate 2 with homogeneous
and polymeric catalystsa
Ligand
Run
Time (days)
3+4/Cub
3+4/boxb
trans/cisc
% ee (trans)d
% ee (cis)d
6a
6b
8a
8b
9a
9b
10a
1
1
1
1
1
1
1
2
1
2
1
1
1
1
11
7
3.2
23
3.2
23
17
70/30
33/67
52/48
37/63
59/41
55/45
57/43
58/42
50/50
54/46
50
70
57
78
58
6
58
52
74
60
40
79
53
72
42
16
56
56
68
60
204
287
1000
113
368
262
860
400
10
101
2.4
141
101
132
61
3
14
4
10b
10e
a Using equimolecular amounts of styrene and ethyl diazoacetate at room temperature.
b Molar ratio calculated using the amount of cyclopropanes determined by GC at total conversion of ethyl diazoacetate.
c Determined by GC.
d Determined by GC. 3R and 4S are the major enantiomers.
e Reaction carried out at 50°C.
ethylenoxy)phenylmethyl
1,3,5-benzenetricarboxylate,
with a reflux condenser. The reaction was heated for 12
h at 80°C. Inorganic salts and Aliquat 336 were
removed by filtration through Florisil®, the solvent was
evaporated and the crude product was crystallized from
ethyl acetate/hexane as a white solid. Mp: 63–65°C.
12. A mixture of dendron 13 (3.03 mmol) or 14 (0.65
mmol) and an equimolar amount of 4-dimethyl-
aminopyridine was dissolved in anhydrous THF (10
mL) under Ar in a 100 mL Schlenk tube. After 5 min,
1,3,5-trischlorocarbonylbenzene (1.01 and 0.22 mmol,
respectively) was added dropwise. The reaction mixture
was stirred for 4 h at room temperature. The amine
hydrochloride was filtered off and the solvent was
evaporated. The solid residue was purified as indicated
below.
1
Yield 90%. H NMR: 7.44 and 7.40 (d, 4H, A2 of A2B2
system, J=8 Hz); 7.38 and 7.34 (d, 4H, B2 of A2B2
system, J=8 Hz); 6.72 (dd, 2H, Jtrans=18 Hz, Jcis=11
Hz); 6.61 (d, 2H, J=2 Hz); 6.53 (t, 1H, J=2 Hz); 5.76
(dd, 2H, Jgem=1 Hz, Jtrans=18 Hz); 5.26 (dd, 2H,
J
gem=1 Hz, Jcis=11 Hz); 5.02 (s, 4H); 4.62 (s, 2H). 13C
NMR: 160.6, 143.9, 137.9, 136.9, 128.2, 126.9, 114.6,
112.8, 106.3, 101.9, 70.4 and 65.8. MS (EI), m/z: 372
(M)+.
Compound 11: was obtained in 90% yield after recrystal-
lization (ethyl acetate/hexane). Mp: 113–115°C. 1H
NMR: 8.90 (s, 3H); 7.39 and 7.36 (d, 12H, A2 of A2B2
system, J=8 Hz); 7.35 and 7.32 (d, 12H, B2 of A2B2
system, J=8 Hz); 6.73–6.63 (m, 12H); 6.56 (t, 3H, J=2
Hz); 5.72 (dd, 6H, Jgem=1 Hz, Jtrans=18 Hz); 5.33 (s,
6H); 5.23 (dd, 6H, Jgem=1 Hz, Jcis=11 Hz); 5.00 (s,
12H). 13C NMR: 167.6, 160.1, 137.7, 136.4, 136.1,
134.9, 131.2, 127.7, 126.4, 114.1, 107.3, 102.1, 69.9 and
67.2. MS (MALDI-TOF), m/z: 1295.5 (M+Na)+.
3.2.3. 4-(p-Vinylphenylmethyloxy)phenol. A mixture of
1,4-hydroquinone (80 mmol), 4-vinylbenzyl chloride (20
mmol), potassium carbonate (20 mmol) and Aliquat
336 (2 mmol) in acetone (75 mL) was placed in a 250
mL round-bottomed flask fitted with a reflux con-
denser. The reaction was heated for 24 h at 80°C. The
inorganic salts were filtered off and the solvent was
evaporated. Chloroform was added to precipitate the
excess 1,4-hydroquinone, which was removed together
with the Aliquat 336 by filtration over Florisil®. The
solvent was evaporated and the crude product was
purified by column chromatography (SiO2; hexane/
ethyl acetate, 9:1). The pure product was obtained by
recrystallization from ethyl acetate/hexane. Mp: 143–
Compound 12: was obtained in 63% yield after recrystal-
lization from dichloromethane/ethanol. Mp: 52–55°C.
