Stereoselective synthesis of 2-C-methylene glycosides and disaccharides via direct allylic substitution of hydroxy group in benzylated glycals

Article abstract of DOI:10.1016/j.tet.2009.11.082

InCl₃ efficiently catalyzes allylic substitution of the hydroxy group of 2-C-hydroxymethyl glycals to afford a diversity of 2-C-methylene alkyl and aryl glycosides as well as disaccharides in high yields. This protocol surpasses the existing methods for the synthesis of 2-C-methylene glycosides as it obviates the need for functionalizing the allylic hydroxy group of glycals. The interest of this methodology relies on the extremely mild conditions required even with a free hydroxyl group at the allylic position of the glycals and that too only with a catalytic amount of InCl₃. The reaction is fast (30 min.), stereoselective and is compatible with a variety of oxygenated nucleophiles including those possessing acid-labile groups. A mechanistic investigation on the direct formation of an α,α-(1→1)linked disaccharide derivative from 2-C-hydroxymethyl galactal reveals that the reaction proceeds through a domino Ferrier rearrangement followed by a facile 1,3-alkoxy migration.

Full text of DOI:10.1016/j.tet.2009.11.082

Tetrahedron 66 (2010) 599–604
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Stereoselective synthesis of 2-C-methylene glycosides and disaccharides
via direct allylic substitution of hydroxy group in benzylated glycals
*
Paramathevar Nagaraj, Namakkal G. Ramesh
Department of Chemistry, Indian Institute of TechnologydDelhi, Hauz Khas, New Delhi 110016, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 August 2009
Received in revised form 16 November 2009
Accepted 19 November 2009
Available online 23 November 2009
InCl3 efficiently catalyzes allylic substitution of the hydroxy group of 2-C-hydroxymethyl glycals to afford
a diversity of 2-C-methylene alkyl and aryl glycosides as well as disaccharides in high yields. This pro-
tocol surpasses the existing methods for the synthesis of 2-C-methylene glycosides as it obviates the
need for functionalizing the allylic hydroxy group of glycals. The interest of this methodology relies on
the extremely mild conditions required even with a free hydroxyl group at the allylic position of the
glycals and that too only with a catalytic amount of InCl3. The reaction is fast (30 min.), stereoselective
and is compatible with a variety of oxygenated nucleophiles including those possessing acid-labile
Keywords:
Indium(III) chloride
Stereoselective synthesis
Glycosides
Ferrier rearrangement
Carbohydrates
groups. A mechanistic investigation on the direct formation of an
a,a-(1/1)linked disaccharide de-
rivative from 2-C-hydroxymethyl galactal reveals that the reaction proceeds through a domino Ferrier
rearrangement followed by a facile 1,3-alkoxy migration.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
conventional Wittig reaction of 2-keto glycosides to the corre-
sponding 2-C-methylene glycosides has practical limitations due
Over the last one decade, 2-C-methylene glycosides have
emerged as versatile chiral intermediates in organic synthesis
owing to the facile synthetic maneuverability of their exocyclic
double bond into a variety of functional groups. 2-C-Methylene
glycosides have found applications in the total synthesis of
natural and biologically important molecules, such as ara-
cyclohexenyl-adenine,1 polyenes,2 C-disaccharides,3 cyclophellitol,4
and restricticin.5 Chmielewski et al. have utilized 2-C-methylene
hydroperoxides, synthesized from 2-C-methlyene glycosides, as
chiral catalysts in enantioselective epoxidation reactions.6 Very
recently, Vankar and Gupta have reported the synthesis of 2-C-
methylene aza sugars enroute their synthetic approach toward
novel glycosidase inhibitors.7 Some of these aza sugars show
promising and selective inhibition properties against glycosidases.
The exo-methylene group of 2-C-methylene glycosides has also
been shown to be a key functionality of molecules involved in
mechanism-based inactivation of ribonucleotide diphosphate re-
ductase.8 In view of these vast applications, there has been
a considerable interest in the synthesis of 2-C-methylene glyco-
sides in recent years. So far, only two general methodologies are
available for synthesis of 2-C-methylene glycosides. The
to the sensitivity of the reaction conditions employed.1–5,9
A
simple and a more convenient approach involving Ferrier rear-
rangement of 2-C-acetoxymethyl glycals 1a developed by Bala-
subramanian et al.10 (Scheme 1) was largely exploited by
a number of other groups due to its simplicity.11 Sinou et al. and
Vankar et al. have reported a palladium catalyzed approach to
2-C-methylene glycosides from the carbonates of 2-C-hydroxy-
methyl glycals 1b.11c,d Hotha et al. recently exploited the alky-
nophilic behavior of AuCl3 to obtain 2-C-methylene glycosides
from the corresponding 2-C-propargyloxymethyl glycals 1c.11a
Obviously, all these latter methodologies10,11 require an additional
step of protecting and/or functionalizing the hydroxy group of
2-C-hydroxymethyl glycals 1d, and further activating them to un-
dergo Ferrier rearrangement. In addition, some of these metho-
dologies suffer from limitations, such as substrate instability,12
expensive catalysts, longer reaction times (1–16 h),11a lack of
stereoselectivity, and requirement of stoichiometric or even more
amounts of catalysts. To our knowledge, except for a very recent
report on a facile transformation of 2-C-hydroxymethyl glycals 1d
to pyrano[2,3-b]benzopyrans, via tandem Ferrier rearrangement-
intramolecular cyclization, mediated by trifluroacetic acid,13 there
is no report on direct Ferrier rearrangement of 2-C-hydroxy-
methyl glycals with oxygen nucleophiles especially under cata-
lytic conditions.
