Microstructure analysis of a CO2 copolymer from styrene oxide at the diad level

Article abstract of DOI:10.1002/asia.201300115

A large amount of interesting information on the alternating copolymerization of CO₂ with terminal epoxides has already been reported, such as the regiochemistry of epoxide ring-opening and the stereochemistry of the carbonate unit sequence in the polymer chain. Moreover, the microstructures of CO₂ copolymers from propylene oxide and cyclohexene oxide have also been well-studied. However, the microstructure of the CO₂ copolymer from styrene oxide (SO), an epoxide that contains an electron-withdrawing group, has not yet been investigated. Herein, we focus on the spectroscopic assignment of the CO₂ copolymer from styrene oxide at the diad level by using three kinds of model dimer compounds, that is, T-T, H-T, and H-H. By comparing the signals in the carbonyl region, we concluded that the signals at δ=154.3, 153.8, and 153.3 ppm in the ¹³C NMR spectrum of poly(styrene carbonate) were due to tail-to-tail, head-to-tail, and head-to-head carbonate linkages, respectively. Moreover, various isotactic and syndiotactic model compounds based on T-T, H-T, and H-H (dimers (R,R)-T-T, (S,S)-T-T, and (R,S)-T-T; (R,R)-H-T, (S,S)-H-T, and (R,S)-H-T; (R,R)-H-H, (S,S)-H-H, and (R,S)-H-H) were synthesized for the further spectroscopic assignment of stereospecific poly(styrene carbonate)s. We found that the carbonate carbon signals were sensitive towards the stereocenters on adjacent styrene oxide ring-opening units. These discoveries were found to be well-matched to the microstructures of the stereoregular poly(styrene carbonate)s that were prepared by using a multichiral Co^III-based catalyst system. T-T races: The spectroscopic assignment of regio- and stereoregular poly(styrene carbonate)s at the diad level was performed by ¹³C NMR studies of three kinds of model compounds, as well as their syndiotactic (R,S) and isotactic (R,R or S,S) dimers. Copyright

Full text of DOI:10.1002/asia.201300115

FULL PAPER
DOI: 10.1002/asia.201300115
Microstructure Analysis of a CO2 Copolymer from Styrene Oxide at the Diad
Level
Guang-Peng Wu,[a] Yu-Ping Zu,[a, b] Peng-Xiang Xu,[a] Wei-Min Ren,[a] and
Xiao-Bing Lu*[a]
Abstract: A large amount of interest-
ing information on the alternating co-
polymerization of CO2 with terminal
epoxides has already been reported,
such as the regiochemistry of epoxide
ring-opening and the stereochemistry
of the carbonate unit sequence in the
polymer chain. Moreover, the micro-
structures of CO2 copolymers from
propylene oxide and cyclohexene oxide
have also been well-studied. However,
the microstructure of the CO2 copoly-
mer from styrene oxide (SO), an epox-
ide that contains an electron-withdraw-
ing group, has not yet been investigat-
ed. Herein, we focus on the spectro-
scopic assignment of the CO2 copoly-
mer from styrene oxide at the diad
level by using three kinds of model
dimer compounds, that is, T-T, H-T,
and H-H. By comparing the signals in
the carbonyl region, we concluded that
the signals at d=154.3, 153.8, and
153.3 ppm in the 13C NMR spectrum of
poly(styrene carbonate) were due to
tail-to-tail, head-to-tail, and head-to-
head carbonate linkages, respectively.
Moreover, various isotactic and syndio-
tactic model compounds based on T-T,
H-T, and H-H (dimers (R,R)-T-T,
(S,S)-T-T, and (R,S)-T-T; (R,R)-H-T,
(S,S)-H-T, and (R,S)-H-T; (R,R)-H-H,
(S,S)-H-H, and (R,S)-H-H) were syn-
thesized for the further spectroscopic
assignment of stereospecific poly(styr-
ene carbonate)s. We found that the car-
bonate carbon signals were sensitive
towards the stereocenters on adjacent
styrene oxide ring-opening units. These
discoveries were found to be well-
matched to the microstructures of the
stereoregular poly(styrene carbonate)s
that were prepared by using a multichi-
ral CoIII-based catalyst system.
Keywords: copolymerization
·
NMR spectroscopy · poylmers · ste-
reochemistry · styrene oxide
Introduction
bonate unit sequence in the resulting polymer chain.[6] In
2004, Chisholm and co-workers synthesized a series of oli-
goether carbonates, R(PO)nOCO2(PO)nR (R=Me, Et, or
H; PO=propylene oxide ring-opened unit; and n=1, 2, 3,
4, 10), as potential models for the microstructural assign-
ment of poly(propylene carbonate) chains by NMR spec-
troscopy (Scheme 1).[7] In a recent study, Rieger and co-
workers studied the microstructure and enantioselective
ring-opening mechanism of poly(propylene carbonate) by
using chiral GC and high-resolution NMR spectrometry.[8]
13C{1H} NMR investigations revealed that the carbon signals
in the carbonate unit had both regio- and stereosensitivity
towards its adjacent epoxide ring-opened units. These stud-
ies greatly contributed to the understanding of various
regio- and stereospecific poly(propylene carbonate)s, as well
as boosting the development of stereospecific catalyst sys-
tems for the copolymerization of CO2 with aliphatic termi-
nal epoxides.[9] More recently, we synthesized poly(propy-
lene carbonate) with >99% head-to-tail content by using
multichiral cobalt complexes.[10] We found that the highly
isotactic poly(propylene carbonate) had a Tg of 478C, which
was 10–128C higher than that of its corresponding irregular
polycarbonate. New stereogradient poly(propylene carbo-
nate)s, which possessed high thermal-decomposition temper-
atures, were synthesized by Nozaki and co-workers.[11] In the
copolymerization of CO2 with meso-epoxides, two structure
patterns (isotactic and syndiotactic microstructures) can be
The control of polymer microstructure is one of the most-
important goals in the area of stereoselective polymerization
catalysis,[1] because the physical properties of a polymer are
mainly determined by the relative stereochemistry of adja-
cent locations in the polymeric chain (that is, the spatial ar-
rangement of atoms or groups in a polymeric unit). Impor-
tantly, the regio- and/or stereochemistry of a polymer pre-
serves the traces of the reaction pathway, which is beneficial
for understanding the polymerization mechanism.[2] There-
fore, the assignment of the stereo- and/or regiochemistry in-
formation of a polymer is one of the most-important tasks
in the field of stereospecific polymerization catalysis.[3,4]
In the alternating copolymerization of CO2 with terminal
epoxides,[5] there are also considerations of regiochemistry
of the epoxide ring-opening and stereochemistry of the car-
[a] G.-P. Wu,+ Y.-P. Zu,+ P.-X. Xu, W.-M. Ren, Prof. Dr. X.-B. Lu
State Key Laboratory of Fine Chemicals
Dalian University of Technology
Dalian 116024 (China)
Fax : (+86)411-84986256
E-mail: lxb-1999@163.com
[b] Y.-P. Zu+
China Haohua (Dalian) Research and Design Institute of Chemical
Industry Co., Ltd
Dalian 116023 (China)
[+] These authors contributed equally to this work.
