Highly efficient deacetylation by use of the neutral organotin catalyst [tBu2SnOH(Cl)]2

Article abstract of DOI:10.1002/1521-3765(20010803)7:15<3321::AID-CHEM3321>3.0.CO;2-H

Deprotection of acetyl esters is effected cleanly by the neutral organotin catalyst, [tBu₂SnOH(Cl)]₂. The mildness of the reaction gives rise to great synthetic versatility and in the process a variety of functional groups are tolerated. Differentiations between primary, secondary, and tertiary alcohols and between acetyl ester and other esters are feasible. No racemization occurs with chiral acetyl esters. Exclusive deprotection of primary acetyl esters in carbohydrates and nucleosides is observed. The crude product thus obtained can be used for further reactions without purification.

Full text of DOI:10.1002/1521-3765(20010803)7:15<3321::AID-CHEM3321>3.0.CO;2-H

FULL PAPER
Highly Efficient Deacetylation by Use of the Neutral
Organotin Catalyst [tBu2SnOH(Cl)]2
Akihiro Orita, Yuuki Hamada, Takehiko Nakano, Shinji Toyoshima, and Junzo Otera*[a]
Abstract: Deprotection of acetyl esters is effected cleanly by the neutral organotin
catalyst, [tBu2SnOH(Cl)]2. The mildness of the reaction gives rise to great synthetic
versatility and in the process a variety of functional groups are tolerated. Differ-
Keywords: acidity ´ catalysts ´ or-
entiations between primary, secondary, and tertiary alcohols and between acetyl ester
ganometallic compounds ´ protect-
and other esters are feasible. No racemization occurs with chiral acetyl esters.
ing groups ´ tin
Exclusive deprotection of primary acetyl esters in carbohydrates and nucleosides is
observed. The crude product thus obtained can be used for further reactions without
purification.
neutral counterpart is more active than the cationic species.
We report herein the mild and efficient deacetylation of acetyl
esters under the catalysis of the neutral organotin dimer.[6]
Introduction
The acetyl ester plays an important role for protection of the
hydroxyl group in organic synthesis.[1] Consequently, numer-
ous methodologies have so far been put forth for the
acetylation of alcohols. In striking contrast, the deprotection
of the acetyl esters is much less studied despite its practical
significance in synthetic processes. It should be carried out
under mild conditions to suppress racemization as well as
decomposition of coexisting functions. Alkaline hydrolysis is
most commonly employed, yet a number of functional groups
are not tolerated in this procedure. Transesterification serves
considerably well to this end.[2] However, this protocol also
requires the use of acidic or basic catalysts in most cases. Thus,
if the transesterification is feasible under milder conditions, it
would be of great synthetic promise.
Previously, we disclosed that 1,3-disubstituted tetraalkyl-
distannoxane catalysts effected smooth transesterification
simply by heating the reaction mixture of the esters in
alcohol.[3] The reaction proceeds under nearly neutral con-
ditions thus allowing various acid- and base-sensitive func-
tions to survive. The catalytic activity of the distannoxane
originates from a template effect induced by unique dimeric
formulation.[4] In this context, we expected the high efficiency
for cationic organotin hydroxide dimers that we had encoun-
tered recently.[5] Surprisingly, however, we have found that a
Results and Discussion
A variety of organotin clusters shown below were screened in
this study. Dinuclear clusters 1 ± 4 have a hydroxy bridge in
common but are different in the bonding mode of the anionic
ligands. Both 1[7] and 2[5] are neutral due to the covalent
bonding of the chlorine atom and nitrate group although the
tin atoms in the former is five-coordinate while six-coordinate
in the latter due to chelation by the nitrate group. The triflate
3[5] is neutral with six-coordinate tin atoms in the solid state
although it does undergo dissociation into a cationic species
with five-coordinate tin in solution. The tert-butyl derivative
4[5] has a cationic formulation both in the solid state and in
solution. Tetranuclear distannoxane 5[4, 8] is non-ionic whereas
Sn12 cluster 6[9] has a dicationic formulation.
The catalytic activity of various organotin compounds
together with conventional Lewis acids was assessed for
deprotection of 2-phenylethyl acetate (7) with methanol (see
Table 1), the results of which are summarized in Table 1.
Notably, 1 exhibited a greater activity than the others. A
quantitative yield of the alcohol was obtained after 3.5 h with
5 mol% of 1 (entry 1) while distannoxane 5 afforded only a
6% yield under the same reaction conditions (entry 2). It was
necessary to keep the reaction mixture under refluxing
temperature for 9 h in order to achieve a quantitative yield
with this catalyst (entry 3). The neutral mono-nuclear com-
pounds Bu2SnCl2, BuSnCl3, and Bu2Sn(OAc)2 were less active
(29%, 21% and 22% yields, respectively, after 24 h: en-
[a] Prof. Dr. J. Otera, Dr. A. Orita, Y. Hamada, T. Nakano, S. Toyoshima
Department of Applied Chemistry
Okayama University of Science
Ridai-cho, Okayama 700-0005 (Japan)
Fax : (‡81)-86-256-4292
E-mail: otera@high.ous.ac.jp
Chem. Eur. J. 2001, 7, No. 15
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3321