* Corresponding author. Tel.: þ91 11 26596584; fax: þ91 11 26581102.
E-mail address: ramesh@chemistry.iitd.ac.in (N.G. Ramesh).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.11.082

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P. Nagaraj, N.G. Ramesh / Tetrahedron 66 (2010) 599–604
Lewis acid
or
presence of 5 mol % of InCl3. The progress of the reaction was
OBn
O
OBn
O
BnO
BnO
BnO
Pd catalysts
monitored by TLC, which indicated a complete consumption of the
starting material in just 30 min and appearance of a new spot.
Upon purification by column chromatography over silica gel and
careful analysis, the product was indeed identified as methyl
glycoside 5, obtained in 88% yield. (Scheme 2, Entry 1, Table 1). The
anomeric configuration of the isolated product was identified as
BnO
R1OH
OR1
OR
2
1
1a R = -COCH3
1b R = -COOR''2
CH
1c R = -CH2C
1d R = H
a
by detailed NMR NOE analysis.33,34 Quite significantly, the re-
action rate, isolated yield and anomeric selectivity of this reaction
were found to be superior than the synthesis of 5 from the Ferrier
rearrangement of 2-C-acetoxymethyl glucal with methanol as
reported by Balasubramanian et al.10b and Ghosh et al.11b It is
worth mentioning that while it requires 30 mol % of InCl3 and 1 h
reaction time to realize the Ferrier rearrangement of 3,4,6-tri-O-
benzyl-2-C-acetoxymethyl glucal with methanol,11b just 5 mol %
of InCl3 was sufficient to carry out the same reaction in 30 min.
and that too with hydroxy as the leaving group. This clearly in-
dicates that hydroxy group, as compared to an acetoxy group, has
a better affinity toward InCl3. Even with BF3$Et2O, a strong Lewis
acid, the reaction of 3,4,6-tri-O-benzyl-2-C-acetoxymethyl glucal
with methanol required a much longer time (2 h).10b Encouraged
with the success, the generality of the reaction was tested with
benzyl and allyl alcohols as nucleophiles (Scheme 2, Entries 2 and
3, Table 1). In these examples also, the reaction was successful and
Scheme 1. Synthesis of 2-C-methylene glycosides through Ferrier type rearrangement.
Direct substitution of hydroxy group in alcohols by nucleophiles
always remains a challenging task in organic chemistry due to their
poor leaving group ability. An equimolar or an excess of an acid is
generally required to perform this transformation which precludes
their use with nucleophiles possessing acid-labile groups. As
a consequence, alcohols are normally converted into good leaving
groups, such as acetates, halides, tosylates etc., before being reacted
with a nucleophile.14 This process inevitably requires an additional
step of pre-activating the hydroxyl group and in addition produces
a stoichiometric amount of salt waste. Even so, catalytic activation
of alcohols is much more difficult to realize and hence great em-
phasis has been given in recent years to develop catalytic version of
this transformation. Successful attempts in this direction include
the use of transition metal complexes of Cu,15 Mo,16 Ru,17 Pd,18 Re,19
the corresponding 2-C-methylene glycosides
6 and 7 were
obtained in good yields. Extension of this reaction to sugar nu-
cleophiles (Scheme 2, Entries 4 and 5, Table 1) resulted in the
formation of unsaturated disaccharides 8 and 9 in high yields and
anomeric selectivity, with the isopropylidene group remaining
intact under the reaction condition. Similarly, the InCl3 catalyzed
reaction of 2-C-hydroxymethyl galactal 4 with a variety of alcohols
also proceeded smoothly to afford the corresponding 2-C-meth-
ylene galactosides, in just 30 min (Scheme 2; Entries 6–10, Table
1). Notable and an interesting example among them is the InCl3
catalyzed reaction of 2-C-hydroxmethyl galactal 4 (possessing
21
Au,20 and salts of La, Sc and Hf as catalysts. Several Lewis acids,
such as FeCl3,22 AuCl3,23 BiCl3,24 Bi(OTf)3,25 BiBr3,26 I2,27 InCl3,28
29
InBr3
have also been reported to catalyze direct substitution of
hydroxy group with various carbon, nitrogen, and oxygen nucleo-
philes. Nucleophilic substitution of hydroxy group catalyzed by
a Brønsted acid has also been reported.30 Noteworthy is that all
these examples dealt with the direct substitution of the hydroxy
group of only reactive alcohols, such as allylic, benzylic or prop-
argylic alcohols.
