Synthesis of orthogonally protected l-glucose, l-mannose, and l-galactose from d-glucose

Article abstract of DOI:10.1016/j.tet.2012.04.001

An efficient route to orthogonally protected l-glucose, l-mannose, and l-galactose is described. Using the strategy to switch the functional groups at C1 and C5 of d-glucose, l-glucose is obtained via a key intermediate C-glycoside. Preparations of l-mannose and l-galactose derivatives from the orthogonally protected l-glucose were accomplished in good yields using the Lattrell-Dax method.

Full text of DOI:10.1016/j.tet.2012.04.001

Tetrahedron 68 (2012) 6981e6989
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of orthogonally protected
-glucose
L
-glucose,
L
-mannose, and -galactose from
L
D
*
*
Yangbing Li, Zhaojun Yin, Bo Wang, Xiang-Bao Meng , Zhong-Jun Li
The State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Science, Peking University, Beijing 100191, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient route to orthogonally protected
L
-glucose,
L
-mannose, and
-glucose,
-galactose derivatives from the orthogonally
-glucose were accomplished in good yields using the LattrelleDax method.
Ó 2012 Elsevier Ltd. All rights reserved.
L
-galactose is described. Using the
Received 16 December 2011
Received in revised form 26 March 2012
Accepted 1 April 2012
strategy to switch the functional groups at C1 and C5 of
termediate C-glycoside. Preparations of -mannose and
protected
D
L-glucose is obtained via a key in-
L
L
L
Available online 9 April 2012
Keywords:
Carbohydrates
L-Hexoses
Protecting groups
LattrelleDax method
1. Introduction
substrates for measuring the
mercial narunginase.11
a-L-mannosidase activity of com-
D
-Sugars are frequently used as sources of chiral centers in the
synthesis of complex natural products and bioactive compounds
because of their abundance in nature. On the contrary, use of
sugars1 in organic synthesis is limited because they are difficult to
obtain. In spite of their limited availability, -sugars are essential
In contrast to the
from natural sources. To meet the demands for
studies, it is necessary to develop an efficient method for their
synthesis. Numerous synthetic approaches toward -pyranosides
have been reported,12 including de novo syntheses,13 homologation
of shorter-chain sugars,13f,g,14 elaboration of -sugars2a,15 and en-
D
-isomers,
L
-sugars are much less available
L-sugars in various
L-
L
L
components of numerous bioactive oligosaccharides, antibiotics,
glycopeptides, terpene glycosides, as well as steroid glycosides and
D
zymatic synthesis.16 However, there are also other concerns in the
synthesis of oligosaccharides, such as difficulties associated with
the regioselective protection of different hydroxyl groups and the
challenges related with the stereoselective assembly of glycosidic
linkages.17 The efficient construction of orthogonally protected
monosaccharide building blocks can greatly facilitate the synthesis
clinically useful nucleosides.2 For examples,
L
-gulopyranosides are
the key constituents of the antitumor drug Bleomycin A23 and the
nucleoside antibiotic Adenomycin;4
-iduronic acid is a typical
component of mammalian dermatan sulfate, heparin, and heparan
sulfate.5 Free
-sugars also showed potential as noncaloric sweet-
eners6 and selective toxic insecticides.7 Wong and Kunz demon-
L
L
of diverse carbohydrates.18 We started to tackle the problem of
sugar synthesis by focusing on the design and synthesis of -hex-
oses with diverse protective groups.13a,19 Here we report an effi-
cient strategy for the synthesis of orthogonally protected -glucose,
-mannose, and -galactose, which can be utilized as versatile
synthetic precursors. The design is based on that -glucose can be
obtained from -glucose via pseudodesymmetrization of an in-
termediate -C-glycoside by switching the groups at C1 and C5.
This strategy takes advantage of latent symmetry elements that are
present in -glucose to produce
-glucose (Scheme 1).15d,20 Several
works with similar strategies have been published. -Glucose was
synthesized by hydroxymethylating reaction and oxidative de-
carboxylation reaction from 2,3,4,6-tetra-O-benzyl- -glucono-1,5-
lactone by Shiosaki, and a modified procedure was reported by
Smid et al.21 Wei synthesized several useful
-glucal derivates by
L-
strated that the use of
L-galactose derivatives in place of
L-fucose to
L
mimic Sialyl Lewis X could improve its bioactivity and stability.8
The mirror-image carbohydrate is often recognized as compo-
nents of biologically relevant molecules and the compounds con-
L
L
L
taining
agricultural value, which are superior to that of their
logs.9 Moreover,
-rhamnose and -mannose were found in extra-
cellular polysaccharide S-130, S-88, and S-198,10 which are useful in
the industry of food and medicine. The phenolic derivatives of
L-sugars often have biological activities of medicinal or
L
D-sugar ana-
D
L
L
b
L-
D
L
mannose that were found in some steroidal glycosides are potent
L
D
* Corresponding authors. Tel.: þ86 010 82801714; fax: þ86 010 82805496; e-mail
L
addresses: xbmeng@bjmu.edu.cn (X.-B. Meng), zjli@bjmu.edu.cn (Z.-J. Li).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.04.001

6982
Y. Li et al. / Tetrahedron 68 (2012) 6981e6989
eliminative decarboxylation from
methods for preparing L-sugars from D
D
-glycal derivatives.15d However,
-sugars, have so far seldom
concerned about efficient protecting groups strategy, with obvious
drawbacks in their application. The -sugars synthesized in this
L
paper with orthogonal protecting groups could be used more easily
and directly.
Scheme 2. Preparation of D-glucose derivative 5.
triethylsilane did not yield any product in CH2Cl2 at room tem-
perature within 1 week. However, we found that a larger amount of
Co2(CO)8 than that was used in the original reports greatly short-
ened the reaction time at elevated temperature. A moderate yield of
6 was given by using benzene as the solvent at 50 ꢀC for 48 h with
triethylsilane (Scheme 3), while a major byproduct 20 was obtained
in 20% yield and no a-C-glucoside was isolated. It was found high
temperature or long reaction time decreased the yield of 6. In ad-
dition, other silanes, such as PhMe2SiH and EtMe2SiH afforded
more complex products.
Scheme 1. Strategy for the synthesis of L-hexoses from D-glucose.
Hence, Our protocols involved five steps: (1) introduction
a permanent protecting group at C3 position of
lective protection of the hydroxyl group at C4 and C6 as an aryli-
dene actal followed by acylation at C1 and C2 position of -glucose,
(3) introduction of a -siloxymethyl group at C1 by Co2(CO)8 cat-
D-glucose, (2) se-
D
b
alyzed siloxymethylation reaction, (4) regioselective ring opening
of arylidene acetal, oxidation the hydroxyl group at C7 position, and
Scheme 3. Synthesis of C-glucoside derivative 6.
decarboxylation to provide the
L-glucose, (5) regioselective re-
moving the protective groups at C2 and C4 positions of
L
-glucose
The byproduct 20 was supposed to be derived from the 5b,
which is considered as the key intermediate in the Co2(CO)8 cata-
lyzed siloxymethylation (Fig. 1).25a,26 The anomeric acetoxy group
of compounꢁd 5 was first activated by silylation, and then displaced
by CoðCOÞ4 to give 5a. Subsequent migratory insertion of CO
resulted in an acylcobalt, which underwent oxidative addition to
triethylsilane and the following by reductive elimination to affor-
ded aldehyde 5b. While reduction of 5b by triethylsilane gave de-
sired product 6, electrophilic addition of this aldehyde by
Et3SiCo(CO)4 directed the reaction to afford 5c. This undesired ad-
duct, by following the same mechanism leading to 5b, was trans-
ferred into 5d. However, the elongated aldehyde seems more prone
to the addition of a second molecule of Et3SiCo(CO)4, rather than
triethylsilane effected reduction, to give a disilylated cobalt in-
derivative followed by epimerization of the hydroxyl groups with
the LattrelleDax22 method enabled the synthesis of differently
protected L-mannose and L-galactose derivatives (Scheme 1).
2. Results and discussion
Synthesis of the key intermediate C-glucoside derivative started
with the readily available 1,2:5,6-di-O-isopropylidene- -gluco-
a-D
furanose 1.23 A benzyl group was introduced to the hydroxyl group
of 1 with benzyl bromide and sodium hydride. Then the iso-
propylidene groups were removed with ion exchange resin (Hþ
form) in water.24 Subsequent regioselective protection of 4,6-diol of
compound 3 with p-methoxybenzylidene followed by acetylation
of the remaining hydroxyl groups afforded 5 in high overall yield
(Scheme 2).
termediate that finally gave rise to the formation of 20 by b-hydride
elimination. Similar result was reported by Murai.26c
The construction of
b
-C-glucoside 6 from 5 by the Co2(CO)8
After synthesis of C-glucoside, the oxidative cleavage of the
hydroxylmethyl group at C5 was explored. First, the TES protecting
group in C-glycoside 6 was replaced with a more stable TBDPS
protecting group. The acetyl group migrated to primary hydroxyl
position in nearly quantitative yield when 5 equiv tetra-n-buty-
lammonium fluride (TBAF) and 1.5 equiv HOAc was used in the
reaction. Similar result was also reported by Passacantilli et al., in
catalyzed siloxymethylation was then carefully investigated. Firstly,
t-BuMe2SiH was chosen in order to introduce a stable silyl ether
protective group. No product was observed within 24 h under the
same conditions reported in the original publication because of its
steric hindrance.25 High temperature and additional amount of
catalyst did not improve the reaction at all. The less bulky

Y. Li et al. / Tetrahedron 68 (2012) 6981e6989
6983
Fig. 1. Possible mechanism to obtain compounds 6 and 20.
which Bz group at C4 migrated to C6 in high yield when a triiso-
propylsilyl group at C6 was removed by TBAF.27 The migration re-
action could be hampered with different ratio of TBAF and HOAc. As
shown in Scheme 4, 5 equiv TBAF and 10 equiv HOAc completely
prevented the migration of acetyl group. The accurate control of
migration allowed us to obtain two different C-glycosides 7 and 8.