J. Otera et al.
FULL PAPER
Table 1. Screening of catalysts for deacetylation of 2-phenylethyl acetate.[a]
H
H
O
tBu
tBu
Sn
tBu
Sn
tBu
Sn
O
O
O
O
O
catalyst
OH
+
Cl
Sn Cl
tBu
OAc
AcOMe
O
N
N
O
Ph
Ph
MeOH
O
H
O
H
7
tBu
tBu
tBu
Catalyst
Reaction
time [h]
Yield [%][b]
Starting
Material [%][b,c]
1
2
2+
H
1
2
3
4
5
6
7
8
9
10
11[e]
12
13
14
15
16
17[e]
18
19
20
21[e]
22
23[e]
24[e]
25[e]
26[e]
1
5
5
3.5
3.5
9[d]
24
24
24
24
6.5[d]
24
97
6
2
85
3
R
R
H
R
R
O
TfO
H2O
OH2
OTf
O
Sn
Sn
R
2 2TfO-
H2O Sn
R
Sn OH
R
96
29
21
22
82
91
10
0
O
H
O
H
R
Bu2SnCl2
BuSnCl3
Bu2Sn(OAc)2
2
62
3: R = Bu
4: R = tBu
72
Cl
Sn
Bu
Bu
2
Bu
Bu
Bu2SnO
(Bu3Sn)2O
(Me3SnOH)2
3
4
4
85
97
89
52
63
O
Sn
Cl
[(BuSn)12O14(OH)6]2+2Cl-
24
Bu
Bu
3.5
3.5
3.5
7.5[d]
24
3.5
3.5
24
3.5
24
3.5
3.5
3.5
24
0
O
Sn
O
Sn
Cl
29
29
98
3
40
53
95
54
91
0
46
67
94
58
2
6
Bu
Bu
5
6
92
57
41
2
40
1
92
50
28
0
Sc(OTf)3
Sc(OTf)3
Sc(OTf)3
Bi(OTf)3
Bi(OTf)3
KOTf
TMSOTf
TMSOTf
TMSOTf
BF3 ´ OEt2
TfOH
tries 4 ± 6). The dimeric nitrate 2 was also found to be less
active than 1 (entries 7 and 8), probably because the bidentate
nitrate ligand retarded the interaction between the substrate
and the tin center. Other neutral di- or polynuclear organotin
oxides and hydroxide also failed to give satisfactory yields
under the same conditions (entries 9 ± 11).[10] We had sup-
posed that the cationic triflates, 3 and 4, are more active than 1
because of their increased acidity. To our surprise, however,
these triflates were found to be much less active (entries 12 ±
14), and, moreover, the Sn12 dication 6 exhibited virtually no
activity as well (entry 15); this is indicative of a mechanism for
which the Lewis acidity is not necessarily of primary
importance. Consistent with these results, even stronger
Lewis acids were not as effective; various metal triflates
failed to afford quantitative yields after 3.5 h (entries 16, 17,
19, 21-23) and, thus, a prolonged reaction time or higher
catalyst loading was required for satisfactory yields (en-
tries 18, 20 and 24).[11] Both BF3 ´ OEt2 and TfOH were
virtually inactive (entries 25 and 26). Apparently, 1 is unique
because no such high catalytic activity is attained with other
organotin derivatives as well as other Lewis acid compounds
with polynuclear structures or stronger acidity.
24
24
33
[a] Reaction conditions: catalyst (5.0 mol%); 2-phenylethyl acetate
(1.0 mmol); methanol (5.0 mL), 308C. [b] Determined by GC. [c] Starting
material recovered. [d] Under reflux. [e] Catalyst concentration:
10.0 mol%.
Table 2. Deacetylation of 7 catalyzed by 1 in various alcohols and co-
solvents.[a]
Alcohol
Co-solvent Reaction Yield [%][b] Starting
time [h]
Material [%][b,c]
1
2
3
4
5
6
7
8
9
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
none
THF
Et2O
19[d]
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5[e]
20
93
92
95
97
93
93
69
47
62
96
88
73
0
5
6
2
2
5
DME
hexane
toluene
CH3CN
acetone
H2O
6
The deacetylation can be run in the presence of co-solvent
(Table 2). A variety of solvents are employable (entries 2 ± 6),
yet polar ones such as CH3CN, acetone, and water suppressed
the reaction (entries 7 ± 9). Ethanol can be used as well
instead of methanol although the reactivity is somewhat lower
(entry 10). The yield was decreased with allyl and isopropyl
alcohols and no reaction was observed with 2,2,2-trihalo
ethanols (entries 11 ± 14).
29
46
33
0
12
0
10 EtOH
11 allyl alcohol
12 (CH3)2CHOH none
13 CF3CH2OH
14 CCl3CH2OH
none
none
24
24
72
72
none
none
94
94
0
[a] Reaction conditions: 1 (5.0 mol%); acetyl ester (1.0 mmol); alcohol
(5.0 mL); co-solvent (5.0 mL); 308C. [b] Determined by GC. [c] Starting
material recovered. [d] Catalyst concentration: 1.0 mol%. [e] MeOH
(10 mL) and H2O (100 mL) were added.
Then, we investigated deacetylation of various acetyl
groups under catalysis of 1 (Table 3). The acetyl groups from
primary alcohols were deprotected smoothly (entries 1 ± 3).
The catalyst concentration could be reduced to a 1 mol%
level though a prolonged reaction time was required (entry 1).
As expected, acid-sensitive substrates were converted to the
parent alcohols without decomposition (entries 4 ± 10). Nota-
bly geranyl acetate 10 did not undergo smooth deacetylation
under standard conditions (entry 4); however, the use of THF
as a co-solvent at 408C successfully effected the deacetylation
(entry 5). A unique chemoselectivity was exemplified by
selective deacetylation of a substrate with an ester group, as
for example the methyl ester group stayed intact (entry 11).
However, this outcome involved transesterification of the
original methyl ester with solvent methanol as is evident from
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Chem. Eur. J. 2001, 7, No. 15

Deacetylation
3321±3327
the result of Equation (1), where the ethyl ester was partially
converted to the methyl ester under the same conditions.
acetate 23 was successfully deprotected (entry 24). Finally,
phenol was smoothly recovered from phenyl acetate (24)
(entry 25).
1 (5 mol %)
With these results at hand, we conducted competition
reactions which led to a variety of synthetically useful
differentiations (Scheme 1). Acetyl groups from primary
alcohols were preferentially or exclusively deprotected in
the presence of a secondary or tertiary alcohol derivative. The
high selectivity for an acetyl group from a secondary alcohol
was also attained in competition with a tertiary alcohol
counterpart. In addition, phenyl acetate was predominantly
deprotected over 2-phenylethyl acetate.
