Chemoselective deacylation of functionalized esters catalyzed by dioxomolybdenum dichloride

Article abstract of DOI:10.1016/j.tet.2010.12.024

Among five different oxidometallic species and two Lewis acids investigated, MoO₂Cl₂ shows the best catalytic and chemoselective activity for the deacylation of esters in methanol at ambient or elevated temperature. Both high efficiency and chemoselectivity were achieved for substrates bearing different ether or ester groups. Acylated mono and disaccharides can also be selectively deacetylated in good yields, leading to useful carbohydrate templates for further synthetic manipulations.

Full text of DOI:10.1016/j.tet.2010.12.024

Tetrahedron 67 (2011) 872e876
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Chemoselective deacylation of functionalized esters catalyzed by
dioxomolybdenum dichloride
,
Cheng-Yuan Liu b, Hui-Ling Chen b, Chih-Min Ko b, Chien-Tien Chen a
*
a Department of Chemistry, National Tsing-Hua University, Hsinchu 300, Taiwan
b Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 August 2010
Received in revised form 1 December 2010
Accepted 10 December 2010
Available online 16 December 2010
Among five different oxidometallic species and two Lewis acids investigated, MoO2Cl2 shows the best
catalytic and chemoselective activity for the deacylation of esters in methanol at ambient or elevated
temperature. Both high efficiency and chemoselectivity were achieved for substrates bearing different
ether or ester groups. Acylated mono and disaccharides can also be selectively deacetylated in good
yields, leading to useful carbohydrate templates for further synthetic manipulations.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
remains to be explored. Therefore, chemoselective deacylation of
esters by milder and neutral catalysts with good functional group
The deacylations of esters, amides, and thioesters are important
transformations in organic synthesis, particularly in carbohydrate
chemistry.1 In the past decade, to aid in drug discovery and bio-
chemical research, new methodologies to achieve efficient carbo-
hydrate synthesis expand rapidly. In the meantime, improving
efficiency with minimal toxic wastes in these synthetic processes
by using milder and neutral catalytic systems remains in great
demands.
Several reliable protocols for deacylation have been well docu-
mented and somewhat standardized in the literature.2 For exam-
ple, K2CO3 in methanol,3 NaHCO3 in H2O2 solution,4 KCN in
ethanol,5 N2H4 in methanol,6 Bu2SnO under reflux conditions,7
Brønsted acids like HCl or HBF4 in methanol,8 and Sc(OTf)3 for
methyl/ethyl esters in warmed EtOH or MeOH.9 Equal or excess
amounts of Sm and I2 were also used for the deprotection of esters
and lactams.10 Recently, triphenyl phosphiteechlorine complex
was used at lower temperature to facilitate the deacylation of
amides.11 Although these reaction protocols are useful, some of
them still involve Harsher reaction conditions by exposing sub-
strates to acid, base media, or at higher temperature. Under such
circumstances, functional groups sensitive to acid or base may not
be fully compatible.
compatibility is highly desirable.
Enzymes are known to deprotect acetate functionality selec-
tively with somewhat limited substrate scope.12 Guanidine/guani-
dinium nitrate (ca. 10 equiv, 4/1) reagent can be used to deprotect
acetate in the presence of N-Troc group.13 Acetate was selectively
removed in 30-O-acetyl-N-4,50-O-dibenzoylcytidin in methanolic
15
ammonia.14 Stoichiometric uses of Lewis acids like BF3$OEt2 and
lanthanide triflate16 to facilitate the deacylation of anomeric ace-
tates were also documented. Besides, methanolysis of methox-
yacetates can be achieved by catalytic Yb(OTf)3 in methanol while
retaining other esters.17
Primary alkyl esters can be selectively unmasked by using Mg
metal in methanol.18 DBU can promote the deacylation of allylic or
primary alcohol-derived acetate without cleavage of benzoate
moiety within the same substrate.19 Accordingly, we hope to es-
tablish a single catalytic system, which involves mild reaction
conditions and exhibits high chemoselectivity.
