Synthesis of erythro and threo furanoid glycals from 1- and 2-phenylselenenyl-carbohydrate derivatives

Article abstract of DOI:10.1016/S0008-6215(01)00256-7

Differently protected erythro and threo furanoid glycals were synthesized by selenoxide elimination when phenyl 1-selenoglycosides were treated in oxidizing conditions (^tBuOOH, Ti(OⁱPr)₄, Et₂ⁱPrN). Th

Full text of DOI:10.1016/S0008-6215(01)00256-7

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Carbohydrate Research 336 (2001) 83–97
Synthesis of erythro and threo furanoid glycals from 1-
and 2-phenylselenenyl–carbohydrate derivativesꢀ
Fernando Bravo, Mohamed Kassou, Yolanda D´ıaz,* Sergio Castillo´n*
Departament de Qu´ımica Anal´ıtica i Qu´ımica Orga`nica, Uni6ersitat Ro6ira i Virgili, Pc¸a. Imperial Tarraco 1,
E-43005 Tarragona, Spain
Received 21 June 2001; received in revised form 7 September 2001; accepted 20 September 2001
Abstract
Differently protected erythro and threo furanoid glycals were synthesized by selenoxide elimination when phenyl
1-selenoglycosides were treated in oxidizing conditions (tBuOOH, Ti(OiPr)4, Et2i PrN). The phenyl 1-selenoglycosides
were obtained from methyl 2-deoxy-D-erythro-pentofuranoside by protection of the primary hydroxyl or both
hydroxyls and further reaction with PhSeH in the presence of BF3·Et2O. Erythro and threo furanoid glycals were also
prepared by treating 2-deoxy-2-phenylselenenyl-1,4-anhydrocyclitols under similar conditions. The 2-deoxy-2-
phenylselenenyl-1,4-anhydrocyclitols were obtained from 4-pentene-1,2,3-triols by a 5-endo selenium electrophilic
induced cyclization. © 2001 Published by Elsevier Science Ltd.
Keywords: Glycal synthesis; Selenoglycosides; 1,4-Anhydro-2-phenylselenenyl-pentitols; Selenoxide elimination; Double bond
formation
1. Introduction
of halo sugars using zinc as the reducing
agent.10 Over the years a wide range of
methodologies for glycal synthesis have been
reported involving: (i) the use of good leaving
groups at C-2 of glycosyl halides;11 (ii) reac-
tion of protected glycosyl halides with a re-
ducing agent such as sodium, potassium and
sodium–naphthalide,12 zinc/silver-graphite,13
potassium-graphite,14 aluminium amalgam,15
samarium(II) iodide,16 lithium in liquid am-
monia (Ireland’s method),17 titanocene dichlo-
ride in THF,18 with vitamin B-12 and Zn as a
source of Co(I),19 with chromium(II) com-
plexes in DMF,20 with zinc dust in the pres-
ence of a N-base in various aprotic solvents;21
(iii) reduction of sugar derivatives with a
sulfur substituent at position 1, i.e., reaction
of 1-thioglycosides and glycosyl phenyl sul-
fones with lithium-naphthalides in THF;22 re-
action of 1-thioglycosides with potassium-
The use of glycals (1,4- or 1,5-anhydro-2-
deoxy-1-enitol) as glycosyl donors has been
extensively discussed in the literature.2 Indeed,
a number of recent articles describe them as
important precursors of oligosaccharides,3 C-
glycosyl
compounds,4
C-nucleosides,5
nucleosides6 and others.†,‡,§ Glycals were first
synthesized by Fischer and Zach, by reduction
ꢀ For preliminary communications see Ref. 1.
* Corresponding authors. Tel.: +34-977-558137; fax:
+34-977-559563 (S.C.); fax: +34-977-559563 (Y.D.).
E-mail addresses: ydiaz@quimica.urv.es (Y. D´ıaz), castil-
lon@quimica.urv.es (S. Castillo´n).
† For use in cyclopropanation and ring expansion see Ref.
7.
‡ For use in a novel class of glycosidation based in a [4+2]
cycloaddition see Ref. 8.
§ For the synthesis of thionucleosides from thioglycals see
Ref. 9.
0008-6215/01/$ - see front matter © 2001 Published by Elsevier Science Ltd.
PII: S0008-6215(01)00256-7

84
F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
Scheme 1. Strategies for the synthesis of furanoid.
Scheme 2. Synthesis of furanoid glycals by elimination of selenoxides. Scheme of retrosynthesis.
graphite in THF;23 reaction of glycosyl phenyl
sulfones with samarium(II) iodide in THF;24
reactions of glycosyl sulfoxides with butyl-
lithium in THF;25 (iv) electrolysis of aceto-
bromo sugars in DMF or acetonitrile;26 (v)
radical-induced elimination from 1-thiogly-
coside-2-xanthates22b,22c and from 2-azido-2-
deoxy-selenoglycosides;27 (vi) elimination from
2-deoxy-pentofuranose derivatives, such as
nucleosides,28 1-O-mesylates29 and 1,2-diols;30
(vii) tungsten and molybdenum-promoted
alkynol endo-cycloisomerization;3c,31 (viii)
ring-closure metathesis32 (Scheme 1 represents
some of these methods applied to furanoid
glycals). Despite the number of methods avail-
able, improvements are still desirable, since
many of these approaches fail in the furanoid
glycal series or meet with problems of protec-
tive group compatibility.
Here we report an efficient procedure for
synthesizing furanoid glycals from 1-1a and
2-phenylselenenyl-1,4-anhydroalditols1b
through oxidation and thermal elimination of
the selenoxide generated at low temperature
(Scheme 2). These seleno-derivatives, in turn,
can be prepared from 2-deoxyribose and from
pentenetriols,33 respectively. Both procedures
are compatible with the presence of a wide
number of protecting groups.
2. Results and discussion
Synthesis of furanoid glycals from 1-
phenylselenenylfuranoside deri6ati6es.—As de-
scribed above, one of the problems associated
with many glycal syntheses is the compatibil-
ity of the protective groups with the basic
conditions. In this context, oxidation of 1-se-
lenofuranosides and subsequent elimination
could overcome this problem.34,35 Moreover,
both selenoxide anomers might be useful start-
ing materials and, therefore, separation would
be not necessary. These 1-seleno-derivatives,
in turn, would be accessible from the corre-
sponding methyl glycosides by glycosylation
with PhSeH and BF3·Et2O.36
2-Deoxy-
D
-erythro-pentose (2-deoxy- -rib-
D
ose) was the starting material of choice be-
cause not only did it provide the stereochemi-
cal pattern required for erythro glycals, but
also it did not require deoxygenation at posi-
tion 2.
Methyl 2-deoxy-
D
-erythro-pentofuranoside
-ery-
(1)37 (readily available from 2-deoxy-
D
thro-pentose) reacted with PhSeH and a sub-
stoichiometric amount of BF3·Et2O, to
provide a mixture of phenyl 1-selenoglycosides
3 and the corresponding pyranosyl derivative.
In order to test the stability of common
protecting groups in the step of formation of

F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
85
Scheme 3. (a) TrCl, py. (b) 0.8 equiv BF3·Et2O, 1.1 equiv PhSeH, −20 °C. (c) TBHP–EtiPr2N–Ti(OiPr)4. (d) TBDPSCl,
imidazole, DMF.
nation but the acidic conditions probably
favored the subsequent aromatization of the
glycal initially formed.
In an attempt to prevent furan formation,
we studied other neutral or weakly acid oxi-
dant systems. Oxidation of 7 with H2O2 in
THF34 afforded glycal 15 in a 30% yield in the
best case.
We next investigated other peroxides such
as tert-butyl hydroperoxide (TBHP) which
have been successfully used for selenide oxida-
tions,34e particularly, in the presence of
Ti(OiPr)4.39 Table 1 shows a brief survey of
the different conditions essayed in the reaction
of 8 with the system TBHP–Ti(OiPr)4.
From these experiments, we concluded the
following: (i) the base is required to neutralize
the phenylselenenic acid (PhSeOH) formed in
the reaction, which may promote either elec-
trophilic addition to the glycal also formed in
the reaction or aromatization of the glycal to
furan (Entries 1 and 2); (ii) titanium isopro-
poxide increases the rate of syn-elimination
(Entries 5 and 6). In the absence of the Lewis
acid, traces of glycal are obtained (Entry 4);
(iii) when substoichiometric amounts of
Ti(OiPr4) were used, the reaction afforded the
glycal in a low yield (Entry 5).
the 1-selenofuranoside, we prepared com-
pounds 2, 4, 5 and 6. When trityl ether 2 was
treated with PhSeH and BF3·Et2O, selenogly-
cosylation took place with concomitant depro-
tection of the trityl group, even when a
substoichiometric amount of the Lewis acid
was used, to give compound 3 (Scheme 3)
slightly contaminated by the 1-seleno-pyran-
osyl derivative.
Compound 1 was then protected at position
5 by reaction with TBDPSCl, imidazole in
DMF to give the tert-butyldiphenylsilyl ether
6 in a 76% yield (Scheme 3).38 Reaction of 6
with PhSeH BF3·Et2O (0.8 equiv) afforded 7
in an excellent yield (92%). Other Lewis acids
such as SnCl4 and Ti(OiPr)4 resulted in a
lower yield of the desired product or did not
afford glycosylation.
Compound 7 was transformed into a set of
differently protected selenoglycosides 10–14
(Scheme 3) by treatment with BnBr, MeI,
MEMCl, TBDMSCl, and Ac2O, respectively.
Similarly, selenoglycosides 8 and 9, with the
same protecting groups at positions 3 and 5,
were available from 4 and 5, by reaction with
PhSeH–BF3·Et2O. Compounds 8 and 9 can be
also obtained from 3, by treating with acetic
anhydride and pivaloyl chloride, respectively.
Oxidation was first attempted with 1-seleno-
derivative 8 using MCPBA as an oxidant at
−20 °C, but only a furan derivative was iso-
lated. MCPBA promoted oxidation and elimi-
When 8 was treated with 1.1 equiv of
TBHP, 1 equiv of EtiPr2N and 1 equiv of
Ti(OiPr)4 at 0 °C, however, the glycal yield
was good (Entry 6). The TBHP–EtiPr2N–

