TMDS as a dual-purpose reductant in the regioselective ring cleavage of hexopyranosyl acetals to ethers

Article abstract of DOI:10.1002/ejoc.201101682

1,1,3,3-Tetramethyldisiloxane (TMDS) has been developed as an excellent dual-purpose reductant for the highly regioselective ring cleavage of various hexopyranosyl 4,6-O-acetals with Cu(OTf)₂ or AlCl₃ to afford the corresponding prim

Full text of DOI:10.1002/ejoc.201101682

FULL PAPER
DOI: 10.1002/ejoc.201101682
TMDS as a Dual-Purpose Reductant in the Regioselective Ring Cleavage of
Hexopyranosyl Acetals to Ethers
Yin-Jie Zhang,[a,b] Wissam Dayoub,[b] Guo-Rong Chen,*[a] and Marc Lemaire*[b]
Keywords: Carbohydrates / Surfactants / Copper / Aluminum / Reduction
1,1,3,3-Tetramethyldisiloxane (TMDS) has been developed
as an excellent dual-purpose reductant for the highly re-
gioselective ring cleavage of various hexopyranosyl 4,6-O-
acetals with Cu(OTf)2 or AlCl3 to afford the corresponding
primary and secondary ethers. Its application to the concise
synthesis of carbohydrate-based surfactants is highlighted.
a few reducing systems that have been reported to directly
reduce unsubstituted hexopyranosyl acetals to the corre-
sponding ethers, and they often result in moderate yields
and low selectivity.[9]
Introduction
Owing to growing interest in environmental issues,
awareness of the ecological impact of surfactants is increas-
ing. Nontoxic and biodegradable carbohydrate-based sur-
factants[1] derived from renewable resources[2] have recently
been gaining attention, because they exhibit good surface
activities.[3] Polyhydroxylated glycoside fatty alkyl chain
ethers are good representatives of these surfactants, show-
ing new valuable properties such as antimicrobial activity
and so on.[4] Furthermore, compared to their well-known
ester counterparts, carbohydrate aliphatic ethers possess
higher stability under acidic and basic conditions. Some
synthetic routes of these compounds have been report-
ed,[4c,5] but the overall yields are extremely low after compli-
cated multistep protection and deprotection of the hydroxy
groups.
Traditional protocols have been developed to reduce 4,6-
O-acetals with various hydride sources including Li-
AlH4,[9a,10] NaH,[11] DIBAL-H,[12] NaBH3CN,[13] BH3,[14]
Et3SiH,[15] PhSiH3,[16] and so on. Nevertheless, most hy-
dride sources used in these methods present drawbacks such
as high price, necessity for rigorously anhydrous conditions,
incompatibility with other functionalities, or release of py-
rophoric and toxic gas in certain cases. Over the past few
years, our group has been studying 1,1,3,3-tetramethyldis-
iloxane (TMDS)[17] as a promising reducing agent, as it is
often efficient, air and water stable, easy to handle, and less
toxic.[18] Very recently, an environmentally benign and atom
economic protocol was described for the metal triflate cata-
lyzed reduction of aromatic and aliphatic acetals to ethers
by TMDS under mild conditions.[19] Herein, we have ex-
plored TMDS as an effective hydride source which allows
the regioselective reductive ring cleavage of sugar acetals to
ethers at either the O6 or O4 position in the presence of
Cu(OTf)2 or AlCl3 (Scheme 1).
Regioselective protection of polyhydroxy groups[6] re-
mains one of the major challenges in the synthesis of biolo-
gically potent and environmentally significant glycoconju-
gates and oligosaccharides.[7] Acetals are widely used for
4,6-O-protection of hexopyranosides because they can be
easily prepared and then be cleaved selectively under appro-
priate reaction conditions to orthogonally yield primary or
secondary alcohols.[8] In carbohydrate chemistry, it is a de-
sirable strategy to carry out direct functionalization of indi-
vidual hydroxy groups without protection and deprotection
steps. However, to the best of our knowledge, there are only
[a] Key Laboratory for Advanced Materials and Institute of Fine
Chemicals, East China University of Science and Technology,
Shanghai 200237, P. R. China
Fax: +86-21-64252758
Scheme 1. TMDS-induced regioselective ring opening of hexopyr-
anosyl 4,6-O-acetals to the secondary ethers (path a) and primary
ethers (path b) with Cu(OTf)2 and AlCl3, respectively.
E-mail: mrs_guorongchen@ecust.edu.cn
[b] Laboratoire de Catalyse, Synthèse et Environnement, Institute
de Chimie et Biochimie Moléculaires et Supramoléculaires
(ICBMS), CNRS UMR5246, Université Lyon 1, Bâtiment
Curien-CPE, 3° étage,
43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne,
France
Fax: +33-472-431-408
E-mail: marc.lemaire@univ-lyon1.fr
Moreover, we proceeded to synthesize glucopyranosyl
long alkyl chain ethers in two straightforward steps
(Scheme 2).
1960
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Eur. J. Org. Chem. 2012, 1960–1966

Regioselective Ring Cleavage of Hexopyranosyl Acetals to Ethers
flates Eu(OTf)3, Yb(OTf)3, and Gd(OTf)3 furnished any
target compound (Table 1, Entries 7–9). A similar lack of
activity has also been described in the literature.[20] No bet-
ter results were gained when the amounts of TMDS and
Cu(OTf)2 were decreased to 1 equiv. and 2 mol-%, respec-
tively.
On the basis of the above results, we chose the TMDS/
Cu(OTf)2 protocol to regioselectively reduce a variety of
4,6-O-benzylidene glycopyranosyl acetals (Table 2). The op-
timized reaction conditions involved the use of 1.5 equiv.
of TMDS and 5 mol-% of Cu(OTf)2 in CH2Cl2 at room
temperature for 4 h.