The protection of the remaining hydroxyl group with TBDPSCl gave
compounds 9 and 10 in good yield. Subsequent regioselective
cleavage of p-methoxybenzylidene was achieved in excellent yield
by using the protocol reported by Wei et al.,28 in which the 2,6-di-
tert-butyl-4-methylpyridine (DTBMP) was added as an acid scav-
enger to improve selectivity of the reaction. The subsequent oxi-
dation of primary hydroxyl groups in 11 and 12 with 2,2,6,6-
tetramethyl-1-piperidinyloxy (TEMPO)/iodosobenzene diacetate
(DIB) reagent system provided the carboxylic acid derivatives,29
which were directly used in the next reaction. The desired L-glu-
cose derivatives 13 and 14 were obtained by oxidative de-
carboxylation mediated by lead tetraacetate.30 Better yields were
obtained with benzeneepyridine mixture as solvent compared
with THFeHOAc mixture or benzene only. The
pound 13 was obtained by inspection of relevant 1H NMR signals,
while the ratio of compound 14 was based on isolated yield.
After the establishment of an efficient route to -glucose, we
went on to the examination of the synthesis of -mannose and
a:b ratio of com-
a:b
L
L
L-
galactose was then examined. The PMB group in compound 14
b
was selectively removed by TFA at low temperature,18a then a two-
step, one pot LattrelleDax epimerization reaction with 15 was
carried out smoothly to give the desired
-mannose derivative 16.31
L
It has been reported that the equatorial neighboring ester groups
could induce formation of inversion compounds in good yields,32
but migration of neighboring acetyl group from C1 to C2 has not
been reported before (Scheme 5).
The hydroxyl group at C1 of compound 16 was epimerized to
axial anomer from equatorial anomer when compound 15 was
converted to 16. The newly formed
a hydroxyl group in 16 was
confirmed by the coupling constant of anomeric carbon and
anomeric hydrogen. The coupling constant is 171.8 Hz. It suggests
that the acetyl group at C1 might participate in the reaction and
a five-membered ring was generated first. After that water in DMF
attacked the C1 from the opposite face of the five-membered ring
and ring was opened with the acetyl group migrated to the C2 to
form compound 16 (Fig. 2).
Scheme 4. Synthesis of L-glucose derivatives 13 and 14.

6984
Y. Li et al. / Tetrahedron 68 (2012) 6981e6989
by trace water to produce either a free 6-hydroxyl group or a free 4-
hydroxyl group (Fig. 3). Similar remote participation mechanism
was found in LattrelleDax epimerization reaction of hydroxyl
group at C2 position with an acetyl group at C4 position.33 Firstly,
H2O was chosen to promote the migration reaction to obtain 19, but
the products of the reaction were still complex. Then we tried to
inhibit the migration reaction to obtain 18. In order to suppress the
neighboring group participation and to prevent migration, we
chose toluene instead of CH3CN as the solvent, because the
neighboring group participation effect is disfavored in nonpolar
solvents.18e,34 Finally, the
-galactose derivative 18 was obtained as
L
the sole product in good yield when the reaction was carried out in
Scheme 5. Synthesis of L-mannose derivative 16.
toluene with TBANO2 at 50 ꢀC.
Fig. 2. Possible mechanism to obtain compound 16.
The TBDPS group in 14
b can also be selectively removed by
TBAF/HOAc. However, the LattrelleDax epimerization reaction with
17 gave complex products with NaNO2 in dry DMF or wet DMF as
shown in Scheme 6. Therefore, we changed the solvent from DMF
to acetonitrile and used tetra-n-butylammonium nitrite (TBANO2)
instead of sodium nitrite because of its low solubility in acetonitrile.
The desired product 19 was obtained in 32% yield, along with 18
and trace unidentified by-products. The results support that acetyl
group at C6 position might participate in this inversion reaction
where a six-membered ring was generated first and then opened
Fig. 3. Remote group participation mechanism to obtain compounds 18 and 19.
3. Conclusion
In summary, we have developed an efficient route for the syn-
thesis of orthogonally protected L-glucose from D-glucose with the
strategy to switch the functional groups at C1 and C5, the strategy
was achieved by using cobalt carbonyl catalyzed siloxymethylation
and lead acetate mediated oxidative decarboxylation as key re-
actions. Protective groups at C2 and C4 were readily removed to
produce the corresponding mono-ols, which were utilized for the
synthesis of differently protected
L-mannose and L-galactose de-
rivatives with the LattrelleDax method. Rapid access to these ver-
satile building blocks will facilitate the construction of
containing oligosaccharides.
L-hexoses
4. Experimental section
4.1. General procedures
All chemicals were purchased as reagent grade and used with-
out further purification, unless otherwise noted. Dichloromethane
was distilled over calcium hydride. Benzene, THF, and toluene were
distilled over sodium. Analytical TLC was performed on silica gel60
F254 precoated on glass plates, with detection by fluorescence and/
or by staining with 5% concentrated sulfuric acid in EtOH. Column
chromatography was performed on silica gel (230e400 mesh).
Optical rotations were measured using a polarimeter at 25 ꢀC. 1H
NMR spectra were recorded using CDCl3, CD3COCD3 or C6D6 as
solvents at 25 ꢀC. Chemical shifts (in ppm) were referenced with
tetramethylsilane (
CD3COCD3
¼2.05 ppm) or C6D6
were calibrated with CDCl3
d
¼0 ppm) in CDCl3 and were calibrated with
(
d
(d
¼7.16 ppm). 13C NMR spectra
(d
¼77.16 ppm), CD3COCD3
(d¼29.84 ppm) or C6D6
(
d¼128.06 ppm). The positions of
hydroxyl groups of mono-ols were determined by the 2D COSY.
High-resolution mass spectrum (HRMS) was obtained using
Scheme 6. Synthesis of L-galactose derivative 18.

Y. Li et al. / Tetrahedron 68 (2012) 6981e6989
6985
electrospray ionization (ESI) mass spectroscopy. Air-sensitive re-
actions were performed in flame-dried glassware under argon.
Organic solvents were evaporated with a rotary evaporator.
55%) as oil. 1H NMR (400 MHz, CDCl3):
d
7.42 (d, J¼8.7 Hz, 2H),
7.33e7.26 (m, 4H), 6.91 (d, J¼8.8 Hz, 2H), 5.53 (s, 1H), 4.96 (dd,
J¼8.8, 9.7 Hz, 1H), 4.88 (d, J¼12.0 Hz, 1H), 4.66 (d, J¼12.0 Hz, 1H),
4.34 (dd, J¼10.5 Hz, 4.9, 1H), 3.81 (s, 3H), 3.79e3.62 (m, 6H),
3.53e3.41 (m, 2H), 1.97 (s, 3H), 0.94 (t, J¼7.9 Hz, 9H), 0.58 (q,
4.1.1. 3-O-Benzyl-4,6-O-p-methoxybenzylidene-D-glucopyranose
(4). Compound 3 (1.0 g, 3.7 mmol) and p-toluenesulfonic acid
(54 mg, 0.29 mmol) was dissolved under Ar in dry DMF (25 mL).
Then p-methoxybenzaldehyde dimethyl acetal (0.68 mL, 3.9 mmol)
was added to the solution. After stirring for 6 h at room tempera-
ture, the reaction was quenched by addition of triethylamine
(0.1 mL). The solvent was removed under reduced pressure, and the
product was purified by flash chromatography (CH2Cl2/MeOH
50:1 / 10:1) to give product (1.34 g 93.2%) as a colorless oil. 1H
J¼7.9 Hz, 6H); 13C NMR (100 MHz, CDCl3):
d 169.8, 160.3, 138.7,
130.1, 128.5, 128.0, 127.8, 127.5, 113.8, 101.4, 82.2, 80.2, 80.2, 74.5,
70.7, 70.6, 69.0, 63.3, 55.5, 21.1, 6.9, 4.6; HRMS (ESI) [MþNa]þ
calcd for C30H42NaO8Si 581.2541, found 581.2547.
4.1.4. 3-O-Acetyl-2,6-anhydro-4-O-benzyl-5,7-O-p-methoxybenzy-
lidene-
D
-glycero-
D
-gulo-heptitol (7) ½a D25
ꢁ15.6 (c 1.3, CHCl3).
