Reactions of Nucleophiles with Reactive Intermediates in the 3,4,6-Tri-O-benzyl-D-glucal-TfOH-n-Bu4NI Reaction System

Article abstract of DOI:10.1081/CAR-120026596

The unique reactive intermediate formed in the 3,4,6-tri-O-benzyl-D-glucal- TfOH (triflic acid)-n-Bu₄NI reaction system (in dichloromethane) reacted with nucleophiles in a regio- and stereoselective manner. These selectivities resulted in hithe

Full text of DOI:10.1081/CAR-120026596

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Reactions of Nucleophiles with Reactive Intermediates
in the 3,4,6‐Tri‐O‐benzyl‐d‐glucal–TfOH–n‐Bu NI
4
Reaction System
a
a
Idil Kasuto Kelson & Ben‐Ami Feit
a
Raymond and Beverly Sackler Faculty of Exact Sciences , School of Chemistry , Tel‐Aviv
University , Israel
Published online: 02 Feb 2007.
To cite this article: Idil Kasuto Kelson & Ben‐Ami Feit (2003) Reactions of Nucleophiles with Reactive Intermediates in the
,4,6‐Tri‐O‐benzyl‐d‐glucal–TfOH–n‐Bu NI Reaction System, Journal of Carbohydrate Chemistry, 22:9, 827-841, DOI: 10.1081/
3
4
CAR-120026596
To link to this article: http://dx.doi.org/10.1081/CAR-120026596
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JOURNAL OF CARBOHYDRATE CHEMISTRY
Vol. 22, No. 9, pp. 827–841, 2003
Reactions of Nucleophiles with Reactive Intermediates
in the 3,4,6-Tri-O-benzyl-D-glucal–TfOH–n-Bu NI
Reaction System
4
*
Idil Kasuto Kelson and Ben-Ami Feit
Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry,
Tel-Aviv University, Israel
ABSTRACT
The unique reactive intermediate formed in the 3,4,6-tri-O-benzyl-D-glucal–TfOH
(
4
triflic acid)–n-Bu NI reaction system (in dichloromethane) reacted with nucleophiles
in a regio- and stereoselective manner. These selectivities resulted in hitherto un-
known compounds, such as benzyl 4,6-di-O-benzyl-2,3-dideoxy-3-iodo-a-glucopy-
ranoside, which was obtained in the presence of an iodide ion as a nucleophile. The
corresponding 2-deoxy a-glycosides were obtained exclusively in the corresponding
reaction with hydroxylic nucleophiles.
Key Words: Carbohydrates; Glucal; Reactive intermediates; Nucleophiles;
Iodosugars; 2-deoxyglycopyranosides.
*
Correspondence: Ben-Ami Feit, Raymond and Beverly Sackler Faculty of Exact Sciences, School
of Chemistry, Tel-Aviv University, Israel; E-mail: feit@post.tau.ac.il.
8
27
DOI: 10.1081/CAR-120026596
0732-8303 (Print); 1532-2327 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

828
Kasuto Kelson and Feit
INTRODUCTION
[
1–4]
Specific combinations of protonic acids with either Lewis acids (e.g., HI–ZnX ,
2
2
RCO H–MX ) or Lewis bases (e.g., TfOH–Me S ), function as effective initiating
3
2
n
2
[1–11]
systems for the living cationic polymerization of alkyl vinyl ethers
[
and other
Such polymerizations are characterized by absence
12–14]
electron-rich vinyl monomers.
of termination of any kind and by a very narrow molecular weight distribution of the
polymers formed. These characteristics are due to a combination of two built-in fea-
tures—R ꢀ R (i—initiation, p—propagation) and a very low equilibrium concen-
i
p
tration of the reactive species of the growing chain ends. Thus, for example, the
following is such an equilibrium for the HI (hexane solution)—ZnX initiated poly-
2
merization of alkyl vinyl ethers (Eq. 1):
We have recently shown that a TfOH–n-Bu NI mixture is an effective initiation
4
system for the living cationic polymerization of isobutyl vinyl ether (IBVE) (in CH Cl
2
2
[
15]
at ꢁ 23°C). It was suggested that the following equilibrium mixture of growing
[16,17]
chain ends was involved in the propagation steps of that polymerization (Eq. 2):
Our working hypothesis was that the reaction of 3,4,6-tri-O-benzyl-D-glucal (1)
with TfOH in the presence of n-Bu NI might result in an analogous equilibrium
mixture (Eq. 3):
4
It was the purpose of the present research to apply the experimental and mecha-
nistic approach which afforded the TfOH–n-Bu NI-initiated living cationic poly-
4
merizations of i-butyl vinyl ether, to reactions of glycals (represented by the glucal
derivative 1) with various nucleophiles. We have assumed that the analogous glucal-
involved equilibrium mixture (Eq. 3) might result in specific/selective reaction path-
ways, in the presence of nucleophiles.
RESULTS AND DISCUSSION
Reactions of 1 with nucleophiles in the 1–TfOH–n-Bu NI reaction system were
4
studied. Nucleophiles of three different types were used—an iodide salt (the n-Bu NI),
4
a nucleophilic olefin (CH2 CH–OR, R = i-Bu) and hydroxylic compounds.

