Asymmetric addition of phenylacetylene to aldehydes catalyzed by soluble optically active polybinaphthols ligand

Article abstract of DOI:10.1016/j.tet.2007.12.058

A chiral polymer ligand was synthesized by the polymerization of (S)-5,5′-dibromo-6,6′-dibutyl-2,2′-binaphthol (S-M-1) with (S)-2,2′-bishexyloxy-1,1′-binaphthyl-6,6′-boronic acid (S-M-2) via Pd-catalyzed Suzuki reaction. The application of the chiral poly

Full text of DOI:10.1016/j.tet.2007.12.058

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 2651e2657
www.elsevier.com/locate/tet
Asymmetric addition of phenylacetylene to aldehydes catalyzed
by soluble optically active polybinaphthols ligand
*
Linglin Wu, Lifei Zheng, Lili Zong, Jinqian Xu, Yixiang Cheng
School of Chemistry and Chemical Engineering, Nanjing University, Hankou 22, Nanjing, Jiangsu 210093, PR China
Received 9 October 2007; received in revised form 19 December 2007; accepted 21 December 2007
Available online 4 January 2008
Abstract
A chiral polymer ligand was synthesized by the polymerization of (S)-5,50-dibromo-6,60-dibutyl-2,20-binaphthol (S-M-1) with (S)-2,20-bish-
exyloxy-1,10-binaphthyl-6,60-boronic acid (S-M-2) via Pd-catalyzed Suzuki reaction. The application of the chiral polymer ligand to the asym-
metric addition of phenylethynyl zinc to various aldehydes has been studied. The results show that the soluble chiral polybinaphthols ligand in
combination with Et2Zn and Ti(OiPr)4 can exhibit excellent enantioselectivity for phenylacetylene addition to both aromatic and aliphatic
aldehydes. The catalytically active center of the repeating unit S-1 used as a catalyst produced the opposite configuration of the propargylic
alcohols to that of S-1, on the contrary, the chiral polymer gave the same configuration as the optically active binaphthol moiety of the poly-
binaphthols ligand. Moreover, the chiral polymer ligand can be easily recovered and reused without loss of catalytic activity as well as enan-
tioselectivity.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: (S)-2,20-Binaphthol; Suzuki coupling; Asymmetric enantioselectivity
1. Introduction
at 5,50-positions in a mild condition to afford a pure product in an
excellent yield when 6,60-positions are occupied by n-butyl
groups. 5,50-Dibromo-6,60-dialkyl-2,20-binaphthol can further
be used as an entry into a wide range of other derivatives by
strategic placement of substituents at thewell-defined molecular
level, which will lead to the outcome of a new generation of
novel binaphthyl-based derivatives for applications in asymmet-
ric catalysis, chiral fluorescent sensors, and electro-optical
devices.
In the past 10 years, Pu et al. have proposed and designed a
series of novel chiral polymer ligands based on polybinaphthols
as the Lewis acid to carry out highly enantioselective organic re-
actions, such as the additions to aldehydes, hetero-DielseAlder
reactions, 1,3-dipolar cycloadditions, reductions of ketones, and
others.4 Unlike the traditional polymeric chiral catalysts, which
are prepared by anchoring a chiral ligand to a flexible and steri-
cally irregular achiral polymer backbone, these stereoregular
chiral BINOL-based polymer ligands can generate regularly ori-
ented catalytic sites along the polybinaphthols chain backbone
and produce a well-defined microenvironment around the
Optically active 1,10-bi-2-naphthol (BINOL) and its deriva-
tives have attracted particular interests because their versatile
backbone can be systematically modified by the introduction
of functional groups based on steric and electronic properties.1
According to the reported literature, the skeletal structure of
BINOL can be selectively halogenated at the 3,30- or 6,60-
positions of binaphthyl, leading to a variety of binaphthyl deriva-
tives.2 But so far there have been few reports on halogenation of
BINOL at the 5,50-positions except that Shimada and Lemaire
reported the direct and facile synthesis of 5,50-diiodo-/5,50-di-
bromo-2,20-bis-(diphenylphosphino)-1,10-binaphthyl (BINAP),
and Pirkle described the synthesis and chiral resolution of race-
mic 5,50-dibromo-6,60,7,70-tetramethyl-2,20-binaphthol.3 Based
on our current study, (S)-BINOL can be specifically brominated
* Corresponding author. Tel.: þ86 25 83592709; fax: þ86 25 83317761.
