DABCO: An efficient promoter for the acetylation of carbohydrates and other substances under solvent-free conditions

Article abstract of DOI:10.1016/j.tetlet.2011.08.141

A simple, mild and efficient solvent-free method for the acetylation of carbohydrates, and their partially protected derivatives, as well as non-carbohydrate substances in excellent yields in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) is described with the advantage of tolerance to various functional groups, short reaction time and ease of product isolation.

Full text of DOI:10.1016/j.tetlet.2011.08.141

Tetrahedron Letters 52 (2011) 5841–5846
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Tetrahedron Letters
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DABCO: an efficient promoter for the acetylation of carbohydrates
and other substances under solvent-free conditions
⇑
Ratnasekhar Ch , Mohit Tyagi, Premanand Ramrao Patil, K.P. Ravindranathan Kartha
Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research, S.A.S. Nagar, Punjab 160062, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple, mild and efficient solvent-free method for the acetylation of carbohydrates, and their partially
protected derivatives, as well as non-carbohydrate substances in excellent yields in the presence of 1,4-
diazabicyclo[2.2.2]octane (DABCO) is described with the advantage of tolerance to various functional
groups, short reaction time and ease of product isolation.
Received 27 June 2011
Revised 22 August 2011
Accepted 24 August 2011
Available online 31 August 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
DABCO
Acetylation
Carbohydrates
Alcohols
Per-O-acetylated hexopyranoses are widely used starting mate-
rials for the synthesis of biologically important oligosaccharides
and glycoconjugates.1 Besides, structural elucidation of many poly-
hydroxylic natural products is very often facilitated by transforma-
tion into their corresponding acetates. Due to the high solubility of
sugar acetates in both liquid and supercritical CO2 they are widely
used as biocompatible and non-toxic renewable materials for the
preparation of functional surfactants for micro emulsion systems;
and they show promise as excipient systems for the pharmaceuti-
cals and as novel co-solvents in biological applications to reduce
the excessive waste of organic solvents utilized in processing.2a,b
Separation and fixation of acidic green house gas (CO2) currently
being of great environmental concern, sugar acetates, like ionic
liquids, hold great potential to be used as materials for the separa-
tion of CO2 from sources such as natural gas and various prepared
fuel gases.2c The procedure most often used for the acetylation of
sugar alcohols involves the use of a large excess of acetic anhydride
along with pyridine that serves as a catalyst cum solvent for the
reaction.3 Use of pyridine derivatives, for example, 4-(N,N-dimeth-
ylamino) pyridine, 4-(1-pyrrolidino)pyridine, etc as co-catalyst to
speed up this transformation is also widely practiced.4 However,
pyridine and its derivatives are very toxic in nature, having
unpleasant odor and are not easy to remove. Acetylation using
imidazole, another basic catalyst, reported recently requires the
use of acetonitrile, a toxic agent, as the solvent.5 Methods that
are environmentally more benign but involving acidic catalysts
such as molecular I2,6 and In(OTf)3 for the per-O-acetylation of
7
sugars reported in the recent past employs a neat condition for
the reaction but using excess acetic anhydride. Other catalysts that
have been shown to be effective for this purpose include Bronstead
acids, such as H2SO4,8a HClO4,8b along with its supported system
HClO4-silica,9 are also effective but their application gets limited
due to the incompatibility with acid labile groups when present
in the molecule. Heterogeneous catalysts such as Montmorillonite
K-1010 and others also serve as catalysts for the acetylation but
isomerization (leading to mixtures of pyranose- and furanose
forms) and longer reaction times have been of great concern. Lewis
acid catalysts such as ZnCl2,11 metal triflates,12a–h trimethylsilyl tri-
flate,12i etc are also versatile promoters of acetylation reaction. But
the cost/availability/toxicity/ and difficulty in handling (mainly
because of their sensitivity to moisture/air) can limit the applica-
tion of these agents. Indium chloride-method reported on the other
hand requires microwave irradiation in acetic anhydride.12j In con-
trast to the many reports on acetylation using acidic catalysts, only
a very few reports are available in the literature on basic catalysts
serving the purpose. Our laboratory has been engaged in the explo-
ration of practical green chemistry that eliminates the use of
substances hazardous to human health and environment13 and
recently we have reported solvent-free syntheses of thioglyco-
sides13a and glycosyl azides13b as well as regioselective tritylation
of hexosides and nucleotides.13c,d The latter methods employ 1,4-
diazabicyclo[2.2.2]octane (DABCO) as the base catalyst and thus
eliminate the need for using pyridine, a toxic solvent, most often
employed as catalyst cum solvent for such reactions. On the other
hand DABCO has been reported to be considerably less toxic than
⇑
Corresponding author.