1H NMR: 8.87 (s, 3H); 7.43 and 7.39 (d, 12H, A2 of
A2B2 system, J=8 Hz); 7.37 and 7.33 (B2 of A2B2
system, J=8 Hz); 6.73 (dd, 6H, Jcis=11 Hz, Jtrans=18
Hz); 6.59 (d, 6H, J=2 Hz); 6.48 (t, 3H, J=2 Hz); 5.74
(dd, 6H, Jgem=1 Hz, Jtrans=18 Hz); 5.28 (s, 6H); 5.25
(dd, 6H, Jgem=1 Hz, Jcis=11 Hz); 4.97 (s, 12H); 4.09
(m, 24H); 3.87 (m, 24H). 13C NMR: 164.6, 160.1, 153.1,
137.6, 137.2, 136.8, 136.4, 134.9, 131.2, 127.6, 126.3,
115.8, 115.6, 114.0, 107.1, 101.6, 99.4, 70.4, 70.0, 69.8,
68.1, 67.6 and 67.2. MS (MALDI-TOF), m/z: 2375.7
(M+Na)+.
1
144°C. Yield 62%. H NMR: 7.44 and 7.41 (d, 2H, A2
of A2B2 system, J=8 Hz); 7.39 and 7.36 (d, 2H, B2 of
A2B2 system, J=8 Hz) 6.87–6.67 (m, 5H); 5.75 (dd, 1H,
J
gem=1 Hz, Jtrans=18 Hz); 5.25 (dd, 1H, Jgem=1 Hz,
Jcis=11 Hz); 4.99 (s, 2H). 13C NMR: 153.0, 149.7,
137.3, 136.8, 136.5, 127.7 126.4, 116.1, 116.0, 114.0 and
70.5. MS (EI), m/z: 226 (M)+.
3.2.2. 3,5-Bis(p-vinylphenylmethyloxy)benzyl alcohol, 13.
A mixture of 3,5-dihydroxybenzyl alcohol (10 mmol),
4-vinylbenzyl chloride (21 mmol), potassium carbonate
(22 mmol) and Aliquat 336 (5%) in 35 mL of acetone
was placed in a 100 mL round-bottomed flask fitted
3.2.4.
1,4-(Hydroxyethyleneoxyethyleneoxy),(p-
vinylphenyl oxymethyloxy)benzene. A mixture of 4-(p-
vinylphenylmethyloxy)phenol (10 mmol), KOH (15
mmol), 2-(2-chloroethoxy)ethanol (12 mmol) and
TBAB (9%) was heated in the absence of solvent for 32

E. D´ıez-Barra et al. / Tetrahedron: Asymmetry 14 (2003) 773–778
777
h at 80°C. Acetone was added and the inorganic salts
were filtered off. The crude product was purified by
column chromatography (SiO2; hexane/ethyl acetate,
3:1). After the undesired products had been removed,
ethyl acetate was then used as eluent. The product was
obtained as a white solid. Mp: 100–101°C (ethanol).
70.4, 70.0, 69.9, 68.2, 67.6 and 65.3. MS (EI), m/z: 732
(M)+.
3.3. Preparation of polymeric catalysts
1
The polymerization mixture was prepared with 40%
(w/w) monomers (in the molar ratio shown in Table 1)
and 60% porogen (toluene/1-dodecanol=1/5 or tolu-
ene/1-dodecanol/DMF=1/4/1, w/w). This mixture was
placed in a glass mould and purged with nitrogen in the
presence of azoisobutyronitrile (1% w/w). The mould
was closed and heated at 80 2°C for 24 h. The mould
was broken and the polymer was washed with THF,
dried by suction and crushed in a mortar. The polymer
was washed in a Soxhlet apparatus with THF for 24 h
and dried under vacuum at 50°C overnight. Typical
yields were in the range 75–95%. The Cu complexes
were prepared by adding the corresponding amount of
polymer (1 equiv. box) to a pre-filtered solution of
Cu(OTf)2 in methanol. The suspension was stirred at
room temperature for 24 h. The solid was filtered off,
thoroughly washed with methanol and dried under
vacuum at 50°C overnight.
