Effective and recyclable dendritic ligands for the enantioselective epoxidation of enones

Article abstract of DOI:10.1016/j.tetasy.2006.02.019

An operationally simple and mild protocol for the catalytic enantioselective epoxidation of enones has been established using a series of chiral pyrrolidinylmethanol-based dendritic catalysts and tert-butyl hydroperoxide (TBHP) as an oxidant. The epoxides

Full text of DOI:10.1016/j.tetasy.2006.02.019

Tetrahedron: Asymmetry 17 (2006) 750–755
Effective and recyclable dendritic ligands for the
enantioselective epoxidation of enones
Xinyuan Liu,a Yawen Li,b Guangyin Wang,a Zhuo Chai,a Yongyong Wua and Gang Zhaoa,b,
*
aLaboratory of Modern Synthetic Organic Chemistry, Shanghai Institution of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, PR China
bDepartment of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, PR China
Received 5 December 2005; revised 15 February 2006; accepted 17 February 2006
Available online 23 March 2006
Abstract—An operationally simple and mild protocol for the catalytic enantioselective epoxidation of enones has been established using
a series of chiral pyrrolidinylmethanol-based dendritic catalysts and tert-butyl hydroperoxide (TBHP) as an oxidant. The epoxides have
been obtained in good yields and ee up to 78%.
ꢀ 2006 Published by Elsevier Ltd.
1. Introduction
Ding et al. reported the highly enantioselective epoxidation
of enones by employing the self-supported heterogeneous
Shibasaki’s catalysts prepared in situ.7 The catalytic asym-
metric epoxidation of enones applying sodium hypochlo-
rite has also been achieved using chiral phase-transfer
catalysis, and the enantioenriched epoxides were generally
obtained with high enantioselectivities.8 Furthermore, the
use of chiral ketones as catalysts for the asymmetric
epoxidation of a broad range of olefins has also been
demonstrated.9
Catalytic asymmetric epoxidation of C–C double bonds
provides access to enantiomerically enriched epoxides,
which are of fundamental importance in organic chemis-
try.1 In recent years, we have seen the dramatic develop-
ment of methods for this purpose. In the field of metal-
catalyzed epoxidations, in particular the Sharpless epoxida-
tion of allylic alcohols, using catalytic amounts of titanium
and tartrate, represents a reaction of great importance.2
Similarly, the asymmetric epoxidation of non-functional-
ized olefins catalyzed by the manganese-salen complexes
(Jacobsen–Katsuki epoxidation) has provided an easy
approach to unfunctionalized epoxides.3 For metal-free
asymmetric epoxidation of olefins using chiral ketones as
catalysts, typically, preparatively useful ees have been
achieved for the first time by Yang et al. using the binaph-
thyl-derived chiral ketones as catalysts.4 On the other
hand, the asymmetric epoxidation of a,b-unsaturated car-
bonyl compounds is another important functionalization
in organic chemistry5 because of the usefulness of the cor-
responding a,b-epoxy carbonyl compounds. Shibasaki
et al. have, via the use of chiral Lewis acid complexes,
developed the catalytic asymmetric epoxidation of a,b-
unsaturated ketones, esters, and amides applying tert-butyl
hydroperoxide as the terminal oxidant.6 Very recently,
Dendrimers are well-defined macromolecules with control-
lable structures. Their applications in catalysis have caused
increasing attention, since dendritic catalysts have the
advantages of complete solubility and can be analyzed with
routine spectroscopic techniques.10 Moreover, the globular
shapes of higher generation dendritic catalysts are suitable
for membrane filtration11 or selective precipitation under
specific conditions.12
Recently, we reported the synthesis of a series of new
polyether dendritic chiral pyrrolidinylmethanol derivatives
and their application in catalytic, highly enantioselective
aryl transfer reactions to aldehydes.13 High catalytic activ-
ity and enantioselectivity were observed, and the higher
generation catalysts could be recovered through solvent
precipitation and reused several times without any appar-
ent loss of activity. We also reported their applications in
the highly enantioselective reduction of ketones and their
derivatives.14 Very recently, Lattanzi et al. reported a
*
Corresponding author. Tel.: +86 21 54925182; fax: +86 21 64166128;
e-mail: zhaog@mail.sioc.ac.cn
0957-4166/$ - see front matter ꢀ 2006 Published by Elsevier Ltd.