E-mail address: rkartha@niper.ac.in (K. P. Ravindranathan Kartha).
Current address. Department of Analytical Chemistry, CSIR-Indian Institute of
Toxicology Research, Lucknow-226001, India.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.08.141

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Ratnasekhar ch et al. / Tetrahedron Letters 52 (2011) 5841–5846
pyridine.13e Herein we like to report another practical application
of DABCO as an efficient, inexpensive and easy to handle reagent
for the acetylation of various carbohydrates using acetic anhydride
as the acetylating agent (Scheme 1).
N
N
O
O
H2N/HO
AcHN/AcO
Ac2O (neat), rt
Quantitative
A set of initial experiments carried out using the commercially
Scheme 1. DABCO-mediated acetylation of carbohydrates.
available methyl
a-D-glucopyranoside (Table 1, entry 1) as the sub-
strate revealed that a molar ratio of the sugar:Ac2O:DABCO = 1:5
Table 1
DABCO-mediated acetylation of carbohydrates, their derivatives and non-carbohydrate substancesa
Entry
Compound structure: R = H ? R = Ac
Reaction
Refs.
16
Time (min)
Yield (%)
97
OR
O
RO
RO
1
55
RO
OCH3
SCH3
OR
O
RO
RO
RO
2
3
4
35
25
50
95
95
94
17
12d
9
OR
O
RO
RO
SPh
OR
OR
O
RO
RO
OR
O
Ph
O
O
5
25
96
18
O
SPh
RO
RO
RO
OR
OTBDMS
O
6
7
65
15
98
96
10e
18
OCH3
OR
O
O
O
SCH3
NPhth
RO
O
OR
O
O
8
25
98
94
19
O
O
OTr
O
RO
RO
9b
45
30
13d
20
RO
OCH3
O
O
O
O
O
10
96
97
HO
OR
OR
O
11
12
80
5
SPh
RO
OR
OR
O
RO
RO
240
96 (
a
- only)
21
OR
ClH.RHN

Ratnasekhar ch et al. / Tetrahedron Letters 52 (2011) 5841–5846
5843
Table 1 (continued)
Entry
Compound structure: R = H ? R = Ac
Reaction
Refs.
Time (min)
Yield (%)
OR
O
13c
14
60
95 (
a
:b = 1.53:1)
:b = 5.35:1)
12d
12d
RO
RO
OR
OR
RO
OR
O
230
94 (a
RO
OR
OR
OR
O
RO
RO
RO
15
16
17
130
55
95 (
95 (
97 (
a:b = 1.85:1)
a:b = 0.27:1)
a - only)
12d
22
OR
OR
OR
RO
O
O
RO
RO
RO
RO
RO
200
22
AcHN
OR
RO
OR
O
O
18
420
94(
a:b = 0.46:1)
5
O
RO
RO
OR
OR
OR
CH2OR
O
19d
270
30
96
97
23
O
OR
OR
RO
7
20
12f
OR
21
22
20
30
95
95
12f
12f
OR
OR
23
40
94
12f
24
65
94
12f
H
H
H
RO
a
Substrate (1 g) with Ac2O, 1.2 mol equiv per OH/NH2 group and DABCO, 1.0 mol equiv were used for the reaction under neat condition.
b
Methyl
combined.
a-D-glucopyranoside was converted to methyl 2,3,4-tri-O-acetyl-6-O-trityl-a-D-glucopyranoside in one-pot on 10 g scale. The time reported is for the two steps
c
The reaction carried out was on 10 g scale.