Reactions of Nucleophiles
829
A cooled solution (ꢁ42 °C) of n-Bu NI and TfOH in CH Cl was added to a
4
2
2
solution of 1 in dichloromethane at 0°C, followed by quenching the reaction mixture
with ethanol after the required reaction period. The ratio of the concentrations of the
reactants used was [TfOH]:[n-Bu NI]:[1] = 1:2:1. A complex mixture of products was
4
obtained, eight of which (total yield 56% based on 1) were isolated, purified and their
structure determined or confirmed (Eq. 4):
Possible reaction pathways leading to the formation of these products are detailed
below (Schemes 1 and 2).
We suggest (Schemes 1 and 2) that several types of reactive intermediates are
involved in the formation of the products isolated. One is the oxaallyl cation salt 9 (cf.
Scheme 1), and the others are the carbocation salts 3 and 12 formed by the addition
reaction TfOH to the glucal derivatives 1 and 10, respectively, in the presence of n-Bu4
NI (cf. Schemes 1 and 2). The anticipated specificity of the n-Bu NI-solvated car-
4
bocation triflate salts 3 and 12 in their reactions with nucleophiles, has been realized (for this
reaction system) by the unique regiospecific and stereospecific formation of a hitherto
unreported iodosaccharide - ethyl 2,3-dideoxy-3-iodoglycoside derivative 6 (Scheme 1)
and by the formation of the 2,2’-dideoxy-a,a-trehalose derivative 7 (Scheme 2). It should
be noted that the benzyl alcohol involved in the formation of the trehalose derivative 7
(Scheme 2) was produced in the reaction leading to the formation of the oxaallyl cation
salt 9 (Scheme 1).
4
Scheme 1. Formation of alkyl 2,3-dideoxy-3-iodoglycoside in the 1-TfOH-n-Bu NI reac-
tion system.

830
Kasuto Kelson and Feit
4
Scheme 2. Formation of the 2,2’-dideoxy-a,a-trehalose derivative 7 in the 1-TfOH-n-Bu NI
reaction system.
Non-anomeric 2-deoxy iodosugars, although quite uncommon, are useful inter-
[
18–30]
mediates in carbohydrate synthesis.
a 3-iodo-2,3-dideoxy saccharide from 3,4,6-tri-O-benzyl-D-galactal, in a synthesis
consisting of several steps.
There is a single report on the preparation of
[
31]
2,3-Dideoxy-3-iodo glycosides might be useful pre-
cursors in carbohydrate synthesis for the preparation of such compounds as 2,3-dideoxy
glycosides, 2-deoxy-3,4-epoxyglycosides, etc. It was therefore of interest to try to
convert the observed one-pot low-yield direct formation of the alkyl 2,3-dideoxy-3-
iodoglycoside 6 into a practical preparation, applying the 1–TfOH–n-Bu NI reaction
4
system. A variety of experimental conditions were screened in this regard. It was found
that performing the reaction (Eq. 5) at room temperature, instead of 0 °C, resulted in a
dramatic change. The target compound, benzyl 4,6-di-O-benzyl-2,3-dideoxy-3-iodo-a-
D-glucopyranoside (13), was formed as the major product. Quenching the reaction
mixture with either EtOH or BnOH had almost no effect on the yield of 13 (Eq. 5):
This clearly indicated that the formation of 13 in this thermodynamically-con-
trolled reaction was completed before the addition of the alcoholic quencher. The
stereospecificity of the nucleophilic attack of the iodide anion on the oxaallylic cation
salt 9, which resulted in retention of the configuration of the C-3 position, could be due
to a neighboring group participation of the C-4 benzyloxy group (Scheme 3).
As mentioned above, the TfOH–n-Bu NI mixture was an effective initiator for the
4
[
15]
living cationic polymerization of isobutyl vinyl ether.
reaction of the reactive intermediate(s) formed in the 1–TfOH–n-Bu NI reaction
We therefore expected that the
4
mixture with CH2 CH–OR would result in a C-glycosidation reaction. To this
end, iso-butyl vinyl ether was added to a cooled (ꢁ23 °C) 1–TfOH–n-Bu NI mix-
4

