Reactions of phenyl and ethyl 2-O-sulfonyl-1-thio-α-d-manno- and β-d-glucopyranosides with thionucleophiles

Article abstract of DOI:10.1016/j.carres.2009.08.041

Persubstituted derivatives of phenyl and ethyl 2-O-sulfonyl-1-thio-α-d-manno- and β-d-glucopyranosides were synthesized and reacted either with PhSNa or with MeSNa. The phenyl-1-thio compounds afforded the dithio-1,2-cis-axial/equatorial-α-d-glucopyranosi

Full text of DOI:10.1016/j.carres.2009.08.041

Carbohydrate Research 344 (2009) 2461–2467
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Reactions of phenyl and ethyl 2-O-sulfonyl-1-thio-a-D-manno- and
b-D-glucopyranosides with thionucleophiles
a,b
András Lipták a, László Lázár a, Anikó Borbás a, , Sándor Antus
*
a Research Group for Carbohydrates of the Hungarian Academy of Sciences, H-4010 Debrecen, PO Box 94, Hungary
b Department of Organic Chemistry, University of Debrecen, H-4010 Debrecen, PO Box 20, Hungary
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 June 2009
Received in revised form 24 August 2009
Accepted 30 August 2009
Available online 4 September 2009
Persubstituted derivatives of phenyl and ethyl 2-O-sulfonyl-1-thio-
sides were synthesized and reacted either with PhSNa or with MeSNa. The phenyl-1-thio compounds
afforded the dithio-1,2-cis-axial/equatorial- -glucopyranosides or dithio-1,2-cis-equatorial/axial-b-D-
mannopyranosides by means of SN2 type of reactions. Starting from the ethyl-1-thio derivatives intramo-
lecular 1,2-thio-migration took place predominantly. In the case of mannosides both nucleophilic
reagents facilitate the formation of 1-SPh- or 1-SEt glycals by elimination. The formation of unsubstituted
glycal could also be observed from the ethyl-1-thio derivatives, especially by using PhSNa as a nucleo-
phile. The 1,2-dithio-glycosides are glycosyl donors affording 1,2-trans-2-thio-glycosides.
Ó 2009 Elsevier Ltd. All rights reserved.
a-D-manno- and b-D-glucopyrano-
a
-D
Keywords:
Nucleophilic substitution of thioglycosides
Thionucleophiles
1,2-Thiomigration
1-Substituted and unsubstituted glycals
1. Introduction
2. Results and discussion
Our present interest in the field of carbohydrate chemistry is
the synthesis of sugar-sulfonic1–4 and sugar methylsulfonic
acids5–8 and their utilization for the preparation of oligosaccharide
sulfonic acids.
Methanesulfonylation of the known12–14 compounds 1–4 re-
sulted in the 2-O-mesyl thioglycosides 5–8 that were characterized
by 1H NMR spectra and TLC (Scheme 1).
Treatment of compound 5 with PhSNa (5 equiv) in DMF at 40 °C
for 24 h gave only a single product 9 (Scheme 2). Both the 1H and
the 13C NMR spectra showed the presence of two SPh groups and
the 3-O-benzyl group, and the 4,6-O-benzylidene skeleton was also
present. The simple NMR spectra did not provide sufficient infor-
mation about the configuration of either C-2 or the anomeric car-
Among the synthetic processes of sugar 2-sulfonic acids the 1,2-
thiomigration procedures9–11 offer very attractive possibilities.
Whenever a suitable thioglycoside bearing a good leaving group
at position 2 is reacted with the appropriate nucleophile (MeONa,
NaN3, and Me3SiN3), the thio group migrates into position 2 while
the nucleophile attacks the anomeric position. Using readily
removable thiol protecting groups [p-methoxybenzyl, (2-naph-
thyl)methyl, trityl, allyl, trimethylsilylethyl, and acetyl] the ob-
tained 2-thio group can be deprotected and can be oxidized to a
sulfonate. In our laboratory gluco- and manno-2-sulfonic acid
derivatives were successfully prepared using this method.2–4
The application of alkoxide- and N3-nucleophiles resulted in
derivatives which cannot be utilized as glycosyl donors. Since our
goal was to prepare 2-thio compounds that are convertible to 2-
sulfonic acids and, at the same time, could serve as glycosyl donors,
the study of the applicability of thionucleophiles in 1,2-thiomigra-
tion reactions was decided. Therefore, phenyl and ethyl 2-O-
3
bon. The disappearance of the large J2,3 coupling constant
suggested the manno-configuration for compound 9. The b-config-
1
15
uration was verified by the measured 155.4 Hz value for JH1–C1
These data confirmed that compound 9 was phenyl 3-O-benzyl-
4,6-O-benzylidene-2-S-phenyl-1-thio-b- -mannopyranoside, iso-
.
D
lated with 47% yield. A 1,2-diphenylthio derivative can be formed
from 5 either in an intramolecular 1,2-thiomigration induced by
the nucleophilic attack of the thiophenolate at the anomeric posi-
tion or by means of an intermolecular nucleophilic substitution of
the 2-O-mesylate with the thiophenolate. The b-anomeric configu-
ration of compound 9 proves the latter mechanism, since the 1,2-
thiomigration would result in inversion of the anomeric configura-
tion via an episulfonium intermediate, or would afford an anomer-
ic mixture via an oxocarbenium ion intermediate.3,12
sulfonyl-1-thio-a-D-manno- and -b-D-glucopyranoside model com-
pounds were synthesized and reacted either with PhSNa or with
MeSNa.
Treatment of 5 with MeSNa (5 equiv) in DMF at 50 °C for 3 h re-
sulted again in a 1,2-dithio compound (10), whose structure deter-
mination was performed similarly to that of compound 9. The
* Corresponding author.
E-mail address: borbasa@puma.unideb.hu (A. Borbás).
1
observed data were as follows:
[a
]
D
+41.8; JC1–H1 155.6 Hz
0008-6215/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2009.08.041

2462
A. Lipták et al. / Carbohydrate Research 344 (2009) 2461–2467
OR
OR
O
O
O
O
Ph
O
Ph
Ph
Ph
O
O
O
O
O
O
O
SPh
SEt
BnO
BnO
BnO
BnO
OR
OR
SPh
SEt
15 R = H
R = Ms
14 R = H
R = Ms
1
5
13 R = H
R = Ms
2
6
15 R = H
R = Ms
4
8
3
7
MsCl /
MsCl /
MsCl /
MsCl /
pyridine
pyridine
pyridine
pyridine
Scheme 1.