EtOOC(CH2)11OH
21 %
EtOOC(CH2)11OAc
+
MeOOC(CH2)11OH
60 %
(1)
MeOH/THF,
0 °C, 20 h
Acetyl groups from secondary alcohols were less reactive
and higher reaction temperatures were needed for quantita-
tive yields (entries 12 ± 20). When the acetyl ester of 8-penta-
decanol (19) was subjected to the reaction, only a 32% yield
of the alcohol was recovered even at 508C (entry 16). The
refluxing conditions increased the yield to some degree but
the concomitant elimination was also accelerated (entry 17).
However, the yield was dramatically improved by adding a
trace amount of water (entry 18). Acetyl groups from the
tertiary alcohols 21 and 22 were resistant towards this
reaction, and elimination occurred under more harsh con-
ditions (entries 21 ± 23). However, a tertiary propargylic
OH
OAc
Ph
Ph
a
96% (3%)
94:6
Ph
OAc
Ph
OH
6% (93%)
C8H17OH
88% (5%)
OH
Table 3. Deacetylation catalyzed by 1.[a]
C8H17OAc
OAc
Yield [%][b]
b
Substrate
Reation conditions [8C/h]
97:3
1
2
3
4
5
PhCH2CH2OAc (7)
PhCH2OAc (8)
C8H17OAc (9)
30/19[c]
30/4.5
30/6
30/24
40/24[e]
93
H7C3
C4H9
H7C3
C4H9
93[d]
93
3% (94%)
geranyl acetate (10)
86
97
OH
OAc
OAc
Ph
Ph
Ph
Ph
c
98% (2%)
OH
OAc
6
30/24
82
100:0
11
O
TBSO
TBSO
THPO
O
OAc
4
7
8
9
30/4
93
92
91
0% (99%)
12
OAc
7
30/5
13
OAc
7
H13C6
OH
30/9[c]
H13C6
Ph
OAc
OAc
14
87% (11%)
OH
d
98:2
OAc
15
Ph
10
11
30/6
97
O
2% (98%)
OH
MeOOC
OAc
11
30/16.5
100
16
OAc
OAc
12
13
14
15
16
17
18
PhCH(Me)OAc (17)
C6H13CH(Me)OAc (18)
30/24
30/24
50/24
30/24
50/24
reflux/24
reflux/48[f]
50
38
91
12
32
72
97
e
77% (15%)
OH
92:8
(C7H15)2CHOAc (19)
Ph
Ph
7% (83%)
Scheme 1. Competitive deacetylation of acetyl esters (0.5 mmol each): The
yield was determined by GC. The percentage of unreacted starting
materials is given in parentheses; a) 1 (0.025 mmol), MeOH (5 mL), THF
(5 mL), 08C, 30 h; b) 1 (0.025 mmol), MeOH (5 mL), 308C, 5 h; c) 1
(0.025 mmol), MeOH (5 mL), 308C, 4.5 h; d) 1 (0.05 mmol), MeOH
(2.5 mL), THF (2.5 mL), 508C, 48 h; e) 1 (0.05 mmol), MeOH (2.5 mL),
CH3CN (2.5 mL), 08C, 1 h.
OAc
19
30/24
25
20
20
21
22
23
reflux/12
reflux/24
50/24
95
22
3
PhCH2C(Me)2OAc (21)
C9H19C(Me)2OAc (22)
reflux/24
21
The applicability of the present protocol to other esters was
also investigated (Table 4). The propionate 25 and acrylate 26
underwent deprotection to some extent while the isobutyrate
27, pivalate 28, and benzoate 29 were virtually inert. Accord-
ingly, the acetyl group could be discriminated from these
esters (Scheme 2). The acetyl groups from the primary alcohol
were deprotected in the presence of 2-phenylethyl pivalate
which survived completely. The corresponding benzoate
24
reflux/24[g]
86
OAc
23
25
phenyl acetate (24)
0/0.5
92
[a] Reaction conditions: 1 (5.0 mol%); acetyl ester (1.0 mmol); MeOH
(5.0 mL). [b] Determined by GC. [c] Catalyst concentration: 1.0 mol%.
[d] Isolated yield. [e] THF (5 mL) was added. [f] H2O (5 mL) was added,
and 1 (10 mol%) was used. [g] Catalyst concentration: 10 mol%.
Chem. Eur. J. 2001, 7, No. 15
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J. Otera et al.
FULL PAPER
Table 4. Deprotection of various 2-phenylethyl esters.[a]
Table 5. Selective deprotection of the primary acetyl ester in various
carbohydrates and nucleosides.[a]
1
OH
OCOR
+
RCOOMe
Substrate
Reaction Yield Product[c]
[8C/h]
Ph
Ph
MeOH
[%][b]
R
Time [h]
Yield [%][b]
OAc
1
2
3
4
5
C2H5 (25)
3.5
16
24
24
24
65
78
16
0
O
OAc
31
OAc
1
2
30/4
88
ˆ
CH2 CH (26)
AcO
AcO
(CH3)2CH (27)
(CH3)3C (28)
C6H5 (29)
OAc
OAc
O
15
0/24
81
96
OAc
32
[a] Reaction conditions: 1 (5.0 mol%); 2-phenylethyl ester (1.0 mmol);
methanol (5.0 mL); 308C. [b] Determined by GC.