ꢂ
Compound 6 (330 mg, 0.59 mmol) was dissolved under Ar at-
mosphere in dry THF (11 mL), acetic acid (0.34 mL, 5.9 mmol), and
tetra-n-butylammonium fluoride (3.0 mL of a 1 M solution in THF,
3.0 mmol) were added to the reaction solution at 0 ꢀC. The re-
action was monitored by TLC. After 10 min, compound 6 dis-
appeared, and then the solution was filtered through 5 cm of
silica gel and eluted with EtOAc. Volatile components in the fil-
trate were removed by azeotropic distillation with toluene
(20 mL). In order to identify the structure of compound 7, the
residue was quickly purified by flash chromatography (petroleum
ether/EtOAc 3:1 /1:1) to give product as a colorless oil. 1H NMR
NMR (400 MHz, CD3COCD3):
d 7.44e7.40 (m, 8H), 7.31e7.22 (m,
6H), 6.94e6.92 (m, 4H), 6.01 (br s, 1H), 5.79 (br s, 1H), 5.58 (s, 2H),
5.22 (d, J¼3.5 Hz, 1H), 4.91 (d, J¼12.0 Hz, 2H), 4.84 (dd, J¼11.9,
3.5 Hz, 2H), 4.69 (d, J¼7.6 Hz, 1H), 4.49 (d, J¼3.2 Hz, 1H), 4.22 (dd,
J¼10.3, 5.0 Hz, 1H), 4.15 (dd, J¼10.1, 4.9 Hz, 1H), 4.04e3.94 (m, 2H),
3.84 (t, J¼9.2 Hz, 1H), 3.79 (s, 6H), 3.75e3.69 (m, 2H), 3.65e3.61 (m,
4H), 3.47e3.41 (m, 2H); 13C NMR (100 MHz, CD3COCD3):
d 160.8,
140.4,140.4, 131.5, 131.4, 128.8, 128.4, 128.3, 128.3, 127.9, 127.9,114.1,
101.9, 101.8, 98.8, 94.4, 82.8, 82.3, 82.1, 79.8, 76.8, 74.8, 74.7, 73.8,
69.7, 69.3, 67.0, 63.2, 55.5; HRMS (ESI) [MþH]þ calcd for C21H25O7
389.1595, found 389.1589.
(400 MHz, CDCl3):
d
7.41 (d, J¼8.7 Hz, 2H), 7.33e7.25 (m, 5H), 6.90
(d, J¼8.72 Hz, 2H), 5.53 (s, 1H), 4.99 (t, J¼9.6 Hz, 1H), 4.89 (d,
J¼12.0 Hz, 1H), 4.68 (d, J¼12.0 Hz, 1H), 4.33 (dd, J¼4.9 Hz, 10.5 Hz,
1H), 3.81 (s, 3H), 3.79e3.65 (m, 4H), 3.55e3.41 (m, 3H), 2.51 (br s,
4.1.2. 3-O-Benzyl-1,2-O-diacetyl-4,6-O-p-methoxybenzylidene-D-
glucopyranose (5). Compound 4 (1.34 g, 3.45 mmol) was dissolved
under Ar in dry CH2Cl2 (15 mL), pyridine (1.7 mL, 21.2 mmol), and
acetic anhydride (1.0 mL, 10.6 mmol) were added to the solution.
The solution was stirred overnight at room temperature and then
the reaction was quenched by addition of MeOH (1.0 mL) at 0 ꢀC.
The solvent was removed under reduced pressure and the residue
1H), 2.01 (s, 3H); 13C NMR (100 MHz, CDCl3):
d 170.8, 160.1, 138.4,
129.8, 128.6, 128.3, 128.1, 127.8, 127.7, 127.4, 113.6, 101.2, 81.8, 79.5,
79.0, 74.4, 70.6, 70.4, 68.6, 61.6, 55.3, 20.9, 20.8; HRMS (ESI)
[MþH]þ calcd for C24H29O8 445.1857, found 445.1858.
was diluted with CH2Cl2, and successively washed with 1 M HCl(aq)
,
4.1.5. 1-O-Acetyl-2,6-anhydro-4-O-benzyl-5,7-O-p-methoxybenzy-
saturated NaHCO3(aq), and brine. The organic layers were dried over
Na2SO4. After removal of the solvent under reduced pressure, the
residue was purified by flash chromatography (petroleum ether/
EtOAc 10:1 / 3:1) to give product (1.6 g, 98%) as semisolids. 1H
lidene-
D
-glycero-
D
-gulo-heptitol (8)
½
a 2D5
ꢂ
ꢁ23.6 (c 2.2,
CHCl3). Compound 6 (850 mg, 1.5 mmol) was dissolved under Ar
atmosphere in dry THF (16 mL), acetic acid (0.13 mL, 2.3 mmol), and
tetra-n-butylammonium fluoride (8.0 mL of a 1 M solution in THF,
8.0 mmol) were added in the reaction solution at 0 ꢀC. The reaction
was monitored by TLC. After about 2 h, compound 6 disappeared
and the migration of the acetyl group has completed. The solution
was filtered through 5 cm of silica gel and eluted with EtOAc. Volatile
components in the filtrate were removed by azeotropic distillation
with toluene (20 mL). In order to identify the structure of compound
8, the residue was quickly purified by flash chromatography (pe-
troleum ether/EtOAc 5:1 /1.5:1) to give product 8 as a colorless oil.
NMR (400 MHz, CDCl3):
d 7.42e7.40 (m, 4H), 7.31e7.26 (m, 10H),
6.91 (d, J¼8.7 Hz, 4H), 6.28 (d, J¼3.8 Hz, 1H), 5.68 (d, J¼8.2 Hz, 1H),
5.53 (d, J¼9.3 Hz, 2H), 5.12 (t, J¼8.5 Hz, 1H), 5.07 (dd, J¼9.7, 3.9 Hz,
1H), 4.88 (t, J¼12.0 Hz, 2H), 4.71 (d, J¼11.9 Hz, 1H), 4.66 (d,
J¼12.0 Hz, 1H), 4.34 (dd, J¼10.4, 4.9 Hz,1H), 4.28 (dd, J¼10.3, 4.8 Hz,
1H), 4.01 (t, J¼9.5 Hz, 1H), 3.93 (dt, J¼4.9, 4.7 Hz, 1H), 3.80 (s, 6H),
3.78e3.70 (m, 5H), 3.59e3.54 (m, 1H), 2.13 (s, 3H), 2.07 (s, 3H), 2.01
(s, 3H), 1.97 (s, 3H); 13C NMR (100 MHz, CDCl3):
d 169.8, 169.3, 169.2,
169.1, 160.2, 160.2, 138.4, 138.1, 129.6, 129.5, 128.4, 128.3, 127.9,
127.8, 127.7, 127.6, 127.4, 113.7, 113.7, 101.4, 101.4, 92.5, 90.0, 81.5,
81.2, 78.4, 75.9, 74.7, 74.3, 71.8, 71.2, 68.6, 68.4, 67.0, 65.0, 55.3, 20.9,
20.8, 20.7, 20.6; HRMS (ESI) [MþH]þ calcd for C25H29O9 473.1806,
found 473.1812.
1H NMR (400 MHz, CDCl3):
d
7.42 (d, J¼8.5 Hz, 2H), 7.36e7.29 (m,
5H), 6.91 (d, J¼8.6 Hz, 2H), 5.54 (s, 1H), 5.01 (d, J¼11.5 Hz, 1H), 4.73
(d, J¼11.5 Hz, 1H), 4.36e4.33 (m, 3H), 3.81 (s, 3H), 3.74 (t, J¼10.3 Hz,
1H), 3.69e3.62 (m, 2H), 3.60e3.45 (m, 3H), 2.63 (d, J¼1.9 Hz, 1H),
2.10 (s, 3H); 13C NMR (100 MHz, CDCl3):
d171.4, 160.2, 138.4, 129.9,
128.7, 128.3, 128.1, 127.4, 113.8, 101.3, 82.0, 81.9, 78.3, 74.9, 70.9, 70.1,
68.9, 63.7, 55.4, 21.0; HRMS (ESI) [MþH]þ calcd for C24H29O8
445.1857, found 445.1861.
4.1.3. 3-O-Acetyl-2,6-anhydro-4-O-benzyl-5,7-O-p-methoxybenzy-
lidene-1-O-triethylsilyl-
D
-glycero-
D
-gulo-heptitol (6) ½a D25
ꢁ8.6 (c
ꢂ
0.6, CHCl3). Co2(CO)8 (60 mg, 0.18 mmol) was added to a flask
under CO atmosphere. Et3SiH (0.96 mL, 6.0 mmol) was then
added and the mixture was stirred for 30 min at room tempera-
ture. A solution of compound 5 (140 mg, 0.30 mmol) in anhydrous
benzene (2.3 mL) was degassed and then added using a syringe.
The solution was stirred under CO atmosphere at 50 ꢀC. The re-
action was monitored by TLC. After about 48 h, compound 5
disappeared, and then the cobalt complex was precipitated by the
dropwise addition of pyridine and air was bubbled through the
solution for 20 min. The content of the flask was filtered through
5 cm of silica gel and eluted with EtOAc. The filtrate was evapo-
rated and the residue was purified by flash chromatography
(petroleum ether/EtOAc 30:1 / 10:1) to give product (90 mg,
4.1.6. 3-O-Acetyl-2,6-anhydro-4-O-benzyl-5,7-O-p-methoxybenzy-
lidene-1-O-tert-butyldiphenylsilyl-
D
-glycero-
D
-gulo-heptitol
(9)
½
a 2D5
ꢂ
ꢁ16.2 (c 0.7, CHCl3). Compound 7 obtained from compound
6 (330 mg, 0.59 mmol) without flash chromatography purifica-
tion was quickly dissolved under Ar atmosphere in dry CH2Cl2
(5.9 mL). Imidazole (158 mg, 2.36 mmol) and tert-butyl-
chlorodiphenylsilane (0.3 mL, 1.17 mmol) were added to the so-
lution, and the solution was stirred for 6 h at room temperature.