Acetals of 2,3-O-benzyl glucoside 1, galactoside 4, and
mannoside 6 underwent ring cleavage in high yields to give
6-ethers 2 (83%), 5 (81%), and 7 (87%) (Table 2, Entries 1–
3). When acetyl, benzoyl, and pivaloyl were used as protect-
ing groups of glucosyl acetal, the TMDS/Cu(OTf)2 protocol
also provided their corresponding 6-ethers as the main
products in good-to-excellent yields (93, 67, and 86%;
Table 2, Entries 4–6).
Scheme 2. Facile preparation of carbohydrate long alkyl chain
ethers by TMDS-Cu(OTf)2 or TMDS-AlCl3 reducing systems.
Results and Discussion
We began our investigation with the reduction of 4,6-O-
benzylidene acetal 1 by using 1.5 equiv. of TMDS (SiH =
3 equiv.) with 5 mol-% metal triflate at room temperature
for 4 h. The results are outlined in Table 1.
We continued to utilize the TMDS/Cu(OTf)2 reducing
system to transform the unsubstituted glycosyl acetals.
Interestingly, the mode of regioselectivity was remarkably
shifted when glucosyl 4,6-O-benzylidene acetal 14 was re-
duced. 4-Ether 15 was afforded as the major product in
49% isolated yield (Table 2, Entry 7). 2,3-OH galactosyl
acetal 16 was sluggish to react (Table 2, Entry 8), indicating
that the equatorial bond (Glc, Man) at the C4 position was
spatially preferred to the axial one (Gal). Similar results can
be found in the literature.[21] 6-Ether 18 was furnished in
83% yield from unprotected mannosyl acetal 17 (Table 2,
Entry 9). The selectivity of C–O bond cleavage was opposite
between 2,3-OH glucosyl and mannosyl acetals. When
phenyl 4,6-O-benzylidene-β-glucopyranoside 19 was re-
duced by TMDS and Cu(OTf)2, 6-benzylated ether 20 was
afforded in 63% yield (Table 2, Entry 10).
Table 1. Optimization of the TMDS-induced metal triflate cata-
lyzed regioselective ring opening of 4,6-O-benzylidene acetal 1.
Entry
Solvent
THF
CH3CN Cu(OTf)2
toluene Cu(OTf)2
CH2Cl2 Cu(OTf)2
CH2Cl2
CH2Cl2
CH2Cl2 Eu(OTf)3
CH2Cl2 Yb(OTf)3
CH2Cl2 Gd(OTf)3
Metal
triflate
Conv.
[%]
Yield of 2
Ratio
of 3/2
[%]
1
2
3
4
5
6
7
8
9
Cu(OTf)2
0
96
95
94
92
21
0
0
67
78
83
65
10
0
–
1:4
1:10
0:1
1:8
1:3
–
Bi(OTf)3
Fe(OTf)2
As an extension of our research work, we made efforts
to produce high value-added carbohydrate-based surfac-
tants. We proceeded to prepare glucosyl alkyl ethers with
0
0
0
0
–
–
Initially, to determine the best solvent required for opti- different chain lengths in two concise steps (Scheme 2). Alk-
mum activity and selectivity, a set of experiments were car- ylidene acetals 21, 23, 25, and 27 were readily synthesized
ried out to reduce 1 with TMDS and Cu(OTf)2 in THF, from methyl glucoside and aliphatic aldehydes, catalyzed by
CH3CN, toluene, and CH2Cl2. Acetal 1 was sluggish to re- (1R)-10-camphorsulfonic acid (CSA). These acetals were
act in THF (Table 1, Entry 1). Treatment of 1 in CH3CN then directly reduced, affording the corresponding 4-ethers
and toluene resulted in nearly full conversion of 1 and good 22, 24, 26, and 28 by TMDS/Cu(OTf)2 (Table 2, Entries 11–
yield of 6-ether 2 (67 and 78%; Table 1, Entries 2 and 3). In 14). The regioselectivity of reduction is in agreement with
these cases, regioisomer 4-ether 3 was detected as a minor unprotected benzylidene acetal of methyl glucoside 14. De-
byproduct. The best result was obtained when the reaction spite the moderate yields of target compounds due to in-
was performed in CH2Cl2. 6-Ether 2 was isolated in a high complete conversion in these cases, this new strategy
yield of 83% as the sole regioisomer and trace amounts of straightforwardly produces long alkyl chain sugar ethers,
3 were not observed (Table 1, Entry 4). Therefore, CH2Cl2 avoiding the following drawbacks: (1) protection and depro-
was selected as the solvent for further optimization.
tection of the hydroxy groups and transetherification;[4c,5]
A combination of TMDS with other metal triflates was (2) harsh reaction conditions involving the use of dangerous
then studied. Although Bi(OTf)3 afforded high selectivity of metal hydrides.[10–13]
6-ether 2 over 4-ether 3, the isolated yield of 2 decreased to
With success in the TMDS/Cu(OTf)2 reductive O4 ring
65% (Table 1, Entry 5). Employment of Fe(OTf)2 resulted cleavage of 1, we then explored the reducing properties of
in a drastic drop in conversion, yield, and selectivity TMDS with AlCl3.[8] With TMDS (1.5 equiv.; SiH =
(Table 1, Entry 6). None of the lanthanide series metal tri- 2 equiv.) and AlCl3 (3 equiv.) in CH2Cl2 at –78 °C to room
Eur. J. Org. Chem. 2012, 1960–1966
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1961

Y.-J. Zhang, W. Dayoub, G.-R. Chen, M. Lemaire
FULL PAPER
Table 2. Reductive ring opening of 4,6-O-benzylidene glycosyl acet- temperature for 4 h, 4-ether 3 was obtained as the major
als to the corresponding ethers under optimized TMDS/Cu-
(OTf)2 conditions.
product (56%) with only a trace amount of 6-ether 2 as the
byproduct (Table 3, Entry 1). AlCl3 probably first coordi-
nates to O6, followed by fast formation of an oxocarbenium
ion in the apolar CH2Cl2 solvent and a rate-controlling re-
ductive step.[8c] Decreasing the amount of AlCl3 to 2 equiv.
gave rise to a marginally improved yield of secondary ether
3 (86%) and the ratio between 3 and 2 was 10:1. A further
decrease to 1.5 equiv. AlCl3 led to even better yield and re-
gioselectivity (Table 3, Entry 3). When the amount of AlCl3
was reduced to 1 or 0.5 equiv., lower conversion of 1 and
lower yield of 3 were observed, and there was no selectivity
between regioisomers 2 and 3 (Table 3, Entries 4 and 5).
