One-Pot Bi(OTf)catalyzed oxidative deprotection of tert -butyldimethyl silyl ethers with TEMPO and co-oxidants

Article abstract of DOI:10.1055/s-0030-1260980

A sequential one-pot synthesis for the oxidation of primary and secondary tert-butyldimethylsilyl (TBDMS) ethers, using catalytic amounts of metal triflates and TEMPO in combination with PhIO or PhI(OAc)in THF or acetonitrile, is described. Acid-sensitive protecting groups such as methylidene, isopropylidene, acetals, and Boc are unaffected under the reaction conditions. Another feature of this procedure is its high selectivity for TBDMS ethers over tert-butyldiphenylsilyl ethers and of aliphatic TBDMS groups over phenolic TBDMS groups. Georg Thieme Verlag Stuttgart - New York.

Full text of DOI:10.1055/s-0030-1260980

2048
LETTER
One-Pot Bi(OTf)3-Catalyzed Oxidative Deprotection of tert-Butyldimethyl
Silyl Ethers with TEMPO and Co-Oxidants
O
xidative Deprot
o
ection of ter
g
t
-Butyldime
t
d
hylSilyl
E
th
a
e
rs n Barnych, Jean-Michel Vatèle*
Université Lyon 1, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires (ICBMS), UMR 5246 CNRS, Equipe SURCOOF,
Bât. Raulin, 43, Blvd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France
E-mail: vatele@univ-lyon1.fr
Received 7 April 2011
and chemoselective method for the oxidative deprotection
Abstract: A sequential one-pot synthesis for the oxidation of pri-
of TBDMS ethers is still in demand.
mary and secondary tert-butyldimethylsilyl (TBDMS) ethers, using
catalytic amounts of metal triflates and TEMPO in combination
with PhIO or PhI(OAc)2 in THF or acetonitrile, is described. Acid-
sensitive protecting groups such as methylidene, isopropylidene,
acetals, and Boc are unaffected under the reaction conditions. An-
other feature of this procedure is its high selectivity for TBDMS
ethers over tert-butyldiphenylsilyl ethers and of aliphatic TBDMS
groups over phenolic TBDMS groups.
In continuation of our interest in exploring the use of
TEMPO/co-oxidant systems in organic synthesis,10 we re-
cently described an Yb(OTf)3-catalyzed oxidation of alco-
hols mediated by TEMPO in combination with PhIO.10b
We report herein our study on the oxidative deprotection
of TBDMS ethers using TEMPO and PhIO or PhI(OAc)2
as co-oxidants, catalyzed by Bi(OTf)3.
Key words: bismuth(III) triflate, carbonyl compounds, oxidation,
silyl ethers, TEMPO
We selected the TBDMS ether of 3-phenyl-1-propanol
(1a) as a model substrate to test the ability of the
Yb(OTf)3/PhIO/TEMPO triad to promote its oxidative
deprotection. After 24 hours at room temperature in
CH2Cl2 or MeCN, no reaction had occurred. Addition of
water or the use of other Lewis acids such as Sc(OTf)3 or
Bi(OTf)3 led to recovery of starting material. After these
unsuccessful attempts, we decided to study a stepwise
one-pot desilylation–oxidation of 1a, and the most signif-
icant results are summarized in Table 1.
