Enantioselective inductivity of optically active helical poly[3-(9-alkylfluoren-9-yl)propylene oxide]s in the addition of methyllithium to aldehydes

Article abstract of DOI:10.1016/j.polymer.2012.05.054

Optically active helical poly[(R or S)-3-(9-alkylfluoren-9-yl)propene oxide]s (poly-AFPOs) were used to induce the enantioselective addition of methyllithium to aldehydes. The addition of methyllithium to 4-methoxybenzaldehyde gave the highest enantioselectivity (88% ee) under the inducement of poly-AFPOs. Poly-AFPOs could be recovered simply by pouring the reaction mixture into methanol in the end of the reaction and separating the precipitated polymer via filtration. The recovered poly-AFPOs could be reused for many times to induce the enantioselective addition of methyllithium to aldehyde without losing their enantioselective inducement ability. The investigation of the optical rotation and the MALDI-ToF MS confirmed that, in the enantioselective addition induced by poly-AFPOs, the lithium cation was embedded in the hole of the helical column of poly-AFPOs, leaving the negative methyl ion outside the one-handed helical column. The methyl anion abutted tightly against the helical polymer and acquired a chiral environment. It was this helically chiral environment that resulted in the enantioselective inducement of the addition reaction.

Full text of DOI:10.1016/j.polymer.2012.05.054

Polymer 53 (2012) 3514e3519
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Enantioselective inductivity of optically active helical
poly[3-(9-alkylfluoren-9-yl)propylene oxide]s in the addition of methyllithium
to aldehydes
Changwei Huang, Nianfa Yang , Anlin Zhang, Liwen Yang*
*
Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Hunan 411105, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 March 2012
Received in revised form
Optically active helical poly[(R or S)-3-(9-alkylfluoren-9-yl)propene oxide]s (poly-AFPOs) were used to induce
the enantioselective addition of methyllithium to aldehydes. The addition of methyllithium to 4-
methoxybenzaldehyde gave the highest enantioselectivity (88% ee) under the inducement of poly-AFPOs.
Poly-AFPOs could be recovered simply by pouring the reaction mixture into methanol in the end of the
reaction and separating the precipitated polymer via filtration. The recovered poly-AFPOs could be reused for
many times to induce the enantioselective addition of methyllithium to aldehyde without losing their
enantioselectiveinducementability. Theinvestigationof theoptical rotationandtheMALDI-ToFMSconfirmed
that, in the enantioselective addition induced by poly-AFPOs, the lithium cation was embedded in the hole of
the helical column of poly-AFPOs, leaving the negative methyl ion outside the one-handed helical column. The
methyl anion abutted tightly against the helical polymer and acquired a chiral environment. It was this
helically chiral environment that resulted in the enantioselective inducement of the addition reaction.
Ó 2012 Elsevier Ltd. All rights reserved.
12 May 2012
Accepted 29 May 2012
Available online 6 June 2012
Keywords:
Helical polyether
Enantioselective inducement
Aldehyde
Methyllithium
1. Introduction
Recently, a new design strategy to use chiral soluble macro-
molecule as a chiral ligand of the chiral catalyst came out. In this new
The use of chiral soluble macromolecule as the chiral ligand of
catalysts has attracted much attention of chemists because the
reisolation of the expensive chiral catalyst by precipitation or
ultrafiltration is easy and all the analytical and kinetic advantages
of a reaction in homogenous phase are maintained. So far, several
types of the chiral soluble macromolecule ligands have been
reported. The common way to prepare a polymeric chiral soluble
ligand is to attach only one chiral coordinating group per polymer
strategy, chiral ligands were bonded to one-handed helical polymer.
E. Yashima et al. synthesized helical poly[N-(4-ethynylbenzyl)
ephedrine] and used this chiral ligand-bearing helical polymer to
induce the enantioselective addition of dialkylzincs to benzalde-
hyde to give products with 30e49% ee (enantiomeric excess) [10].
They also synthesized a series of optically active, dynamic helical
poly(phenylacetylene)s bearing oligopeptide pendants consisting
of a combination of L-alanine and achiral glycine residues and
[
1e5]. Carsten Bolm reported asymmetric dihydroxylation with
investigated their abilities as asymmetric polymeric organo-
catalysts for the epoxidation of chalcone derivatives with hydrogen
peroxide in alkaline water [11]. With these helical poly(-
phenylacetylene)s catalysts, epoxide products with up to 21e38%
ee were obtained.
MeO-polyethyleneglycol-bound ligands [1]. Q. Fan et al. reported
that binaphthol-cored and bis(diphenylphosphino)binapthyl-cored
dendrimers were used as chiral ligands for the preparation of
enantioselective catalyst [6,7]. An improved way is the preparation
of multiple-site polymeric chiral ligands with uniform microenvi-
ronments. The polybinaphthols and poly[bis(diphenylphosphino)
binapthyl] are successful examples of this strategy [8,9].