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Xiao-Bing Lu et al.
oxides or cyclohexene oxide
and its derivatives. The synthe-
sis of copolymers from CO2 and
epoxides that contain electron-
withdrawing substituents, such
as styrene oxide (SO), have
only rarely been reported.[16]
Recently, we reported the com-
pletely alternating copolymeri-
zation of styrene oxide and CO2
Scheme 1. Copolymerization of CO2 with propylene oxide and the synthesis of model compounds for studying
the microstructure of poly(propylene carbonate) by Chisholm and co-workers.[7]
by using cobaltACHTUNGTNER(NUNG III) catalyst sys-
tems, in which the resultant
formed.[12] In 2001, Nozaki and co-workers completed the
spectroscopic assignment of poly(cyclohexene carbonate) on
the basis of the spectroscopic analysis of various isotactic
and syndiotactic model dimers and tetramers (Scheme 2).[13]
The determination of various isotactic-enriched or syndio-
polycarbonate exhibited excellent thermal stability (ther-
molysis temperature >3008C) and had a relatively high
glass-transition temperature of 808C.[17] In addition, the
electron-withdrawing group on the benzene ring of styrene
oxide causes significant differences in catalyst activity, poly-
mer selectivity, and stereochemistry control,[18] in compari-
son with propylene oxide, during the copolymerization with
CO2. Unfortunately, the microstructure of the resultant
poly(styrene carbonate) remains unclear. The purpose of
this study is to synthesize some model compounds of various
poly(styrene carbonate)s and further identify their micro-
structures.
Results and Discussion
In the CO2 copolymers from styrene oxide, there are three
possible linkages for neighboring carbonate units, which are
dependent on the regioselectivity of the epoxide ring-open-
ing. The head-to-tail carbonate linkage is produced by suc-
ꢀ
Scheme 2. Copolymerization of CO2 with cyclohexene oxide and the syn-
thesis of a model compound for studying the microstructure of poly(cy-
clohexene carbonate) by Nozaki and co-workers.[13]
cessive epoxide ring-opening at either the methylene Cb
O
ꢀ
or methine Ca O bonds, whilst the formation of head-to-
tactic-enriched poly(cyclohexene carbonate)s in subsequent
experiments was realized on the basis of previous spectro-
scopic assignments.[14] More recent, highly stereoregular pol-
y(cyclohexene carbonate)s with a high melting point (Tm) of
about 215–2308C were synthesized and their unique crystal-
lization behavior was revealed.[12b,15]
head or tail-to-tail linkages involves alternating ring-opening
ꢀ
at the methylene Cb O bond of one epoxide and the me-
ꢀ
thine Ca O bond of the following epoxide (Scheme 3). To
assign the carbonate signals of the poly(styrene carbonate)
microstructure, we first synthesized three model compounds
(T-T, H-T, and H-H) to simulate three carbonate linkages in
this CO2 copolymer, including tail-to-tail, head-to-tail, and
head-to-head linkages (Scheme 4). Notably, the successful
synthesis of a model compound with head-to-tail linkages
should show an ultraviolet absorption of the aromatic struc-
ture, which would make the purification of resulting inter-
mediate and the final product by column chromatography
very convenient. As shown in Scheme 4, the treatment of 2-
methoxy-2-phenylethanol ((rac)-1) with 1,1’-(carbonyl diimi-
dazole) (Im2CO) in a 1:1 molar ratio produced imidazole-1-
carboxylic ester ((rac)-2). After purification, this product
was allowed to react with one equivalent of (rac)-1 in the
presence of NaH, thus affording the T-T dimer in about
95% total yield. In a similar manner, the H-H dimer was
easily synthesized from 2-methoxy-1-phenylethanol ((rac)-3)
in 92% total yield. Slightly different from the T-T and H-H
dimers, dimer H-T was synthesized by an alternative treat-
Nevertheless, these investigations on CO2 copolymers
have been associated with the use of aliphatic terminal ep-
Abstract in Chinese:
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sensitive to the configuration of
the stereocenters on the poly-
mer chain. As is evident from
an inspection of the dimer
model H-T and T-T oligomers
in the 13C NMR spectrum (Fig-
ure 1D), the carbonate carbon
resonance splits into two peaks.
To identify the influence of ad-
jacent stereocenters on the car-
bonyl group, we synthesized
a series of syndiotactic and iso-
tactic dimers based on T-T, H-
T, and H-H model compounds
((R,R)-T-T,
(S,S)-T-T,
and
Scheme 3. Regiochemistry in poly(styrene carbonate)s that are derived from the alternating copolymerization
of CO2 and styrene oxide.
(R,S)-T-T; (R,R)-H-T, (S,S)-H-
T, and (R,S)-H-T; (R,R)-H-H,
(S,S)-H-H, and (R,S)-H-H) and
measured their 13C NMR spec-
tra in the carbonate carbon
region.
To synthesize syndiotactic
and isotactic dimers, four kinds
of monoprotected 1-phenyl-
ethane-1,2-diols with different
chirality that is, (R)-1, (S)-1,
(R)-3, and (S)-3, are required
(Scheme 5 and Scheme 6). In
the presence of an acid-binding
agent, the treatment of 1-phe-
nylethane-1,2-diol with one
equivalent of methyl iodide
Scheme 4. Synthetic strategies for model dimer oligomers T-T, H-T, and H-H to simulate poly(styrene carbo-
nate)s.
ment of 2-methoxy-2-phenylethanol and 2-methoxy-1-phe-
nylethanol.