E-mail address: yxcheng@nju.edu.cn (Y. Cheng).
0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.12.058

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L. Wu et al. / Tetrahedron 64 (2008) 2651e2657
catalytically chiral centers. Therefore it is possible to systemat-
ically adjust the microenvironment of the catalytic sites in these
chiral polymer ligands to achieve the desired catalytic activity
and stereoselectivity.5 Chan et al. also reported earlier the solu-
ble polymer-supported catalysts incorporating the chiral BINAP
units in the polymer main chain, which showed high activity and
stereoselectivity in asymmetric hydrogenation.6 The use of
soluble chiral polymer catalysts in asymmetric synthesis has
important practical advantages. These soluble chiral polymers
can catalyse asymmetric reactions in a homogeneous manner
and thus have similar catalytic activity and stereoselectivity as
the homogeneous parent system. When the reaction is com-
pleted, polymeric catalysts can beeasily separated from the reac-
tion mixture by simple filtration or precipitation upon the
addition of methanol. In addition, the recycling and recovery
of chiral catalyst is particularly important since it is often
more expensive to obtain these optically pure ligands.5b,7
The enantioselective alkynylzinc addition to aldehydes is
a very useful method for the synthesis of chiral propargyl
alcohols, which are important versatile building blocks for
asymmetric synthesis.8 Since Ishizaki and Hoshino reported
the first addition of alkynylzinc reagents to aldehydes in
1994,9 some chiral ligands, such as N-methylephedrine,8c sul-
fonamide alcohol,10 BINOL, and its derivatives,11 have suc-
cessfully been applied to this reaction in recent years. The
BINOL derivative ligands show excellent enantioselectivity
for the alkynylzinc addition to aromatic aldehydes. In this pa-
per, we report the synthesis and asymmetric enantioselectivity
of a soluble chiral polymer ligand incorporating the alternative
(S)-2,20-binaphthol at 5,50-positions and (S)-1,10-binaphthyl at
6,60-positions. The chiral moieties of (S)-2,20-bishexyloxy-
1,10-binaphthyl and (S)-6,60-dibutyl-2,20-binaphthol can regu-
larly distribute along the polymer chain. This kind of
polybinaphthols ligand substituted at 5,50-positions of (S)-
2,20-binaphthol has not been reported so far. When the result-
ing chiral polymer was used to catalyze the addition reactions
of phenylethynyl zinc to both aromatic and aliphatic
aldehydes, the resulting products were obtained in excellent
enantioselectivity. Moreover, the chiral polymer ligand can
be easily recovered and reused without loss of catalytic activ-
ity as well as enantioselectivity.