Given this background, we reasoned that glycals bearing a free
hydroxy group at the allylic position are ideal substrates to be
exploited for catalytic allylic substitution of hydroxy group. Such
a methodology would obviate the need for an additional step of
protecting the hydroxyl group and use of expensive chemicals to
further activate them. Since water being the only by-product from
such a reaction, it would be environmentally benign. A recent re-
port of Baba et al. on direct allylic substitution of alcohols with
carbon nucleophiles using InCl3 at high temperatures31 prompted
us to explore the catalytic behavior of InCl3 toward glycals pos-
sessing a free hydroxyl group the allylic position. Our initial success
in this direction leading to a facile and stereoselective synthesis of
2,3-unsaturated glycosides has been recently communicated.32
Subsequently, we had investigated the versatility of this catalytic
transformation with 2-C-hydroxymethyl glycals in presence of
a wide array of oxygen nucleophiles. In this paper, we report the
first example of a direct catalytic allylic substitution of the free
hydroxy group of 2-C-hydroxymethyl glycals by oxygen nucleo-
philes. The reaction proceeds at ambient temperature yielding
a variety of 2-C-methylene alkyl and aryl glycosides as well as di-
saccharides. A mechanistic investigation on the one-pot conversion
a primary allylic hydroxyl group) with 4,6-O-isopropylidene-D-
glucal (Entry 10, Table 1) (possessing a secondary allylic hydroxyl
group). In this case, as both the reactants have a free hydroxyl
group at the allylic position one may expect the formation of two
types of products 14 (Entry 10, Table 1) and 15 (Fig. 1). However,
the reaction was found to be highly selective leading to an ex-
clusive formation of the unsaturated disaccharide 14, obtained
from the reaction of 4,6-O-isopropylidene-D-glucal as a glycosyl
acceptor and galactal 4 as a glycosyl donor. Formation of the other
compound 15 (Fig. 1) was not observed as evidenced from the 1H
NMR spectrum of the product. This selectivity may be attributed
to the greater coordinating tendency of InCl3 toward a primary
allylic hydroxy group over the secondary allylic one. The double
unsaturation present in compound 14 provides scope for further
synthetic manipulations toward complex carbohydrates.
R1
R1
R-OH (1.2 equiv.)
InCl3 (5 mol%)
OBn
O
OBn
O
R2
BnO
R2
BnO
CH2Cl2, 0.5 h
OR
30 0
C
OH
5-9 R1 = H, R2 = OBn
of 2-C-hydroxymethyl galactal to an
a,
a-(1/1)linked disaccharide
3 R1 = H, R2 = OBn
4 R1 = OBn, R2 = H
10-14 R1 = OBn, R2 = H
derivative,33 confirms that the reaction proceeds through a domino
Ferrier rearrangement followed by a stereoselective 1,3-alkoxy
migration pathway.
Scheme 2. Synthesis of 2-C-methylene glycosides via InCl3 catalyzed Ferrier
rearrangement of 2-C-hydroxymethyl glycals 3 and 4.
2. Results and discussion
It is well documented in literature that Lewis acid (BF3$Et2O35 or
11b
InCl3
)
catalyzed or Brønsted acid (trifluoroacetic acid)
Following our earlier procedure,32 initially, we treated 3,4,6-
mediated13 Ferrier rearrangement of 2-C-acetoxymethyl glycals
1a or 2-C-hydroxymethyl glycals 3 or 4 afforded directly chiral
tri-O-benzyl-2-C-hydroxymethyl glucal 3, obtained in two steps
from tri-O-benzyl-
D
-glucal,10,11 with methanol (1.2 equiv) in
pyrano[2,3-b]benzopyrans 17 through
a
domino Ferrier

P. Nagaraj, N.G. Ramesh / Tetrahedron 66 (2010) 599–604
601
Table 1
well as with a few substituted phenols and the 2-C-methylene aryl
glycosides were isolated in high yields. The reaction of 2-C-
hydroxymethyl galactal 4 with phenols also proceeded with equal
ease (Scheme 4; Table 2, Entries 4 and 5). Noteworthy is that earlier
attempts to obtain 2-C-methylene aryl glycosides by conventional
Ferrier rearrangement were all unsuccessful.11b,35 With a view of
investigating the further reactivity of 2-C-methylene aryl glyco-
sides with InCl3, we then exposed the isolated 2-C-methylene aryl
glycoside 22 to 5 mol % of InCl3 in CH2Cl2. Glycoside 22 underwent
a smooth intramolecular cyclization, under this condition, to afford
pyrano[2,3-b]benzopyran 23 in 3 h (Scheme 5). The tunability of
the reaction condition toward the desired product (either toward
the 2-C-methylene aryl glycoside or pyrano[2,3-b]benzopyran)
thus highlights the added advantage of the present protocol.
Synthesis of 2-C-methylene glycosides via InCl3 catalyzed Ferrier rearrangement of
2-C-hydroxymethyl glycals 3 and 4
Entry
Reactant
R
Product
Yieldb (%)
Ratioc
(a:b)
1
2
3
3
3
3
CH3–
C6H5CH2–
–CH2CH]CH2
5a
6a
7a
88
85
85
95:5 (100)
80:20 (67:33)
82:18 (90:10)
O
O
O
4
5
3
3
8
79
73
83:17 (92:8)
83:17 (90:10)
O
O
O
O
O
O
O
9
OBn
O
OBn
O
6
7
8
4
4
4
CH3–
C6H5CH2–
–CH2CH]CH2
10a
11a
12a
92
93
80
93:7 (96:4)
89:11 (88:12)
91:9 (100)
OH
BnO
R
BnO
BnO
1a
O
R
CH2Cl2, 30 0
Lewis acid
C
O
O
R
9
4
13
82
91:9 (100)
O
O
17
16
not isolable
O
O
Scheme 3. Literature synthesis of pyrano[2,3-b]benzopyrans through a domino Ferrier
rearrangement–intramolecular cyclization.11b,13,35
10
4
14
87
89:11(100)
O
O
O
a
Spectral data are consistent with literature reported values (see Ref. 33).