F. Sanda et al. synthesized an L-threonine-based helical poly(N-
propargylamide)-Ru complex. With this threonine-based helical
poly(N-propargylamide)-Ru complex as a catalyst for hydro-
gentransfer reaction of ketones, the ee values of the formed alco-
hols ranged from 12 to 36% [12].
K. Terada et al. synthesized helical polyphenylacetylenes
carrying L-valine or N-methyl-L-valine moieties at the side chains
and used these helical polymers as catalysts of the asymmetric
reduction of aromatic ketimines to afford optically active amines
*
Corresponding authors. Tel.: þ86 0731 58293833.
E-mail addresses: nfyang@xtu.edu.cn (N. Yang), yangliwen_0519@163.com,
yangnianfa888@yahoo.com.cn (L. Yang).
0
032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2012.05.054

C. Huang et al. / Polymer 53 (2012) 3514e3519
3515
(
2e28% ee) [13]. Soon later, they synthesized helical poly-
phenylacetylene and polystyrene derivatives carrying -proline
moieties at the side chains. With these -proline-carrying helical
2. Result and discussion
L
L
We used the addition of methyllithium to aldehyde as model
reaction to examine the enantioselective inductivity of poly-(R)-
EFPO. The reaction was catalyzed by titanium(IV) isopropoxide. The
results are listed in Table 1.
polymers as catalysts, the ee values of the products of the asym-
metric aldol reactions of acetone with aromatic aldehydes were
2
2
e18% and that of cyclohexanone with p-nitrobenzaldehyde were
e68% [14].
Under the inducement of poly-(R)-EFPO, all of the addition of
methyllithium to aldehydes showed enantioselectivity. The abso-
lute configuration of the products were determined by comparing
their optically active properties and the retaining times on chiral
high performance liquid chromatography (HPLC) column with that
reported by literature except the product 4,4,4-triphenyl-2-
butanol. All of the configuration of the addition products were S
except 4,4,4-triphenyl-2-butanol. We did not know the absolute
configuration of 4,4,4-triphenyl-2-butanol because it was a new
compound. All of the HPLC spectra of the isolated products took on
a single peak when C-18 HPLC column was used and they split into
two peaks when Chiralcel ODeH column was used. The ee of the
isolated products were measured by means of chiral HPLC analysis.
The ee of products depended on the group connected with the
carbonyl of the aldehyde. The enantioselectivity of the reaction of
4-methoxybenzaldehyde was highest and that of 2-
pyridylaldehyde was second high. The reason why the enantiose-
lectivity depend on the substituent group is unknown. Maybe it is
relative to the coordination of the substituent group.
Several years ago, a more novel strategy was put forward: the
helically chiral superstrucrure of one-handed helical polymer was
used as an only chiral element of the chiral catalyst.
R. Michael et al. followed the work of Okamoto et al. [15,16] and
prepared a chiral polymer by helix-sense selective anionic poly-
merization of sterically congested 1-(3-pyridyl)dibenzosuberyl
methacrylate (3PyDBSMA). They used this one-handed helical
poly-3PyDBSMA as a chiral ligand in the asymmetrically catalyzed
allylic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl
malonate and products with 29e33% ee were obtained [16]. This set
a precedent for using helical chirality of a polymer as an only chiral
element of a catalyst although the ee was low. Soon later, they
improved the enantioselectivity of the reaction by introducing two
nitrogen atoms into the aromatic ring of the lateral group borne by
the helical polymer and the ee increased to 60% [17]. Using pyridyl
N-oxide substituted helically chiral poly(methacrylate)s as the
chiral element of the catalyst to catalyze the asymmetric allylation
of benzaldehyde with allyltrichlorosilane, the products with
1
4e19% ee were obtained [18].
The substituent at 9-position of the fluorene ring of the poly-
AFPO had a slight influence on the enantioselectivity of the reac-
tion. Table 2 shows the enantioselective inductivity of poly[3-(9-
methylfluoren-9-yl)propene oxide] (poly-MFPO) and poly[3-(9-
propylfluoren-9-yl)propene oxide] (poly-PFPO) to the addition of
methyllithium to 4-methoxylbenzaldehyde.
The product’s ee of the addition of methyllithium to 4-
methoxybenzaldehyde was 69e71% under the inducement of
poly-MFPO (run 1e2 in Table 2) while that was 74% (run 3 in
Table 1) under the inducement of poly-EFPO, suggesting that the
enantioselective inductivity of poly-MFPO was slight poorer than
that of poly-EFPO. But the enantioselective inductivity of poly-PFPO
was slight better than that of poly-EFPO because the ee of the
product was 76e78% (run 3e4 in Table 2) and higher than 74%.