86
F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
Table 1
Trials of oxidation of 1-selenoglycoside 8 with 1.1 equiv of TBHP
Entry
Time (min)
EtiPr2N (equiv)
Temp (°C)
Ti(OiPr)4 (equiv)
15 (%)
1
2
3
4
5
6
60
120
30
60
20
0
0
1
1
1
1
0
20
0
20
0
0
0
0
0
0.5
1
5
54
84
30
0
Ti(OiPr)4 system was also applied to the oxi-
dation of seleno-derivatives 9–14 (Scheme 3,
Table 2).
then carried out using 1.1 equiv of TBHP, 0.8
equiv of base and 1 equiv of Ti(OiPr)4 at lower
temperatures (−10 °C) to produce glycal 21
in a 68% yield (Entry 8). Few reports on the
synthesis of furanoid glycals with acyl protec-
tive groups have been published.
Dipivaloyl derivative 9, was oxidized under
the same conditions as those used for 8 to
produce the dipivaloyl glycal 16 in a 71% yield
(Entry 3). This compound proved to be stable
to purification and was fully characterized.
In order to have differently protected gly-
cals with a pivaloyl group at position 5, com-
pound 3 was treated with 1.1 equiv of PivCl in
pyridine, but oxidation of this compound led
to an untractable mixture. The same result
was observed starting from 7. Attempts at
protecting the 3-OH in the 5-O-pivaloyl
selenofuranoside with BnBr or MeI led to a
mixture of starting material and the 3-O-
pivaloyl derivative.
Although, oxidation–elimination proved
efficient with only 1.1 equiv of TBHP, the use
of twofold excess of oxidant is desirable for
the following reasons: (i) to accelerate the
reaction of the least reactive seleno-anomer, as
observed in several reactions; and (ii) to pro-
mote the oxidation of PhSeOH to PhSeO2H,
which does not undergo addition to alkenes
under the reactions conditions.
In these conditions, compounds 8, 10, 11,
12 and 13 were oxidized with TBHP to afford
glycals 15, 17, 18, 19 and 20 in yields of 84,
65, 72, 81 and 60%, respectively (Entries 1, 3,
4, 5 and 6, Table 2).
Oxidation of 14 using an excess of oxidant
and base produced glycal 21, but because of
aromatization the yield was low. Formation of
the furan derivative is favored both in acid or
basic medium due to the presence of the labile
acetate protective group. Oxidation of 14 was
Glycals with the threo configuration were
available by inversion of the configuration at
position 3 on the corresponding methyl -ery-
D
thro-pentofuranosides. Various highly efficient
methods for this purpose have been reported.
Of these, the Mitsunobu reaction40 is known
to be very sensitive to steric hindrance,41 as it
is the case with the threo derivative. Moriarty
et al.42 described a method for inverting the
configuration of hindered alcohols in high
yields using sodium nitrite as a nucleophile. In
particular, neopentyl alcohol was reactive to-
wards Moriarty’s conditions but it was not
affected by the Mitsunobu reaction condi-
tions. Thus, compound 6 was then trans-
formed into 22 by treatment with Tf2O and
pyridine in CH2Cl2 at −20 °C. Reaction of 22
with KNO2 and 18-crown-ether in DMF led
Table 2
Synthesis of erythro-configurated glycals 15–21 from the cor-
responding 1-phenylselenenylfuranosides 8–14
a
Entry
Seleno-
derivative
Conditions
Glycal
Yield
(%)
1
2
3
4
5
6
7
8
9
B
A
B
B
B
B
A
15
16
17
18
19
20
21
84
71
65
72
81
60
68
10
11
12
13
14
a (A) 1.1 equiv of TBHP, 0.8 equiv of EtiPr2N and 1 equiv
of Ti(OiPr)4 in CH2Cl2 at 0 °C. (B) 2.3 equiv of TBHP, 1.7
equiv of EtiPr2N and 1 equiv of Ti(OiPr)4 in CH2Cl2 at 0 °C.
to the methyl 2-deoxy- -threo-pentofuran-
D

F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
87
Scheme 4. Tf2O, py, CH2Cl2, −20 °C, 91%. (b) KNO2, 18-crown-ether, DMF, 62%. (c) PhSeH, BF3·Et2O, CH2Cl2, 93%. (d)
Bu4NF, THF, 91%.
The yields were in general lower than those of
the erythro glycals.
oside (23) in a 62% yield (Scheme 4). Com-
pound 23 was then treated with PhSeH–
BF3·Et2O using the standard conditions to
produce 24. Compound 24 was the precursor
of a set of 3,5-differently protected seleno-
derivatives 26–29, which were obtained in a
moderate to excellent yield (Scheme 4).
Desilylation with Bu4NF in THF provided
the unprotected seleno-derivative 25 which
was subsequently transformed into the diac-
etate and dibenzyl derivatives 30 and 31 in
excellent yields.
Threo-configurated glycals may also be
available from xylose. Dyatkina et al.43 trans-
formed xylose into the methyl 3,5-di-O-ben-
zyl-2-deoxy-a,b-threo-pentofuranoside
(38)
through a series of sequences that involved
deoxygenation of the hydroxyl function at C-2
with selective protection at the other posi-
tions, from which selenoglycoside 31 was ob-
tained in 96% yield (Scheme 5). This new
route makes threo glycals accessible from an
inexpensive material such as xylose, and con-
firms the generalization of this method.
Surprisingly, it was not possible to synthe-
size
phenyl
3-O-benzyl-5-O-tert-butyldi-
-threo-pen-
Synthesis of glycals from 2-deoxy-2-phenyl-
seleneny-1,4-anhydroalditols.—The good re-
sults obtained in the synthesis of glycals from
1-seleno-derivatives encouraged us to try a
phenylsilyl-2-deoxy-1-seleno-a,b-
D
tofuranoside. When compound 23 was pro-
tected at position 3 as a benzyl ether,
1-selenoglycoside formation did not take
place. On the other hand, as it was discussed
previously, reaction of 23 to the correspond-
ing seleno-derivative 24 proceeded efficiently
but, in this case, subsequent benzylation at
position 3 was unsuccessful. We assume that
there must be a high steric hindrance in the
final protected seleno-derivative that prevents
the reaction from taking place.
Table 3
Synthesis of threo-configurated glycals 32–37 from the corre-
sponding 1-phenylselenenylfuranosides 26–31
a
Entry
Seleno-
derivative
Conditions
Glycal
Yield
(%)
1
2
3
4
5
6
26
27
28
29
30
31
B
B
B
A
A
B
32
33
34
35
36
37
68
53
74
68
70
87
Seleno-derivatives 26–31 were then trans-
formed into the corresponding glycals 32–37,
respectively, using TBHP–EtiPr2N–Ti(OiPr)4
at 0 °C in the same conditions as those used
for the erythro glycals (Scheme 4, Table 3).¶
a (A) 1.1 equiv of TBHP, 0.8 equiv of EtiPr2N and 1 equiv
of Ti(OiPr)4 in CH2Cl2 at 0 °C. (B) 2.3 equiv of TBHP, 1.7
equiv of EtiPr2N and 1 equiv of Ti(OiPr)4 in CH2Cl2 at 0 °C.
¶ Glycal 37 was used as a starting material in a formal
synthesis of AZT. Ref. 6b.

