Stereoselective synthesis of β-C-D-glucopyranosides using the reaction of TMSCN and Grignard reagents with cyclic five-membered sulfonium salt intermediates

Article abstract of DOI:10.1016/S0040-4020(01)00160-0

In the presence of a Lewis acid, ArSCl adducts of tri-O-benzyl-D-glucal react with vinyl ethers to form cyclic five-membered sulfonium salt intermediates. The latter are capable of reacting with TMSCN and Grignard reagents furnishing exclusively 2-S-(aryl)-2-thio-β-C-D-glucopyranosides. The one-pot reaction also proceeds with high stereoselectivity of C-C bond formation in the lateral chain providing exclusively or predominantly C-glycosides with (S)-configuration of the chiral center in the lateral chain.

Full text of DOI:10.1016/S0040-4020(01)00160-0

TETRAHEDRON
Pergamon
Tetrahedron 57 12001) 2973±2980
Stereoselective synthesis of b-C-d-glucopyranosides using the
reaction of TMSCN and Grignard reagents with cyclic
®ve-membered sulfonium salt intermediates
Hui Liu and Irina P. Smoliakovap
Chemistry Department, University of North Dakota, Grand Forks, ND 58202-9024, USA
Received 20 December 2000; accepted 6 February 2001
AbstractÐIn the presence of a Lewis acid, ArSCl adducts of tri-O-benzyl-d-glucal react with vinyl ethers to form cyclic ®ve-membered
sulfonium salt intermediates. The latter are capable of reacting with TMSCN and Grignard reagents furnishing exclusively 2-S-1aryl)-2-thio-
b-C-d-glucopyranosides. The one-pot reaction also proceeds with high stereoselectivity of C±C bond formation in the lateral chain providing
exclusively or predominantly C-glycosides with 1S)-con®guration of the chiral center in the lateral chain. q 2001 Elsevier Science Ltd. All
rights reserved.
1.Introduction
hydride ion to furnish aldehydes or ketones, acetals, and
ethers, respectively 1Scheme 2).9
Synthesis of C-glycosides and related compounds has been
an important direction in modern synthetic organic
chemistry.1 These non-hydrolyzable analogs of O-glyco-
sides have a number of valuable properties and applica-
tions,2 including their use as chiral precursors in syntheses
of other compounds.3 The major challenge in the prepara-
tion of C-glycosides is to obtain a- or b-isomers with high
stereoselectivity.1 One possible approach to solve this
problem is the use of cyclic intermediates.4 Recently, we
have shown that episulfonium-like intermediates 13a,b),
generated in the presence of a Lewis acid from ArSCl
adducts 12a,b) of glycals 1e.g. 1a,b), react with a number
of C-nucleophiles, including silyl enol ethers,5±7 allyl-
trimethylsilane,5±7 Grignard reagents,8 and vinyl ethers9 to
form C-glycosides 1Scheme 1).
In this paper, we disclose our results on the synthesis of
C-glycosides with a functionalized lateral chain using the
reaction of the ®ve-membered sulfonium intermediates with
TMSCN and Grignard reagents.
2.Results and discussion
Intermediate 5, forming in the reaction of p-TolSCl adduct
12) of tri-O-benzyl-d-glucal 11) with 1-methoxy-2-methyl-
propene 14) in the presence of SnCl4, was selected as the
model sulfonium salt and was prepared as previously
described.9 It was found that TMSCN reacted with
sulfonium salt 5 at temperatures above 2408C to give
1
C-glycoside 6 in 86% yield 1Scheme 3). The H NMR
In all the reactions, major isomers were b-gluco 1starting
from d-glucals) or b-galacto 1from d-galactal) derivatives.
In addition, small amounts of the corresponding a-manno
isomers were isolated as well. For the C-nucleophiles
studied, the best ratio of the isomers, b-gluco/a-manno $
97:3, was achieved using the 2,4,6-mesitylthio derivatives
and SnCl4 in CH2Cl2. In the case of vinyl ethers,9 the
reaction had a second intermediate, the ®ve-membered
sulfonium salt.10,11 It was demonstrated that this inter-
mediate can be quenched with H2O, MeOH, or a donor of
spectrum analysis revealed that the isolated product has
b-gluco structure 1J1,2ˆJ2,3ˆ10.3 Hz). The 13C NMR spec-
trum of the isolated product contained only one set of the
signals, con®rming that the reaction also proceeded with
complete stereocontrol of the C±C bond formation in the
lateral chain. It is signi®cant that no diastereomers of 6 were
detected in the reaction mixture.
To extend this work, we studied the reaction of sulfonium
salt 5 with Grignard reagents. The latter were chosen
because of their availability, easy handling, and the possi-
bility of introducing different groups in the lateral chain of
C-glycosides. Also, organomagnesium compounds have
been reported to be excellent nucleophiles in a similar reac-
tion, the ArS-mediated coupling of two vinyl ethers.10 We
found that sulfonium salt 5 readily reacted with MeMgBr in
Keywords: C-glycosides; episulfonium ions; sulfonium salts; Grignard
reagents; trimethylsilylcyanide.
p
Corresponding author. Fax: 11-701-777-2331;
e-mail: ismoliakova@mail.chem.und.nodak.edu
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020101)00160-0

2974
H. Liu, I. P. Smoliakova / Tetrahedron 57 /2001) 2973±2980
Scheme 1.
Scheme 2.
the range of 220±1208C to give C-glycoside 7 in a high
yield 1Scheme 3). Again, the isolated product was a single
isomer having the b-gluco con®guration. Similarly,
PhMgBr and methallylmagnesium chloride reacted with
sulfonium salt 5 to provide responding C-glycosides 8 and
10 in a high yield 1Scheme 3). In both the cases, the
compounds were only isomers of b-gluco con®guration
11H NMR data) and no traces of other isomers were
detected.
studied here, the substitution of SnCl4 for ZnCl2 or LiClO4
did not improve the ratio of the isomers 13:2 and 5:2,
respectively).
Since the size of the substituents in the reaction complex
might be important for the stereochemical outcome, we
replaced the MeO group with an EtO substituent in the
sulfonium intermediate by reacting pyranosyl chloride 2a
with 1-ethoxy-2-methylpropene 112, Scheme 4). The
reaction of intermediate 13 with allylmagnesium bromide
gave a high yield of C-glycoside 14, however without any
signi®cant improvement of the stereoselectivity.
