A novel application of tin-based alkoxide anion for deacetylation

Article abstract of DOI:10.1016/j.jorganchem.2006.12.011

A stannylene acetal, in the presence of CsF, is able to cleave both aromatic and aliphatic acetates rapidly and efficiently under room temperature. Control experiments indicate that both the stannylene acetal and CsF are required and play significant roles in the deacetylation process. Thus, it is likely that the tin-based alkoxide anion generated by a stannylene acetal and CsF is responsible for deacetylation.

Full text of DOI:10.1016/j.jorganchem.2006.12.011

Journal of Organometallic Chemistry 692 (2007) 1619–1622
www.elsevier.com/locate/jorganchem
Note
A novel application of tin-based alkoxide anion for deacetylation
*
Weiying Lin , Lingliang long, Daiwei Peng, Cancheng Guo
College of Chemistry and Chemical Engineering, Hunan University, Changsha, Hunan 410082, PR China
Received 29 September 2006; received in revised form 5 December 2006; accepted 12 December 2006
Available online 20 December 2006
Abstract
A stannylene acetal, in the presence of CsF, is able to cleave both aromatic and aliphatic acetates rapidly and efficiently under room
temperature. Control experiments indicate that both the stannylene acetal and CsF are required and play significant roles in the deacet-
ylation process. Thus, it is likely that the tin-based alkoxide anion generated by a stannylene acetal and CsF is responsible for
deacetylation.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Stannylene acetal; Cesium fluoride; Alkoxide anion; Deacetylation
1
. Introduction
of simple aromatic and aliphatic acetates (containing an
aromatic moiety for convenience of monitoring the reac-
tion progress by TLC under UV light) were treated with
2,2-dibutyl-[1,3,2]dioxastanninane 1 in the presence of
CsF (Table 1), a nucleophile that is believed to promote
dibutylstannylene acetal-based reactions [10]. 2,2-dibutyl-
[1,3,2]dioxastanninane 1 was readily prepared in situ by
treating dibutyltin oxide and 1,3-propanediol in refluxing
methanol for 3 h followed by sequential removal of meth-
anol and any remaining water as a benzene azeotrope.
The resulting 1 was used for deacetylation without further
purification. Both aromatic (substrates 2–7) and aliphatic
(substrates 8–13) acetates react rapidly with 1 and CsF in
DMF at room temperature to afford the corresponding
alcohols (2–13) in excellent yields after silica gel column
chromatography. TLC analysis indicated that the reaction
was essentially complete within 1 h. The electron withdraw-
ing and donating groups, as well as sterically crowded sub-
stituents on the aromatic rings have no apparent effect on
the deacetylation reaction.
Dibutylstannylene acetals have been broadly employed
to prepare monoprotection and further functionalization
of diols and carbohydrates [1–8]. However, we report
herein, for the first time, that a stannylene acetal, in the
presence of CsF, is able to cleave both aromatic and ali-
phatic acetates rapidly and efficiently under room temper-
ature. Control experiments indicate that both the
stannylene acetal and CsF are required and play significant
roles in the deacetylation process. Thus, it is likely that the
tin-based alkoxide anion generated by a stannylene acetal
and CsF is responsible for deacetylation.
2
. Results and discussion
We reasoned that alkoxide anions generated from dibu-
tylstannylene acetals are highly reactive, in conjunction
with our earlier work on alkylation of ecdysteroid [9], we
decided to investigate whether highly reactive dibutylstann-
ylene acetals could remove acetyl group to furnish free
alcohols under mild conditions efficiently in the presence
of a nucleophile such as CsF. To test this notion, a series
To determine whether the above deacetylation reaction
by 2,2-dibutyl-[1,3,2]dioxastanninane 1 and CsF was a rad-
ical or non-radical based mechanism, the deacetylation
reaction was conducted in the presence of 1, CsF, and a rad-
ical inhibitor, p-dinitrobenzene, we did not observe mark-
edly changes of either reaction rate or yield. This supports
*
Corresponding author. Tel./fax: +86 731 8821464.
E-mail address: weiyinglin@hnu.cn (W. Lin).
0
022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.12.011