Reactions of Nucleophiles
831
Scheme 3. The stereospecific formation of the iodo sugar 13.
ture dissolved in dichloromethane. The reaction mixture was quenched with EtOH. The
ratio of concentrations of the reactants used was [1]:[TfOH]:[n-Bu NI]: [IBVE] =
4
1:1:2.1:1.1. The only products obtained under these conditions were the ethyl and
isobutyl 2-deoxy glycosides 5 (84%) and 14 (16%), respectively. Poly (IBVE) was
obtained, in addition, when the above ratio of concentrations was 1:1:2.1:10.2. The
poly (IBVE) obtained had no sugar moiety end group, indicating that a C-glycosidation
reaction did not occur (Eq. 6):
Formation of the ethyl glycoside 5 was presumably due to reaction of the quencher
ethanol with the reactive intermediate 3 (cf. Scheme 2). The high yield of 5 and the
low yield of 14 indicates the i-butyl glycoside 14 indicated that the formation of 14 is
relatively slow and that the reactive intermediate 3 is quite stable under the experi-
mental conditions applied.
Formation of the isobutyl 2-deoxyglycoside 14 pointed to the selectivity features of
reactive intermediate in the 2–3 equilibrium mixture (cf. Scheme 2) demonstrated in its
reactions with nucleophiles. We suggest that the reaction leading to the formation of 14
took place in this case exclusively via the etheric oxygen of the IBVE rather than via
its electron-rich double bond. The following is a plausible mechanism for the unusual
formation of an alkyl 2-deoxy glycoside in the acid-catalyzed reaction of a glucal with
an alkyl vinyl ether (Scheme 4). It should be noted that Ferrier-type rearrangement
products were not detected.
The quantitative and exclusive conversion of the glucal 1 to the mixture of the
derived ethyl and isobutyl 2-deoxyglycosides 5 and 14, respectively (cf. Eq. 6), led us
to apply hydroxylic compounds to react as nucleophiles in the 1–TfOH–n-Bu NI
4
reaction system, for preparing 2-deoxyglycosides directly from the glucal 1. Protonic
and Lewis acid-catalyzed reactions of hydroxylic compounds with glycals to affect
their direct conversion to the derived 2-deoxyglycosides, have been reported in a few

832
Kasuto Kelson and Feit
4 2
Scheme 4. Formation of the iso-butylglycoside in the 1-TfOH-n-Bu NI-CH = CH-OR. (R = iso-
butyl).
[
32–38]
cases.
structural moieties of sugar-containing natural products and bioactive materials.
It should be mentioned in this regard that 2-deoxy-glycosides are significant
[39–42]
Thus, the reaction of 1 with each of several hydroxylic compounds (16) was carried
out in methylene chloride at low temperature (Eq. 7). The ratio of concentrations of the
reactants used was [1]:[TfOH]:[Bu NI]:[ROH] = 1:1:2:3. Catalytic amounts of TfOH
4
and n-Bu NI were also effective. The reactions performed resulted in most cases
4
(cf. Table 1) in the corresponding 2-deoxyglycosides with a high a stereoselectivity. No
Ferrier-type rearrangement products were detected (Eq. 7). The resulsts are summarized
in Table 1.
This reaction system turned out to be an efficient new route (in addition to the few
[
32–38]
existing ones
) for the direct acid-catalyzed one-pot conversion of glucals to the
derived 2-deoxyglycosides, and might be applicable as well to other glycals.
In conclusion, it was demonstrated that carbocation salts formed by reacting 3,4,6-
tri-O-benzyl-D-glucal 1 with a specific combination of a protonic acid (TfOH) and a
Lewis acid (n-Bu NI), which was effective in initiating a living cationic polymerization
4
of alkyl vinyl ethers, reacted with nucleophiles in unique regioselective and stereo-
specific reaction pathways. The preliminary results obtained point to an interesting
potential for a novel chemistry of glycals in their reactions with nucleophiles in the
presence of other specific combinations of protonic and Lewis acids, which are ef-
fective in inducing living cationic polymerizations of alkyl vinyl ethers.
EXPERIMENTAL
1 13
General methods. H and C NMR spectra were obtained on Bruker AC-200
(200 MHz), Bruker AC-250 Cryospec (250 MHz), Bruker ARX-500 (500 MHz) and
Bruker DRX-600 (600 MHz) spectrometers, in CDCl , downfield from tetramethylsilane
3
as internal standard. Values of chemical shifts (d) and couplings (J) are given in ppm and
Hz, respectively. FABMS were obtained using a Finnigan MAT 312 Mass Spectrometer

