Synthesis of several polyethers derived from BINOL and their application in the asymmetric borane reduction of prochiral ketones

Article abstract of DOI:10.1016/j.tetasy.2014.12.012

Several novel epoxy monomers, (S,S)- or (S,R)-3-(glycidyloxy)methyl-2,2′-bis(methoxymethyloxy)-1,1′-binaphthalene and (S,S)- or (S,R)-6-(glycidyloxy)methyl-2,2′-bis(methoxymethyloxy)-1,1′-binaphthalene, which were derived from chiral BINOL and epichlorohydrin, were synthesized and underwent anionic polymerization and deprotection of the MOM groups to obtain soluble polyethers. These polyethers were used to induce the enantioselective borane reduction of prochiral ketones. The substrates gave up to 98% yield with over 99% ee values. The recovered polyethers could be reused many times to induce the enantioselective reduction of prochiral ketones without losing their enantioselective induction ability.

Full text of DOI:10.1016/j.tetasy.2014.12.012

Tetrahedron: Asymmetry 26 (2015) 173–179
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Synthesis of several polyethers derived from BINOL and their
application in the asymmetric borane reduction of prochiral ketones
⇑
⇑
An-Lin Zhang, Zeng-da Yu, Li-Wen Yang , Nian-Fa Yang
Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Hunan 411105, PR China
a r t i c l e i n f o
a b s t r a c t
Several novel epoxy monomers, (S,S)- or (S,R)-3-(glycidyloxy)methyl-2,20-bis(methoxymethyloxy)-1,
10-binaphthalene and (S,S)- or (S,R)-6-(glycidyloxy)methyl-2,20-bis(methoxymethyloxy)-1,10-binaphtha-
lene, which were derived from chiral BINOL and epichlorohydrin, were synthesized and underwent anio-
nic polymerization and deprotection of the MOM groups to obtain soluble polyethers. These polyethers
were used to induce the enantioselective borane reduction of prochiral ketones. The substrates gave up to
98% yield with over 99% ee values. The recovered polyethers could be reused many times to induce the
enantioselective reduction of prochiral ketones without losing their enantioselective induction ability.
Ó 2015 Elsevier Ltd. All rights reserved.
Article history:
Received 2 November 2014
Accepted 19 December 2014
1. Introduction
employed in asymmetric hydrogenations,18–20 epoxidations,21–24
Diels–Alder reactions,25–27 and asymmetric alkylations.28–31
Polymeric chiral catalysts have attracted considerable attention
since they offer alternative methods to separate and reuse expen-
sive and often toxic chemicals.1–4 Due to the solubility difference
between macromolecules and small molecules, polymeric reagents
or catalysts can be easily separated from the reaction mixture by
simple filtration or by precipitation with the addition of a nonsol-
vent.5 The recovery of chiral catalysts is particularly important
since it is often quite expensive to obtain these enantiomerically
pure materials. Using polymeric catalysts also makes it possible
to carry out reactions in flow reactors or in flow membrane
reactors for large-scale production.6 Customarily, polymeric chiral
catalysts are prepared by anchoring a chiral metal or nonmetal
complex to a flexible and sterically irregular achiral polymer back-
bone.7–12 It is generally observed that polymeric chiral catalysts
are usually less efficient than their monomeric version. This
indicates that the microenvironment of the catalytic sites in the
polymers is very important for their effectiveness in steric control.
The flexible and sterically irregular polymer backbone of the tradi-
tional polymeric chiral catalysts generates randomly oriented cat-
alytic sites which cannot be systematically modified to achieve the
desired catalytic activity and stereoselectivity.
Among the growing list of ligands being subjected to such a study,
chiral BINOL derivatives have occupied a prominent position due
to their ability to form highly enantioselective catalysts with main
group elements,32,33 transition metals,34,35 and rare earth
elements.36,37 A broad range of metallic complexes containing
BINOL that are multifunctional in nature have also been reported.38
The immobilization of BINOL derivatives has earlier been achieved
by grafting onto a sterically irregular polymer backbone39–42 or by
cross-linking copolymerization.43 A variety of soluble BINOL-
derived polymer ligands have been used for asymmetric catalytic
reactions.44–46 However, only a few polymeric chiral ligands have
been used for inducing enantioselective borane reduction of
ketones.47 We envisaged that the use of soluble polymer supports
might allow the ligands to suitably orient themselves during com-
plexation leading to better catalysts.48,49 To the best of our knowl-
edge, chiral polyethers such as poly-(S)-4,4-diphenyl-1-butene
oxide50 and poly-(S)-3-(9-alkylfluoren-9-yl)propene oxides51,52
have been proved to dissolve well and take a stable conformation
in solution. Herein, we have designed and synthesized several sol-
uble polyethers derived from BINOL in order to achieve better cat-
alytic activity and stereoselectivity in borane reduction of ketones.
Optically active binaphthyl compounds have been extensively
applied in asymmetric catalysis13–15 and in molecular recogni-
tion.16,17 It is worth mentioning that all types of BINOL-derived
chiral ligands have been immobilized in the past and successfully
2. Results and discussion
The BINOL derivative (S)-3-formyl-2,20-bis(methoxymethyl-
oxy)-1,10-binaphthalene (S)-1 was readily prepared following the
literature procedure from commercially available (S)-BINOL.53 The
reduction of (S)-1 with NaBH4 gave 3-hydroxymethyl-2,
20-bis(methoxymethyl)-1,10-binaphthol (S)-2 (Scheme 1). The
⇑
Corresponding authors.