Isolated yields after column chromatography.
b
c
1OBn
O
R
OH
1.2 equiv.)
R
Anomeric ratios were obtained from 1H NMR spectra of the crude product;
R2
3 or 4
values in parenthesis refer to the anomeric ratio of the products obtained after
column chromatography.
BnO
InCl3 (5 mol%)
CH2Cl2, 30 0C, 0.5 h
O
R
18-20R1 = H, R2 = OBn
21-22R1 = OBn, R2 = H
O
O
O
Scheme 4. Synthesis of 2-C-methylene aryl glycosides via InCl3 catalyzed Ferrier
rearrangement of 2-C-hydroxymethyl glycals 3 and 4 with phenols.
O
O
Table 2
OBn
Synthesis of 2-C-methylene aryl glycosides via InCl3 catalyzed Ferrier rearrange-
ment of 2-C-hydroxymethyl glycals 3 and 4 with phenols
BnO
OBn
15
Entry
Reactant
R0
Product
Yieldb (%)
Ratioc(
a:b)
1
2
3
4
5
3
3
3
4
4
–H
18
84
78
82
81
88
89:11(90:10)
81:19 (88:12)
81:19 (93:7)
100 (100)
Figure 1. Structure of compound 15.
–Me
–OMe
–Me
–OMe
19a
20a
21a
22a
rearrangement–intramolecular cyclization (Scheme 3). Except for
a couple of examples reported by Vankar and Gupta,11c in none of
the other cases, the intermediate 2-C-methylene aryl glycosides 16
could be isolated. The Mitsunobu approach34 reported earlier for
the synthesis of 2-C-methylene aryl glycosides lacked stereo and
regioselectivity and also required an excess of Ph3P (2.2 equiv) and
DEAD (2.4 equiv). In carbohydrate chemistry, 2,3-unsaturated aryl
glycosides have served as useful precursors for palladium catalyzed
stereoselective synthesis of C-glycosides and C-aryl glycosides.36
On the contrary, the chemistry of 2-C-methylene aryl glycosides
remains largely unexplored mainly due to the paucity of convenient
methods for their synthesis. Thus, there is a need for the de-
velopment of a simple and a reliable methodology in order to un-
ravel the synthetic potential of 2-C-methylene aryl glycosides. With
this aim, we investigated the InCl3 catalyzed reaction of 2-C-
hydroxymethyl glucal 3 with phenol. As in the case of alcohols, the
reaction of 2-C-hydroxymethyl glucal with phenol in presence of
5 mol % of InCl3, was also found to be very facile. The reaction was
over in half an hour affording the 2-C-methylene aryl glycoside 18
88:12 (90:10)
a
Spectral data are consistent with literature reported values (see Ref.34).
Isolated yields after column chromatography.
b
c
Anomeric ratios were obtained from 1H NMR spectra of the crude products;
values in parenthesis refer to the anomeric ratio of the products obtained after
column chromatography.
OBn
O
BnO
InCl3 (5 mol%)
22
O
CH2Cl2, 30 0
3 h, 84 %
C
23
OMe
Scheme 5. Synthesis of pyrano[2,3-b]benzopyran 23 from 2-C-methylene aryl glyco-
side 22.
Previously, we had reported a facile and rapid one-pot conver-
in 84% yield with an anomeric ratio of 90:10, the
a
-anomer being
sion of 2-C-hydroxymethyl galactal 4 to an a,a-(1/1)linked di-
the major one (Scheme 4; Entry 1, Table 2). Under this condition,
formation of pyrano[2,3-b]benzopyran such as 17 was not ob-
served. The reaction was found to be general with unsubstituted as
saccharide derivative 25 in presence of 20 mol % of InCl3 (Scheme
6).33 Initially, 1,3-alkoxy migration followed by an in-situ glyco-
sidation reaction was believed to be the reaction pathway as the

602
P. Nagaraj, N.G. Ramesh / Tetrahedron 66 (2010) 599–604
intermediate 24 could not be isolated. In order to have an insight in
to the exact mechanistic pathway, the reaction was re-investigated
with 5 mol % of InCl3. Thus, when 2-C-hydroxymethyl galactal 4
was treated with 5 mol % of InCl3 in dry CH2Cl2, the starting ma-
terial was completely consumed in 0.5 h. Interestingly, the 1H NMR
spectrum of the product isolated from the reaction was different
a,a-(1/1)linked disaccharide derivative from 2-C-hydroxymethyl
galactal. We strongly believe that the simplicity of the methodology
reported here would spur on further research activities in the area
of unsaturated glycosides.