Table 3. Optimization of TMDS-induced AlCl3-assisted regioselec-
tive ring opening of 4,6-O-benzylidene acetal 1.
Entry
AlCl3
[equiv.]
Conv. [%]
Yield of 3
Ratio 3/2
[%]
1
2
3
4
5
3
2
1.5
1
100
100
100
95
56
86
88
33
27
19:1
10:1
11:1
1:1.2
1.1:1
0.5
62
With the optimized reaction conditions (1 equiv. TMDS,
1.5 equiv. AlCl3, CH2Cl2, –78 °C to r.t., 4 h), we examined
the reduction of carbohydrate acetals bearing various pro-
tecting groups to check the compatibility of this reagent
system (Table 4). When benzyl-protected glucosyl, galacto-
syl, and mannosyl acetals 1, 4, and 6 were reduced by
TMDS/AlCl3, the corresponding 4-ether 3, 29, and 30 were
isolated in 88, 80, and 86% yield (Table 4, Entries 1–3). As
to acyl-protected benzylidene acetals 8, 10, and 12, the re-
gioselectivity of the C–O bond cleavage was remarkably
shifted, all furnishing 6-ethers as the main products in
good-to-excellent yields (Table 4, Entries 4–6). When it
comes to unsubstituted 4,6-O-benzylidene acetals, acetal
rings were also opened on O4 positions like acyl-protected
acetals (Table 4, Entries 7–10). Compared with TMDS/Cu-
(OTf)2 (Table 2, Entries 7–10), the TMDS/AlCl3 reducing
system gave higher yields for these benzyl ethers of unpro-
tected methyl glycosides.
Next, 4,6-O-alkylidene glucosyl acetals were reduced by
TMDS/AlCl3 system to prepare 6-O-alkyl carbohydrate-
based surfactants. Corresponding 6-ethers 33–36 were ob-
tained, in concordance with the regioselectivity of other un-
protected benzylidene glycosyl acetals. This synthetic route
for carbohydrate long chain ethers is also concise and avo-
ids the main drawbacks of the already reported methodolo-
gies, as mentioned before. Moreover, TMDS/AlCl3 consti-
tutes a good complementary system to TMDS/Cu(OTf)2,
as both 6-ethers and 4-ethers can be synthesized by using
[a] Reaction conditions: TMDS (1.5 equiv.), Cu(OTf)2 (5 mol-%),
CH2Cl2, r.t., 4 h (Entries 1–10) and overnight (Entries 11–14).
[b] Acetal 23 (20%) was recovered. [c] Acetal 25 (32%) was reco-
vered. [d] Acetal 27 (25%) was recovered.
1962
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Regioselective Ring Cleavage of Hexopyranosyl Acetals to Ethers
Table 4. Reductive ring opening of 4,6-O-benzylidene glycosyl acet- these two pathways. Finally, being common to both sys-
als to the corresponding ethers under optimized TMDS/AlCl3 con-
ditions.
tems, TMDS demonstrates its efficiency as a dual-purpose
reductant, allowing the preparation of two different ether
regioisomers starting from the same carbohydrate acetal.
Conclusions
In conclusion, 1,1,3,3-tetramethyldisiloxane (TMDS) has
been successfully developed as a safe, efficient, and dual-
purpose reductant for the highly regioselective ring cleavage
of 4,6-O-benzylidene and alkylidene glycosyl acetals. The
reactions were either catalyzed by Cu(OTf)2 or assisted by
AlCl3, yielding primary or secondary ethers. Furthermore,
these novel protocols were applied in the direct and selective
reduction of acetal rings on unprotected hexopyranosides,
affording a straightforward pathway to prepare carbo-
hydrate-based long aliphatic chain ethers.
Experimental Section
General: The reported products in this paper are mainly known
products and have already been described in the literature.[4c,5,14a,22]
All purchased chemicals and reagents were of high commercially
1
available grade. Solvents were purified by standard procedures. H
NMR and 13C NMR spectra were recorded with a Bruker ALX-
300, DRX-300, or DRX 400 spectrometer in solvents using tet-
ramethylsilane as the internal standard (chemical shifts in ppm).
All reactions were monitored by TLC (thin-layer chromatography)
with detection by UV or by spraying with 6 n H2SO4 and charring
at 300 °C. Optical rotations were measured by using a Perkin–El-
mer 343 polarimeter at room temperature and a 10-cm 1-mL cell.
High-resolution mass spectra (HRMS) were recorded with a
Bruker Micro TOF-Q II spectrometer using standard conditions.
General Procedure for the TMDS/Cu(OTf)2 Regioselective Re-
duction Reactions: To a solution of 4,6-O-glycosyl acetal (0.2 mmol)
in CH2Cl2 (1.5 mL) was added Cu(OTf)2 (3.7 mg, 0.01 mmol,
5 mol-%) and 1,1,3,3-tetramethyldisiloxane (TMDS; 40.0 mg,
0.3 mmol, 1.5 equiv.) at room temperature. After stirring overnight,
the mixture was diluted with CH2Cl2, washed with HCl aq. and
water, dried with MgSO4, filtered, and concentrated. The crude
product was then purified by column chromatography.
Methyl 2,3,6-Tri-O-benzyl-α-D-glucopyranoside (2): Yield: 83%;
colorless syrup. Rf (cyclohexane/EtOAc, 3:2) = 0.63. [α]D = +37.5
(c = 0.12, CH2Cl2). 1H NMR (300 MHz, CDCl3): δ = 7.55–7.14
(m, 15 H), 5.01 (d, J = 11.4 Hz, 1 H), 4.76 (t, J = 11.1 Hz, 2 H),
4.71–4.63 (m, 2 H), 4.57 (d, J = 5.5 Hz, 2 H), 3.80 (t, J = 9.1 Hz,
1 H), 3.76–3.66 (m, 3 H), 3.66–3.58 (m, 1 H), 3.54 (dd, J = 9.5,
3.5 Hz, 1 H), 3.39 (s, 3 H) ppm. HRMS (ESI): calcd. for
C28H32NaO6 [M + Na]+ 487.2097; found 487.2091.