doi:10.1016/j.tetasy.2006.02.019

X. Liu et al. / Tetrahedron: Asymmetry 17 (2006) 750–755
751
new methodology for the catalytic asymmetric epoxidation
of a broad range of enones catalyzed by the bifunctional
organocatalyst a,a-diphenyl-L-pyrrolidinemethanol. The
epoxides have been obtained in good yields and with up
to 80% ee.15 Jørgensen et al. also reported the first asym-
metric organocatalytic epoxidation of a,b-unsaturated
aldehydes using a pyrrolidine derivative as the catalyst with
good to high yields and enantioselectivities.16 Being inter-
ested in the development of mild and convenient methodol-
ogies of asymmetric reactions using recyclable catalysts, we
herein report the enantioselective epoxidation of enones
using the polyether dendritic chiral pyrrolidinylmethanol
derivatives and tert-butyl hydroperoxide (TBHP) as an
oxidant.
tocol, no reaction of 13a with TBHP occurred to give the
corresponding epoxide, probably due to poor solubility
of the dendritic catalyst in the reaction media (Table 1,
entry 1). Since apolar and non-coordinating solvents
furnished better results in Lattanzi’s report, the reaction
was performed in CCl4. When using 8 (30 mol %) as cata-
lyst, we found that the reaction proceeded well to give
(2R,3S)-14a as the sole product in 60% yield and 66% ee
(Table 1, entry 2). To investigate the effect of dendritic
branches on the catalytic activity and stereoselectivity of
the pyrrolidinylmethanol, we tested dendrimers 7–12 in
the enantioselective epoxidation under the same condi-
tions. In general, good conversion of enone 13a was
achieved, and the corresponding optically active epoxide
was obtained in good yields. The enantioselectivities were
moderate to good (41–71%), with the (2R,3S)-configured
product 14a was formed predominantly (Table 1, entries
2–7). Among all the dendritic chiral catalysts evaluated in
this reaction, the second-generation ligand 12 was the best
one in terms of yield and ee (Table 1, entry 7).
2. Results and discussion
The chiral dendrimers were synthesized as shown in
Scheme 1. The pyrrolidinylmethanol ligands 1–6 were
firstly synthesized according to the published method.13
Hydrolysis of the ester moieties with KOH afforded the
corresponding alcohols 7–12 in 61–96% yields. These
ligands were purified by flash column chromatography
With these promising results, attention was then turned to
modifying the above protocol in anticipation of obtaining
better results. Inspired by Shibasaki et al.’s report in which
the catalytic asymmetric epoxidation of enones was greatly
improved by carrying out the reaction in the presence
1
and characterized by H and 13C NMR spectra, MALDI
mass spectrometry and elemental analysis.
5
˚
of 4 A MS, we found that after optimizing the reaction
conditions, a slightly higher enantioselectivity and substan-
tial improvement in the yield could be observed under the
same conditions when 9, 11 and 12 were used as the cata-
lysts (Table 1, entries 8–10). Carrying out the epoxidation
with 30 mol % of 12 at 0 ꢁC had a deleterious effect on
the level of selectivity, even though good conversion was
A preliminary study was performed to test the catalytic
property of these reagents in the asymmetric organocata-
lytic epoxidation of enones 13a with TBHP (Table 1).
The reaction was performed using 30 mol % of dendritic
catalysts in different solvents. When employing catalyst 8,
in hexane at room temperature according to Lattanzi’s pro-
Ph
Ph
O
Ph
Ph
O
O
O
O
O
O
O
O
O
KOH
N
N
H
THF, EtOH
O
OH
Ph
Ph
Ph
Ph
O
n
n
O
O
O
O
1
2
3
4
n = 0
n = 1
n = 2
n = 3
7
8
9
n = 0
n = 1
n = 2
10 n = 3
Ph
Ph
Ph
Ph
O
O
O
O
O
O
O
O
KOH
N
N
H
THF, EtOH
O
OH
Ph
Ph
Ph
Ph
O
n
n
O
O
5
6
n = 1
n = 2
11 n = 1
12 n = 2
Scheme 1.