PhSNa (5 equiv),
DMF, 40 oC, 24h
MeSNa (5 equiv),
DMF, 50 oC, 3h
SPh
SMe
O
O
Ph
Ph
O
O
O
O
SPh
5
SPh
BnO
BnO
10 (60%)
9 (47%)
NBS,
acetone-H2O
SMe
O
O
Ph
O
BnO
OH
11 (40%)
Scheme 2.
suggesting the b-anomeric configuration. However, one question to
be answered remained: the substituents of the thio groups at the
anomeric center and at C-2. It is known that thioglycosides can
be selectively cleaved with NBS.16 Following this procedure from
Treatment of 6 with 5 equiv of MeSNa in DMF at 50 °C for 8 h
resulted in three products (Scheme 3). The major component 14
1
([a
]
+4.9; JC1–H1 151.1 Hz) was an 1,2-cis-dithio-derivative,
D
whose NBS-mediated hydrolysis delivered, again, the cyclic-hemi-
compound 10, 3-O-benzyl-4,6-O-benzylidene-2-S-methyl-
a,b-D
-
acetal 11, showing that the primary product 14 was ethyl 3-O-ben-
mannopyranose (11) could be isolated and characterized. The pres-
ence of the methylthio group at C-2 of 11 proves that an intermo-
lecular nucleophilic displacement reaction occurred.
zyl-4,6-O-benzylidene-2-S-methyl-1-thio-b-
D
-mannopyranoside.
-mannopyranoside
The second component, the methyl thio-
a
-
D
1
(15, [
a]
D
+102.7; JC1–H1 168.8 Hz) was a 1,2-trans-dithio com-
We also studied the reactivity of compound 6 toward PhSNa
(Scheme 3). Two products were formed, the 1,2-thiomigrated com-
pound formed upon an intramolecular 1,2-thiomigration reaction.
The third compound in the reaction mixture was the elimination
product 13.
The a-D-mannopyranoside-type starting compounds, such as 7
and 8 were also investigated (Scheme 5). Compound 7 was reacted
pound 12 ([
ratio of ꢀ1:2.
The 1H and 13C NMR data confirmed the structure of 12 as
phenyl 3-O-benzyl-4,6-O-benzylidene-2-S-ethyl-1-thio- -man-
a]
D +114.1 and 1JC1–H1 170.4 Hz) and the glycal 13 in a
a
-D
with 3 equiv of PhSNa at 60 °C for 24 h and two products could be
1
nopyranoside resulting from an intramolecular nucleophilic rear-
detected (16 and 17). Compound 16 (3J1,2 4.9 Hz; JC1–H1 169.4 Hz
rangement reaction. The main product, 1,5-anhydro-3-O-benzyl-
and [
a] +283.6) proved to be phenyl 3-O-benzyl-4,6-O-benzyli-
D
4,6-O-benzylidene-2-deoxy-
D
-arabino-hex-1-enitol
(13:
[
a]
dene-2-S-phenyl-1-thio-a-D-glucopyranoside, produced by an SN2
D
À27.6) formed in an elimination reaction. The elimination pre-
sumably goes via vicinal intramolecular nucleophilic substitution
to give an episulfonium ion I which is then attacked by a free
intermolecular nucleophilic displacement reaction. This reaction
did not affect the anomeric center, but changed the configuration
at C-2. The second product 17 was an unsaturated sugar and
proved to be phenyl 3-O-benzyl-4,6-O-benzylidene-2-deoxy-1-
sulfide to form
a disulfide II and the glycal product 13
(Scheme 4). Compound 13 was first isolated by Sinaÿ and co-
workers17 using reductive lithiation at C-1, followed by a rapid
elimination of the C-2 substituent of the fully protected phenyl
thioglycopyranoside.
thio-D-arabino-hex-1-enopyranoside. Preparation of such type of
compounds was published18 most recently. The formation of the
above-mentioned unsaturated compounds is explained by the
elimination of methanesulfonic acid.
SEt
O
O
Ph
Ph
O
O
O
O
PhSNa (5
+
BnO
BnO
equiv),
SPh
Ph
DMF, 50 oC, 8h
12 (17%)
13 (39%)
6
SMe
SEt
O
O
O
Ph
13 (8%)
+
O
+
O
O
SEt
MeSNa (5 equiv),
DMF, 50 oC, 8h
BnO
BnO
SMe
14 (40%)
15 (8%)
NBS,
acetone-H2O
11 (49%)
Scheme 3.

A. Lipták et al. / Carbohydrate Research 344 (2009) 2461–2467
2463
SR
S
O
Ph
O
Ph
Et
O
O
Ph
O
SEt
O
O
NaSR
O
O
BnO
+
Et S S R
BnO
BnO
OMs
6
I
II
13
R= Me or Ph
Scheme 4.
PhSNa (3 equiv),
DMF, 60 oC, 24h
MeSNa (5 equiv),
DMF, 50 oC, 3h
O
O
O
Ph
Ph
Ph
Ph
O
O
+
O
+
O
O
O
17 (50%)
7
BnO
BnO
BnO
SPh
MeS
PhS
SPh
SPh
16 (32%)
17 (30%)
18 (11%)
PhSNa (5 equiv),
DMF, 70 oC, 24h
MeSNa (5 equiv),
DMF, 50 oC, 8h
O
O
Ph
O
O
O
O
13 (28%)
+
8
BnO
BnO
SEt
EtS
SPh
19 (24%)
20 (52%)
Scheme 5.
The mesyl ester 7 was also treated with MeSNa (5 equiv) at
50 °C for 3 h, and again, two products could be isolated. The 1,2-
cis-axial/equatorial dithio-derivative proved to be phenyl 3-O-ben-
tion about their structure: in the case of the b-mannopyranoside
derivatives (10 and 14) NBS cleaved the thioaglycones, but did
not affect the C2-S-substituents. In the case of compounds 18
and 19 the substituents of the 1,2-dithio moieties were determined
by glycosylation reactions. The NIS-AgOTf-catalyzed glycosylation
reaction of 19 using MeOH as an aglycon resulted in 21, and the
glycosylation of 18 under the same conditions gave 22. This reac-
tion works also well with the mannosyl donor 10, furnishing com-
pound 23 (Scheme 6). All the three 1,2-dithio glycosyl donors
afforded stereoselectively the 1,2-trans glycosides.
zyl-4,6-O-benzylidene-2-S-methyl-1-thio-
a
-
D
-glucopyranoside
(18; J1,2 5.3 Hz; 1JC1–H1 169.9 Hz; [
ponent was 17.