4. Experimental
from that of a,a-(1/1)linked disaccharide derivative 25 observed
earlier. After careful analysis of the 1H NMR and 13C NMR spectral
data, the product was identified to be a disaccharide 26 arising out
of self Ferrier rearrangement of one molecule of 2-C-hydroxy-
methyl galactal with another one (Scheme 6). Subsequently, the
disaccharide 26 on exposure to an additional 5 mol % of InCl3
4.1. General considerations
All solvents were purified using standard procedures. Thin-layer
chromatography (TLC) was performed on Merck silica gel pre-
coated on aluminum plates. Flash column chromatography was
performed on 230–400 mesh silica gel. Optical rotations were
recorded on an Autopol V (Rudolph Research Flanders, New Jersey)
instrument. All the rotations were measured at 589 nm (sodium D0
line). Melting points of the compounds are uncorrected. IR spectra
were taken within the range 4000–400 cmꢀ1 as KBr pellets on
a Nicolet (Madison, USA) FTIR spectrophotometer (Model Protege
460). All the 1H and 13C NMR spectra were recorded on a 300 MHz
Bruker Spectrospin DPX FT NMR. Chemical shifts are reported as
underwent
a
stereoselective 1,3-alkoxy migration reaction33
affording the a,a-(1/1)linked disaccharide 25 derivative in 3 h, in
an isolated yield of 84%, whose spectral data were identical with
the compound reported earlier. Alternatively, reaction of 2-C-
hydroxymethyl galactal 4 with 5 mol % of InCl3 yielded directly the
a
,a
-(1/1)linked disaccharide derivative 25 in 3 h, in 84% yield.
These experiments clearly reveal that the direct formation of the
-(1/1)linked disaccharide derivative from 2-C-hydroxymethyl
a,a
galactal 4 proceeds through an initial Ferrier rearrangement fol-
lowed by a stereoselective 1,3-alkoxy migration and not via the
pathway earlier thought of.
d
values (ppm) relative to internal standard Me4Si. Mass spectra
were recorded using Applied Biosystems Q-Star instrument.
4.1.1. 6-O-(3,4,6-Tri-O-benzyl-2-deoxy-2-C-methylene-
hexopyranosyl)-1,2:3,4-di-O-isopropylidene- -galactopyranose
8. Glycal 3 (220 mg, 0.493 mmol) was stirred with 1,2:3,4-di-O-
isopropylidene- -galactopyranose (153 mg, 0.591 mmol) in pres-
ence of 5 mol % of anhydrous InCl3 (5.4 mg, 0.024 mmol) in dry
dichloromethane (5 mL) under argon atmosphere at room tem-
perature for 30 min after which the reaction mixture was quenched
with water and extracted with chloroform (2ꢁ50 mL). The organic
layer was dried over sodium sulfate, filtered and then concentrated.
The crude product was purified by column chromatography (30%
EtOAc/Hexane) to give the title compound 8 (268 mg, 79%) as
a colorless liquid. The product was obtained a mixture of anomers
D-arabino-
a-D
OBn
O
BnO
BnO
D
InCl3 (20 mol%)
CH2Cl2, 30 0C,
10 min, 80%
OH
not isolated
24
OBn
O
BnO
BnO
InCl3 (5 mol%)
4
O
CH2Cl2, rt, 3 h, 84%.
BnO
BnO
O
OBn
25
OBn
O
BnO
BnO
InCl3 (5 mol%)
CH2Cl2, 30 0C,
30 min. 78%
(
a
:
b
¼92:8) from which the anomers were not separated. Rf (30%
InCl3 (5 mol%)
CH2Cl2, 30 0C,
3 h, 84%
O
EtOAc/Hexane) 0.43; Specific rotation reported here is for the
28
anomeric mixture; [
2986, 2911, 1663, 1495, 1455, 1375, 1312, 1253, 1210, 1071, 1003, 916,
858, 740, 698 cmꢀ1
dH and dC values reported here correspond to
the signals of only -anomer taken from a mixture of and
anomers; dH (300 MHz, CDCl3) 7.36–7.15 (15H, m, aromatic),
a
]
ꢀ2.6 (c 1.20, CHCl3); ymax (KBr) 3061, 3030,
D
OBn
OBn
O
BnO
;
26
a
a
isolated
b
d
5.52 (1H, d, J¼4.5 Hz, H-1), 5.29 (1H, s, H-7a0), 5.24 (1H, s, H-10), 5.14
(1H, s, H-7b0), 4.86 (1H, d, J¼10.5 Hz, OCH2Ph), 4.76 (1H, d,
J¼11.4 Hz, OCH2Ph), 4.70 (1H, d, J¼11.4 Hz, OCH2Ph), 4.64 (1H, d,
J¼12.6 Hz, OCH2Ph), 4.58–4.43 (4H, m), 4.31–4.22 (2H, m), 4.00–
3.98 (2H, m), 3.70–3.61 (5H, m), 1.52 (3H, s, (CH3)2C), 1.43 (3H, s,
(CH3)2C), 1.32 (6H, s, (CH3)2C); dC (75 MHz, CDCl3) 142.2, 138.3,
138.3, 138.1, 128.4, 128.2, 127.9, 127.8, 127.6, 127.6, 127.5, 110.7, 109.2,
108.5, 101.1, 96.2, 81.1, 79.8, 74.9, 73.4, 73.3, 71.7, 70.8, 70.5, 68.5,
65.6, 65.3, 29.1, 25.9, 24.9, 24.5; HRMS (ESI): [MþNa]þ found:
711.3138. C40H48O10Na requires 711.3145.
Scheme 6. Direct formation of the a,a-(1/1)linked disaccharide derivative via Ferrier
rearrangement followed by 1,3-alkoxy migration: A mechanistic investigation.