2. Results and discussion
2.1. Syntheses and features of monomers and polymer
The chiral repeating units S-1, S-2, and the chiral monomers
S-M-1, S-M-2 were synthesized from the starting product (S)-
BINOL (Scheme 1). S-M-1 was prepared in an overall yield of
46% by a five-step synthesis. The hydroxyl groups of 6,60-di-
bromo-2,20-binaphthol were first protected by methoxymethyl
chloride (MOMCl) according to the literature.2def,12 (S)-6,60-Di-
butyl-2,20-binaphthol (S-1) could be obtained by deprotection of
MOM groups of (S)-6,60-dibutyl-2,20-bis(methoxymeth-
oxy)-1,10-binaphthyl, which was obtained by the reaction of
(S)-6,60-dibromo-2,20-bis(methoxymethoxy)-1,10-binaphthyl
with n-butyllithium at ꢀ78 ꢁC under a N2 atmosphere, and
followed by the addition of n-butyl bromide at ꢀ78 ꢁC. S-M-1
can be directly obtained by electrophilic aromatic bromination
of (S)-6,60-dibutyl-2,20-binaphthol (S-1) at 5,50-positions in
CH2Cl2 at ꢀ78 ꢁC with 1.05 equiv of bromine without any fur-
1
ther purification in a very high yield of 99%. H NMR of (S)-
6,60-dibutyl-2,20-binaphthol has a single peak of 5,50-position
1
protons at 7.66 ppm, but this single peak disappears in the H
NMR of S-M-1, which can be attributed to bromination at
5,50-positions of (S)-6,60-dibutyl-2,20-binaphthol. The repeating
unit S-2 can be synthesized by the etherification of hydroxyl
groups of (S)-BINOL with n-hexyl bromide in the presence
of K2CO3 in refluxing CH3CN solution. S-M-2 can be obtained
from (S)-6,60-dibromo-2,20-bishexyloxy-1,10-binaphthyl accord-
ing to the reported literatures.13
Based on Lin’s report,12b,14 while (S)-6,60-dichloro-2,20-bis-
ethoxy-1,10-binaphthyl was chosen as the starting material,
bromination could undergo at 4,40-positions in CH2Cl2 at
Br
n-Bu
n-Bu
Br
(1) Br2
-78 °C
(1) n-BuLi
Br2
-78 °C
-78 °C
OH
OH
OH
OH
OMOM
OMOM
(2) NaH MOMCl
(2) n-BuBr
-78 °C
(3) HCl
n-Bu
Br
n-Bu
Br
S-1
(OH)2B
S-M-1
Br
(1) Br2
-78 °C
(1) n-BuLi,
-78 °C
OH
OH
OC6H13-n
OC6H13-n
OC6H13-n
OC6H13-n
(2) n-C6H13Br
(2) B(OMe)3
(3) HCl
Br
(OH)2B
S-BINOL
S-M-2
n-C6H13Br
OC6H13-n
OC6H13-n
S-2
Scheme 1. Synthesis procedures of S-1, S-2, S-M-1, and S-M-2.

L. Wu et al. / Tetrahedron 64 (2008) 2651e2657
2653
ꢀ78 ꢁC with 10 equiv of bromine to directly afford a pure prod-
100
uct 4,40-dibromo-6,60-dichloro-2,20-bisethoxy-1,10-binaphthyl
in a very high yield of 98%. Pu also reported preparation of
(R)- or (S)-4,40,6,60-tetrabromo-2,20-bishexyloxy-1,10-binaph-
thyl in AcOH under room temperature with 10 equiv of bromine
when optically pure 2,20-bishexyloxy-1,10-binaphthyl was used
as a starting material.14b Herein, (S)-6,60-dibutyl-2,20-binaph-
thol can undergo bromination substitution at 5,50-positions at
lower temperature with almost equivalent bromine because the
butyl substituent groups at 6,60-positions of BINOL will directly
affect the reactivity and regioselectivity of 5,50-positions. The
reactivity of BINOL toward electrophile will be greatly en-
hanced by n-butyl substituent groups, which donate electron
density to the BINOL. The bromination activating effect can
be attributed to the large increase of electron density at 5,50-
positions of BINOL. Therefore, orientation of bromination is
predominated by the only choice of 5,50-positions.
90
80
70
60
100
200
300
400
500
Temperature (°C)
600
700
800
Figure 1. TGA curve of the chiral polymer ligand.
and tends to completely decompose at 700 ꢁC. A total loss of
about 41% is observed when the polymer was heated to
800 ꢁC.