When BnMgBr was employed in the reaction with the
sulfonium salt, the isolated product 9 was a mixture of
two diastereomers in a ratio of 8:1 1Scheme 3). The
compounds were separated using TLC chromatography
We also synthesized sulfonium salt 15 with the bulky 2,4,6-
trimethylphenyl 1mesityl, Mes) substituent at the sulfur
atom 1Scheme 5). The introduction of the bulky aryl
group affected the stereoselectivity of the reaction;
however, still two diastereomers of 16 11S)/1R)ˆ4:1) were
formed.
1
and analyzed by H NMR spectroscopy. The two isomers
both had the b-gluco con®guration and differed only in the
absolute con®guration of the chiral center in the lateral
chain.
The reaction of allylmagnesium bromide with intermediate
5 proceeded with poor stereoselectivity, providing two
b-gluco isomers 11 in a ratio of 3:1. In order to improve
the stereoselectivity, we varied a number of parameters/
conditions of the reaction. First, different Lewis acids
were used in the reaction of sulfonium intermediate 5
with allylmagnesium bromide. It is well known that the
change of a Lewis acid in various reactions may lead to
different stereochemical results;12 however, in the reaction
We then extended our investigation to see if the sulfonium
intermediates obtained from other vinyl ethers react with
TMSCN and Grignard reagents in a highly stereoselective
fashion as well. It was found that sulfonium intermediate 18
prepared from pyranosyl chloride 2a and methyl vinyl ether
117) reacted with TMSCN and PhMgBr to furnish b-C-d-
glucopyranosides 19 and 20, respectively, with high
stereoselectivity 11R)/1S) $ 95:5) though in a low yield

H. Liu, I. P. Smoliakova / Tetrahedron 57 /2001) 2973±2980
2975
Scheme 3.
Scheme 4.
Scheme 5.

2976
H. Liu, I. P. Smoliakova / Tetrahedron 57 /2001) 2973±2980
Scheme 6.
1Scheme 6). Similar results were obtained with sulfonium
salt 22 prepared from a-substituted vinyl ether 21
1Scheme 7).
sides 7±8, 10, 16, 19, 20, 23 and major isomers of 9, 11,
and 14 have the same con®guration as glycoside 6.
In order to explain the observed stereoselectivity, we
considered possible structures of the sulfonium intermediate
in detail. For the similar sulfonium salts prepared by
the ArS-mediated dimerization of two vinyl ethers, the
S±C1OR) bond length was determined to be somewhat
longer than it was expected for the ordinary C±S bond.11
In all the reactions studied, we observed either the exclusive
or predominant formation of one diastereomer. Using X-ray
crystal analysis of the sulfoxide prepared from C-glycoside
6, the 1R) absolute con®guration of the chiral center in the
lateral chain has been established. Presumably, C-glyco-
Scheme 7.
Scheme 8.
Figure 1. Coordination of SnL52 with the sulfonium intermediates.

H. Liu, I. P. Smoliakova / Tetrahedron 57 /2001) 2973±2980
2977
Scheme 9.
Based on these data, we suggest that intermediate 5 is likely
to exist as an equilibrating mixture of two isomeric forms,
1R)-5 and 1S)-5 1Scheme 8). Isomer 1R)-5, having the alkoxy
group trans relative to the hydrogen at C12) of the pyranose
ring, must be the predominant one. The SN2-like attack of
a nucleophile would give the product with the inverse
con®guration of the chiral center.
carbonyl compound was formed that further reacted with
triallylborane. It is noteworthy that triallylborane is known
to react with both ketones/aldehydes and water.
In summary, we describe a highly stereoselective method
for synthesis of 2-1S-aryl)-2-thio-b-C-d-glucopyranosides
having different functional groups in the lateral chain. The
proposed protocol involves an ef®cient one-pot coupling
of four components: glucal, ArSCl, vinyl ether, and external
C-nucleophile.
Another contributing, if not determining, factor to the
stereoselectivity of the reaction is the possible chelate effect.
We suggest that the tin atom is coordinated with the sulfur
and oxygen atoms of the sulfonium salt 1Fig. 1). Because of
the steric hindrance, formation of the chelate complex with
intermediate 1S)-5 would be unlikely. The coordination of
the metal with isomer 1R)-5 appears to be more probable and
leads to an increase in the stability of the 1R)-intermediate.
Thus, the possible chelate effect also predicts the preferable
3.Experimental
3.1. Instrumentation and materials
1H and 13C NMR spectra were recorded on a Bruker Avance
500 spectrometer. Chemical shifts are given in ppm relative
to TMS; coupling constants, J, are provided in Hz. Mass
spectrometric data were obtained on a Finnigan MAT 95
mass spectrometer. IR spectra were recorded on an ATI
Mattson Genesis Series FTIR spectrometer. Optical
rotation data were measured on an Autopol III automatic
polarimeter. Preparative TLC was carried out by using glass
plates, 200£250 mm, with an un®xed layer of Aldrich silica
gel 60, 230±400 mesh. Analytical TLC was performed on E.
Merck precoated plates of silica gel 60 F254. All reactions
were carried out under an atmosphere of dry nitrogen using
oven-dried or ¯ame-dried glassware and freshly distilled
and dried solvents.
²
formation of the 1R)-product.
It is noteworthy that in the reactions studied, RMgBr also
reacted with SnCl4 and, as a result, organotin by-products,
e.g. Bn4Sn and Ph3SnOH, were isolated as well.13 In the case
of PhMgBr, BnMgBr and methallylmagnesium chloride, the
use of 4 equiv. of the Grignard reagents was suf®cient and
increasing these quantities up to 8 equiv. did not result in a
noticeable change in the yield or stereoselectivity. However,
for MeMgBr and allylmagnesium bromide, the reaction of
the sulfonium intermediates with 4 equiv. of the Grignard
reagents did not take place. Apparently, under these reaction
conditions, the Grignard reagents were converted to Me4Sn
and similar organotin species, which were nonreactive
toward the sulfonium intermediates. The use of 8 equiv. of
MeMgBr and allylmagnesium bromide, however, provided
high yields of the desired C-glycosides.
Arylsulfenyl chlorides were obtained from 4-methylbenze-
nethiol and 2,4,6-trimethylaryl 1mesityl) disul®de using
SO2Cl2.15 Methyl vinyl ether was synthesized from
n-butyl vinyl ether and MeOH in the presence of
Hg1OAc)2.16 1-Methoxy-2-methylpropene and 1-ethoxy-2-
methylpropene were prepared by pyrolysis of the corre-
sponding acetals using p-toluenesulfonic acid as a catalyst.