a]D +209.9) and the second com-
Treatment of compound 8 with PhSNa (5 equiv) at 70 °C for 24 h
furnished two compounds (19 and 13). All measured parameters
for 19 are very similar to those of compounds 16 and 18. Character-
istic data for 19 are: 3J1,2 5.3 Hz; 1JC1–H1 169.6 Hz; [
a]D +169.5. The
second component is the unsaturated 13, formed by the mecha-
nism shown in Scheme 4. The formation of compound 19 was as-
sumed in an intramolecular 1,2-thiomigration reaction via an
oxocarbenium intermediate.3,12 This type of reaction would afford
In conclusion, in the reactions of phenyl and ethyl 2-O-sulfonyl-
1-thio-a-D-manno- and b-D-glucopyranosides with PhSNa or with
MeSNa three different displacement reactions and two different
elimination processes could be observed. Reactions of 5 and 7, both
with anomeric SPh group, only undergo direct nucleophilic substi-
tution reaction, both with PhSNa and MeSNa as reagents. Only 7,
with axial leaving group, undergoes direct methanesulfonic acid
elimination with both reagents, as well.
both anomers, however, we could isolate only the
Using MeSNa as the nucleophilic reagent, only one compound,
ethyl 3-O-benzyl-4,6-O-benzylidene-2-deoxy-1-thio- -arabino-hex-1-
enopyranoside (20) was formed.
a-product.
D
Determination of the structure of the products formed upon
transformation of compounds 5–8 gave the opportunity to ap-
proach the mechanism of the reactions. Besides the spectroscopic
methods (NMR and MS) chemical tools provided valuable informa-
In contrast, 6 and 8, with anomeric SEt group, typically do not
show direct nucleophilic substitution reaction. With PhSNa as a re-
agent, both undergo intramolecular substitution to an episulfoni-
um or an oxocarbenium intermediate, followed by a subsequent
NBS, acetone-H2O
NBS, acetone-H2O
10
14
11
18
(40%)
(49%)
10
19
NIS, AgOTf,
NIS, AgOTf,
NIS, AgOTf,
MeOH, -15 oC
MeOH, -30 oC
MeOH, -15 oC
SMe
O
O
O
Ph
Ph
O
Ph
O
O
O
O
O
OMe
OMe
BnO
BnO
BnO
MeS
EtS
21 (72%)
OMe
23 (80%)
22 (84%)
Scheme 6.

2464
A. Lipták et al. / Carbohydrate Research 344 (2009) 2461–2467
nucleophilic attack on the anomeric carbon (leading to 12 and 19)
or on sulfur, leading to 13. With MeSNa as a reagent, the situation
is more complicated for 6, with both substitution patterns ob-
served as well as elimination affording 13. With 8 having an axial
leaving group, direct elimination is favored to give 20.
rated. The residue was purified by silica gel chromatography
(CH2Cl2/EtOAc 95:5).
3.6. General method E for the synthesis of methyl glycosides
(21–23)
To a solution of 0.5 mmol of thioglycoside (10, 18, and 19) in
dichloromethane (10 mL) were added successively 3 Å molecular
3. Experimental
sieves (300 mg) and 202 lL (5 mmol) of dry MeOH, and the mix-
3.1. General methods
ture was stirred at rt for 1 h. Then it was cooled to À15 °C (for
10 and 18) or À30 °C (for 19) and a mixture of 135 mg (0.6 mmol)
Optical rotations were measured at room temperature with a
Perkin–Elmer 241 automatic polarimeter. Melting points were
determined on a Kofler hot-stage apparatus and are uncorrected.
TLC was performed on Kieselgel 60 F254 (Merck) with detection
by immersing into 5% ethanolic sulfuric acid solution. Column
chromatography was performed on Silica Gel 60 (E. Merck,
0.063–0.200 mm). The organic solutions were dried over MgSO4
and concentrated in vacuo. The 1H (360 MHz) and 13C NMR
(90 MHz) spectra were recorded with AM-360 spectrometer in
CDCl3 solution. Chemical shifts are referenced to Me4Si (0.00 ppm
for 1H) or to the residual solvent signals (77.00 ppm for 13C).
of NIS in dry THF (300
toluene (300
lL) and 20 mg (0.075 mmol) of AgOTf in dry
L) was added. The mixture was kept at À15 to
l
À30 °C until the TLC showed a complete conversion of the starting
material (30 min). The reaction was quenched by the addition of
70 lL (1 mmol) of Et3N. Insoluble materials were removed by fil-
tration through Celite, the filtrate was diluted with dichlorometh-
ane, extracted three times with water, dried, and evaporated.
3.7. Phenyl 3-O-benzyl-4,6-O-benzylidene-2-O-
methanesulfonyl-1-thio-b-D-glucopyranoside (5)
Compound 1 (1.35 g, 3 mmol) was converted by method A to
give the crude 5; 1H NMR (CDCl3): d 7.55–7.26 (m, 15H, aromatic),
5.55 (s, 1H, PhCH), 4.96 and 4.74 (2d, 1-1H, PhCH2), 4.76 (d, 1H, 3J1,2
9.9 Hz, H-1), 4.62 (t, 1H, 3J2,3 8.6 Hz, H-2), 4.37 (dd, 1H, 3J5,6a 5.0 Hz,
2J6a,6b 10.5 Hz, H-6a), 3.86 (t, 1H, 3J3,4 9.1 Hz, H-3), 3.78 (t, 1H, 3J5,6b
3.2. General method A for the formation of 2-O-
methanesulfonyl derivatives (5–8)
To a solution of 3.0 mmol of the appropriate 2-OH derivative
(1–4) in 10 mL of dry pyridine 348 lL (4.50 mmol) of methanesul-
3
10.2 Hz, H-6b), 3.73 (t, 1H, J4,5 9.3 Hz, H-4), 3.48 (ddd, 1H, H-5),
3.02 (s, 3H, CH3); 13C NMR (CDCl3): d 137.3–125.9 (aromatic),
101.1 (PhCH), 86.7 (C-1), 81.2, 80.0 and 79.3 (C-2, C-3 and C-4),
74.8 (PhCH2), 70.2 (C-5), 68.3 (C-6), 39.5 (CH3).
fonyl chloride was added and the mixture was stirred at rt for 4 h.
The mixture was diluted with 100 mL of dichloromethane and
washed with 1 M aqueous HCl solution until the aqueous phase re-
mained slightly acidic, then washed with water, saturated NaHCO3
solution and water. The crude product was used for the next step
without purification.