Methyl 2,3,6-Tri-O-benzyl-α-D-galactopyranoside (5): Yield: 81%;
colorless syrup. Rf (cyclohexane/EtOAc, 3:2) = 0.72. [α]D = +56 (c
1
= 0.21, CH2Cl2). H NMR (300 MHz, CDCl3): δ = 7.48–7.15 (m,
15 H), 4.80 (dd, J = 11.8, 6.5 Hz, 2 H), 4.73 (d, J = 6.1 Hz, 1 H),
4.68 (s, 2 H), 4.57 (d, J = 4.4 Hz, 2 H), 4.05 (s, 1 H), 3.93–3.84 (m,
3 H), 3.76–3.63 (m, 2 H), 3.38 (s, 3 H), 2.60 (s, 1 H) ppm. HRMS
(ESI): calcd. for C28H32NaO6 [M + Na]+ 487.2097; found 487.2084.
[a] Reaction conditions: TMDS (1 equiv.), AlCl3 (1.5 equiv.),
CH2Cl2, –78 °C to r.t., 4 h (Entries 1–10) and overnight (En-
tries 11–14). [b] Acetal 23 (30%) was recovered. [c] Acetal 25 (15%)
was recovered. [d] Acetal 27 (35%) was recovered.
Methyl 2,3,6-Tri-O-benzyl-α-D-mannopyranoside (7): Yield: 87%;
colorless syrup. Rf (cyclohexane/EtOAc, 2:1) = 0.68. [α]D = –6.3 (c
1
= 0.27, CH2Cl2). H NMR (300 MHz, CDCl3): δ = 7.49–7.17 (m,
Eur. J. Org. Chem. 2012, 1960–1966
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1963

Y.-J. Zhang, W. Dayoub, G.-R. Chen, M. Lemaire
FULL PAPER
15 H), 4.80 (d, J = 1.4 Hz, 1 H), 4.68 (d, J = 4.9 Hz, 2 H), 4.65–
4.56 (m, 3 H), 4.51 (d, J = 11.8 Hz, 1 H), 4.04 (d, J = 9.4 Hz, 1
Methyl 4-O-Pentyl-α-
D-glucopyranoside (22): Yield: 42%; white so-
lid. Rf (EtOH/EtOAc, 1:10) = 0.50. [α]D = +85 (c = 0.06, CH2Cl2).
H), 3.84–3.67 (m, 5 H), 3.36 (s, 3 H), 2.37 (br. s, 1 H) ppm. HRMS 1H NMR (300 MHz, CDCl3): δ = 4.73 (d, J = 3.8 Hz, 1 H), 3.95–
(ESI): calcd. for C28H32NaO6 [M + Na]+ 487.2097; found 487.2088.
Methyl 2,3-Di-O-acetyl-6-O-benzyl-α- -glucopyranoside (9): Yield:
93%; colorless syrup. Rf (cyclohexane/EtOAc, 2:3) = 0.68. [α]D
3.87 (m, 1 H), 3.87–3.76 (m, 2 H), 3.70–3.60 (m, 2 H), 3.58–3.53
(m, 1 H), 3.49 (d, J = 9.5 Hz, 1 H), 3.45–3.37 (m, 4 H), 2.22 (br.
s, 3 H), 1.63–1.55 (m, 2 H), 1.36–1.29 (m, 4 H), 0.89 (t, J = 7.0 Hz,
3 H) ppm. 13C NMR (101 MHz, CDCl3): δ = 99.8, 82.8, 73.4, 72.9,
71.2, 70.4, 62.7, 55.5, 30.2, 28.4, 22.7, 14.3 ppm. HRMS (ESI):
calcd. for C12H24NaO6 [M + Na]+ 287.1471; found 287.1454.
D
=
1
+106 (c = 0.40, CH2Cl2). H NMR (300 MHz, CDCl3): δ = 7.45–
7.22 (m, 5 H), 5.32 (t, J = 9.3 Hz, 1 H), 4.97–4.83 (m, 2 H), 4.69–
4.54 (m, 2 H), 3.88–3.69 (m, 4 H), 3.40 (s, 3 H), 2.09 (s, 3 H), 2.08
(s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 171.6, 170.4, 137.9,
128.5, 127.8, 127.7, 96.9, 73.8, 73.2, 70.9, 70.4, 70.2, 69.5, 55.3,
21.0, 20.9 ppm. HRMS (ESI): calcd. for C18H24NaO8 [M + Na]+
391.1369; found 391.1353.
Methyl 4-O-Octyl-α-D-glucopyranoside (24): Yield: 57%; white so-
lid. Rf (EtOH/EtOAc, 1:10) = 0.71. [α]D = +65.7 (c = 0.07,
1
CH2Cl2). H NMR (300 MHz, CDCl3): δ = 4.74 (d, J = 3.8 Hz, 1
H), 4.00–3.90 (m, 1 H), 3.89–3.79 (m, 2 H), 3.79–3.57 (m, 3 H),
3.57–3.45 (m, 2 H), 3.43 (s, 3 H), 2.17 (br. s, 3 H), 1.65–1.54 (m, 2
H), 1.32–1.21 (m, 10 H), 0.87 (t, J = 6.5 Hz, 3 H) ppm. 13C NMR
(101 MHz, CDCl3): δ = 99.8, 82.8, 73.4, 72.9, 71.2, 70.4, 62.7, 55.5,
32.0, 30.5, 29.6, 29.4, 26.2, 22.8, 14.2 ppm. HRMS (ESI): calcd. for
C15H30NaO6 [M + Na]+ 329.1940; found 329.1934.