Yield 60%. H NMR: 7.44 and 7.40 (d, 2H, A2 of A2B2
system, J=8 Hz); 7.39 and 7.35 (d, 2H, B2 of A2B2
system, J=8 Hz); 6.91–6.81 (m, 4H); 6.72 (dd, 1H,
Jcis=11 Hz, Jtrans=18 Hz); 5.75 (dd, 1H, Jgem=1 Hz,
Jtrans=18 Hz); 5.25 (dd, 1H, Jgem=1 Hz, Jcis=11 Hz);
5.00 (s, 2H); 4.09 (t, 2H, J=5 Hz); 3.83 (t, 2H, J=4
Hz); 3.74 (t, 2H, J=4 Hz); 3.68 (t, 2H, J=4 Hz). 13C
NMR: 153.2, 153.0, 137.3, 136.8, 136.5, 127.7, 126.4,
115.9, 115.7, 114.0, 72.5, 70.4, 69.8, 68.1 and 61.8. MS
(EI), m/z: 314 (M)+.
3.2.5. 1,4-(Bromoethyleneoxyethyleneoxy)(p-vinylphenyl-
oxy-methyloxy)benzene. In a flame-dried Schlenk tube
was placed carbon tetrabromide (15 mmol), 1,4-
(hydroxyethyleneoxyethyleneoxy),(p-vinylphenyloxy-
methyloxy)benzene (4 mmol) and triphenylphosphine
(15 mmol); dry THF was added (20 mL) and the
mixture was stirred at room temperature under an
argon atmosphere for 4 h. Triphenylphosphine oxide
formed was filtered off and the solvent was evaporated.
The crude product was purified by column chromatog-
raphy (SiO2; hexane/ethyl acetate, 8:1). For further
purification the product was crystallized from ethanol.
3.4. Catalytic tests
To a suspension of the corresponding supported cata-
lyst (20 mg), styrene (175 mg, 1.68 mmol) and n-decane
(25 mg) in methylene chloride (3 mL) under an Ar
atmosphere, was slowly added a solution of ethyl dia-
zoacetate (96 mg, 0.84 mmol) in methylene chloride (0.5
mL) using a syringe pump. The reaction was monitored
by gas chromatography and, after consumption of the
diazoacetate, a second portion of diazoacetate was
added in the same way. After completion of the reac-
tion the catalyst was filtered off, washed with methylene
chloride and dried. The recovered catalysts were reused
following the same method.
1
Mp: 72–74°C. Yield 87%. H NMR: 7.44 and 7.40 (d,
2H, A2 of A2B2 system, J=8 Hz); 7.39 and 7.35 (d, 2H,
B2 of A2B2 system, J=8 Hz); 6.91–6.81 (m, 4H); 6.72
(dd, 1H, Jcis=11 Hz, Jtrans=18 Hz); 5.75 (dd, 1H,
J
gem=1 Hz, Jtrans=18 Hz); 5.25 (dd, 1H, Jgem=1 Hz,
Jcis=11 Hz); 5.00 (s, 2H); 4.09 (t, 2H, J=5 Hz);
3.91–3.82 (m, 4H); 3.49 (t, 2H, J=6 Hz). 13C NMR:
153.2, 153.0, 137.3, 136.8, 136.5, 127.7, 126.4, 115.9,
115.7, 114.0, 71.4, 70.4, 69.8, 68.1 and 30.2. MS (EI),
m/z: 376 (M)+, 378 (M+2)+.
Yields and trans/cis selectivities were determined with a
cross-linked methylsilicone column: 25 m×0.2 mm×0.33
mm. Oven temperature program: 70°C (3 min), 15°C/
min to 200°C (5 min). Retention times: ethyl diazoac-
etate 4.28 min, styrene 5.03 min, n-decane 6.93 min,
diethyl fumarate 8.73 min, diethyl maleate 9.04 min,
cis-cyclopropanes 4 11.84 min, trans-cyclopropanes 3
12.35 min. The asymmetric induction (Scheme 1) was
determined with a Cyclodex-B column: 30 m×0.25 mm×
0.25 mm. Oven temperature program: 125°C isotherm.