OAc
O
O
O
33
3
4
30/24[d]
C8H17OH
(93 %)
C8H17OAc
a
b
O
Ph(CH2)2OCOtBu
Ph(CH2)2OCOtBu (100 %)
O
AcO
OAc
O
PhCH(CH3)OAc
PhCH(CH3)OH (91 %)
Ph(CH2)2OCOtBu (98 %)
34
0/24
55
O
Ph(CH2)2OCOtBu
O
C8H17OH
Ph(CH2)2OCOPh (84 %)
Ph(CH2)2OH (5 %)
(94 %)
OAc
O
C8H17OAc
c
OAc
35
5
6
7
20/7
82
88
44
Ph(CH2)2OCOPh
AcO
AcO
OMe
OAc
Scheme 2. Discriminative deacetylation of primary acetyl ester: The yield
was determined by GC; a) 1 (0.05 mmol), MeOH, 308C, 6 h; b) 1
(0.05 mmol), MeOH, reflux, 24 h; c) 1 (0.05 mmol), MeOH, 308C, 24 h.
OAc
O
0/20[d]
0/24
OAc
36
AcO
OMe
OAc
OMe
slightly suffered deprotection in competition with octyl
acetate.[12]
The mildness of the present protocol was also exemplified
by the deacetylation of chiral acetyl esters (S)-17 and (S)-30 of
secondary alcohols and amino alcohols. No racemization was
observed in the product alcohols (Scheme 3).
O
37
OAc
AcO
OAc
AcO
AcO
HO
AcO
44
OAc
OAc
O
38
O
8
9
0/18
30/3
47
86
H
H
O
O
O
O
CCl3
CCl3
OAc
OH
OAc
a
c
b
OAc
SPh
Ph
Ph
Ph
100% ee
O
OAc
(0.5 mmol)
(S)-17
90%
39
AcO
AcO
OAc
OAc
OH
OAc
OAc
d
SPh
O
OAc
Ph
NHAc
92%
10
11
30/4
91
85
40
Ph
100% ee
NHAc
Ph
NHAc
(0.5 mmol)
(S)-30
OAc
OAc
O
Scheme 3. Deacetylation of chiral acetyl esters: a) 1 (0.025 mmol), MeOH
(2.5 mL), reflux, 24 h; b) 1) Ac2O/pyridine; 2) HPLC analysis (Daicel
chiral OD column, iPrOH/hexanes 10%, flow rate 1.0 mLmin 1); c) 1
(0.025 mmol), MeOH (2.5 mL), THF (2.5 mL), 308C, 5.5 h; d) 1) Ac2O/
pyridine; 2) HPLC analysis (Daicel chiral AD column, iPrOH/Hex 10%,
flow rate 1.0 mLmin 1).
30/2[d]
OAc
41
SPh
AcO
AcO
AcO
O
HN
12
13
30/24[d]
89
77
O
O
N
42
One of the most crucial demands for the acetyl group
protection lies in the carbohydrate chemistry.[13] Table 5 shows
the usefulness of our method for selective cleavage of the
primary acetyl ester. a-d-Glucose pentaacetate 31 underwent
deprotection exclusively at the 6-position (entry 1). This is
quite unique in that only the primary acetyl ester could be
cleaved leaving the secondary acetyl groups intact.[14] More-
over, the anomeric acetyl group is usually cleaved in the
presence of secondary acetyl groups,[15] and no reaction took
place at the anomeric position in the present protocol. It
AcO OAc
NHAc
NH2
N
N
N
0/24
O
O
N
AcO
O
O
HO
43
45
AcO OAc
AcO OAc
[a] Reaction conditions: 1 (5.0 mol%); acetyl ester (1.0 mmol); MeOH
(5.0 mL); THF (5.0 mL). [b] Isolated yield of the product with the primary
hydroxyl group. [d] Without THF.
3324
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Chem. Eur. J. 2001, 7, No. 15

Deacetylation
3321±3327
should be noted, however, that no clean outcome was
obtained with b-d-glucose pentaacetate; this is probably due
to the interaction between the acetyl groups at the anomeric
center and 6-positions. Tri-O-acetyl-d-glucal 32 was some-
what labile under the same conditions but in this case a
satisfactory yield was attained by lowering the reaction
temperature to 08C (entry 2). The acetonide in 33 was
completely inert (entry 3), yet a d-xylofuranose derivative
34 gave rise to a lower yield (entry 4). The substitution of the
anomeric acetyl group of a-d-glucose or mannose pentaace-
tate with methoxy group 35 and 36 showed no influence
(entries 5 and 6). Notably, the corresponding b-methoxy
derivative 37, in contrast to the pentaacetate, was deprotected,
though the yield was modest, probably because of suppression
of the acetyl transfer (entry 7). The unique selectivity is
highlighted in entry 8 where solely the primary acetyl ester is
cleaved. The problem at the anomeric position was com-
pletely overcome by use of chemically stable thiosugars. Thus,
the 1-phenylthio derivatives of glucose, galactose, and man-
nose 39 ± 41 underwent smooth deprotection of the primary
acetyl ester even for the b-isomers (entries 9 ± 11). No
epimerization was detected in all cases. Finally, it was revealed
that nucleosides could be successfully employed resulting in
exclusive deprotection of the primary acetyl ester for example
in tri-O-acetyluridine 42 (entry 12). With tetraacetylcytidine
43, both the primary and N-acetyl groups were cleaved
leaving the secondary ones intact (entry 13).
Since the above deacetylation is so clean that the product
could be used for further reaction without purification. Such
advantage was exemplified in two cases. The first example is
the facile preparation of cytidine with two different protective
groups in a selective manner (Scheme 4). Tetraacetylcytidine
43 was deacetylated as already described and the solvents
were evaporated after filtration through a thin pad of silica
gel. Treatment of the residue directly with pivaloyl chloride in
pyridine afforded cytidine with primary and N-pivaloyl
groups together with the secondary acetyl groups in 76%
overall yield.