3.8. Ethyl 3-O-benzyl-4,6-O-benzylidene-2-O-methanesulfonyl-
1-thio-b-D-glucopyranoside (6)
3.3. General method B for the reactions of 2-O-methanesulfonyl
derivatives with sodium thiophenolate. Formation of 9, 12, 13,
16, 17, and 19
Compound 2 (1.21 g, 3 mmol) was converted by method A to
give the crude 6; 1H NMR (CDCl3): d 7.47–7.25 (m, 10H, aromatic),
5.57 (s, 1H, PhCH), 4.98 and 4.76 (2d, 1-1H, PhCH2), 4.60 (t, 1H, 3J2,3
3
3
7.2 Hz, H-2), 4.56 (d, 1H, J1,2 9.9 Hz, H-1), 4.37 (dd, 1H, J5,6a
2
3
To a solution of 1.0 mmol of the appropriate 2-O-mesyl deriva-
tive (5–8) in 5 mL of N,N-DMF 661 mg (5 mmol) of sodium thio-
phenolate was added and the mixture was stirred at 40–70 °C
until complete conversion of the starting material (8–24 h) was de-
tected. The mixture was diluted with 50 mL of dichloromethane,
washed with water, dried, and evaporated.
5.0 Hz, J6a,6b 10.5 Hz, H-6a), 3.85 (t, 1H, J3,4 9.2 Hz, H-3), 3.77 (t,
3
3
1H, J5,6b 10.3 Hz, H-6b), 3.76 (t, 1H, J4,5 9.3 Hz, H-4), 3.50 (ddd,
1H, H-5), 3.00 (s, 3H, OCH3), 2.75 (q, 2H, CH2), 1.29 (t, 3H, CH3);
13C NMR (CDCl3): d 137.3–125.8 (aromatic), 101.1 (PhCH), 83.8
(C-1), 81.5, 79.9 and 79.4 (C-2, C-3 and C-4), 74.8 (PhCH2), 70.3
(C-5), 68.3 (C-6), 39.4 (OCH3), 24.1 (CH2), 14.7 (CH3).
3.4. General method C for the reactions of 2-O-methanesulfonyl
derivatives with sodium thiomethylate. Formation of 10, 13–15,
17, 18, and 20
3.9. Phenyl 3-O-benzyl-4,6-O-benzylidene-2-O-
methanesulfonyl-1-thio-a-D-manno-pyranoside (7)
Compound 3 (1.35 g, 3 mmol) was converted by method A to
give the crude 7; 1H NMR (CDCl3): d 7.52–7.30 (m, 15H, aromatic),
To a solution of 1.0 mmol of 2-O-mesyl derivative (5–8) in 5 mL
of N,N-DMF 350.5 mg (5 mmol) of sodium thiomethylate was
added and the mixture was stirred at 50 °C until a complete con-
version of the starting material (3–8 h) was detected. The mixture
was diluted with 50 mL of dichloromethane, washed with water,
dried, and evaporated.
3
3
5.64 (s, 1H, PhCH), 5.62 (d, 1H, J1,2 1.2 Hz, H-1), 5.24 (dd, 1H, J2,3
2.9 Hz, H-2), 4.87 and 4.76 (2d, 1-1H, PhCH2), 4.35 (ddd, 1H, H-5),
3
2
3
4.24 (dd, 1H, J5,6a 4.8 Hz, J6a,6b 10.3 Hz, H-6a), 4.14 (t, 1H, J4,5
3
3
9.3 Hz, H-4), 4.06 (dd, 1H, J3,4 9.9 Hz, H-3), 3.87 (t, 1H, J5,6b
10.2 Hz, H-6b), 3.02 (s, 3H, CH3); 13C NMR (CDCl3): d 137.2–126.0
(aromatic), 101.5 (PhCH), 87.8 (C-1), 79.9, 78.8 and 73.8 (C-2, C-3
and C-4), 73.6 (PhCH2), 68.2 (C-6), 65.2 (C-5), 38.7 (CH3).
3.5. General method D for the removal of the thio aglycone
with NBS. Formation of 11
3.10. Ethyl 3-O-benzyl-4,6-O-benzylidene-2-O-
To a solution of 0.5 mmol of the thioglycoside (10, 14) in ace-
tone–water 15:1 (6 mL) 178 mg (1 mmol) of NBS was added and
after 10 min the reaction was quenched by adding solid NaHCO3
(390 mg). The mixture was stirred for 10 min, evaporated in vacuo
at rt, and then diluted with dichloromethane (50 mL). The organic
phase was washed with water until neutral pH, dried, and evapo-
methanesulfonyl-1-thio-a-D-mannopyranoside (8)
Compound 4 (1.21 g, 3 mmol) was converted by method A to
give the crude 8; 1H NMR (CDCl3): d 7.51–7.30 (m, 10H, aromatic),
3
3
5.63 (s, 1H, PhCH), 5.41 (d, 1H, J1,2 0.9 Hz, H-1), 5.08 (dd, 1H, J2,3
3.0 Hz, H-2), 4.83 and 4.72 (2d, 1-1H, PhCH2), 4.27–4.19 (m, 2H,

A. Lipták et al. / Carbohydrate Research 344 (2009) 2461–2467
2465
3
3
H-5 and H-6a), 4.09 (t, 1H, J4,5 9.2 Hz, H-4), 4.00 (dd, 1H, J3,4
9.2 Hz, H-3), 3.88 (t, 1H, H-6b), 3.02 (s, 3H, OCH3), 2.65 (q, 2H,
CH2), 1.29 (t, 3H, CH3); 13C NMR (CDCl3): d 137.3–126.0 (aromatic),
101.5 (PhCH), 84.3 (C-1), 80.4, 78.9 and 73.9 (C-2, C-3 and C-4),
73.6 (PhCH2), 68.3 (C-6), 64.6 (C-5), 38.7 (OCH3), 25.9 (CH2), 14.9
(CH3).
ane/EtOAc 85:15); [
a
]
+114.1 (c 0.24, CHCl3); 1H NMR (CDCl3): d
D
7.50–7.29 (m, 15H, aromatic), 5.65 and 5.63 (2s, 1-1H, H-1 and
PhCH), 4.86 and 4.76 (2d, 1-1H, PhCH2), 4.37 (ddd, 1H, H-5),
4.26–4.13 (m, 3H) and 3.86 (t, 1H) (H-3, H-4, H-6a and H-6b),
3
3.49 (d, 1H, J2,3 3.9 Hz, H-2), 2.71 (q, 2H, CH2), 1.25 (t, 3H, CH3);
13C NMR (CDCl3): d 138.1-126.0 (aromatic), 101.5 (PhCH), 89.4
1
(C-1, JC1–H1 170.4 Hz), 80.1 and 75.1 (C-3 and C-4), 72.9 (PhCH2),
3.11. Phenyl 3-O-benzyl-4,6-O-benzylidene-2-S-phenyl-1-thio-
68.4 (C-6), 65.6 (C-5), 52.0 (C-2), 27.9 (CH2) 14.6 (CH3). Anal. Calcd
for C28H30O4S2 (494.67): C, 67.99; H, 6.11. Found: C, 68.44; H, 5.97.