Methyl 2,3-Di-O-benzoyl-6-O-benzyl-α-D-glucopyranoside (11):
Yield: 67%; colorless syrup. Rf (cyclohexane/EtOAc, 3:1) = 0.31.
1
[α]D = +100 (c = 0.02, CH2Cl2). H NMR (300 MHz, CDCl3): δ =
8.05–7.92 (m, 4 H), 7.54–7.46 (m, 2 H), 7.42–7.27 (m, 9 H), 5.85–
5.75 (m, 1 H), 5.27 (dd, J = 10.2, 3.6 Hz, 1 H), 5.16 (d, J = 3.6 Hz,
1 H), 4.66 (d, J = 5.3 Hz, 2 H), 4.06–3.93 (m, 2 H), 3.91–3.79 (m,
2 H), 3.44 (s, 3 H) ppm. 13C NMR (101 MHz, CDCl3): δ = 167.2,
166.1, 137.9, 133.4, 130.2, 130.0, 129.9, 129.5, 129.3, 128.5, 128.5,
128.4, 127.8, 127.8, 97.2, 74.1, 73.8, 71.6, 70.5, 70.4, 69.5,
55.5 ppm. HRMS (ESI): calcd. for C28H28NaO8 [M + Na]+
515.1682; found 515.1682.
Methyl 4-O-Decanyl-α-D-glucopyranoside (26): Yield: 52%; white
solid. Rf (EtOH/EtOAc, 1:10) = 0.74. [α]D = +63.3 (c = 0.03,
1
CH2Cl2). H NMR (300 MHz, CDCl3): δ = 4.74 (d, J = 3.8 Hz, 1
H), 4.00–3.91 (m, 1 H), 3.90–3.80 (m, 2 H), 3.70–3.61 (m, 2 H),
3.57 (dd, J = 9.2, 3.7 Hz, 1 H), 3.51 (t, J = 9.2 Hz, 1 H), 3.47–3.37
(m, 4 H), 2.02 (br. s, 3 H), 1.73–1.50 (m, 4 H), 1.33–1.22 (m, 12
H), 0.88 (t, J = 6.6 Hz, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ
= 99.8, 82.9, 73.4, 73.0, 71.1, 70.5, 62.8, 55.5, 32.0, 30.5, 29.8, 29.7,
29.6, 29.5, 26.2, 22.8, 14.3 ppm. HRMS (ESI): calcd. for
C17H34NaO6 [M + Na]+ 357.2253; found 357.2243.
Methyl
2,3-Di-O-pivaloyl-4,6-O-benzylidene-α-D-glucopyranoside
(13): Yield: 86%; colorless syrup. Rf (cyclohexane/EtOAc, 2:1) =
0.74. [α]D = +90 (c = 0.11, CH2Cl2). 1H NMR (300 MHz, CDCl3):
δ = 7.33 (dd, J = 6.7, 3.2 Hz, 2 H), 7.29–7.21 (m, 3 H), 5.55 (t, J
= 9.8 Hz, 1 H), 5.43 (s, 1 H), 4.86 (d, J = 3.8 Hz, 1 H), 4.78 (dd,
J = 9.9, 3.8 Hz, 1 H), 4.23 (dd, J = 10.1, 4.7 Hz, 1 H), 3.84 (td, J
= 9.9, 4.7 Hz, 1 H), 3.68 (t, J = 10.2 Hz, 1 H), 3.58 (t, J = 9.6 Hz,
1 H), 3.30 (s, 3 H), 1.11 (s, 9 H), 1.09 (s, 9 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 178.0, 177.0, 137.1, 128.9, 128.2, 126.0,
101.2, 97.8, 79.5, 71.5, 68.9, 68.6, 62.4, 55.6, 38.8, 38.8, 27.2, 27.0,
27.0, 27.0 ppm. HRMS (ESI): calcd. for C24H34NaO8 [M + Na]+
473.2151; found 473.2153.
Methyl 4-O-Dodecyl-α-D-glucopyranoside (28): Yield: 45%; white
solid. Rf (EtOH/EtOAc, 1:10) = 0.83. [α]D = +70 (c = 0.06,
1
CH2Cl2). H NMR (300 MHz, CDCl3): δ = 4.74 (d, J = 3.8 Hz, 1
H), 3.99–3.90 (m, 1 H), 3.86 (dd, J = 11.7, 3.7 Hz, 1 H), 3.79 (dd,
J = 11.7, 4.4 Hz, 1 H), 3.75–3.66 (m, 1 H), 3.65–3.62 (m, 1 H),
3.62–3.53 (m, 2 H), 3.49 (d, J = 9.4 Hz, 1 H), 3.44 (s, 3 H), 3.39
(d, J = 9.0 Hz, 1 H), 1.63–1.55 (m, 2 H), 1.29–1.23 (m, 18 H), 0.88
(t, J = 6.6 Hz, 3 H) ppm. 13C NMR (101 MHz, CDCl3): δ = 99.8,
82.9, 73.4, 72.9, 71.2, 70.5, 62.7, 55.5, 32.1, 30.5, 29.8, 29.8, 29.7,
29.6, 29.5, 26.2, 22.8, 14.3 ppm. HRMS (ESI): calcd. for
C19H38NaO6 [M + Na]+ 385.2566; found 385.2555.
Methyl 4-O-Benzyl-α-D-glucopyranoside (15): Yield: 49%; white so-
lid. Rf (EtOAc) = 0.47. [α]D = +125 (c = 1, CHCl3). 1H NMR
(300 MHz, [D6]DMSO): δ = 7.45–7.38 (m, 2 H), 7.35–7.24 (m, 3
H), 5.09 (d, J = 6.5 Hz, 1 H), 4.94 (d, J = 7.1 Hz, 1 H), 4.79 (s, 2
H), 4.56 (d, J = 3.5 Hz, 1 H), 4.51 (t, J = 5.9 Hz, 1 H), 3.66 (ddd,
J = 11.6, 5.7, 2.0 Hz, 1 H), 3.54–3.42 (m, 2 H), 3.30 (s, 3 H) ppm.