The absolute configuration of the addition products depended
on the polymer monomer’s configuration which determined the
helix sense (P helix or M helix) of the polymer. The configuration of
the product was S under the inducement of poly-(R)-AFPO (run 1
and run 3 in Table 2) while that was R under the inducement of
poly-(S)-AFPO (run 2 and run 4 in Table 2).
T. Yamamoto bonded a diphenyl diphenylphosphino group to
a helical polymer molecule to obtain polyquinoxaline-based heli-
cally chiral phosphine and used this polyer-based helically chiral
phosphine as a chiral ligand to form a chiral palladium complex.
Using this chiral palladium complex to catalyze the asymmetric
hydrosilylation of styrenes, 70e96% ee were achieved [19,20].
Eiji Yashima synthesized functional poly(phenyl isocyanide)s
with macromolecular helicity memory and used them as asym-
metric organocatalysts to catalyze the reaction of benzaldehyde
with diethylzinc to obtain products with 18e48% ee [21].
D. Zhang and J. Deng reported optically active helical substituted
polyacetylenes which solely catalyzed asymmetric Aldol reaction
between cyclohexanone and p-nitrobenzaldehyde, with ee up to
8
0% [22].
More recently, we synthesized poly[3-(9-alkylfluoren-9-yl)
propene oxide]s (poly-AFPOs) and proved that these poly-AFPOs
kept a stable helical conformation in solution (Scheme 1) [23].
Chart 1 shows the steric structure of poly[3-(9-ethylfluoren-
9
8
-yl)propene oxide] (poly-(R)-EFPO) simulated by “Chem3D Ultra
.0” software, in which the red one is oxygen atom.
From Fig.1, we find that there is a hole in the center of the helical
Poly-AFPO could be recovered simply by pouring the reaction
mixture into methanol in the end of the reaction and separating the
precipitated polymer via filtration. The recovered poly-AFPO could
be reused for many times to induce the asymmetric addition of
methyllithium to aldehyde without losing its enantioselective
inducement ability. Table 3 shows the enantioselective inducing
ability of the recovered poly-(R)-EFPO for the asymmetric addition
of methyllithium to 4-methoxybenzaldehyde. After poly-(R)-EFPO
was reused for eight times, the ee of the addition product did not
change obviously.
column of poly-(R)-EFPO and oxygen atoms are around the hole.
We believe that, when the solution of poly-(R)-EFPO is mixed with
organometallic compound, the oxygen-rounding hole should hold
metal cation, leaving species with negative charge near the chiral
helical column. When these negative species react with electro-
philes, the reaction must be enantioselective. If this asymmetric
inducement mechanism does work, it will be a new asymmetric
catalysis strategy. Here, we report this research work.
1
The specific rotation, the H NMR spectrum, the GPC spectrum
and the MALDI-ToF MS (Matrix-Assisted Laser Desorption/Ioniza-
tion Time of Flight Mass Spectrometry) spectrum of the recovered
poly-(R)-EFPOs were the same as that of the original one, indicating
that the polymer chemical structure and stereostructure remained
unchanged through catalysis.
We put forward the following mechanism for the enantiose-
lective inducement in the enantioselective addition: the lithium
cation is embedded in the hole of one-handed helical column of the
polymer, leaving the negative methyl ion outside the one-handed
Scheme 1. The synthesis of poly-AFPOs.

3516
C. Huang et al. / Polymer 53 (2012) 3514e3519
þ
Fig. 1. The MALDI-ToF MS spectra of poly-(R)-EFPO and its complex with Li . A: The MALDI-ToF MS spectrum of poly-(R)-EFPO; B: The MALDI-ToF MS spectrum of poly-(R)-EFPO
þ
complex with Li .
helical column; the methyl anion abuts tightly against the helical
polymer and acquires chiral environment. It is this helically chiral
environment that results in the enantioselective inducement of the
reaction. The helically chiral environment can be described by
Chart 2.
To prove this speculation, the specific rotations of poly-(R)-EFPO
in toluene in the present of methyllithium or the mixture of
methyllithium and titanium(IV) isopropoxide were examined. The
additives’ concentrations used in the investigation of optical rota-
tion behavior are the same as that used in enantioselectively
catalytic reaction. The results of optical rotation examination are
listed in Table 4.