The crystalline 13 was isolated with 39% yield (127 mg); mp
b-
D-mannopyranoside (9)
Compound 5 (529 mg, 1 mmol) was converted by method B.
The crude product was purified by silica gel chromatography (hex-
ane/EtOAc 95:5) to give 255 mg of 9 (47%); Rf 0.41 (hexane/EtOAc
104–105 °C (ethanol); Rf 0.41 (hexane/EtOAc 85:15); [
a
]
À7.6 (c
D
0.11, CHCl3); 1H NMR (CDCl3): d 7.52–7.25 (m, 10H, aromatic),
6.50 (d, 1H, H-1), 5.64 (s, 1H, PhCH), 4.83–4.70 (m, 3H, H-2 and
PhCH2), 4.39–4.35 (m, 2H), 4.03 (t, 1H) and 3.92–3.82 (m, 2H)
(H-3, H-4, H-5, H-6a and H-6b); 13C NMR (CDCl3): d 144.4 (C-1),
138.4–126.0 (aromatic), 102.3 (C-2), 101.2 (PhCH), 80.0 and 73.1
(C-3 and C-4), 72.0 (PhCH2), 68.6 (C-5), 68.4 (C-6). Anal. Calcd for
C20H20O4 (324.37): C, 74.06; H, 6.21. Found: C, 74.25; H, 6.39.
8:2); [
a
]
+4.5 (c 0.11, CHCl3); 1H NMR (CDCl3): d 7.73–7.08 (m,
D
3
20H, aromatic), 5.62 (s, 1H, PhCH), 5.07 (d, 1H, J1,2 1.4 Hz, H-1),
3
2
4.54 and 4.42 (2d, 1-1H, PhCH2), 4.30 (dd, 1H, J5,6a 4.8 Hz, J6a,6b
10.4 Hz, H-6a), 4.13 (t, 1H) and 3.89–3.84 (m, 3H) (H-2, H-3, H-4
and H-6b), 3.40 (ddd, 1H, H-5); 13C NMR (CDCl3): d 137.7–125.9
1
(aromatic), 101.4 (PhCH), 90.1 (C-1, JC1–H1 155.4 Hz), 79.3 and
78.2 (C-3 and C-4), 72.2 (PhCH2), 72.1 (C-5), 68.3 (C-6), 59.3 (C-
2). Anal. Calcd for C32H30O4S2 (542.71): C, 70.82; H, 5.57. Found:
C, 71.09; H, 5.59.
3.15. Ethyl 3-O-benzyl-4,6-O-benzylidene-2-S-methyl-1-thio-b-
D-mannopyranoside (14) and methyl 3-O-benzyl-4,6-O-
benzylidene-2-S-ethyl-1-thio- -mannopyranoside (15)
a-D
3.12. Phenyl 3-O-benzyl-4,6-O-benzylidene-2-S-methyl-1-thio-
Compound 6 (481 mg, 1 mmol) was converted using method C
to give a mixture of 13, 14, and 15 which were separated by silica
gel chromatography (hexane/EtOAc 9:1 and CH2Cl2/hexane 8:2).
Compound 13 was isolated with 8% yield (26 mg).
b-
D-mannopyranoside (10)
Compound 5 (529 mg, 1 mmol) was converted by method C.
The crude product was purified by silica gel chromatography (hex-
ane/EtOAc 95:5) followed by crystallization from ethanol to give
288 mg of 10 (60%); mp 166–168 °C; Rf 0.35 (hexane/EtOAc
Compound 14 was isolated with 40% yield (173 mg); Rf 0.33
(hexane/EtOAc 85:15); [a]
+4.9 (c 0.10, CHCl3); 1H NMR (CDCl3):
D
d 7.50–7.25 (m, 10H, aromatic), 5.61 (s, 1H, PhCH), 4.87 and 4.76
3
85:15); [
a
]
+41.8 (c 0.15, CHCl3); 1H NMR (CDCl3): d 7.47–7.26
(2d, 1-1H, PhCH2), 4.82 (d, 1H, J1,2 1.5 Hz, H-1), 4.27 (dd, 1H,
D
3
2
3
(m, 15H, aromatic), 5.61 (s, 1H, PhCH), 5.03 (d, 1H, J1,2 1.8 Hz, H-
1), 4.87 and 4.74 (2d, 1-1H, PhCH2), 4.30 (dd, 1H, J5,6a 4.8 Hz,
3J5,6a 4.8 Hz, J6a,6b 10.5 Hz, H-6a), 4.14 (t, 1H, J4,5 9.4 Hz, H-4),
3
3
3
3.89 (dd, 1H, J3,4 9.5 Hz, H-3), 3.84 (t, 1H, J5,6b 10.3 Hz, H-6b),
3.39 (ddd, 1H, H-5), 3.28 (dd, 1H, J2,3 4.2 Hz, H-2), 2.72 (q, 2H,
2J6a,6b 10.4 Hz, H-6a), 4.18 (t, 1H), 3.92–3.81 (m, 2H) and 3.45–
3.33 (m, 2H) (H-2, H-3, H-4, H-5 and H-6b), 2.41 (s, 3H, CH3); 13C
NMR (CDCl3): d 138.1–126.0 (aromatic), 101.4 (PhCH), 90.2 (C-1,
1JC1–H1 155.6 Hz), 79.7 and 78.9 (C-3 and C-4), 72.9 (PhCH2), 72.1
(C-5), 68.4 (C-6), 56.4 (C-2), 19.1 (CH3). Anal. Calcd for
C27H28O4S2 (480.64): C, 67.47; H, 5.87. Found: C, 67.21; H, 5.93.
3
CH2), 2.36 (s, 3H, SCH3) 1.27 (t, 3H, CH3); 13C NMR (CDCl3): d
138.2–125.9 (aromatic), 101.4 (PhCH), 87.3 (C-1, 1JC1–H1 151.1 Hz),
79.8 and 79.0 (C-3 and C-4), 72.8 (PhCH2), 72.2 (C-5), 68.4 (C-6),
56.2 (C-2), 26.1 (CH2), 19.0 (SCH3), 15.0 (CH3). Anal. Calcd for
C23H28O4S2 (432.60): C, 63.86; H, 6.52. Found: C, 64.11; H, 6.74.