88
F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
glycal 15 from diastereomer 39 by reaction
with H2O2 and pyridine in dichloromethane
for 6 h produced the corresponding selenox-
ide. No reaction even occurred when the se-
lenoxide was heated in dichloromethane to
force thermal elimination. Paquette reported
that whenever elimination can only take place
at a carbon bonded to an oxygen, the selenox-
ide was unusually stable and required more
drastic conditions for elimination.44 Reaction
in refluxing dichloroethane for 24 h led to a
mixture of decomposition products. The re-
sults were the same for compounds 42, 46 and
48.
Oxidation was then performed with the
TBHP–EtiPr2N–Ti(OiPr)4 system, which had
provided good results starting from 1-seleno-
derivatives (Scheme 6, Table 4). Reaction of
39 using the standard conditions produced
selenoxide very quickly (15 min), probably
due to the homogeneity of the reaction
medium, but it proved resistant to elimina-
tion. Reflux for 36 h, however, led to glycal 15
in a 62% yield. No traces of the 2,5-dihydro-
furan were detected. Compounds 42, 46 and
48 were also submitted to these reaction con-
ditions (Entries 2, 3 and 4). Formation of the
selenoxide was rapid in all cases, but subse-
quent elimination to yield the corresponding
glycals (15 from 39 or 42, and 37 from 46 or
48) required heating for 48 h. Both epimers at
C-2 39 and 42 underwent identical regioselec-
tive outcome, as we observed no syn elimina-
tion of selenoxide towards the more
substituted position to produce the 2,5-
dihydrofuran.
Scheme 5. (a) Ref. 43. (b) PhSeH, BF3·Et2O, CH2Cl2, 96%.
similar approach using 2-seleno-derivatives as
precursors. Elimination of selenoxide from
these derivatives may proceed on both b-car-
bon atoms, which, in turn, are bonded to
oxygen atoms, to yield the desired glycal or
the 2,5-dihydrofuran.
In order to make 2-deoxy-2-phenylsele-
nenyl-1,4-anhydroalditols available we system-
atically explored the synthesis of tetrahydro-
furan derivatives by electrophile-induced cy-
clization of 4-pentene-1,2,3-triols.33
We showed that the course of cyclization
(5-exo vs. 5-endo) depends on the electrophilic
species used (I+, Se+), the nucleophile coun-
teranion and the protective groups. In particu-
lar, 5-endo products of interest may be
synthesized by selenium-promoted cyclization
from 4-pentene-1,2,3-triols appropriately pro-
tected at the primary hydroxyl group (Scheme
6). Both diastereomeric selenenyl-tetra-
hydrofurans were then separated by chro-
matographic techniques. The corresponding
4-pentene-1,2,3-triols, in turn, were accessible
from 2,3-O-isopropylidene-glyceraldehyde by
addition of vinylmagnesium chloride, benzyla-
tion of the free hydroxyl group, acetal hydrol-
ysis and selective protection of the primary
hydroxyl function.
We initially tried oxidation on single
diastereomers. Our first attempts to prepare
Scheme 6. (a) EtiPrN–TBHP–Ti(OiPr)4, CH2Cl2 or C2H4Cl2, 0 °C“reflux.

F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
89
Table 4
3. Experimental
Synthesis of threo- and erythro-configurated glycals from the
2-deoxy-2-phenylselenenyl-1,4-anhydroalditols 39–44 and 46–
49
General methods.—Melting points are un-
corrected. Optical rotations were measured at
1
13
a
25 °C in 10 cm cells. H and C NMR spectra
were recorded on a Varian Unity-400 spec-
trometer operating at 399.93 (1H) and 99.98
MHz (13C), respectively, using CDCl3 as a
solvent at 30 °C with TMS as internal stan-
dard. Elemental analyses were determined at
the ‘Servei de Recursos Cientifics (Universitat
Rovira i Virgili)’. Flash-column chromatogra-
phy was performed using Silica Gel 60 A CC
(40–63 microns). Preparative-layer chro-
matography was performed on Silica Gel 60.
Radial chromatography was performed on 1,
2 or 4 mm plates of silica gel, depending on
the amount of product. Medium-pressure
chromatography (MPLC) was performed us-
ing Silica Gel 60 A CC (6–35 microns). Band
separation was monitored by UV. TLC plates
were prepared with Kieselgel 60 PF254. Sol-
vents for chromatography were distilled at
atmospheric pressure prior to use. Reaction
solvents were purified and dried by using stan-
dard procedures.
Entry
Seleno-
derivative
Conditions
Glycal
Yield
(%)
1
2
3
4
5
6
7
8
9
39
42
46
48
40+43
47+49
40+43
47+49
41+44
A
A
A
A
A
A
B
15
15
37
37
17
50
17
50
45
62
61
73
74
82
65
94
82
89
B
B
a (A) TBHP, Ti(OiPr)4, EtiPr2N, CH2Cl2, 0 °C–reflux, 48 h.
(B) TBHP, Ti(OiPr)4, C2H4Cl2, 0 °C–reflux, 3 h.
This prompted us to try oxidation starting
from the diastereomeric mixture of 2-deoxy-2-
phenylselenenyl-1,4-anhydroalditols obtained
from the 5-endo selenoetherification. Treat-
ment of the mixture 40/43 and 47/49 with
TBHP–EtiPr2N–Ti(OiPr)
in
refluxing
dichloromethane afforded glycals 17 and 50 in
82 and 65% yields, respectively (Entries 5 and
6). Furthermore, reaction in refluxing
dichloroethane instead of dichloromethane af-
forded glycals in considerably shorter reaction
times (ca. 3 h) and better yields (Entries 7, 8
and 9).
In conclusion, both erythro- and threo-
configurated glycals have been efficiently syn-
thesized by oxidative elimination of 1-phenyl-
selenenylfuranosides and 2-phenylselenenyl-
Synthesis of furanoid glycals from phenyl
1-selenofuranosides: general procedure for con-
6ersion of methyl furanosides into the corre-
sponding phenyl 1-selenofuranosides.—To a
solution of differently protected 2-methyl de-
oxyribofuranoside (1 mmol) in dry CH2Cl2 (3
mL) under argon atmosphere at −20 °C,
BF3·Et2O (0.8 mmol) was added dropwise.
The resulting mixture was allowed to warm to
−10 °C, and stirred for 10 min. The yellow
solution was then cooled to −20 °C and
phenylselenol (1.1 mmol) was added. The re-
action mixture was maintained at this temper-
ature until completion. Pyridine was then
added, and the mixture was warmed to rt. The
solvent was removed at reduced temperature,
and the resulting crude product was purified
by flash chromatography.
1,4-anhydroalditols.
nosides were synthesized from 2-deoxy-
erythro-pentose via the corresponding methyl
furanosides. 4-Phenylselenenyltetrahydro-
1-Phenylselenenylfura-
D
-
furans were obtained through an unusual 5-
endo selenoetherification of 4-pentene-1,2,3-
triols, which are obtained from inexpensive
D
-mannitol. Despite the instability of some
protective groups such as esters, this method
provides an efficient strategy for the synthesis
of furanoid glycals, particularly for those with
ether protective groups. The use of selenoxides
ensures that elimination proceeds in mild con-
ditions, which favors the easy obtention and
stability of the desired glycals.
General procedure for glycal synthesis from
phenyl 1-selenofuranosides (A)..—Ethyldiiso-
propylamine (0.8 mmol) was added to a cold
solution (0 °C) of phenyl selenoglycoside (1
mmol) in dry CH2Cl2 (6 mL). tert-Butylhy-
droperoxide (1 mmol) was then added drop-
wise to this mixture over a period of 5 min.