The reaction was carried out at 55 °C.
d
(1.2 mol equiv per OH group):1 was optimal for the reaction. Under
these conditions a facile reaction took place leading to the forma-
water, it could be obtained as a colorless solid upon the addition
of crushed ice to the reaction mixture and separation by filtration
and drying. The product could be made free of the amine and its
salt by washing with cold water, thus eliminating the need for an
acidic work-up as usually is the case at the instance of pyridine
in the classical method. The proposed mechanism for the acetyla-
tion of sugars is shown in Scheme 2 in which the role of DABCO is
tion of the desired methyl 2,3,4,6-tetra-O-acetyl-a-D-glucopyrano-
side14 in a virtually quantitative yield. The authenticity of the
product was obtained from its NMR spectroscopic data and a com-
parison of the physical constants with literature data. It may be
emphasized that as the per-O-acetylated product is insoluble in

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Ratnasekhar ch et al. / Tetrahedron Letters 52 (2011) 5841–5846
ried out at room temperature except that of b-cyclodextrin (Table
δ
O
O
1, entry 19) which required approximately 50 °C for the reaction to
be completed in a reasonably short time period. A multi-gram scale
(10 g) reaction (Table 1, entry 13) carried out was also proved very
effective yielding the desired per-O-acetylated product, again, in
nearly quantitative isolated yield. Moreover, the reactions carried
out on multi-gram quantities were significantly faster compared
to those using a gram (or less) of the starting material, the heat
of reaction helping in the acceleration of the reaction rate in the
former (see Table 1, entry 13). One-pot successive tritylation (reg-
ioselective) and acetylation could also be carried out with ease (cf.
DABCO/DMAP-assisted one-pot tritylation–acetylation protocol in
CH2Cl2 we have reported earlier13d) in very high overall yields.
DABCO HOAc
O
O
δ
N
O
N+
AcO
N
OAc
3
N
HO
O
1
2
Scheme 2. Proposed mechanism for the DABCO-mediated acetylation of
carbohydrates.
essentially as an acyl transfer agent. Thus, the initial reaction of
one of the nucleophilic nitrogens in the molecule with Ac2O can
give rise to the N-acetylated intermediate 2 which upon reaction
with the alcoholic functionality of sugar 1 would lead to the forma-
tion of the desired acetate 3 after the deprotonation assisted by the
acetate base (Scheme 2).
Thus, methyl
lated by treatment with trityl chloride (2 mol equiv) in dichloro-
methane at rt for 2 h and the generated methyl 6-O-trityl-
a-D-glucopyranoside could be regioselectively trity-
a-D-
In order to establish the effectiveness and the acceptability of
the method in a wider context of synthetic carbohydrate chemis-
try, acetylation of a variety of carbohydrates and their derivatives
was subsequently carried out and the results are presented in Ta-
ble 1. In all the cases studied clean and complete conversion was
observed and the respective per-O-acetylated product desired
was isolated in essentially quantitative yield without the need
for purification by column chromatography. The anomeric ratio
glucopyranoside was acetylated in the same pot by reacting with
Ac2O (1.2 mol equiv/OH group) in the presence of DABCO (1 mol e-
quiv) for 40 min to obtain, after chromatographic purification, the
desired methyl 2,3,4-tri-O-acetyl-6-O-trityl-a-D-glucopyranoside
in 88% yield.15 The acetylation of amino sugars (Table 1, entries
12 and 17), which usually requires up to 24 h by the conventional
method in pyridine, could also be achieved appreciably faster (in
2–4 h) using the current method.