E-mail addresses: yangliwen_0519@163.com (L.-W. Yang), nfyang@mail.sdu.
edu.cn (N.-F. Yang).
http://dx.doi.org/10.1016/j.tetasy.2014.12.012
0957-4166/Ó 2015 Elsevier Ltd. All rights reserved.

174
A.-L. Zhang et al. / Tetrahedron: Asymmetry 26 (2015) 173–179
CHO
OH
OMOM
OMOM
OMOM
OMOM
a
92%
2
(S)-
(S)-1
O
HO
H
n
O
O
O
OMOM
OMOM
c
OH
OH
b
84%
86%
3
(S,S)-
poly-4
O
HO
H
n
O
O
O
OMOM
OMOM
e
OH
OH
d
85%
80%
5
(S,R)-
poly-6
Scheme 1. The synthetic route for poly-4 and poly-6. (a) NaBH4, THF, rt, 30 min, 92%; (b) (S)-epichlorohydrin, KOH, TBAB, THF, rt, 12 h, 86%; (c) KOH, 120 °C, 6 h; then HCl,
THF, rt, 24 h, 84%; (d) (R)-epichlorohydrin, .KOH, TBAB, THF, rt, 20 h, 80%; (e) KOH, 120 °C, 12 h; then HCl, THF, rt, 24 h, 85%.
coupling of (S)-epichlorohydrin or (R)-epichlorohydrin with (S)-2
was successfully carried out using KOH as the deprotonation reagent
to afford the monomer (S,S)-3 or (S,R)-5 with good yield (80–86%) in
the presence of tetrabutylammonium bromide (TBAB) (Scheme 1).
In most cases, the polymerization of (S,S)-3 and (S,R)-5 was carried
out in bulk using KOH as an initiator, followed by deprotection of
the MOM group to afford poly-4 (Mn = 6000, PDI = 2.12) and poly-
6 (Mn = 5600, PDI = 2.24) in high yields (Scheme 1). The low molec-
ular weight BINOL derivatives poly-40 (Mn = 3200; PDI = 2.16) and
poly-400 (Mn = 1100; PDI = 2.42) were also prepared from (S,S)-3
using different doses of KOH as the initiator. We were also interested
in similar systems wherein the dendritic segments were attached to
the BINOL core at the 6 positions, which are sufficiently far apart
from the catalytic active center so that primary steric effect is an
unimportant factor. Accordingly poly-10 (Mn = 5200, PDI = 2.02)
and poly-12 (Mn = 5600, PDI = 2.41) were synthesized as outlined
in Scheme 2. Herein, (S)-6-formyl-2,20-bis(methoxymethyloxy)-
1,10-binaphthalene (S)-7 was first synthesized from (S)-1,1-bi-2-
naphthol.54 The key BINOL derivative, (S)-6-hydroxymethyl-2,
20-bis(methoxymethyl)-1,10-binaphthol (S)-8 was then synthesized
by reducing (S)-7 with NaBH4 (Scheme 2). Compound (S)-8 was sub-
sequently coupled to chiral (S)- or (R)-epichlorohydrin by
OHC
HO
OMOM
a
OMOM
OMOM
OMOM
85%
8
(S)-
(S)-7
O
OH
H
n
O
O
O
OH
OH
OMOM
OMOM
c
b
85%
82%
10
poly-
(S,S)-9
O
OH
H
n
O
O
O
OH
OH
OMOM
OMOM
e
80%
d
82%
poly-12
(S,R)-11
Scheme 2. The synthetic route for poly-10 and poly-12. (a) NaBH4, THF, 0 °C, 60 min, 85%; (b) (S)-epichlorohydrin, KOH, TBAB, THF, rt, 12 h, 82%; (c) KOH, xylene 120 °C, 12 h;
then HCl, THF, rt, 24 h, 85%; (d) (R)-epichlorohydrin, KOH, TBAB, THF, rt, 20 h, 80%; (e) KOH, xylene, 120 °C, 20 h; then HCl, THF, rt, 24 h, 82%.

A.-L. Zhang et al. / Tetrahedron: Asymmetry 26 (2015) 173–179
175
Table 1
Table 2
Optimization and catalyst screening for the borane reduction of 4-methylacetophe-
Asymmetric reduction of prochiral ketonea
nonea
O
ligand, BH3.THF
toluene, 30oC
HO
R1
H
O
OH
R1
R2
R2
BH3.THF/ ligand
solvent
∗
Entry
Ketone
Yieldb (%)
Eec (%)
Config.d
H3C
H3C
1
2
3
4
5
6
7
8
40-Chloroacetophenone
2-Bromoacetophenone
40-Bromoacetophenone
40-Fluoroacetophenone
40-Nitroacetophenone
40-Chloropropiophenone
40-Methylacetophenone
40-Methoxyacetophenone
30-Methoxyacetophenone
10-Acetylnaphthalene
Propiophenone
98
94
98
95
98
90
96
93
95
96
90
92
95
90
>99
>99
>99
>99
>99
>99
>99
>99
>99
90
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
(S)
Entry
Ligand (mol %)
Solvent
Temp (°C) Yieldb (%)
Eec,d,e (%)
1
2
3
4
5
6
7
8
Poly-4 (5)
Poly-4 (5)
Poly-4 (5)
Poly-4 (5)
Poly-4 (1)
Poly-4 (10)
Poly-4 (5)
Poly-40 (5)
Poly-400 (5)
Poly-6 (5)
Poly-10 (5)
Poly-12 (5)
Toluene
THF
DCM
0
0
0
90
92
94
96
90
90
96
92
90
90
93
90
90
80
82
93
76
85
>99
92
80
96
76
65
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
50
50
50
30
30
30
30
30
30
9
10
11
12
13
14
92
90
65
60
9
Acetophenone
Pinacolone
2-Butanone
10
11
12
a
n(Ketone)/n(BH3ꢀTHF)/(poly-4) = 1:1.1:0.05.