3. Conclusions
In conclusion, we have demonstrated for the first time that InCl3
efficiently catalyzes a direct allylic substitution of hydroxy group of
2-C-hydroxymethyl glycals with a wide array of oxygen nucleo-
philes. Synthetic significance of the present protocol is that it
demonstrates that prior protection of the allylic hydroxy groups of
glycals is not a pre-requisite to realize Ferrier rearrangement suc-
cessfully. Since only 5 mol % of the InCl3 is required, the reaction
condition is mild thus making it compatible for glycosyl acceptors
having acid-labile groups, which is not the case with most of the
literature available routes. The methodology is simple, void of ex-
pensive chemicals and versatile resulting in the formation of a wide
variety of unsaturated alkyl glycosides, aryl glycosides as well as
disaccharides. Stereoselectivity of the reaction is comparable with
other methods and even higher in some cases. The methodology
paves way for the isolation of 2-C-methylene aryl glycosides for
which no reliable method is available. Initial Ferrier rearrangement
followed by a stereoselective 1,3-alkoxy migration has been shown
to be the mechanistic pathway for the direct formation of the
4.1.2. 3-O-(3,4,6-Tri-O-benzyl-2-deoxy-2-C-methylene-
hexopyranosyl)-1,2:5,6-di-O-isopropylidene- -glucofuranose
9. Glycal 3 (197 mg, 0.441 mmol) was stirred with 1,2:5,6-di-O-
isopropylidene- -glucofuranose (137 mg, 0.529 mmol) in pres-
D-arabino-
a-D
D
ence of 5 mol % of anhydrous InCl3 (4.8 mg, 0.022 mmol) in dry
dichloromethane (5 mL) under argon atmosphere at room tem-
perature for 30 min after which the reaction mixture was
quenched with water and extracted with chloroform (2ꢁ50 mL).
The organic layer was dried over sodium sulfate, filtered and
then concentrated. The crude product was purified by column
chromatography (30% EtOAc/Hexane) to give the title compound
9 (220 mg, 73%) as a colorless liquid. The product was obtained
as mixture of anomers (
a
:
b
¼90:10) from which the anomers

P. Nagaraj, N.G. Ramesh / Tetrahedron 66 (2010) 599–604
603
were not separated. Rf (30% EtOAc/Hexane) 0.38; Specific rota-
102.7, 101.4, 99.5, 78.2, 75.2, 74.0, 73.5, 72.9, 71.7, 70.9, 69.6,
69.3, 61.7, 29.0, 19.2; HRMS (ESI): [MþNa]þ found: 637.2767.
C37H42O8Na requires 637.2777.
28
tion reported here is for the anomeric mixture; [
CHCl3); ymax (KBr) 3062, 3030, 2986, 2929, 1612, 1495, 1455,
1373, 1322, 1252, 1214, 1072, 1030, 850, 742, 699, 633 cmꢀ1
dH
and dC values reported here correspond to the signals of only
anomer taken from a mixture of and anomers; dH (300 MHz,
CDCl3)
7.41–7.20 (15H, m, aromatic), 5.88 (1H, d, J¼3.0 Hz, H-
a
]
17.3 (c 0.80,
D
;
a
-
4.1.5. Phenyl 3,4,6-tri-O-benzyl-2-deoxy-2-C-methylene-D-arabino-
a
b
hexopyranoside 18. Glycal 3 (210 mg, 0.45 mmol) was stirred
with phenol (50.8 mg, 0.540 mmol), in presence of 5 mol % an-
hydrous InCl3 (4.9 mg, 0.022 mmol) in dry dichloromethane
(5 mL) under argon atmosphere at room temperature for 30 min
after which the reaction mixture was quenched with water and
extracted with chloroform (2ꢁ50 mL). The organic layer was
dried over sodium sulfate, filtered and then concentrated. The
crude product was purified by column chromatography (10%
EtOAc/Hexane) to give the title compound 18 (198 mg, 84%) as
a colorless liquid. The product was obtained as mixture of
d
1), 5.53 (1H, s, H-10), 5.32 (1H, s, H-7a0), 5.19 (1H, s, H-7b0), 4.90
(1H, d, J¼10.5 Hz, OCH2Ph), 4.80 (1H, d, J¼11.4 Hz, OCH2Ph), 4.74
(1H, d, J¼11.4 Hz, OCH2Ph), 4.70–4.64(2H, m), 4.56–4.50 (2H, m)
4.44–4.38 (2H, m), 4.24–4.10 (3H, m), 4.04–3.99 (2H, m), 3.84–
3.63 (3H, m), 1.53 (3H, s, (CH3)2C), 1.45 (3H, s, (CH3)2C), 1.38 (3H,
s, (CH3)2C), 1.29 (3H, s, (CH3)2C); dC (75 MHz, CDCl3) 141.5, 138.1,
138.0, 138.0, 128.4, 128.4, 128.3, 128.0, 127.9, 127.8, 127.7, 127.7,
127.6, 111.9, 111.0, 109.2, 105.2, 101.8, 83.8, 81.5, 80.9, 79.6, 79.5,
75.0, 73.5, 73.4, 72.3, 68.7, 67.7, 26.8, 26.7, 26.1, 25.4; HRMS
(ESI): [MþNa]þ found: 711.3165. C40H48O10Na requires 711.3145.