BzO
BzO
HO
O
BzO
BzO
OBz
O
46
O
OAc
a
O
OBz
+
OBz
AcO
OAc
OAc
O
Br
OAc
OBz
AcO
OAc
OAc
89 % based on the bromide
BzO
HO
O
O
BzO
BzO
OBz
O
O
47
BzO
O
OBz
O
a
OBz
+
O
Br
O
O
O
O
OBz
O
O
94 % based on the bromide
Scheme 5. Glycosylation using crude deacetylated donor (obtained from
1.3 mmol fully protected monosaccharide) and 1.0 mmol bromide):
a) AgOTf (1.3 mmol), tetramethylurea (2.0 mmol), 3 Š MS, CH2Cl2, RT,
18 h.
Finally, it should be noted that the simple operation has
another advantage of the present protocols. The catalyst 1 is
stable in the air and thus inert atmosphere is not necessary.
Thus, the reaction is carried out for example in the following
fashion: The methanol solution of an acetyl ester is stirred at
an ambient temperature or 308C in the presence of a catalytic
amount of 1. Upon the completion of the reaction, the solvent
is evaporated and the residue is purified by distillation or
column chromatography. The catalyst remains in the reaction
flask or on the silica gel. Thus, no aqueous workup was
required.
In conclusion, 1 has proven to be a highly efficient catalyst
for the deprotection of acetyl esters despite its virtually
neutral character. On the basis of the unique examples
disclosed in this study, the catalyst will find a wide spectrum of
synthetic applications.
NHAc
N
NH2
N
NHPiv
N
Experimental Section
N
N
N
a
b
O
O
O
AcO
HO
PivO
General methods: All reactions of deacylation were carried out in the air,
unless otherwise noted. MeOH and EtOH was distilled from the
corresponding magnesium alkoxide, and kept under molecular sieves
(4 Š MS). Allyl alcohol, (CH3)2CHOH, CF3CH2OH, and CCl3CH2OH
were used without any further removal of residual moisture. Tetrahydro-
furan (THF) and Et2O were distilled from sodium/benzophenone. Dime-
thoxyethane (DME), toluene, CH3CN, and acetone were distilled from
CaH2. NMR spectra were recorded at 258C on Varian Gemini-300, JEOL
Lambda300 and JEOL Lambda500 instruments and calibrated with
tetramethylsilane (TMS) as an internal reference. Mass spectra were
recorded on a Jeol MStation JMS-700 spectrometer. GC analysis was
performed on Shimadzu GC17A attached with CBP1 and CBP5 capillary
columns. HPLC analysis was performed on Shimadzu LC-10AS and SPD-
10A UV detector attached with Daicel chiral OD or AD column.
Elemental analyses were performed by the Perkin ± Elmer PE2400. Silica
gel (Daiso gel IR-60) was used for column chromatography. All the tin
clusters were prepared according to the literature methods: 1,[7] 2,[5] 3,[5] 4,[5]
5[4, 8] and 6.[9] Bu2SnCl2, BuSnCl3, Bu2SnO, (Bu3Sn)2O, (Me3SnOH)2,
Sc(OTf)3, KOTf, TMSOTf, BF3 ´ OEt2, and TfOH were commercially
O
O
O
AcO OAc
AcO OAc
AcO OAc
76 %
43
Scheme 4. Deacetylation of tetraacetylcytidine followed by pivalation:
a) 1 (5 mol%), MeOH/THF, 308C, 24 h; b) tBuCOCl, pyridine, RT, 24 h.
The second example is the glycosylation with the crude
deacetylated products (Scheme 5). The crude glucose and
galactose products as obtained above were, upon exposure to
tetra-O-benzoate-a-d-glucopyranosyl bromide in the pres-
ence of AgOTf,[16] efficiently converted to dissacharides 46
and 47. The respective carbohydrate units are installed by
completely different protecting groups. The catalyst utilized in
the deacetylation could be separated by a simple filtration
through a thin pad of silica gel.
[17]
[18]
available. Bu2Sn(OTf)2 and Bi(OTf)3 were prepared according to the
Chem. Eur. J. 2001, 7, No. 15
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3325

J. Otera et al.
FULL PAPER
literature methods. a-d-Glucopyranosyl bromide tetrabenzoate was com-
mercially available.
tography on silica gel to give pure 1,2,3,4-tetra-O-acetyl-a-d-glucose[29] in
88% yield. The deacetylated products obtained by treatment of 31,[29] 32,[30]
34,[31] 35,[29] 36,[32] 37,[33] and 41[34] with methanol in the presence of catalyst 1
are reported previously, and the deacetylated pyranose derived from 33 is a
commercially available.
5-Acetyl-a-chlorarose (44): 1H NMR (CDCl3, 258C, TMS): d ˆ 6.13 (d, J ˆ
3.8 Hz, 1H), 5.56 (d, J ˆ 3.1 Hz, 1H), 5.34 (s, 1H), 5.11 ± 5.06 (m, 1H), 4.93
(dd, J ˆ 3.1, 9.5 Hz, 1H), 4.68 (d, J ˆ 3.8 Hz, 1H), 4.04 ± 3.70 (m, 2H), 2.08
(s, 3H), 2.05 (s, 3H), 1.98 ± 1.85 (br, 1H); 13C NMR (CDCl3, 258C, TMS):
d ˆ 170.2, 169.3, 107.4, 105.6, 97.0, 85.3, 78.3, 73.9, 69.9, 62.4, 20.9, 20.6;
elemental analysis calcd (%) for C12H15O8Cl3: C 36.62, H 3.84; found C
36.78, H 4.05.
Phenyl 2,3,4-tri-O-acetyl-1-thio-d-glucopyranoside: 1H NMR (CDCl3,
258C, TMS): d ˆ 7.51 ± 7.46 (m, 2H), 7.37 ± 7.30 (m, 3H), 5.27 (t, J ˆ
9.5 Hz, 1H), 5.03 ± 4.95 (m, 2H), 4.76 (d, J ˆ 10.1 Hz, 1H), 3.77 ± 3.73 (m,
1H), 3.62 ± 3.54 (m, 2H), 2.20 ± 2.17 (br, 1H), 2.09 (s, 3H), 2.04 (s, 3H), 2.00
(s, 3H); 13C NMR (CDCl3, 258C, TMS): d ˆ 170.2, 169.9, 169.3, 132.7, 131.7,
129.0, 128.4, 85.6, 78.2, 73.8, 70.1, 68.4, 61.4, 20.7, 20.6, 20.5; elemental
analysis calcd (%) for C18H22O8S: C 54.26, H 5.57; found C 54.28, H 5.75.