A typical Suzuki reaction condition was applied to the po-
lymerization (Scheme 2).15 The CeC cross coupling process
was easily carried out in THF and aqueous K2CO3 solution
in the presence of a catalytic amount (5 mol %) of Pd(PPh3)4
at 85 ꢁC under the protection of a N2 atmosphere. The poly-
merization went on in a good yield (95.3%) after 48 h. In
this paper, the GPC result of the polymer shows the moderate
molecular weight. This kind of soluble polymer ligand used as
the catalyst for asymmetric addition of alkynylzinc to benzal-
dehyde can undergo homogeneous reaction. Generally, the sol-
uble polymer ligands can afford higher catalytic activity and
enantioselectivity than the insoluble polymer polybinaphthols
catalysts due to the homogeneous asymmetric reaction.5b,16
The recovered and reused polymer ligand could still show simi-
lar enantioselectivity (entries 4 and 9).
The polymer ligand is an air stable solid with pale color
and shows good solubility in some common solvents such
as THF, CH2Cl2, CHCl3, toluene, and DMF, which can be at-
tributed to the nonplanarity of the twisted polymer in the
main-chain backbone and the flexible n-butyl or n-hexyloxy
substitutent groups as the side chain of the polymer. Polymer
ligand shows no glass transition temperature (Tg). Thermo-
gravimetric analysis (TGA) of the polymer catalyst was car-
ried out under a N2 atmosphere at a heating rate of 10 ꢁC/
min. According to Figure 1, there is no loss of weight before
280 ꢁC. However, polymer ligand undergoes an apparent one-
step degradation at temperature ranging from 350 to 580 ꢁC,
2.2. CD spectra
The specific rotation values ([a]2D0) of the repeating units
(S)-6,60-dibutyl-2,20-binaphthol (S-1) and (S)-2,20-bishexy-
loxy-1,10-binaphthyl (S-2) are þ82.9 (c 0.31, CH2Cl2) and
ꢀ88.9 (c 0.72, CH2Cl2), but [a]2D0 of the chiral polymer ligand
is þ20 (c 0.5, CH2Cl2). CD spectral data of S-1, S-2, and the
chiral polymer ligand in CH2Cl2 are listed in Table 1. S-1, S-2,
and the polymer ligand exhibit intense CD signals with
negative and positive Cotton effects in their CD spectra
(Fig. 2). We can find great difference from CD spectra of S-
1
1, S-2, and the chiral polymer ligand. La band position of
the chiral ligand polymer is almost similar as the chiral repeat-
ing units S-1 and S-2. On the contrary, 1La and 1Bb band inten-
sities of the repeating units S-1 and S-2 are as more than two
1
times as that of the chiral polymer ligand. Bb bands of S-1
and S-2 appear at 238 and 240 nm, but the chiral polymer
ligand appears at 250 nm and shows red-shift of about
10 nm relative to S-1 and S-2. Herein, we first report the syn-
thesis of a soluble chiral polymer ligand incorporating the
alternative (S)-2,20-binaphthol at 5,50-positions and (S)-1,10-
binaphthyl at 6,60-positions. The chiral moieties of (S)-2,20-
bishexyloxy-1,10-binaphthyl and (S)-6,60-dibutyl-2,20-binaphthol
are alternatively organized in a regular chiral polymer chain.
But the resulting polymer ligand has smaller specific rotation
value, which can be attributed to the counteracting result of
the opposite specific rotation signal of the repeating units
S-1 and S-2 in the regular arrangement of the main-chain
backbone.
HO
OH
n-Bu
Pd(PPh3)4
K2 CO3 (a.q.)
Table 1
CD spectral data of the repeating units S-1, S-2, and the polymer ligand
S-M-1 +
S-M-2
OC6H13-n
OC6H13-n
Bu-n
THF
S-1 (ꢂ106)
S-2 (ꢂ106)
P-1 (ꢂ105)
n
[q]
(lmax in nm)
ꢀ1.29 (226.0)
ꢀ0.776 (227.9)
ꢀ4.06 (224.0)
þ1.59 (238.0)
þ1.09 (240.1)
þ3.82 (250.3)
Scheme 2. Synthesis procedure of the chiral polymer ligand.