Reactions of Nucleophiles
833
(
(
70 ev) and the EIMS were obtained using a Finnigan MAT 8430 Mass Spectrometer
70 ev). Silica gel 60 (Baker: 0.04–0.063 mm or ICN: 0.03–0.063 mm) was used for
flash chromatography. All solvents were purified and dried by standard methods.
The 3,4,6-tri-O-benzyl-D-glucal (1)–TfOH–n-Bu NI reaction system. The re-
4
action was carried out using two two-neck flasks equipped with an argon inlet, a rubber
septum and magnetic stirring, under strictly dry conditions. Tetrabutylammonium io-
dide (1.779 g, 4.815 mmol) was introduced to one of the two flasks, followed by 5.0
mL of dry dichloromethane. The solution was cooled to ꢁ 42 °C. Triflic acid (0.20
mL, 2.26 mmol) was injected into the cooled solution, resulting in a colour change to
yellow. A portion of the mixture (0.63 mL, 0.224 mmol of TfOH, 3.06 mmol n-Bu NI)
4
was injected into the second flask, which contained a solution of 3,4,6-tri-O-benzyl-D-
glucal (1) (0.257 g, 0.618 mmol) in 13.0 mL of dry dichloromethane, at 0 °C. The
mixture in the second flask was stirred for 3.75 h at 0 °C followed by quenching with
ethyl alcohol (0.20 mL, 3.43 mmol). Stirring was continued for 0.5 h at 0 °C, a
saturated solution of sodium thiosulfate added, and the mixture was brought to room
temperature. Dichloromethane was added, and the mixture was washed with a saturated
sodium thiosulfate solution followed by extraction of the aqueous layer with dichlor-
omethane. The combined extracts were washed with a saturated solution of sodium
hydrogen carbonate and then with water, dried over magnesium sulfate and filtered.
The solvent was removed from the filtrate under reduced pressure. The residue was
subjected to flash chromatography on two different silica gel columns using as eluents
petroleum ether: ethyl acetate, 9:1 and 8:2, respectively. Not all the products com-
prising the crude residue were isolated and their structure confirmed.
1
13
The following are the H NMR, C NMR and MS data of the new products which
were isolated.
3,4,6-Tri-O-benzyl-2-deoxy- -D-arabino-hexopyranosyl-(1 ! 1)-3,4,6-tri-O-ben-
zyl-2-deoxy- -D-arabino-hexopyranoside (7 ). 0.0238 g (0.028 mmol, 9.1%) of
7
7
was obtained as the a–a isomer, as a colorless viscous oil. The spectral data of
is given hereby: H NMR (600 MHz, a–a isomer) d: 1.72 (ddd, 1H,
1
J2ax,2eq ꢂ J
ꢂ 12.9 Hz, J
= 2.2 Hz, H-2 ), 2.14 (ddd, 1H, J
= 4.8 Hz, H-
2ax,3
2ax,1
ax
2eq,3
2eq), 3.64 (dd, 1H, J ꢂ J ꢂ 9.1 Hz, H-4), 3.65 (dd, 1H, J = 10.5 Hz, J6’,5 = 2.2
4,3
4,5
6’,6
Hz, H-6’), 3.72 (bd, 1H, H-5), 3.76 (dd, 1H, J = 3.75 Hz, H-6), 3.94 (ddd, 1H, H-3),
6
,5
4
.52 (d, 1H, J = 11.9 Hz, CH Ph), 4.53 (d, 1H, J = 10.2 Hz, CH Ph), 4.61 (d, CH Ph,
2 2 2
1
H), 4.63 (d, J = 10.9 Hz, CH Ph, 1H), 4.65 (d, CH Ph, 1H), 4.99 (d, 1H, CH Ph), 5.23
2
2
2
1
3
(
d, 1H, H-1), 7.20–7.35 (m, 30H, 6Ph); C NMR (600 MHz) d: 35.04 (C-2), 68.81 (C-
6
), 71.49 (C-5), 71.79 (CH Ph), 73.50 (CH Ph), 75.16 (CH Ph), 77.20 (C-3), 78.12 (C-
2 2 2
4
), 92.79 (C-1), 127.60–128.41 (Ph), 138.14 (Ph), 138.40 (Ph), 138.54 (Ph).
+
HR-FABMS Calcd for C H NaO : 873.397854. Obs. MNa = 873.400790.
5
4
58
9
Ethyl 4,6-Di-O-benzyl-2,3-dideoxy-3-iodo- -D-glucopyranoside (6 ). 0.0136 g
0.028 mmol, 4.6%) of 6 was obtained as the a isomer, as a colorless viscous oil. The
(
1
spectral data of 6 is given hereby: H NMR (200 MHz, a isomer) d: 1.16 (t, 3H,
J1@,1’ = 7.1 Hz, H-1@), 2.46 (ddd, 1H J2ax,2eq ꢂ J = 13.3 Hz, J2ax,1 = 3.4 Hz, H-2ax),
2ax,3
2.57 (ddd, 1H, J2eq,3 = 5.5 Hz, J2eq,1 = 1.3 Hz, H-2 ), 3.41 (dq, 1H, J
eq
= 9.5 Hz,
1’b,1’a
Hz, H-1’b), 3.57–3.87 (m, 5H, H-1’a, H-4, H-5, 2H-6), 4.40–4.61 (3H), 4.40–4.61 (m,