Phenyl 2,3,4-tri-O-acetyl-1-thio-d-galactopyranoside: 1H NMR (CDCl3,
258C, TMS): d ˆ 7.46 ± 7.51 (m, 2H), 7.30 ± 7.37 (m, 3H), 5.40 (d, J ˆ 3.3 Hz,
1H), 5.28 (t, J ˆ 9.9 Hz, 1H), 5.09 (dd, J ˆ 3.3, 9.9 Hz, 1H), 4.76 (d, J ˆ
9.9 Hz, 1H), 3.86 ± 3.67 (m, 2H), 3.60 ± 3.44 (m, 1H), 2.33 ± 2.20 (br, 1H),
2.14 (s, 3H), 2.10 (s, 3H), 2.00 (s, 3H); 13C NMR (CDCl3, 258C, TMS): d ˆ
171.1, 167.0, 169.5, 132.4, 132.2, 129.0, 128.1, 86.5, 77.3, 72.0, 68.0, 67.5, 60.8,
20.8, 20.7, 20.6; elemental analysis calcd (%) for C18H22O8S: C 54.26, H 5.57;
found C 54.42, H 5.68.
Preparation of the acetyl esters: Acetyl esters 7 ± 24 were prepared by
acetylation of the corresponding alcohol using Ac2O/pyridine. The starting
alcohols to acetyl esters 7 ± 11, 17, 18, 21, 23, and 24 were commercially
available. Acetyl esters 12, 13, and 15 were prepared from mono-tert-
butyldimethylsilyl-protected butanediol[19] and heptanediol,[20] and aceto-
nide-protected propandiol,[21] respectively. Acetyl ester 14 was accessible
by acetylation of THP-protected heptanediol.[22] Acetyl ester 16 was
prepared by acetylation of methyl 12-hydroxydodecanoate[23] which was
obtained by methyl esterification of 12-hydroxyl acid utilizing trimethylsil-
yldiazomethane in MeOH. Ethyl 12-acetoxydodecanoate[24] was prepared
by acetylation of 12-hydroxyl ester which was derived from hydroxyl acid
by treatments of SOCl2 and ethanol. Acetyl esters 19 and 20 were prepared
by acetylation of pentadecan-8-ol[25] and 1,2,3,4-tetrahydronaphthol[26]
derived by the LiAlH4 reduction of 8-pentadecanone and 1-tetralone.
Acetyl esters 22 was prepared by acetylation of 2-methyl-2-undecanol[27]
which was obtained by the treatment of 2-undecanone with MeMgBr.
2-Phenylethyl esters 25 ± 29 were obtained by the reaction of 2-phenyl-
ethanol with the corresponding acid chloride, respectively, in pyridine in
the presence of dimethylaminopyridine (DMAP). Optically active acetyl
esters (S)-17 and (S)-30 were prepared by acetylation of commercially
available (S)-1-phenylethanol and (S)-2-phenylglycinol with Ac2O in
pyridine. Polyacetyl esters such as 31, 32 and 36 were commercially
available. Other acetyl esters such as 33 ± 35, 37, 38, 42, and 43 were
prepared by acetylation of the corresponding commercially available
pyranose, furanose, and nucleoside with Ac2O in pyridine. 1-Phenylthio-d-
glucopyranoside such as 39, 40, and 41 were prepared from the corre-
sponding pyranose pentaacetate according to the procedure reported
before.[28]
2,3-Diacetyluridine: 1H NMR (CDCl3, 258C, TMS): d ˆ 9.40 ± 9.30 (br,
1H), 7.78 (d, J ˆ 8.2 Hz, 1H), 6.08 (m, 1H), 5.80 (d, J ˆ 8.2 Hz, 1H), 5.55 ±
5.42 (m, 2H), 4.22 (s, 1H), 4.08 ± 3.67 (m, 2H), 3.20 ± 3.00 (br, 1H), 2.14 (s,
3H), 2.09 (s, 3H); 13C NMR (CDCl3, 258C, TMS): d ˆ 170.2, 169.9, 163.7,
150.7, 140.9, 103.1, 87.1, 83.5, 73.0, 71.2, 61.6, 20.6, 20.4; MS (FAB): m/z (%):
Deacetylation of 2-phenylethyl acetate (7) (Representative procedure):
2-Phenylethyl acetate (7; 82.1 mg, 0.5 mmol), 1 (14.3 mg, 0.025 mmol) and
methanol (5 mL) were added to a round-bottomed flask, and the mixture
was stirred at 308C for 3.5 h. After addition of AcOEt, the reaction mixture
was filtered through a thin pad of silica gel, and GC analysis showed the
formation of 2-phenylethanol in 97% yield. All the alcohols produced by
deacetylation in Table 3 are commercially available or reported before. See
the Section of preparation of acetyl esters described above.
‡
329 (14) [M‡H] , 217 (100).
2,3-Diacetylcytidine: 1H NMR ([D6]DMSO, 258C, TMS): d ˆ 7.81 (d, J ˆ
7.5 Hz, 1H), 7.30 (br, 2H), 6.01 (d, J ˆ 5.5 Hz, 1H), 5.75 (d, J ˆ 7.5 Hz, 1H),
5.33 ± 5.27 (m, 2H), 4.08 (d, J ˆ 3.1 Hz, 1H), 3.66 ± 3.54 (m, 2H), 2.07 (s,
3H), 2.00 (s, 3H); 13C NMR ([D6]DMSO, 258C, TMS): d ˆ 169.7, 169.4,
165.7, 155.0, 141.5, 94.9, 86.7, 82.5, 72.7, 70.8, 60.8, 20.5, 20.3; MS (FAB): m/z
Deacetylation of ethyl 12-acetoxydodecanoate with MeOH [Eq. (1)]:
‡
(%): 328 (65) [M‡H] , 217 (100).