The solvent was then removed under reduced pressure. The
residue was purified by column chromatography (petroleum
ether/EtOAc 30:1 /12:1) to give product (314.6 mg, 78% from 6)
as a colorless oil. 1H NMR (400 MHz, CDCl3):
d 7.69e7.64 (m, 4H),

6986
Y. Li et al. / Tetrahedron 68 (2012) 6981e6989
7.43e7.34 (m, 8H), 7.32e7.23 (m, 5H), 6.91 (d, J¼8.8 Hz, 2H), 5.53
(s, 1H), 5.12e5.07 (m, 1H), 4.88 (d, J¼12.0 Hz, 1H), 4.65 (d,
J¼12.0 Hz, 1H), 4.25 (dd, J¼4.9, 10.4 Hz, 1H), 3.80 (s, 3H),
3.73e3.66 (m, 5H), 3.49 (ddd, J¼10.0, 4.4, 3.0 Hz, 1H), 3.42e3.36
(m, 1H), 1.85 (s, 3H), 1.04 (s, 9H); 13C NMR (100 MHz, CDCl3):
CH2Cl2) and warmed to 0 ꢀC over a period of 10 min. The mixture
was stirred at 0 ꢀC for 2 h, cooled to ꢁ20 ꢀC, and treated with
triethylamine (0.2 mL), then quenched by the dropwise addition of
MeOH (6.0 mL) until effervescence ceased. The solvent was then
removed under reduced pressure. The residue was purified by
column chromatography (petroleum ether/EtOAc 10:1 / 2:1) to
give product (246 mg, 98%) as a colorless oil. 1H NMR (400 MHz,
d
169.5, 160.1, 138.5, 135.9, 135.8, 133.5, 130.0, 129.7, 128.4, 127.9,
127.7, 127.7, 127.4, 113.7, 101.3, 82.1, 80.1, 79.6, 74.3, 70.4, 69.9,
68.8, 63.4, 55.4, 26.9, 20.9, 19.4; HRMS (ESI) [MþH]þ calcd for
C40H47O8Si 683.3035, found 683.3047.
CDCl3):
d
7.65 (d, J¼6.9 Hz, 2H), 7.60 (d, J¼7.2 Hz, 2H), 7.40e7.18 (m,
9H), 6.99 (d, J¼8.1 Hz, 2H), 6.81 (br s, 2H), 6.74 (d, J¼8.2 Hz, 2H),
4.79 (d, J¼11.7 Hz, 1H), 4.42e4.38 (m, 3H), 4.06e4.03 (d, J¼11.8 Hz,
2H), 3.87e3.41 (m, 11H), 1.97 (s, 3H), 0.93 (s, 9H); 13C NMR
4.1.7. 1-O-Acetyl-2,6-anhydro-4-O-benzyl-5,7-O-p-methoxybenzy-
lidene-3-O-tert-butyldiphenylsilyl-
D
-glycero-
D
-gulo-heptitol (10)
(100 MHz, CDCl3): d 170.7, 159.5, 139.0, 136.3, 135.9, 133.9, 132.7,
½
a 2D5
ꢂ
ꢁ78.4 (c 1.0, CHCl3). Compound 8 obtained from com-
130.0, 129.7, 129.6, 129.5, 128.3, 127.9, 127.6, 126.8, 126.7, 114.0, 84.9,
79.2, 78.8, 78.6, 74.1, 72.8, 71.9, 64.3, 62.1, 55.3, 27.1, 20.9, 19.8;
HRMS (ESI) [MþNa]þ calcd for C40H48NaO8Si 707.3011, found
707.3016.
pound 6 (850 mg, 1.5 mmol) without flash chromatography
purification was quickly dissolved under Ar atmosphere in dry
DMF (15 mL). Imidazole (805 mg, 12.1 mmol) and tert-butyl-
chlorodiphenylsilane (1.6 mL, 6.3 mmol) were added to the so-
lution, and the solution was stirred for 6 h at 50 ꢀC. The solvent
was then removed under reduced pressure. The residue was
purified by column chromatography (petroleum ether/EtOAc
25:1 / 10:1) to give product (883.0 mg, 85% from 6) as white
4.1.10. 3-O-Benzyl-1,4-O-diacetyl-2-O-p-methoxybenzyl-6-O-tert-
butyldiphenylsilyl- -glucopyranose (13). To a solution of compound
L
11 (125 mg, 0.18 mmol) in a mixed solvent of water and CH2Cl2 (1/2
ratio 4.5 mL) was consecutively added 2,2,6,6,-tetramethyl-1-
piperidinyloxy (15 mg, 0.09 mmol) and iodosobenzene diacetate
(150 mg, 0.47 mmol). The reaction stirred at room temperature and
was monitored by TLC. After about 4 h, compound 11 disappeared,
and then the solution was diluted with EtOAc, and the mixture was
sequentially washed with 5% Na2S2O3(aq), saturated KH2PO4(aq). The
organic layer was dried over Na2SO4 and the solvent was removed
under reduced pressure to get the corresponding carboxylic acid
without further purification. Then the residue was dissolved under
Ar atmosphere in a mixture of dry benzene (4.5 mL) and dry pyr-
idine (0.45 mL). Lead tetraacetate (0.8 g,1.8 mmol) was added to the
solution and the mixture was heated to reflux overnight and the
solid was removed by filtration. The solvent was removed under
reduced pressure and the residue was diluted with CH2Cl2, and was
washed with 1 M HCl(aq), saturated NaHCO3(aq) and brine. The or-
ganic layers were dried over Na2SO4 and the solvent was removed
under reduced pressure. The residue was purified by column
chromatography (petroleum ether/EtOAc 20:1 / 4:1) to give
solids. 1H NMR (400 MHz, CDCl3):
d 7.65e7.60 (m, 4H), 7.40e7.34
(m, 4H), 7.23e7.17 (m, 4H), 7.14e7.09 (m, 3H), 6.78 (d, J¼8.8 Hz,
2H), 6.67 (d, J¼6.5 Hz, 2H), 5.30 (s, 1H), 4.66 (d, J¼11.2 Hz, 1H),
4.47 (d, J¼11.7 Hz, 1H), 4.29 (dd, J¼10.3, 4.0 Hz, 1H), 4.22 (dd,
J¼11.9, 3.7 Hz, 1H), 3.79e3.71 (m, 7H), 3.60 (t, J¼9.9 Hz, 1H),
3.53e3.47 (m, 2H), 1.99 (s, 3H), 0.95 (s, 9H); 13C NMR (100 MHz,
CDCl3): d 170.7, 160.0, 139.0, 136.4, 135.6, 134.4, 132.0, 129.7, 129.6,
129.4, 127.7, 127.5, 127.4, 127.3, 126.8, 113.5, 101.0, 82.8, 82.1, 78.9,
72.5, 71.8, 69.9, 68.8, 63.9, 55.2, 27.1, 20.9, 19.7; HRMS (ESI)
[MþH]þ calcd for C40H47O8Si 683.3035, found 683.3040.
4.1.8. 3-O-Acetyl-2,6-anhydro-4-O-benzyl-5-O-p-methoxybenzyl-1-
O-tert-butyldiphenylsilyl-
D
-glycero-
D
-gulo-heptitol (11) ½a D25
ꢁ12.0 (c
ꢂ
0.7, CHCl3). Compound 9 (170 mg, 0.25 mmol) and 2,6-di-tert-butyl-
4-methylpyridine (DTBMP,130 mg, 0.63 mmol) were added under Ar
atmosphere in dry CH2Cl2 (2.5 mL). The reaction solution was cooled
to ꢁ20 ꢀC and treated with boraneeTHF complex (1.25 mL of 1 M
solution in THF). The mixture was stirred at ꢁ20 ꢀC for 15 min, then
treated with Bu2BOTf (0.5 mL of 1 M solution in CH2Cl2) and warmed
to 0 ꢀC over a period of 10 min. The mixture was stirred at 0 ꢀC for 2 h,
cooled to ꢁ20 ꢀC, and treated with triethylamine (0.15 mL), then
quenched by the dropwise addition of MeOH (4.0 mL) until effer-
vescence ceased. The solvent was then removed under reduced
pressure. The residue was purified by column chromatography (pe-
troleum ether/EtOAc 10:1 / 2.5:1) to give product (145 mg, 85%) as
product 13 (80 mg, 62%, 13
(400 MHz, CDCl3):
a
/13
b
¼1: 0.9) as a colorless oil. 1H NMR
d
7.64e7.62 (m, 8H), 7.40e7.20 (m, 26H), 6.85 (d,
J¼8.6 Hz, 4H), 6.37 (d, J¼3.5 Hz, 1H), 5.65e5.63 (m, 1H), 5.17e5.08
(m, 2H), 4.87 (d, J¼11.6 Hz, 1H), 4.80 (d, J¼11.5 Hz, 1H), 4.69e4.56
(m, 6H), 3.86e3.78 (m, 8H), 3.72e3.61 (m, 7H), 3.55e3.51 (ddd,
J¼9.9, 4.3, 3.0 Hz, 1H), 2.14 (s, 3H), 2.12 (s, 3H), 1.81 (s, 3H), 1.78 (s,
3H), 1.04 (s, 9H), 1.03 (s, 9H); 13C NMR (100 MHz, CDCl3):
d 169.4,
169.3, 169.3, 169.1, 159.5, 159.4, 138.5, 138.2, 135.7, 135.7, 133.4,
133.3, 133.2, 133.2, 130.1, 129.8, 129.7, 129.6, 129.6, 128.4, 128.4,
127.9, 127.8, 127.7, 127.6, 113.9, 113.9, 93.8, 89.8, 82.2, 80.7, 79.1, 78.6,
75.4, 75.2, 75.2, 74.7, 73.1, 72.9, 69.5, 69.3, 62.8, 62.6, 55.3, 55.3, 26.7,
21.1, 21.0, 20.8, 19.2, 19.2; HRMS (ESI) [MþNa]þ calcd for
C41H48NaO9Si 735.2960, found 735.2971.