834
Kasuto Kelson and Feit

Reactions of Nucleophiles
835
H-3), 4.42 (d, J = 12.1 Hz, CH Ph), 4.51 (d, J = 10.0 Hz, CH Ph), 4.68 & 4.71 (d, 2H,
2
2
1
CH Ph; bs, H-1), 4.94 (d, 1H, CH Ph, 1H), 7.26–7.39 (m, 10H, 2Ph); C NMR (200
3
2
2
MHz) d: 14.96 (C-1@), 26.77 (C-3), 47.90 (C-2), 62.62 (C-1’), 69.29 (C-6), 72.59 (C-5),
3.72 (CH Ph), 74.63 (CH Ph), 79.90 (C-4), 97.42 (C-1), 127.84–128.40 (Ph), 137.75
7
2
2
(
Ph), 137.86 (Ph).
HR FABMS Calcd for C H INaO : 505.085181. Obs. MNa = 505.084370.
+
2
2
27
4
Ethyl 4,6-Di-O-benzyl-2,3-dideoxy-3-iodo- -D-glucopyranoside (6 ). 0.0170 g
0.035 mmol, 5.7%) of 6 was obtained as the b isomer, as a colorless viscous oil. The
spectral data of 6 is given hereby: H NMR (200 MHz, a isomer) d: 1.23 (t, 3H,
(
1
J1@,1’ = 7.1 Hz, H-1@), 2.36 (dt, 1H, J2ax,2eq ꢂ J
ꢂ 13.1 Hz, J
= 9.2 Hz, H-2ax),
.61 (ddd, 1H, J2eq,3 = 4.8 Hz, J2eq,1 = 1.8 Hz, H-2 ), 3.38 (ddd, 1H, J = 9.1 Hz,
2ax,3
2ax,1
2
eq 5,4
J5,6 ꢂ J ꢂ 1.9 Hz, H-5), 3.52 (dq, 1H, J
= 9.4 Hz, H-1’b), 3.67–3.83 (m, 3H,
1’b,1’a
5,6’
H-4, 2H-6), 3.93 (dq, 1H, H-1’a), 4.14 (ddd, 1H, J = 10.2 Hz, H-3), 4.40 (dd, 1H, H-
3
,4
1
), 4.50 (d, 1H, J = 10.2 Hz, CH Ph), 4.56 (d, 1H, J = 12.5 Hz, CH Ph), 4.56 (d, 1H,
2
2
1
3
CH Ph), 4.93 (d, 1H, CH Ph), 7.26–7.35 (m, 10H, 2Ph); C NMR d: 15.16 (C-1@),
2
2
2
6.21 (C-3), 44.64 (C-2), 64.82 (C-1’), 69.29 (C-6), 73.65 (CH Ph), 74.87 (CH Ph),
2
2
7
7.68 (C-5), 79.76 (C-4), 100.92 (C-1), 127.72–128.38 (Ph), 137.64 (Ph), 138.07 (Ph).
+
HR-FABMS Calcd for C H INaO : 505.085181. Obs. MNa = 505.084132.
2
2
27
4
Ethyl 2,3-Dideoxy-4,6-bis-O-benzyl- -D-erythro-hex-2-enopyranoside (8).
.0072 g (0.020 mmol, 3.3%) of 8 was obtained as a mixture of a and b isomers,
together with 4, as a colorless viscous oil. The molar ratio of 8 and 4 were deduced
0
1
from the H NMR spectrum of the mixture. The obtained mass and yield were cal-
culated from the molar ratio of 8 and 4 and from the mixture’s mass. The spectral data
[4,49]
of the a-isomer of 8, was in accordance with that reported.
Benzyl 4,6-Di-O-benzyl-2,3-dideoxy-3-iodo- -D-glucopyranoside (13). The re-
action was carried out using two two-neck flasks equipped with an argon inlet, a
rubber septum and magnetic stirring, under strictly dry conditions. Tetrabu-
tylammonium iodide (1.073 g, 2.095 mmol) was introduced to one of the flasks, fol-
lowed by 3.0 mL of dry dichloromethane, and the solution was cooled to ꢁ42 °C.
Triflic acid (0.13 mL, 1.47 mmol) was injected into the cooled solution changing its
colour to yellow. The obtained mixture (2.0 mL, 0.94 mmol of TfOH, 1.34 mmol of n-
Bu NI) was injected into the second flask which contained 3,4,6-tri-O-benzyl-D-glucal
4
(
1) (0.3925 g, 0.942 mmol) dissolved in 14.0 mL of dry dichloromethane at room
temperature. The mixture in the second flask which turned brown, was stirred for 3 h at
room temperature and was then quenched with benzyl alcohol (0.15 mL, 1.44 mmol).
Stirring was continued for 0.5 h and the reaction mixture was subjected to the same
workup described above to give the crude product (viscous liquid).
Notes to Table 1:
a
1
Determined by H NMR.
b
1
Reported in the reference cited, including H NMR.
c
Reported in the reference cited, spectral data not included.
d 1
H NMR data in the reference is given for the L-isomer.