Recently, we have been investigating the new catalytic profiles
of vanadyl and oxidometallic species. By identifying some cata-
lystesubstrate adducts by ESI-MS analysis from catalytic acylation
of alcohols, amphoteric character of some catalysts was revealed. So
far, we have examined several CeX bond forming events like ac-
ylation and phosphorylation20aec of protic nucleophiles, esterifi-
cation, and transesterification,20d,e acetal formation of diols,20f
thioglycosylation of peracetylated sugars,20g conjugate additions
by protic and C-centered nucleophiles.20h,i In particular, based on
our experiences from catalytic transesterification and acylation, we
sought to examine the feasibility of our catalytic system in che-
moselective deacylation of esters.
In total synthesis and carbohydrate chemistry, key in-
termediates often contain two or more ester moieties under similar
steric environments that need subsequent differentiation. So far,
selectively deprotecting one ester while retaining the others
* Corresponding author. Tel.: þ886 3 5715131x33363; fax: þ886 3 5711082;
e-mail address: ctchen@mx.nthu.edu.tw (C.-T. Chen).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.12.024

C.-Y. Liu et al. / Tetrahedron 67 (2011) 872e876
873
2. Results and discussion
may introduce chelating effect22 toward Lewis acids and can also be
smoothly removed at 45 ꢀC with prolonged reaction time (136 h)
under the new catalytic deacylation protocol (entry 7).
In the initial tests on the reactivity of five different oxidometallic
species and two Lewis acids (5 mol %), methanolysis of 2-phenyl-
ethyl acetate was examined in deuterated methanol. The conver-
sion for each catalytic reaction was determined by the relative
integration values of the methylene signals next to acetate and
hydroxyl group, in respective 1H NMR spectra (Table 1).
Table 2
Effects of acyl groups on the deacylation of selected substrates catalyzed by MoO2Cl2
in CD3OD
5 mol% MoO2Cl2
CD3OD
O
O
R1
R1 OD
+
R2
D3CO
R2
Yield,b
O
Table 1
Methanolysis of 2-phenylethyl acetate in CD3OD catalyzed by five different oxido-
metallic species and two Lewis acids
a
Entry
1
Substrate
T, ꢀC t, h t1/2
,
h
Product
%
5 mol%
O
O
M(O)mLn
Ph
OD
OD
OAc
+
rt
27
44
4.1
8.7
98
CD3
+
CD3OD
Ph
Ph
Ph
O
O
1a
O
1a
Ph
Ph
Cl
a
OD
OD
Temp, ꢀC
t1/2
,
2
3
rt
97
96
Entry
M(O)mLn
Time, h
h
Yield,b
%
Ph
Ph
O
O
1b
O
1
2
3
4
5
6
7
MoO2Cl2
Sc(OTf)3
VO(OTf)2
Yb(OTf)3
VOCl2
rt
rt
rt
rt
45
45
60
27
55
44
194
92
194
469
4.1
98
98
92
94
97
95
99
10.0
25.3
65.1
32.7
33.0
49.0
t
O Bu
65
290 108.3
290 185.8
1c
Bu2SnO
TiO(acac)2
O
OD
OD
4
65
75
Ph
Ph
Ph
a
The reaction time at 50% conversion.
Isolated yields of purified materials.