The protection of hydroxyl functions as silyl ethers has
been recognized as one of the most useful protecting
methods in organic synthesis because of the ease of intro-
duction, stability to a variety of reagents, cleavage under
mild conditions, and the possibility to fine-tune their rela-
tive stability by changing the substituents on the silicon.1
Although the major goal of such a protection is to block
oxidation, in some cases, it is necessary to achieve the
transformation of silyl ethers to their corresponding car-
bonyl compounds. This transformation is usually carried
out in a two-step procedure involving desilylation fol-
lowed by oxidation of the free alcohol. A direct method
for such a transformation has the advantages to increase
the overall efficiency of the process, desirable in a long
synthetic scheme, and to allow a chemoselective oxidative
deprotection of primary silyl ethers in the presence of sec-
ondary ethers or of two primary silyl ethers of different
stabilities.2,3 If a wide variety of methods has been report-
ed for oxidative cleavage of trimethylsilyl ethers to carbo-
nyl compounds,2,4 there are only few procedures for one-
step removal and oxidation of the tert-butyldimethylsilyl
(TBDMS) group. These include chromium(VI)-based re-
agents,5 DDQ under UV irradiation,6 NBS in the presence
of b-cyclodextrin,7 PdCl2(MeCN)2 in catalytic amounts,8
catalytic N-hydroxyphthalimide and O2, Co(II).9 Howev-
er, some of these procedures utilize either toxic reagents
in stoichiometric amounts,5a,b,d,e require harsh condi-
Table 1 Study on the Kinetics of Lewis Acid Catalyzed Desilyla-
tion–Oxidation of 1-tert-Butyldimethylsilyloxy-3-phenylpropane
(1a) in Different Solventsa,b
CHO
solvent–H2O
OTBDMS
Lewis acid
TEMPO/co-oxidant
1a
2a
Entry Catalyst (mol%)
Solvent
Time for each step Yield
(h)
(%)c
1
2
3
4
5
6
7
Yb(OTf)3 (2)
Sc(OTf)3 (2)
La(OTf)3 (2)
Bi(OTf)3 (2)
Bi(OTf)3 (5)
Bi(OTf)3 (2)
TfOH (2)
MeCN
MeCN
MeCN
MeCN
THF
24; 2.5
2; 3
71
79
2; 2
78
1.5; 2.5
5; 0.5
1.5; 2
1; 2.5
80
57
MeCN
MeCN
75d
70
tions,5a,8 are not compatible with
functionalities7 or give low yields.5c,6 Therefore, a mild
a number of
a With 5 equiv of H2O and in the presence of TEMPO (5 mol%) and
co-oxidants.
b PhIO (1.5 equiv) was used as oxidant except for entry 6 where
PhI(OAc)2 (1.4 equiv) was used.
c Isolated yield.
SYNLETT 2011, No. 14, pp 2048–2052
Advanced online publication: 03.08.2011
x
x
.x
x
.2
0
1
1
d A yield of 10% of 3-phenylpropionic acid was isolated.
DOI: 10.1055/s-0030-1260980; Art ID: D10511ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Oxidative Deprotection of tert-Butyldimethyl Silyl Ethers
2049
Based on literature precedents concerning the beneficial more effective than Sc(OTf)3 for the deprotection of tri-
role of water on the rate of deprotection of TBDMS ethers isopropyl (TIPS) ether 4 (Table 2, entries 3, 4) and alde-
with Lewis acids,8,11TBDMS ether 1a was stirred at room hyde 2a was obtained in good yields. The difference in the
temperature in acetonitrile containing 5 equivalents of catalytic activity between Bi(OTf)3 and Sc(OTf)3 for the
water and Yb(OTf)3 (2 mol%). The deprotection was deprotection of TBDPS and TIPS ethers may be explained
slow, and 24 hours were necessary for completion from the observations that solutions of Bi(OTf)3 in
(Table 1, entry 1). Addition to the reaction mixture of MeCN–H2O very rapidly become cloudy (about 15 min).
TEMPO (5 mol%) and of PhIO (1.5 equiv) oxidized 3- In light of literature precedents, we propose that the pre-
phenyl-1-propanol to afford aldehyde 2a in an acceptable cipitate formed12 is the result of the partial hydrolysis of
yield. We then examined the catalytic activity of several Bi(OTf)3 which also releases triflic acid.13 Therefore the
Lewis acids. Other lanthanide triflates such as Sc(OTf)3 superior catalytic activity of Bi(OTf)3 in comparison with
and La(OTf)3 improved considerably the reaction rate of that of Sc(OTf)3 is likely a consequence of the presence of
silyl ether cleavage and the overall yield (Table 1, entries traces of triflic acid in the reaction mixture.
2, 3); Bi(OTf)3 had a similar effect (Table 1, entry 4). THF
We next studied the scope and limitations of our oxidative
used as solvent lowered the reaction rate of the desilyla-
deprotection on a variety of TBDMS ethers (Table 3).We
tion process and decreased the efficiency of the overall
selected Bi(OTf)3 as the Lewis acid because it has the ad-
process (Table 1, entry 5). Bis(acetoxy)iodobenzene used
vantages over lanthanide triflates to be less expensive and
as the final oxidant afforded 3-phenyl-1-propanal (2a) in
an acceptable yield but also 10% of its corresponding acid
(Table 1, entry 6). TfOH was also an effective catalyst for
the oxidative deprotection of 1a albeit the yield of the
transformation being lower than when using metallic tri-
flates (Table 1, entry 7).