90
F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
mL, 0.156 mmol) as described in the general
procedure for glycal synthesis (B) and subse-
quent purification through a small neutral sil-
ica gel pad afforded 0.050 g (84%, overall
yield) of compound 15 as a syrup; [h]D25
Subsequent addition of titanium isopropoxide
(1 mmol) gave a yellowish solution that was
stirred at 0 °C until completion (ca. 45 min)
and then warmed to rt. The solvent was re-
moved under low pressure and the crude ob-
1
+145.0° (c 1.614, CHCl3); H NMR (CDCl3,
tained
was
purified
by
column
300 MHz): l 7.35–7.24 (m, 10 H, Ph), 6.58 (d,
1 H, J1,2 2.7 Hz, H-1); 5,15 (dd, 1 H, J2,3 2.4
Hz, H-2), 4.64–4.61 (m, 1 H, H-3), 4.57–4.48
(m, 1 H, H-4), 4.59 (d, 1 H, Jgem 12.2 Hz,
CH2Ph), 4.54 (d, 1 H, CH2Ph), 4.50 (s, 2 H,
CH2Ph), 3.54 (dd, 1 H, J5,4 6.5, J5,5% 10.1 Hz,
chromatography.
General procedure for glycal synthesis from
phenyl 1-selenofuranosides (B)..—This proce-
dure is similar to A using ethyldiisopropy-
lamine (1.7 mmol), phenyl selenoglycoside (1
mmol) in dry CH2Cl2 (6 mL), tert-butylhy-
droperoxide (2.3 mmol) and titanium isopro-
poxide (1 mmol).
13
H-5), 3.41 (dd, 1 H, H-5%); C NMR (CDCl3,
75.4 MHz): l 150.4 (C-1), 138.9–127.6 (Ph),
100.5 (C-2), 84.8 (C-4), 82.6 (C-3), 73.4
(CH2Ph), 69.8 (CH2Ph), 69.6 (C-5). Anal
Calcd for C19H20O3: C, 77.02; H, 6.75. Found
C, 77.37; H, 6.43.
Phenyl
5-O-(tert-butyldiphenylsilyl)-2-de-
oxy-1-seleno-h,i-erythro-pentofuranoside
(7).—Starting from 6 and following the gen-
eral procedure, 7 as a mixture of anomers (a/b
1:2), was obtained as a thick yellow syrup in
1,4-Anhydro-2-deoxy-3,5-di-O-pi6aloyl-
erythro-pent-1-enitol (16).—Compound
D
-
1
82% yield. 7a: H NMR (CDCl3): l 7.69–7.18
5
(m, 15 H, Ph); 6.02 (dd, 1 H, J1,2% 2.5, J1,2 7.2
Hz, H-1); 4.45–4.38 (m, 1 H, H-3); 4.25–4.21
(m, 1 H, H-4); 3.84 (dd, 1 H, J5,4 3.8, J5,5% 10.9
Hz, H-5), 3.71 (dd, 1 H, J5%,4 4.8 Hz, H-5);
2.76 (m, 1 H, J2,3 7.2, J2,2% 14.2 Hz, H-2); 2.37
(d, 1 H, JOH,3 7.4 Hz, OH); 2.21 (m, 1 H, J2%1
2.5, J2%,3 2.5, J2%,2 14.2 Hz, H-2); 1.04 (s, 9 H,
Me3CSi); 13C NMR (CDCl3): l 135.6, 133.8,
129.8, 129.7, 129.0, 128.9, 127.7, 127.5 (Ph);
86.8 (C-1); 83.3 (C-4); 73.3 (C-3); 63.9 (C-5);
42.7 (C-2); 26.8 (Me3CSi); 19.2 (Me3CSi). 7b:
1H NMR (CDCl3): l 7.70–7.19 (m, 15 H, Ph);
5.82 (dd, 1 H, J1,2 6.3, J1,2% 7.1 Hz, H-1);
4.44–4.39 (m, 1 H, H-3); 3.99 (m, 1 H, J4,3
2.9, J4,5 4.7, J4,5% 7.2 Hz, H-4); 3.77 (dd, 1 H,
J5,5% 10.5 Hz, H-5); 3.54 (dd, 1 H, J5%,5 10.4 Hz,
H-5%); 2.36 (ddd, 1 H, J2,3 4.0, J2,1 6.3, J2,2% 13.6
Hz, H-2); 2.26 (m, 1 H, J2%,3 6.0 Hz, H-2%); 2.02
(bs, 1 H, OH); 1.04 (s, 9 H, Me3CSi); 13C
NMR (CDCl3): l 135.6, 134.2, 133.0, 129.8,
129.0, 127.7, 127.5 (Ph); 87.7 (C-1); 81.5 (C-4);
73.5 (C-3); 64.3 (C-5); 41.7 (C-2); 26.9
(Me3CSi); 19.2 (Me3CSi).
(0.632g, 2 mmol) was transformed into the
phenyl 1-selenoglycoside 9 (0.696 g, 79%) with
PhSeH and BF3·Et2O following the general
procedure for synthesizing selenoglycosides.
This compound was then treated following the
general procedure of glycal synthesis (A) to
give compound 16 (0.324 g, 71%) as an oil;
1
[h]2D5 +188.00° (c 2.025, CHCl3); H NMR
(CDCl3, 300 MHz): l 6.61 (d, 1 H, J1,2 2.4 Hz,
H-1); 5.59 (t, 1 H, J3,2 =J3,4 2.7 Hz, H-3), 5.15
(dd, 1 H, H-2), 4.55 (td, 1 H, J4,5%=J4,5 5.1
Hz, H-4), 4.25 (d, 2 H, H-5,H-5%), 1.15 (m, 18
H); 13C NMR (CDCl3, 75.4 MHz): l 178.4
(CO), 178.1 (CO), 151.6 (C-1), 99.5 (C-2), 83.6
(C-4), 78.5 (C-3), 63.3 (C-5), 27.2, 27.1, 27.0
(CH3). Anal Calcd for C15H24O5: C, 63.36; H,
8.51. Found C, 63.69; H, 8.80.
1,4-Anhydro-3-O-benzyl-5-O-(tert-butyl-
diphenylsilyl)-2-deoxy- -erythro-pent-1-enitol
D
(17).—Compound 7 (0.5 g, 0.98 mmol) was
dissolved in dry THF (3 mL) and added to a
suspension of NaH (80%, 0.035 g, 1.17 mmol)
in THF (3 mL). Benzyl bromide (0.196 mL,
1.17 mmol) was then added and the mixture
was stirred for 2.5 h. Addition of MeOH and
evaporation of the solvent afforded a residue
that was purified by column chromatography
in EtOAc–hexane to yield 0.40 g (68%) of 10
as a syrup. This material was then treated
following the general procedure for glycal syn-
thesis (B) to give glycal 17 (0.186 g, 71%)
1,4-Anhydro-3,5-di-O-benzyl-2-deoxy- -ery-
D
thro-pent-1-enitol (15).—Compound 4 (0.066
g, 0.2 mmol) was transformed into the phenyl
1-selenoglycoside 8 (0.071 g, 78%) with PhSeH
and BF3·Et2O following the general procedure
for synthesizing selenoglycosides. Oxidation of
8 with TBHP (0.12 mL, 0.359 mmol), EtiPr2N
(0.046 mL, 0.265 mmol) and Ti(OiPr)4 (0.045