Other chemicals were purchased from Aldrich Chemical.
It is interesting that the reaction of intermediate 22 with
MeMgBr provided b-C-d-glucoside 25 bearing a hydroxyl
group in the lateral chain 1Scheme 9). The compound was
isolated in a single isomeric form, but we could not deter-
mine the absolute con®guration of the chiral center in the
lateral chain. We suggest that, under the conditions used, the
Grignard reagent did not react with the sulfonium salt 22.
After quenching the reaction mixture with ice±water, inter-
mediate 22 was instantly converted to the corresponding
aldehyde 249 that further reacted with MeMgBr. Similar
results were observed in previous studies of the reaction
of triallylborane with cyclic sulfonium salts that had been
generated from simple vinyl ethers.14 No reaction was
observed between the sulfonium salt and triallylborane.
However, when water was introduced, the corresponding
3.2. General procedure for synthesis of C-glycosides
6±11, 14, 16, 19, 22, and 24
To a solution of 0.208 g tri-O-benzyl-d-glucal 10.5 mmol) in
CH2Cl2 120 mL), 0.28 mL 1.8 M solution of p-TolSCl
10.5 mmol) in CH2Cl2 was added dropwise at room tempera-
ture. The color changed from yellow to colorless within
20 min. The mixture then was cooled to 2788C, and
0.6 mL of 1.0 M solution of vinyl ether 10.6 mmol) in
CH2Cl2 was added, followed by 0.6 mL of 1.0 M solution
of SnCl4 10.6 mmol) in CH2Cl2. The mixture was stirred
at 2788C for 30 min, then 2 mmol 1TMSCN or 3.0 M
solution of PhMgBr in ether) or 4 mmol 11.0 M solution
of allylmagnesium bromide in ether, 0.5 M solution of
²
Reactions of intermediate 1.R)-5 give cyano derivatives 6 and 19 with
the 1R) absolute con®guration; however, other products have the 1S)
con®guration due to different priorities of the CN and alkyl groups.

2978
H. Liu, I. P. Smoliakova / Tetrahedron 57 /2001) 2973±2980
2-methylallylmagnesium bromide in THF, 3.0 M solution of
MeMgBr in ether or 2.0 M solution of BnMgBr in ether) of a
C±Nu was added. The temperature was slowly raised to
2308C within 2 h. Then the mixture was stirred at rt for
12 h, quenched with saturated solution of NaHCO3,
extracted with ether, and dried over Na2SO4. Preparative
TLC of the crude material after solvent removal in vacuum
afforded a C-glycoside. Yields and isomer ratios of the
C-glycosides are given in Schemes 3±6.
24H, H-Arom); 13C NMR: 19.5, 19.6, and 21.1 13CH3
groups), 43.9 1C1CH3)2), 50.2 1CHS), 56.9 1OCH3), 70.3,
73.2, 73.4, and 74.3 14OCH2 groups), 77.9, 78.0, 82.1,
82.6, and 86.8 15CHO groups), 127.1, 127.4, 127.5, 127.7,
127.8, 128.1, 128.2, 128.3, 128.4, 128.9, 129.6, 129.7,
129.8, 131.4, 132.5, 136.7, 138.2, 138.3, 138.6, and 139.0
1C-Arom); HRMS: Calcd for C45H50SO5Na 725.3277;
Found: 1MNa)1 m/e 725.3255.
3.2.4. 13S)-3-Methoxy-2-methyl-4-phenyl-2-C-[3,4,6-tri-
O-benzyl-2-S-1p-tolyl)-2-thio-b-d-glucopyranosyl]butane
[13S)-9, major isomer]. Rf 0.36 11:9 ether±hexane);
3.2.1. 12R)-2-Methoxy-3-methyl-3-C-[3,4,6-tri-O-benzyl-
2-S-1p-tolyl)-2-thio-b-d-glucopyranosyl]butanenitrile 16).
Rf 0.43 11:2 ether±hexane); [a]28 ˆ238.18 1c 0.0359,
[a]20 ˆ230.98 1c 0.0042, CHCl3); 1H NMR: 1.00 and
D
D
1
CHCl3); IR 1neat, n, cm21): 2233 w 1CN); H NMR: 1.06
1.18 1two s, 6H, C1CH3)2), 2.34 1s, 3H, CH3), 2.57 1dd,
0
0
0
0
0
00
and 1.25 1two s, 6H, C1CH3)2), 2.31 1s, 3H, CH3), 3.26 1br. t,
J1,2ˆJ2,3ˆ10.3 Hz, 1H, H-2), 3.46 1m, 1H, H-5), 3.48 1s, 3H,
OCH3), 3.58 1d, 1H, H-1), 3.65 1m, 3H, H-3, H-4 and H-6a),
3.70 1dd, J5,6bˆ11.0 Hz, 1H, H-6b), 4.48 1s, 1H, CHCN),
4.52 and 4.58 1two d, JABˆ12.2 Hz, 2H, CH2Ph), 4.60 and
4.77 1two d, JABˆ11.0 Hz, 2H, CH2Ph), 4.77 and 4.88 1two
d, JABˆ10.4 Hz, 2H, CH2Ph), 7.28 1m, 19H, H-Arom); 13C
NMR: 19.9, 21.1, and 21.4 13CH3 groups), 42.9 1C1CH3)2),
52.8 1CHS), 58.6 1OCH3), 69.5, 73.6, 74.8, and 76.4
14OCH2 groups), 79.1, 79.7, 82.2, and 85.4 14CHOR
groups), 117.6 1CN), 127.9, 127.9, 128.0, 128.1, 128.2,
128.5, 128.6, 128.8, 128.9, 130.3 and 130.9 1C-Arom);
HRMS 1EI): Calcd for C40H45SO5N 651.3016; Found: M1
m/e 651.3034.