a
b
Reaction was carried out on a 1.0 mmol scale in 5 mL of solvent, molar of
Isolated yields after purification by column chromatography (silica gel, 10%
p-CH3PhCOCH3, BH3ꢀTHF = 1.0:1.1, reaction time: 6 h.
ethyl acetate in petroleum ether).
b
c
Isolated yields after purification by column chromatography (silica gel, 10%
Determined by HPLC analysis using chiral column.
Absolute configurations were assigned by comparison with the sign of specific
d
ethyl acetate in petroleum ether).
c
rotations reported in the literature.55–58
Determined by HPLC analysis using chiral column.
Absolute configurations were assigned by comparison with the sign of the
d
specific rotations reported in the literature.
e
(S)-Product was isolated by column chromatography.
none substrate had no obvious effect on the enantioselectivity
(entries 1–9). For example, ketones with the electron-withdrawing
group were reduced to their corresponding alcohols with over 99%
ee (entries 1–6), while, functionalized acetophenone with electron-
donating substitute also gave over 99% ee (entries 7–9). Acetophe-
none and propiophenone without a substituent on the benzene
ring, as well as 10-acetylnaphthalene, furnished the corresponding
alcohols with slightly lower ee values (entries 10–12). Poly-4 has
also been used to reduce some aliphatic ketones, including pinaco-
lone and 2-butanone with moderate ee (entries 13 and 14).
Compared with most of small molecule catalysts, the poor sol-
ubility of the polyether derived from binaphthyl in several organic
solvents such as methanol, ethanol, and petroleum ether enabled
its easy recovery by a simple precipitation method, allowing it to
be recycled. We decided to test the recyclability of our reagents.
In order to determine the recycling ability of the catalyst, poly-4
was recovered after the catalytic process by precipitation from
the reaction mixture with the addition of methanol, and after
simple filtration through a silica pad, reused in the reduction of
4-methylacetophenone by borane under the optimized reaction
conditions (Table 3). We were pleased to observe that the recov-
ered catalyst retained its high activity and enantioselectivity (over
99% ee) and can be reused six times without a loss of reactivity or
enantioselectivity.
etherification to afford the monomers (S,S)-9 and (S,R)-11, respec-
tively (Scheme 2). In order to obtain higher molecular weight, the
solution polymerization of (S,S)-9 and (S,R)-11 was conducted in
xylene. The MOM protecting groups were finally removed by acid
treatment to afford polymers poly-10 and poly-12. Both polymers
were soluble in solvents such as toluene and THF and readily precip-
itated upon the addition of methanol or petroleum ether.
With these chiral polyethers in hand, their efficiency and
activity were examined in detail with 4-methylacetophenone as
a substrate (Table 1). Initially the reaction was conducted in the
presence of 5 mol % poly-4 in toluene at 0 °C and afforded the
(S)-product with 90% ee (entry 1). When other solvents such as
THF and dichloromethane were used, the ee decreased (entries 2
and 3). Increasing the reaction temperature to 50 °C, resulted in a
better yield and ee value (entry 4). Varying the catalyst loading
had a negative effect on the ee values (entries 5 and 6). We were
encouraged to observe that over 99% ee was obtained in the pres-
ence of 5 mol % poly-4 at 30 °C (entry 7). Poly-40 and poly-400 with
relatively low molecular weight were also used as chiral ligands for
the asymmetric borane reduction of 4-methylacetophenone
(Table 1, entries 8 and 9) in order to investigate the effect of differ-
ent molecular weights on the enantioselectivity of polymer
ligands. Under the same conditions, poly-40 showed slightly lower
enantioselectivity than that of poly-4, while poly-400 shows signif-
icantly decreased enantioselectivity with the same substrate. The
enantioselectivity decreased slightly when changing catalyst from
poly-4 to poly-6 (entry 10), which may be due to the existence of
the (R)-isomer polyether backbone reducing the steric differentia-
tion between the Si- and Re-face of the transition states. As
expected, the chiral polyether catalyst based on 6-substitued
BINOL poly-10 and poly-12, gave modest enantioselectivity
(Table 1, entries 11 and 12). It can be inferred that the presence
of substituents on the 6-position of BINOL would disorder the
desired transition states.