Ethyl 12-acetoxydodecanoate (286.4 mg, 1.0 mmol),
1
(28.6 mg,
Deacetylation of cytidine tetraacetate (43) and the subsequent pivalation
0.05 mmol), methanol (5 mL), and THF (5 mL) were added to a round-
bottomed flask, and the mixture was stirred at 08C for 20 h. After addition
of AcOEt, the reaction mixture was filtered through a thin pad of silica gel,
and GC analysis showed the formations of ethyl and methyl 12-hydroxy-
dodecanoate in 21% and 60% yield, respectively.
(Representative procedure): Tetraacetate 43 (411 mg, 1.0 mmol),
1
(28.5 mg, 0.05 mmol), THF (5 mL), and methanol (5 mL) were added to
a round-bottomed flask, and the mixture was stirred at 308C for 24 h. After
addition of CH2Cl2, the reaction mixture was filtered through a thin pad of
silica gel, and the filtrate was concentrated to give a crude product of 2,3-di-
O-acetylcytidine. To the crude product obtained were added tBuCOCl
(4.0 mmol) and pyridine (5 mL), and the mixture was stirred at rt for 24 h.
After usual aqueous workup (AcOEt/water), the organic layer was dried
and evaporated to give a crude product of the pivalate, which was subjected
to a column chromatography on silica gel to give pure 2',3'-di-O-acetyl-5'-
O,N6-dipivaloylcytidine in 76% yield.
Competitive deacetylation of 2-phenylethyl acetate (7) and (1S)-phenyl-
ethyl acetate (17) (Representative procedure): Acetate
7 (82.1 mg,
5.0 mmol), 17 (82.1 mg, 0.5 mmol), 1 (14.3 mg, 0.025 mmol), THF (5 mL),
and methanol (5 mL) were added to a round-bottomed flask. Then, the
mixture was stirred at 08C for 30 h. After addition of AcOEt, the reaction
mixture was filtered through a thin pad of silica gel, and GC analysis
showed the formations of 2- and 1-phenylethanol in 96% and 6% yield,
respectively.
2',3'-Di-O-acetyl-5'-N6,O-dipivaloylcytidine: 1H NMR (CDCl3, 258C,
TMS): d ˆ 8.18 ± 8.10 (br, 1H), 7.91 (d, J ˆ 7.6 Hz, 1H), 7.48 (d, J ˆ 7.3 Hz,
1H), 6.25 (d, J ˆ 4.6 Hz, 1H), 5.38 (t, J ˆ 4.9 Hz, 1H), 5.33 (t, J ˆ 4.9 Hz,
1H), 4.43 (dd, J ˆ 13.1, 3.1 Hz, 2H), 4.34 (d, J ˆ 10.1 Hz, 1H), 2.12 (s, 3H),
2.11 (s, 3H), 1.29 (s, 9H), 1.26 (s, 9H); 13C NMR (CDCl3, 258C, TMS): d ˆ
178.1, 177.8, 169.6, 169.5, 162.5, 154.9, 143.5, 96.8, 87.8, 80.0, 73.9, 69.7, 62.8,
Deacetylation of (S)-1-phenylethyl acetate [(S)-17] (Representative pro-
cedure): Acetate (S)-17 (82.1 mg, 0.5 mmol), 1 (14.3 mg, 0.025 mmol) and
methanol (2.5 mL) were added to a round-bottomed flask, and the mixture
was heated at reflux for 24 h. After addition of AcOEt, the reaction
mixture was filtered through a thin pad of silica gel, and the filtrate was
concentrated. The crude product was subjected to a column chromatog-
raphy on silica gel to give pure (S)-1-phenylethanol in 90% yield. The
treatment of (S)-1-phenylethanol obtained here with Ac2O (5 mL) and
pyridine (10 mL) gave acetyl ester (S)-17, quantitatively, which showed
100% ee of optical purity on HPLC analysis (Daicel chiral OD column,
iPrOH/hexanes 10%, flow rate 1.0 mLmin 1).
‡
40.3, 38.8, 27.2, 27.0, 20.5; MS (FAB): m/z (%): 496 (90) [M‡H] , 301 (100).
Deacetylation of a-d-glucose pentaacetate (31) and the subsequent
glucosylation (Representative procedure): Pentaacetate 31 (507 mg,
1.3 mmol), 1 (37.1 mg, 0.065 mmol), THF (7 mL) and methanol (7 mL)
were added to a round-bottomed flask, and the mixture was stirred at 308C
for 4 h. After addition of AcOEt, the reaction mixture was filtered through
a thin pad of silica gel, and the filtrate was concentrated to give a crude
product of a-d-glucose tetraacetate (484 mg). To another round-bottomed
flask was added molecular sieves 3 Š (500 mg), which was heated to 1508C
under reduced pressure for 3 h. To this flask were added the crude 1,2,3,4-
tetra-O-acetyl-a-d-glucopyranoside obtained above, tetra-O-benzoate-a-
d-glucopyranosyl bromide (660 mg, 1.0 mmol) and CH2Cl2 (5 mL) followed
by tetramethylurea (0.25 mL). After the mixture had been stirred at rt for
Deacetylation of a-d-glucose pentaacetate (31) (Representative proce-
dure): Pentaacetate 31 (390 mg, 1.0 mmol), 1 (28.5 mg, 0.05 mmol), THF
(5 mL) and methanol (5 mL) were added to a round-bottomed flask, and
the mixture was stirred at 308C for 4 h. After addition of AcOEt, the
reaction mixture was filtered through a thin pad of silica gel, and the filtrate
was concentrated. The crude product was subjected to a column chroma-
3326
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Chem. Eur. J. 2001, 7, No. 15

Deacetylation
3321±3327
15 min, AgOTf (452 mg, 1.3 mmol) was added. Then, the mixture was
stirred in the dark at rt for 18 h. After addition of CH2Cl2, the reaction
mixture was filtered through a thin pad of celite. The filtrate was washed
with sat. aq. NaHCO3 (Â3) and sat. aq. NaCl (Â3), and dried over Na2SO4.