J4a ,4b ˆ13.4 Hz, J4a ,3 ˆ9.9 Hz, 1H, H-4a ), 2.85 1dd,
J4b ,3 ˆ2.3 Hz, 1H, H-4b0), 2.91 1s, 3H, OCH3), 3.40 1dd,
J1,2ˆ9.0 Hz, J2,3ˆ7.3 Hz, 1H, H-2), 3.42 1ddd, J4,5ˆ9.2 Hz,
J5,6aˆ2.3 Hz, J5,6bˆ4.9 Hz, 1H, H-5), 3.48 1d, 1H, H-1),
3.56 1dd, 1H, H-30), 3.58 1dd, J4,5ˆ9.2 Hz, J3,4ˆ7.0 Hz,
1H, H-4), 3.63 1dd, J5,6aˆ2.3 Hz, J6a,6bˆ10.9 Hz, 1H,
H-6a), 3.65 1dd J5,6bˆ4.9 Hz, 1H, H-6b), 3.69 1dd, 1H,
H-3), 4.48 and 4.68 1two d, JABˆ11.2 Hz, 2H, CH2Ph),
4.61 1m, 2H, CH2Ph), 4.62 and 4.85 1two d, JABˆ10.8 Hz,
2H, CH2Ph), 7.23 1m, 19H, H-Arom); 13C NMR: 19.5, 19.6,
and 21.1 13CH3 groups), 37.0 1CH2Ph), 43.9 1C1CH3)2), 51.3
1CHS), 61.2 1OCH3), 69.6, 73.2, 73.7, and 74.8 14OCH2
groups), 78.6, 79.0, 83.5, 83.6, and 87.8 15CHO groups),
127.5, 127.6, 127.8, 127.7, 127.9, 128.1, 128.2, 128.3,
128.4, 129.6, 129.8, 131.7, 132.7; 136.5, 138.2, 138.4,
138.5, and 140.8 1C-Arom); HRMS: Calcd for C46H52O5S
716.3522; Found: M1 m/e 716.3557.
3.2.2. 12S)-3-Methoxy-2-methyl-2-C-[3,4,6-tri-O-benzyl-
2-S-1p-tolyl)-2-thio-b-d-glucopyranosyl]butane 17). Rf
0.47 11:2 ether±hexane); [a]20 ˆ239.38 1c 0.0207,
D
CHCl3); IR 1neat, n, cm21): 1497 s 1arom. ring); 1H
NMR: 0.99 and 1.01 1two s, 6H, C1CH3)2), 1.05 1d,
JABˆ6.2 Hz, 3H, CH3), 2.34 1s, 3H, CH3), 3.31 1s, 3H,
OCH3), 3.38 1t, J1,2ˆ8.9 Hz, J2,3ˆ9.0 Hz, 1H, H-2), 3.40
1m, 1H, H-5), 3.45 1d, 1H, H-1), 3.53 1dd, J3,4ˆ6.4 Hz,
1H, H-3), 3.57 1quart., JABˆ6.2 Hz, 1H, CHCH3), 3.64
1m, 2H, H-6), 3.66 1br. t, J4,5 < 7.5 Hz, 1H, H-4), 4.45
and 4.65 1two d, JABˆ11.2 Hz, 2H, CH2Ph), 4.54 and 4.60
1two d, JABˆ12.1 Hz, 2H, CH2Ph), 4.57 and 4.80 1two d,
JABˆ9.8 Hz, 2H, CH2Ph), 7.26 1m, 19H, H-Arom); 13C
NMR: 12.7, 19.5, 19.6, and 21.1 14CH3 groups), 42.9
1C1CH3)2), 50.9 1CHS), 57.0 1OCH3), 70.0, 73.2, 73.6, and
74.6 14OCH2 groups), 78.7, 79.2, 80.1, 83.2 and 83.4
15CHO groups), 127.4, 127.5, 127.6, 127.7, 127.8, 127.9,
128.0, 128.1, 128.2, 128.3, 129.7, 132.8, 136.4, 138.3, and
138.6 1C-Arom); HRMS: Calcd for C40H48SO5Na 663.3120;
Found: 1MNa)1 m/e 663.3098.
3.2.5. 13R)-3-Methoxy-2-methyl-4-phenyl-2-C-[3,4,6-tri-
O-benzyl-2-S-1p-tolyl)-2-thio-b-d-glucopyranosyl]butane
[13R)-9, minor isomer]. Rf 0.34 11:9 ether±hexane);
[a]20 ˆ241.48 1c 0.0007, CHCl3); IR 1neat, n, cm21):
D
1
1496 s 1arom. ring); H NMR: 0.97 and 1.14 1two s, 6H,
0
0
C1CH3)2), 2.34 1s, 3H, CH3), 2.62 1dd, J4a ,4b ˆ13.5 Hz,
0
0
0
0
0
J4a ,3 ˆ10.0 Hz, 1H, H-4a ), 2.89 1dd, J4b ,3 ˆ2.3 Hz, 1H,
H-4b0), 2.91 1s, 3H, OCH3), 3.38 1dd, J1,2ˆ8.4 Hz, J2,3ˆ
6.5 Hz, 1H, H-2), 3.48 1ddd, J4,5ˆ8.8 Hz, J5,6aˆ2.6 Hz,
J5,6bˆ5.3 Hz, 1H, H-5), 3.54 1dd, J3,4ˆ5.4 Hz, 1H, H-4),
3.58 1dd, J6a,6bˆ10.9 Hz, 1H, H-6a), 3.62 1dd, 1H, H-6b),
3.66 1d, 1H, H-1), 3.73 1dd, 1H, H-3), 3.78 1dd, 1H, H-30),
4.38 and 4.59 1two d, JABˆ11.4 Hz, 2H, CH2Ph), 4.51 and
4.55 1two d, JABˆ12.2 Hz, 2H, CH2Ph), 4.50 and 4.77 1two
d, JABˆ11.1 Hz, 2H, CH2Ph), 7.24 1m, 19H, H-Arom); 13
C
NMR: 19.2, 19.6 and 21.1 13CH3 groups), 37.4 1CH2Ph),
43.9 1C1CH3)2), 49.9 1CHS), 60.7 1OCH3), 70.2, 73.0, 73.2,
and 73.8 14OCH2 groups), 78.3, 78.7, 81.8, 82.3, and 87.0
15CHO groups), 127.4, 127.5, 127.8, 128.1, 128.2, 128.3,
128.4, 129.6, 129.7, 129.8, 131.7, and 132.5 1C-Arom);
HRMS: Calcd for C46H52SO5Na 739.3433; Found:
1MNa)1 m/e 739.3409.