Table 3
Recycling experiments of poly-4 in the reduction of 4-methylacetophenone
O
OH
BH3.THF/ poly-4
toluene, 30oC
H3C
H3C
Cycle
1
2
3
4
5
6
Recoverya (%)
Yieldb (%)
Eec (%)
90
95
>99
92
93
>99
92
90
>99
89
96
>99
86
92
>99
90
96
>99
With the optimized conditions in hand, we next investigated
the scope of the reduction with respect to the ketones. As summa-
rized in Table 2, a variety of ketones were smoothly reduced to
alcohols with excellent yields and enantioselectivities. Impor-
tantly, the presence of substituents on the phenyl ring of acetophe-
a
Reaction was carried out on
a 1.0 mmol scale in 5 mL toluene, molar of
p-CH3PhCOCH3, BH3ꢀTHF = 1.0:1.1.
b
c
Isolated yields by column chromatography.
Determined by HPLC analysis using a Daicel Chiralcel column.

176
A.-L. Zhang et al. / Tetrahedron: Asymmetry 26 (2015) 173–179
washed with a solution of 1:1 brine and water and the combined
3. Conclusion
organic layers were concentrated. Further purification was accom-
plished using silica column chromatography with 20% ethyl ace-
tate in petroleum ether to give the corresponding epoxide. Yield,
In conclusion, several novel, recoverable, chiral polyethers
derived from binaphthyl have been synthesized, which were used
as efficient catalysts in the enantioselective borane reduction of
prochiral ketones with excellent enantioselectivities (over 99%
ee). The reduction permits extensive recycling of the polyether cat-
alyst without loss of activity over six cycles.
20
86%, [
a
]
365 = ꢁ502.8 (c 0.1, THF), Elem. Anal. Calcd for C28H28O6:
C, 73.03; H, 6.13; Found: C, 73.09; H 6.18. 1H NMR (CDCl3) d 8.06
(s, 1H, Ar-H), 7.97–7.95 (d, J = 8.8 Hz, 1H, Ar-H), 7.91–7.85 (m,
2H, Ar-H), 7.59–7.56 (d, J = 9.0 Hz, 1H, Ar-H), 7.39–7.35 (m, 2H,
Ar-H), 7.26–7.15 (m, 4H, Ar-H), 5.12–5.10 (d, J = 6.4 Hz, 1H,
OCH2), 5.02–5.01 (d, J = 6.8 Hz, 1H, OCH2), 4.94–4.92 (d,
J = 7.6 Hz, 2H, OCH2), 4.65–4.63 (d, J = 5.2 Hz, 1H, OCH2), 4.56–
4.55 (d, J = 5.2 Hz, 1H, OCH2), 3.93–3.92 (d, J = 2.8 Hz, 1H, CH),
3.66–3.64 (m, 1H, CH2), 3.29 (s, 1H, CH2), 3.16 (s, 3H, OCH3), 2.89
(s, 3H, OCH3), 2.86–2.84 (m, 1H, CH2), 2.70 (s, 1H, CH2). 13C NMR
4. Experimental
4.1. General
All reagents were used as supplied commercially unless
otherwise noted. THF and toluene were distilled from sodium
under N2 before use. (S)-3-Formyl-2,20-bis(methoxymethoxy)-1,
10-binaphthyl (S)-1 and (S)-6-formyl-2,20-bis(methoxymethoxy)-
1,10-binaphthyl (S)-7 were prepared according to the litera-
ture.50–54 Optically active epichlorohydrin was purchased from
Yueyang Branch Company, Shenzhen Yawangkangli Technology
Co., Ltd. 1H NMR and 13C NMR spectra were performed on a Bruker
ARX 400 MHz spectrometer using tetramethylsilane (TMS) as the
internal standard. Optical rotation data were measured on a Perkin
Elmer Model 341 LC Polarimeter at 365 nm. GPC analysis was per-
formed with a JASCO-GPC system consisting of DG-1580-53 degas-
ser, PU-980 HPLC pump, UV-970 UV/Vis detector, RI-930 RI
detector, and CO-2065-plus column oven (at 38 °C) using two con-
nected Shodex GPC-KF-804L columns in THF (sample concentra-
tion = 1 wt %; flow rate = 1.0 mL/min). The molecular weight was
calibrated with a commercially available polystyrene.
(101 MHz, CDCl3)
d 153.01, 151.89, 134.11, 133.65, 131.57,
130.94, 129.81, 128.50, 127.94, 126.70, 126.10, 125.92, 125.58,
125.58, 124.99, 124.17, 120.88, 116.66, 99.32, 95.08, 72.14, 69.33,
56.60, 55.92, 50.85, 44.41.