1620
W. Lin et al. / Journal of Organometallic Chemistry 692 (2007) 1619–1622
a non-radical mechanism. Furthermore, when the acetates
were treated with dibutyltin oxide (instead of 1) and CsF
in the absence of 1,3-propanediol, or when the acetates were
treated with 2,2-dibutyl-[1,3,2]dioxastanninane 1 in the
absence of CsF, the deacetylation reaction proceeded at a
much slower rate, the deacetylation reaction barely
occurred (less than 5% product formed) after overnight. In
addition, when the acetates were treated with CsF alone,
the deacetylation reaction did not occur. These control
experiments indicate that both 1 and CsF are required and
play significant roles in the deacetylation process. A plausi-
ble mechanism for the deacetylation by 2,2-dibutyl-
Table 1
Deacetylation of aromatic and aliphatic acetates with 2,2-dibutyl-[1,3,2]dioxastanninane 1 and CsF at room temperature
O
Bu
Sn
Bu
O
1
R
OAc
R
OH
-13
CsF, rt
2
Acetate
Reaction time (h)
1
Isolated yield (%)
Product
Product no.
2
OAc
85
84
90
92
98
85
OH
OAc
1
OH
3
4
5
6
7
OMe
OAc
OMe
OH
0
1
0
0
.5
O N
OAc
O N
2
OH
2
OAc
OH
.5
.5
AcO
O
O
HO
O
O
OAc
OH
0
0
.5
.5
83
84
8
9
MeO
MeO
OAc
OH
OAc
OH
O
O
1
0
0
1
83
85
92
95
O
O
10
11
12
13
OAc
OH
.5
.5
OAc
OH
OAc
OH