The specific rotation absolute values of poly-(R)-EFPO in toluene
without any additive were 469e203 varying as the examining
wavelength with its rotation signs being positive (entry 1 in
Table 4) and the specific rotations remained unchanged on standing
for 15 h (entry 5 in Table 4). When methyllithium was added, the
specific rotation absolute values of poly-(R)-EFPO decreased to
187e77 and their signs changed to negative (entry 2 in Table 4),
implying that the coordination of the polymer with lithium cation
took place. The specific rotations of Li-coordinated poly-(R)-EFPO
remained unchanged on standing for 15 h (entry 6 in Table 4),
indicating that the coordination was stable. When both methyl-
lithium and titanium(IV) isopropoxide were added, the specific
rotations of poly-(R)-EFPO were almost the same as the case where
only methyllithium was added (comparing the entry 4 with the
entry 2 in Table 4) and the rotations decreased very much on
standing for 15 h. However, when only titanium(IV) isopropoxide
was added, the optical rotations remained unchanged even if on
standing for 15 h (entry 3 and entry 7 in Table 4). These indicated
titanium cation did not take part in the interaction with the poly-
mer. The fact that the rotations of the mixture of poly-(R)-EFPO,
methyllithium and titanium(IV) isopropoxide decreased on
standing for 15 h implied that titanium(IV) isopropoxide had a slow
Table 1
The enantioselective reactions of methyllithium with aldehydes under the induce-
a
ment of poly-(R)-EFPO .
Entry
R
Product
Yield (%)b
ee (%)c
Config.d
1
2
3
4
5
6
7
8
Phenyl
78
82
88
86
74
79
93
65
80
25
39
74
31
53
12
37
8
S
S
S
S
S
S
S
þ
S
4-chlorophenyl
4-methoxyphenyl
2-phenylvinyl
2-pyridyl
4-dimethylaminophenyl
2-naphthyl
2,2,2-triphenylethyl
4-methoxyphenyl
e
9
88
a
All reactions were carried out on a scale of 1.0 mmol of aldehyde with 2.0 mmol
i-
ꢁ
of CH
3
Li and 2.0 mmol of Ti(O Pr)
4
in 15 mL of toluene for 24 h at ꢀ5 C in the
w n
presence of poly-(R)-EFPO (1.0 mmol), the molecular weight and M /M of poly-(R)-
EFPO were 4300 and 1.04 respectively (determined by GPC: polystyrene as standard,
2
3
0
THF as solvent) and the specific rotation ð½
a
ꢂ
Þ of poly-(R)-EFPO was 1014
65
(
c ¼ 10.00 mg/mL in THF).
b
Isolated yields purified by chromatography on silica column.
The enantiomeric excesses were determined by HPLC analysis using a chiral
c
column (Chiralcel OD-H; eluent, hexaneeisopropyl alcohol 98:2; flow rate, 0.8 mL/
min; UV detector, 254 nm, c ¼ 5 g/L).
d
The absolute configuration was assigned by comparison of the sign of the
specific rotation with that reported by literatures or that of authentic commercial
reagent.
e
i-
3.0 mmol of CH
3 4
Li, 3.0 mmol of Ti(O Pr) and 2.0 mmol of poly-(R)-EFPO were
Chart 1. Poly-(R)-EFPO simulated by “Chem3D Ultra 8.0” software.
used.

C. Huang et al. / Polymer 53 (2012) 3514e3519
3517
Table 2
The enantioselective inductivity of poly-MFPO and poly-PFPO toward the addition of
a
methyllithium to 4-methoxybenzaldehyde .
Run Poly-AFPOb
Product
ꢃ 10ꢀ
3 c
M
/M c
a
½ ꢂ
20
d
Yield (%)e ee (%)f Config.g
M
n
w
n
3
65
1
2
3
4
Poly-(R)-MFPO 3.8
Poly-(S)-MFPO 3.8
Poly-(R)-PFPO 4.8
Poly-(S)-PFPO 4.8
1.05
1.06
1.08
1.06
þ826 76
ꢀ835 81
þ1327 83
ꢀ1346 87
69
71
78
76
S
R
S
R
a
All reactions were carried out on a scale of 1.0 mmol of 4-methoxybenzaldehyde
iꢀ
with 2 mmol of CH
3
Li and 2.0 mmol of Ti(O Pr)
4
in 15 mL of toluene for 24 h
ꢁ
at ꢀ5 C in the presence of poly-AFPO (1.0 mmol).
b
The letter in the bracket () is the configuration of the monomer of poly-AFPO.
Determined by GPC (polystyrene as standard, THF as solvent).
c ¼ 10.00 mg/mL (in THF).
Chart 2. The helically chiral environment of methyl anion.
c
d
e
f
Isolated yields purified by chromatography on silica column.
The enantiomeric excesses were determined by HPLC analysis using a chiral
þ
formation of the complex of poly-(R)-EFPO with Li (atom weight:
7).
column (Chiralcel OD-H, eluent, hexaneeisopropyl alcohol 98:2, flow rate, 0.8 mL/
min, UV detector, 254 nm, c ¼ 5 g/L).