F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
91
(0.500 g, 0.97 mmol) in CH2Cl2 was treated
with EtiPr2N (0.185 mL, 1.067 mmol) and
MEMCl (0.140 mL, 1.067 mmol) to give, after
purification by column chromatography, 0.425
g (73%) of 12. This compound was then
treated following the general procedure for
glycal synthesis (B) to give 0.340 g (81%) of 19
as an oil, after purification by column chro-
matography in 1:12 EtOAc–hexane; [h]D25
as an oil, after purification by column chro-
matography over neutral silica gel (1:20
EtOAc–hexane); [h]2D5 +21.2° (c 1.110,
1
CHCl3); H NMR (CDCl3): l 7.70–7.18 (m,
15 H, Ph); 6.54 (dd, 1 H, J1,3 1.2, J1,2 2.6 Hz,
H-1); 5.15 (td, 1 H, J2,4 1.3, J2,3 2.6 Hz, H-2);
4.76 (ddd, 1 H, J3,4 4.0 Hz, H-3); 4.55 (dddd,
1 H, J4,5 5.3, J4,5% 6.5 Hz, H-4); 4.54 (d, 1 H,
Jgem 11.8 Hz, CH2); 4.48 (d, 1 H, CH2); 3.75
(dd, 1 H, J5,5% 10.7 Hz, H-5); 3.58 (dd, 1 H,
H-5); 1.06 (s, 9 H, (CH3)3CSi); 13C NMR
(CDCl3): l 150.4 (C-1); 138.3, 135.6, 133.2,
129.7, 128.3, 127.7, 127.5 (Ph); 100.5 (C-2);
86.1 (C-4); 82.7 (C-3); 69.6 (OCH2Ph); 63.5
(C-5); 26.8 (CH3)3CSi); 19.2 ((CH3)3CSi).
Anal Calcd for C28H32O3Si: C, 75.64; H, 7.25.
Found C, 75.99; H, 7.57.
1
+46.7° (c 1.215, CHCl3); H NMR (CDCl3):
l 7.77–7.34 (m, 10 H, Ph); 6.53 (d, 1 H, J1,2
2.7 Hz, H-1); 5.15 (t, 1 H, J2,3 2.7 Hz, H-2);
4.87 (m, 1 H, J3,4 2.8 Hz, H-3); 4.79 (s, 2 H,
OCH2O); 4.49 (td, 1 H, J4,5 =J4,5% 5.6 Hz,
H-4); 3.77 (dd, 1 H, J5,5% 10.7 Hz, H-5); 3.73–
3.67 (m, 2 H, OCH2); 3.64 (dd, 1 H, H-5); 3.53
(t, 2 H, JCH ,CH 4.5 Hz, CH2O); 3.36 (s, 3 H,
2
1,4-Anhydro-5-O-(tert-butyldiphenylsilyl)-
OCH3); 1.05 (s2, 9 H, (CH3)3CSi); 13C NMR
(CDCl3): l 150.3 (C-1); 135.6, 133.2, 129.7,
127.6 (Ph); 101.0 (C-2); 94.1 (OCH2O); 86.7
(C-3); 81.5 (C-4); 71.6 (OCH2); 66.9 (CH2O);
63.5 (C-5); 58.9 (OCH3); 26.7 (Me3CSi); 19.2
(Me3CSi). Anal Calcd for C25H34O5Si: C,
67.84; H, 7.74. Found C, 68.03; H, 7.78.
1,4-Anhydro-3-O-(tert-butyldimethylsilyl)-
2-deoxy-3-O-methyl- -erythro-pent-1-enitol
D
(18).—Compound 7 (0.115 g, 0.224 mmol)
was dissolved in dry THF (2 mL) and added
to a suspension of NaH (80%, 0.012 g, 1.17
mmol) in THF (1.5 mL). The reaction mixture
was stirred for 20 min and after protection
from light, methyl iodide (0.035 g, 1.17 mmol)
was added and the mixture was stirred
overnight. Addition of MeOH and evapora-
tion of the solvent afforded a residue that was
purified by column chromatography in
EtOAc–hexane 1.20 to yield 0.090 g (76%) of
11 as a syrup. This material was then treated
using the general procedure for glycal synthe-
sis (B) to give 0.045 g (72%) of 18 as an oil,
after purification by column chromatography
in 1:12 EtOAc–hexane; [h]2D5 +115.0° (c 1.3,
CHCl3); 1H NMR (CDCl3, 300 MHz): l
7.71–7.24 (m, 10 H, Ph), 6.54 (d, 1 H, J1,2 2.7
Hz, H-1); 5.14 (t, 1 H, J2,3 2.7 Hz, H-2), 4.54
(t, 1 H, J3,4 2.7 Hz, H-3), 4.45 (ddd, 1 H, J4,5
5.4, J4,5% 6.0 Hz, H-4), 3.76 (dd, 1 H, J5,5% 10.5
Hz, H-5), 3.57 (dd, 1 H, H-5), 3.29 (s, 3 H,
OCH3), 1.06 (s, 9 H, (CH3)3CSi); 13C NMR
(CDCl3, 75.4 MHz): l 150.4 (C-1), 135.6,
133.2, 129.8, 127.7 (Ph), 100.1 (C-2), 85.6
(C-4), 84.2 (C-3), 63.5 (C-5), 54.8 (OCH3),
26.7 (CH3)3CSi), 19.2 ((CH3)3CSi). Anal
Calcd for C22H28O3Si: C, 71.55; H, 7.64.
Found C, 71.49; H, 7.78.
5-O-(tert-butyldiphenylsilyl)-2-deoxy-
D
-ery-
thro-pent-1-enitol (20).—1,8-Diazabicyclo-
[5,4,0]undec-7-ene (DBU) (0.5 g, 3.25 mmol)
was added to a cold solution (0 °C) of 7 (1.27
g, 2.5 mmol) in dry benzene (25 mL) and the
mixture was stirred for 10 min. The cold bath
was then removed and tert-butyldimethylsilyl
chloride (0.45 g, 3 mmol) was added. The
mixture was stirred for 20 h. The solvent was
then removed under diminished pressure and
the residue was purified by column chro-
matography with 1:15 EtOAc–hexane to af-
ford 1.23 g (79%) of an anomeric mixture of
13 as a syrup. This compound (1 g, 1.60
mmol) was treated in the general procedure
for glycal synthesis (B) to give a residue which
was purified by column chromatography in
1:75 EtOAc–hexane to yield glycal 20 (0.45 g,
1
60%) as an oil; H NMR (CDCl3): l 7.73–
7.30 (m, 10 H, Ph); 6.48 (dd, 1 H, J1,3 0.9, J1,2
2.7 Hz, H-1); 5.02 (t, 1 H, J2,3 2.7 Hz, H-2);
4.95 (td, 1 H, J3,4 2.7 Hz, H-3); 4.34 (td, 1 H,
J4,5 5.4, J4,5% 5.4 Hz, H-4); 3.70 (dd, 1 H, J5,5%
10.9 Hz, H-5); 3.62 (dd, 1 H, H-5%); 1.04 (s, 9
H, Me3CSi); 0.87 (s, 9 H, Me3CSi); 0.05 (s, 6
H, (Me)2Si); 13C NMR (CDCl3): l 149.1 (C-
1,4-Anhydro-5-O-(tert-butyldiphenylsilyl)-2-
deoxy-3-O-(methoxyethoxymethylene)- -ery-
D
thro-pent-1-enitol (19).—A solution of 7

92
F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
J1,2 4.5 Hz, H-1); 4.37 (m, 1 H, H-4), 3.79 (d,
1 H, Jgem 10.8 Hz, H-5), 3.74 (dd, 1 H, J5%,4 1.2
Hz, H-5), 3.36 (s, 3 H, OMe), 2.34 (m, 2 H,
1); 135.6, 133.2, 129.7, 127.7 (Ph); 103.4 (C-2);
89.0 (C-4); 76.0 (C-3); 63.6 (C-5); 26.7
((CH3)3CSi);
25.8
((CH3)3CSi);
19.2
t
H-2, H-2%), 1.02 (s, 9 H, Bu); 13C NMR
((CH3)3CSi); 19.0 (Me3CSi); −4.2 ((CH3)2Si);
−4.4 ((Me)2Si). Anal Calcd for C27H40O3Si2:
C, 69.18; H, 8.60. Found C, 69.02; H, 8.51.
3-O-Acetyl-1,4-anhydro-5-O-(tert-butyl-
(CDCl3, 75.4 MHz): l 135.5, 129.9, 129.8,
127.8, 127.7 (Ph), 104.7 (C-1), 88.1 (C-3), 83.8
(C-4), 62.9 (C-5), 54.9 (OCH3), 39.8 (C-2),
1
26.6, 19.1 (tBu). 22b: H NMR (CDCl3, 300
diphenylsilyl)-2-deoxy- -erythro-pent-1-enitol
D
(21).—Compound 7 (0.127 g, 0.25 mmol) was
acetylated by reaction with Ac2O (1 mL) in
dry pyridine (2 mL), overnight. The solvent
was distilled off and the residue dissolved in
CH2Cl2. The solution was washed with water,
dried with MgSO4 and evaporated to afford
0.119 g (86%) of crude 14. This material
(0.102 g, 0.186 mmol) was then treated in the
general procedure for glycal synthesis (A). The
resulting reaction mixture was then filtered
through a small pad of neutral silica gel to
yield 0.050 g (68%) of 21 as an oil; [h]D25
MHz): l 7.70, 7.31 (m, 10 H, Ph), 5.57 (ddd,
1 H, J3,2 6.0, J3,2% 3.1, J3,4 1.5 Hz, H-3), 5.17
(dd, 1 H, J1,2 5.4, J1,2% 3.6 Hz, H-1); 4.33 (ddd,
1 H, J4,5 4.8, J4,5% 7.8 Hz, H-4), 3.74 (dd, 1 H,
Jgem 10.8 Hz, H-5), 3.61 (dd, 1 H, H-5%), 2.44
(ddd, 1 H, Jgem 15.0 Hz, H-2), 2.30 (ddd, 1 H,
t
H-2%), 1.03 (s, 9 H, Bu); 13C NMR (CDCl3,
75.4 MHz): l 135.5, 129.9, 1278, 127.6 (Ph),
105.1 (C-1), 89.2 (C-3), 84.0 (C-4), 63.7 (C-5),
55.7 (OCH3), 39.3 (C-2), 26.7, 19.1 (tBu).
Methyl 5-O-(tert-butyldiphenylsilyl)-2-de-
oxy-h,i- -threo-pentofuranoside (23).—In a
D
1
+31.0° (c 1.952, CHCl3); H NMR (CDCl3,
flask fitted with a magnetic stirring bar, 0.170
g (0.34 mmol) of 22 was dissolved in dry
DMF (12 mL), and KNO2 (0.173 g, 2.03
mmol) was then added. Once the mixture had
turned into a homogeneous solution, 0.90 g
(0.34 mmol) of 18-crown-6 ether and 0.030 g
of water were added. The mixture was stirred
overnight at rt. The solvent was then removed
under diminished pressure and the resulting
residue was purified by column chromatogra-
phy in 1:4 EtOAc–hexane to afford 0.083 g
(62%) of an anomeric mixture of 23 as syrup;
300 MHz): l 7.68–7.30 (m, 10 H, Ph), 6.63 (d,
1 H, J1,2 1.4 Hz, H-1); 5.81 (dd, J3,2 1.2, J3,4
2.1 Hz, H-3), 5.17 (dd, 1 H, H-2), 4.50 (m, 1
H, H-4), 3.84 (dd, 1 H, J5,4 5.1, J5,5% 10.8 Hz,
H-5), 3.76 (dd, 1 H, J5%,4 4.8 Hz, H-5), 2.04 (s,
3 H, COCH3), 1.04 (s, 9 H, Me3CSi); 13C
NMR (CDCl3, 75.4 MHz): l 170.7 (CO),
151.8 (C-1), 135.5–129.7, 128.9–127.6 (Ph),
99.5 (C-2), 86.1 (C-4), 78.8 (C-3), 63.5 (C-5),
26.6 ((CH3)3CSi), 19.2 (Me3CSi), 21.2 (Me).
Anal. Calcd for C23H28O4Si: C, 69.66; H, 7.12.
Found C, 69.42; H, 7.23.
1
23a: H NMR (CDCl3, 300 MHz): l 7.78,
Methyl 5-O-(tert-butyldiphenylsilyl)-2-de-
7.29 (m, 10 H, Ph), 5.15 (t, 1 H, J1,2 J1,2% 4.1
Hz, H-1); 4.60 (m, 1 H, H-3), 4.03 (m, 3 H,
H-4, H-5, H-5%), 3.34 (s, 3 H, OCH3), 2.99 (d,
1 H, JOH,3 4.0 Hz, OH), 2.17 (t, 2 H, H-2,
oxy-3-O-(trifluoromethanesulfonyl)-h,i- -ery-
D
thro-pentofuranoside (22).—In an oven-dried
round-bottomed flask, provided with a mag-
netic stirring bar, a solution of 0.2 g (0.56
mmol) of 6 in dry CH2Cl2 (2 mL) was treated
with dry pyridine (0.2 mL, 2.47 mmol) and the
solution was stirred for 10 min under inert
atmosphere. The solution was then cooled to
−20 °C and triflic anhydride (0.104 mL, 0.6
mmol) was added. The resulting mixture was
stirred for 15 min at low temperature and was
then left for 45 min to warm to rt. Purification
through a small pad of neutral silica gel pro-
duced 0.250 g (91%) of an anomeric mixture
of triflate 22 as a syrup; 22a: 1H NMR
(CDCl3, 300 MHz): l 7.71, 7.29 (m 10 H, Ph),
5.55 (d, 1 H, J3,2 6.4 Hz, H-3), 5.15 (d, 1 H,
t
H-2%), 1.04 (s, 9 H, Bu); 13C NMR (CDCl3,
75.4 MHz): l 135.6, 135.5, 129.9, 127.8, 127.6
(Ph), 104.5 (C-1), 79.1 (C-4), 72.6 (C-3), 62.9
(C-5), 55.2 (OCH3), 42.6 (C-2), 26.7, 19.1
1
(tBu). 23b: H NMR (CDCl3, 300 MHz): l
7.79, 7.26 (m, 10 H, Ph), 5.04 (dd, 1 H, J1,2
3.2, J1,2% 1.2 Hz, H-1); 4.33 (ddd, 1 H, J3,2 6.0,
J3,2% 3.6, J3,OH 9.0 Hz, H-3), 4.08 (m, 1 H,
H-4), 4.05 (d, 1 H, Jgem 10.2 Hz, H-5), 3.87
(dd, 1 H, J5%,4 5.7 Hz, H-5%), 3.30 (s, 3 H,
OMe), 2.94 (d, 1 H, OH), 2.12 (m, 2 H, H-2,
t
H-2%), 1.05 (s, 9 H, Bu); 13C NMR (CDCl3,
75.4 MHz): l 135.7, 135.6, 129.6, 127.7, 127.6