anomers (
a
:
b
¼90:10) from which the anomers were not sepa-
rated. Rf (10% EtOAc/Hexane) 0.30; Specific rotation reported
28
here is for the anomeric mixture; [
(KBr) 3063, 3031, 2922, 2858, 1740, 1593, 1492, 1455, 1403, 1359,
1320, 1220, 1100, 1033, 980, 922, 845, 744, 696 cmꢀ1
dH and dC
values reported here correspond to the signals of only -anomer
taken from a mixture of and anomers; dH (300 MHz, CDCl3)
a
]
24.0 (c 0.50, CHCl3); ymax
D
4.1.3. 6-O-(3,4,6-Tri-O-benzyl-2-deoxy-2-C-methylene-
pyranosyl)-1,2:3,4-di-O-isopropylidene- -galactopyranose
13. Glycal 4 (220 mg, 0.493 mmol) was stirred with 1,2:3,4-di-O-
isopropylidene- -galactopyranose (153 mg, 0.591 mmol) in pres-
D-lyxo-hexo-
a
-
D
;
a
D
a
b
ence of 5 mol % of anhydrous InCl3 (5.4 mg, 0.024 mmol) in dry
dichloromethane (5 mL) under argon atmosphere at room tem-
perature for 30 min after which the reaction mixture was quenched
with water and extracted with chloroform (2ꢁ50 mL). The organic
layer was dried over sodium sulfate, filtered and then concentrated.
The crude product was purified by column chromatography (30%
EtOAc/Hexane) to give the title compound 13 (280 mg, 82%) as
7.41–6.98 (20H, m, aromatic), 5.89 (1H, s, H-1), 5.39 (1H, s, H-
7a), 5.24 (1H, s, H-7b), 4.89 (1H, d, J¼10.8 Hz, OCH2Ph), 4.83 (1H,
d, J¼11.4 Hz, OCH2Ph), 4.77 (1H, d, J¼11.4 Hz, OCH2Ph), 4.64–
4.58 (2H, m), 4.51 (1H, d, J¼10.8 Hz, OCH2Ph), 4.41 (1H, d,
J¼12.0 Hz, OCH2Ph), 4.07–4.04 (1H, m), 3.81–3.68 (2H, m), 3.60
(1H, dd, J¼10.5, 1.5 Hz, H-6); dC (75 MHz, CDCl3) 156.3, 141.4,
138.2, 137.9, 129.7, 129.4, 128.4, 128.3, 128.2, 127.8, 127.7, 127.6,
127.6, 127.5, 122.1, 116.7, 111.4, 99.8, 81.0, 79.6, 75.0, 73.5, 73.3,
72.1, 68.4; HRMS (ESI): [MþNa]þ found: 545.2282. C34H34O5Na
requires 545.2304.
a colorless liquid. The product was obtained as a pure
a
-anomer. Rf
28
(30% EtOAc/Hexane) 0.41; [
3061, 3030, 2986, 2922, 1734, 1608, 1494, 1455, 1374, 1305, 1252,
1211, 1163, 1070, 1001, 912, 811, 743, 699 cmꢀ1
dH (300 MHz, CDCl3)
a]
D
ꢀ5.3 (c 0.60, CHCl3); ymax (KBr)
;
7.36–7.23 (15H, m, aromatic), 5.51 (1H, d, J¼5.1 Hz, H-1), 5.40 (1H, s,
H-7a0), 5.26 (1H, s, H-10), 5.24 (1H, s, H-7b0), 4.89 (1H, d, J¼11.7 Hz,
OCH2Ph), 4.71–4.57 (4H, m), 4.48–4.37 (3H, m), 4.31–4.29 (1H, m),
4.24–4.17 (2H, m), 4.00 (2H, br s), 3.77–3.73 (2H, m), 3.56–3.54 (2H,
m), 1.51 (3H, s, (CH3)2C), 1.41 (3H, s, (CH3)2C), 1.32 (6H, s, (CH3)2C);
dC (75 MHz, CDCl3) 140.7, 138.7, 138.4, 138.1, 128.4, 128.3, 128.3,
128.1, 127.8, 127.6, 127.5, 127.1, 111.5, 109.2, 108.5, 101.1, 96.3, 78.1,
75.3, 74.0, 73.3, 71.6, 71.0, 70.6, 70.5, 69.0, 65.8, 65.4, 26.1, 25.9, 24.9,
24.5; HRMS (ESI): [MþNa]þ found: 711.3125. C40H48O10Na requires
711.3145.