As shown in Figure 1A–C, the carbonyl resonance in the
13C NMR spectra of the three model compounds T-T, H-T,
and H-H appears at d=154.9, 154.4, and 153.9 ppm, respec-
tively. Figure 1D shows the carbonyl region in the 13C NMR
Scheme 5. Unsuccessful route towards chiral compounds 1 and 3 by using
spectrum of an equimolar mixture of the three model com-
pounds. By comparing Figure 1D and E, the three groups of
signals at d=154.3, 153.8, and 153.3 ppm, which are ob-
served in atactic poly(styrene carbonate) (Mn =12000, Mw/
Mn =1.09), could be attributed to tail-to-tail, head-to-tail,
and head-to-head linkages, respectively. In addition, it
should be noted that the small chemical-shift differences
(d=0.6 ppm) between the model dimer compound (d=
154.9, 154.4, and 153.9 ppm) and the SO/CO2 copolymer
(d=154.3, 153.8, and 153.3 ppm) are probably due to the
terminal methyl groups, which do not exist in the main
chain of the copolymer. Further examining the three car-
bonate linkages of the SO/CO2 copolymer (Figure 1E)
shows that there are more than two resonances in each
group of tail-to-tail, head-to-tail, and head-to-head regions,
thus indicating that the carbonate carbon atom should be
methyl iodide.
predominantly produces the corresponding dihydroxymethyl
product (Scheme 5), because the mono-hydroxymethyl inter-
mediates are much more reactive than the parent diol. The
increased reactivity is probably due to the strong intramo-
lecular hydrogen bonding of the diol group. For synthesizing
a monoprotected primary alcohol derivative, such as (R)-
1 and (R)-2, we adopted an indirect approach,[19] as shown
in Scheme 6. Our synthetic route began with the hydrolytic
kinetic resolution of (rac)-SO by using Jacobsen’s catalyst,
followed by selective protection of the primary hydroxy
group as its tert-butyldimethylsilyl (TBDMS) ether ((R)-6
and (S)-6). Then, further reaction with an equimolar
amount of iodomethane in the presence of NaH gave com-
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Xiao-Bing Lu et al.
proach for the synthesis of monoprotected alcohol deriva-
tives (R)-3 and (S)-3, as shown in Scheme 6. The reaction of
one equivalent of methoxymethyl chloride with compounds
(R)-6 or (S)-6 in the presence of diisopropylethylamine
(DIPEA) gave intermediates (R)-8 and (S)-8, which were
treated with TBAF for desilication to give compounds (R)-9
and (S)-9, respectively. The methylation of intermediates
(R)-9 and (S)-9 and subsequent deprotection by using dilute
hydrochloric acid afforded compounds (R)-3 and (S)-3 in
moderate overall yields, respectively.
By using the same method for the synthesis of model
dimer compounds T-T, H-T, and H-H (Scheme 4), three
kinds of syndiotactic and isotactic dimers in each class were
also prepared with (R)-1, (S)-1, (R)-3, and (S)-3 as starting
materials (Scheme 7). Three isomers of model compounds
T-T and H-T are assigned in Figure 2. For the three isomers
of model T-T with different stereosequences, the carbonate
carbon signal of isotactic dimers (R,R)-T-T and (S,S)-T-T
both appeared at d=154.93 ppm in the 13C NMR spectrum;
the carbonate carbon signal of syndiotactic dimer (R,S)-T-T
(d=154.91 ppm) appeared at a slightly higher field than the
isotactic dimers (d=154.93 ppm). Similarly, the small differ-
ence between the isotactic and syndiotactic isomers of
model H-T can also be unequivocally identified in Fig-
ure 2b. Isotactic dimers (R,R)-H-T and (S,S)-H-T showed
a signal at d=154.38 ppm, which was at higher field than
syndiotactic dimer (R,S)-H-T (d=154.41 ppm). Three kinds
of isomers with different stereosequences of model H-H
((R,R)-H-H, (S,S)-H-H, and
Figure 1. Carbonyl region in the 13C NMR spectra of A) T-T; B) H-T;
C) H-H; D) an equimolar mixture of T-T, H-T, and H-H; and E) atactic
poly(styrene carbonate).
(R,S)-H-H) were also well-pre-
pared. Disappointingly, the
13C NMR signal of the carbon-
ate carbon atom did not show
resolution between its isotactic
and syndiotactic dimers, which
were
all
found
at
d=
153.88 ppm. It is probable that
the distance between the chiral
centers and the carbonate
carbon atom is too close to be
resolved by 13C NMR spectros-
copy. These results clearly indi-
cate that the stereosequence of
the model dimer has a signifi-
cant impact on the 13C NMR
signal of the carbonate carbon
atom. Accordingly, we can con-
clude that the multi-response
signals at d=154.3, 153.8,
153.3 ppm in the SO/CO2 copo-
Scheme 6. Successful route towards chiral compounds 1 and 3. Reaction conditions: a) TBDMSCl, Et3N,
DMAP, CH2Cl2; b) MeI, NaH, THF; c) TBAF, CH3CN; d) DIPEA, MOMCl, CH2Cl2; e) TBAF, CH3CN;
f) MeI, NaH, THF; g) HCl, THF.
pounds (R)-7 and (S)-7, respectively. Finally, the selective
deprotection of the primary alcohol group with tetrabuty-
lammonium fluoride (TBAF) in MeCN yielded the corre-
sponding chiral methoxyalcohols ((R)-1 and (S)-1) in excel-
lent yields.
lymer are attributed to the stereosequences that are associ-
ated with the adjacent styrene oxide ring-opening units.
In a recent publication, we reported a new catalyst system
III
ꢀ
based on unsymmetrical (S,S,S)-salen Co complexes that
contained a derived chiral-BINOL unit (BINOL=1,1’-bi-2-
naphthol) for the asymmetric copolymerization of CO2 and
racemic propylene oxide under mild conditions.[20] Both the
Based on these above-mentioned synthetic steps for com-
pounds (R)-1 and (S)-1, next, we devised an indirect ap-
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Xiao-Bing Lu et al.
Conclusions
Three kinds of model com-
pounds, that is, T-T, H-T, and
H-H, were synthesized for the
microstructural assignment of
poly(styrene carbonate) by
NMR spectroscopy. Further-
more, one syndiotactic R,S
dimer and two isotactic dimers
(R,R and S,S) in each model
linkage unit were also prepared
to study the stereosensitivity at
the diad level. 13C NMR investi-
gations of these compounds re-
vealed that the carbonate
carbon signals showed both
regio- and stereosensitivity at
the diad level towards the adja-
cent epoxide ring-opened unit
and we concluded that the sig-
nals of poly(styrene carbonate)
Scheme 7. Corresponding isotactic and syndiotactic dimers of compounds T-T, H-T, and H-H.
at
d=154.3,
153.8,
and
153.3 ppm were attributed to
tail-to-tail, head-to-tail, and
head-to-head carbonate linkag-
es, respectively. The syndiotac-
tic and isotatic diads matched
well with the microstructures of
the stereoregular poly(styrene
carbonate)s in our previous
studies.[18]
Figure 2. Assignment of the carbonate signals in the 13C NMR spectra of isotactic and syndiotactic model com-
pounds a) T-T and b) H’-T at the diad level.