F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
93
H, J5%,4 6.2, J5%,5 10.2 Hz, H-5%); 2.62 (ddd, 1 H,
J2b,3 1.9, J2b,1 7.1, J2b,2a 14.5 Hz, H-2b); 2.19
(dt, 1 H, J2a,1 5.8, J2a,3 5.8, J2a,2b 14.5 Hz, H2a);
13C NMR (CDCl3): l 138.4, 137.8, 133.9,
128.9, 128.4, 128.3, 127.7, 127.4, 127.4, (Ph);
82.1 (C-1); 80.3 (C-4); 77.8, (C-3); 73.3, 71.3 (2
(Ph), 105.1 (C-1), 84.6 (C-4), 71.5 (C-3), 63.7
(C-5), 54.7 (OCH3), 41.4 (C-2), 26.8, 18.9
(tBu).
Phenyl
5-O-(tert-butyldiphenylsilyl)-2-de-
- threo - pentofuranoside
oxy - 1 - seleno - h,i -
D
(24).—Following the general procedure, com-
pound 23 (0.200 g 0.52 mmol) in CH2Cl2 (1.5
mL) was treated with BF3·Et2O (0.522 mL,
0.416 mmol) and PhSeH (0.06 mL, 0.572
mmol) for 50 min. The residue obtained after
evaporation of the solvent was purified by
column chromatography to yield 0.214 g
(80%) of 24 (17:3 a/b mixture) as a thick
1
OCH2Ph); 67.7 (C-5); 40.1 (C-2). 31b: H
NMR (CDCl3): l 7.68–7.18 (m, 15 H, Ph);
5.85 (dd, 1 H, J1,2b 3.8, J1,2a 6.2 Hz, H-1); 4.68
(d, 1 H, Jgem 12.1 Hz, CH2); 4.63 (d, 1 H,
CH2); 4.55 (d, 1 H, CH2); 4.46 (d, 1 H, CH2);
4.28 (ddd, 1 H, J4,3 4.4, J4,5 5.4, J4,5% 6.7 Hz,
H-4); 4.21 (td, 1 H, J3,2b 2.6, J3,2a 4.4 Hz, H-3);
3.91 (dd, 1 H, J5,5% 10.2 Hz, H-5); 3.86 (dd, 1
H, J5%,4 6.7, J5%,5 10.2 Hz, H-5); 2.59–2.47 (m, 2
H, H-2a, H-2b); 13C NMR (CDCl3): l 138.2,
137.8, 133.3, 128.9, 128.3, 127.7 (Ph); 83.7
(C-1), 83.1 (C-4); 77.4, (C-3), 73.4, 71.3 (2
OCH2Ph); 69.3 (C-5); 39.9 (C-2).
1
yellow syrup. 24a: H NMR (CDCl3, 300
MHz): l 7.80, 7.20 (m, 10 H, Ph), 6.11 (t, 1 H,
J1,2=J1,2% 6.5 Hz, H-1); 4.55 (m, 1 H, H-3),
4.17 (m, 1 H, H-4), 4.14 (d, 1 H, Jgem 12.6 Hz,
H-5), 4.07 (dd, 1 H, J5%,4 5.4 Hz, H-5%), 3.33 (d,
1 H, JOH,3 4.8 Hz, OH), 2.54 (ddd, 1 H, Jgem
14.3, J2,3 5.8 Hz, H-2), 2.33 (td, 1 H, J2%,3 6.8
Synthesis of 31 from 38.—A cold (−20 °C)
solution of 4 g (12.18 mmol) of methyl 2-de-
oxyfuranoside 31 in CH2Cl2 (36 mL) was
treated with 1.22 mL (9.74 mmol) of BF3·Et2O
and PhSeH (1.42 mL, 13.40 mmol) and stirred
at low temperature for 1 h. The residue ob-
tained after the standard work-up was purified
by column chromatography (1:10 hexane–
EtOAc then hexane) to afford 5.3 g (96%) of
31 as a syrup.
t
Hz, H-2%), 1.09 (s, 9 H, Bu); 13C NMR
(CDCl3, 75.4 MHz): l 135.6, 133.5, 129.9,
128.9, 127.8, 127.7, 127.3 (Ph), 82.3 (C-1), 80.2
(C-4), 72.7 (C-3), 62.5 (C-5), 43.5 (C-2), 26.7,
19.1 (tBu).
Phenyl 3,5-di-O-benzyl-2-deoxy-1-seleno-
h,i-D
-threo-pentofuranoside
(31).—Com-
pound 24 (0.226 g, 0.442 mmol) was dissolved
in dry THF (1 mL) and treated with Bu4NF
(0.127 g, 0.487 mmol) at 0 °C for 1 h. The
solvent was then removed under diminished
pressure and the residue was purified by chro-
matography in 1:1 EtOAc–hexane to yield
0.110 g (91%) of 25 as an oil. Compound 25
(0.205 g, 0.750 mmol) was dissolved in dry
THF (5 mL) and added to a suspension of
NaH (80%, 0.055 g, 1.80 mmol) in 5 mL of
THF. Benzyl bromide (0.300 mL, 1.80 mmol)
was then added and the mixture was stirred
for 2.5 h. Addition of MeOH and evaporation
of the solvent afforded a residue that was
purified by column chromatography in 1:15
EtOAc–hexane to yield 0.305 g (90%) of 31 as
1,4-Anhydro-5-O-(tert-butyldiphenylsilyl)-2-
deoxy-3-O-methyl- -threo-pent-1-enitol (32).
D
—Compound 24 (0.100 g, 0.195 mmol) was
dissolved in dry THF (2 mL) and added to a
suspension of NaH (80%, 0.010 g, 1.02 mmol)
in THF (1.5 mL). The reaction mixture was
stirred for 20 min and it was then protected
from light. Methyl iodide (0.035, 1.02 mmol)
was then added and the mixture was stirred
overnight. Addition of MeOH and evapora-
tion of the solvent afforded a residue that was
purified by column chromatography in 1:20
EtOAc–hexane to yield 0.080 g (0.152 mmol,
78%) of 26 as a syrup. This material was then
treated following the general procedure for
glycal synthesis (B) to obtain a residue that
was purified by column chromatography in
1:12 EtOAc–hexane to give 0.039 g (68%) of
32 as an oil; [h]D25 −54.60° (c 2.823, CHCl3);
1H NMR (CDCl3, 300 MHz): l 7.74–7.24 (m,
10 H, Ph), 6.46 (d, 1 H, J1,2 2.7 Hz, H-1); 4.94
(dd, 1 H, J3,2 2.7, J3,4 6.9 Hz, H-3), 4.71
1
a syrup. 31a: H NMR (CDCl3): l 7.67–7.15
(m, 15 H, Ph); 6.04 (dd, 1 H, J1,2a 5.8, J1,2b 7.1
Hz, H-1); 4.61 (d, 1 H, Jgem 11.8 Hz, CH2);
4.56 (d, 1 H, Jgem 12.1 Hz, CH2); 4.53 (d, 1 H,
Jgem 11.8 Hz, CH2); 4.42 (d, 1 H, CH2); 4.35
(ddd, 1 H, J4,3 3.9, J4,5% 5.8, J4,5 6.2 Hz, H-4);
4.14 (ddd, 1 H, J3,2b 1.9, J3,2a 5.8 Hz, H-3);
3.89 (dd, 1 H, J5,5% 10.2 Hz, H-5); 3.78 (dd, 1