The MALDI-ToF MS spectrum of poly-(R)-EFPO treated with only
g
The absolute configuration was assigned by comparison of the sign of the
titanium(IV) isopropoxide was the same as that of the untreated
poly-(R)-EFPO (Fig. 1A), indicating the polymer did not coordinated
with Titanium cation.
specific rotation with that reported by literatures.
When poly-(R)-EFPO was treated with the mixture of methyl-
lithium and titanium(IV) isopropoxide, its MALDI-ToF MS spectrum
was the same as that of the poly-(R)-EFPO treated only with
methyllithium (Fig. 1B). The MALDI-ToF MS spectrum of the poly-
interaction with methyllithium. The poly-(R)-EFPO recovered from
the enantioselective reaction had the same chiroptical properties,
which indicated the interaction of the polymer with lithium cation
was reversible after methanol was added.
The investigation of MALDI-ToF MS confirmed the formation of
complex of poly-(R)-EFPO with lithium cation.
(R)-EFPO separated directly from the enantioselective addition
reaction without quenching with water also was the same as that of
the poly-(R)-EFPO treated with methyllithium (Fig. 1B). After the
poly-(R)-EFPO treated by methyllithium was reprecipitated from
methanol, its MALDI-ToF MS spectrum changed back to Fig. 1A, the
MALDI-ToF MS spectrum of poly-(R)-EFPO. These indicated that
poly-(R)-EFPO formed a complex with methyllithium but not with
titanium(IV) isopropoxide and that the lithium-complex was
destroyed after the polymer was reprecipitated from methanol.
Yukio Yokoyama et al. have investigated alkali-cation affinities
of polyoxyethylene dodecylethers by electrospray mass spectrom-
etry [24]. The electrospray ionization (ESI) mass spectrum showed
mainly the peaks of the complexes of polyoxyethylene dodecy-
lether with one alkali-cation when there were 5e8 oxyethylene
units in the polyoxyethylene dodecylether. The two alkali-cation
Fig. 1A is the MALDI-ToF MS spectrum of poly-(R)-EFPO. The
molecular weight of EFPO (C18
H18O, the monomer of poly-(R)-
EFPO) is 250.1. There are peaks at 2274 m/z, 2524 m/z, 2774 m/z and
3
2
026 m/z on Fig. 1A. 2274, 2524, 2774 and 3026 can be written as
50.1 ꢃ n þ 23, where n is 9, 10, 11 and 12 respectively. The
molecular weight of poly-(R)-EFPO is 250.1 ꢃ n þ 18. Under irra-
diation of laser, the poly-(R)-EFPO reacted with Matrix, lost a water
molecule (molecule weight: 18) and combined a Na (atom weight:
þ
2
3) which came from the matrix or the glassware. Therefore, the
peaks at (250.1 ꢃ n þ 23) m/z imply the formation of complex of
þ
poly-(R)-EFPO with Na .
Fig. 1B is the MALDI-ToF MS spectrum of poly-(R)-EFPO treated
with methyllithium. On Fig. 1B, there are peaks at 2258 m/z,
2
2
508 m/z, 2759 m/z and 3009 m/z. and these value can be written as
50.1 ꢃ n þ 7 where n is 9, 10, 11 and 12 respectively, indicating the
Table 4
ꢁ
The specific rotations of poly-(R)-EFPO in toluene at 10 C in the presence of the
additives .
a
Entry
Additives
Timeb
[a
]
436
[a
]
546
[a]
578
[a]
589
Table 3
The recycling and the reuse of the poly-(R)-EFPO in enantioselective addition of
methyllithium to 4-methoxybenzaldehyde .
1
2
3
4
5
6
7
8
None
10 min
10 min
10 min
10 min
15 h
15 h
15 h
15 h
þ469
ꢀ187
þ463
ꢀ173
þ462
ꢀ183
þ463
ꢀ4.2
þ245
ꢀ95
þ213
ꢀ81
þ203
ꢀ77
a
c
CH
Ti(O Pr)
3
Li
iꢀ
d
4
þ242
ꢀ97
þ209
ꢀ83
þ199
ꢀ81
Recycling time
1
2
3
4
5
6
7
8
i-
e
e
CH
None
3
Li þ Ti(O Pr)
4
Yield (%)b
86
75
89
74
85
73
87
76
84
74
86
75
85
72
87
73
þ242
ꢀ93
þ211
ꢀ79
þ202
ꢀ74
ee (%)c
CH
Li
c
3
i-
d
Ti(O Pr)
CH
Li þ Ti(O Pr)
4
þ241
ꢀ4.1
þ208
ꢀ3.8
þ198
ꢀ3.6
a
All reactions were carried out on a scale of 1.0 mmol of 4-methoxybenzaldehyde
i-
iꢀ
3
4
with 2.0 mmol of CH
3
Li and 2.0 mmol of Ti(O Pr)
4
in 15 mL of toluene for 24 h
ꢁ
a
at ꢀ5 C in the presence of poly-(R)-EFPO (1.0 mmol).