a colorless oil.1H NMR (400 MHz, CDCl3):
d
7.66 (t, J¼8.0 Hz, 2H), 7.65
(t, J¼8.1 Hz, 2H), 7.44e7.27 (m, 11H), 7.21 (d, J¼8.6 Hz, 2H), 6.86 (d,
J¼8.6 Hz, 2H), 5.00 (t, J¼9.6 Hz, 1H), 4.83 (d, J¼11.4 Hz, 1H), 4.74 (d,
J¼10.5 Hz,1H), 4.66 (d, J¼11.4 Hz,1H), 4.55 (d, J¼10.5 Hz,1H), 3.79 (s,
3H), 3.75e3.58 (m, 5H), 3.54 (t, J¼9.3 Hz, 1H), 3.44e3.40 (m, 1H),
3.29e3.25 (m,1H), 1.83 (s, 3H), 1.68 (t, J¼6.3 Hz,1H), 1.04 (s, 9H); 13C
NMR (100 MHz, CDCl3):
d
169.6,159.5,138.4,135.8,135.7,135.7,133.6,
4.1.11. 3-O-Benzyl-1,6-O-diacetyl-2-O-p-methoxybenzyl-4-O-tert-
133.5,130.1, 129.8, 129.8, 129.8, 128.5, 128.4, 127.9,127.9,127.8, 127.7,
114.0, 84.5, 79.0, 78.7, 77.8, 75.3, 74.9, 70.4, 63.4, 62.1, 55.3, 26.8, 20.9,
19.3; HRMS (ESI) [MþNH4]þ calcd for C40H52NO8Si 702.3457, found
702.3464.
butyldiphenylsilyl-
b-
L
-glucopyranose (14
b
)
½
a 2D5
ꢂ
ꢁ51.0 (c 0.7,
CHCl3). To a solution of compound 12 (90 mg, 0.13 mmol) in
a mixed solvent of water and CH2Cl2 (1/2 ratio 3 mL) was consec-
utively added 2,2,6,6,-tetramethyl-1-piperidinyloxy (10 mg,
0.06 mmol) and iodosobenzene diacetate (106 mg, 0.33 mmol). The
reaction was stirred at room temperature and monitored by TLC.
After about 4 h, compound 12 disappeared, and then the solution
was diluted with EtOAc, and the mixture was sequentially washed
with 5% Na2S2O3(aq), saturated KH2PO4(aq). The organic layer was
dried over Na2SO4 and the solvent was removed under reduced
pressure to get the corresponding carboxylic acid without further
purification. Then the residue was dissolved under Ar atmosphere
in a mixture of dry benzene (2 mL) and dry pyridine (0.2 mL). Lead
4.1.9. 1-O-Acetyl-2,6-anhydro-4-O-benzyl-5-O-p-methoxybenzyl-3-
O-tert-butyldiphenylsilyl-
D
-glycero-
D
-gulo-heptitol (12) ½a D25
ꢁ55.4
ꢂ
(c 1.0, CHCl3). Compound 10 (250 mg, 0.37 mmol) and 2,6-di-tert-
butyl-4-methylpyridine (DTBMP, 190 mg, 0.92 mmol) were added
under Ar atmosphere in dry CH2Cl2 (3.7 mL). The reaction solution
was cooled to ꢁ20 ꢀC and treated with boraneeTHF complex
(1.85 mL of 1 M solution in THF). The mixture was stirred at ꢁ20 ꢀC
for 15 min, then treated with Bu2BOTf (0.19 mL of 1 M solution in

Y. Li et al. / Tetrahedron 68 (2012) 6981e6989
6987
tetraacetate (585 mg, 1.3 mmol) was added to the solution and the
mixture was heated to reflux overnight and the solid was removed
by filtration. The solution was removed under reduced pressure and
the residue was diluted with CH2Cl2, and was washed with 1 M
HCl(aq), saturated NaHCO3(aq) and brine. The organic layers were
dried over Na2SO4 and the solvent was removed under reduced
pressure. The residue was purified by column chromatography
(petroleum ether/EtOAc 20:1 / 3:1) to give product 14 (68.4 mg,
pyridine (0.035 mL, 0.43 mmol). The reaction was cooled to ꢁ20 ꢀC.
Trifluoromethanesulfonic anhydride (0.035 mL, 0.21 mmol) was
then added dropwise, and the reaction mixture was slowly warmed
to 0 ꢀC and stirred for 2 h. The reaction was concentrated under
high vacuum. The crude mixture was dissolved in DMF (3 mL), then
water (0.3 mL) was added, and the reaction mixture was stirred for
2 h at 50 ꢀC. Then the reaction mixture was concentrated under
high vacuum and purified by flash chromatography (petroleum
ether/EtOAc 8:1 / 2.5:1) to give product (26 mg, 87%) as a colorless
73%, 14
a
/14b
¼1:3.6) as a colorless oil. 1H NMR (400 MHz, CDCl3):
d
7.61 (t, J¼7.8 Hz, 4H), 7.39e7.31 (m, 5H), 7.24 (t, J¼7.5 Hz, 1H), 7.17
oil. 1H NMR (400 MHz, CDCl3):
d 7.63e7.60 (m, 2H, AreH),
(d, J¼3.6 Hz, 3H), 7.00 (d, J¼8.5 Hz, 2H), 6.75 (d, J¼8.3 Hz, 4H), 5.71
(d, J¼7.7 Hz,1H), 4.63 (d, J¼11.5 Hz,1H), 4.54 (d, J¼10.7 Hz,1H), 4.35
(t, J¼12.5 Hz, 2H), 4.14 (dd, J¼12.0, 3.9 Hz, 1H), 3.91e3.86 (m, 3H),
3.73e3.67 (m, 4H), 3.49 (t, J¼7.7 Hz, 1H), 2.01 (s, 3H), 1.96 (s, 3H),
7.52e7.50 (m, 2H, AreH), 7.43e7.31 (m, 4H, AreH), 7.19e7.09 (m,
5H, AreH), 6.53 (d, J¼7.0 Hz, 2H, AreH), 5.27 (t, J¼2.7 Hz, 1H, H-2),
5.17 (dd, J¼3.8, 2.4 Hz, 1H, H-1), 4.51 (dd, J¼11.8, 1.9 Hz, 1H), 4.30
(dd, J¼11.8, 5.1 Hz, 1H), 4.25e4.19 (m, 2H), 4.03 (t, J¼9.0 Hz, 1H, H-
4), 3.87 (dd, J¼8.9, 3.0 Hz, 1H, H-3), 3.67 (d, J¼10.3 Hz, 1H), 2.93 (d,
J¼4.1 Hz, 1H, eOH), 2.06 (s, 3H, eCOCH3), 1.80 (s, 3H, eCOCH3), 0.94
0.94 (s, 9H); 13C NMR (100 MHz, CDCl3):
d 170.6, 169.2, 159.3, 138.8,
136.3, 135.8, 133.9, 132.2, 129.8, 129.7, 129.6, 129.3, 127.8, 127.8,
127.5, 127.0, 126.9, 113.9, 93.9, 83.4, 81.0, 75.2, 73.8, 72.5, 71.1, 63.5,
55.3, 27.0, 21.1, 20.8, 19.6; HRMS (ESI) [MþNa]þ calcd for
C41H48NaO9Si 735.2960, found 735.2964.
(s, 9H, eSiC(CH3)3); 13C NMR (100 MHz, CDCl3):
d 170.9, 170.1, 137.4,
136.5, 136.4, 135.7, 135.7, 134.6, 132.4, 129.4, 128.3, 128.2, 128.0,
127.8, 127.7, 127.5, 127.4, 127.3, 127.3, 92.5, 77.4, 71.9, 70.0, 68.7, 68.0,
63.9, 27.1, 27.0, 21.0, 20.7, 19.8; HRMS (ESI) [MþNH4]þ calcd for
C33H44NO8Si 610.2831, found 610.2841.
4.1.12. 3-O-Benzyl-1,6-O-diacetyl-2-O-p-methoxybenzyl-4-O-tert-
a 25
butyldiphenylsilyl-
a
-
L
-glucopyranose (14
a
)
½ ꢂD ꢁ71.2 (c 0.7,
CHCl3). 1H NMR (400 MHz, CDCl3):
d
7.63 (d, J¼6.6 Hz, 2H), 7.59 (d,
4.1.15. 3-O-Benzyl-1,6-O-diacetyl-2-O-p-methoxybenzyl-
b
-
L
-gluco-
J¼6.9 Hz, 2H), 7.40e7.33 (m, 5H), 7.25e7.16 (m, 4H), 6.95 (d,
J¼8.5 Hz, 2H), 6.72e6.70 (m, 4H), 6.27 (d, J¼3.5 Hz, 1H), 4.74 (d,
J¼11.5 Hz, 1H), 4.37 (t, J¼10.6 Hz, 2H), 4.23e4.18 (m, 2H), 4.06e4.03
(m, 1H), 3.87e3.76 (m, 3H), 3.73 (s, 3H), 3.51 (dd, J¼8.5, 3.7 Hz, 1H),
2.22 (s, 3H), 1.98 (s, 3H), 0.93 (s, 9H); 13C NMR (100 MHz, CDCl3):
pyranose (17) ½a D25
ꢂ
þ8.0 (c 1.0, CHCl3). Compound 14
b (240 mg,
0.34 mmol) was dissolved under Ar atmosphere in dry THF (10 mL),
acetic acid (0.5 mL, 8.7 mmol), and tetrabutylammonium fluoride
(6.8 mL of a 1 M solution in THF, 6.8 mmol) were added to the re-
action solution and it was stirred at 50 ꢀC. The reaction was mon-
d
170.7, 169.6, 159.6, 139.3, 136.4, 135.8, 134.2, 132.2, 130.0, 129.7,
itored by TLC. After about 5 h, compound 14b disappeared, and
129.5, 129.3, 127.8, 127.5, 127.0, 126.8, 113.9, 89.3, 80.2, 79.9, 72.8,
72.5, 72.2, 71.0, 63.5, 55.3, 27.2, 21.3, 20.9, 19.8; HRMS (ESI)
[MþNH4]þ calcd for C41H52NO9Si 730.3406, found 730.3421.