13C NMR (75 MHz, [D6]DMSO): δ = 139.7, 127.8, 127.4, 126.9,
99.8, 82.3, 73.7, 72.8, 71.8, 69.8, 60.8, 54.2 ppm. HRMS (ESI):
calcd. for C14H20NaO6 [M + Na]+ 307.1158; found 307.1151.
General Procedure for the TMDS/AlCl3 Regioselective Reduction
Reactions: To a solution of 4,6-O-glycosyl acetal (0.2 mmol) in
CH2Cl2 (1.5 mL) was added AlCl3 (40.0 mg, 0.3 mmol, 1.5 equiv.)
and TMDS (40.0 mg, 0.3 mmol, 1.5 equiv.) at –78 °C. After stirring
at room temperature overnight, the mixture was diluted with
CH2Cl2, washed with HCl aq. and water, dried with MgSO4, fil-
tered, and concentrated. The crude product was then purified by
column chromatography.
Methyl 6-O-benzyl-α-D-mannopyranoside (18): Yield: 83%; white
solid. Rf (EtOH/EtOAc, 1:5) = 0.73. [α]D = +69.7 (c = 0.71,
CHCl3). 1H NMR (300 MHz, [D6]DMSO): δ = 7.49–7.20 (m, 5 H),
4.83 (d, J = 11.3 Hz, 1 H), 4.52 (s, 3 H), 3.72 (d, J = 10.0 Hz, 1
H), 3.60 (s, 1 H), 3.56–3.33 (m, 6 H), 3.25 (s, 3 H) ppm. 13C NMR
(75 MHz, [D6]DMSO): δ = 138.8, 128.2, 127.4, 127.3, 101.0, 72.4,
72.2, 71.0, 70.1, 70.1, 66.9, 54.0 ppm. HRMS (ESI): calcd. for
C14H20NaO6 [M + Na]+ 307.1158; found 307.1152.
Methyl 2,3,4-Tri-O-benzyl-α-D-glucopyranoside (3): Yield: 88%;
white solid. Rf (cyclohexane/EtOAc, 3:2) = 0.40. [α]D = +50 (c =
1
0.04, CH2Cl2). H NMR (300 MHz, CDCl3): δ = 7.42–7.25 (m, 15
H), 4.99 (d, J = 10.9 Hz, 1 H), 4.89 (d, J = 11.1 Hz, 1 H), 4.86–
4.81 (m, 1 H), 4.77 (d, J = 9.2 Hz, 1 H), 4.67 (d, J = 7.2 Hz, 1 H),
4.63 (d, J = 6.1 Hz, 1 H), 4.57 (d, J = 3.6 Hz, 1 H), 4.01 (t, J =
9.0 Hz, 1 H), 3.81–3.63 (m, 3 H), 3.58–3.46 (m, 2 H), 3.37 (s, 3 H)
ppm. HRMS (ESI): calcd. for C28H32NaO6 [M + Na]+ 487.2097;
found 487.2090.
Phenyl 6-O-(Phenylmethyl)-β-D-glucopyranoside (20): Yield: 63%;
1
white solid. Rf (EtOH/EtOAc, 1:10) = 0.52. H NMR (300 MHz,
CD3OD): δ = 7.44–7.20 (m, 7 H), 7.21–7.08 (m, 2 H), 7.01 (t, J =
7.3 Hz, 1 H), 4.56 (s, 2 H), 4.10 (dd, J = 14.3, 7.1 Hz, 2 H), 3.89
(d, J = 8.9 Hz, 1 H), 3.77–3.56 (m, 2 H), 3.55–3.26 (m, 4 H) ppm.
Methyl 2,3,4-Tri-O-benzyl-α-D-galactopyranoside (29): Yield: 80%;
13C NMR (75 MHz, CD3OD): δ = 159.0, 139.7, 130.4, 129.3, 128.7, colorless syrup. Rf (cyclohexane/EtOAc, 3:2) = 0.25. 1H NMR
128.5, 123.4, 117.8, 102.2, 78.0, 77.1, 74.9, 74.3, 71.7, 70.8 ppm.
HRMS (ESI): calcd. for C19H22NaO6 [M + Na]+ 369.1314; found
369.1310.
(300 MHz, CDCl3): δ = 7.44–7.27 (m, 15 H), 4.98 (d, J = 11.6 Hz,
1 H), 4.93–4.81 (m, 2 H), 4.76 (d, J = 11.8 Hz, 1 H), 4.72–4.62 (m,
3 H), 4.06 (dd, J = 10.0, 3.6 Hz, 1 H), 3.94 (dd, J = 10.0, 2.8 Hz,
1964
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 1960–1966

Regioselective Ring Cleavage of Hexopyranosyl Acetals to Ethers
1 H), 3.88 (d, J = 2.6 Hz, 1 H), 3.77–3.65 (m, 2 H), 3.77–3.65 (m,
1 H), 3.36 (s, 3 H) ppm. 13C NMR (101 MHz, CDCl3): δ = 138.9,
138.6, 138.3, 128.8, 128.6, 128.6, 128.5, 128.2, 127.1, 99.0, 79.3,
77.4, 76.6, 75.2, 74.6, 73.8, 70.4, 62.6, 55.5 ppm.
δ = 99.60, 74.5, 72.2, 72.1, 71.2, 70.5, 70.4, 55.3, 32.0, 29.8, 29.8,
29.8, 29.7, 29.7, 29.5, 26.2, 22.8, 14.2 ppm. HRMS (ESI): calcd. for
C19H38NaO6 [M + Na]+ 385.2566; found 385.2557.
General Procedure for the Preparation of Long Alkyl Chain Glucosyl
Acetals: To a solution of methyl α-d-glucopyranoside (1941.8 mg,
10 mmol) in DMF (15 mL) was added the long alkyl chain alde-
hyde (10 mmol, 1 equiv.) and (1R)-10-camphorsulfonic acid (CSA;
232.3 mg, 1 mmol, 0.1 equiv.). After stirring at 90 °C overnight, the
mixture was concentrated, diluted with CH2Cl2, washed with water,
dried with MgSO4, filtered, and concentrated. The crude product
was then purified by column chromatography.