After filtration and concentration, the crude product was subjected to a
column chromatography on silica gel to give pure dissacharide in 89%
yield.
C. J. Salomon, E. G. Mata, O. A. Mascaretti, Tetrahedron Lett. 1991,
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[11] It was recently reported that Sc(OTf)3-catalyzed transesterification of
esters containing a coordinative group adjacent to an ester group in
MeOH/H2O: H. Kajiro, S. Mitamura, A. Mori, T. Hiyama, Bull. Chem.
Soc. Jpn. 1999, 72, 1553.
[12] Deacetylation in the presence of a benzoyl group: N. Kunesch, C.
Miet, J. Poisson, Tetrahedron Lett. 1987, 28, 3569; L. H. B. Baptistella,
J. F. dos Santos, K. C. Ballbio, A. J. Marsaioli, Synthesis 1989, 436; N.
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Sweers, C.-H. Wong, J. Am. Chem. Soc. 1986, 108, 6421; W. J. Hennen,
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2,3,4,6-Tetra-O-benzoyl-a-d-glucopyranosyl-(1 ! 6)-1,2,3,4-tetra-O-acetyl-
1
a-d-glucopyranoside (46): H NMR (CDCl3, 258C, TMS): d ˆ 8.03 (d, J ˆ
7.3 Hz, 2H), 7.96 (d, J ˆ 7.1 Hz, 2H), 7.90 (d, J ˆ 7.1 Hz, 2H), 7.82 (d, J ˆ
7.1 Hz, 2H), 7.58 ± 7.25 (m, 12H), 6.17 (d, J ˆ 3.7 Hz, 1H), 5.90 (t, J ˆ
9.5 Hz, 1H), 5.67 (t, J ˆ 9.5 Hz, 1H), 5.50 (dd, J ˆ 7.9, 9.5 Hz, 1H), 5.37
(t, J ˆ 9.9 Hz, 1H), 4.95 ± 4.88 (m, 3H), 4.64 (dd, J ˆ 3.1, 12.1 Hz, 1H), 4.49
(dd, J ˆ 4.7, 12.1 Hz, 1H), 4.19 ± 4.11 (m, 1H), 4.09 ± 4.02 (m, 1H), 3.95 (dd,
J ˆ 2.2, 11.5 Hz, 1H), 3.67 (dd, J ˆ 6.6, 11.5 Hz, 1H), 1.97 (s, 9H), 1.94 (s,
3H); 13C NMR (CDCl3, 258C, TMS): d ˆ 170.1, 169.5, 169.4, 168.6, 166.1,
165.7, 165.2, 165.1, 133.4, 133.2 (2C), 133.1, 129.7 (2C), 129.6 (2C), 129.5,
129.1, 128.7, 128.6, 128.4 (2C), 128.3, 128.2, 101.0, 88.7, 72.7, 72.2, 71.5, 71.2,
69.6, 69.5, 69.2, 68.5, 67.5, 62.9, 20.7, 20.6, 20.5, 20.4; elemental analysis calcd
(%) for C48H46O19: C 62.20, H 5.00; found C 61.97, H 4.92.
2,3,4,6-Tetra-O-benzoyl-a-d-glucopyranosyl-1,2:3,4-di-O-isopropylidene-
a-d-galactopyranoside (47): 1H NMR (CDCl3, 258C, TMS): d ˆ 8.05 ± 8.00
(m, 2H), 7.99 ± 7.95 (m, 2H), 7.92 ± 7.87 (m, 2H), 7.85 ± 7.81 (m, 2H), 7.58 ±
7.45 (m, 2H), 7.44 ± 7.25 (m, 10H), 5.90 (t, J ˆ 9.7 Hz, 1H), 5.67 (t, J ˆ
9.5 Hz, 1H), 5.53 (dd, J ˆ 7.9, 9.7 Hz, 1H), 5.42 (d, J ˆ 5.1 Hz, 1H), 5.04 (d,
J ˆ 7.9 Hz, 1H), 4.64 (dd, J ˆ 3.1, 12.3 Hz, 1H), 4.49 (dd, J ˆ 5.1, 11.9 Hz,
1H), 4.43 (dd, J ˆ 2.6, 8.0 Hz, 1H), 4.21 (dd, J ˆ 2.4, 5.0 Hz, 1H), 4.19 ± 4.13
(m, 1H), 4.10 (d, J ˆ 8.0 Hz, 1H), 4.02 (dd, J ˆ 3.0, 10.1 Hz, 1H), 3.92 ± 3.80
(m, 2H), 1.37 (s, 3H), 1.24 (s, 3H), 1.21 (s, 3H), 1.20 (s, 3H); 13C NMR
(CDCl3, 258C, TMS): d ˆ 166.2, 165.8, 165.2, 165.1, 133.4, 133.2, 133.0 (2C),
129.9, 129.8, 129.7 (2C), 129.6, 129.3, 128.9, 128.8, 128.5, 128.4, 128.3, 128.2,
109.2, 108.5, 101.2, 96.1, 72.9, 72.1, 71.8, 70.9, 70.5, 70.3, 69.8, 68.3, 67.5, 63.2,
25.9, 25.7, 24.8, 24.2; elemental analysis calcd (%) for C46H46O15: C 65.86, H
5.53; found C 65.84, H 5.64.
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Received: December 15, 2000 [F2940]
Chem. Eur. J. 2001, 7, No. 15
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