(
a
:b) of the acetylated product obtained in the case of the reducing
A comparative evaluation of some of the literature methods, the
classical pyridine-mediated reaction along with a few of the more
recently reported methods comprising of acidic, basic as well as
neutral promoters, was then carried out on three representative
sugar substrates and the results are summarized in Table 2. In all
cases studied the DABCO-mediated reaction was proved substan-
tially superior in terms of one or more of the parameters such as
the reaction time, requirement of a solvent for the reaction, reac-
tion yield and the convenience of carrying out the reaction (e.g.,
the reaction temp, see Table 2).
sugars was determined by 1H NMR spectroscopic analysis of the
isolated product mixture. Importantly, no furanosyl acetates were
found to be formed in the case of free sugars (Table 1, entries 12–
17) as evidenced by the NMR spectra of the acetylated products
isolated. In general, the completely unprotected sugars underwent
acetylation slower than their partially protected analogues (Table
1, entries 12–19) as to be expected from their relative solubility
characteristics in acetic anhydride. Again, as was expected, the
most common protecting groups such as TBDMS, TBDPS, trityl,
benzylidene and isopropylidene groups were very stable under
the conditions of acetylation. All reactions could be effectively car-
Further, in order to establish the general applicability of the
method to other types of organic compounds, the work was
Table 2
Comparison of the current method with some of the reported methodsa
Compound structure: R = H ? R = Ac
Catalyst
Reaction
Refs.
Time (min)
Yield (%)
LiClO4
TsOHb
Pyridine
DABCO
50
10
8
4
93
90
96
96
19
24
3
CH2OR
O
O
—
OR
RO
7
e
HClO4
H2SO4
22
3
6
—
—
8a,8b
3
—
OR
e
O
Pyridined
DABCO
95
94
RO
RO
3.5
OR
RHN
OR
O
c
I2
3.0
5
12
0.75
2
40f
80
6
12d
25
3
5
O
Cu(OTf)2
Al2O3
30g
95
98
98
O
Pyridined
Imidazoleb
DABCO
O
O
0.3
—
a
b
c
d
e
f
Substrate (1 g) with Ac2O, 1.2 mol equiv per OH/NH2 group and DABCO, 1.0 mol equiv, were used for the reaction at rt under neat condition.
Acetonitrile was used as the solvent.
The starting sugar used was hydrochloride salt.
Pyridine was used as the solvent.
Per-O-acetylation does not take place.
The remaining was degraded product to avoid degradation the reaction needs to be held at icebath temp or below.
The reaction not complete.
g

Ratnasekhar ch et al. / Tetrahedron Letters 52 (2011) 5841–5846
5845
Table 3
DABCO-mediated acylation/alkylation/silylation of carbohydrates and their derivativesa
Sugar substrate
Reagent, RCl
Reaction
Refs.
Time (min)
Yield (%)
93
OR
O
RO
RO
BzCl (Under neat condition)b
1.5
18
OR
RO
R = H R = Bz
OR
O
RO
RO
TBDMSCl (CH2Cl2)
2
92
98
26
RO
OCH3
R = H R = TBDMS
OR
O
RO
RO
TrCl (CH2Cl2)
3.5
13d
RO
OCH3
R = H R = Tr
a
Substrate (1.0 g) with RCl, 1.2 mol equiv per OH group and DABCO, 1.0 mol equiv in CH2Cl2 (20 mL), were used for the reaction at rt.
No solvent was used.
b
extended to a few of the representative non-carbohydrate hydrox-
ylic substrates [aryl (phenol, Table 1, entry 20), aryl-substituted al-
kyl (benzyl alcohol, Table 1, entry 21), alkyl (octanol, Table 1, entry
22), substituted/hindered/chiral (menthol, Table 1, entry 23) and
steroidal (cholesterol, Table 1, entry 24)] and it was found that
acetylation can be carried out with equal ease and efficiency in
all of the cases (Table 1, entries 20–24).
Acknowledgments
R.C. and M.T. sincerely thank the Council of Scientific and Industrial
Research, New Delhi for Research Fellowship and P.R.P. acknowledges
NIPER, S.A.S. Nagar for providing the financial support.