chiral diaminocyclohexane backbone and the S-configured
2’-isopropyloxy-1,1’-binaphthyl ligand cooperatively provide
a chiral environment around the central metal ion for this
III
ꢀ
reaction. When the unsymmetrical (S,S,S)-salen Co com-
plex with PPNY (PPN=bis(triphenylphosphine)iminium,
Y=2,4-dinitrophenoxide) were tested in the copolymeriza-
tion of CO2 and (R)-SO (Figure 3), 92% enantioselectivity
for the R configuration was observed. This result indicates
that the stereochemistry of the methine carbon atom of (R)-
styrene oxide was retained up to 96% during the copoly-
merization with CO2.[18b] Accordingly, the isotactic signals
should dominate the microstructure of the resulting copoly-
mer. The 13C NMR spectrum of the resulted copolymer is
shown in Figure 3, from which two peaks (d=153.94 and
153.85 ppm) were observed in part of head-to-tail carbonate
linkage. By comparing the integral-area ratio of the two
peaks, the signal at d=153.94 ppm can be assigned to syn-
diotactic sensitivity and the large peak at d=153.85 ppm is
ascribed to the isotactic sensitivity that is caused by the ad-
jacent styrene oxide ring-opening units. This result is consis-
III
ꢀ
Figure 3. Binary catalyst system of an unsymmetrical (S,S,S)-salen Co
complex and PPNY (PPN=bis(triphenylphosphine)iminium, Y=2,4-di-
nitrophenoxide) for the copolymerization of CO2 with (R)-styrene oxide
and the carbonyl region of the 13C NMR spectrum of the resulting copo-
lymer.
tent with our assignment of the model diad compounds, in
which the peak of isotactic diad appears at higher field than
the syndiotactic diad, as shown in Figure 2.
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Xiao-Bing Lu et al.
78.36 (1CH), 75.08, 75.04 (1CH2), 70.97 (1CH2), 59.01 (1CH3),
56.85 ppm (1CH3).
Experimental Section
General Methods
Bis(2-methoxy-1-phenylethyl) Carbonate (H-H)
All of the manipulations that involved air- and/or water-sensitive com-
pounds were performed under an argon atmosphere with standard
Schlenk techniques. All of the solvents were distilled under an argon at-
mosphere after drying over an appropriate drying reagent. Gel C-200
was used for column chromatography on silica gel. 1H and 13C NMR
spectra were recorded on Varian INOVA-400 MHz and Bruker 500 MHz
(13C: 125 MHz) spectrometers, respectively. 1H NMR shifts were refer-
enced to an internal standard (TMS, d=0 ppm) and to the solvent;
13C NMR shifts were referenced to CDCl3 (d=77.0 ppm).
To a stirring solution of 2-methoxy-1-phenylethanol ((rac)-3; 0.456 g,
3.00 mmol) in THF (20 mL) was added NaH (72 mg, 3.00 mmol) and the
solution was stirred for 1 h at RT. Then, a solution of (rac)-4 (0.74 g,
3.00 mmol) in THF (10 mL) was slowly added. After 4 h, the reaction
mixture was diluted with Et2O (50 mL) and washed with water (3ꢁ
30 mL). The organic phase was dried over anhydrous MgSO4 and concen-
trated under reduced pressure. The resulting residue was purified by
column chromatography on silica gel (petroleum ether/EtOAc, 5:1) to
obtain H-H as a colorless oil (0.89 g, 90% yield). Rf =0.45 (petroleum
ether/EtOAc, 5:1); 1H NMR (CDCl3): d=3.39 (s, 6H), 3.56–3.59 (m,
2H), 3.72–3.77 (m, 2H), 5.77 (q, 2H), 7.27–7.33 ppm (m, 10H); 13C NMR
(CDCl3): d=153.88 (1C), 136.78 (2C), 128.31 (2CH), 128.23 (4CH),
126.38 (4CH), 78.28 (2CH), 75.06 (2CH2), 58.98 ppm (2CH3).
2-Methoxy-2-phenylethyl-1H-imidazole-1-carboxylate ((rac)-2)
To
a stirring solution of 2-methoxy-2-phenylethanol ((rac)-1; 1.52 g,
10.00 mmol) in dry THF (50 mL) was slowly added carbonyl diimidazole
(4.86 g, 30.00 mmol). After the addition was complete, the reaction was
stirred for 12 h at RT. Then, the reaction mixture was diluted with Et2O
(100 mL) and washed with water (3ꢁ50 mL). The organic phase was
dried over anhydrous MgSO4 and concentrated under reduced pressure
to afford 1-imidazolecarboxylate as a white solid (2.41 g, 98% yield).
1H NMR (CDCl3): d=3.27 (s, 3H), 4.41–4.53 (m, 3H), 7.03 (s, 1H), 7.32–
7.39 (m, 6H), 8.09 ppm (s, 1H).
(R)-2-((tert-Butyldimethylsilyl)oxy)-1-phenylethanol ((R)-6)
(R)-1-Phenylethane-1,2-diol ((R)-5; 0.68 g, 5 mmol)[21] and 4-dimethyla-
minopyridine (DMAP; 0.061 g, 0.5 mmol) were dissolved in dry CH2Cl2
(30 mL) under a N2 atmosphere. Then, Et3N (1.1 mL, 7.5 mmol) and
TBDMSCl (1.13 g, 7.5 mmol in CH2Cl2) were added dropwise. The reac-
tion mixture was stirred for 4 h, after which a saturated aqueous solution
of NH4Cl (20 mL) was added. The aqueous layer was extracted with
CH2Cl2 (3ꢁ20 mL) and the combined organic layers were dried over an-
hydrous Na2SO4. The solvent was removed by rotary evaporation and the
resulting oil was purified by column chromatography on silica gel (petro-
leum ether/EtOAc, 20:1) to afford compound (R)-6 as a colorless oil
(1.23 g, 98% yield). [a]D20 =ꢀ30.38 (c=0.1, CHCl3); 1H NMR (CDCl3):
d=7.27–7.38 (m, 5H), 4.73–4.77 (m, 1H), 3.75–3.78 (d, J=4.0 Hz, 1H),
3.52–3.3.57 (d, J=8.0 Hz, 1H), 2.95–2.96 (d, J=4.0 Hz, 1H), 0.91 (s, 9H),
0.07 (s, 3H), 0.06 ppm (s, 3H).
Bis(2-methoxy-2-phenylethyl) Carbonate (T-T)
To a stirring solution of 2-methoxy-2-phenylethanol ((rac)-1; 0.456 g,
3.00 mmol) in THF (20 mL) was added NaH (72 mg, 3.00 mmol). After
the resultant solution had been stirred for 1 h at RT, a solution of (rac)-2
(0.74 g, 3.00 mmol) in THF (10 mL) was slowly added. After 4 h, the re-
action mixture was diluted with Et2O (50 mL) and washed with water
(3ꢁ30 mL). The organic phase was dried over anhydrous MgSO4 and
concentrated under reduced pressure. The resulting residue was purified
by column chromatography on silica gel (petroleum ether/EtOAc, 5:1) to
obtain compound T-T as a colorless oil (0.94 g, 95% yield). Rf =0.45 (pe-
(S)-2-((tert-Butyldimethylsilyl)oxy)-1-phenylethanol ((S)-6)
1
troleum ether/EtOAc, 5:1); H NMR (CDCl3): d=3.28 (s, 6H), 4.16–4.19
All of the synthesis steps for compound (S)-6 were the same as for (R)-6
(see above), except for the replacement of compound (R)-5 with (S)-5.