In a similar manner, compound (S,R)-5 was prepared from (S)-
3-hydroxymethyl-2,20-bis(methoxymethyloxy)-1,10-binaphthalene
20
(S)-2 and (R)-epichlorohydrin. Yield, 80%, [
a]
365 = ꢁ471.0 (c 0.1,
THF), Elem. Anal. Calcd for C28H28O6: C, 73.03; H, 6.13; Found:
C, 73.09; H, 6.16. 1H NMR (CDCl3) d 8.06 (s, 1H, Ar-H), 7.97–
7.94 (d, J = 9.2 Hz, 1H, Ar-H), 7.91–7.85 (m, 2H, Ar-H), 7.58–7.56
(d, J = 9.0 Hz, 1H, Ar-H), 7.37–7.35 (m, 2H, Ar-H), 7.26–7.15 (m,
4H, Ar-H), 5.11–5.10 (d, J = 6.4 Hz, 1H, OCH2), 5.02–5.01 (d,
J = 6.8 Hz, 1H, OCH2), 4.94–4.92 (d, J = 7.6 Hz, 2H, OCH2), 4.65–
4.63 (d, J = 5.2 Hz, 1H, OCH2), 4.56–4.55 (d, J = 5.2 Hz, 1H, OCH2),
3.96–3.92 (dd, J = 2.4, 5.8 Hz, 1H, CH), 3.66–3.61 (m, 1H, CH2),
3.29 (s, 1H, CH2), 3.16 (s, 3H, OCH3), 2.90 (s, 3H, OCH3), 2.87–
2.84 (m, 1H, CH2), 2.70 (s, 1H, CH2). 13C NMR (101 MHz, CDCl3)
d 153.01, 151.90, 134.11, 133.66, 131.57, 130.94, 129.85, 128.52,
128.00, 127.89, 126.70, 126.10, 125.75, 125.62, 124.99, 124.17,
120.88, 116.66, 99.32, 95.08, 71.83, 69.34, 56.62, 55.92, 50.85,
44.40.
4.2. (S)-3-Hydroxymethyl-2,20-bis(methoxymethyloxy)-1,10-
binaphthalene (S)-2
At first, NaBH4 (1.52 g, 40 mmol) was added to a solution of (S)-
3-formyl-2,20-bis(methoxymethyloxy)-1,10-binaphthalene
(S)-1
4.4. Preparation of poly-4 and poly-6
(14.77 g, 36.7 mmol) in THF (40 mL) at 0 °C. After stirring for
30 min at room temperature, water was added to the reaction mix-
ture. After being stirred for 30 min, the solvent was removed under
reduced pressure at room temperature. To the mixture were added
saturated NH4CI and AcOEt, and the AcOEt extracts were washed
with brine and dried over Na2SO4. The solvent was removed under
reduced pressure at room temperature. Purification by flash chro-
matography (SiO2, ethyl acetate/petroleum ether = 1:3) gave (S)-3-
hydroxymethyl-2,20-bis(methoxymethyloxy)-1,10-binaphthalene
A test tube with a stirrer bar was charged with 10.00 mmol of
epoxide monomer (S,S)-3 or (S,R)-5 and
a desired amount
(0.4 mmol for example) of KOH under an argon atmosphere, and
then sealed with the flame of a Bunsen burner. The test tube was
put into an oil bath thermostated at the desired temperature (such
as 120 °C). The reaction mixture was then stirred for 6 h. During
this time, the mixture turned auburn and became more and more
viscous until the magnetic bar could no longer move. The reaction
mixture was then cooled to room temperature and the tube was
opened. Next, THF (10 mL) was added to give a homogenous solu-
tion, after which 2 ml of hydrochloric acid was added dropwise to
the tube at 0 °C. After being stirred for 24 h at room temperature,
the THF solution was poured into methanol (100 mL). The formed
precipitate was filtered and washed with methanol. The above-
mentioned process, that is, the solving and precipitating, was
repeated, then the obtained precipitation was dried in vacuo at
50 °C to obtain polymer poly-4 (or poly-6), yield 84–85%. 1H
NMR d/ppm: 7.92–6.76 [br, 15H, Ar-H], 4.37–4.09 [br, 3H,
in 92% yield as a colorless viscous oil. [
a]
20 = ꢁ65.8 (c 0.05, THF);
D
Elem. Anal. Calcd for C25H24O5: C, 74.24; H, 5.98. Found: C,
74.28; H, 6.00. 1H NMR (CDCl3) d 3.15 (s, 3H), 3.25 (s, 3H), 3.44
(dd, J = 7.0, 7.0 Hz, 1H), 4.46 (d, J = 6.0 Hz, 1H), 4.68 (d, J = 6.2 Hz,
1H), 4.90 (dd, J = 7.0, 12.5 Hz, 1H), 4.92 (dd, J = 6.8, 12.4 Hz, 1H),
5.03 (d, J = 7.2 Hz, 1H), 5.12 (d, J = 7.2 Hz, 1H), 7.11–7.45 (m, 6H),
7.60 (d, J = 9.1 Hz, 1H), 7.86–7.90 (m, 2H), 7.96 (s, 1H), 7.97 (d,
J = 9.1 Hz, 1H); 13C NMR (CDC13) d 55.90, 56.98, 61.99, 94.80,
99.25, 116.42, 120.40, 124.19, 125.13, 125.27, 125.44, 125.60,
126.18, 126.79, 127.90, 127.95, 129.01, 129.64, 129.97, 131.01,
133.66, 133.74, 134.28, 152.69, 153.05.