much less toxic.14,15 As can be seen in Table 3, primary
TBDMS ethers were readily and efficiently oxidized to al-
dehydes in excellent yields (Table 3, entries 1–4) with the
exception of the substrate 1e where the prenyl group was
partially cleaved (Table 3, entry 5). In the presence of
acid-sensitive functional groups, such as isopropylidene
We next examined the capacity of the Met(OTf)3/ and Boc groups, the oxidation step was best effected with
TEMPO/PhIO system to promote the oxidative deprotec- TEMPO/PhI(OAc)2 in the presence of NaHCO3 (Table 3,
tion of bulkier silyl ethers (Table 2).
entries 6, 7).16 In both substrates, bearing an epimerizable
center, no racemization occurred. Chemoselective oxida-
tion of a TBDMS ether in the presence of a TBDPS ether
occurred in a high yield (Table 3, entry 8). Similar high
chemoselectivity was observed between an aliphatic
TBDMS ether and a phenolic TBDMS ether (Table 3, en-
try 9). On the other hand, selectivity between 1°-TBDMS
ether and 2°-TBDMS ether was only moderate. Under op-
timized conditions, using THF as solvent known to favor
selective cleavage of 1°-TBDMS ether,17 5-(tert-bu-
tyldimethylsilyloxy)heptanal 2j was obtained in 51%
yield accompanied by the corresponding lactone (18%
yield; Table 3, entry 10). Next, we turned our attention to
the oxidative deprotection of secondary TBDMS ethers
(Table 3, entries 11–14). Ketones 2k–n were obtained in
good to excellent yields (69–85%). High loading of
Bi(OTf)3 (15 mol%) and long reaction time (48 h) were
necessary for the oxidation of the hindered TBDMS ether
of borneol (Table 3, entry 13). As the TBDMS ether of
cholestanol was only slightly soluble in acetonitrile, the
oxidative deprotection was effected in THF. Surprisingly,
the oxidation occurred very rapidly to furnish
cholestanone 2n in an excellent yield (Table 3, entry 14).
Finally, we submitted the di-TBDMS ethers of cis-cyclo-
hexane-1,2-dimethanol (1o) to our desilylation–oxidation
protocol, and the corresponding lactone 2o was obtained
in a good yield (Table 3, entry 15). We also tested the se-
lectivity of our procedure on a substrate bearing three dif-
ferent silicon protecting groups (Scheme 1) and observed
a remarkable solvent effect on the chemoselectivity. In ac-
etonitrile, 3°-triethylsilyl (TES) and 1°-TBDMS groups
were selectively deprotected in the presence of a 1°-
TBDPS group to provide the acetylenic aldehyde 7 in
Table 2 Lewis Acid Catalyzed Oxidative Deprotection of TIPS and
TBDPS Ethers of 3-Phenyl-1-propanol to Aldehyde 2a in the Pres-
ence of TEMPO–PhIO Systema
Entry Substrate
Lewis acid
(mol%)
Time for each Yield
step (h)
(%)b
4 OTBDPS
4 OTBDPS
1
Sc(OTf)3 (15) 24; 3
Bi(OTf)3 (15) 4; 3
62
3
2
67
75
71
3
3
OTIPS
3
Sc(OTf)3 (2)
Bi(OTf)3 (2)
6; 2.5
4
3
OTIPS
4
1.5; 3
4
a In MeCN–H2O (5 equiv).
b Isolated yield.
In the presence of 15 mol% of Sc(OTf)3, deprotection of
the tert-butyldiphenylsilyl (TBDPS) ether of 4-phenyl-1-
butanol (3) was relatively slow (24 h) and the overall yield
modest (Table 2, entry 1). Conversely, Bi(OTf)3 efficient-
ly deprotected 3 but did not improve the yield for the two-
step procedure (Table 2, entry 2). Similarly, Bi(OTf)3 was
Synlett 2011, No. 14, 2048–2052 © Thieme Stuttgart · New York

2050
B. Barnych, J.-M. Vatèle
LETTER
CHO
CHO
TESO
TBDPSO
Et
HO
Et
TESO
TBDPSO
Et
THF–H2O
a
MeCN–H2O
b
OTBDMS
TBDPSO
7 (83%)
6 (68%)
Scheme 1 Reagents and conditions: (a) Bi(OTf)3 (4 mol%), r.t., 16 h then TEMPO (5 mol%), PhIO (1.5 equiv), 0 °C, 1 h; (b) Sc(OTf)3
(1 mol%), r.t., 6 h then PhIO (1.5 equiv), TEMPO (5 mol%), 0 °C, 1 h.