[a]2D0 =30.08 (c=0.1, CHCl3); 1H NMR (CDCl3): d=7.27–7.38 (m, 5H),
4.73–4.77 (m, 1H), 3.75–3.78 (d, J=4.0 Hz, 1H), 3.52–3.3.57 (d, J=
8.0 Hz, 1H), 2.95–2.96 (d, J=4.0 Hz, 1H), 0.91 (s, 9H), 0.07 (s, 3H),
0.06 ppm (s, 3H).
(m, 2H), 4.28 (q, 2H), 4.44–4.48 (m, 2H), 7.25–7.39 ppm (m, 10H);
13C NMR (CDCl3): d=154.93, 154.91 (1C), 137.45, 137.41 (2C), 128.48
(4CH), 128.25 (2CH), 126.85 (4CH), 81.32, 81.30 (2CH), 71.00, 70.95
(2CH2), 56.86 ppm (2CH3).
2-Methoxy-1-phenylethyl-1H-imidazole-1-carboxylate ((rac)-4)
(R)-tert-Butyl(2-methoxy-2-phenylethoxy)dimethylsilane ((R)-7)
To
a stirring solution of 2-methoxy-1-phenylethanol ((rac)-3; 1.52 g,
Compound (R)-6 (1.8 g, 7 mmol) was dissolved in THF (30 mL) and
NaH (0.34 g, 14 mmol) was added. After about 1 h, a solution of MeI
(1.2 g, 8.4 mmol) in THF was added dropwise. The reaction mixture was
stirred in the dark overnight and a saturated aqueous solution of NaCl
(20 mL) was added. The crude reaction was extracted with EtOAc (3ꢁ
20 mL) and the combined organic layers were dried over anhydrous
Na2SO4. The solvent was removed under vacuum and the resulting oil
was purified by column chromatography on silica gel (petroleum ether/
EtOAc, 20:1) to afford compound (R)-7 as a colorless oil (1.7 g, 90%
yield). [a]2D0 =ꢀ58.28 (c=0.2, CHCl3); 1H NMR (CDCl3): d=7.30–7.40
(m, 5H), 4.26–4.29 (t, 1H), 3.82–3.88 (m, 1H), 3.672–3.711 (m, 1H), 3.35
(s, 3H), 0.90 (s, 9H), 0.037 (s, 3H), 0.00 ppm (s, 3H).
10.00 mmol) in dry THF (50 mL) was slowly added carbonyl diimidazole
(4.86 g, 30.00 mmol). After the addition was complete, the reaction was
stirred for 12 h at RT. Then, the reaction mixture was diluted with Et2O
(100 mL) and washed with water (50ꢁ3 mL). The organic phase was
dried over anhydrous MgSO4 and concentrated under reduced pressure
to afford 1-imidazolecarboxylate as a white solid (2.31 g, 94% yield).
1H NMR (CDCl3): d=3.43 (s, 3H), 3.68 (d, J=1.60, 3.20 Hz, 1H), 3.88
(d, J=8.40 Hz, 1H), 6.13–6.16 (q, 1H), 7.07 (s, 1H), 7.3–7.47 (m, 6H),
8.13 ppm (s, 1H).
2-Methoxy-1-phenylethyl(2-methoxy-2-phenylethyl) Carbonate (H-T)
To a stirring solution of 2-methoxy-2-phenylethanol ((rac)-1; 0.456 g,
3.00 mmol) in THF (20 mL) was added NaH (72 mg, 3.00 mmol) and the
solution was stirred for 1 h at RT. Then, a solution of (rac)-4 (0.74 g,
3.00 mmol) in THF (10 mL) was slowly added. After 4 h, the reaction
mixture was diluted with Et2O (50 mL) and washed with water (3ꢁ
30 mL). The organic phase was dried over anhydrous MgSO4 and concen-
trated under reduced pressure. The resulting residue was purified by
column chromatography on silica gel (petroleum ether/EtOAc, 5:1) to
obtain H-T as a colorless oil (0.94 g, 95% yield). Rf =0.45 (petroleum
(S)-tert-Butyl(2-methoxy-2-phenylethoxy)dimethylsilane ((S)-7)
All of the synthesis steps for compound (S)-7 were the same as for (R)-7
(see above), except for the replacement of compound (R)-6 with (S)-6.
[a]2D0 =60.18 (c=0.2, CHCl3); 1H NMR (CDCl3): d=7.30–7.40 (m, 5H),
4.26–4.29 (t, 1H), 3.82–3.88 (m, 1H), 3.672–3.711 (m, 1H), 3.35 (s, 3H),
0.90 (s, 9H), 0.037 (s, 3H), 0.00 ppm (s, 3H).
(R)-2-Methoxy-2-phenylethanol ((R)-1)
1
ether/EtOAc, 5:1); H NMR (CDCl3): d=3.26 (s, 3H), 3.40 (s, 3H), 3.55–
3.59 (m, 1H), 3.72–3.77 (m, 1H), 4.13–4.27 (m, 2H), 4.41–4.47 (m, 1H),
5.78 (q, 1H), 7.30–7.37 ppm (m, 10H); 13C NMR (CDCl3): d=154.41,
154.38 (1C), 137.39 (1C), 136.70 (1C), 128.45 (2CH), 128.38 (2CH),
128.21 (2H), 126.81 (2CH), 126.50 (2CH), 81.26, 81.24 (1CH), 78.40,
Compound (R)-7 (0.53 g, 2 mmol) was dissolved in MeCN (2 mL) and
TBAF (1.04 g, 4 mmol) was added. The reaction mixture was stirred
overnight and the solvent was removed under vacuum. The resulting oil
was purified by column chromatography on silica gel (petroleum ether/
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Xiao-Bing Lu et al.
EtOAc, 1:1) to afford compound (R)-1 as a colorless oil (0.22 g, 73%
(S)-(2-Methoxy-1-(methoxymethoxy)ethyl)benzene ((S)-10)
yield). [a]2D0 =ꢀ105.18 (c=0.1, CHCl3); 1H NMR (CDCl3): d=7.30–7.37
(m, 5H), 4.30–4.31 (d, J=4.8 Hz, 1H), 3.62–3.70 (q, 2H), 3.31 (s, 3H),
2.30–2.32 ppm (d, J=7.6 Hz).