250 mg of poly-(R)-EFPO in 25 mL of toluene (c ¼ 10.0 g/L).
b
b
c
Isolated yields purified by chromatography on silica column.
The enantiomeric excesses were determined by HPLC analysis using a chiral
Standing time after mixing.
c
0.2 mmol of CH
0.2 mmol of Ti(O Pr)
0.2 mmol of CH Li and 0.2 mmol of Ti(O Pr) .
3
Li.
d
e
iꢀ
column (Chiralcel ODeH; eluent, hexaneeisopropyl alcohol 98:2; flow rate, 0.8 mL/
min; UV detector, 254 nm, c ¼ 5 g/L).
4
.
iꢀ
3
4

3518
C. Huang et al. / Polymer 53 (2012) 3514e3519
enantioselective addition induced by poly-AFPOs, the lithium
cation was embedded in the hole of the helical column of the
polymer, leaving the negative methyl ion outside the one-handed
helical column. The methyl anion abutted tightly against the
helical polymer and acquired a chiral environment. It was this
helically chiral environment that resulted in the enantioselective
inducement of the reaction.
Chart 3. The structure of the model compound of monomeric unit of poly-(R)-EFPO
(R)-EFMEG].
[
4. Experimental
complex formed when the average numbers of oxyethylene unit
were more than 13. Polyoxyethylene dodecylether selected mainly
4
.1. Instruments and materials
þ
þ
þ
þ
K , Na and Li to coordinate, with K complex signal intensity
being highest. In the case of 6 oxyethylene units, the order of
1H NMR and 13C NMR spectra were taken on Bruck Avance 400
using CDCl
3
as a solvent and tetramethylsilane as an internal
þ
þ
þ
complex ion signal intensity was K > Na > Li . The complex
standard at 400 MHz and 100 MHz respectively. The chiral HPLC
was measured on Dionex P680 using Chiracel ODeH as chiral
column (25 cm ꢃ 0.46 cm). Optical rotations were measured on
a PerkineElmer 341 LC polarimeter. GPC was measured on Waters
signal intensity of other alkali-cation with larger diameter, such as
þ
þ
Rb , Cs , etc, was very weak. These results imply that the hole
formed by polyoxyethylene cannot hold cations with large diam-
eter. The main chains of poly-AFPOs are exactly polyoxyethylene
and have the same size hole as that of polyoxyethylene. Therefore,
the complex of titanium cation, whose diameter is much more
larger than potassium cation, could not be observed in the MALDI-
ToF MS spectrum of poly-(R)-EFPO treated with the mixture of
methyllithium and titanium(IV) isopropoxide.
1
515 GPC instrument with polystyrene as a standard and THF as
eluent.
Methyllithium (1.6
M
in diethyl ether) and titanium(IV) iso-
propoxide were from Aladdin Company. All liquid aldehydes were
freshly distilled before use. Toluene were fluxed with sodium and
benzophenone and distilled before use. Other reagents were
common commercial available reagent without special treatment.
In fact, the ee value was not higher enough in the enantiose-
lective addition of the addition of methyllithium to 4-
methoxybenzaldehyde induced by poly-(R)-EFPO and there was
(R
or S)-3-(9-alkylfluoren-9-yl)propene oxides (AFPOs) were
prepared according to literature [23].
some racemate in the product. The racemate might result from the
þ
fact that there were some CH
3
Li molecules whose Li did not enter
4
.2. The preparation of poly-(R or S)-AFPOs
the center of the helical polymer and it was these uncoordinated
CH
3
Li molecules that resulted in the formation of some racemate. In
A flask with a stir bar was charged with 50.0 mmol of AFPO
þ
order to make the Li coordination as complete as possible, we
increased the quantity of poly-(R)-EFPO in the addition of meth-
yllithium to 4-methoxybenzaldehyde. As expected, the ee was
increased from 74% to 88% (run 9 in Table 2), indicating some
monomer and a desired amount (4.0 mmol for example) of KOH
under argon atmosphere. The flask was deoxygenated for three
times by bubbling oxygen-free argon and then was put into an oil
ꢁ
bath thermostated at 130 C. The reaction mixture was stirred for
3
racemate resulted from the uncoordinated CH Li indeed.
2
4 h. During this time, the mixture turned to auburn and got more
In order to further prove that the enantioselectivity resulted
form the chirality of the helical conformation of the polymer rather
than the chirality of the asymmetric carbon, (R)-9-ethylfluoren-9-
ylmehtylethylene glycol diethyl ether [(R)-EFMEG, Chart 3], the
model compound of monomeric unit of poly-(R)-EFPO, was
synthesized.
and more viscous. The reaction mixture was cooled to room
temperature. THF (30 mL) was added to give a homogenous solu-
tion. The THF solution was poured into methanol (180 mL). The
formed precipitation was filtered and washed with methanol. The
above-mentioned process, solving and precipitating, was repeated.