83% yield; whereas predominant oxidative cleavage of
the TBDMS ether was accomplished in THF to furnish the
bissilyl ether 6 in a good yield.
a
b
CO2H
Ph
3 OTBDMS
Ph
CO2Et
9 (81%)
Ph
8 (82%)
2
Scheme 2 Reagents and conditions: (a) Bi(OTf)3 (2 mol%),
MeCN–H2O (2:1), r.t., 90 min then TEMPO (5 mol%), PhI(OAc)2
(2.6 equiv), r.t., 24 h; (b) first step as in (a) then TEMPO (5 mol%),
PhIO (1.5 equiv), 2 h, cooled to 0 °C then Ph3P=CHCO2Et (1.6
equiv), r.t., 1 h (E/Z ratio = 4:1).
Applications of our desilylation–oxidation procedure to a
one-pot preparation of acids and a,b-unsaturated esters
from TBDMS ethers are illustrated in Scheme 2. In the
presence of an excess of PhI(OAc)2, the silyl ether 1a was
oxidized to the acid 8 in an excellent yield. In combination
with (carboethoxymethylene) triphenylphosphorane, the
Bi(OTf)3/TEMPO/PhIO system allowed the conversion
of silyl ether 1a into a,b-unsaturated ester 9, via a three-
step sequence, in a pleasing 81% yield.18
metal triflates, TIPS and TBDPS ethers can be also oxi-
dized in fair to good yields. This method is highly selec-
tive for the TBDMS group over the TBDPS group and
aliphatic TBDMS ethers over TBDMS aromatic ethers.
Because of its mild reaction conditions, chemoselectivity,
easy workup, and high yields, this protocol represents a
valuable alternative to existing methods.
In summary, we have shown that the Bi(OTf)3/TEMPO/
hypervalent iodine(III) system constitutes an efficient and
mild method for the oxidation of a variety of TBDMS
ethers, even sterically hindered ones, to aldehydes and ke-
tones in good to excellent yields. With a higher loading of
Table 3 Two-Step, One-Pot Bi(OTf)3-Catalyzed Oxidative Deprotection of TBDMS Ethers Mediated by TEMPO
Entry
Substrate
Conditionsa
Time for each step (h) Product, yield (%)b
CHO
OTBDMS
OTBDMS
1
A
2; 2.5
1a
2a 80
CHO
O
O
2
3
4
5
A
A
A
A
1; 1
O
O
1b
2b 78
OTBDMS
CHO
0.5; 0.5
2c 82
1c
CHO
OTBDMS
1; 0.5
1d
1e
2d 83
1.5; 2
CHO
O
OTBDMS
O
2e 62c
OTBDMS
CHO
6
7
B
B
1.5; 2
1.5; 3
N
N
Boc
1f
Boc
2f 74
OTBDMS
O
CHO
O
O
O
O
O
O
O
O
O
1g
2g 71
Synlett 2011, No. 14, 2048–2052 © Thieme Stuttgart · New York

LETTER
Oxidative Deprotection of tert-Butyldimethyl Silyl Ethers
2051
Table 3 Two-Step, One-Pot Bi(OTf)3-Catalyzed Oxidative Deprotection of TBDMS Ethers Mediated by TEMPO (continued)
Entry
8
Substrate
Conditionsa
Ad
Time for each step (h) Product, yield (%)b
CHO
TBDPSO
OTBDMS
1.5;2.5
TBDPSO
1h
2h 80
CHO
OTBDMS
9
A
C
2; 4
TBDMSO
TBDMSO
2i 74
1i
10
6; 1
CHO
TBDMSO
OTBDMS
TBDMSO
1j
2j 51e
O
OTBDMS
11
12
13
A
1.5; 7
1k
1l
2k 76
Af
Af
2; 12
O
OTBDMS
2l 79
2.5; 48
O
OTBDMS
2m 69
1m
3
3
14
15
Cf
15; 2.5
O
TBDMSO
2n 85
O
1n
OTBDMS
OTBDMS
A
2; 3
O
1o
2o 71
a Conditions A: MeCN–H2O (5 equiv), Bi(OTf)3 (2 mol%) then TEMPO (5 mol%), PhIO (1.5 equiv). Conditions B: MeCN–H2O (5 equiv),
Bi(OTf)3 (1 mol%) then HCO3Na (3 equiv), TEMPO (5 mol%), PhI(OAc)2 (1.2 equiv). Conditions C: THF–H2O (5 equiv), Bi(OTf)3 (2 mol%),
then TEMPO (5 mol%), PhIO (1.7 equiv).
b Isolated yield.
c A partial cleavage of the prenyl ether was observed.
d Sc(OTf)3 (1 mol%) was used.
e 18% of the corresponding lactone was isolated.
f Amount of Bi(OTf)3: entry 12 (5 mol%); entry 13 (15 mol%); entry 14 (10 mol%).