References
It may be pointed out that the use of acetic anhydride as an acyl
donor reagent in the acetylation reactions under neat conditions
described above, in particular in the case of per-O-acetylation of
unprotected carbohydrates, was found to be well suited as the ace-
tic acid formed as a by-product in the reaction served as an excel-
lent solvent for the acetylated product. Moreover it was also found
to be commercially much cheaper than acetyl chloride, a popular
alternative for the purpose, besides the fact that it is also more sta-
ble and easier to handle as a reagent compared to the latter.
Finally, the reaction was also proved equally applicable to the
synthesis of per-O-benzoylated sugar derivatives such as penta-
1. (a) Garegg, P. J. Adv. Carbohydr. Chem. Biochem. 1997, 52, 179; (b) Zhang, Z.;
Ollmann, I. R.; Ye, X.-S.; Wischnat, R.; Baasov, T.; Wong, C.-H. J. Am. Chem. Soc.
1999, 121, 734; (c) Ye, X.-S.; Wong, C.-H. J. Org. Chem. 2000, 65, 2410.
2. (a) Raveendran, P.; Wallen, S. L. J. Am. Chem. Soc. 2002, 124, 7274; (b) Potluri, V.
K.; Xu, J. H.; Enick, R. M.; Beckman, E.; Hamilton, A. D. Org. Lett. 2002, 4, 2333;
(c) Ma, S-. L.; Wu, Y.-T.; Michael, L. H.; Scott, L. W.; Christine, S. G. J. Phys. Chem.
B 2010, 114, 3809.
3. (a) Hudson, C. S.; Dale, J. K. J. Am. Chem. Soc. 1915, 37, 1264; (b) Wolfrom, M. L.;
Thompson, A. Methods Carbohydr. Chem. 1963, 2, 211.
4. (a) Hofle, G.; Steglich, W.; Vorbruggen, H. Angew. Chem., Int. Ed. Engl. 1978, 17,
569; (b) Scriven, E. F. V. Chem. Soc. Rev. 1983, 12, 129.
5. Tiwari, P.; Kumar, R.; Prakash, R. M.; Misra, A. K. Eur. J. Org. Chem. 2005, 20,
4265.
O-benzoyl-
a
-
D
-glucopyranose (Table 3, entry 1) using BzCl as the
6. Kartha, K. P. R.; Field, R. A. Tetrahedron 1997, 53, 11753.
7. (a) Giri, S. K.; Verma, M.; Kartha, K. P. R. J. Carbohydr. Chem. 2008, 27, 464; (b)
Bizier, N. P.; Atkins, S. R.; Helland, L. C.; Colvin, S. F.; Twitchell, J. R.; Cloninger,
M. J. Carbohydr. Res. 2008, 343, 1814.
8. (a) Hyatt, J. A.; Tindall, G. W. Heterocycles 1993, 35, 227; (b) Binch, H.; Stangier,
K.; Thiem J. Carbohydr. Res. 1998, 306, 409.
9. Misra, A. K.; Tiwari, P.; Madhusudan, S. K. Carbohydr. Res. 2005, 340, 325.
10. (a) Bhaskar, P. M.; Loganathan, D. Tetrahedron Lett. 1998, 39, 2215; (b)
Kumareswaran, R.; Pachamuthu, K.; Vankar, Y. D. Synlett 2000, 1652; (c)
Bhaskar, P. M.; Loganathan, D. Synlett 1999, 129; (d) Curini, M.; Epifano, F.;
Marcotullio, M. C.; Rosati, O.; Rossi, M. Synth. Commun. 2000, 30, 1319; (e)
Adinolfi, M.; Barone, G.; Iadonisi, A.; Schiattarella, M. Tetrahedron Lett. 2003, 44,
4661; (f) Shi, L.; Zhang, G.; Pan, F. Tetrahedron 2008, 64, 2572; (g) Mueller, R.;
Oftring, A. Anionic Surfactants as Catalysts for Complete Acylation of Polyols;
BASF: Germany, 1994. p 4.