W. Lin et al. / Journal of Organometallic Chemistry 692 (2007) 1619–1622
1621
O
Cs
O
O
OH
OH
O
R
Bu
2
SnO
Bu
Bu
O Cs
Sn
Bu
Bu
O
O
Cs
Sn
O
OAc
R
Sn
Cs+F-
O
+
Bu
Bu
R
O Cs
O
O
F
2
OSnBu F
F
2
OSnBu F
Scheme 1.
1
[
1,3,2]dioxastanninane 1 and CsF is outlined in Scheme 1.
Compound 3: H NMR (300 MHz, CDCl , TMS): d
3
Dibutyltin oxide initially condenses with 1,3-propanediol
to give 1. The added nucleophile, fluoride is believed to pro-
mote dibutylstannylene acetal-based reactions by attacking
the tin atom of 1 to form a pentacoordinated intermediate,
which equilibrates a highly reactive alkoxide anion [10].
Nucleophilic attack by the alkoxide anion on the electro-
philic carbon of acetates should then remove the acetyl
group to furnish the free hydroxyl-bearing products.
7.24 (d, 2H), 6.94 (d, 2H), 4.82 (s, 1H), 2.48 (s, 3H); MS
+
(EI) m/z 108 (M ).
1
Compound 4: H NMR (300 MHz, CD OD, TMS): d
3
6.85–6.89 (m, 1H), 6.74–6.80 (m, 3H), 3.81 (s, 3H); MS
+
(EI) m/z 124 (M ).
1
Compound 5: H NMR (300 MHz, CD OD, TMS): d
3
8.06–8.11 (m, 2H), 6.83–6.88 (m, 2H); HRMS calc. for
+
C H NO (M+H) , 140.0348; found, 140.0354.
6
6
3
1
Compound 6: H NMR (300 MHz, CDCl , TMS): d
3
3
. Conclusions
8.00–7.88 (m, 3H), 7.65–7.58 (m, 2H), 7.36–7.30 (m, 2H),
+
5
.32 (s, 1H); HRMS calc. for C H O (M ), 144.0575;
10 8
In summary, in conjunction with CsF, a stannylene ace-
tal 1, has been shown able to deacetylate rapidly (less than
h) and efficiently (over 80%) both aromatic and aliphatic
found,144.0577.
Compound 7: H NMR (300 MHz, CD OD, TMS): d
7.58 (d, 1H), 6.83 (d, 1H), 6.69 (d, 1H), 6.09 (s, 1H) 2.42
(s, 3H); HRMS calc. for C H O (M+H) , 177.0552;
found, 177.0554.
Compound 8: H NMR (300 MHz, CDCl , TMS): d
7.47 (d, 2H), 7.09 (d, 2H), 4.80 (s, 2H), 4.00 (s, 3H), 2.00
(s, 1H); HRMS calc. for C H O (M ), 138.0681; found,
138.0683.
Compound 9: H NMR (300 MHz, CDCl , TMS): d
7.46–7.59 (m, 5H), 5.08 (t, 1H), 2.22 (s, 1H), 1.69 (d,
1
3
1
+
acetates under very mild conditions (room temperature).
Control experiments indicate that both the stannylene ace-
tal and CsF are required and play significant roles in the
deacetylation process. The deacetylation reaction likely
proceeds by a non-radical transesterification mechanism
via a highly reactive fluoride-generated tin-based alkoxide
anion. This novel application of tin-based alkoxide anion
for deacetylation should open a new avenue for the further
developments of tin chemistry.
1
0
9
3
1
3
+
8
10
2
1
3
+
3H); MS (FAB) m/z 105 (MÀH O+H) .
2
1
Compound 10: H NMR (300 MHz, CDCl , TMS): d
3
4
. Experimental
7.05 (s, 1H), 6.98 (d, 2H), 6.14 (s, 2H), 4.75 (s, 2H), 2.20
+
(
s, 1H); HRMS calc. for C H O (M ), 152.0473; found,
8
8
3
4
.1. Typical experimental procedure
152.0473.
1
Compound 11: H NMR (300 MHz, CDCl , TMS): d
3
A suspension of dibutyltin oxide (200 mg, 0.803 mmol)
7.25–7.34 (m, 2H), 7.21–7.25 (m, 3H), 3.84 (t, 2H), 2.86
+
and 1,3-propanediol (47 mg, 0.617 mmol) in anhydrous
methanol (12 ml) was heated to reflux for 3 h under argon.
After the solvent was removed under reduced pressure, the
residue was subsequently azeotroped with anhydrous ben-
zene. To the resulting 2,2-dibutyl-[1,3,2]dioxastanninane 1,
(t, 2H), 2.05 (s, 1H); HRMS calc. for C H O(M ),
8
10
122.0732; found, 122.0749.
1
Compound 12: H NMR (300 MHz, CD OD, TMS): d
3
7.29–7.21 (m, 2H), 7.21–7.11 (m, 3H), 3.59 (t, 2H), 2.70
(t, 2H), 2.56 (s, 1H), 1.81–1.91 (m, 2H); MS (EI) m/z 136
+
CsF (94 mg, 0.617 mmol), aromatic or aliphatic acetates
˚
(M ).
1
(
0.474 mmol), 3 A molecular sieves (100 mg), and anhy-
Compound 13: H NMR (300 MHz, CDCl , TMS): d
3
drous DMF (2 ml) were added. The reaction mixture was
stirred at room temperature for 0.5–1 h, and then the reac-
tion was quenched by addition of brine. After extraction
three times with ethyl acetate, the combined organic phases
were dried over Na SO , filtered through a glass funnel and
7.29–7.19 (m, 2H), 7.19–7.12 (m, 3H), 3.58 (t, 2H), 2.63
(t, 2H), 1.98 (s, 1H), 1.53–1.74 (m, 4H); MS (EI) m/z 150
+
(M ).
Acknowledgments
2
4
concentrated. Purification by flash column chromatogra-
phy (methylene chloride/methanol: 1/20) furnished the
Funding was partially provided by the Hunan Univer-
sity ‘‘985 Project’’ and research funds. The preliminary
work was performed in the lab of Dr. Lawrence of Albert
Einstein College of Medicine.
alcohol (2–13).
1
Compound 2: H NMR (300 MHz, CD OD, TMS): d
3
+
7
.1–7.18 (m, 2H), 6.75–6.82 (m, 3H); MS (EI) m/z 94 (M ).

1
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[5] S. David, Carbohydr. Res. 331 (2001) 327.
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