752
X. Liu et al. / Tetrahedron: Asymmetry 17 (2006) 750–755
Table 1. Screening reaction conditions for the epoxidation of 13aa
O
O
O
Cat./ TBHP
solvent, rt
14a
T (h)
13a
Entry
Catalyst
Solvent
Oxidant
T (ꢁC)
Yield (%)b
ee (%)c (config)d
1
2
3
4
5
6
7
8
8
Hexane
CCl4
CCl4
CCl4
CCl4
CCl4
CCl4
CCl4
CCl4
CCl4
CCl4
CCl4/hexane = 1:1
Benzene
CH2Cl2
CCl4
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
H2O2
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
0
48
144
120
144
144
144
144
144
144
144
144
96
Trace
60
59
64
73
67
70
85
86
84
80
65
66
20
0
nde
66
41
67
68
69
71
69
73
74
13
66
69
54
—
8
7
9
10
11
12
˚
9 + 4 A MS
10 + 4 A MS
12 + 4 A MS
12 + 4 A MS
11 + 4 A MS
11 + 4 A MS
11 + 4 A MS
11
˚
˚
˚
˚
˚
˚
9
10
11
12
13
14
15
rt
rt
rt
rt
96
144
48
a Unless otherwise specified, the reaction was carried out with 1.2 equiv of TBHP in the presence of 30 mol % of catalyst.
b After column chromatography.
c Enantiomeric excess was determined by the HPLC analysis by using a chiral Daicel Chiralcel OD column.
d The absolute configuration of 14a was determined to be (2R,3S) by comparison of the HPLC retention time with known data.
e Not determined.
achieved (Table 1, entry 11). When the reaction was carried
out in benzene, hexane/CCl4 = 1:1 (v/v), and CH2Cl2, the
reaction yield was lowered (compared with entry 9, Table 1)
and the enantioselectivity moderately reduced (Table 1, en-
tries 12–14). Notably, when the epoxidation was performed
with hydrogen peroxide (H2O2) as an oxidant, no reaction
occurred under conditions otherwise identical to those
reports in entry 9 (Table 1, entry 15). From these results,
we concluded that using catalyst 12, TBHP in CCl4 in the
under the same reaction conditions, an electron-donating
substituent did not react with TBHP, due to its low reac-
tivity (Table 2, entry 8). Specifically, when an enone bear-
ing an ortho-chloro substituent on the b-phenyl group
was used as a substrate, it was found that corresponding
product was obtained in 90% yield with 57% ee (Table 2,
entry 9). In contrast, the product was obtained in 85% yield
with 37% ee when using a,a-diphenyl-L-pyrrolidinemetha-
nol as a bifunctional organocatalyst (Table 2, entry 10).
The result in entry 11 shows that the protocol can be
successfully extended to a substrate having an alkyl substi-
tuent. Specifically, when (E)-4-methyl-1-phenylpent-1-en-3-
one, bearing a strong steric bulk at the b-position was used
as a substrate, it was found that no reaction occurred under
the same reaction conditions (Table 2, entry 12). As the
mechanism of this reaction is similar to Lattanzi’s results,15
we suggest that the chiral pyrrolidinylmethanol-based
dendritic catalysts also serve as bifunctional catalysts
giving rise to the simultaneous activation of the enone
and the alkyl hydroperoxide by the hydroxy and amino
groups, respectively.
˚
presence of 4 A MS at room temperature was the most
effective protocol for the epoxidation of chalcone 13a.
To demonstrate the scope and potential for the organocat-
alytic epoxidation, a series of different substituted enones
13 were reacted with TBHP at room temperature in the
presence of 12 (30 mol %) as the catalyst. The results are
summarized in Table 2. As shown, almost all reactions pro-
ceeded in reasonable reaction times when 30 mol % of 12
was used at room temperature and diastereoisomerically
pure trans-(2R,3S)-epoxides 14 were obtained. Different
types of electronic substitution on the phenyl ring of the
carbonyl group furnished results comparable to those
achieved in the epoxidation of 13 (Table 2, entries 2–5).