acyl donor reagent and to the regioselective 6-O-silylation of ald-
ohexopyranosides using TBDMSCl as the silyl donor reagent (Table
3, entry 2). In the case of benzoylation of sugars under neat condi-
tion the use of the acid chloride (BzCl), being a liquid, as the acyl
donor reagent was proved more convenient compared to the solid
benzoic anhydride, the alternative reagent for the purpose. Like-
wise, TBDMSCl being a solid, the reaction was carried out in a sol-
vent and CH2Cl2 (in place of the conventional solvents such as
pyridine and DMF) was found to serve the purpose well. DABCO
is also a highly efficient promoter of regioselective 6-O-tritylation
of hexosides as reported earlier (Table 3, entry 3).13d
In conclusion, a simple and convenient method has been devel-
oped for the acetylation of a variety of carbohydrates and their
derivatives under solvent-free conditions. The method is highly
efficient and yields the desired product in high yields under mild
reaction conditions within short reaction times. The method is
characterized by its ease of operation, and the use of a relatively
less-toxic, easily available and inexpensive catalyst. Perbenzoyla-
tion of sugars, regioselective tritylation/silylation of hexosides fol-
lowed by, if desired, global acetylation of the remaining hydroxyl
groups on them in the same pot are some of the other reactions
possible in high overall yield using DABCO as a convenient
promoter.
11. Baker, R. H.; Bordwell, F. G. In Organic Synthesis Collective; Wiley: NewYork,
1955; vol. 3, P 141.
12. (a) Bartoli, G.; Dalpozzo, R.; De Nino, A.; Maiuolo, L.; Nardi, M.; Procopio, A.;
Tagarelli, A. Green Chem. 2004, 6, 191; (b) Ke, W.; Whitfield, D. M. Carbohydr.
Res. 2004, 339, 2841; (c) Lee, J.-C.; Tai, C.-A.; Hung, S.-C. Tetrahedron Lett. 2002,
43, 851; (d) Tai, C.-A.; Kulkarni, S. S.; Hung, S.-C. J. Org. Chem. 2003, 68, 8719;
(e) Karimi, B.; Maleki J. Org. Chem. 2003, 68, 4951; (f) Orita, A.; Tanahashi, C.;
Kakuda, A.; Otera, J. J. Org. Chem. 2001, 66, 8926; (g) Mohammadpoor-Baltork,
I.; Aliyan, H.; Khosrapour, A. R. Tetrahedron 2001, 57, 5851; (h) Chen, C.-T.; Kuo,
J.-H.; Li, C.-H.; Barhate, N. B.; Hon, S.-W.; Li, T.-W.; Chao, S.-D.; Liu, C.-C.; Li, Y.-
C.; Chang, I.-H.; Lin, J.-S.; Liu, C.-J.; Chou, Y.-C. Org. Lett. 2001, 3, 3729; (i)
Procopiou, P. A.; Baugh, S. P. D.; Flack, S. S.; Inglis, G. G. A. J. Org. Chem. 1998, 63,
2342; (j) Das, S. K.; Reddy, K. A.; Krovvidi, V. L. N. R.; Mukkanti, K. Carbohydr.
Res. 2005, 340, 1387.
13. (a) Patil, P. R.; Kartha, K. P. R. Green Chem. 2009, 11, 953; (b) Mugunthan, G.;
Kartha, K. P. R. J. Carbohydr. Chem. 2008, 27, 294; (c) Patil, P. R.; Kartha, K. P. R. J.