ꢁ
The precipitation was dried at 50 C to obtain poly-AFPOs, yield
(R)-EFMEG was used to replace the poly-(R)-EFPO to induce the
7
2e86%.
Poly-(R)-EFPO H NMR
br, 7H, >CHOe, eCH e, eCH
4300;
addition of the addition of methyllithium to 4-
1
d
/ppm: 7.76e6.52 [br, 8H, Ar], 2.15e1.46
Oe, eCH CH ], 0.20e0.19 [br, 3H,
/M 1.04;
methoxybenzaldehyde. The experiment result showed that, in the
presence of the same quantity of (R)-EFMEG, the addition reaction
gave product with 0.5% ee. This ee value was so small that it could
be ignored, indicating that the enantioselectivity of the addition
reaction results form the chirality of the helical conformation of the
polymer rather than the chirality of the asymmetric carbon.
[
2
2
2
3
20
eCH
2
CH
3
];
M
n
¼
M
w
n
¼
½
a
ꢂ
¼ þ1014
3
65
(c ¼ 10.00 mg/mL in THF).
1
Poly-MFPO H NMR d/ppm: 7.76e6.59 [br, 8H, Ar], 2.12e1.98
[
br, 1H, >CHOe], 1.90e1.74 [br, 2H, eCH e], 1.44e1.40[br, 2H,
3800;
þ826, S-isomer:
2
eCH
M
2
Oe], 1.33e1.22 [br, 3H, eCH
3
];
M
n
¼
w
M /
2
3
0
n
¼
1.05e1.06; R-isomer:
½
a
ꢂ
65
¼
2
0
3
. Conclusion
½
a
ꢂ
¼ ꢀ835 (c ¼ 10.00 mg/mL in THF).
3
65
1
Poly-PFPO H NMR
7H, >CHOe, eCH e, eCH
4800;
d
/ppm: 7.75e6.48 [br, 8H, Ar], 2.12e1.31 [br,
Oe, eCH CH CH ], 0.73e0.49 [br, 5H,
/M 1.06e1.08; R-isomer:
¼ ꢀ1346 (c ¼ 10.00 mg/mL in TFH).
Poly-AFPOs give enantioselective inducement toward the addi-
2
2
2
2
¼
3
tion of methyllithium to aldehyde. The ee of the enantioselectively
induced addition product depends on the group connected with
the carbonyl of the aldehyde. Among the investigated substrates,
the reaction of 4-methoxybenzaldehyde gave the highest enan-
tioselectivity up to 78% ee. Poly-AFPOs can be recovered simply by
pouring the reaction mixture into methanol in the end of the
reaction and separating the precipitated polymer via filtration. The
recovered poly-AFPOs can be reused to induce the enantioselective
addition of methyllithium to aldehyde for many times without
losing their enantioselective inducement ability. The investigation
of the optical rotation and the MALDI-ToF MS confirmed that, in the
eCH
2
CH
2
CH
3
];
M
n
¼
M
w
n
2
3
0
20
365
½
a
ꢂ
¼ þ1327, S-isomer: ½ ꢂ
a
65
4.3. The preparation of (R)-9-ethylfluoren-9-ylmehtylethylene
glycol diethyl ether [(R)-EFMEG]
(R)-3-(9-ethylfluoren-9-yl)propylene oxide (10.0 g, 0.040 mol)
was added to a solution of CH
CH CH
3
CH
2
OK (33.6 g, 0.400 mol) in
ꢁ
3
2
OH (120 mL). The mixture was stirred at 50 C overnight.
Water (60 mL) was added at the end of the reaction and the mixture
was concentrated under reduced pressure. The concentrated

C. Huang et al. / Polymer 53 (2012) 3514e3519
3519
residue was extracted with diethyl ether (3 ꢃ 30 mL). The extract
was washed with water, dried over anhydrous MgSO and
concentrated under reduced pressure to obtain (R)-1-ethyoxyl-3-
filtrated. The filtrate was concentrated under reduced pressure and
the residue was chromatographed on silica gel to obtain the addi-
tion product. The ee of the product was measured with chiral HPLC.
The filtrated cake was recovered for recycling.