It was found that 4-nitro chalcone could be transformed
to the epoxide in 93% yield with 73% ee (Table 2, entry
4). However, the p-C6H5-C6H4 derivative was converted
slowly to the epoxide in 77% ee, which can be attributed
to the poor solubility of the enone in the reaction media
(Table 2, entry 5). Enones with para electron-withdrawing
substituents in the b-phenyl group were all converted to the
corresponding optically active epoxides in good yields and
enantioselectivities (Table 2, entries 6 and 7). However,
A significant advantage of dendritic catalysts is that they
can be easily separated from substrates and products
through precipitation, due to the different solubilities in
methanol. Therefore, these dendritic catalysts were tested
by the precipitation method. After the completion of the
reaction, dry methanol was added to the reaction mixture,
and catalyst 12 was almost quantitatively precipitated and
recovered via filtration. The recovered catalyst was reused
at least five times with little or no loss of activity and
enantioselectivity (Table 3).

X. Liu et al. / Tetrahedron: Asymmetry 17 (2006) 750–755
Table 2. Catalytic enantioselective epoxidation of enones promoted by 12 and TBHPa
753
O
O
12 (30 mol%)
O
R1
R1
R2
R2
CCl4, TBHP
4A MS, rt
13
14
Entry
R1
R2
T (h)
Yield (%)b
ee (%)c (config.)d
1
2
3
4
5
6
7
8
Ph
Ph
Ph
Ph
Ph
Ph
144
144
144
120
144
120
120
200
120
120
144
120
84
90
92
93
60
90
90
Trace
90
74 (2R,3S)
73 (2R,3S)
74 (2R,3S)
73 (2R,3S)
77 (2R,3S)
73 (2R,3S)
78 (2R,3S)
nd
56 (2R,3S)
37 (2R,3S)
69 (2R,3S)
ndg
p-Cl–C6H4
p-F–C6H4
p-NO2–C6H4
p-C6H5–C6H4
Ph
p-F–C6H4
Ph
Ph
p-Cl–C6H4
p-Cl–C6H4
p-MeO–C6H4
o-Cl–C6H4
o-Cl–C6H4
Ph
9
10e
11f
12
Ph
CH3
i-Pr
85
70
Trace
Ph
a Unless otherwise specified, the reaction was carried out with 1.2 equiv of TBHP in the presence of 30 mol % of catalyst 12.
b After column chromatography.
c Enantiomeric excess was determined by the HPLC analysis by using the chiral column.
d The absolute configuration of 14 was determined to be (2R,3S) by comparison of the HPLC retention times with known data.
e Using a,a-diphenyl-L-pyrrolidinemethanol as the bifunctional organocatalyst.
f 50 mol % catalyst was used in this reaction.
g Not determined.
Although the reaction mechanism is not clear, a possible
mechanism for this epoxidation of enones was proposed
according to the catalytic cycle by Lattanzi (Scheme 2).15
Table 3. Recycling use of dendritic catalyst in asymmetric epoxidation of
chalcone 13aa
Entry
Catalyst
T (h)
Yield (%)b
ee (%)c
1
2
3
4
5
12
144
144
144
144
144
84
84
80
81
83
74
73
72
73
72
12 (second)
12 (third)
12 (fourth)
12 (fifth)
3. Conclusion
In conclusion, a series of new dendritic chiral pyrrolidinyl-
methanol derivatives were synthesized and proven to be
highly effective bifunctional organocatalysts for the asym-
metric catalytic epoxidation with tert-butyl hydroperoxide
(TBHP) as an oxidant. This study opens up a new frontier
for the development of highly effective and easily separable
a Unless otherwise specified, the reaction was carried out with 1.2 equiv of
TBHP in the presence of 30 mol % of catalyst.
b After column chromatography.
c Enantiomeric excess was determined by the HPLC analysis using a chiral
Daicel Chiralcel OD column.