5846
Ratnasekhar ch et al. / Tetrahedron Letters 52 (2011) 5841–5846
Carbohydr. Chem. 2008, 27, 279; (d) Gadakh, B. K.; Patil, P. R.; Malik, S.; Kartha,
K. P. R. Synth. Commun. 2009, 39, 2430; (e) Baghernejad, B. Eur. J. Org. Chem.
2010, 1, 54.
then stirred at rt until the reaction was complete (TLC, eluent, CH2Cl2:MeOH,
9:1). Complete dissolution of the sugar occurred upon completion of the
reaction. Ac2O (1.2 mol equiv per OH group) and DABCO (1.2 mol equiv) were
then added to the reaction mixture and the stirring was continued at rt. When
the acetylation was complete (TLC, eluent, EtOAc:n-Hex, 1:3) the mixture was
diluted with CH2Cl2 and was washed with cold water in a separating funnel.
The organic layer was dried (Na2SO4), concentrated to dryness under reduced
pressure and was purified by chromatography on silica gel (eluent, EtOAc:n-
14. Typical procedure: Acetylation of methyl
a-D-glucopyranoside. DABCO
(1.0 mol equiv) was added to a suspension of the sugar (10.0 g, 51.5 mmol)
in Ac2O (1.2 mol equiv per OH group) and the mixture was stirred at rt. After
completion of the reaction (TLC, eluent, EtOAc:n-Hex, 2:3) the mixture was
poured onto crushed ice and was stirred for a few min when precipitation of
the desired methyl 2,3,4,6-tetra-O-acetyl-
a-
D-glucopyranoside took place
Hex, 1:9) to yield pure methyl 2,3,4-tri-O-acetyl-6-O-trityl-
a-D-
along with dissolution of DABCO in water (the latter indicated by TLC and
viewing the spot in an iodine chamber). The product was isolated by filtration
at the pump followed by washing with ice-cold water and drying. It was pure
enough for direct further use. Yield, 18.3 g, 98%. An analytically pure sample
was obtained by recrystallization from 95% ethanol.
It may be noted that addition of DABCO and stirring lead to warming up of the
reaction mixture. In reactions carried out on 10–20 g scale this is advantageous
in that considerable rate enhancement can be obtained in such cases. However
in reactions on a much larger scale (50–100 g and above) the addition of
DABCO should preferably be carried out portion-wise to keep the reaction
mixture from getting over heated.
glucopyranaoside. Yield, 25.5 g, 88%.
16. Horton, D.; Lauterbach, J. H. J. Org. Chem. 1969, 34, 86.
17. Das, S. K.; Roy, N. Carbohydr. Res. 1996, 296, 1079.
18. Tiwari, P.; Misra, A. K. Carbohydr. Res. 2005, 341, 339.
19. Lu, K.-C.; Hsieh, S.-Y.; Patkar, L. N.; Chen, C.-T.; Lin, C.-C. Tetrahedron 2004, 60,
8967.
20. Tsui, H.-C.; Paquette, L. A. J. Org. Chem. 1998, 63, 9968.
21. (a) Murugesan, S.; Karst, N.; Islam, T.; Wiencek, J. M.; Linhardt, R. J. Synlett
2003, 1283; (b) Forsyth, S. A.; MacFarlane, D. R.; Thomson, R. J.; von Itzstein, M.
Chem. Commun. 2002, 7, 714.
22. Bonner, W. A. J. Org. Chem 1961, 26, 908–911.
15. Typical procedure: One-pot sequential tritylation–acetylation of methyl
a
-
D
-
23. Zhao, -T. L.; Shen, L. H.; Liu, Z. W.; Jian, L. J. Mater Sci. 2009, 44, 1813.
24. Chao, S.-C.; Chen, M.-C.; Lin, S.-C.; Mong, K.-K. T. Carbohydr. Res. 2008, 343, 957.
25. Yadav, V. K.; Babu, G. K. J. Org. Chem. 2004, 69, 577.
26. Bartoszewicz, A.; Kalek, M.; Stawinski, J. Tetrahedron 2008, 64, 8843.
glucopyranoside. Methyl- -glucopyranoside (10.0 g, 51.5 mmol) was
a-D
suspended in anhydrous methylene chloride (100 ml) and DABCO
(2 mol equiv) followed by TrCl (2 mol equiv) were added. The mixture was