1d
O
b
O
Ph
It was found that MoO2Cl2 was the most effective in catalyzing the
5
6
65
45
290 204.2
69
92
Ph
Ph
deacetylationatambienttemperaturein27h(t1/2, 4.1h). Theresulting
2-phenylethanol was isolated in 98% purified yield after aqueous
workup. Sc(OTf)3 showed also good reactivity. The methanolysis (98%
yield, in 55 h) was about 2.5 times slower than that catalyzed by
MoO2Cl2. Vanadyl triflate was about six times slower in terms of the
reaction rate. The deacetylation reaction was completed in 44 h. The
reaction rate (t1/2, 65.1h)mediatedbyYb(OTf)3 is 16 timesslowerthan
that catalyzed MoO2Cl2. Conversely, the same test reaction proceeded
effective only at 45 ꢀC with prolonged reaction time (92 h) by vanadyl
chloride. Di-n-butyltin oxide (Bu2SnO) has been documented as an
efficient catalyst to trigger the NAS of functionalized esters in boiling
methanol or ethanol.21 As a comparison, the deacetylation proceeded
sluggishlyat 45ꢀC when catalyzed by Bu2SnO, reaching completion in
194 h. In addition, although TiO(acac)2 possesses excellent catalytic
efficiencyintransesterificationofmethylestersinrefluxedtoluene,20e
the performance was unsatisfactory in the test reaction at 60 ꢀC. It
took 469 h for completion with 99% conversion. By taking the t1/2
values and reaction temperature factor into account, the reaction
catalyzed by MoO2Cl2 is about 16, 16, and 96 times faster than those
catalyzed by VOCl2, Bu2SnO, and TiO(acac)2, respectively.
The possibility of performing chemoselective deprotection of es-
ters with the optimal catalyst-MoO2Cl2 was further evaluated by first
studying the rate profiles for the deacylation of a series of 2-phenyl-
ethyl esters 1aee in CD3OD. The reaction progresses for each deacy-
lation were monitored by 1H NMR spectrometry. It was found that
chloroacetyl group removal in 1b is slower than the acetyl group re-
movalin 1abyafactorof2(entries1and2inTable 2). Bytakingthet1/2
valuesandreactiontemperaturefactorintoaccount,thedeacetylation
of 1awas 211e398timesfasterthant-Boc, pivaloyl,andbenzoylgroup
removalsat65ꢀC(entries 3e5). Inviewofthe dramaticratedifference
in the methanolysis of 1aee catalyzed by MoO2Cl2, acetate could be
selectively removed without cleavage of any pivalate, benzoate, or
tert-butyl carbonate for substrates bearing multiple ester functional-
ities. The rate of deacetylation also highly depends on the steric at-
tribute of the alcohol component in the acetates. The rate for
removing primary acetate in 1a was about 28 times faster than the
rateofsecondaryacetateremovalin1f (entries1and6,Table 2),which
may be also suitable for chemoselective deacetylation in carbohy-
drates. Furthermore, N-acetylated oxazolidinone like 1g generally
O
1e
OAc
OD
O
147
136
29.7
58.8
Ph
1f
O
O
7
45
95
O
N
O
ND
1g
a
The reaction time at 50% conversion.
Isolated yields of purified materials.
b
Thioglycosides serve as important building blocks for the prepa-
ration of oligosaccharides. With extension of a handy protocol for
catalytic thioglycosylation of peracetylated sugars by MoO2Cl2,20g,23
we selected a series of acetate-containing, mono, and disaccharides
as substrates forcatalytic deacetylationbyMoO2Cl2 inMeOH(Table 3).
Per-O-acetylated glucosamine-derived thioglycosides 2aec
with three different amino-protecting groups (Ac, Bz, and Phth)
were first examined by the new deacylation protocol at 65 ꢀC. To
our delight, only the acetate groups in 2aec were selectively
transesterified by MeOH in 11e60 h with intact amino-protecting
groups at C2 substituents. The resultant triols 3aec were isolated in
94e99% yields (entries 1e3). Thioglycosides 2d and 2e derived
from 2,3,4,6-tetra-O-acetyalted galactose and glucose can be simi-
larly unmasked in 87 and 97% yields, respectively.
Notably, benzyl etheras wellas thioetherat the glycosidic linkage
is tolerant under the reaction conditions. The acetate groups in ga-
lactose-derived thioglycosides 2f and 2g can be smoothly and se-
lectively removed in 86 and 97% yields (entries 6 and 7), respectively.
Besides, thioacetates are also amenable to deacetylation by this
catalytic protocol. The thioacetate in 2h was deacetylated with
concomitant formation of the disulfide in 94% yield (entry 8). The
desired free thiol 3h can be obtained quantitatively by the treat-
ment of the disulfide with NaBH4. This free thiol 3h has been fur-
ther applied to the synthesis of disaccharide 2i by thioglycosylation
of b-D-glucose pentaacetate with 3h in the presence of catalytic
MoO2Cl2.20g The acetates in disaccharide 2i can be fully unmasked
to form 3i in 94% yield (entry 9).