+
t-BuOOH
+
t-BuOO
N
H
N
H H
OH
OH
O
t-BuOH
R2
R1
N
H H
O
+
t-BuO
H
O
N
H H
OH
t-BuO O
R2
O
O
R1
R2
R1
Scheme 2.

754
X. Liu et al. / Tetrahedron: Asymmetry 17 (2006) 750–755
chiral bifunctional organocatalyst. Work is currently being
focused on gaining detailed insight into the nature of the
dendritic effect and the exploration of these catalysts in
other reactions.
d 1.52–1.69 (m, 5H), 2.86–3.02 (m, 2H), 4.08 (t, J = 7.8 Hz,
1H), 4.93 (s, 28H), 4.99 (s, 32H), 6.52–6.55 (m, 14H, Ar),
6.63–6.66 (m, 28H, Ar), 6.82–6.85 (m, 4H, Ar), 7.26–
7.37 (m, 84H, Ar); MALDI MS (IAA): m/e
3417.5 ([MꢁH2O+H]+); Anal. Calcd for C227H199NO31:
C, 79.33; H, 5.84; N, 0.41. Found: C, 79.41; H, 5.82; N,
0.40.
4. Experimental
4.1.5. Catalyst 11 (n = 1). 94% yield, white foam, mp 45–
General: All reactions were carried out under a dry Ar
atmosphere. CCl4 was freshly distilled from CaH2 before
use. Enones were prepared according to the reported pro-
cedures and further purified by silica gel column.17 All
NMR spectra were recorded in CDCl3 as the solvent unless
otherwise stated.
20
46 ꢁC; ½aꢀD ¼ ꢁ22:35 (c 0.95, CHCl3); IR (Film): 3358,
2871, 1596, 1496, 1451, 1156 cmꢁ1 1H NMR (CDCl3,
;
TMS, 300 MHz) d 1.19–1.73 (m, 5H), 2.86–3.01 (m, 2H),
4.15 (t, J = 7.6 Hz, 1H), 4.95 (s, 4H), 5.00 (s, 8H), 6.55
(m, 2H), 6.66–6.67 (m, 4H), 6.74–6.76 (m, 2H), 7.04–7.41
(m, 26H); Anal. Calcd for C59H55NO7: C, 79.62; H, 6.23;
N, 1.57. Found: C, 79.44; H, 6.29; N, 1.44.
4.1. Synthesis of catalysts
4.1.6. Catalyst 12 (n = 2). 96% yield, white foam, mp 60–
All the dendrimeric bromides,18 prolinol cores and the link-
ing of dendrimers with prolinol core were prepared accord-
ing to the literature.13,14 Hydrolysis of the carbonyl group
with potassium hydroxide in dimethyl sulfoxide at 80 ꢁC
for 4 h and after purification by silica gel chromatography
using CH2Cl2/acetone (1:1) as eluent gave the correspond-
ing dendrimeric catalysts 7–12:
20
61 ꢁC; ½aꢀD ¼ ꢁ10:45 (c 1.00, CHCl3); IR (Film): 3359,
2872, 1597, 1507, 1452, 1156 cmꢁ1 1H NMR (CDCl3,
;
TMS, 300 MHz) d 0.90–1.12 (m, 2H), 1.70–1.96 (m, 2H),
3.11 (t, J = 7.6 Hz, 1H), 3.61–3.68 (m, 1H), 4.44 (m, 1H),
4.93 (s, 12H), 4.99 (s, 16H), 6.55 (m, 6H), 6.66 (m, 12H);
6.92–6.99 (m, 6H) 7.31–7.37 (m, 48H); MALDI MS
(IAA): m/e 1721.7 ([MꢁH2O+H]+); Anal. Calcd for
C115H103NO15: C, 79.42; H, 5.97; N, 0.81. Found: C,
79.18; H, 5.91; N, 0.53.
4.1.1. Catalyst
7
(n = 0). 66% yield, colorless oil.