Retention times: (1S,2R)-cyclopropane (4S) 28.3 min,
(1R,2S)-cyclopropane (4R) 29.1 min, (1R,2R)-cyclo-
propane (3R) 33.9 min, (1S,2S)-cyclopropane (3S) 34.3
min.
3.2.6. 3,5-Bis(p-vinylphenylmethyloxy-p-phenyloxyethyl-
ene oxyethylenoxy)benzyl alcohol, 14. A mixture of
1,4-(bromoethyleneoxyethyleneoxy),(p - vinylphenyloxy-
methyloxy)benzene (2.65 mmol), KOH (2.70 mmol),
3,5-dihydroxybenzyl alcohol (1.07 mmol) and tetra-
butylammonium bromide TBAB (9%) was heated with-
out solvent for 24 h at 80°C. Ethyl acetate (20 mL) was
added, the inorganic salts were filtered off and the
solvent was evaporated. The crude product was purified
by column chromatography (SiO2; hexane/ethyl acetate,
1:1). The desired compound was obtained as a white
solid after crystallization from ethanol. Mp: 105–107°C.
1
Yield 68%. H NMR: 7.44 and 7.40 (d, 4H, A2 of A2B2
system, J=8 Hz); 7.39 and 7.35 (d, 4H, B2 of A2B2
system, J=8 Hz); 6.91–6.81 (m, 8H); 6.72 (dd, 2H,
Jcis=11 Hz, Jtrans=18 Hz); 6.53 (d, 2H, J=2 Hz); 6.43
(t, 1H, J=2 Hz); 5.75 (dd, 2H, Jgem=1 Hz, Jtrans=18
Hz); 5.25 (dd, 2H, Jgem=1 Hz, Jcis=11 Hz); 4.99 (s,
4H); 4.60 (s, 2H); 4.15–4.07 (m, 8H); 3.92–3.86 (m, 8H).
13C NMR: 160.1, 153.1, 143.3, 137.3, 136.8, 136.5,
127.7, 126.4, 115.8, 115.7, 114.0, 105.6, 100.9, 99.4,
Acknowledgements
This work was made possible by the generous financial
support of the C.I.C.Y.T. (project PPQ2002-04012) and
the Junta de Comunidades de Castilla-La Mancha (pro-

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E. D´ıez-Barra et al. / Tetrahedron: Asymmetry 14 (2003) 773–778
ject GC-02-013). C.I.H. is indebted to the M.C.Y.T. for
a grant.
4. (a) Annunziata, R.; Benaglia, M.; Cinquini, M.; Cozzi,
F.; Pitillo, M. J. Org. Chem. 2001, 66, 3160–3166; (b)
Glos, M.; Reiser, O. Org. Lett. 2000, 2, 2045–2048.
5. (a) Rechavi, D.; Lemaire, M. Org. Lett. 2001, 3, 2493–
2496; (b) Clarke, R. J.; Shannon, I. J. Chem. Commun.
2001, 1936–1937; (c) Park, J. K.; Kim, S.-W.; Hyeon, T.;
Kim, B. M. Tetrahedron: Asymmetry 2001, 12, 2931–
2935; (d) Corma, A.; Garc´ıa, H.; Moussaif, A.; Sabater,
M. J.; Zniber, R.; Redouane, A. Chem. Commun. 2002,
1058–1059.
6. Burguete, M. I.; Fraile, J. M.; Garc´ıa, J. I.; Garc´ıa-Ver-
dugo, E.; Herrer´ıas, C. I.; Luis, S. V.; Mayoral, J. A. J.
Org. Chem. 2001, 66, 8893–8901.
7. Burguete, M. I.; Fraile, J. M.; Garc´ıa, J. I.; Garc´ıa-Ver-
dugo, E.; Luis, S. V.; Mayoral, J. A. Org. Lett. 2000, 2,
3905–3908.
8. (a) Orlandi, S.; Mandoli, A.; Pini, D.; Salvadori, P.
Angew. Chem. 2001, 113, 2587–2589; (b) Hallman, K.;
Moberg, C. Tetrahedron: Asymmetry 2001, 12, 1475–
1478; (c) Cornejo, A.; Fraile, J. M.; Garc´ıa, J. I.; Garc´ıa-
Verdugo, E.; Gil, M. J.; Legarreta, G.; Luis, S. V.;
Mart´ınez-Merino, V.; Mayoral, J. A. Org. Lett. 2002, 4,
3927–3930.