3.2.3. 13S)-3-Methoxy-2-methyl-3-phenyl-2-C-[3,4,6-tri-
O-benzyl-2-S-1p-tolyl)-2-thio-b-d-glucopyranosyl]pro-
pane 18). Rf 0.36 11:4 ether±hexane); [a]20 ˆ222.48 1c
D
0.0264, CHCl3); IR 1neat, n, cm21): 1493 s 1arom. ring);
1H NMR: 0.92 and 1.09 1two s, 6H, C1CH3)2), 2.34 1s, 3H,
CH3), 3.19 1s, 3H, OCH3), 3.28 1d, J1,2ˆ8.5 Hz, 1H, H-1),
3.40 1dd, J2,3ˆ8.8 Hz, 1H, H-2), 3.42 1ddd, J4,5ˆ7.0 Hz,
J5,6aˆ3.4 Hz, J5,6bˆ7.9 Hz, 1H, H-5), 3.51 1dd, J2,3ˆ
8.8 Hz, J3,4ˆ6.0 Hz, 1H, H-3), 3.63 1dd, J3,4ˆ6.0 Hz, 1H,
H-4), 3.64 1m, 1H, H-6b), 3.70 1m, 2H, H-6), 4.42 and 4.62
1two d, JABˆ11.2 Hz, 2H, CH2Ph), 4.54 and 4.79 1two d,
JABˆ11.0 Hz, 2H, CH2Ph), 4.60 and 4.65 1two d,
JABˆ12.3 Hz, 2H, CH2Ph), 4.65 1s, 1H, H-30), 7.25 1m,
3.2.6. 14S)-4-Methoxy-2,5-dimethyl-5-C-[3,4,6-tri-O-ben-
zyl-2-S-1p-tolyl)-2-thio-b-d-glucopyranosyl]-1-hexene
110). Rf 0.42 11:8 ether±hexane); [a]28 ˆ243.78 1c 0.0036,
D
1
CHCl3); IR 1neat, n, cm21): 1647 1CvC); H NMR: 0.96
and 1.12 1two s, 6H, C1CH3)2), 1.72 1s, 3H, CH3Cv), 2.15
1m, 2H, CH2Cv), 2.31 1s, 3H, CH3), 3.36 1s, 3H, OCH3),
0
0
3.39 1m, 3H, H-2, H-4, and H-5), 3.55 1dd, J3 ,4a ˆ9.2 Hz,
J3 ,4b ˆ3.8 Hz, 1H, H-30), 3.61 1dd, J6a,6bˆ11.0 Hz,
0
0

H. Liu, I. P. Smoliakova / Tetrahedron 57 /2001) 2973±2980
2979
J5,6aˆ2.2 Hz, 1H, H-6a), 3.62 1m, 1H, H-4), 3.67 1d,
2.44 1m, 1H, H-3b0), 2.47 1s, 6H, ortho-CH3 of Mes), 3.34
1dd, J1ˆ8.6 Hz, J2ˆ3.4 Hz, 1H, H-40), 3.41 1m, 2H, H-3 and
H-4), 3.46 1s, 3H, OCH3), 3.52 1m, 2H, H-2 and H-6b), 3.57
1d, J1,2ˆ4.7 Hz, 1H, H-1), 3.60 1dd, Jˆ11.0, 2.3 Hz, 1H,
H-6b), 3.76 1m, 1H, H-5), 3.80 and 4.27 1two d,
J1,2ˆ6.8 Hz, 1H, H-1), 3.69 1dd, J6a,6bˆ11.0 Hz, J5,6b
ˆ
4.6 Hz, 1H, H-6a), 4.49 and 4.67 1two d, JABˆ11.1 Hz,
2H, CH2Ph), 4.55 and 4.57 1two d, JABˆ12.4 Hz, 2H,
CH2Ph), 4.60 and 4.82 1two d, JABˆ10.8 Hz, 2H, CH2Ph),
4.80 and 4.85 1two br. s, 2H, H-10), 7.25 1m, 19H, H-Arom);
13C NMR: 20.0, 20.1, 21.0, and 22.9 14CH3 groups), 39.1
1CH2Cv), 43.8 1C1CH3)2), 51.1 1CHS), 60.8 1OCH3), 69.5,
73.2, 73.7, and 74.7 14OCH2 groups), 78.6, 78.9, 83.3, 83.6,
and 84.2 15CHO groups), 112.5 1CvCH2), 127.4, 127.5,
127.6, 127.8, 128.1, 128.3, 128.4, 129.8, 131.0, 132.7 and
136.3 1C-Arom), 144.3 1CvCH2). HRMS: Calcd for
C43H52O5S 680.3522; Found: M1 m/e 680.3535.
JABˆ12.0 Hz, 2H, CH2Ph), 3.91 and 3.99 1two d, JAB
ˆ
11.8 Hz, 2H, CH2Ph), 4.53 and 4.56 1two d, JABˆ12.2 Hz,
2H, CH2Ph), 5.05 1m, 2H, H-10), 5.93 1m, 1H, H-20), 7.20
1m, 19H, H-Arom); 13C NMR: 18.5 and 20.1 1C1CH3)2),
21.0 1para-CH3), 22.3 1ortho-CH3), 35.3 1CH2Cv), 42.7
1C1CH3)2), 43.1 1CHS), 60.7 1OCH3), 69.9, 70.9, 71.0, and
73.1 14OCH2 groups), 76.7, 78.1, 78.2, 84.7, and 86.1
15CHO groups), 115.9 1vCH2), 127.3, 127.4, 127.5,
127.6, 127.8, 128.06, 128.11, 128.15, 128.2, 128.5, 128.6,
129.2, 137.7, 137.9, and 138.6 1C-Arom), 143.3 1vCH);
HRMS: Calcd for C44H54SO5Na 717.3590; Found:
1MNa)1 m/e 717.3590.