94
F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
matography in 1:75 EtOAc–hexane to give
0.028 g (78%) of glycal 34 as an oil; [h]D25
(t, 1 H, H-2), 4.29 (m, 1 H, H-4), 3.86 (s, 1 H,
H-5), 3.83 (d, 1 H, J5%,4 3.3 Hz, H-5), 3.47 (s,
1
t
3 H, OMe), 1.02 (s, 9 H, Bu); 13C NMR
−18.2° (c 1.717, CHCl3); H NMR (CDCl3,
300 MHz): l 7.76–7.30 (m, 10 H, Ph), 6.63 (d,
1 H, J1,2 2.1 Hz, H-1); 5.8 (dd, 1 H, J2,3 2.7
Hz, H-2), 4.87 (dd, 1 H, J3,4 4.2 Hz, H-3), 4.34
(ddd, 1 H, J4,5 3.9, J4,5% 7.8 Hz, H-4), 4.05 (dd,
1 H, J5%,5 11.7 Hz, H-5), 3.92 (dd, 1 H, H-5%),
(CDCl3, 75.4 MHz): l 149.40 (C-1), 135.89–
129.58–127.47 (Ph), 104.09 (C-2), 83.60 (C-4),
74.44 (C-3), 70.80 (C-5), 59.23 (OCH3),
26.80–19.27 (tBu).). Anal Calcd for
C22H28O3Si: C, 71.55; H, 7.64. Found C,
71.51; H, 7.71.
t
t
1.1 (s, 9 H, Bu), 0.79 (s, 9 H, Bu), 0.02 (s, 6
H, 2 Me); 13C NMR (CDCl3 75.4 MHz): l
149.5 (C-1), 135.6, 129.5, 127.6 (Ph), 103.9
(C-2), 85.7 (C-4), 73.3 (C-3), 62.6 (C-5), 26.8,
25.7, 19.3 (tBu). Anal Calcd for C27H40O3Si2:
C, 69.18; H, 8.60. Found C, 69.28; H, 8.41.
3-O-Acetyl-1,4-anhydro-5-O-(tert-butyldi-
1,4 - Anhydro - 5 - O - (tert-butyldiphenylsilyl)-
2 - deoxy - 3 - O - (methoxyethoxymethylene) - -
D
threo-pent-1-enitol (33).—A solution of 24
(0.082 g, 0.159 mmol) in CH2Cl2 was treated
with EtiPr2N (0.030 mL, 0.175 mmol) and
MEMCl (0.023 mL, 0.175 mmol) to give of 27
(0.046 g, 0.077 mmol, 48%). Treatment of this
compound using the general procedure for
glycal synthesis (B) and subsequent purifica-
tion by column chromatography in 1:20
EtOAc–hexane gave 0.018 g (53%) of product
phenylsilyl) - 2 - deoxy -
D
- threo - pent - 1 - enitol
(35).—Compound 24 (0.148 g, 0.290 mmol)
was dissolved in dry pyridine (2 mL) and
treated with Ac2O (1 mL) overnight. The sol-
vent was distilled off and the residue dissolved
in CH2Cl2. The solution was washed with
water, dried with MgSO4 and evaporated to
afford 0.130 g (81%) g of crude 29. This
material was pure enough to be treated using
the general procedure for glycal synthesis (A).
The resulting reaction mixture was then
filtered through a small pad of neutral silica
gel to yield 0.050 g (68%) of 35 as an oil; [h]D25
1
33 as an oil; H NMR (CDCl3, 300 MHz): l
7.74–7.28 (m, 10 H, Ph), 6.61 (d, 1 H, J1,2 2.7
Hz, H-1); 5.24 (dd, 1 H, J2,3 2.4 Hz, H-2), 4.82
(s, 2 H, OCH2O), 4.75 (dd, 1 H, J3,4 6.4 Hz,
H-3), 4.40 (q, 1 H, J4,5 6.4, J4,5% 6.1 Hz, H-4),
4.06 (dd, 1 H, J5,5% 10.8 Hz, H-5), 3.95 (dd, 1
H, H-5%), 3.51 (m, 4 H, OCH2CH2O), 3.39 (s,
t
3 H, OCH3), 1.02 (s, 9 H, Bu); 13C NMR
1
−8.5° (c 3.505, CHCl3); H NMR (CDCl3,
(CDCl3, 75.4 MHz): l 150.2 (C-1), 135.6,
135.5, 129.6, 127.7, 127.5 (Ph), 102.2 (C-2),
94.5 (OCH2O), 84.4 (C-4), 78.1 (C-3), 71.6
(C-5), 66.7, 61.3 (OCH2CH2O), 59.0 (OCH3),
26.8, 19.2 (tBu). Anal Calcd for C25H34O5Si:
C, 67.84; H, 7.74. Found C, 67.99; H, 7.81.
1,4-Anhydro-5-O-(tert-butyldiphenylsilyl)-3-
300 MHz): l 7.76–7.20 (m, 10 H, Ph), 6.66 (d,
1 H, J1,2 2.4 Hz, H-1); 5.82 (dd, 1 H, J3,2 2.7,
J3,4 6.9 Hz, H-3), 5.20 (t, 1 H, H-2), 4.46 (m,
1 H, H-4), 3.99 (m, 2 H, H-5, H-5%), 1.9 (s, 3
t
13
H, Me), 1.05 (s, 9 H, Bu); C NMR (CDCl3,
75.4 MHz): l 170.2 (CO), 151.8 (C-1), 135.5–
129.7–127.6 (Ph), 100.8 (C-2), 83.2 (C-4), 74.9
(C-3), 60.9 (C-5), 26.6–19.1 (tBu), 21.0 (Me).
Anal. Calcd for C23H28O4Si: C, 69.66; H, 7.12.
Found C, 69.31; H, 7.40.
O-(tert-butyldimethylsilyl)-2-deoxy- -threo-
D
pent-1-enitol (34).—1,8-Diazabicyclo[5,4,0]-
undec-7-ene (DBU) (0.032 g, 0.208 mmol) was
added to a cold solution (0 °C) of 24 (0.080 g,
0.16 mmol) in dry benzene (2 mL) and the
mixture was stirred for 10 min. The cold bath
was then removed and tert-butyldimethylsilyl
chloride (0.029 g, 0.192 mmol) was added.
The mixture was stirred for 20 h. The solvent
was then removed under reduced pressure and
the residue was purified by column chro-
matography with 1:15 EtOAc–hexane to af-
ford 0.063 g (63%) of 28 as a syrup. This
material was then treated using the general
procedure for glycal synthesis (B) resulting in
a residue which was purified by column chro-
3,5-Di-O-acetyl-1,4-anhydro-2-deoxy-
threo-pent-1-enitol (36).—Compound
D
24
-
(0.226 g, 0.442 mmol) dissolved in dry THF (1
mL) was treated with Bu4NF (0.127 g, 0.487
mmol) at 0 °C for 1 h. The solvent was then
removed under diminished pressure and the
residue purified by chromatography in 1:1
EtOAc–hexane to yield 0.110 g (91%) of 25 as
an oil. Compound 25 (0.100 g, 0.366 mmol)
was treated with dry pyridine (1.2 mL) and
Ac2O (0.5 mL) and the mixture was allowed
to react overnight. Pyridine was removed by
codistillation with toluene (3×2 mL)) under