–CH2O–], 3.54–3.15 [br, 7H, ˜CHO–, –CH2–, –CH2O–]. Poly-4, yield
20
4.3. (S,S)-3-(Glycidyloxy)methyl-2,20-bis(methoxymethyloxy)-
1,10-binaphthalene (S,S)-3
84%, [
a
]
365 = ꢁ844.8 (c 0.05, THF); Mn = 6.0 ꢂ 103; PDI = Mw/
20
Mn = 2.12. Poly-6, yield 85%,
[
a]
365 = ꢁ712.2 (c 0.05, THF);
Mn = 5.6 ꢂ 103; PDI = Mw/Mn = 2.24. poly-40 and poly-400 were pre-
pared according to the procedure mentioned above using 1 mmol
To a solution of (S)-2 (4.6 g, 10 mmol) in dry THF (30 ml), pow-
dered potassium hydroxide (400 mol %) and tetrabutylammonium
bromide (10 mol %) were added and stirred for 2 h at room temper-
ature. Next (S)-epichlorohydrin (200 mol %) was added and stirred
for 20 h. The mixture was then extracted with ethyl acetate and
and 3 mmol KOH as initiator, respectively. Poly-40, yield, 68%,
365 = ꢁ832.6 (c 0.05, THF), Mn = 3.2 ꢂ 103; PDI = Mw/
20
[a]
20
Mn = 2.16. poly-400, yield, 76%, [
a
]
365 = ꢁ828.25 (c 0.05, THF),
Mn = 1.1 ꢂ 103; PDI = Mw/Mn = 2.42.

A.-L. Zhang et al. / Tetrahedron: Asymmetry 26 (2015) 173–179
177
4.5. (S)-6-Hydroxymethyl-2,20-bis(methoxymethyloxy)-1,10-
binaphthalene (S)-8
into an oil bath thermostated at the desired temperature (120 °C).
The reaction mixture was stirred for 20 h. During this time, the
mixture turned auburn and became more and more viscous. The
reaction mixture was then cooled to room temperature and the
tube was opened. Next, THF (10 mL) was added to give a homoge-
nous solution. Next, 2 ml of hydrochloric acid was added dropwise
to the tube at 0 °C. After being stirred for 24 h at room tempera-
ture, the THF solution was poured into methanol (100 mL). The
formed precipitate was filtered and washed with methanol. The
above-mentioned process, that is, the solving and precipitating,
was repeated, then the obtained precipitation was dried in vacuo
at 50 °C to obtain poly-10 and poly-12, respectively. Yield 82–
85%. 1H NMR d/ppm: 7.92–6.76 [br, 10H, Ar-H], 4.57–4.19 [br,
To an ice cooled solution of (S)-3-formyl-2,20-bis(methoxym-
ethyloxy)-1,10-binaphthalene (S)-7 (9.25 g, 23 mmol) in THF
(100 mL) was added NaBH4 (1.73 g, 46 mmol) and the solution
was stirred at this temperature for 60 min. The mixture was then
poured into ice-cold water (100 mL) and the product extracted
with ethyl acetate. After drying over anhydrous Na2SO4, the solu-
tion was concentrated to afford (S)-8 as a colorless foamy solid
(85% yield). A portion of the solid was purified by flash column
chromatography for analysis. [
a]
20 = ꢁ58.2 (c 0.05, THF); Elem.
D
Anal. Calcd for C25H24O5: C, 74.24; H, 5.98. Found: C, 74.26; H,
6.01. 1H NMR (CDCl3) 3.05 (s, 3H), 3.06 (s, 3H), 4.71 (s, 2H), 4.88
(d, J = 6.7 Hz, 2H), 4.96 (d, J = 3.4 Hz, 1H), 4.99 (d, J = 3.4 Hz, 1H),
7.02–7.17 (m, 4H), 7.23 (t, J = 6.8 Hz, 1H), 7.46 (d, J = 9.0 Hz, 2H),
7.76 (s, 1H), 7.78 (d, J = 8.0 Hz, 1H), 7.82 (d, J = 5.6 Hz, 1H), 7.87
(d, J = 5.6 Hz, 1H); 13C NMR (CDCl3) 55.81, 65.42, 95.10, 95.21,
117.29, 117.38, 121.10, 121.22, 123.90, 125.30, 125.58, 125.57,
125.91, 126.20, 127.71, 129.27, 129.28, 129.69, 129.68, 133.39,
133.81, 136.29, 152.50, 152.61.
2H, –CH2O–], 3.57–2.92 [br, 5H, ˜CHO–, –CH2–, –CH2O–]. Poly-
20
10, yield 85%,
[
a]
365 = ꢁ342.4 (c 0.05, THF); Mn = 5.2 ꢂ 103;
20
PDI = Mw/Mn = 2.02. Poly-12, yield 82%, [
a]
365 = ꢁ296.2 (c 0.05,
THF); Mn = 5.6 ꢂ 103; PDI = Mw/Mn = 2.41.
4.8. General procedure for the catalytic reduction of prochiral
ketones
To
a 25 ml round-bottom flask was added 0.05 mmol
4.6. (S,S)-6-(Glycidyloxy)methyl-2,20-bis(methoxymethyloxy)-
1,10-binaphthalene (S,S)-9
(0.05 equiv) of chiral ligand in 5 ml of THF. Under a nitrogen atmo-
sphere and at 0 °C, BH3ꢀTHF (5 M) (1.1 mmol, 1.1 equiv) was added.
The mixture was stirred at 0 °C for 0.5 h and then warmed to 30 °C
for a further hour. The ketone (1 mmol) in 2 ml of THF was added
slowly over a period of 0.5 h under the same temperature and stir-
red for 6 h. The reaction mixture was cooled to 0 °C and quenched
with a 1 M aqueous HCl solution (8 ml), then extracted with ethyl
acetate (3 ml ꢂ 10 ml). The combined organic layer was washed
twice with brine and dried with anhydrous MgSO4. The solvent
was removed under reduced pressure. The residue was passed
through a short silica gel column to afford a pure product before
being subjected to HPLC analysis.