then the solution was filtered through 5 cm of silica gel and eluted
with EtOAc. The solvent was removed under reduced pressure and
the residue was diluted with CH2Cl2, and was washed with satu-
rated NaHCO3(aq) and brine. The organic layers were dried over
Na2SO4. The residue was purified by column chromatography (pe-
troleum ether/EtOAc 6:1 / 1.5:1) to give product (140 mg 88%) as
4.1.13. 3-O-Benzyl-1,6-O-diacetyl-4-O-tert-butyldiphenylsilyl-b-L-
glucopyranose (15) ½a D25
ꢁ24.0 (c 1.0, CHCl3). To a stirred solution of
ꢂ
compound 14
b
(75 mg, 0.1 mmol) in CH2Cl2 (10 mL), trifluroacetic
a colorless semisolids. 1H NMR (400 MHz, C6D6):
d
7.32 (d, J¼7.2 Hz,
acid (0.8 mL) was added at ꢁ20 ꢀC. After stirring for 2 h at this
2H, AreH), 7.20e7.11 (m, 5H, AreH), 6.76 (d, J¼8.6 Hz, 2H, AreH),
5.85 (d, J¼8.1 Hz, 1H, H-1), 4.88 (d, J¼11.6 Hz, 1H, eCH2Ar), 4.78 (d,
J¼11.6 Hz, 1H, eCH2Ar), 4.69 (d, J¼11.2 Hz, 1H, eCH2Ar), 4.65 (d,
J¼11.3 Hz, 1H, eCH2Ar), 4.36 (dd, J¼12.3, 4.4 Hz, 1H, H-6a), 4.14 (dd,
J¼12.3, 2.1 Hz, 1H, H-6b), 3.58 (t, J¼8.4 Hz, 1H, H-2), 3.47 (dt, J¼8.9,
3.6 Hz, 1H, H-4), 3.42 (t, J¼8.8 Hz, 1H, H-3), 3.28 (s, 3H, -ArOCH3),
3.22 (ddd, J¼9.4, 4.3, 2.1 Hz, 1H, H-5), 2.38 (d, J¼3.6 Hz, 1H, eOH),
1.60 (s, 3H, eCOCH3), 1.57 (s, 3H, eCOCH3); 13C NMR (100 MHz,
temperature, the reaction mixture turned purple and compound
14b disappeared. The mixture was then quenched by saturated
NaHCO3(aq). The mixture was diluted with CH2Cl2 and washed with
NaHCO3(aq) and brine. The organic layers were dried over Na2SO4
and the solvent was removed under reduced pressure. The residue
was purified by column chromatography (petroleum ether/EtOAc
10:1 / 4:1) to give product (60 mg, 96%) as a colorless oil. 1H NMR
(400 MHz, CDCl3):
d
7.66e7.64 (m, 4H), 7.43e7.36 (m, 4H), 7.30 (t,
CDCl3): d 171.8, 169.2, 159.5, 138.4, 130.1, 129.7, 128.7, 128.2, 114.0,
J¼7.4 Hz, 2H), 7.21e7.20 (m, 3H), 6.92e6.90 (m, 2H), 5.65 (d,
J¼6.7 Hz, 1H), 4.50 (d, J¼11.9 Hz, 1H), 4.30 (dd, J¼2.8 Hz, 11.9 Hz,
1H), 4.19 (dd, J¼5.2 Hz, 11.9 Hz, 1H), 4.00 (d, J¼11.9 Hz, 1H),
3.89e3.81 (m, 2H), 3.66 (t, J¼6.9 Hz, 1H), 3.59e3.54 (dd, J¼6.8 Hz,
11.9 Hz, 1H), 2.42 (d, J¼5.4 Hz, 1H), 2.05 (s, 3H), 1.93 (s, 3H), 0.99 (s,
94.2, 83.8, 80.3, 75.6, 74.7, 74.7, 69.7, 63.0, 55.4, 21.2, 21.0; HRMS
(ESI) [MþNH4]þ calcd for C25H34NO9 492.2228, found 492.2231.
4.1.16. 3-O-Benzyl-1,6-O-diacetyl-2-O-p-methoxybenzyl-
b
-
L
-gal-
actopyranose (18) ½a D25
ꢂ
ꢁ19.6 (c 1.0, CHCl3). To a solution of com-
9H); 1H NMR (400 MHz, CD3COCD3):
d
7.72 (d, J¼6.3 Hz, 2H, AreH),
pound 17 (25 mg, 0.05 mmol) in dry CH2Cl2 (3 mL) was added
pyridine (0.035 mL, 0.43 mmol). The reaction was cooled to ꢁ20 ꢀC.
Trifluoromethanesulfonic anhydride (0.035 mL, 0.21 mmol) was
then added dropwise, and the reaction mixture was slowly warmed
to 0 ꢀC and stirred for 2 h. The resulting mixture was subsequently
diluted with CH2Cl2 and washed with 1 M HCl(aq), saturated NaH-
CO3(aq) and brine quickly. The organic layer was dried over Na2SO4
and concentrated under reduced pressure at low temperature. The
residue was used directly without further purification. The pro-
tected triflate residue was dissolved in dry toluene (3 mL). Tetra-n-
butylammonium nitrite (80 mg, 0.27 mmol) was added to the
solution. After stirring at 50 ꢀC for 2 h, the mixture was diluted with
CH2Cl2 and washed with brine. The organic layer was dried with
Na2SO4 and the solvent was removed under reduced pressure and
purified by flash chromatography (petroleum ether/EtOAc
10:1 / 2.5:1) to give product (19 mg, 76%) as a colorless oil.
7.66 (d, J¼6.9 Hz, 2H, AreH), 7.48e7.38 (m, 4H, AreH), 7.27 (t,
J¼7.5 Hz, 2H, AreH), 7.16e7.14 (m, 3H, AreH), 6.78e6.76 (m, 2H,
AreH), 5.59 (d, J¼8.0 Hz, 1H, H-1), 4.90 (d, J¼11.0 Hz, 1H, eCH2Ph),
4.79 (d, J¼4.6 Hz, 1H, -OH), 4.39 (dd, J¼12.0, 1.7 Hz, 1H, H-6a), 4.20
(dd, J¼12.0, 4.4 Hz, 1H, 6b), 3.96 (ddd, J¼8.9, 4.3, 1.9 Hz, 1H, H-5),
3.84e3.76 (m,3H), 3.53e3.48 (m, 1H, H-2), 2.02 (s, 3H, eCOCH3),
1.94 (s, 3H, eCOCH3), 0.94 (s, 9H, eSiC(CH3)3); 13C NMR (100 MHz,
CDCl3):
d 170.6, 169.5, 138.8, 136.3, 135.8, 133.7, 132.3, 130.0, 129.8,
128.3, 127.7, 127.4, 127.3, 93.8, 82.4, 75.4, 72.6, 72.1, 70.3, 63.6, 27.1,
21.1, 20.9, 19.6; HRMS (ESI) [MþNa]þ calcd for C33H40NaO8Si
615.2385, found 615.2385.
4.1.14. 3-O-Benzyl-2,6-O-diacetyl-4-O-tert-butyldiphenylsilyl-a-L-
mannopyranose (16) ½a D25
ꢁ34.0 (c 0.8, CHCl3). To a solution of
ꢂ
compound 15 (30 mg, 0.05 mmol) in dry CH2Cl2 (3 mL) was added

6988
Y. Li et al. / Tetrahedron 68 (2012) 6981e6989
S. T.; Stubbe, J. J. Am. Chem. Soc. 1998, 120, 9139e9148; (d) Katano, K.; An, H.;
1H NMR (400 MHz, C6D6):
d
7.24e7.11 (m, 7H, AreH), 6.77 (d,
Aoyagi, Y.; Overhand, M.; Sucheck, S. J.; Steven, W. C., Jr.; Hess, C. D.; Zhou, X.;
Hecht, S. M. J. Am. Chem. Soc. 1998, 120, 11285e11296; (e) Boger, D. L.; Cai, H.
Angew. Chem., Int. Ed. 1999, 38, 448e476.
4. Ogita, T.; Otake, N.; Miyazaki, Y.; Yonehara, H.; Macfarlane, R. D.; McNeal, C. J.
Tetrahedron Lett. 1980, 21, 3203e3206.