9. Burguete, M. I.; D´ıez-Barra, E.; Fraile, J. M.; Garc´ıa, J.
I.; Garc´ıa-Verdugo, E.; Gonza´lez, R.; Herrer´ıas, C. I.;
Luis, S. V.; Mayoral, J. A.; Sa´nchez-Verdu´, P. Bioorg.
Med. Chem. Lett. 2002, 12, 1821–1824.
References
1. (a) Comprehensive Asymmetric Catalysis; Jacobsen, E. N.;
Pfaltz, A.; Yamamoto, H., Eds.; Springer-Verlag: Berlin-
Heidelberg, 1999; (b) Chiral Catalyst Immobilization and
Recycling; De Vos, D. E.; Vankelecom, I. F. J.; Jacobs,
P. A., Eds.; Wiley-VCH: Weinheim, 2000; (c) Chapman,
A. G.; Reger, T. S.; Janda, K. D. Tetrahedron 2001, 57,
4637–4662; (d) Pu, L. Tetrahedron: Asymmetry 1998, 9,
1457–1477.
2. (a) Jo¨nsson, C.; Hallman, K.; Andersson, H.; Stemme,
G.; Malkoch, M.; Malmstro¨m, E.; Hult, A.; Moberg, C.
Bioorg. Med. Chem. Lett. 2002, 12, 1857–1861; (b)
Rechavi, D.; Lemaire, M. Chem. Rev. 2002, 102, 3467–
3494.
3. (a) Fraile, J. M.; Garc´ıa, J. I.; Mayoral, J. A.; Tarnai, T.
Tetrahedron: Asymmetry 1997, 8, 2089–2092; (b) Fraile, J.
M.; Garc´ıa, J. I.; Mayoral, J. A.; Tarnai, T.; Harmer, M.
A. J. Catal. 1999, 186, 214–221; (c) Alonso, P. J.; Fraile,
J. M.; Garc´ıa, J.; Garc´ıa, J. I.; Mart´ınez, J. I.; Mayoral,
J. A.; Sa´nchez, M. C. Langmuir 2000, 16, 5607–5612; (d)
Fraile, J. M.; Garc´ıa, J. I.; Harmer, M. A.; Herrer´ıas, C.
I.; Mayoral, J. A. J. Mol. Catal. A 2001, 165, 211–218; (e)
Ferna´ndez, A. I.; Fraile, J. M.; Garc´ıa, J. I.; Herrer´ıas, C.
I.; Mayoral, J. A.; Salvatella, L. Catal. Commun. 2001, 2,
165–170; (f) Taylor, S.; Gullick, J.; McMorn, P.; Bethell,
D.; Bulman-Page, P. C.; Hancock, F. E.; King, F.;
Hutchings, G. J. J. Chem. Soc., Perkin Trans. 2 2001,
1714–1723; (g) Fraile, J. M.; Garc´ıa, J. I.; Harmer, M.
A.; Herrer´ıas, C. I.; Mayoral, J. A.; Reiser, O.; Werner,
H. J. Mater. Chem. 2002, 12, 3290–3295; (h) Cornejo, A.;
Fraile, J. M.; Garc´ıa, J. I.; Gil, M. J.; Herrer´ıas, C. I.;
Legarreta, G.; Mart´ınez-Merino, V.; Mayoral, J. A. J.
Mol. Catal. A, in press.
10. Evans, D. A.; Woerpel, K. A.; Hinman, M. M.; Faul, M.
M. J. Am. Chem. Soc. 1991, 113, 726–728.
11. (a) Svec, F.; Fre´chet, J. M. J. Chem. Mater. 1995, 7,
707–715; (b) Svec, F.; Fre´chet, J. M. J. Science 1996, 273,
205–211; (c) Xie, S.; Svec, F.; Fre´chet, J. M. J. Chem.
Mater. 1998, 10, 4072–4078; (d) Svec, F.; Fre´chet, J. M.
J. Ind. Eng. Chem. Res. 1999, 38, 34–48; (e) Hird, N.;
Hughes, I.; Hunter, D.; Morrison, M. G. J. T.; Sherring-
ton, D. C.; Stevenson, L. Tetrahedron 1999, 55, 9575–
9584.
12. Davies, P. J.; Grove, D. M.; van Koten, G. Organometal-
lics 1997, 16, 800–802.