874
C.-Y. Liu et al. / Tetrahedron 67 (2011) 872e876
Table 3
Deacetylation of acetate-containing, functionalized saccharides catalyzed by MoO2Cl2 in CH3OH
5 mo%
P
P
MoO2Cl2
R1 = CH3; P = OBn or NR2
XR' = OMe or STol
O
O
R1CO2
XR'
HO
XR'
MeOH, 65 oC
Entry
1
Substrate
AcO
t, h
Product
Yield,a
95
%
HO
O
O
33
AcO
HO
2a
STol
STol
STol
3a
3b
AcO
HO
NHAc
NHAc
AcO
HO
O
O
2
3
4
60
11
36
94
99
87
HO
AcO
STol 2b
HO
AcO
NHBz
NHBz
HO
AcO
O
O
AcO
HO
2c
2d
2e
2f
STol 3c
STol
NPhTh
AcO
HO
NPhTh
OAc
OH
AcO
AcO
HO
O
O
3d
STol
STol
STol
HO
OAc
OH
HO
AcO
O
O
5
6
33
69
97
86
AcO
AcO
HO
3e
3f
STol
STol
HO
OAc
OH
OBn
OBn
O
BnO
BnO
BnO
BnO
O
STol
STol
OAc
OH
OAc
OH
O
BnO
BnO
BnO
BnO
O
7
8
8
97
94
3g
2g
STol
OBn
OBn
S
AcS
BnO
O
O
BnO
3h
2h
112
BnO
BnO
BnO
BnO
OCH3
OCH3
2
AcO
AcO
HO
HO
O
O
S
S
HO
AcO
9
74
94
3i
2i
O
O
AcO
HO
BnO
BnO
BnO
BnO
BnO
BnO
OCH3
OCH3
OAc
OH
O
AcO
AcO
HO
HO
OAc
O
OH
O
O
3j
10
61
62
97
92
2j
O
O
STol
STol
STol
STol
AcO
HO
OH
AcO
OAc
OH
OH
OH
O
OAc
O
OAc
O
HO
HO
3k
AcO
AcO
O
11
2k
O
O
HO
AcO
AcO
OH
OAc
OH
a
Isolated yields of purified materials.
Other common peracylated disaccharides like 2j and 2k can also
be completely deacetylated in 61e62 h to provide 3j and 3k in 97%
and 92% yields, respectively.
temperature to ambient temperature, the trityl group at C6 was
selectively removed with intact secondary acetates albeit of with
a discrete amount of acetyl group transfer in the products (5a/5a0,
76/24, entry 1). The acetate groups at C2, C3, and C4 positions in
4b were completely removed in 66 h at 65 ꢀC in MeOH with
benzoate moiety remained intact, leading to 5b in 88% yield
(entry 3). In marked contrast, methanolysis of 4b by Sc(OTf)3
(5 mol %) led to 5b (56%) along with the fully deprotected 3d
(41%) under similar reaction conditions (entry 4).25 Treatment of
4b in methanolic NH3 at ambient temperature in 1.5 h also led to
The C6 position of galactose-based b-thioglycoside was further
modified to trityl ether or different esters to test the feasibility for
chemoselective deprotection of trityl or acetate groups in these
substrates, Table 4.