J¼8.6 Hz, 2H, AreH), 5.82 (d, J¼8.2 Hz, 1H, H-1), 4.68 (s, 2H,
eCH2Ar), 4.51 (dd, J¼11.6, 7.4 Hz, 1H, H-6a), 4.44 (dd, J¼11.6, 4.5 Hz,
1H, H-6b), 4.38 (d, J¼11.7 Hz, 1H, eCH2Ar), 4.32 (d, J¼11.7 Hz, 1H,
eCH2Ar), 3.90 (dd, J¼9.2, 8.4 Hz, 1H, H-2), 3.54 (d, J¼2.5 Hz, 1H, H-
4), 3.44 (dd, J¼6.5, 4.9 Hz, 1H, H-5), 3.29 (s, 3H, -ArOCH3), 3.19 (dd,
J¼9.4, 3.4 Hz, 1H, H-3), 2.22 (br s, 1H, -OH), 1.65 (s, 3H, eCOCH3),
5. (a) Arungundram, S.; Al-Mafraji, K.; Asong, J.; Leach, F. E., III; Amster, I. J.; Venot,
A.; Turnbull, J. E.; Boons, G. J. J. Am. Chem. Soc. 2009, 131, 17394e17405; (b) Polat,
T.; Wong, C. H. J. Am. Chem. Soc. 2007, 129, 12795e12800; (c) Lindahl, U. Pure
Appl. Chem. 1997, 69, 1897e1902; (d) Rabenstein, D. L. Nat. Prod. Rep. 2002, 19,
312e331.
1.63 (s, 3H, eCOCH3); 13C NMR (100 MHz, C6D6):
d 170.3, 169.1,
159.9, 138.5, 131.1, 129.7, 128.8, 128.7, 114.1, 114.1, 94.5, 81.2, 77.5,
75.0, 73.4, 72.4, 67.0, 63.8, 54.8, 20.6, 20.4; HRMS (ESI) [MþNa]þ
calcd for C25H30NaO9 497.1782, found 497.1778.
6. (a) Shallenberger, R. S.; Acree, T. E.; Lee, C. Y. Nature 1969, 221, 555e556; (b)
Levin, G. V. U.S. Patent 4,262,032, 1981.
7. Levin, G. V.; Zehner, L. R. U.S. Patent 5,166,193, 1992.
8. (a) Tsai, C. Y.; Huang, X. F.; Wong, C. H. Tetrahedron Lett. 2000, 41, 9499e9503; (b)
Filser, C.; Kowalczyk, D.; Jones, C.; Wild, M. K.; Ipe, U.; Vestweber, D.; Kunz, H.
Angew. Chem., Int. Ed. 2007, 46, 2108e2111.
9. (a) Boulineau, F. P.; Wei, A. J. Org. Chem. 2004, 69, 3391e3399; (b) Berkowitz, D.
B.; Danishefsky, S. J.; Schulte, G. K. J. Am. Chem. Soc. 1992, 114, 4518e4529; (c)
Flekhter, O. B.; Baltina, L. A.; Tolstikov, G. A. J. Nat. Prod. 2000, 63, 992e994; (d)
Kozlov, I. A.; Mao, S.; Xu, Y.; Huang, X.; Lee, L.; Sears, P. S.; Gao, C.; Coyle, A. R.;
Janda, K. D.; Wong, C.-H. ChemBioChem 2001, 2, 741e746.
4.1.17. 3-O-Benzyl-1,4-O-diacetyl-2-O-p-methoxybenzyl-b-L-gal-
actopyranose (19) ½a D25
ꢂ
þ4.4 (c 0.4, CHCl3). 1H NMR (400 MHz,
C6D6):
d
7.37 (d, J¼7.4 Hz, 2H, AreH), 7.23 (d, J¼8.6 Hz, 2H, AreH),
7.21e7.10 (m, 3H, AreH), 6.77 (d, J¼8.6 Hz, 2H, AreH), 5.84 (d,
J¼8.1 Hz, 1H, H-1), 5.36 (d, J¼2.9 Hz, 1H, H-4), 4.81 (d, J¼11.2 Hz, 1H,
eCH2Ar), 4.72 (d, J¼11.2 Hz, 1H, eCH2Ar), 4.58 (d, J¼11.4 Hz, 1H,
eCH2Ar), 4.36 (d, J¼11.4 Hz, 1H, eCH2Ar), 3.95 (t, J¼8.9 Hz, 1H, H-2),
3.66e3.63 (m, 1H, H-6a), 3.46e3.42 (m, 1H, H-6b), 3.36 (dd, J¼9.6,
3.4 Hz, 1H, H-3), 3.29 (s, 3H, eArOCH3), 3.26 (t, J¼7.1 Hz, 1H, H-5),
10. (a) Jansson, P. E.; Lindbery, B.; Widmalm, G.; Sandford, P. A. Carbohydr. Res.
1985, 139, 217e223; (b) Jansson, P. E.; Kumar, N. S.; Lindbery, B. Carbohydr. Res.
1986, 156, 165e172; (c) Chowdhury, T. A.; Lindbery, B.; Lindquist, U.; Baird, J.
Carbohydr. Res. 1987, 161, 127e132.
11. (a) Kubelka, W. Phytochemistry 1974, 13, 1805e1808; (b) Esaki, S.; Ohishi, A.;
Katsumata, A.; Sugiyama, N.; Kamiya, S. Biosci., Biotechnol., Biochem. 1993, 57,
2099e2103.
1.91 (br s, 1H, eOH), 1.67 (s, 3H, eCOCH3), 1.65 (s, 3H, eCOCH3); 13
C
NMR (100 MHz, C6D6): d 170.9,169.0,159.8, 138.5, 131.1,129.6, 127.4,
12. For a review, see: D’Alonzo,
13, 71e98.
D.; Guaragna, A.; Palumbo, G. Curr. Org. Chem. 2009,
114.1, 94.5, 80.0, 77.9, 75.2, 74.5, 72.2, 67.2, 60.9, 54.8, 20.5, 20.3;
HRMS (ESI) [MþNa]þ calcd for C25H30NaO9 497.1782, found
497.1787.
13. See for example: (a) Northrup, A. B.; MacMillan, D. W. C. Science 2004, 305,
1752e1755; (b) Covell, D. J.; Vermeulen, N. A.; Labenz, N. A.; White, M. C. An-
gew. Chem., Int. Ed. 2006, 45, 8217e8220; (c) Han, S. B.; Kong, J. R.; Krische, M. J.
Org. Lett. 2008, 10, 4133e4135; (d) Ahmed, M. M.; Berry, B. P.; Hunter, T. J.;
ꢀ
Tomcik, D. J.; O’Doherty, G. A. Org. Lett. 2005, 7, 745e748; (e) Cordova, A.;
4.1.18. 4-O-Acetyl-3,7-anhydro-5-O-benzyl-1,2-O-ditriethylsilyl-6,8-
ꢀ
Ibrahem, I.; Casas, J.; Sunden, H.; Engqvist, M.; Reyes, E. Chem.dEur. J. 2005, 11,
O-p-methoxybenzylidene-
D
-glycero-
D
-gulo-oct-1-enitol (20)
½ ꢂ
a 2D5
4772e4784; (f) Guaragna, A.; Napolitano, C.; D’Alonzo, D.; Pedatella, S.; Pal-
umbo, G. Org. Lett. 2006, 8, 4863e4866; (g) Guaragna, A.; D’Alonzo, D.; Paolella,
C.; Napolitano, C.; Palumbo, G. J. Org. Chem. 2010, 75, 3558e3568.
þ15.9 (c 1.0, CHCl3). 1H NMR (400 MHz, C6D6):
d
7.56 (d, J¼8.7 Hz,
2H, AreH), 7.38 (d, J¼7.4 Hz, 2H, AreH), 7.21e7.13 (m, 2H, AreH),
7.06 (t, J¼7.4 Hz, 1H, AreH), 6.84 (t, J¼8.7 Hz, 2H, AreH), 5.86 (s,
1H), 5.68 (d, J¼9.3 Hz, 1H, H-4), 5.27 (s, 1H), 5.04 (d, J¼12.2 Hz, 1H,
eCH2Ar), 4.80 (d, J¼12.2 Hz, 1H, -CH2Ar), 4.19 (dd, J¼10.3, 4.9 Hz,
1H, H-8a), 3.79 (t, J¼9.1 Hz, 1H, H-5), 3.72 (t, J¼9.1 Hz, 1H, H-6), 3.51
(t, J¼10.2 Hz, 1H, H-8b), 3.45 (d, J¼9.8 Hz, 1H, H-3), 3.33 (dt, J¼4.9,
4.8 Hz, 1H, H-7), 3.27 (s, 3H, eArOCH3), 1.77 (s, 3H, eCOCH3), 1.19 (t,
J¼7.9 Hz, 9H, eSiCH2CH3), 0.96 (t, J¼7.9 Hz, 9H, eSiCH2CH3), 0.90 (q,
J¼8.1 Hz, 6H, eSiCH2CH3), 0.61 (q, J¼7.9 Hz, 6H, eSiCH2CH3); 13C
14. (a) Ermolenko, L.; Sasaki, N. A. J. Org. Chem. 2006, 71, 693e703; (b) Ermolenko,
L.; Sasaki, N. A.; Potier, P. Helv. Chim. Acta 2003, 86, 3578e3582; (c) Dondoni, A.;
Marra, A.; Massi, A. J. Org. Chem. 1997, 62, 6261e6267.
15. (a) See for example: Takahashi, H.; Hitomi, Y.; Iwai, Y.; Ikegami, S. J. Am. Chem.