2654
L. Wu et al. / Tetrahedron 64 (2008) 2651e2657
Table 2
Reaction of phenylacetylene with aldehyde in the presence of chiral liganda
1600000
1200000
800000
400000
0
S-1
S-2
P-1
OH
[chiral polymer]
Ph
H
RCHO
Ph
+
i
ZnEt2
*
Ti(OPr)4
R
Entry Solvent
Aldehyde
Yieldb (%) eec (%) Configurationd
1e
2e
3
Toluene
Toluene
Toluene
Toluene
Toluene
70
73
83
75
76
76
82
87
85
96
R
R
S
S
S
CHO
-400000
-800000
CHO
CHO
-1200000
4f
5
CHO
CHO
220 240 260 280 300 320 340 360 380 400
Wavelength (nm)
6
Figure 2. CD spectra of the repeating units S-1, S-2, and the chiral polymer
ligand.
Cl
6
Toluene
85
67
S
CHO
2.3. Asymmetric addition reactions of phenylacetylene with
aldehydes
7
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
80
90
89
79
84
86
89
81
92
90
97
61
S
S
S
S
S
S
F
CHO
8
The asymmetric addition reactions of phenylacetylene
with aldehydes in combination with Et2Zn and Ti(OiPr)4
were carried out in the presence of the chiral polymer ligand
in different solvents. The reactions were conducted at room
temperature using phenylacetylene, Et2Zn, Ti(OiPr)4, chiral
polymer ligand (based on the repeating unit), and aldehyde
with a molar ratio of 4:4:1:0.1:1. Chiral ligand (10 mol %)
in combination with Et2Zn and Ti(OiPr)4 were used as the
addition reaction catalyst. In order to evaluate the efficiency
of the chiral ligand for enantioselectivity of asymmetric ad-
dition, a variety of aldehydes were chosen as substrates in
THF, CH2Cl2, and toluene. The enantioselective data are
summarized in Table 2. The polymer catalyst shows excellent
solubility in toluene, THF, and CH2Cl2, but quantitatively
precipitated upon the addition of methanol. The different
solubility provided a convenient and reliable method for
the recycling of the chiral polymeric ligand. According to
Table 2, we can find that this kind of soluble polybinaphthols
ligand shows to be a good catalyst for the addition reactions
of aldehydes with an excellent enantioselectivity and a moder-
ate yield. The main side products of the asymmetric addition
reaction can be attributed to the competitive reaction of di-
ethylzinc and alkynylzinc to aldehydes. The results show
that the resulting chiral polymer is an excellent enantioselec-
tive catalyst not only for the alkynylzinc addition to aromatic
aldehydes, but also for the alkynylzinc addition to aliphatic
aldehydes in the three solvents. Traditionally, polymeric chi-
ral catalysts are prepared by anchoring a chiral ligand to
a flexible and sterically irregular achiral polymer backbone.
It is generally observed that the polymer-supported chiral
catalysts are usually less efficient than their monomeric ver-
sion, which indicates that the microenvironment of the cata-
lytic sites in the polymers is very important for their
effectiveness in steric control. The flexible and sterically
irregular polymer backbone of the traditional polymeric
F3C
F3C
CHO
CHO
9f
10
11
12
CHO
H3C
CHO
CHO
CH3O
CHO
13
14
THF
THF
80
90
98
98
S
S
F
CHO
15
THF
86
57
S
CHO
16
17
18
19
THF
85
80
84
84
96
94
87
91
S
S
S
S
H3C
CHO
CHO
CH2Cl2
CH2Cl2
CH2Cl2
F
CHO
CHO
20
CH2Cl2
78
96
S
H3C
CHO
Phenylacetylene/Et2Zn/Ti(OiPr)4/ligand (based on the repeating unit)/
a
aldehyde¼4:4:1:0.1:1.
b
Isolated yields.