4.1.6. 1,5-Anhydro-3,4,6-tri-O-benzyl-2-deoxy-2-C-(3,4,6-tri-O-ben-
zyl-2-deoxy-2-C-methylene-a-D-lyxo-hexopyranosyloxy)-methyl-D-
lyxo-hex-1-enitol 26. Glycal 4 (135 mg, 0.302 mmol) was stirred
with 5 mol % of anhydrous InCl3 (3.3 mg, 0.0235 mmol) in dry
dichloromethane (5 mL) under argon atmosphere at room tem-
perature for 30 min after which the reaction mixture was
quenched with water and extracted with chloroform (2ꢁ50 mL).
The organic layer was dried over sodium sulfate, filtered and then
concentrated. The crude product was purified by column chro-
matography (20% EtOAc/Hexane) to give the title compound 26
(104 mg, 78%) as a colorless liquid. Product was obtained as
28
4.1.4. 1,5-Anhydro-3-O-(3,4,6-tri-O-benzyl-2-deoxy-2-C-methylene-
a pure
a-anomer. Rf (20% EtOAc/Hexane) 0.25; [
a]
3.3 (c 0.30,
D
D
-lyxo-hexopyranosyl)-2-deoxy-4,6-O-isopropylidene-
1-enitol 14. Glycal 4 (300 mg, 0.672 mmol) was stirred with
4,6-O-isopropylidene- -glucal (150 mg, 0.807 mmol), in presence
D
-arabino-hex-
CHCl3); ymax (KBr) 3030, 2918, 2866, 1658, 1500, 1456, 1357, 1254,
2094, 1012, 913, 742, 696 cmꢀ1
;
dH (300 MHz, CDCl3) 7.35–7.24
D
(30H, m, aromatic), 6.39 (1H, s, H-1), 5.36 (1H, s, H-7a0), 5.18 (1H,
s, H-10), 5.13 (1H, s, H-7b0), 4.89 (1H, d, J¼11.7 Hz, OCH2Ph), 4.78
(1H, d, J¼12.0 Hz, OCH2Ph), 4.75 (1H, d, J¼11.1 Hz, OCH2Ph), 4.70–
4.60 (4H, m), 4.57 (1H, d, J¼11.1 Hz, OCH2Ph), 4.50 (1H, d,
J¼11.7 Hz, OCH2Ph), 4.40–4.31 (5H, m), 4.25 (1H, m), 4.19 (1H, m),
4.09 (1H, t, J¼6.3 Hz), 3.94 (2H, br s), 3.86–3.75 (2H, m), 3.66 (1H,
dd, J¼10.2, 4.2 Hz, H-6), 3.51–3.49 (2H, m); dC (75 MHz, CDCl3)
143.7, 141.1, 138.6, 138.4, 138.10, 138.0, 137.9, 128.4, 128.3, 128.1,
128.0, 127.9, 127.7, 127.6, 127.5, 127.4, 127.1, 111.0, 108.9, 98.9, 78.1,
75.7, 75.2, 74.0, 73.5, 73.4, 73.1, 71.4, 71.3, 70.7, 69.3, 68.1, 64.2;
HRMS (ESI): [MþNa]þ found: 897.3974. C56H58O9Na requires
897.3979.
of 5 mol % of anhydrous InCl3 (7.0 mg, 0.0336 mmol) in dry
dichloromethane (5 mL) under argon atmosphere at room tem-
perature for 30 min after which the reaction mixture was
quenched with water and extracted with chloroform (2ꢁ50 mL).
The organic layer was dried over sodium sulfate, filtered and
then concentrated. The crude product was purified by column
chromatography (30% EtOAc/Hexane) to give the title compound
14 (360 mg, 87%) as a colorless liquid. The product was obtained
as a pure
0.20, CHCl3); ymax (KBr) 3029, 2922, 2858, 1640, 1456, 1370,
1309, 1267, 1230, 1155, 1099, 1004, 868, 744, 698 cmꢀ1
dH
(300 MHz, CDCl3) 7.37–7.23 (15H, m, aromatic), 6.28 (1H, dd,
28
a
-anomer. Rf (30% EtOAc/Hexane) 0.33; [
a
]
ꢀ5.5 (c
D
;
d
J¼6.0, 1.5 Hz, H-1), 5.65 (1H, s, H-10), 5.39 (1H, s, H-7a0), 5.20
(1H, s, H-7b0), 4.89 (1H, d, J¼12.0 Hz, OCH2Ph), 4.73–4.60 (4H,
m), 4.50–4.38 (4H, m), 4.17 (1H, t, J¼6.3 Hz), 4.02–3.91 (3H, m),
3.84–3.75 (2H, m), 3.59–3.57 (2H, m), 1.51 (3H, s, (CH3)2C), 1.39
(3H, s, (CH3)2C); dC (75 MHz, CDCl3) 144.6, 140.9, 138.6, 138.4,
138.0, 128.4, 128.4, 128.4, 128.1, 127.8, 127.7, 127.5, 127.1, 111.3,
Acknowledgements
We are grateful to the Department of Science and Technology,
New Delhi, India for financial support. P.N. thanks IIT-Delhi for
a senior research fellowship.

604
P. Nagaraj, N.G. Ramesh / Tetrahedron 66 (2010) 599–604
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