All of the synthesis steps for compound (S)-10 were the same as for (R)-
10 (see above), except for the replacement of compound (R)-9 with (S)-
9. [a]2D0 =+171.98 (c=2.3, CH2Cl2); 1H NMR (CDCl3): d=7.28–7.35 (m,
5H), 4.81–4.83 (d, J=3.6, Hz, 1H), 4.58–4.65 (q, 2H), 3.62–3.67 (d, J=
8.0 Hz, 1H), 3.47–3.50 (d, J=3.6 Hz, 1H), 3.39 (s, 3H), 3.37 ppm (s, 3H).
(S)-2-Methoxy-2-phenylethanol ((S)-1)
All of the synthesis steps for (S)-1 were the same as for (R)-1 (see
above), except for the replacement of compound (R)-7 with (S)-7. [a]D20
=
(R)-2-Methoxy-1-phenylethanol ((R)-3)
108.08 (c=0.1, CHCl3); 1H NMR (CDCl3): d=7.30–7.37 (m, 5H), 4.30–
4.31 (d, J=4.8 Hz, 1H), 3.62–3.70 (q, 2H), 3.31 (s, 3H), 2.30–2.32 ppm
(d, J=7.6 Hz).
Compound (R)-10 (0.19 g, 1 mmol) was dissolved in THF (1.7 mL) and
6m HCl (1.7 mL, 10 mmol) was added dropwise. Then, the reaction mix-
ture was stirred for 4 h, after which time a saturated aqueous solution of
NaHCO3 solution was added. The crude reaction was extracted with
EtOAc (10ꢁ3 mL) and the combined organic layers were dried over an-
hydrous Na2SO4. The solvent was removed under vacuum and the result-
ing oil was purified by column chromatography on silica gel (petroleum
ether/EtOAc, 1:1) to afford compound (R)-3 as a colorless oil (0.12 g,
79% yield). [a]2D0 =ꢀ56.38 (c=1.1, CHCl3). 1H NMR (CDCl3): d=7.25–
7.39 (m, 5H), 4.87–4.89 (d, J=8.8 Hz, 1H), 3.54–3.55 (q, 1H), 3.52–3.53
(q, 1H), 3.42 ppm (s, 3H).
(R)-8,8,9,9-tetramethyl-5-phenyl-2,4,7-trioxa-8-siladecane ((R)-8)
A
solution of compound (R)-6 (1 g, 4 mmol) and DIPEA (2.8 mL,
16 mmol) in CH2Cl2 (30 mL) was stirred for 1 h, chloromethyl methyl
ether (MOMCl; 0.5 mL, 6 mmol) was added dropwise, and the mixture
was stirred for a further 2 h at RT. Then, water was added and the mix-
ture was extracted with CH2Cl2 (3ꢁ20 mL). The organic layer was dried
over anhydrous Na2SO4 and the solvent was removed under reduced
pressure. The resulting residue was purified by column chromatography
on silica gel (petroleum ether/EtOAc, 20:1) to obtain compound (R)-8 as
(S)-2-Methoxy-1-phenylethanol ((S)-3)
a
colorless oil (0.93 g, 80% yield. [a]2D0 =ꢀ89.78 (c=1.05, CH2Cl2);
1H NMR (CDCl3): d=7.27–7.35 (m, 5H), 4.69–4.72 (d, J=4.4 Hz, 2H),
4.61–4.68 (t, 1H), 3.81–3.3.85 (d, J=7.6 Hz, 1H), 3.68–3.3.72 (d, J=
4.4 Hz, 1H), 3.39 (s, 3H), 0.89 (s, 9H), 0.032 (s, 3H), 0.022 ppm (s, 3H).
All of the synthesis steps for compound (S)-3 were the same as for (R)-3
(see above), except for the replacement of compound (R)-10 by (S)-10.
[a]2D0 =54.38 (c=1.1, CHCl3); 1H NMR (CDCl3): d=7.25–7.39 (m, 5H),
4.87–4.89 (d, J=8.8 Hz, 1H), 3.54–3.55 (q, 1H), 3.52–3.53 (q, 1H),
3.42 ppm (s, 3H).
(S)-8,8,9,9-tetramethyl-5-phenyl-2,4,7-trioxa-8-siladecane ((S)-8)
All of the synthesis steps for compound (S)-8 were the same as for (R)-8
(see above), except for the replacement of compound (R)-6 with (S)-6.
[a]2D0 =+96.58 (c=1.13, CH2Cl2); 1H NMR (CDCl3): d=7.27–7.35 (m,
5H), 4.69–4.72 (d, J=4.4 Hz, 2H), 4.61–4.68 (t, 1H), 3.81–3.3.85 (d, J=
7.6 Hz, 1H), 3.68–3.3.72 (d, J=4.4 Hz, 1H), 3.39 (s, 3H), 0.89 (s, 9H),
0.032 (s, 3H), 0.022 ppm (s, 3H).
(R)-2-Methoxy-2-phenylethyl-1H-imidazole-1-carboxylate ((R)-2)
All of the synthesis steps for compound (R)-2 were the same as for (rac)-
2 (see above), except for the replacement of compound (rac)-1 with (R)-
1. [a]2D0 =ꢀ70.48 (c=1.15, CH2Cl2); 1H NMR (CDCl3): d=3.27 (s, 3H),
4.41–4.53 (m, 3H), 7.03 (s, 1H), 7.32–7.39 (m, 6H), 8.09 ppm (s, 1H).
(S)-2-Methoxy-2-phenylethyl-1H-imidazole-1-carboxylate ((S)-2)
(R)-2-(Methoxymethoxy)-2-phenylethanol ((R)-9)
All of the synthesis steps for compound (S)-2 were the same as for (rac)-
2 (see above), except for the replacement of compound (rac)-1 with (S)-
1. [a]2D0 =+64.68 (c=1.70, CH2Cl2); 1H NMR (CDCl3): d=3.27 (s, 3H),
4.41–4.53 (m, 3H), 7.03 (s, 1H), 7.32–7.39 (m, 6H), 8.09 ppm (s, 1H).
Compound (R)-8 (0.96 g, 3 mmol) was dissolved in MeCN (30 mL) and
TBAF (1.56 g, 6 mmol) was added. Then, the reaction was stirred over-
night and the solvent was removed under vacuum. The resulting oil was
purified by column chromatography on silica gel (petroleum ether/
EtOAc, 1:1) to afford compound (R)-9 as a colorless oil (0.51 g, 87%
yield). [a]2D0 =ꢀ82.38 (c=1.85, CH2Cl2); 1H NMR (CDCl3): d=7.28–7.37
(m, 5H), 4.70–4.73 (d, J=3.6 Hz, 2H), 4.64–4.68 (t, 1H), 3.66–3.78 (m,
2H), 3.41 ppm (s, 3H).