Determined by HPLC on Chiralcel OD-H column eluted with hexane/
c
2-propanol (90:10, v/v) at 1.0 mL/min and detected at 254 nm.
d
Absolute configuration of the corresponding propargylic alcohols.
S-1 was used as the ligand.
The chiral polymer catalyst was reused.
e
f

L. Wu et al. / Tetrahedron 64 (2008) 2651e2657
2655
chiral catalysts generates randomly oriented catalytic sites,
4. Experimental
which can not be systematically modified to achieve the
desired catalytic active center and stereoselectivity.17 Based
on our study, the polymer catalyst incorporating optically
active (S)-6,60-dibutyl-2,20-binaphthol moiety in the polymer
main chain can show higher enantioselectivity than the cata-
lytically active center of the repeating unit S-1 (entries 1, 3
and 2, 10).
When the polymer ligand was used as the catalyst, the ab-
solute configuration of the corresponding propargylic alcohol
products is assigned as S by comparing its HPLC data with
those previously reported literature,11b,18 which is the same
as the optically active binaphthol moiety of the polymer cata-
lyst. On the contrary, while the small molecule ligands, such
as optically active BINOL or the modified BINOL deriva-
tives, were used as the catalyst for the enantioselective alky-
nylzinc addition to aldehydes, the resulting configuration of
4.1. General
1H and 13C NMR spectral measurements were recorded on
a 300-Bruker spectrometer with TMS as an internal standard.
FTIR spectra were taken on a Nexus 870 FT-IR spectrometer.
Specific rotation was determined with a Rudolph Research
Analytical Autopol I apparatus. The ee value determination
was carried out using chiral PeE Series200 HPLC with
a Chiralpak OD-H column on a Waters chromatograph
with a PeE Series200 UV/vis-detector. All solvents and
reagents were of commercially available A.R. grade. (S)-
2,20-Binaphthol (BINOL) was purchased from Aldrich and
directly used without purification. All reactions were per-
formed under a N2 atmosphere using Schlenk tube tech-
niques. THF and toluene were purified by distillation from
sodium in the presence of benzophenone. CH2Cl2 was dis-
tilled from P2O5.
the propargylic alcohols is opposite to the configuration of
11a,b,18
the chiral catalyst.
Based on our study, we draw the
same conclusion that the R configuration of the propargylic
alcohols can be obtained (entries 1 and 2) when the catalyt-
ically active center of the repeating unit S-1 was used as the
enantioselective catalyst for asymmetric addition reactions of
phenylethynyl zinc to propionaldehyde and benzaldehyde in
toluene. Currently, we are further doing the study on the
change feature of the configuration of the propargylic alco-
hols based on other asymmetric addition reactions using
the small molecule BINOL derivative catalysts and polybi-
naphthols ligands. In this paper, when the recycled chiral
polymer ligand was reused for the asymmetric addition reac-
tion of phenylethynyl zinc to propionaldehyde and p-trifluoro-
methylbenzaldehyde in toluene, 85% and 92% ee could be
obtained (entries 4 and 9). The results show that the recycled
polymer catalyst can keep similar enantioselectivity as the
original chiral polymer ligand.
4.2. Synthesis of (S)-6,60-dibutyl-2,20-binaphthol (S-1)
(S)-6,60-Dibromo-2,20-bis(methoxymethoxy)-1,10-binaphthyl
(2.0 g, 3.8 mmol) was dissolved in anhydrous THF (30.0 mL).
n-BuLi (3.8 mL, 2.5 M in hexanes, 9.5 mmol) was added by
syringe injection at ꢀ78 ꢁC under N2 atmosphere. After the
reaction mixture was stirred for 10 min, n-C4H9Br (2.1 g,
15.2 mmol) was added to the above solution at ꢀ78 ꢁC under
a N2 atmosphere. The reaction mixture was gradually warmed
to room temperature and stirred overnight. The mixture was
extracted with ethyl acetate (2ꢂ50 mL). The combined or-
ganic layers were washed with water and brine, and then dried
over anhydrous Na2SO4. After the removal of solvent under
reduced pressure, the crude product was purified by column
chromatography (petroleum ether/ethyl acetate) (30:1, v/v)
to afford a colorless viscous product (0.93 g, 51% yield).