Compound 15 was isolated with 8% yield (35 mg); Rf 0.39 (hex-
3.13. 3-O-Benzyl-4,6-O-benzylidene-2-S-methyl-
a,b-
D-
ane/EtOAc 85:15); [a]
+102.7 (c 0.13, CHCl3); 1H NMR (CDCl3): d
D
mannopyranose (11)
7.51–7.26 (m, 10H, aromatic), 5.62 (s, 1H, PhCH), 5.33 (s, 1H, H-
1), 4.82 and 4.71 (2d, 1-1H, PhCH2), 4.23–4.09 (m, 4H) and 3.88
(t, 1H) (H-3, H-4, H-5, H-6a and H-6b), 3.33 (d, 1H, J2,3 3.9 Hz,
3
Compound 10 (240 mg, 0.5 mmol) was converted by method D
to give 78 mg of 11 (40%) and compound 14 (216 mg, 0.5 mmol)
was converted by method D to give 95 mg of 11 (49%); Rf 0.41
(CH2Cl2/EtOAc 9:1); 1H NMR (CDCl3): d 7.51–7.25 (m, 10H, aro-
H-2), 2.72 (q, 2H, CH2), 2.12 (s, 3H, SCH3) 1.27 (t, 3H, CH3); 13C
NMR (CDCl3): d 138.2–125.9 (aromatic), 101.5 (PhCH), 87.2 (C-1,
1JC1–H1 168.8 Hz), 80.2 and 75.2 (C-3 and C-4), 72.9 (PhCH2), 68.7
(C-6), 64.7 (C-5), 51.6 (C-2), 27.9 (CH2), 14.6 and 14.1 (SCH3 and
CH3). Anal. Calcd for C23H28O4S2 (432.60): C, 63.86; H, 6.52. Found:
C, 64.24; H, 6.71.
matic), 5.63 and 5.59 (2s, 0.6H and 0.4H, PhCH and PhCHb), 5.40
a
(s, 0.6H, H-1 ), 4.94–4.63 (m, 2.4H, PhCH2 ,b) and H-1b), 4.32–
a
a
3.74 (m, 5H, H-3 ,b, H-4 ,b, H-5 ,b, H-6a
and H-6b ,b), 3.39–
a
a
a
a
,b
a
3.31 (m, 0.4H, OHb), 3.24–3.22 (m, 1H, H-2 ,b), 2.97 (s, 0.6H,OH ),
a
a
2.29 and 2.26 (2s, 3H, CH3 ,b); 13C NMR (CDCl3): d 138.4–126.0
3.16. Phenyl 3-O-benzyl-4,6-O-benzylidene-2-S-phenyl-1-thio-
a
(aromatic), 101.5 and 101.4 (PhCH ,b), 95.9 and 93.5 (C-1 ,b),
a-D-glucopyranoside (16) and phenyl 3-O-benzyl-4,6-O-
a
a
80.1, 79.9, 77.6 and 74.8 (C-3
and C-4 ,b), 73.2 and 72.9
benzylidene-2-deoxy-D-arabino-1-thio-hex-1-enopyranoside
a
,b
a
(PhCH2 ,b), 68.8 and 68.4 (C-6 ,b),67.2 and 64.4 (C-5 ,b), 59.3 and
(17)
a
a
a
53.2 (C-2 ,b). Anal. Calcd for C21H24O5S (388.48): C, 64.93; H,
a
6.23. Found: C, 63.87; H, 6.44.
Compound 7 (529 mg, 1 mmol) was converted using method B
to give a mixture of 16 and 17 which were separated by silica gel
chromatography (CH2Cl2/hexane 1:1) The crystalline 16 was iso-
lated with 32% yield (174 mg); mp 126 °C (ethanol); Rf 0.35
3.14. Phenyl 3-O-benzyl-4,6-O-benzylidene-2-S-ethyl-1-thio-
-mannopyranoside (12) and 1,5-anhydro-3-O-benzyl-4,6-O-
benzylidene-2-deoxy- -arabino-hex-1-enitol (13)
a-
D
D
(CH2Cl2/hexane 1:1); [a]
D +118.6 (c 0.10, CHCl3); 1H NMR (CDCl3):
d 7.58–7.24 (m, 20H, aromatic), 5.60 (s, 1H, PhCH), 5.50 (d, 1H, 3J1,2
4.9 Hz, H-1), 4.94 and 4.86 (2d, 1-1H, PhCH2), 4.51 (ddd, 1H, H-5),
Compound 6 (481 mg, 1 mmol) was converted using method B
to give a mixture of 12 and 13 which were separated by silica gel
chromatography (hexane/EtOAc 9:1 and CH2Cl2/EtOAc 99.5:0.5).
Compound 12 was isolated with 17% yield (84 mg); Rf 0.40 (hex-
3
2
4.20 (dd, 1H, J5,6a 4.7 Hz, J6a,6b 10.3 Hz, H-6a), 3.97 (t, 1H) and
3.80–3.72 (m, 3H) (H-2, H-3, H-4 and H-6b); 13C NMR (CDCl3): d
137.9–125.9 (aromatic), 101.4 (PhCH), 90.0 (C-1, 1JC1–H1

2466
A. Lipták et al. / Carbohydrate Research 344 (2009) 2461–2467
169.4 Hz), 84.0 and 78.4 (C-3 and C-4), 75.8 (PhCH2), 68.7 (C-6),
64.5 (C-5), 54.9 (C-2). Anal. Calcd for C32H30O4S2 (542.71): C,
70.82; H, 5.57. Found: C, 70.33; H, 5.61.
(C-3 and C-4), 69.4 (PhCH2), 69.0 (C-6), 63.6 (C-5), 26.0 (CH2),
15.4 (CH3). Anal. Calcd for C22H24O4S (384.49): C, 68.72; H, 6.29.
Found: C, 69.13; H, 6.44.
The crystalline 17 was isolated with 30% yield (130 mg); mp
ꢀ160–168 °C (hexane/EtOAc 9:1) decomposed; Rf 0.39 (CH2Cl2/
3.20. Methyl 3-O-benzyl-4,6-O-benzylidene-2-S-ethyl-b-D-
glucopyranoside (21)
hexane 1:1); [
a]
+283.6 (c 0.21, CHCl3); 1H NMR (CDCl3): d
D
7.55–7.22 (m, 15H, aromatic), 5.86 (dd, 1H, H-2), 5.61 (s, 1H,
PhCH), 4.96–4.78 (m, 3H, H-3 and PhCH2), 4.45 (m, 1H, H-5),
4.37–4.30 (m, 2H, H-4, and H-6a), 3.86 (t, 1H, H-6b); 13C NMR
(CDCl3): d 152.8 (C-1), 137.2–126.4 (aromatic), 102.2 (PhCH),
96.9 (C-2), 85.1 and 74.8 (C-3 and C-4), 69.6 (PhCH2), 68.9 (C-6),
64.2 (C-5). Anal. Calcd for C26H24O4S (432.53): C, 72.20; H, 5.59.