836
Kasuto Kelson and Feit
The crude product was subjected to flash chromatography using a petroleum ether:
ethyl acetate mixture (9:1, respectively) as eluent, to yield 0.331 g (0.608 mmol,
4.5%) of 13 as colorless viscous oil, which solidified at ꢁ20°C to a white solid
6
1
(mp 73–74°C). The spectral features of the product are as follows: H NMR (200
MHz, a isomer) d: 2.49 (ddd, 1H, J2ax,2eq ꢂ J
ꢂ 13.4Hz, J
= 3.4 Hz, H-2ax),
.62 (ddd, 1H, J2eq,3 = 5.3 Hz, J2eq,1 = 1.4 Hz, H-2eq), 3.61 (bd, 1H, J = 9.2 Hz, H-
6,6’
2ax,3
2ax,1
2
6
), 3.75–3.88 (m, 3H, H-4, H-5, H-6’), 4.43 (d, 1H, J = 10.0 Hz, CH Ph), 4.44–4.52
2
(
m, 1H, H-3), 4.44 (d, 1H, J = 11.8 Hz, CH Ph), 4.53 (d, 1H, J = 12.0 Hz, CH Ph),
2
2
4
7
6
4
.64 (d, 1H, CH Ph), 4.71 (d, 1H, CH Ph), 4.77 (bd, 1H, H-1), 4.94 (d, 1H, CH Ph),
2 2 2
1
3
.22–7.42 (m, 15H, 3Ph); C NMR (200 MHz) d: 26.50 (C-3), 43.45 (C-2), 68.93 (C-
/CH Ph), 69.13 (C-6/CH Ph), 72.83 (C-5), 73.67 (CH Ph), 74.61 (CH Ph), 79.77 (C-
), 97.05 (C-1), 128.42–128.86 (Ph), 137.38 (Ph), 137.65 (Ph), 137.81 (Ph).
2
2
2
2
+
HR-FABMS Calcd for C H INaO : 567.100831. Obs. MNa = 567.099747.
29
2
7
4
The reaction of 3,4,6-tri-O-benzyl-D-glucal with isobutyl vinyl ether in the
presence of n-Bu NI–TfOH. The reaction setup consisted of two flasks as described
4
above. A mixture of TfOH (0.2 mL, 2.26 mmol) and n-Bu NI (1.77 g, 4.81 mmol)
4
dissolved in dichloromethane (5 mL) cooled to ꢁ 42°C was prepared as described
above. 1 mL of this solution (0.43 mmol of TfOH, 0.93 mmol of n-Bu NI) was injected
4
into the second flask which contained a solution of 3,4,6-tri-O-benzyl-D-glucal (1)
(
0.198 g, 0.474 mmol) in dichloromethane (12 mL) at ꢁ 23°C. The mixture was stirred
for 15 min at ꢁ 23°C and isobutyl vinyl ether (0.065 mL, 0.498 mmol) was injected to
it over 5–10 min. Stirring was continued for 2.25 h at ꢁ 23°C, ethanol added (0.15
mL, 2.57 mmol) and then workup was carried out as described above. The crude
product obtained was flash chromatographed (eluent: petroleum ether: ethylacetate 9:1)
to yield two main products: a) ethyl 3,4,6-tri-O-benzyl-2-deoxy-a/b-D-arabino-hex-
opyranoside (5), a colourless viscous liquid, (0.185 g, 0.400 mmol, 84%) as a 1:1
mixture of the a and b isomers, b) isobutyl 3,4,6-tri-O-benzyl-2-deoxy-a-D-arabino-
hexopyranoside (14 ) (0.028 g, 0.050 mmol 11.8%) and the b-isomer (14 ) (0.008 g,
0
.016 mmol, 3.4%).
1
2
3
4
5
1
Poly(isobutyl vinyl ether), –[CH CH (OCH CH (CH ) )] – (15). H NMR
2
2
3 2
n
(200 MHz) d: 0.90 (d, 6H, J5,6 = 5.9 Hz, 6H-5), 1.32–2.00 (m, 3H, H-4, 2H-1), 2.98–
3
.31 (m, 2H, 2H-3), 3.35–3.7 (m, 1H, H-2).
General procedure for the preparation of 2-deoxy-3,4,6-tri-O-benzyl-D-gluco-
pyranosides in the 1–n-Bu NI–TfOH–ROH reaction system. Two two-neck flasks
4
equipped with an argon inlet, a rubber septum and magnetic stirring were assembled
under strictly dry conditions. Tetra n-butyl ammonium iodide (1.667 g, 4.513 mmol)
and dichloromethane (4.7 mL) were introduced into one of the flasks which was then
kept at ꢁ42 °C. 3,4,6-Tri-O-benzyl-D-glucal 1 (0.200 g, 0.481 mmol), the hydroxyl
compound ROH (1.463 mmol) and dichloromethane (13.0 mL) were introduced into the
second flask and the mixture kept at ꢁ23 °C. Triflic acid (0.05 mL, 0.565 mmol) was
then injected into the first flask. The mixture in this flask turned yellow. One mL of
this mixture was injected into the second flask and the mixture was stirred for 2 h at
ꢁ
23 °C. The reaction mixture was then quenched with a saturated solution of sodium
thiosulfate, dichloromethane added, the aqueous layer extracted by dichloromethane.