Similar to our previous observation,24 the trityl group in 4a
was cleaved along with complete deacetylation (entry 2) at 65 ꢀC
(entry 2, Table 4). Nevertheless, by lowering the reaction

C.-Y. Liu et al. / Tetrahedron 67 (2011) 872e876
875
Table 4
Chemoselective deprotection of galactose-based
b-thioglycoside by MoO2Cl2
OR
OH
O
OAc
O
OR
O
HO
AcO
AcO
AcO
HO
HO
catalyst
O
AcO
STol
AcO
STol
STol
STol
MeOH
OAc
4a: R = CPh3
4b: R = C(O)Ph
4c: R = C(O)C(CH3)3
OAc
5a
OAc
5a'
OH
5b: R = C(O)Ph
5c: R = C(O)C(CH3)3
Entry
Substrate
Catalyst
MoO2Cl2
T, ꢀC
t, h
Product
Yield,a
%
OH
O
AcO
AcO
5a
STol
STol
STol
OCPh3
AcO
AcO
OAc
OAc
91 [5a/5a0 (76:24)c]
b
O
1
rt
6
4a
STol
HO
AcO
OAc
O
5a'
OAc
OCPh3
O
OH
O
AcO
AcO
HO
HO
b
b
2
3
4
5
MoO2Cl2
MoO2Cl2
65
65
65
rt
41
66
70
95
88
4a
4b
4b
4b
3d
STol
OAc
OH
OC(O)Ph
O
OC(O)Ph
O
HO
HO
AcO
AcO
5b
STol
STol
OAc
OH
OC(O)Ph
O
AcO
AcO
b
Sc(OTf)2
5b/3d
5b/3d
56:41
61:27
75
STol
OAc
OC(O)Ph
O
AcO
AcO
NH3 in MeOH
1.5
STol
OAc
O
O
O
O
O
AcO
AcO
HO
HO
b
6
MoO2Cl2
45
168
4c
5c
O
STol
STol
OAc
OH
a
Isolated yields of purified materials.
b
c
5 mol %.
Determined by 1H NMR spectrometry.
3d (27%) resulting from both deacetylation and debenzoylation.25
The desired product 5b was isolated in only 61% (entry 5). With
the C6 hydroxyl group protected into a pivalate, 4c was com-
pletely deacetylated at 45 ꢀC in 168 h, providing 5c in 75% yield
(entry 6).
For the further application of this protocol, the important in-
termediates 3aee in carbohydrate synthesis can be readily pre-
pared by sequential peracetylation,20b thioglycosylation,20g and
deacetylation of glucose and galactose, respectively, in high yields
by the same catalyst (i.e., MoO2Cl2), Scheme 1.
OAc
OH
O
OAc
O
Y
AcO
AcO
S
O
HO
HO
OH
AcO
AcO
OA c
5 mol%
3 mol% MoO2Cl2
1.3 equiv
MoO 2Cl2
Y
Y
Y = NHAc Y = OAc
2a (92%) 2d (91%)
Y = NPhth 2e (90%)
2b (90%)
p-MeC6H4SH
90-91%
Ac2O-HOAc
rt, 2.5-6d
CH2Cl2, rt
14-20h
ref-20g
unpublished data
based on ref-20b
OAc
O
OAc
O
OH
OH
OAc
O
OAc
O
O
AcO
AcO
O
O
HO
HO
O
OAc
AcO
AcO
AcO
O
OH
HO
STol
OAc
AcO
OH
OAc
OH
OAc
OAc
90%
2j (94%)
2h (90%)
Scheme 1. Preparation of peracetylated thioglycosides by sequential peracetylation and thioglycosylation by MoO2Cl2.

876
C.-Y. Liu et al. / Tetrahedron 67 (2011) 872e876
3. Conclusion
References and notes
1. (a) Huang, K.-T.; Wu, B.-C.; Lin, C.-C.; Luo, S.-C.; Chen, C.; Wong, C.-H.; Lin, C.-C.
Carbohydr. Res. 2006, 341, 2151; (b) Schwarz, J. B.; Kuduk, S. D.; Chen, X.-T.;
Sames, D.; Glunz, P. W.; Danishefsky, S. J. J. Am. Chem. Soc. 1999, 121, 2662.
2. Wuts, P. G. M.; Greene, T. W. Greene’s Protective Groups in Organic Synthesis;
Wiley: New York, NY, 2007.
3. Plattner, J. J.; Gless, R. D.; Rapoport, H. J. Am. Chem. Soc. 1972, 94, 8613.
4. Zheng, Q. Y.; Darbie, L. G.; Cheng, X.; Murray, C. K. Tetrahedron Lett. 1995, 36,
2001.