Typical Procedure for the Oxidation of TBDMS Ethers
Conditions A (Table 3, Entry 1)
Conditions B (Table 3, Entry 6)
To (2R)-1-(tert-butoxycarbonyl)-2-[(tert-butyldimethylsilyl)oxy-
methyl]pyrrolidine (1f,20 0.15 g, 0.47 mmol) in MeCN (3 mL) were
successively added H2O (42 mL, 5 equiv) and Bi(OTf)3 (3.1 mg, 1
mol%). The reaction mixture was stirred for 1.5 h (monitored by
TLC, PE–Et2O, 1:1), and NaHCO3 (0.12 g, 3 equiv), TEMPO (3.7
mg, 5 mol%), and PhI(OAc)2 (0.184 g, 1.2 equiv) were successively
added. The suspension was stirred for 2 h at r.t. and concentrated in
vacuo. Flash chromatography of the residue (PE–Et2O, 1:1) gave
(R)-(tert-butoxycarbonyl)prolinal 2f as an oil (70 mg, 74%). IR
(neat): 3453, 1738, 1704, 1695 cm–1. 1H NMR (300 MHz, CDCl3,
rotamers): d = 1.38 (s), 1.43 (s, total 9 H), 1.70–2.10 (m, 4 H), 3.46
(m, 2 H), 4.00 (m, 0.6 H), 4.15 (m, 0.4 H), 9.41 (d, 0.6 H, J = 3.3
Hz), 9.50 (m, 0.4 H). 13C NMR (100 MHz, CDCl3, rotamers): d =
To a solution of 1-(tert-butyldimethylsilyloxy)-3-phenylpropane
(1a, 0.1 g, 0.4 mmol) in MeCN (2.5 mL) were successively added
distilled H2O (36 mL, 5 equiv) and Bi(OTf)3 (5.2 mg, 2 mol%). After
stirring the reaction mixture for 2 h (monitored by TLC, 10% Et2O
in PE), TEMPO (3.1 mg, 5 mol%), and PhIO (0.132 g, 1.5 equiv)
were added. The suspension was stirred for 2.5 h at r.t. and concen-
trated in vacuo. The crude product was purified by chromatography
on silica gel (PE–Et2O, 9:1) to give hydrocinnamaldehyde (2a) as a
colorless oil (43 mg, 80%). Physical data are in accordance with
those described in the literature.19
Synlett 2011, No. 14, 2048–2052 © Thieme Stuttgart · New York

2052
B. Barnych, J.-M. Vatèle
LETTER
24.0, 24.8, 26.7, 28.0, 28.3, 46.7, 46.9, 64.9, 65.1, 80.2, 80.7, 154.0,
155.0, 200.5, 200.8. [a]D20 +99.2 (c 0.9, CHCl3); lit.21 [a]D24 –96.1
(c 0.6, CHCl3). Physical data are in agreement with those de-
scribed.21
Relat. Elem. 1999, 155, 81. (f) Zhang, S.; Xu, L.; Trudelle,
M. L. Synthesis 2005, 1757.
(6) Piva, O.; Amougay, A.; Pete, J.-P. Tetrahedron Lett. 1991,
32, 3993.
(7) Reddy, M. S.; Narender, M.; Nageswar, Y. V. D.; Rao, K. R.
Synthesis 2005, 714.