The product was dissolved in the mixed solvents of 10 mL
THF and 10 mL methanol. Hydrochloric acid (15 mL, 12 M)
solution was added to the above solution. The solution was
stirred at room temperature for 8 h. After the removal of all
solvents under reduced pressure, the residue was extracted
with ethyl acetate (2ꢂ30 mL). The combined organic layers
were washed with 2 M NaHCO3 solution and brine twice,
and then dried over anhydrous Na2SO4. The crude product
was purified by column chromatography on silica gel (petro-
leum ether/ethyl acetate) (20:1, v/v) to afford a white solid
product (0.71 g, 93.4% yield). Mp: 72e74 ꢁC. [a]D20 þ82.9
(c 0.31, CH2Cl2). 1H NMR (300 MHz, CDCl3) d 7.89 (d,
J¼8.9 Hz, 2H), 7.66 (s, 2H), 7.34 (d, J¼8.9 Hz, 2H), 7.14
(dd, J¼8.6 Hz, 2H), 7.08 (d, J¼8.6 Hz, 2H), 4.96 (s, 2H),
2.72 (t, J¼7.7 Hz, 4H), 1.68e1.60 (m, 4H), 1.42e1.34 (m,
4H), 0.93 (t, J¼7.3 Hz, 6H). 13C NMR (75 MHz, CDCl3)
d 152.5, 139.0, 132.1, 131.2, 130.0, 129.4, 127.3, 124.6,
118.0, 111.3, 35.9, 33.9, 22.8, 14.4. nmax (KBr) 3503.4,
3421.9, 2950.1, 2921.8, 1598.1, 1507.3, 1474.1, 1363.7,
3. Conclusion
Pd-catalyzed Suzuki reaction was found to offer a simple
access to the optically active polybinaphthols ligand. The chi-
ral polymer ligand shows good solubility in some common
solvents due to the nonplanarity of the twisted polymers in
the main-chain backbone and flexible hexyloxy and n-butyl
group substitutent on naphthyl rings as side chain of the poly-
mer ligand, so that the asymmetric addition reactions can be
carried out in homogeneous solution. The results indicate
that the chiral polymer in combination with Et2Zn and
Ti(OiPr)4 can catalyze the asymmetric phenylacetylene addi-
tion to both aromatic and aliphatic aldehydes with high enan-
tioselectivity to produce the chiral propargyl alcohols. Small
molecule BINOL derivative catalyst produced the opposite
configuration of the propargylic alcohols to that of the deriva-
tive, but the chiral polymer ligand incorporating 6,60-dibutyl-
2,20-binaphthol moiety at 5,50-positions afforded the same
configuration as the catalytically active center. The chiral
polymer ligand can be easily recovered and reused without
loss of catalytic activity as well as enantioselectivity.
1214.1, 1142.6, 1124.5, 952.2, 880.6, 827.1 cmꢀ1
.

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L. Wu et al. / Tetrahedron 64 (2008) 2651e2657
4.3. Synthesis of (S)-5,50-dibromo-6,60-dibutyl-2,20-
binaphthol (S-M-1)
on the BINOL unit) (0.025 mmol, 10 mol %) was added to the
solution. The homogenous solution was stirred at room temper-
ature for 1 h, and then aldehyde (0.25 mmol) was added via
syringe. The resulting mixture was stirred at room temperature
for 24 h. The solution was quenched by adding saturated NH4Cl
(2 mL). The solution was extracted with CH2Cl2 (3ꢂ5 mL).