F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
95
quentially added under argon atmosphere. Af-
ter 20 min, TLC control showed that the
starting material was fully consumed with the
appearance of a new product that did not
migrate in the elution system (3:1 hexane–
EtOAc). The mixture was then refluxed up to
the reaction was complete (ca. 48 h in CH2Cl2,
3 h in (CH2)2Cl2). The solvent was evaporated
under diminished pressure, and the glycal was
purified by ‘flash’ chromatography with neu-
tral silica gel.
Synthesis of 15 from 39.—Starting from 39
(0.089 g, 0.20 mmol) and following the general
procedure for glycal synthesis (C), 0.036 g
(62%) of 15 were obtained, after purification
by ‘flash’ chromatography eluting with 10:1
hexane–EtOAc.
diminished pressure. The resulting residue ob-
tained was dissolved in CH2Cl2 (10 mL) and
washed with water (4 mL), dried with MgSO4
and evaporated to dryness to yield 30 in a
quantitative yield. Crude 30 proved to be pure
by TLC and 0.130 g (0.364 mmol) of this
material was treated following the general
procedure for glycal synthesis (A). The result-
ing reaction mixture was then filtered through
a small pad of neutral silica gel–Et3N with
hexane and then 1:20 EtOAc–hexane to yield
0.046 g (63%) of 36 as an oil that decomposes
1
slowly on standing; H NMR (CDCl3, 300
MHz): l 6.67 (d, 1 H, J1,2 2.4 Hz, H-1); 5.84
(dd, 1 H, J3,2 2.7, J3,4 7.2 Hz, H-3), 5.23 (dd, 1
H, H-2), 4.59 (ddd, 1 H, J4,5% 6.9, J4,5 6.1 Hz,
H-4), 4.46 (dd, 1 H, J5.5% 12.0 Hz, H-5), 4.32
(dd, 1 H, H-5%), 2.19 (s, 3 H, Me), 2.06 (s, 3 H,
Synthesis of 37 from 46.—A total of 0.044 g
of 46 (0.10 mmol) were treated under the
general procedure conditions (C). The result-
ing residue was purified by column chro-
matography (10:1 hexane–EtOAc), to furnish
0.021 g (73%) of 37.
13
CH3); C NMR (CDCl3, 75.4 MHz): l 170.5
(CO), 170.2 (CO), 151.7 (C-1), 100.8 (C-2),
80.2 (C-4), 75.2 (C-3), 61.4 (C-5), 20.9–20.7
(2×CH3).
1,4-Anhydro-3,5-di-O-benzyl-2-deoxy-
threo-pent-1-enitol (37).—Compound
D
-
31
Synthesis of 17 from 40+ 43.—The mixture
40+43 (0.139 g, 0.24 mmol) was heated fol-
lowing the general procedure (C). The result-
ing residue was purified by ‘flash’
chromatography with neutral silica gel (20:1
hexane–EtOAc) to obtain glycal 17 (0.097 g,
94%).
(0.250 g, 0.55 mmol) was treated following the
general procedure for glycal synthesis (B), and
the resulting residue was purified by column
chromatography in 1:20 EtOAc–hexane to
give 0.142 g (87%) of glycal 37 as a colorless
1
oil; [h]2D5 −12.9° (c 1.174, CHCl3); H NMR
(CDCl3, 300 MHz): l 7.27–7.10 (m, 10 H,
Ph), 6.50 (d, 1 H, J1,2 2.6 Hz, H-1); 5.13 (dd,
1 H, J2,3 2.8 Hz, H-2), 4.53 (d, 1 H, Jgem 11.9
Hz, OCH2Ph), 4.44 (d, 1 H, OCH2Ph), 4.39
(d, 1 H, OCH2Ph), 4.31 (d, 1 H, OCH2Ph),
4.55–4.28 (m, 2 H, H-3, H-4); 13C NMR
(CDCl3, 75.4 MHz): l 150.4 (C-1), 128.1–
127.3 (Ph), 101.2 (C-2), 83.1 (C-4), 79.2 (C-3),
73.3–70.5 (OCH2Ph), 67.6 (C-5). Anal Calcd
for C19H20O3: C, 77.02; H, 6.75. Found C,
77.33; H, 6.67.
General procedure for synthesis of furanoid
glycals from 2-deoxy-2-phenylselenenyl-1,4-
anhydroalditols (C).—In a round-bottomed,
single necked flask, 0.17 mmol of seleno-
derivative or the mixture of seleno-derivatives
was dissolved in dry CH2Cl2 (10 mL) or
(CH2)2Cl2. The flask was immersed in a wa-
ter–ice bath, and EtiPr2N (50 mL, 0.29 mmol),
TBHP 3 M (135 mL) in toluene (0.40 mmol)
and Ti(OiPr)4 (50 mL, 0.17 mmol) were se-
1,4-Anhydro-3,5-di-O-(tert-butyldiphenyl)-
silyl-2-deoxy- -erythro-pent-1-enitol (45).—
D
A 1:1 mixture of 41 and 44 (0.071 g, 0.09
mmol) was treated following the general pro-
cedure (C) to obtain 50 mg (89%) of glycal 45,
after purification by column chromatography
1
(20:1 hexane–EtOAc); H NMR (CDCl3, 300
MHz): l 7.8–7.2 (m, 20 H, Ph), 6.55 (dd, 1 H,
J1,2 2.7, J1,3 0.7 Hz, H-1); 4.90 (td, 1 H, J2,3 J3,4
2.7 Hz, H-2), 4.84 (t, 1 H, H-3), 4.47 (ddd, 1
H, J4,5% 5.7, J4,5 4.5 Hz, H-4), 3.41 (dd, 1 H,
J5,5% 10.8 Hz, H-5), 3.58 (dd, 1 H, J5,5% 10.8 Hz,
H-5%), 1.04 (s, 9 H, 3×CH3), 0.95 (s, 9 H,
3×Me); 13C NMR (CDCl3, 75.4 MHz): l
149.4 (C-1), 135.9, 135.8, 135.7, 134.1, 129.8,
129.7, 127.8, 127.7 (Ph), 103.4 (C-2), 89.1
(C-4), 76.8 (C-3), 63.7 (C-5), 26.8 (Me), 26.5
(Me), 19.1, 18.9. Anal. Calcd for C37H44O3Si2:
C, 74.95; H, 7.48. Found C, 74.79; H, 7.40.
1,4-Anhydro-3-O-benzyl-5-O-(tert-butyldi-
phenyl)silyl - 2 - deoxy -
D
- threo - pent - 1 - enitol

96
F. Bra6o et al. / Carbohydrate Research 336 (2001) 83–97
6. (a) Robles, R.; Rodr´ıguez, C.; Izquierdo, I.; Plaza, M. T.;
Mota, A. Tetrahedron: Asymmetry 1997, 8, 2959–2965;
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1997, 53, 10921–10938;
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(50).—Following the general procedure for
glycal synthesis (C), 0.107 g (0.18 mmol) of
the mixture of 47 and 49 afforded glycal 50
(0.065 g, 82%) as a colorless oil, after purifica-
tion on neutral silica gel (15:1 hexane–
1
EtOAc); [h]D −6.78° (c 1.519, CHCl3); H
NMR (CDCl3, 300 MHz): l 7.8–7.2 (m, 15 H,
Ph), 6.61 (d, 1 H, J1,2 2.4 Hz, H-1); 5.24 (t, 1
H, J2,3 2.7 Hz, H-2), 4.61 (dd, 1 H, J3,4 6.9 Hz,
H-3), 4.51 (d, 1 H, JAB 12.0 Hz, CH2Ph), 4.45
(d, 1 H, JAB 12.0 Hz, CH2Ph), 4.39 (q, 1 H,
J3,4:J4,5:J4,5% 6.4 Hz, H-4), 4.18 (dd, 1 H,
J5,5% 11.0 Hz, H-5), 4.03 (dd, 1 H, H-5%), 1.05
(s, 9 H, 3×Me); 13C NMR (CDCl3, 75.4
MHz): l 150.6 (C-1), 138.6, 135.7, 135.7,
129.7, 128.4, 127.8, 127.5 (Ph), 101.6 (C-2),
84.9 (C-4), 79.2 (C-3), 70.8 (CH2Ph), 61.4
(C-5), 26.7 (CH3), 19.1 (CMe3). Anal. Calcd
for C28H32O3Si: C, 75.64; H, 7.25. Found C,
75.41; H, 7.11.
10. (a) Fischer, E.; Zach, K. Sitzungsber. Kl. Preuss. Akad.
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Acknowledgements
Financial support by DGECIT PB-98-1510
(Ministerio de Educacio´n y Cultura, Spain) is
acknowledged. F.B. thanks the CIRIT (Gen-
eralitat de Catalunya) for a grant. Technical
assistance by the ‘Servei de Recursos Cientifics
(URV)’ is acknowledged.
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