(R)-2-Methoxy-1-phenylethyl-1H-imidazole-1-carboxylate ((R)-4)
All of the synthesis steps for compound (R)-4 were the same as for (rac)-
4 (see above), except for the replacement of compound (rac)-3 with (R)-
3. [a]2D0 =ꢀ34.28 (c=1.41, CH2Cl2); 1H NMR (CDCl3): d=3.43 (s, 3H),
3.68 (d, J=3.20 Hz, 1H), 3.88 (d, J=8.40 Hz, 1H), 6.13–6.16 (q, 1H),
7.07 (s, 1H), 7.3–7.47 (m, 6H), 8.13 ppm (s, 1H).
(S)-2-(Methoxymethoxy)-2-phenylethanol ((S)-9)
All of the synthesis steps for compound (S)-9 were the same as for (R)-9
(see above), except for the replacement of compound (R)-8 with (S)-8.
[a]2D0 =+81.68 (c=1.81, CH2Cl2); 1H NMR (CDCl3): d=7.28–7.37 (m,
5H), 4.70–4.73 (d, J=3.6 Hz, 2H), 4.64–4.68 (t, 1H), 3.66–3.78 (m, 2H),
3.41 ppm (s, 3H).
(S)-2-Methoxy-1-phenylethyl-1H-imidazole-1-carboxylate ((S)-4)
All of the synthesis steps for compound (S)-4 were the same as for (rac)-
4 (see above), except for the replacement of compound (rac)-3 with (S)-
3. [a]2D0 =+31.78 (c=1.35, CH2Cl2); 1H NMR (CDCl3): d=3.43 (s, 3H),
3.68 (d, J=3.20 Hz, 1H), 3.88 (d, J=8.40 Hz, 1H), 6.13–6.16 (q, 1H),
7.07 (s, 1H), 7.3–7.47 (m, 6H), 8.13 ppm (s, 1H).
(R)-(2-Methoxy-1-(methoxymethoxy)ethyl)benzene ((R)-10)
Compound (R)-9 (1.6 g, 9 mmol) was dissolved in THF (30 mL) and
NaH (0.24 g, 9.9 mmol) was added. After about 1 h, a solution of MeI
(1.41 g, 9.9 mmol) in THF was added dropwise. The reaction mixture was
stirred in the dark overnight and a saturated aqueous solution of NaCl
(20 mL) was added. The crude mixture was extracted with EtOAc (3ꢁ
20 mL) and the combined organic layers were dried over anhydrous
Na2SO4. The solvent was removed under vacuum and the resulting oil
was purified by column chromatography on silica gel (petroleum ether/
EtOAc, 5:1) to afford compound (R)-10 as a colorless oil (1.51 g, 86%
yield). [a]2D0 =ꢀ177.18 (c=1.91, CH2Cl2); 1H NMR (CDCl3): d=7.28–7.35
(m, 5H), 4.81–4.83 (d, J=3.6, Hz, 1H), 4.58–4.65 (q, 2H), 3.62–3.67 (d,
J=8.0 Hz, 1H), 3.47–3.50 (d, J=3.6 Hz, 1H), 3.39 (s, 3H), 3.37 ppm (s,
3H).
Bis((S)-2-methoxy-2-phenylethyl) Carbonate ((S,S)-T-T)
To a stirring solution of (S)-2-methoxy-2-phenylethanol ((S)-1, 0.456 g,
3.00 mmol) in THF (20 mL) was added NaH (72 mg, 3.00 mmol) and the
solution was stirred for 1 h at RT. Then, a solution of compound (S)-2
(0.74 g, 3.00 mmol) in THF (10 mL) was slowly added. After 4 h, the re-
action mixture was diluted with Et2O (50 mL) and washed with water
(3ꢁ30 mL). The organic phase was dried over anhydrous MgSO4 and
concentrated under reduced pressure. The resulting residue was purified
by column chromatography on silica gel (petroleum ether/EtOAc, 5:1) to
obtain compound (S,S)-T-T as a colorless oil (0.94 g, 95% yield). Rf =
0.45 (petroleum ether/EtOAc, 5:1); ½aꢁ2D0 =+98.78 (c=1.87, CH2Cl2);
1H NMR (CDCl3): d=7.25–7.39 (m, 10H), 4.44–4.48 (m, 2H), 4.28 (q,
2H), 4.16–4.19 (m, 2H), 3.28 ppm (s, 6H); 13C NMR (CDCl3): d=154.93,
154.91 (1C), 137.45 (2C), 128.48 (4CH), 128.25 (2CH), 126.85 (4CH),
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Xiao-Bing Lu et al.
81.32 (2CH), 71.00 (2CH2), 56.86 ppm (2CH3); elemental analysis calcd
(%) for C19H22O5: C 69.07, H 6.71; found: C 69.07, H 6.74.
56.85 ppm (1CH3); elemental analysis calcd (%) for C19H22O5: C 69.07,
H 6.71; found: C 69.20, H 6.75.
Bis((S)-2-methoxy-1-phenylethyl) Carbonate ((S,S)-H-H)
Bis((R)-2-methoxy-2-phenylethyl) Carbonate ((R,R)-T-T)
To a stirring solution of (S)-2-methoxy-1-phenylethanol ((S)-3; 0.456 g,
3.00 mmol) in THF (20 mL) was added NaH (72 mg, 3.00 mmol) and the
solution was stirred for 1 h at RT. Then, a solution of compound (S)-4
(0.74 g, 3.00 mmol) in THF (10 mL) was slowly added. After 4 h, the re-
action mixture was diluted with Et2O (50 mL) and washed with water
(3ꢁ30 mL). The organic phase was dried over anhydrous MgSO4 and
concentrated under reduced pressure. The resulting residue was purified
by column chromatography on silica gel (petroleum ether/EtOAc, 5:1) to
obtain compound (S,S)-H-H as a colorless oil (0.89 g, 90% yield). Rf =
0.45 (petroleum ether/EtOAc, 5:1); [a]2D0 =+1108 (c=1.75, CH2Cl2);
1H NMR (CDCl3): d=7.27–7.33 (m, 10H), 5.77 (q, 2H), 3.72–3.77 (m,
2H), 3.56–3.59 (m, 2H), 3.39 ppm (s, 6H); 13C NMR (CDCl3): d=153.88
(1C), 136.78 (2C), 128.31 (2CH), 128.23 (4CH), 126.38 (4CH), 78.28
(2CH), 75.06 (2CH2), 58.98 ppm (2CH3); elemental analysis calcd (%)
for C19H22O5: C 69.07, H 6.71; found: C 69.14, H 6.79.
All of the synthesis steps for (R,R)-T-T were the same as for (S,S)-T-T
(see above), except for the replacement of compounds (S)-1 and (S)-2
with (R)-1 and (R)-2, respectively. [a]2D0 =ꢀ99.58 (c=1.01, CH2Cl2);
1H NMR (CDCl3): d=7.25–7.39 (m, 10H), 4.44–4.48 (m, 2H), 4.28 (q,
2H), 4.16–4.19 (m, 2H), 3.28 ppm (s, 6H); 13C NMR (CDCl3): d=154.93,
154.91 (1C), 137.45 (2C), 128.48 (4CH), 128.25 (2CH), 126.85 (4CH),
81.32 (2CH), 71.00 (2CH2), 56.86 ppm (2CH3); elemental analysis calcd
(%) for C19H22O5: C 69.07, H 6.71; found: C 69.13, H 6.85.