½aꢀD ¼ ꢁ59:6 (c 1.00, CHCl3); IR (Film): 3358, 1607,
1507, 1454, 1241 cmꢁ1 1H NMR (300 MHz, CDCl3) d
20
;
4.2. Typical procedure for the asymmetric epoxidation
of enones
1.50–1.71 (m, 4H), 2.85–3.02 (m, 2H), 4.19 (t, J = 7.3 Hz,
1H), 4.99 (s, 2H), 5.00 (s, 2H), 6.86–6.90 (m, 4H, Ar),
7.23–7.46 (m, 14H, Ar); 13C NMR (75 MHz, CDCl3) d
25.5, 26.3, 46.7, 64.7, 69.9, 70.0, 76.6, 114.1, 114.2, 114.4,
126.6, 127.0, 127.4, 127.5, 127.6, 127.9, 128.0, 128.5,
137.1, 137.2, 138.4, 140.9, 157.3, 157.4; MS (ESI) m/z
466.1 (M++1, 100%) HRMS-ESI: m/z (M++1) calcd for
C31H32NO3: 466.23829; found: 466.23767.
To a solution of enone 13a (20.8 mg, 0.1 mmol), catalyst
˚
12 (30 mol %, 53 mg) and 4 A MS (73 mg) in CCl4
(0.4 mL) was added TBHP (0.13 mmol, 18 lL) at room
temperature (23 ꢁC) and stirring was maintained for the
˚
indicated time. Then, the 4 A MS powder was filtered
off and washed with CCl4 (2 · 0.5 mL). The filtrate was
then diluted with MeOH and the catalyst precipitated
immediately to recover 50 mg (94.3%). After filtration,
the organic layer was concentrated under vacuum to
afford the crude epoxide, which was further purified
by flash chromatography on silica gel (petroleum
ether/diethyl ether 20:1) to yield product 14a 18.8 mg
(84%).
4.1.2. Catalyst 8 (n = 1). 95% yield, white foam, mp
20
45 ꢁC; ½aꢀD ¼ ꢁ32:3 (c 0.93, CHCl3). IR (Film) 3359,
1596, 1506, 1452, 1159 cmꢁ1; 1H NMR (300 MHz, CDCl3)
d 1.53–1.79 (m, 5H), 2.94–3.04 (m, 2H), 4.19 (t, J = 6.3 Hz,
1H), 4.95 (s, 4H), 5.03 (s, 8H), 6.56–6.57 (m, 2H, Ar), 6.66–
6.67 (m, 4H, Ar), 6.86–6.93 (m, 4H, Ar), 7.25–7.47 (m,
24H, Ar). MALDI MS (IAA): m/e 872.4 [MꢁH2O+H]+;
Anal. Calcd for C59H55NO7: C, 79.62; H, 6.23; N, 1.57.
Found: C, 79.58; H, 6.27; N, 1.45.
4.3. trans-(2R,3S)-Epoxy-1,3-diphenyl-propan-1-one 14a6a
The compound was obtained as a white solid; mp 88–
23
90 ꢁC; ½aꢀD ¼ ꢁ116:3 (c 0.40, CHCl3) for 74% ee; 1H
4.1.3. Catalyst 9 (n = 2). 83% yield, white foam, mp 57–
20
59 ꢁC; ½aꢀD ¼ ꢁ25:8 (c 1.25, CHCl3); IR (Film): 3353,
NMR (300 MHz, CDCl3) d 4.01 (d, J = 1.8 Hz, 1H), 4.23
(d, J = 1.8 Hz, 1H), 7.32–7.45 (m, 7H), 7.54 (d,
J = 7.2 Hz, 1H), 7.94 (d, J = 7.8 Hz, 2H); HPLC: Daicel
Chiral OD column, hexane/i-PrOH = 9:1, 1.0 mL/min,
k = 254 nm, tR(2S,3R) = 14.7 min, tR(2R,3S) = 15.6 min.