In conclusion, we have established the relative rate profiles for
the deacetylation of esters in the presence of five different oxido-
metallic species and two commonly used Lewis acids. Chemo-
selective deacetylation was achievable for esters with varying acyl
attributes (i.e., acetyl vs t-Boc, pivaloyl, and benzoyl), sterics and/or
electronics in the leaving groups by using a catalytic amount
(1e5 mol %) of MoO2Cl2 in warmed MeOH, which was more ef-
fective than Sc(OTf)3 or methanolic NH3 catalyzed system. In
combination with our recently developed catalytic peracetyaltion,
thioglycosylation, and acetal formation of 4,6-diols,20f this new
catalytic deacetylation protocol is thus suitable for routine syn-
thesis of mono and disaccharides. Investigation toward oligosac-
charide synthesis via a sequence of these catalytic transformations
by MoO2Cl2 or VO(OTf)2 is currently underway.
5. Herzig, J.; Nudelman, A.; Gottlieb, H. E.; Fischer, B. J. Org. Chem. 1986, 51, 727.
6. Roush, W. R.; Lin, X.-F. J. Am. Chem. Soc. 1995, 117, 2236.
ꢀ
7. Perez, M. G.; Maier, M. S. Tetrahedron Lett. 1995, 36, 3311.
8. (a) Yamamoto, N.; Nishikawa, T.; Isobe, M. Synlett 1995, 505 (special issue); (b)
Pozsgay, V. J. Am. Chem. Soc. 1995, 117, 6673.
9. Remme, N.; Koschek, K.; Schneider, C. Synlett 2007, 491.
10. Yanada, R.; Negoro, N.; Bessho, K.; Yanado, K. Synlett 1995, 1261.
11. Spaggiari, A.; Blaszczak, L. C.; Prati, F. Org. Lett. 2004, 6, 3885.
12. (a) Naemura, K.; Takahashi, N.; Chikamatsu, H. Chem. Lett. 1988, 30, 1717; (b)
Johnson, C. R.; Senanayake, C. H. J. Org. Chem. 1989, 54, 735; (c) Houille, O.;
ꢀ
Schmittberger, T.; Uguen, D. Tetrahedron Lett. 1996, 37, 625; (d) Lopez, R.;
ꢀ
~
ꢀ
Montero, E.; Sanchez, F.; Canada, J.; Fernandez-Mayoralas, A. J. Org. Chem. 1994,
59, 7027; (e) Holla, E. W.; Sinnwell, V.; Klaffke, W. Synlett 1992, 413; (f) Itoh, T.;
Uzu, A.; Kanda, N.; Takagi, Y. Tetrahedron Lett. 1996, 37, 91; (g) Takabe, K.; Mase,
N.; Hisano, T.; Yoda, H. Tetrahedron Lett. 2003, 44, 3267; (h) Hisano, T.; Onodera,
K.; Toyabe, Y.; Mase, N.; Yoda, H.; Takabe, K. Tetrahedron Lett. 2005, 46, 6293.
13. Ellervik, U.; Magnusson, G. Tetrahedron Lett. 1997, 38, 1627.
4. Experimental
4.1. General procedure for the catalytic deacylation
14. Neilson, T.; Werstiuk, E. S. Can. J. Chem. 1971, 49, 493.
In a 25-mL, two-necked, round-bottomed flask equipped with
an addition funnel was placed MoO2Cl2 (5 mol %) followed by the
addition of anhydrous methanol (2 mL) under N2 atmosphere. To
this solution was slowly added a solution of an acetate-containing
sugar (1 mmol) in methanol (3 mL) at ambient temperature via the
addition funnel. After completion of the reaction as evidenced by
TLC analysis, the reaction mixture was concentrated in vacuo and
the residue was quenched with cold saturated aqueous NaHCO3
(5 mL). Methylene chloride (10 mL) was added to the reaction
mixture. The organic layer was separated and washed with brine,
dried (MgSO4), filtered, and evaporated. The crude residue was
purified by column chromatography on silica gel. The product was
characterized by routine spectroscopic methods.