Found: C, 71.89; H, 5.47.
Compound 19 (247 mg, 0.5 mmol) was converted using method
E and the crude product was purified by silica gel chromatography
(CH2Cl2/EtOAc 99:1) to give 150 mg of 21 (72%); Rf 0.32 (CH2Cl2/
EtOAc 98:2); [
a
]
D
À69.5 (c 0.13, CHCl3); 1H NMR (CDCl3): d 7.50–
7.26 (m, 10H, aromatic), 5.59 (s, 1H, PhCH), 4.90 and 4.82 (2d, 1-
3
3
1H, PhCH2), 4.37 (d, 1H, J1,2 8.7 Hz, H-1), 4.36 (dd, 1H, J5,6a
2
3
5.1 Hz, J6a,6b 10.4 Hz, H-6a), 3.80 (t, 1H, J5,6b 10.3 Hz, H-6b),
3
3
3.17. Phenyl 3-O-benzyl-4,6-O-benzylidene-2-S-methyl-1-thio-
3.71 (t, 1H, J4,5 9.1 Hz, H-4), 3.57 (s, 3H, OCH3), 3.50 (dd, 1H, J3,4
8.9 Hz, H-3), 3.42 (ddd, 1H, H-5), 2.76 (m, 2H, CH2), 2.72 (dd, 1H,
3J2,3 10.5 Hz, H-2), 1.27 (t, 3H, CH3); 13C NMR (CDCl3): d 138.3–
126.0 (aromatic), 106.3 (C-1), 101.2 (PhCH), 82.8 and 79.6 (C-3
and C-4), 75.9 (PhCH2), 68.8 (C-6), 65.9 (C-5), 57.6 (OCH3), 52.4
(C-2), 27.3 (CH2), 14.9 (CH3). Anal. Calcd for C23H28O5S (416.53):
C, 66.32; H, 6.78. Found: C, 66.89; H, 6.33.
a-
D-glucopyranoside (18)
Compound 7 (529 mg, 1 mmol) was converted using method C
to give a mixture of 17 and 18 which were separated by silica gel
chromatography (CH2Cl2/hexane 1:1). Compound 17 was isolated
with 50% yield (216 mg).
The crystalline 18 was isolated with 11% yield (53 mg); mp
163–165 °C (ethanol); Rf 0.23 (CH2Cl2/hexane 1:1); [
a
]
+209.9 (c
3.21. Methyl 3-O-benzyl-4,6-O-benzylidene-2-S-methyl-b-D-
glucopyranoside (22)
D
0.12, CHCl3); 1H NMR (CDCl3): d 7.52–7.27 (m, 15H, aromatic),
5.60 (s, 1H, PhCH), 5.59 (d, 1H, H-1), 4.98 and 4.85 (2d, 1-1H,
3
2
PhCH2), 4.46 (ddd, 1H, H-5), 4.23 (dd, 1H, J5,6a 4.9 Hz, J6a,6b
Compound 18 (240 mg, 0.5 mmol) was converted using method
E and the crude product was purified by silica gel chromatography
(hexane/EtOAc 9:1) to give 170 mg of 22 (84%); Rf 0.41 (hexane/
3
3
10.3 Hz, H-6a), 3.93 (dd, 1H, J3,4 9.1 Hz, H-3), 3.77 (t, 1H, J5,6b
3
3
10.1 Hz, H-6b), 3.72 (t, 1H, J4,5 9.3 Hz, H-4), 3.19 (dd, 1H, J1,2
3
5.3 Hz, J2,3 10.7 Hz, H-2), 2.28 (s, 3H, CH3); 13C NMR (CDCl3): d
EtOAc 8:2); [
a
]
À62.4 (c 0.33, CHCl3); 1H NMR (CDCl3): d 7.50–
D
138.2–126.0 (aromatic), 101.4 (PhCH), 89.9 (C-1, 1JC1–H1
169.9 Hz), 84.0 and 80.3 (C-3 and C-4), 75.7 (PhCH2), 68.7 (C-6),
64.3 (C-5), 53.4 (C-2), 17.6 (CH3). Anal. Calcd for C27H28O4S2
(480.64): C, 67.47; H, 5.87. Found: C, 68.01; H, 5.97.
7.26 (m, 10H, aromatic), 5.60 (s, 1H, PhCH), 4.92 and 4.82 (2d, 1-
3
3
1H, PhCH2), 4.39 (d, 1H, J1,2 8.7 Hz, H-1), 4.36 (dd, 1H, J5,6a
2
3
5.0 Hz, J6a,6b 10.6 Hz, H-6a), 3.80 (t, 1H, J5,6b 10.3 Hz, H-6b),
3
3
3.72 (t, 1H, J4,5 9.1 Hz, H-4), 3.58 (s, 3H, OCH3), 3.52 (dd, 1H, J3,4
3
8.9 Hz, H-3), 3.41 (ddd, 1H, H-5), 2.66 (dd, 1H, J2,3 10.5 Hz, H-2),
3.18. Phenyl 3-O-benzyl-4,6-O-benzylidene-2-S-ethyl-1-thio-
-glucopyranoside (19)
a
-
2.27 (s, 3H, CH3); 13C NMR (CDCl3): d 138.2–126.0 (aromatic),
106.1 (C-1), 101.2 (PhCH), 82.9 and 79.1 (C-3 and C-4), 75.7
(PhCH2), 68.7 (C-6), 65.9 (C-5), 57.5 (OCH3), 54.2 (C-2), 16.5
(CH3). Anal. Calcd for C22H26O5S (402.50): C, 65.65; H, 6.51. Found:
C, 66.04; H, 6.40.