Reactions of Nucleophiles
837
The combined organic layers were washed with water, dried over anhydrous magne-
sium sulfate, filtered and the solvent removed from the filtrate. The residue was
subjected to flash chromatography on a silica gel column. The ROH (16a–f) substrates
used, the derived 2-deoxy glycosides (17a–f) obtained and their yields are detailed in
the Results and Discussion section. The following are hitherto unreported spectral data
of the 17-type products obtained (cf. Table 1).
Methyl (3,4,6-Tri-O-benzyl-2-deoxy- -D-arabino-hexopyranosyl)-(1 ! 6)-
[43,45–47]
2,3,4-tri-O-benzyl- -D-glucopyranoside)(17c).
ddd, 1H, J2axb,2eqb = 12.9 Hz, J2axb,3b = 11.7 Hz, J2axb,1b = 3.4 Hz, H-2 b), 2.29 (dd,
1
(
(
H NMR (500 MHz): d =1.67
ax
1
5
H, J2eqb,3b = 4.9 Hz, H-2 b), 3.34 (s, 3H, H-1’a), 3.47–3.82 (m, 9H, H-2a, H-4a, H-
eq
a, 2H-6a, H-4b, H-5b, 2H-6b), 3.93 (ddd, 1H, J3b,4b = 8.9 Hz, H-3b), 3.99 (dd, 1H,
ꢂ 9.3 Hz, H-3a), 4.40 (d, 1H, J = 12.1 Hz, CH Ph), 4.47 (d, 1H, J = 11.0
J3a,4a ꢂ J
3a,2a
2
Hz, CH Ph), 4.54 (d, 1H, J = 11.1 Hz, CH Ph), 4.56 (d, 1H, J = 12.1 Hz, CH Ph),
2
2
2
4.59–4.64 (m, 3H, 2CH Ph, H-1a), 4.67 (d, 1H, J = 12.8 Hz, CH Ph), 4.78 (d, 1H,
CH Ph), 4.79 (d, 1H, J = 10.6 Hz, CH Ph), 4.86 (d, 1H, CH Ph), 4.90 (d, 1H, CH Ph),
2
2
2
2
2
2
1
3
4
.98 (bs, H-1b), 4.99 (d, CH Ph), (4.98–4.99: 2H), 7.13–7.35 (m, 30H, 6Ph);
2
C
NMR (200 MHz): d = 35.37 (C-2b), 55.06 (C-1’a), 65.79 (C-6a/b), 68.97 (C-6a/b),
9.89 (C-5a/b), 71.04 (C-5a/b), 71.70 (CH Ph), 73.26 (CH Ph), 73.44 (CH Ph), 74.82
6
2
2
2
(
2CH Ph), 75.72 (CH Ph), 77.27 & 77.96 & 78.30 (C-4b, C-3b, C-4a), 80.23 (C-2a),
2 2
82.23 (C-3a), 97.81 (C-1b), 97.97 (C-1a), 127.50–128.34 (Ar), 138.29 (Ar), 138.45
(
Ph), 138.67 (Ph), 138.83 (Ph).
HR-FABMS Calcd for C H NaO : 903.408419. Obs. MNa = 903.408619.
+
5
5
60
10
3
isopropylidene- -D-galactopyranose (17d).
,4,6-Tri-O-benzyl-2-deoxy- -D-arabino-hexopyranosyl-(1 ! 6)-1,2:3,4-di-O-
[43,48]
1
H NMR (200 MHz): d = 1.33 (s,
3
H, CH ), 1.34 (s, 3H, CH ), 1.43 (s, 3H, CH ), 1.52 (s, 3H, CH ), 1.73 (ddd, 1H,
3
3
3
3
J2axb,2eqb ꢂ J
ꢂ 12.8 Hz, J
= 3.6 Hz, H-2 b), 2.33 (dd, 1H, J