To a solution of (S)-2 (4.6 g, 10 mmol) in dry THF (30 ml), pow-
dered potassium hydroxide (400 mol %) and tetrabutylammonium
bromide (10 mol %) were added and stirred for 2 h at room temper-
ature. Next (S)-epichlorohydrin (200 mol %) was added and stirred
for 12 h after which the mixture was extracted with ethyl acetate
and washed with a solution of 1:1 brine and water and the com-
bined organic layers were concentrated. Further purification was
accomplished using silica column chromatography with 20% ethyl
acetate in petroleum ether to give the corresponding epoxide.
20
Yield: 82%; [
C
a]
365 = ꢁ154.5 (c 0.1, THF); Elem. Anal. Calcd for
28H28O6: C, 73.03; H, 6.13; Found: C, 73.08; H 6.16. 1H NMR
4.8.1. 1-Phenylethanol
(CDCl3) d 7.96–7.92 (m, 2H, Ar-H), 7.88–7.83 (t, J = 3.0 Hz, 2H, Ar-
H), 7.58–7.56 (d, J = 9.0 Hz, 2H, Ar-H), 7.35–7.33 (t, J = 8.0 Hz, 1H,
Ar-H), 7.22–7.12 (m, 4H, Ar-H), 5.08–5.05 (m, 2H, CH2O), 4.98–
4.96 (m, 2H, CH2O), 4.70–4.67 (dd, J = 2.4, 6.0 Hz, 2H, OCH2),
3.77–3.76 (dd, J = 2.8, 5.4 Hz, 1H, CH), 3.49–3.47 (m, 1H, CH2),
3.18 (s, 1H, CH2), 3.15 (s, 3H, CH3), 3.14 (s, 3H, CH3), 2.79–2.78 (t,
J = 3.2 Hz, 1H, CH2), 2.61 (s, 1H, CH2). 13C NMR (101 MHz, CDCl3)
d 152.92, 152.72, 129.38, 126.69, 126.26, 125.99, 125.56, 124.07,
117.65, 117.45, 95.38, 73.44, 70.89, 55.80, 50.84, 44.30.
The enantiomeric excess was determined by HPLC (chiralcel
OD-H column, hexane/2-propanol = 98:2, 0.8 ml/min, k = 254 nm,
retention time: t(S) = 10.64 min, t(R) = 12.04 min). 1H NMR
(400 MHz, CDCl3) d: 7.37–7.26 (m, 5H, Ar-H), 4.90 (q, J = 5.8 Hz,
1H, CH), 1.45 (d, J = 5.8 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3)
d: 144.7, 128.3, 127.4, 125.3, 70.4, 25.2.
4.8.2. 1-(2-Bromophenyl)ethanol
In a similar manner, compound (S,R)-11 was prepared from (S)-
The enantiomeric excess was determined by HPLC (chiralcel
OD-H column, hexane/2-propanol = 92:8, 0.8 ml/min, k = 254 nm,
retention time: t(S) = 16.3 min). 1H NMR (400 MHz) d: 7.25–7.40
(m, 5H, Ar-H), 4.94–4.92 (d, J = 8.0 Hz, 1H, CH), 3.66–3.63 (d,
J = 10.0 Hz, 1H, CH2), 3.57–3.52 (m, 1H, CH2); 13C NMR (100 MHz,
CDCl3) d: 140.3, 128.6, 128.3, 125.9, 73.7, 39.9.
6-hydroxymethyl-2,20-bis(methoxymethyloxy)-1,10-binaphthalene
20
(S)-7 and (R)-epichlorohydrin. Yield: 80%; [
a
]
365 = ꢁ102.4 (c 0.1,
THF); Elem. Anal. Calcd for C28H28O6: C, 73.03; H, 6.13; Found: C,
73.06; H, 6.18. 1H NMR (CDCl3) d 7.96–7.92 (m, 2H, Ar-H), 7.88–
7.83 (t, J = 3.2 Hz, 2H, Ar-H), 7.59–7.57 (d, J = 9.0 Hz, 2H, Ar-H),
7.35–7.33 (t, J = 8.0 Hz, 1H, Ar-H), 7.22–7.12 (m, 4H, Ar-H), 5.08–
5.06 (m, 2H, CH2O), 4.98–4.96 (m, 2H, CH2O), 4.71–4.68 (dd,
J = 2.4, 6.0 Hz, 2H, OCH2), 3.79–3.77 (dd, J = 2.8, 5.4 Hz, 1H, CH),
3.50–3.48 (m, 1H, CH2), 3.17 (s, 1H, CH2), 3.16 (s, 3H, CH3), 3.15
(s, 3H, CH3), 2.79–2.78 (t, J = 3.2 Hz, 1H, CH2), 2.62 (s, 1H, CH2).
13C NMR (101 MHz, CDCl3) d 152.85, 152.75, 134.07, 133.67,
129.97, 129.76, 129.38, 127.86, 126.68, 126.27, 125.99, 125.57,
124.07, 117.55, 95.41, 73.44, 70.88, 55.81, 50.83, 44.30.