Methyl 2,3,4-Tri-O-benzyl-α-D-mannopyranoside (30): Yield: 86%;
colorless syrup. Rf (cyclohexane/EtOAc, 2:1) = 0.37. [α]D = +8.7 (c
1
= 0.39, CH2Cl2). H NMR (300 MHz, CDCl3): δ = 7.54–7.25 (m,
15 H), 4.96 (d, J = 10.9 Hz, 1 H), 4.80 (d, J = 12.4 Hz, 1 H), 4.76–
4.67 (m, 3 H), 4.64 (s, 2 H), 4.00–3.76 (m, 5 H), 3.69–3.59 (m, 1 H),
3.31 (s, 3 H), 1.70 (br. s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ
= 138.8, 138.7, 138.6, 128.7, 128.4, 128.2, 128.0, 127.9, 99.7, 80.5,
77.8, 77.4, 76.9, 75.5, 75.2, 75.0, 73.3, 72.5, 72.3, 62.8, 55.1 ppm.
HRMS (ESI): calcd. for C28H32NaO6 [M + Na]+ 487.2097; found
487.2091.
Methyl 4,6-O-Pentylidene-α-D-glucopyranoside (21): Yield: 53%;
white solid. Rf (cyclohexane/EtOAc, 3:2) = 0.34. [α]D = +68.2 (c =
0.28, CH2Cl2). 1H NMR (300 MHz, CDCl3): δ = 4.73 (dd, J = 8.3,
3.5 Hz, 1 H), 4.08 (dd, J = 9.9, 4.6 Hz, 1 H), 3.82 (t, J = 9.2 Hz, 1
H), 3.71–3.48 (m, 4 H), 3.39 (s, 3 H), 3.22 (t, J = 9.3 Hz, 1 H), 2.43
(br. s, 2 H), 1.74–1.54 (m, 2 H), 1.42–1.21 (m, 4 H), 0.86 (t, J =
7.0 Hz, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 102.8, 99.9,
80.5, 73.0, 71.6, 68.5, 62.6, 55.5, 34.0, 26.2, 22.6, 14.0 ppm. HRMS
(ESI): calcd. for C12H22NaO6 [M + Na]+ 285.1314; found 285.1298.
Methyl 6-O-Benzyl-α-D-glucopyranoside (31): Yield: 80%; white so-
1
lid. Rf (EtOH/EtOAc, 1:5) = 0.52. [α]D = +93 (c = 1, CHCl3). H
NMR (300 MHz, [D6]DMSO): δ = 7.47–7.17 (m, 5 H), 4.98 (d, J
= 5.8 Hz, 1 H), 4.75 (dd, J = 17.6, 5.6 Hz, 2 H), 4.60–4.46 (m, 3
H), 3.68 (d, J = 9.0 Hz, 1 H), 3.57–3.44 (m, 2 H), 3.27 (s, 3 H)
ppm. 13C NMR (101 MHz, [D6]DMSO): δ = 138.6, 128.2, 127.3,
127.2, 99.7, 73.4, 72.2, 71.9, 71.1, 70.4, 69.8, 54.3 ppm. HRMS
(ESI): calcd. for C14H20NaO6 [M + Na]+ 307.1158; found 307.1153.
Methyl 4,6-O-Octylidene-α-D-glucopyranoside (23): Yield: 57%;
white solid. Rf (cyclohexane/EtOAc, 3:2) = 0.31. [α]D = +98 (c =
0.61, CH2Cl2). 1H NMR (300 MHz, CDCl3): δ = 4.75 (d, J =
3.8 Hz, 1 H), 4.54 (t, J = 5.0 Hz, 1 H), 3.87 (t, J = 9.3 Hz, 1 H),
3.65 (dd, J = 10.0, 4.6 Hz, 1 H), 3.59 (dd, J = 9.3, 3.9 Hz, 2 H),
3.50 (t, J = 10.2 Hz, 2 H), 3.43 (s, 3 H), 3.26 (t, J = 9.3 Hz, 1 H),
1.71–1.60 (m, 2 H), 1.39–1.18 (m, 10 H), 0.88 (t, J = 6.7 Hz, 3 H)
ppm. 13C NMR (75 MHz, CDCl3): δ = 102.8, 100.0, 80.5, 72.9,
71.3, 68.5, 62.6, 55.4, 34.3, 31.8, 29.5, 29.2, 24.1, 22.7, 14.1 ppm.
HRMS (ESI): calcd. for C15H28NaO6 [M + Na]+ 327.1784; found
329.1786.
Methyl 6-O-Benzyl-α-D-galactopyranoside (32): Yield: 82%; white
solid. Rf (EtOH/EtOAc, 1:5) = 0.49. [α]D = +102 (c = 0.2, CHCl3).
1H NMR (300 MHz, [D6]DMSO): δ = 7.43–7.21 (m, 5 H), 4.65–
4.41 (m, 6 H), 3.76 (t, J = 5.8 Hz, 1 H), 3.68 (br. s, 1 H), 3.63–3.46
(m, 4 H), 3.26 (s, 3 H) ppm. 13C NMR (75 MHz, [D6]DMSO): δ =
138.6, 128.2, 127.3, 100.1, 72.2, 69.9, 69.5, 69.3, 69.3, 68.3,
54.5 ppm. HRMS (ESI): calcd. for C14H20NaO6 [M + Na]+
307.1158; found 307.1162.
Methyl 6-O-Pentyl-α-D-glucopyranoside (33): Yield: 86%; white so-
Methyl 4,6-O-Decanylidene-α-D-glucopyranoside (25): Yield: 57%;
lid. Rf (EtOH/EtOAc, 1:10) = 0.39. [α]D = +98 (c = 0.16, CH2Cl2).