Conditions C (Table 3, Entry 10)
To a solution of 1,5-di-[1-(tert-butyldimethylsilyloxy)]heptane (1j,
0.15 g, 0.41 mmol) in THF (3 mL) were added H2O (38 mL, 5 equiv)
and Bi(OTf)3 (5.4 mg, 2 mol%). The solution was stirred for 6 h
(TLC monitoring, ether-petroleum ether, 1:1), cooled to 0 °C and
TEMPO (3.2 mg, 5 mol%) and PhIO (0.165 g, 1.8 equiv) were add-
ed. The reaction mixture was stirred 30 min at 0 °C and 30 min at
room temperature. After concentration in vacuo, the residue was pu-
rified by chromatography on silica gel (PE–Et2O, 95:5) to afford the
desired aldehyde 2j as a colorless oil (0.052 g, 51%). IR (neat):
1729 cm–1. 1H NMR (300 MHz, CDCl3): d = 0.02 (s, 6 H), 0.86 (t,
3 H, J = 7.2 Hz, Me), 0.87 (s, 9 H), 1.44 (m, 4 H), 1.65 (m, 2 H),
2.40 (t, 2 H, J = 7.5 Hz), 3.59 (m, 1 H), 9.74 (s, 1 H, CHO). 13C
NMR (100 MHz, CDCl3): d = –4.4, –4.3, 9.6, 18.1, 18.2, 26.0 (3 C),
29.8, 35.9, 44.2, 73.1, 202.7. Physical data are in agreement with
those described in the literature.22 Further elution with Et2O–PE
(8) Wilson, N. S.; Keay, B. A. J. Org. Chem. 1996, 61, 2918.
(9) Karimi, B.; Rajabi, J. Org. Lett. 2004, 6, 2841.
(10) (a) Vatèle, J.-M. Tetrahedron Lett. 2006, 47, 715.
(b) Vatèle, J.-M. Synlett 2006, 2055. (c) Vatèle, J.-M.
Synlett 2008, 1785. (d) Vatèle, J.-M. Synlett 2009, 2143.
(e) Vatèle, J.-M. Tetrahedron 2010, 66, 904.
(11) (a) Oriyama, T.; Kobayashi, Y.; Noda, K. Synlett 1998,
1047. (b) Crouch, R. D.; Polizz, J. M.; Cleiman, R. A.; Yi,
J.; Romany, C. A. Tetrahedron Lett. 2002, 43, 7151.
(12) By analogy of the structure of the precipitate formed during
the hydrolysis of Bi(NTf)2 and other salts, the structure of
the hydrolysis product of Bi(OTf)3 may be
[Bi6O4(OH)4](OTf)6·xH2O (a) Lazarini, F. Acta Cystallogr.,
Sect. B: Struct. Sci. 1979, 35, 448. (b) Sundvall, B. Inorg.
Chem. 1983, 22, 1906. (c) Kawamura, M.; Cui, D.-M.;
Shimada, S. Tetrahedron 2006, 62, 9201.
(2:1) gave 5-heptanolide (0.01 g, 18%). IR (neat): 1740 cm–1. H
1
NMR (300 MHz, CDCl3): d = 0.96 (t, 3 H, J = 7.5 Hz), 1.43–1.91
(m, 6 H), 2.40–2.60 (m, 2 H), 4.15–4.25 (m, 1 H). 13C NMR (100
MHz, CDCl3): d = 9.4, 18.5, 27.3, 28.8, 29.5, 81.9, 172.0. NMR
data are in accordance with those described in the literature.23
(13) (a) Wabnitz, T. C.; Yu, J.-Q.; Spencer, J. B. Chem. Eur. J.
2004, 10, 484. (b) Ollevier, T.; Nadeau, E.; Guay-Bégin,
A.-A. Tetrahedron Lett. 2006, 47, 8351. (c) Narsaiah, A.
V.; Reddy, B. V. S.; Premalatha, K.; Reddy, S. S.; Yadav,
J. S. Catal. Lett. 2009, 131, 480. (d) Bouguerne, B.;
Hoffmann, P.; Lherbet, C. Synth. Commun. 2010, 40, 915.
(e) Hoa Kwie, F.; Baudoin-Dehoux, C.; Blonski, C.;
Lherbet, C. Synth. Commun. 2010, 40, 1082.
(14) In Organobismuth Chemistry; Suzuki, H.; Matano, Y., Eds.;
Elsevier: Amsterdam, 2001, 18.
(15) For a review on Bi(OTf)3 in organic synthesis, see: Gaspard-
Iloughmane, H.; Le Roux, C. Eur. J. Org. Chem. 2004,
2517.
Acknowledgment
The authors thank Miss Du Nan for preliminary experiments. B.B.
thanks the ‘French Ministère de la Recherche et de l’Enseignement
Supérieur’ for a doctoral grant.
References and Notes
(16) In the presence of PhIO/TEMPO system, diacetone
galactose gave mainly polar products.
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(3) For examples of chemoselective oxidative deprotection of
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(17) (a) Nelson, T. D.; Crouch, R. D. Synthesis 1996, 1031.
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