3.2.7. 14S)-4-Methoxy-5-methyl-5-C-[3,4,6-tri-O-benzyl-
2-S-1p-tolyl)-2-thio-b-d-glucopyranosyl]-1-hexene [14S)-
11, major isomer]. Rf 0.34 11:9 ethyl acetate±hexane);
[a]20 ˆ252.18 1c 0.0022, CHCl3); IR 1neat, n, cm21):
D
1639 1CvC); 1H NMR: 0.96 and 1.15 1two s, 6H,
C1CH3)2), 2.18 1m, 1H, H-3a0), 2.31 1m, 1H, H-3b0), 2.33
1s, 3H, CH3), 3.38 1s, 3H, OCH3), 3.37 1m, 4H, H-1, H-2,
H-5, and H-30), 3.56 1dd, J2,3ˆ9.2 Hz, J3,4ˆ6.8 Hz, 1H,
H-3), 3.62 1dd, J6a,6bˆ11.0 Hz, J5,6aˆ2.3 Hz, 1H, H-6a),
3.65 1dd, J5,6aˆ5.0 Hz, 1H, H-6b), 3.68 1br. t, J3,4ˆJ4,5ˆ
6.8 Hz, 1H, H-4), 4.48 and 4.67 1two d, JABˆ11.2 Hz, 2H,
CH2Ph), 4.54 and 4.58 1two d, JABˆ12.3 Hz, 2H, CH2Ph),
4.62 and 4.85 1two d, JABˆ10.8 Hz, 2H, CH2Ph), 4.99 1m,
2H, H-10), 5.86 1m, 1H, H-20), 7.25 1m, 19H, H-Arom); 13C
NMR: 20.1, 20.1, and 21.4 13CH3 groups), 35.5 1CH2Cv),
43.6 1C1CH3)2), 51.5 1CHS), 60.6 1OCH3), 69.7, 73.2, 74.8,
and 75.9 14OCH2 groups), 78.5, 79.2, 83.4, 83.8, and 85.9
15CHO groups), 115.7 1vCH2), 127.4, 127.5, 127.6, 127.7,
127.8, 127.9, 128.0, 128.3, 128.4, 129.6, 129.8, 131.0,
133.3, and 136.5 1C-Arom), 137.5 1vCH); HRMS: Calcd
for C42H50O5S 666.3392; Found: M1 m/e 666.3366.
3.2.10. 12S)-2-Methoxy-3-C-[3,4,6-tri-O-benzyl-2-S-1p-
tolyl)-2-thio-b-d-glucopyranosyl]propanenitrile 119). Rf
0.29 11:2 ether±hexane); [a]28 ˆ230.08 1c 0.0012,
D
1
CHCl3); IR 1neat, n, cm21): 2243 w 1CN); H NMR: 2.32
0
0
1s, 3H, CH3), 1.96 and 2.71 1two ddd, J1a ,1b ˆ13.8 Hz,
0
0
0
0
0
0
J1a ,1ˆ10.0 Hz, J1b ,1ˆ2.6 Hz, J1a ,2 ˆ5.2 Hz, J1b ,2 ˆ9.7 Hz,
2H, H-1a0 and H-1b0), 2.91 1t, J1,2ˆJ2,3ˆ10.6 Hz, 1H, H-2),
3.36 1ddd, J4,5ˆ8.4 Hz, J5,6aˆ2.0 Hz, J5,6bˆ3.6 Hz, 1H,
H-5), 3.43 1s, 3H, OCH3), 3.55 1m, 2H, H-1 and H-3),
3.68 1m, 1H, H-3), 3.70 and 3.75 1two dd, J6a,6bˆ11.0 Hz,
2H, H-6a and H-6b), 4.30 1dd, 1H, H-20), 4.50 and 4.59 1two
d, JABˆ12.2 Hz, 2H, CH2Ph), 4.58 and 4.83 1two d,
JABˆ10.8 Hz, 2H, CH2Ph), 4.88 and 5.06 1two d, JAB
ˆ
10.3 Hz, 2H, CH2Ph), 7.28 1m, 19H, H-Arom); 13C NMR:
21.1 1CH3), 36.1 1CH2), 56.8 1CHS), 58.0 1OCH3), 68.7,
73.4, 75.0, and 76.2 14OCH2), 68.4, 76.4, 78.6, 79.4, and
84.2 15OCH groups), 117.8 1CN), 127.6, 127.7, 127.8,
127.9, 128.0, 128.1, 128.3, 128.4, 128.5, 130.0, 130.1,
130.7, 132.5, 132.7, 134.5, 137.6, and 138.1 1C-Arom);
HRMS: Calcd for C38H41SO5N 623.2705; Found: M1 m/e
623.2727.
3.2.8. 14R)-4-Methoxy-5-methyl-5-C-[3,4,6-tri-O-benzyl-
2-S-1p-tolyl)-2-thio-b-d-glucopyranosyl]-1-hexene [14R)-
11, minor isomer]. Rf 0.33 11:9 ethyl acetate±hexane, 1:9);
[a]20 ˆ241.18 1c 0.0009, CHCl3); IR 1neat, n, cm21): 1640
D
1CvC); 1H NMR: 0.87 and 1.05 1two s, 6H, C1CH3)2), 2.20
1m, 1H, H-3a0), 2.33 1m, 1H, H-3b0), 2.34 1s, 3H, CH3), 3.32
1s, 3H, OCH3), 3.34 1m, 1H, H-2), 3.47 1ddd, J4,5ˆ8.9 Hz,
J5,6aˆ2.6 Hz, J5,6bˆ4.9 Hz, 1H, H-5), 3.53 1dd, J3,4ˆ5.4 Hz,
1H, H-4), 3.57 1dd, J6a,6bˆ9.0 Hz, 1H, H-6a), 3.63 1m, 3H,
H-6b, H-1, H-40), 3.72 1dd, J2,3ˆ6.5 Hz, 1H, H-3), 4.40 and
4.60 1two d, JABˆ11.3 Hz, 2H, CH2Ph), 4.51 and 4.77 1two
d, JABˆ10.9 Hz, 2H, CH2Ph), 4.53 and 4.57 1two d,
JABˆ11.3 Hz, 2H, CH2Ph), 5.03 and 5.13 1two m, 2H,
H-10), 5.96 1m, 1H, H-20), 7.25 1m, 19H, H-Arom); 13C
NMR: 19.9, 19.3, and 21.1 13CH3 groups), 35.7 1CH2Cv),
43.7 1C1CH3)2), 49.9 1CHS), 60.5 1OCH3), 70.2, 73.1, 73.2,
and 73.9 14OCH2 groups), 78.2, 78.8, 82.1, 82.2, and 84.5
15CHO groups), 115.9 1vCH2), 127.4, 127.5, 127.6, 127.7,
127.8, 127.9, 128.0, 128.3, 128.4, 129.6, 129.8, 131.0, 133.3,
and 136.5 1C-Arom), and 137.5 1vCH); HRMS: Calcd for
C42H50SO5Na 689.3277; Found: 1MNa)1 m/e 689.3303.