4
(
9
9-ethylfluoren-9-yl)propan-2-ol [(R)-EEFPL] as colorless oil in
2
3
4
24
8.5% yield. (R)-EEFPL: ½
a
ꢂ
¼ ꢀ79, ½
a
ꢂ
589 ¼ ꢀ23 (c ¼ 10.00 mg/
65
589
1
mL in THF). H NMR
J ¼ 6.5 Hz, 1H, Ar), 7.34e7.32 (m, 5H, Ar), 3.22e3.09 (q, 3H,
CHOHe, eOCH CH OCH CH ),
), 2.83 (d, J ¼ 5.3 Hz, 2H, eCH
.33e2.19 (q, 2H, eCH e), 2.09e2.01 (m, 2H, eCH CH ), 1.57 (s, 1H,
OH), 1.03 (t, J ¼ 6.9 Hz, 3H, eOCH CH ), 0.28 (t, J ¼ 7.3 Hz, 3H,
149.46, 149.19, 141.20, 141.06, 127.31, 127.30,
27.19, 127.02, 123.56, 123.12, 120.03, 119.92, 74.63, 67.78, 66.26,
3.91, 43.27, 33.84, 14.95, 8.00. Calcd for C20 : C, 81.03; H, 8.18;
O, 10.80. Found: C, 80.99; H, 8.23; O, 10.85.
d/ppm: 7.73e7.70 (m, 2H, Ar), 7.47e7.45 (d,
4.5. The method of recycling of the poly-AFPOs
>
2
3
2
2
3
The recovered poly-AFPO (40 g) was dissolved in 100 mL of THF
2
2
2
3
to give a turbidity solution. After filtration, the THF solution was
poured into 600 mL of methanol. The formed precipitation was
filtered and washed with methanol. The obtained filtrated cake was
2
3
13
2 3
eCH CH ). C NMR d
1
5
ꢁ
dried at 50 C to obtain recovered poly-AFPO, yield 96e98%. The
24 2
H O
recovered poly-AFPO was used for the next enantioselectively
induced addition experiment.
1
To a vigorously stirred suspension of NaH (2.56 g, 0.107 mol) in
DMF (60 mL) was added dropwise a solution of (R)-EEFPL (24.0 g,
The recovered Poly-(R)-EFPO H NMR
d
/ppm: 7.76e6.51 [br, 8H,
e, eCH Oe, eCH CH ],
¼ 4300; M /M ¼ 1.05;
¼ þ1008 (c ¼ 10.00 mg/mL in THF).
Ar], 2.15e1.46 [br, 7H, >CHOe, eCH
2
2
2
3
0
.081 mol) in DMF (80 mL). After the addition was complete, bro-
0
.20e0.19 [br, 3H, eCH
2
CH
3
]; M
n
w
n
2
3
0
moethane (12.7 g, 0.117 mol) was added and the mixture was
a
½ ꢂ
65
ꢁ
heated at 80 C and the reaction was monitored by TLC. After 5 h,
addition NaH (1.28 g, 0.054 mol) and bromoethane (6.35 g,
Acknowledgments
0
8
.059 mol) were added and the resulting mixture was heated at
0 C for furtheranother 1.5 h. The cooled mixture was poured into
ꢁ
We thank National Science Foundation of China (20972131,
1
50 mL of dilute hydrochloric acid and extracted with diethyl ether
3 ꢃ 80 mL). The combined ether extracts were washed succes-
sively with 2 Na SO , 2 Na CO , and with water and dried over
anhydrous MgSO . After the solvent was evaporated, the residue
21172186) for financial support of this work.
(
M
2
3
M
2
3
Appendix A. Supplementary material
4
was purified by chromatography on a silica-gel column with 6%
ethyl acetate in hexanes as eluent to give 21.0 g of (R)-EFMEG as
Supplementary data related to this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.polymer.2012.05.054.
2
3
6
26
a pale yellow oil (80%). (R)-EFMEG: ½
a
ꢂ
¼ ꢀ35.5, ½
a
ꢂ
¼ ꢀ4.5
65
589
1
(
c ¼ 10.00 mg/mL in THF). H NMR
.44e7.42. (d, J ¼ 7.6 Hz, 1H), 7.31e7.30 (m, 5H, Ar), 3.21e2.88 (q,
H, eCH OCH CH , >CHOCH CH ), 2.51e2.45 (q, 2H, eCH e), 2.31
m, 2H, eCH OCH CH ), 2.01 (q, 2H, eCH CH
), 1.05 (t, J ¼ 6.9 Hz,
H,eCH OCH CH CH ), 0.29 (t,
), 0.66 (t, J ¼ 7.0 Hz, 3H, >CHOCH
149.78, 149.54, 141.54, 140.96,
27.07, 126.73, 126.70, 126.73, 124.01, 123.33, 119.63, 119.49, 75.47,
d/ppm: 7.71e7.69 (m, 2H, Ar),
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[
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[
4
ꢁ
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Ti(O Pr)
4
was added dropwise and the mixture was stirred
ꢁ
ꢁ
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trated under reduced pressure to obtain an off-white residue. The
residue was added into 25 mL of methanol. The mixture was irra-
diated with ultrasound (53 W, 40 kHz) for 30 min and, then,