1
2872, 1596, 1506, 1452, 1157 cmꢁ1; H NMR (300 MHz,
CDCl3) d 1.52–1.69 (m, 5H), 2.86–3.02 (m, 2H), 4.10 (t,
J = 7.5 Hz, 1H), 4.93 (s, 12H), 5.00 (s, 16H), 6.51–6.56
(m, 6H, Ar), 6.63–6.67 (m, 12H, Ar), 6.85–6.87 (m, 4H,
Ar), 7.29–7.41 (m, 44H, Ar); MALDI MS (IAA): m/e
1721.7 ([MꢁH2O+H]+); Anal. Calcd for C115H103NO15:
C, 79.42; H, 5.97; N, 0.81. Found: C, 79.40; H, 5.94; N,
0.76.
Acknowledgements
We are grateful to the National Natural Science Founda-
tion of China for financial support (Nos. 20172064,
203900502, 20532040, QT program), and Shanghai Natural
Science Council.
4.1.4. Catalyst 10 (n = 3). 61% yield, white foam, mp 61–
20
63 ꢁC; ½aꢀD ¼ ꢁ5:3 (c 0.8, CHCl3); IR (Film): 3400, 2872,
1598, 1498, 1452, 1216 cmꢁ1; 1H NMR (300 MHz, CDCl3)

X. Liu et al. / Tetrahedron: Asymmetry 17 (2006) 750–755
755
7. Wang, X. W.; Shi, L.; Li, M. X.; Ding, K. L. Angew. Chem.,
Int. Ed. 2005, 44, 6362.
References
8. Ooi, T.; Ohara, D.; Tamura, M.; Maruoka, K. J. Am. Chem.
Soc. 2004, 126, 6844.
9. Shi, Y. Acc. Chem. Res. 2004, 37, 488.
1. (a) Johnson, R. S.; Sharpless, K. B. In Comprehensive Organic
Synthesis; Trost, B. M., Flemming, I., Eds.; Pergamon Press:
New York, 1991; Vol. 7, p 389; (b) Catalytic Asymmetric
Synthesis; Ojima, I., Ed., 2nd ed.; Wiley: New York, 2000; (c)
Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz,
A., Yamamoto, H., Eds.; Springer: New York, 1999; (d)
Noyori, R. Asymmetric Catalysis in Organic Synthesis; John
Wiley & Sons: New York, 1994; (e) Benaglia, M.; Puglisi, A.;
Cozzi, F. Chem. Rev. 2003, 103, 3401.
2. (a) Katsuki, K.; Sharpless, K. B. J. Am. Chem. Soc. 1980,
102, 5974; (b) Hanson, R. M.; Sharpless, K. B. J. Org. Chem.
1986, 51, 1992.
3. (a) Zhang, W.; Loebach, J. L.; Wilson, S. R.; Jacobsen, E. N.
J. Am. Chem. Soc. 1990, 112, 2801; (b) Katsuki, T. Coord.
Chem. Rev. 1995, 140, 189; (c) Irie, R.; Noda, K.; Ito, Y.;
Katsuki, T. Tetrahedron Lett. 1991, 32, 1055; (d) Hosoya, N.;
Hatayama, A.; Irie, R.; Sasaki, H.; Katsuki, T. Tetrahedron
1994, 50, 4311; (e) Fukuda, T.; Irie, R.; Katsuki, T. Synlett
1995, 197.
10. For recent reviews on dendritic catalysts, see: (a) Oosterom,
G. E.; Reek, J. N. H.; Kamer, P. C. J.; van Leeuwen, P. W. N.
M. Angew. Chem., Int. Ed. 2001, 40, 1828; (b) Astruc, D.;
Chardac, F. Chem. Rev. 2001, 101, 2991; (c) Crooks, R. M.;
Zhao, M.; Sun, L.; Chechik, V.; Yueng, L. K. Acc. Chem.
Res. 2001, 34, 181; (d) Reek, J. N. H.; de Groot, D.;
Oosterom, G. E.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.
Rev. Mol. Biotechnol. 2002, 90, 159; (e) Twyman, L. J.; King,
A. S. H.; Martin, I. K. Chem. Soc. Rev. 2002, 31, 69; (f) van
Heerbeek, R.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.;
Reek, J. N. H. Chem. Rev. 2002, 102, 3717; (g) Fan, Q.-H.; Li,
Y.-M.; Chan, A. S. C. Chem. Rev. 2002, 102, 3385; (h)
Caminade, A.-M.; Maraval, V.; Laurent, R.; Majoral, J.-P.