3.2.11. 11S)-1-Methoxy-1-phenyl-2-C-[3,4,6-tri-O-ben-
zyl-2-S-1p-tolyl)-2-thio-b-glucopyranosyl]ethane 120). Rf
0.43 1CHCl3); [a]D
ˆ221.58 1c 0.0015, CHCl3); 1H
21.0
0
NMR 1500 MHz): 1.56 and 2.73 1two ddd, J1,2a ˆ11.3 Hz,
0
0
0
0
0
0
0
J1,2b ˆ1.7 Hz, J2a 2b ˆ12.4 Hz, J1 ,2a ˆ2.5 Hz, J1 ,2b
ˆ
10.7 Hz, 2H, H-2b0), 2.28 1s, 3H, CH3), 2.83 1t, J2,3ˆ
10.5 Hz, J1,2ˆ10.6 Hz, 1H, H-2), 3.19 1s, 3H, OCH3), 3.42
1ddd, J4,5ˆ9.5 Hz, J5,6aˆ6.3 Hz, J5,6bˆ3.2 Hz, 1H, H-5),
3.60 1dd, J3,4ˆ8.8 Hz, J2,3ˆ10.5 Hz, 1H, H-3), 3.63 1dd,
1H, H-4), 3.69 1ddd, 1H, H-1), 3.73 1m, 2H, H-6a and
H-6b), 4.42 1dd, 1H, H-10), 4.60 1two d, JABˆ12.2 Hz, 2H,
CH2Ph), 4.75 1two d, JABˆ10.9 Hz, 2H, CH2Ph), 4.95 1two
d, JABˆ10.4 Hz, 2H, CH2Ph), 7.28 1m, 24H, H-Arom); 13C
NMR 1125 MHz): 21.0 1CH3), 41.7 1CH2), 56.8 1CHS), 57.1
1OCH3), 69.6, 73.8, 75.2, and 76.4 14OCH2 groups), 77.2,
79.1, 80.3, and 85.4 14CHOR groups), 126.7, 127.4, 127.6,
127.7, 127.8, 128.0, 128.3, 128.4, 128.6, 128.7, 128.8,
130.0, 122.5, 132.8, and 142.6 1C-Arom); HRMS: Calcd
for C43H46SO5Na 697.2928; Found: 1MNa)1 m/e 697.2964.
3.2.9. 14S)-4-Methoxy-5-methyl-5-C-[3,4,6-tri-O-benzyl-
2-S-1mesityl)-2-thio-b-d-glucopyranosyl]-1-hexene [14R)-
16). Rf 0.47 16:1 hexane±ethyl acetate); [a]21 ˆ233.08 1c
3.2.12. 13S)-2-Methoxy-2-trimethylsilyl-3-C-[3,4,6-tri-O-
benzyl-2-S-1p-tolyl)-2-thio-b-glucopyranosyl]propaneni-
D
0.0021, CHCl3); 1H NMR: 0.97 and 1.07 1two s, 6H,
C1CH3)2), 2.20 1m, 1H, H-3a0), 2.30 1s, 3H, para-CH3),
trile 123). Rf 0.53 11:6 ether±hexane); [a]22 ˆ254.38 1c
D

2980
H. Liu, I. P. Smoliakova / Tetrahedron 57 /2001) 2973±2980
1
0.0015, CHCl3); IR 1neat, n, cm21): 2212 1CN); H NMR:
Tetrahedron Organic Chemistry Series, Vol. 13; Elsevier:
Tarrytown, NY, 1995. 1b) Postema, M. H. D. C-Glycoside
Synthesis, CRC: Boca Raton, FL, 1995. 1c) Nicotra, F. Top.
Curr. Chem. 1997, 187, 55. 1d) Du, Y.; Linhardt, R. J.;
Vlahov, I. R. Tetrahedron 1998, 54, 9913±9959. 1e) Beau,
J.-M.; Gallagher, T. Top. Curr. Chem. 1998, 187, 1.
1f) Jaramillo, C.; Knapp, S. Synthesis 1994, 1.
0
0
0
0.13 1s, 9H, Si1CH3)3), 1.62 1dd, J3a ,1ˆ9.8 Hz, J3a ,3b
ˆ
14.8 Hz, 1H, H-3a0), 2.18 1s, 3H,0 CH3), 2.59 1dd, J3b ,1
ˆ
0
0
0
1.2 Hz, J3a ,3b ˆ14.8 Hz, 1H, H-3b ), 2.85 1t, J1,2ˆ10.6 Hz,
J2,3ˆ10.6 Hz, 1H, H-2), 3.25 1m, J5,6aˆ1.9 Hz, J6a,6b
ˆ
9.8 Hz, 1H, H-6a), 3.42 1s, 3H, OCH3), 3.46 1dd, J2,3ˆ
0
10.6 Hz, J3,4ˆ8.7 Hz, 1H, H-3), 3.53 1m, J1,3a ˆ9.8 Hz,
0
2. 1a) Rohr, J.; Thiericke, R. Nat. Prod. Rep. 1992, 103.
1b) Murenetz, N. V. Antibiot. Khimioter. 1990, 35, 47.
1c) Hacksell, U.; Daves, Jr., G. D. Prog. Med. Chem. 1985,
22, 1.
J1,3b ˆ1.2 Hz, J1,2ˆ10.6 Hz, 1H, H-1), 3.68 1m, J5,6b
ˆ
10.2 Hz, J6a,6bˆ9.8 Hz, 1H, H-6b), 3.70 1m, J3,4ˆ8.7 Hz,
J4,5ˆ6.3 Hz, 1H, H-4), 3.60 1m, J4,5ˆ6.3 Hz, J5,6aˆ1.9 Hz,
J5,6bˆ10.2 Hz, 1H, H-5), 4.45 and 4.57 1two d, JAB
ˆ
3. 1a) Hanessian, S. Total Synthesis of Natural Products: The
Chiron Approach, Pergamon: Oxford, 1983. 1b) Wolbers, P.;
Hoffmann, H. M. R. Tetrahedron 1999, 55, 1905. 1c) Paterson,
L.; Keown, L. E. Tetrahedron Lett. 1997, 38, 5727±5730.
1d) Smith III, A. B.; Zhuang, L.; Brook, C. S.; Boldi, A. M.;
McBriar, M. D.; Moser, W. H.; Murase, N.; Nakayama, K.;
Verhoest, P. R.; Lin, Q. Tetrahedron Lett. 1997, 38, 8667±
8610.