Soc. 2000, 122, 2995e3000; (b) Takahashi, H.; Shida, T.; Hitomi, Y.; Iwai, Y.;
Miyama, N.; Nishiyama, K.; Sawada, D.; Ikegami, S. Chem.dEur. J. 2006, 12,
5868e5877; (c) Boulineau, F. P.; Wei, A. Org. Lett. 2002, 4, 2281e2283; (d)
Boulineau, F. P.; Wei, A. Org. Lett. 2004, 6, 119e121; (e) Cheng, G.; Fan, R.;
ꢀ
Hernandez-Torres, J. M.; Boulineau, F. P.; Wei, A. Org. Lett. 2007, 9, 4849e4852;
(f) Weymouth-Wilson, A. C.; Clarkson, R. A.; Jones, N. A.; Best, D.; Wilson, F. X.;
ꢀ
Pino-Gonzalez, M.-S.; Fleet, G. W. J. Tetrahedron Lett. 2009, 50, 6307e6310.
16. See for example: (a) Takata, G.; Uechi, K.; Taniguchi, E.; Kanbara, Y.; Yoshihara,
A.; Morimoto, K.; Izumori, K. Biosci. Biotechnol. Biochem. 2011, 75, 1006e1009;
(b) Gullapalli, P.; Yoshihara, A.; Morimoto, K.; Rao, D.; Akimitsu, K.; Jenkinson,
S. F.; Fleet, G. W. J.; Izumori, K. Tetrahedron Lett. 2010, 51, 895e898; (c) Rao, D.;
Gullapalli, P.; Yoshihara, A.; Jenkinson, S. F.; Morimoto, K.; Takata, G.; Akimitsu,
K.; Tajima, S.; Fleet, G. W. J.; Izumori, K. J. Biosci. Bioeng. 2008, 106, 473e480; (d)
Gullapalli, P.; Shiji, T.; Rao, D.; Yoshihara, A.; Morimoto, K.; Takata, G.; Fleet, G.
W. J.; Izumori, K. Tetrahedron: Asymmetry 2007, 18, 1995e2000.
NMR (100 MHz, C6D6):
d 168.1, 160.6, 139.4, 132.7, 130.9, 128.5,
127.9,126.2, 126.1,113.8,101.6,101.6, 82.4, 80.5, 79.8, 74.1, 70.8, 69.8,
69.0, 54.8, 54.8, 20.8, 20.8, 7.3, 7.2, 6.8, 6.7, 6.1, 4.6; HRMS (ESI)
[MþNa]þ calcd for C37H56NaO9Si2 723.3355, found 723.3356.
Acknowledgements
17. Wang, C. C.; Lee, J. C.; Luo, S. Y.; Kulkarni, S. S.; Huang, Y. W.; Lee, C. C.; Chang, K.
L.; Hung, S. C. Nature 2007, 446, 896e899 and references therein cited.
18. See for example: (a) Wong, C. H.; Ye, X. S.; Zhang, Z. Y. J. Am. Chem. Soc. 1998,
120, 7137e7138; (b) Ye, X. S.; Wong, C. H. J. Org. Chem. 2000, 65, 2410e2431; (c)
Muramatsu, W.; Mishiro, K.; Ueda, Y.; Furuta, T.; Kawabata, T. Eur. J. Org. Chem.
2010, 827e831; (d) Boltje, T. J.; Li, C.; Boons, G. J. Org. Lett. 2010, 12, 4636e4639;
(e) Emmadi, M.; Kulkarni, S. S. J. Org. Chem. 2011, 76, 4703e4709; (f) Com-
postella, F.; Ronchi, S.; Panza, L.; Mariotti, S.; Mori, L.; De Libero, G.; Ronchetti, F.
Chem.dEur. J. 2006, 12, 5587e5595; (g) Castoldi, S.; Cravini, M.; Micheli, F.;
Piga, E.; Russo, G.; Seneci, P.; Lay, L. Eur. J. Org. Chem. 2004, 2853e2862.
19. Timmer, M. S. M.; Adibekian, A.; Seeberger, P. H. Angew. Chem., Int. Ed. 2005, 44,
7605e7607.
20. Hoffmann,H.M.R.;Dunkel,R.;Mentzel,M.;Reuter,H.;Stark,C.B.W.Chem.dEur.J.
2001,7,4771e4789.
21. (a) Shiozaki, M. J. Org. Chem. 1991, 56, 528e532; (b) Smid, P.; Noort, D.;
Broxterman, H. J. G.; van Straten, N. C. R.; van der Marel, G. A.; van Boom, J. H.
Recl. Trav. Chim. Pays-Bas 1992, 111, 524e528.
This work was financially supported by the National Natural
Science Foundation of China (No. 20732001 and No. 20972012) and
the National Basic Research Program of China (No. 2012CB822100).
Supplementary data
1H NMR and 13C NMR spectra for all new products and 2D COSY
spectra for compounds 15e20. Supplementary data associated with
this article can be found in the online version, at doi:10.1016/
j.tet.2012.04.001. These data include MOL files and InChIKeys of the
most important compounds described in this article.
22. (a) Lattrell, R.; Lohaus, G. Justus Liebigs Ann. Chem. 1974, 901e920; (b) Albert, R.;
€
Dax, K.; Link, R. W.; Stutz, A. E. Carbohydr. Res. 1983, 118, C5eC6.
References and notes
23. Pedatella, S.; Guaragna, A.; D’Alonzo, D.; De Nisco, M.; Palumbo, G. Synthesis
2006, 305e308.
1. McNaught, A. D. Pure Appl. Chem. 1996, 6, 1919e2008.
24. Leigh, C. D.; Bertozzi, C. R. J. Org. Chem. 2008, 73, 1008e1017.
25. (a) Chatani, N.; Ikeda, T.; Sano, T.; Sonoda, N.; Kurosawa, H.; Kawasaki, Y.;
Murai, S. J. Org. Chem. 1988, 53, 3387e3389; (b) Spak, S. J.; Martin, O. R. Tet-
rahedron 2000, 56, 217e224; (c) van Well, R. M.; Meijer, M. E. A.; Overkleeft, H.
S.; van Boom, J. H.; van der Marel, G. A.; Overhand, M. Tetrahedron 2003, 59,
2423e2434; (d) Filippov, D. V.; van den Elst, H.; Tromp, C. M.; van der Marel, G.
2. (a) Lee, J. C.; Chang, S. W.; Liao, C. C.; Chi, F. C.; Chen, C. S.; Wen, Y. S.; Wang, C.
C.; Kulkarni, S. S.; Puranik, R.; Liu, Y. H.; Hung, S. C. Chem.dEur. J. 2004, 10,
399e415; (b) Dictionary of Carbohydrates; Collins, P. M., Ed.; Chapman and Hall:
London, 1998.
3. (a) Burger, R. M. Chem. Rev. 1998, 98, 1153e1169; (b) Claussen, C. A.; Long, E. C.
Chem. Rev. 1999, 99, 2797e2816; (c) Boger, D. L.; Ramsey, T. M.; Cai, H.; Hoehen,

Y. Li et al. / Tetrahedron 68 (2012) 6981e6989
6989
A.; van Boeckel, C. A. A.; Overkleeft, H. S.; van Boom, J. H. Synlett 2004,
773e778.
2165e2168; (d) Dinkelaar, J.; van den Bos, L. J.; Hogendorf, W. F. J.; Lodder, G.;
Overkleeft, H. S.; Codee, J. D. C.; van der Marel, G. A. Chem.dEur. J. 2008, 14,
ꢀ
26. (a) Murai, S.; Sonoda, N. Angew. Chem., Int. Ed. Engl. 1979, 18, 837e846; (b)
Chatani, N.; Murai, T.; Ikeda, T.; Sano, T.; Kajikawa, Y.; Ohe, K.; Murai, S. Tet-
rahedron 1992, 48, 2013e2024; (c) Murai, S.; Seki, Y. J. Mol. Catal. 1987, 41,
197e207.
9400e9411.
30. (a) Vasella, A.; Wyler, R. Helv. Chim. Acta 1991, 74, 451e463; (b) Wallimann, K.;
Vasella, A. Helv. Chim. Acta 1990, 73, 1359e1372; (c) Kumar, N. S.; Ratnayake, R.
M. S. K.; Widmalm, G.; Jansson, P. E. Carbohydr. Res. 1996, 291, 109e114.
31. (a) Wang, G.; Zhang, W.; Lu, Z.; Wang, P.; Zhang, X.; Li, Y. J. Org. Chem. 2009, 74,
2508e2515; (b) Cai, Y.; Ling, C.; Bundle, D. R. J. Org. Chem. 2009, 74, 580e589.
27. Graziani, A.; Passacantilli, P.; Piancatelli, G.; Tani, S. Tetrahedron Lett. 2001, 42,
3857e3860.
ꢀ
€
28. Hernandez-Torres, J. M.; Achkar, J.; Wei, A. J. Org. Chem. 2004, 69, 7206e7211.
32. Dong, H.; Pei, Z.; Ramstrom, O. J. Org. Chem. 2006, 71, 3306e3309.
33. Dong, H.; Pei, Z.; Angelin, M.; Bystrom, S.; Ramstrom, O. J. Org. Chem. 2007, 72,
€
€
29. (a) De Mico, A.; Margarita, R.; Parlanti, L.; Vescovi, A.; Piancatelli, G. J. Org.
Chem. 1997, 62, 6974e6977; (b) Epp, J. B.; Widlanski, T. S. J. Org. Chem. 1999, 64,
293e295; (c) van den Bos, L. J.; Codee, J. D. C.; van der Toorn, J. C.; Boltje, T. J.;
3694e3701.
ꢀ
€
34. Dong, H.; Rahm, M.; Brinck, T.; Ramstrom, O. J. Am. Chem. Soc. 2008, 130,
van Boom, J. H.; Overkleeft, H. S.; van der Marel, G. A. Org. Lett. 2004, 6,
15270e15271 and references cited therein.