D
Compound 8 (481 mg, 1 mmol) was converted using method B
to give a mixture of 13 and 19 which were separated by silica gel
chromatography (hexane/EtOAc 93:7). Compound 13 was isolated
with 28% yield (91 mg). The crystalline 19 was isolated with 24%
yield (119 mg); mp 147–149 °C (ethanol); Rf 0.38 (hexane/EtOAc
3.22. Methyl 3-O-benzyl-4,6-O-benzylidene-2-S-methyl-a-D-
mannopyranoside (23)
85:15); [
a
]
+169.5 (c 0.15, CHCl3); 1H NMR (CDCl3): d 7.52–7.25
D
3
(m, 15H, aromatic), 5.61 (s, 1H, PhCH), 5.58 (d, 1H, J1,2 5.3 Hz, H-
Compound 10 (240 mg, 0.5 mmol) was converted using method
E and the crude product was purified by silica gel chromatography
(hexane/EtOAc 9:1) to give 161 mg of 23 (80%); Rf 0.42 (hexane/
1), 4.97 and 4.85 (2d, 1-1H, PhCH2), 4.47 (ddd, 1H, H-5), 4.23 (dd,
3
2
3
1H, J5,6a 4.9 Hz, J6a,6b 10.3 Hz, H-6a), 3.92 (dd, 1H, J3,4 9.2 Hz,
3
3
H-3), 3.78 (t, 1H, J5,6b 10.3 Hz, H-6b), 3.72 (t, 1H, J4,5 9.3 Hz, H-
EtOAc 8:2); [a]
+40.8 (c 0.10, CHCl3); 1H NMR (CDCl3): d 7.50–
D
3
4), 3.25 (dd, 1H, J2,3 10.6 Hz, H-2), 2.78 (q, 2H, CH2), 1.24 (t, 3H,
7.26 (m, 10H, aromatic), 5.62 (s, 1H, PhCH), 4.88 (s, 1H, H-1),
4.83 and 4.72 (2d, 1-1H, PhCH2), 4.25–4.12 (m, 3H) and 3.87–
3.78 (m, 2H) (H-3, H-4, H-5, H-6a and H-6b), 3.35 (s, 3H, OCH3),
3.22 (d, 1H, H-2), 2.27 (s, 3H, CH3); 13C NMR (CDCl3): d 137.6–
CH3); 13C NMR (CDCl3): d 138.3–126.0 (aromatic), 101.4 (PhCH),
1
90.2 (C-1, JC1–H1 169.6 Hz), 84.0 and 80.3 (C-3 and C-4), 75.9
(PhCH2), 68.7 (C-6), 64.4 (C-5), 51.2 (C-2), 28.2 (CH2), 14.6 (CH3).
Anal. Calcd for C28H30O4S2 (494.67): C, 67.99; H, 6.11. Found: C,
68.31; H, 6.23.
1
126.0 (aromatic), 102.2 (C-1, JC1–H1 171.8 Hz), 101.5 (PhCH), 80.0
and 75.4 (C-3 and C-4), 72.8 (PhCH2), 68.8 (C-6), 64.1 (C-5), 54.9
(OCH3), 52.9 (C-2), 17.6 (CH3). Anal. Calcd for C22H26O5S (402.50):
C, 65.65; H, 6.51. Found: C, 65.17; H, 6.72.
3.19. Ethyl 3-O-benzyl-4,6-O-benzylidene-2-deoxy-D-arabino-1-
thio-hex-1-enopyranoside (20)
Acknowledgments
Compound 8 (481 mg, 1 mmol) was converted using method C
and the crude product was purified by silica gel chromatography
(hexane/EtOAc 9:1) to give 200 mg of 20 (52%); Rf 0.43 (hexane/
This work was supported by the Hungarian Scientific Research
Fund (OTKA AT 048798 and OTKA K 62802) and by the Hungarian
Academy of Sciences.
EtOAc 85:15); [
a]
+122.9 (c 0.16, CHCl3); 1H NMR (CDCl3): d
D
7.53–7.30 (m, 10H, aromatic), 5.65 (d, 1H, H-2), 5.59 (s, 1H, PhCH),
4.90 and 4.76 (2d, 1-1H, PhCH2), 4.79 (d, 1H, H-3), 4.34–4.26 (m,
3H) and 3.86–3.81 (m, 1H) (H-4, H-5, H-6a and H-6b), 2.65 (m,
2H, CH2), 1.29 (t, 3H, CH3); 13C NMR (CDCl3): d 152.0 (C-1),
137.2–126.4 (aromatic), 102.1 (PhCH), 97.3 (C-2), 81.3 and 74.9
References
1. Lipták, A.; Balla, E.; Jánossy, L.; Sajtos, F.; Szilágyi, L. Tetrahedron Lett. 2004, 45,
839–842.

A. Lipták et al. / Carbohydrate Research 344 (2009) 2461–2467
2467
2. Lipták, A.; Sajtos, F.; Jánossy, L.; Gehle, D.; Szilágyi, L. Org. Lett. 2003, 5, 3671–
3674.
10. Nicolaou, K. C.; Ladduwahetty, L.; Randall, J. L.; Chuholwski, A. J. Am. Chem. Soc.
1986, 108, 2466–2467.
3. Lázár, L.; Bajza, I.; Jakab, Zs.; Lipták, A. Synlett 2005, 2242–2244.
4. Sajtos, F.; Lázár, L.; Borbás, A.; Bajza, I.; Lipták, A. Tetrahedron Lett. 2005, 46,
5191–5194.
11. Johnston, B. D.; Pinto, B. M. J. Org. Chem. 2000, 65, 4607–4617.
12. Zuurmond, H. M.; van der Klein, P. A.; van der Marel, G. A.; van Boom, J. H.
Tetrahedron 1993, 49, 6501–6514.
5. Borbás, A.; Szabovik, G.; Antal, Zs.; Herczegh, P.; Agócs, A.; Lipták, A.
Tetrahedron Lett. 1999, 40, 3639–3642.
6. Borbás, A.; Szabovik, G.; Antal, Zs.; Fehér, K.; Csávás, M.; Szilágyi, L.; Herczegh,
P.; Lipták, A. Tetrahedron: Asymmetry 2000, 11, 549–566.
7. Lázár, L.; Csávás, M.; Borbás, A.; Gyémánt, Gy.; Lipták, A. Arkivoc 2004, VII, 196–
207.
8. Borbás, A.; Csávás, M.; Szilágyi, L.; Májer, G.; Szilágyi, L. J. Carbohydr. Chem.
2004, 23, 133–146.
9. Ryan, K. J.; Acton, E. M.; Godman, L. J. Org. Chem. 1971, 36, 2646–2657.
13. Szurmai, Z.; Balatoni, L.; Lipták, A. Carbohydr. Res. 1994, 254, 301–310.
14. Garreg, P. J.; Kvarnstroem, I.; Niklasson, A.; Niklasson, G.; Swensson, S. J.
Carbohydr. Chem. 1993, 7, 933–954.
15. Bock, K.; Pedersen, C. J. Chem. Soc., Perkin Trans. 2 1974, 293–297.
16. Nicolaou, K. C.; Seitz, S. P.; Papahatjis, D. P. J. Am. Chem. Soc. 1983, 105, 2430–2434.
17. Fernandez-Mayoralas, A.; Marra, A.; Trumtel, M.; Veyrieres, A.; Sinaÿ, P.
Carbohydr. Res. 1989, 188, 81–95.
18. Wang, Y.; Li, Q.; Chang, S.; Wu, Y.; Guo, D.; Fan, Q.-H.; Wang, X.; Zhang, L.-H.;
Ye, X.-S. Org. Lett. 2005, 7, 5577–5579.