1H NMR (300 MHz, CDCl3): δ = 4.74 (d, J = 3.6 Hz, 1 H), 4.14
(br. s, 3 H), 3.87–3.60 (m, 4 H), 3.58–3.41 (m, 4 H), 3.40 (s, 3 H),
1.66–1.50 (m, 2 H), 1.37–1.26 (m, 4 H), 0.88 (t, J = 6.8 Hz, 3 H)
ppm. 13C NMR (101 MHz, CDCl3): δ = 99.6, 74.4, 72.2, 72.1, 71.1,
70.4, 70.4, 55.3, 29.4, 28.3, 22.6, 14.1 ppm. HRMS (ESI): calcd. for
C12H24NaO6 [M + Na]+ 287.1471; found 287.1468.
white solid. Rf (cyclohexane/EtOAc, 3:2) = 0.30. [α]D = +108 (c =
0.15, CH2Cl2). 1H NMR (300 MHz, CDCl3): δ = 4.71 (d, J =
3.8 Hz, 1 H), 4.50 (t, J = 5.0 Hz, 1 H), 4.11–4.03 (m, 1 H), 3.82 (t,
J = 9.3 Hz, 1 H), 3.57 (ddd, J = 13.1, 9.7, 4.2 Hz, 2 H), 3.46 (t, J
= 10.2 Hz, 1 H), 3.38 (s, 3 H), 3.36 (br. s, 2 H), 3.21 (t, J = 9.3 Hz,
1 H), 1.71–1.54 (m, 2 H), 1.41–1.31 (m, 2 H), 1.28–1.19 (m, 12 H),
0.84 (t, J = 6.7 Hz, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
102.8, 100.0, 80.5, 72.9, 71.5, 68.6, 62.6, 55.4, 34.3, 31.9, 29.6, 29.6,
29.5, 29.4, 24.2, 22.7, 14.2 ppm. HRMS (ESI): calcd. for
C17H32NaO6 [M + Na]+ 355.2097; found 355.2090.
Methyl 6-O-Octyl-α-D-glucopyranoside (34): Yield: 47%; white so-
lid. Rf (EtOH/EtOAc, 1:10) = 0.51. [α]D = +84 (c = 0.20, CH2Cl2).
1H NMR (300 MHz, CDCl3): δ = 4.75 (d, J = 3.3 Hz, 1 H), 4.01
(br. s, 3 H), 3.83–3.60 (m, 4 H), 3.60–3.43 (m, 4 H), 3.41 (s, 3 H),
1.75–1.47 (m, 2 H), 1.38–1.19 (m, 10 H), 0.87 (t, J = 6.5 Hz, 3 H)
ppm. 13C NMR (101 MHz, CDCl3): δ = 99.6, 74.4, 72.2, 72.1, 71.2,
70.5, 70.4, 55.3, 32.0, 29.7, 29.6, 29.4, 26.2, 22.8, 14.2 ppm. HRMS
(ESI): calcd. for C15H30NaO6 [M + Na]+ 329.1940; found 329.1928.
Methyl 4,6-O-Dodecylidene-α-D-glucopyranoside (27): Yield: 61%;
white solid. Rf (cyclohexane/EtOAc, 3:2) = 0.18. [α]D = +106 (c =
0.14, CH2Cl2). 1H NMR (300 MHz, CDCl3): δ = 4.69 (d, J =
3.7 Hz, 1 H), 4.48 (t, J = 5.0 Hz, 1 H), 4.05 (dd, J = 9.9, 4.6 Hz, 1
H), 3.90–3.62 (m, 3 H), 3.56 (ddd, J = 13.1, 9.5, 4.2 Hz, 2 H), 3.44
(t, J = 10.2 Hz, 1 H), 3.36 (s, 3 H), 3.20 (t, J = 9.3 Hz, 1 H), 1.68–
1.51 (m, 2 H), 1.39–1.29 (m, 2 H), 1.27–1.11 (m, 16 H), 0.83 (t, J
= 6.7 Hz, 3 H) ppm. HRMS (ESI): calcd. for C19H36NaO6 [M +
Na]+ 383.2410; found 383.2398.
Methyl 6-O-Decanyl-α-D-glucopyranoside (35): Yield: 63%; white
solid. Rf (EtOH/EtOAc, 1:10) = 0.53. [α]D = +82.4 (c = 0.29,
1
CH2Cl2). H NMR (300 MHz, CDCl3): δ = 4.73 (d, J = 3.6 Hz, 1
H), 4.34 (br. s, 3 H), 3.73 (t, J = 9.3 Hz, 1 H), 3.70–3.57 (m, 3 H),
3.56–3.41 (m, 4 H), 3.39 (s, 3 H), 1.64–1.49 (m, 2 H), 1.34–1.20 (m,
14 H), 0.86 (t, J = 6.6 Hz, 3 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 99.6, 74.4, 72.2, 72.0, 71.0, 70.6, 70.4, 55.2, 32.0, 29.7, 29.7,
29.7, 29.6, 29.4, 26.2, 22.8, 14.2 ppm. HRMS (ESI): calcd. for
C17H34NaO6 [M + Na]+ 357.2253; found 357.2243.
Acknowledgments
China Scholarship Council is warmly thanked for PhD grants to
Y.-J. Z. Financial support allocated in the framework of the Rhone-
Alps International Mobility (MIRA) collaborative program is
gratefully received.
Methyl 6-O-Dodecyl-α-D-glucopyranoside (36): Yield: 55%; white
solid. Rf (EtOH/EtOAc, 1:10) = 0.67. [α]D = +86 (c = 0.21,
1
CH2Cl2). H NMR (300 MHz, CDCl3): δ = 4.74 (d, J = 3.6 Hz, 1
H), 4.05 (br. s, 3 H), 3.74 (t, J = 9.2 Hz, 1 H), 3.70–3.58 (m, 3 H),
3.57–3.44 (m, 4 H), 3.41 (s, 3 H), 1.67–1.51 (m, 2 H), 1.38–1.18 (m,
18 H), 0.87 (t, J = 6.6 Hz, 3 H) ppm. 13C NMR (101 MHz, CDCl3):
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Received: November 23, 2011
Published Online: February 14, 2012
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