Curr. Org. Chem. 2002, 6, 739.
11. For a review on the nanofiltration technique in dendritic
catalyst recycling, see: Dijkstra, H. P.; van Klink, G. P. M.;
van Koten, G. Acc. Chem. Res. 2002, 35, 798.
4. (a) Yang, D.; Yip, Y.-C.; Tang, M.-W.; Wong, M.-K. J. Am.
Chem. Soc. 1996, 118, 491; (b) Yang, D.; Wang, X.-C.; Wong,
M.-K.; Yip, Y.-C.; Tang, M.-W. J. Am. Chem. Soc. 1996,
118, 11311; (c) Yang, D.; Wong, M.-K.; Yip, Y.-C.; Wang,
X.-C.; Tang, M.-W.; Zheng, J.-H.; Cheung, K.-K. J. Am.
Chem. Soc. 1998, 120, 5943.
12. For selected reports on dendritic catalyst recycling by
precipitation, see: (a) Reetz, M. T.; Lohmer, G.; Schwickardi,
R. Angew. Chem., Int. Ed. 1997, 36, 1526; (b) Petrucci-Samija,
M.; Guillemette, V.; Dasgupta, M.; Kakkar, A. K. J. Am.
Chem. Soc. 1999, 121, 1968; (c) Hu, Q.-S.; Pugh, V.; Sabat,
M.; Pu, L. J. Org. Chem. 1999, 64, 7528; (d) Fan, Q.-H.;
Chen, Y.-M.; Chen, X.-M.; Jiang, D.-Z.; Xi, F.; Chan, A. S.
C. Chem. Commun. 2000, 789; (e) Maraval, V.; Caminade, A.-
M.; Majoral, J.-P. Organometallics 2000, 19, 4025.
13. Liu, X.-Y.; Wu, X.-Y.; Chai, Z.; Wu, Y.-Y.; Zhao, G.; Zhu,
S.-Z. J. Org. Chem. 2005, 70, 7432.
14. Wang, G.-Y.; Liu, X.-Y.; Zhao, G. Synlett, in press.
15. Lattanzi, A. Org. Lett. 2005, 7, 2579.
5. For a review, see: Porter, M. J.; Skidmore, J. Chem. Commun.
´
2000, 1215; See also: Julia, S.; Masana, J.; Vega, J. C. Angew.
Chem., Int. Ed. Engl. 1980, 19, 929.
6. (a) Bougauchi, M.; Watanabe, S.; Arai, T.; Sasai, H.;
Shibasaki, M. J. Am. Chem. Soc. 1997, 119, 2329; (b)
Nemoto, T.; Ohshima, T.; Shibasaki, M. J. Am. Chem. Soc.
2001, 123, 9474; (c) Nemoto, T.; Ohshima, T.; Yamaguchi,
K.; Shibasaki, M. J. Am. Chem. Soc. 2001, 123, 2725; (d)
Nemoto, T.; Kakei, H.; Gnanadesikan, V.; Tosaki, S.;
Ohshima, T.; Shibasaki, M. J. Am. Chem. Soc. 2002, 124,
14544; (e) Matsunaga, S.; Kinoshita, T.; Okada, S.; Harada,
S.; Shibasaki, M. J. Am. Chem. Soc. 2004, 126, 7559; (f)
Kakei, H.; Tsuji, R.; Ohshima, T.; Shibasaki, M. J. Am.
Chem. Soc. 2005, 127, 8962.
´
16. Marigo, M.; Franzen, J.; Poulsen, T. B.; Zhuang, W.;
Jørgensen, K. A. J. Am. Chem. Soc. 2005, 127, 6964.
17. Sinisterra, J. V.; Garcia-Raso, A.; Cabello, J. A.; Marinas, J.
M. Synthesis 1984, 502.
´
18. Hawker, C. J.; Frechet, J. M. J. J. Am. Chem. Soc. 1990, 112,
7638.