15. Askin, D.; Angst, C.; Danishefsky, S. J. Org. Chem. 1987, 52, 622.
ꢀ
16. Tran, A. T.; Deydier, S.; Bonnaffe, D.; Narvor, C. L. Tetrahedron Lett. 2008, 49, 2163.
17. (a) Hanamoto, T.; Sugimoto, Y.; Yokoyama, T.; Inanaga, J. J. Org. Chem. 1996, 61,
4491; (b) Sharma, G. V. M.; Ilangovan, A. Synlett 1999, 1963.
18. Xu, Y.-C.; Bizuneh, A.; Walker, C. J. Org. Chem. 1996, 61, 9086.
19. Baptistella, L. H. B.; Dos Santos, J. F.; Ballabio, K. C.; Marsaioli, A. J. Synthesis
1989, 436.
20. (a) 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; (b) Chen, C.-T.; Kuo, J.-H.; Pawar, V. D.; Munot, Y. S.; Weng, S.-S.; Ku, C.-
H.; Liu, C.-Y. J. Org. Chem. 2005, 70, 1188; (c) Liu, C.-Y.; Pawar, V. D.; Kao, J.-Q.;
Chen, C.-T. Adv. Synth. Catal. 2010, 352, 188; (d) Chen, C.-T.; Munot, Y. S. J. Org.
Chem. 2005, 70, 8625; (e) Chen, C.-T.; Kuo, J.-H.; Ku, C.-H.; Weng, S.-S.; Liu, C.-Y.
J. Org. Chem. 2005, 70, 1328; (f) Chen, C.-T.; Weng, S.-S.; Kao, J.-Q.; Lin, C.-C.; Jan,
M.-D. Org. Lett. 2005, 7, 3343; (g) Weng, S.-S.; Lin, Y.-D.; Chen, C.-T. Org. Lett.
2006, 8, 5633; (h) Lin, Y.-D.; Kao, J.-Q.; Chen, C.-T. Org. Lett. 2007, 9, 5195; (i)
Chen, C.-T.; Lin, Y.-D.; Liu, C.-Y. Tetrahedron 2009, 65, 10470.
21. (a) Baumhof, P.; Mazitschek, R.; Giannis, A. Angew. Chem., Int. Ed. 2001, 40, 3672;
(b) Wang, S.-M.; Zhang, Y.-B.; Liu, H.-M.; Tu, G.-B.; Wang, K.-R. Steroids 2007, 72,
26.
Acknowledgements
22. Evans, D. A.; Fandrick, K. R.; Song, H.-J.; Scheidt, K. A.; Xu, R. J. Am. Chem. Soc.
We thank the National Science Council of Taiwan for a generous
financial support of this research.
2007, 129, 10029.
23. For application of MoO2Cl2 in organic transformation, see: (a) Jeyakumar, K.;
Chand, D. K. J. Chem. Sci. 2009, 121, 111 For the application of dioxomolybdenum
(VI) complexes in organic synthesis, see: (b) Sakakura, A.; Kondo, R.; Ishihara,
K. Org. Lett. 2005, 7, 1971; (c) Sakakura, A.; Umemura, S.; Kondo, R.; Ishihara, K.
Adv. Synth. Catal. 2007, 349, 551; (d) Sakakura, A.; Kondo, R.; Umemura, S.;
Ishihara, K. Adv. Synth. Catal. 2007, 349, 1641.
24. Yan, M.-C.; Chen, Y.-N.; Wu, H.-T.; Lin, C.-C.; Chen, C.-T.; Lin, C.-C. J. Org. Chem.
2007, 72, 299.
25. Competing debenzoylation leading to 3d was observed right at the beginning
of the catalytic reaction.
Supplementary data
Supplementary data related to this article can be found online
version at doi:10.1016/j.tet.2010.12.024. These data include MOL
files and InChIKeys of the most important compounds described in
this article.