ax
= 4.8
2eqb,3b
2axb,3b
2axb,1b
Hz, H-2 b), 3.49–3.84 (m, 6H, 2H-6a, H-4b, H-5b, 2H-6b), 3.91–4.05 (m, 2H, H-5a,
eq
H-3b), 4.22 (dd, 1H, J4a,3a = 8.1 Hz, J4a,5a = 1.6 Hz, H-4a), 4.31 (dd, 1H, J2a,1a = 5.0
Hz, J2a,3a = 2.4 Hz, H-2a), 4.46–4.71 (m, 6H H-3a, 5CH Ph), 4.88 (d, 1H, J = 10.7 Hz,
2
1
CH Ph), 5.02 (bd, 1H, H-1b), 5.51 (1H, d, H-1a), 7.14–7.37 (15H, m, 3Ph); C NMR
3
2
(
200 MHz): d = 24.62 (CH ), 24.97 (CH ), 26.06 (CH ), 26.16 (CH ), 35.50 (C-2b),
3
3
3
3
6
7
1
1
5.47 (C-6a), 65.79 (C-5a), 68.92 (C-6b), 70.76 & 71.07 (C-3a, C-4a, C-3b, C-5b),
1.82 (CH Ph), 73.51 (CH Ph), 74.92 (CH Ph), 77.70 (C-4b), 78.35 (C-2a), 96.40 (C-
2
2
2
b), 97.32 (C-1a), 108.56 (C-7a), 109.34 (C-8a), 127.57–128.33 (Ph), 138.29 (Ph),
38.70 (Ph), 138.86 (Ph).
+
HR-FABMS Calcd for C H NaO : 699.314518. Obs. MNa = 699.315523.
3
9
48
10
3
isopropylidene- -D-glucofuranoside (17e).
,4,6-Tri-O-benzyl-2-deoxy- -D-arabino-hexopyranosyl-(1 ! 3)-1,2:3,4-di-O-
[45]
1
H NMR (200 MHz) d: 1.25 (s, 3H,
CH ), 1.32 (s, 3H, CH ), 1.40 (s, 3H, CH ), 1.48 (s, 3H, CH ), 1.71 (1H, ddd,
3
3
3
3
J2axb,2eqb ꢂ J
ꢂ 12.8 Hz, J
= 3.4 Hz, H-2 b), 2.27 (dd, 1H, J
ax
= 4.2
2eqb,3b
2axb,3b
2axb,1b
Hz, H-2 b), 3.42–4.29 (m, 10H, H-3a, H-4a, H-5a, 2 H-6a, H-3b, H-4b, H-5b, 2H-6b),
eq
4.48–4.71 (m, 6H, 5CH Ph, H-2a (1H, d, J
CH Ph), 5.24 (bd, 1H, H-1b), 5.81 (d, 1H, H-1a), 7.15–7.35 (m, 15H, 3Ph); C NMR
= 3.6 Hz)), 4.89 (d, 1H, J = 10.6 Hz,
2a,1a
2
1
3
2
(
200 MHz): d = 25.47 (CH ), 26.92 (CH ), 38.84 (C-2a), 67.79 (C-6a), 69.03 (C-6b),
3
3

838
Kasuto Kelson and Feit
7
1.81 (C-5), 71.94 (CH Ph), 72.58 (C-5a), 73.66 (CH Ph), 75.28 (CH Ph), 77.31
2
2
2
(
1
C-3b), 78.23 (C-3a/4b), 80.34 (C-3a/4b), 81.42 (C-4a), 83.85 (C-2a), 98.78 (C-1b),
05.36 (C-1a), 109.18 (C-7, C-8), 127.75–128.49 (Ph), 135.81 (Ph), 138.13 (Ph).
+
HR-FABMS Calcd for C H NaO : 699.316923. Obs. MNa = 699.315842.
3
9
48
10
ACKNOWLEDGMENT
Useful discussions with Professor Richard R. Schmidt of Konstanz University,
Germany, are gratefully acknowledged.
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Received January 6, 2003
Accepted August 4, 2003