11.8 Hz, 2H, CH2Ph), 4.59 and 4.77 1two d, JABˆ10.8 Hz,
2H, CH2Ph), 4.82 and 4.96 1two d, JABˆ10.3 Hz, 2H,
CH2Ph), 7.23 1m, 19H, H-Arom); 13C NMR: 23.9
[Si1CH3)3], 21.1 1CH3), 36.5 1CH2), 55.9 1OCH3), 57.6
1CHS), 69.2 1CTMS), 68.8, 74.1, 75.3, and 76.6 14OCH2
groups), 76.9, 79.1, 79.8, and 84.8 14CHO groups), 119.6
1CN), 127.5, 127.6, 127.7, 127.8, 127.9, 128.1, 128.3, 128.4,
129.8, 132.1, 137.3, 138.4. and 138.5 1C-Arom); HRMS:
Calcd for C41H49SO5Si 695.3101; Found: M1 m/e 695.3112.
4. Smoliakova, I. P. Curr. Org. Chem. 2000, 4, 589±608.
5. Smoliakova, I. P.; Caple, R.; Gregory, D.; Smit, W. A.;
Shashkov, A. S.; Chizhov, O. S. J. Org. Chem. 1995, 60,
1221±1227.
3.2.13. 2-Trimethylsilyl-3-C-[3,4,6-tri-O-benzyl-2-S-1p-
tolyl)-2-thio-b-glucopyranosyl]-2-propanol 125). Rf 0.25
13:1 ether±hexane); [a]22 ˆ115.88 1c 0.0033, CHCl3); IR
6. Smoliakova, I. P.; Kim, Y. H.; Barnes, M. J.; Caple, R.; Smit,
W. A.; Shashkov, A. S. Mendeleev Commun. 1995, 15±16.
7. Han, M.; Koikov, L. K.; Smoliakova, I. P. Carbohydr. Res.
2000, 323, 202±207.
D
1neat, n, cm21): 3507 1OH); 1H NMR: 20.04 1s, 9H,
Si1CH3)3), 1.26 1s, 3H, CH3), 1.27 1s, 1H, OH), 1.62 1dd,
J3a ,3b ˆ14.8 Hz, J3a ,1ˆ10.6 Hz, 1H, H-3a0), 2.24 1dd,
0
0
0
J3a ,3b ˆ14.8 Hz, J3b ,1ˆ2.0 Hz, 1H, H-3b0), 2.35 1s, 3H,
CH3), 2.98 1t, J2,3ˆJ1,2ˆ10.3 Hz, 1H, H-2), 3.51 1m, 1H,
H-5), 3.60 1m, 1H, H-3), 3.63 1m, 2H, H-4, H-6a), 3.68
1dd, J6a,6bˆ10.7 Hz, J5,6bˆ2.28 Hz, 1H, H-6b), 3.83 1ddd,
8. Smoliakova, I. P.; Caple, R.; Brenny, J. W.; Smit, W. A.;
Kryschenko, Y. K.; Shashkov, A. S.; Chizov, O. S.; Krimer,
M. Z.; Morar, G. V.; Kalyan, Y. B. Synlett 1995, 275±276.
9. Smoliakova, I. P.; Han, M.; Gong, J.; Caple, R.; Smit, W. A.
Tetrahedron 1999, 55, 4559±4572.
0
0
0
0
0
J1,2ˆ10.3 Hz, J3a ,1ˆ10.6 Hz, J3b ,1ˆ2.0 Hz, 1H, H-1), 4.48
and 4.55 1two d, JABˆ12.1 Hz, 2H, CH2Ph), 4.58 and 4.85
1two d, JABˆ10.8 Hz, 2H, CH2Ph), 4.92 and 5.11 1two d,
JABˆ10.3 Hz, 2H, CH2Ph), 7.32 1m, 19H, H-Arom); 13C
NMR: 24.6 [Si1CH3)3], 21.0 and 22.5 1two CH3), 38.9
1CH2), 57.7 1CHS), 65.1 1CTMS) 69.2, 73.4, 74.9, and
76.2 14OCH2 groups), 78.4, 79.4, 79.6, and 84.2 14CHO
groups), 127.6, 127.7, 127.8, 127.9, 128.1, 128.3, 128.4,
128.5, 131.4, 132.6, 137.5, 137.9, 138.0, and 138.4
1C-Arom); HRMS: Calcd for C40H50SO5SiNa 693.3046;
Found: 1MNa)1 m/e 693.3046.
10. 1a) Koikov, L. N.; Han, M.; Wellman, D. M.; Kelly, J. A.;
Smoliakova, I. P. Synth. Commun. 2000, 30, 3451.
1b) Smoliakova, I. P.; Smit, W. A.; Osinov, B. D. Tetrahedron
Lett. 1991, 32, 2601±2604. 1c) Smoliakova, I. P.; Caple, R.;
Magnuson, V. R.; Polyakov, V. R.; Smit, W. A.; Shashkov,
A. S.; Ohinov, B. D. J. Chem. Soc., Perkin Trans. 1 1995,
1065±1069.
11. In a similar reaction with more simple substrates, such
intermediates were isolated and their structures were proven
by X-ray crystallographic analysis: Lazareva, M. I.;
Kryschenko, Y. K.; Caple, R.; Wake®eld, D.; Hayford, A.;
Smit, W. A.; Shashkov, A. S. Tetrahedron Lett. 1998, 39,
8787±3790.
Acknowledgements
12. Santelli, M.; Pons, J.-M. Lewis Acids and Selectivity in
Organic Synthesis, CRC: Boca Raton, FL, 1996.
Authors acknowledge the National Institute of General
Medical Sciences 1grant No. 1 R15 GM/OD55965-01) and
the University of North Dakota for ®nancial support. The
UND NMR facility was funded by the National Science
Foundation 1grant No. CHE-9871134). We also would
like to thank Ms. Jianchun Gong for performing some of
the experiments.
13. Spessard, G. O.; Miessler, G. L. Organometallic Chemistry,
Prentice-Hall: Upper Saddle River, NJ, 1996; p. 118.
14. Smoliakova, I. P.; Smit, W. A.; Bubnov, Y. N.; Shashkov,
A. S. Bull. Acad. Sci. USSR, Div. Chem. 1990, 1100±1107.
15. Fiser, M.; Fiser, L. F. P. Reagents for Organic Synthesis, Vol.
5; Wiley: New York, 1975; p. 523.
16. Burgstahler, A. W.; Nordin, I. C. J. Am. Chem. Soc. 1961, 38,
198±206.
References
1. 1a) Levy, D. E.; Tang, C. The Chemistry of C-Glycosides,