4.8.3. 1-(4-Methoxyphenyl)ethanol
The enantiomeric excess was determined by HPLC (chiralcel
OD-H column), hexane/2-propanol = 98:2, 0.8 ml/min, k = 254 nm,
retention time: t(S) = 21.54 min. 1H NMR (400 MHz) d: 7.36–7.30
(m, 2H, Ar-H), 6.89–6.87 (m, 2H, Ar-H), 4.88–4.84 (m, J = 6.6 Hz,
1H, CH), 3.80 (s, 3H, OCH3), 1.47 (d, J = 6.6 Hz, 3H, CH3); 13C NMR
(100 MHz, CDCl3) d: 158.9, 138.0, 126.7, 113.8, 69.9, 55.3, 25.0.
4.7. Preparation of poly-10 and poly-12
4.8.4. 1-(4-Bromophenyl)ethanol
The enantiomeric excess was determined by HPLC (chiralcel
OD-H column), n-hexane/isopropanol = 98:2, 0.8 ml/min, retention
time: t(S) = 9.61 min. 1H NMR (400 MHz) d: 7.47–7.43 (m, 2H,
Ar-H), 7.26–7.21 (m, 2H, Ar-H), 4.83 (q, J = 6.3 Hz, 1H, CH), 1.44
A test tube with a stirrer bar was charged with 10.00 mmol of
(S,S)-9 or (S,R)-11, a desired amount (0.34 mmol for example) of
KOH and 1.5 mL xylene under an argon atmosphere and then
sealed with the flame of a Bunsen burner. The test tube was placed

178
A.-L. Zhang et al. / Tetrahedron: Asymmetry 26 (2015) 173–179
(d, J = 6.6 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3) d: 144.7, 131.3,
127.0, 121.0, 69.4, 25.0.
(m, 4H, Ar-H), 4.89–4.86 (q, J = 6.8 Hz, 1H, CH), 1.45 (d, J = 6.4 Hz,
3H, CH3); 13C NMR (100 MHz, CDCl3) d: 144.4, 133.2, 128.8,
126.0, 69.9, 25.4.
4.8.5. 1-(4-Fluorophenyl)ethanol
4.8.13. Pinacolyl alcohol
The enantiomeric excess was determined by HPLC (chiralcel
OD-H column), hexane/2-propanol = 98:2, 0.8 ml/min, k = 254 nm,
retention time: t(S) = 11.18 min. 1H NMR (400 MHz) d: 7.36–7.32
(m, 2H, Ar-H), 7.06–7.00 (m, 2H, Ar-H), 4.92–4.87 (q, J = 6.6 Hz,
1H, CH), 1.48 (d, J = 6.6 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3)
d: 162.0, 141.5, 127.0, 126.9, 114.9, 69.3, 24.9.
Colorless oil;
[a]
25 = +3.52 (c 0.01, CHCl3) 65% ee; {lit.58
D
[
a
]
25 = ꢁ5.2 (c 0.29, CCl4), (R)-configuration, 96% ee}. 1H NMR
D
(400 MHz, CDCl3) d: 3.47 (q, J = 7.0 Hz, 1H, CHOH), 1.56 (br s, 1H,
OH), 1.12 (d, J = 6.5 Hz, 3H, CHCH3), 0.89 (s, 9H, C(CH3)3). 13C
NMR (100 MHz, CDCl3) d: 75.9, 35.1, 25.7, 18.2.
4.8.14. 2-Butanol
4.8.6. 1-(4-Nitrophenyl)ethanol
Colorless oil; [
a
]
D
25 = +8.1 (neat) 60% ee; {lit.59
[
a]
25 = ꢁ13.2
D
The enantiomeric excess was determined by HPLC (chiralcel
OD-H column), hexane/2-propanol = 98:2, 0.8 ml/min, k = 254 nm,
retention time: t(S) = 8.53 min. 1H NMR (400 MHz, CDCl3)
d: 8.22–8.20 (d, J = 9.2 Hz, 2H, Ar-H), 7.56–7.53 (d, J = 8.4 Hz, 2H,
Ar-H), 5.01 (q, J = 6.8, 1H, CH), 1.51 (d, J = 6.4 Hz, 3H, CH3); 13C
NMR (100 MHz, CDCl3) d: 153.1, 147.0, 126.0, 123.6, 69.3, 25.3.
(neat), (R)-configuration, 98% ee}. 1H NMR (400 MHz, CDCl3) d:
3.75–3.71 (m, 1H, CHOH), 1.55–1.38 (m, 2H, CH2), 1.2–1.08 (m,
3H, CH3), 0.92–0.88 (m, 3H, CH3). 13C NMR (100 MHz, CDCl3) d:
69.5, 32.1, 22.8, 10.0.
Acknowledgments
4.8.7. 1-(4-Chlorophenyl)propan-1-ol
We gratefully thank the National Science Foundation of China
(21172186) and the Higher Education Doctoral Science Foundation
of China (No. 20134301110004) for financial support of this work.
The enantiomeric excess was determined by HPLC (chiralcel
OD-H column), hexane/2-propanol = 98:2, 0.7 ml/min, k = 254 nm,
retention time: t(S) = 13.34 min. 1H NMR (400 MHz, CDCl3)
d: 7.33–7.28 (m, 4H, Ar-H), 4.62–4.57 (m, 1H, CH), 1.82–1.71 (m,
2H, CH), 0.93–0.90 (t, J = 7.4 Hz, 3H, CH3). 13C NMR (100 MHz,
CDCl3) d: 143.0, 133.0, 128.4, 127.4, 75.2, 31.9, 10.0.
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