(R)-2-Methoxy-2-phenylethyl((S)-2-methoxy-2-phenylethyl) Carbonate
((R,S)-T-T)
All of the synthesis steps for (R,S)-T-T were the same as for (R,R)-T-T
(see above), except for the replacement of compound (R)-2 with (S)-2.
[a]2D0 =0.28 (c=1.0, CHCl3); 1H NMR (CDCl3): d=7.25–7.39 (m, 10H),
4.44–4.48 (m, 2H), 4.28 (q, 2H), 4.16–4.19 (m, 2H), 3.28 ppm (s, 6H);
13C NMR (CDCl3): d=154.91 (1C), 137.41 (2C), 128.48 (4CH), 128.25
(2CH), 126.85 (4CH), 81.32 (2CH), 70.95 (2CH2), 56.86 ppm (2CH3); el-
emental analysis calcd (%) for C19H22O5: C 69.07, H 6.71; found: C 69.13,
H 6.82.
Bis((R)-2-methoxy-1-phenylethyl) Carbonate ((R,R)-H-H)
All of the synthesis steps for compound (R,R)-H-H were the same as for
(S,S)-H-H (see above), except for the replacement of compounds (S)-3
and (S)-4 with (R)-3 and (R)-4, respectively. ½aꢁ2D0 =ꢀ112.38 (c=0.99,
CH2Cl2); 1H NMR (CDCl3): d=7.27–7.33 (m, 10H), 5.77 (q, 2H), 3.72–
3.77 (m, 2H), 3.56–3.59 (m, 2H), 3.39 ppm (s, 6H); 13C NMR (CDCl3):
d=153.88 (1C), 136.78 (2C), 128.31 (2CH), 128.23 (4CH), 126.38
(4CH), 78.28 (2CH), 75.06 (2CH2), 58.98 ppm (2CH3); elemental analy-
sis calcd (%) for C19H22O5: C 69.07, H 6.71; found: C 69.13, H 6.85.
(S)-2-Methoxy-1-phenylethyl((S)-2-methoxy-2-phenylethyl) Carbonate
((S,S)-H-T)
To a stirring solution of (S)-2-methoxy-2-phenylethanol ((S)-1; 0.456 g,
3.00 mmol) in THF (20 mL) was added NaH (72 mg, 3.00 mmol) and the
solution was stirred for 1 h at RT. Then, a solution of compound (S)-4
(0.74 g, 3.00 mmol) in THF (10 mL) was slowly added. After 4 h, the re-
action mixture was diluted with Et2O (50 mL) and washed with water
(3ꢁ30 mL). The organic phase was dried over anhydrous MgSO4 and
concentrated under reduced pressure. The resulting residue was purified
by column chromatography on silica gel (petroleum ether/EtOAc, 5:1) to
obtain compound (S,S)-H-T as a colorless oil (0.94 g, 95% yield). Rf =
0.45 (petroleum ether/EtOAc, 5:1); ½aꢁ2D0 =+109.98 (c=1.62, CH2Cl2).
1H NMR (CDCl3): d=7.30–7.37 (m, 10H), 5.78 (q, 1H), 4.41–4.47 (m,
1H), 4.13–4.27 (m, 2H), 3.72–3.77 (m, 1H), 3.55–3.59 (m, 1H), 3.40 (s,
3H), 3.26 ppm (s, 3H); 13C NMR (CDCl3): d=154.38 (1C), 137.39 (1C),
136.70 (1C), 128.45 (2CH), 128.38 (2CH), 128.21 (2H), 126.81 (2CH),
126.50 (2CH), 81.26 (1CH), 78.40 (1CH), 75.08 (1CH2), 70.97 (1CH2),
59.01 (1CH3), 56.85 ppm (1CH3); elemental analysis calcd (%) for
C19H22O5: C 69.07, H 6.71; found: C 69.09, H 6.75.
(R)-2-Methoxy-1-phenylethyl((S)-2-methoxy-1-phenylethyl) Carbonate
((R,S)-H-H)
All of the synthesis steps for compound (R,S)-H-H were the same as for
(R,R)-H-H (see above), except for the replacement of compound (R)-3
with (S)-3. [a]2D0 =0.18 (c=0.1, CHCl3); 1H NMR (CDCl3): d=7.27–7.33
(m, 10H), 5.77 (q, 2H), 3.72–3.77 (m, 2H), 3.56–3.59 (m, 2H), 3.39 ppm
(s, 6H); 13C NMR (CDCl3): d=153.88 (1C), 136.78 (2C), 128.31 (2CH),
128.23 (4CH), 126.38 (4CH), 78.28 (2CH), 75.06 (2CH2), 58.98 ppm
(2CH3); elemental analysis calcd (%) for C19H22O5: C 69.07, H 6.71;
found: C 69.12, H 6.83.
Acknowledgements
(R)-2-Methoxy-1-phenylethyl((R)-2-methoxy-2-phenylethyl) Carbonate
((R,R)-H-T)
This work was supported by the National Natural Science Foundation of
China (NSFC; 21134002 and 21104007) and the National Basic Research
Program of China (973 Program; 2009CB825300). X.-B. Lu gratefully ac-
knowledges the Chang Jiang Scholars Program (T2011056) of the Minis-
try of Education of the People’s Republic of China.
All of the synthesis steps for (R,R)-H-T were the same as for (S,S)-H-T
(see above), except for the replacement of compounds (S)-1 and (S)-4
with (R)-1 and (R)-4, respectively. [a]2D0 =ꢀ113.68 (c=1.02, CH2Cl2);
1H NMR (CDCl3): d=7.30–7.37 (m, 10H), 5.78 (q, 1H), 4.41–4.47 (m,
1H), 4.13–4.27 (m, 2H), 3.72–3.77 (m, 1H), 3.55–3.59 (m, 1H), 3.40 (s,
3H), 3.26 ppm (s, 3H); 13C NMR (CDCl3): d=154.38 (1C), 137.39 (1C),
136.70 (1C), 128.45 (2CH), 128.38 (2CH), 128.21 (2H), 126.81 (2CH),
126.50 (2CH), 81.26 (1CH), 78.40 (1CH), 75.08 (1CH2), 70.97 (1CH2),
59.01 (1CH3), 56.85 ppm (1CH3); elemental analysis calcd (%) for
C19H22O5: C 69.07, H 6.71; found: C 69.10, H 6.83.
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Received: January 27, 2013
Revised: February 19, 2013
Published online: May 24, 2013
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