The combined organic layers were washed with water and
brine, and then dried over anhydrous Na2SO4. The CH2Cl2 so-
lution was concentrated in vacuo and treated with MeOH, and
then the polymer was filtrated and washed with water. The chi-
ral polymer was washed with 1 N HCl several times to recover
the chiral ligand for the next reaction of phenylacetylene to al-
dehydes. The MeOH solution was concentrated under reduced
pressure, and the crude product can be purified by flash column
chromatography on silica gel (petroleum ether/ethyl acetate)
(18:1, v/v) to afford a pure product. Enantiomeric excess values
were determined by HPLC with a Chiralcel OD-H column.
Bromine (0.14 mL, 2.8 mmol in 5 mL CH2Cl2) was slowly
added to a solution of (R)-6,60-dibutyl-2,20-binaphthol (0.52 g,
1.33 mmol) in CH2Cl2 (10 mL) at ꢀ78 ꢁC over 1 h. The solution
was stirred overnight and gradually warmed to room tempera-
ture. The reaction was quenched with saturated NaHSO3
solution (15 mL). The mixture was extracted with CH2Cl2
(2ꢂ30 mL). The combined organic layers were washed with
water and saturated brine, and then dried over anhydrous
Na2SO4. After the removal of solvent, a pure solid product
S-M-1 can directly be obtainedin theyield of 99% (0.73 g) with-
out further purification. Mp: 48e50 ꢁC. [a]D20 ꢀ13.3 (c 0.23,
1
CH2Cl2). H NMR (300 MHz, CDCl3) d 8.52 (d, J¼9.0 Hz,
2H), 7.46 (d, J¼9.6 Hz, 2H), 7.17 (d, J¼8.4 Hz, 2H), 7.01 (d,
J¼8.7 Hz, 2H), 5.04 (s, 2H), 2.93e2.92 (m, 4H), 1.67e1.62
(m, 4H), 1.49e1.42 (m, 4H), 0.99e0.94 (m, 6H). 13C NMR
(75 MHz, CDCl3) d 153.1, 139.1, 133.4, 131.5, 130.2, 128.9,
124.6, 124.0, 119.2, 111.3, 37.3, 32.7, 23.0, 14.3. nmax (KBr)
3530.2, 3027.4, 2956.5, 2928.9, 1597.9, 1567.3, 1467.1,
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Nos. 20474028, 20774042) and Jiangsu
Provincial Natural Science Foundation (No. BK2004086).
1367.7, 1248.7, 1212.0, 1154.1, 1132.9, 970.7, 819.2 cmꢀ1
.
MS (ESI) m/z¼554.4 (Mþ1). Anal. Calcd for C28H28Br2O2:
C, 60.45; H, 5.07. Found: C, 60.41; H, 5.11.
References and notes
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was dissolved in THF (10 mL) and K2CO3 (15 mL, 1 M aqueous
solution) and kept stirring at 85 ꢁC under N2. After refluxing for
48 h, the reaction mixture was cooled to room temperature, and
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vacuum at room temperature for 24 h. The final yield was
95.3% (610 mg). [a]2D0 þ20.0 (c 0.1, THF). Mw¼10,760,
Mn¼9950, PDI¼1.08. 1H NMR (300 MHz, CDCl3) d 0.82 (br,
12H), 1.18 (br, 20H), 1.50 (br, 8H), 4.09 (d, 4H), 5.06 (s, 2H),
7.32 (br, 6H), 7.43e7.77 (m, 8H), 7.88 (d, 2H), 8.03 (s, 2H).
nmax (KBr) 3532.2, 3406.5, 3059.2, 2953.1, 2925.9, 2856.4,
1909.8, 1777.1, 1657.3, 1592.9, 1463.5, 1382.7, 1338.0,
´
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