Efficient deprotection of tetrahydropyranyl ethers by bismuth(III) salts

Article abstract of DOI:10.1081/SCC-120004252

Treatment of tetrahydropyranyl(THP) ethers with bismuth(III) salts including BiC13, Bi(TFA)3 and Bi(OTf)3 in methanol provides a simple and efficient process for deprotection of these ethers and the parent alcohols were obtained in excellent yields.

Full text of DOI:10.1081/SCC-120004252

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EFFICIENT DEPROTECTION OF TETRAHYDROPYRANYL
ETHERS BY BISMUTH(III) SALTS
Iraj Mohammadpoor-Baltork a , Bahram Kharamesh a & Sadegh Kolagar a
a Department of Chemistry , Isfahan University , Isfahan, 81744, Iran
Published online: 16 Aug 2006.
To cite this article: Iraj Mohammadpoor-Baltork , Bahram Kharamesh & Sadegh Kolagar (2002) EFFICIENT DEPROTECTION
OF TETRAHYDROPYRANYL ETHERS BY BISMUTH(III) SALTS, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 32:11, 1633-1637, DOI: 10.1081/SCC-120004252
To link to this article: http://dx.doi.org/10.1081/SCC-120004252
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SYNTHETIC COMMUNICATIONS, 32(11), 1633–1637 (2002)
EFFICIENT DEPROTECTION OF
TETRAHYDROPYRANYL ETHERS BY
BISMUTH(III) SALTS
*
Iraj Mohammadpoor-Baltork, Bahram Kharamesh,
and Sadegh Kolagar
Department of Chemistry, Isfahan University,
Isfahan 81744, Iran
ABSTRACT
Treatment
of
tetrahydropyranyl(THP)
ethers
with
bismuth(III) salts including BiCl3, Bi(TFA)3 and Bi(OTf )3
in methanol provides a simple and efficient process for depro-
tection of these ethers and the parent alcohols were obtained
in excellent yields.
The protection of alcohols as their tetrahydropyranyl ethers is a useful
and representative method in modern synthetic chemistry due to their sta-
bility toward basic media, Grignard reagents, lithium alkyls, alkylating and
acylating reagents and reactions involving oxidation and reduction by inor-
ganic hydrides.[1] Deprotection of these ethers to their corresponding alco-
hols under mild conditions is also of practical importance and many
methods and catalysts have already been applied for this conversion.[2–9]
*Corresponding author.
1633
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1634
MOHAMMADPOOR-BALTORK, KHARAMESH, AND KOLAGAR
Although some of these methods are useful, there is still a need for an
efficient and excellent yielding alternative catalyst that can work under
mild conditions and shorter reaction times.
Over recent years, the catalytic activity of bismuth(III) derivatives as
Lewis acids has been demonstrated in organic transformations.[10] In con-
nection with our ongoing work on catalysis by Bi(II) salts,[11–14] we herein
report a simple and efficient method for the cleavage of tetrahydropyranyl
ethers using BiCl3, Bi(TFA)3 and Bi(OTf )3 as catalysts (Scheme 1).
Scheme 1.
As shown in Table 1, when a variety of tetrahydropyranyl ethers were
treated with catalytic amounts of BiCl3, Bi(TFA)3 and Bi(OTf )3 in refluxing
methanol, the corresponding alcohols were obtained in excellent yields. The
experimental results showthat Bi(OTf ) is more reactive than BiCl3 and
3
Bi(TFA)3 for this transformation. It is important to note that tert-butyl-
dimethylsilyl (TBDMS) ether and ester remained unchanged in the reaction
mixture (Table 2).
In conclusion, the present procedure provides a simple and convenient
methodology for the deprotection of THP ethers. In addition, high yields
and short reaction times, easy workup, availability, stability and non-
toxicity of the catalysts make this procedure a useful and attractive
alternative to the currently available methods.
EXPERIMENTAL
General Procedure for Deprotection of THP Ethers
To a solution of THP ether (1 mmol) in methanol (3 ml) was added the
catalyst (0.03 mmol of BiCl3, 0.05 mmol of Bi(TFA)3 and 0.01 mmol of
Bi(OTf)3). The reaction mixture was stirred under reflux conditions for
the length of time indicated in Table 1. The progress of the reaction was
followed by TLC. Evaporation of the solvent followed by chromatography

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DEPROTECTION OF THP ETHERS
1635
Table 1. Deprotection of THP Ethers Catalyzed by Bi(III) Saltsa
Yieldb (%) of Alcohol (Time, min)
Run
1
THP Ether
BiCl3
Bi(TFA)3
95 (30)
Bi(OTf)3
96 (20)
97 (3)
2
3
95 (30)
97 (15)
93 (45)
97 (15)
98 (3)
98 (3)
4
97 (15)
94 (30)
97 (3)
5
6
98 (5)
97 (10)
85 (60)
99 (2)
97 (5)
93 (35)
7
8
9
94 (35)
94 (15)
95 (15)
80 (60)
92 (40)
96 (20)
96 (5)
95 (10)
98 (3)
(continued )

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1636
MOHAMMADPOOR-BALTORK, KHARAMESH, AND KOLAGAR
Table 1. Continued
Yieldb (%) of Alcohol (Time, min)
Run
10
THP Ether
BiCl3
Bi(TFA)3
93 (25)
Bi(OTf)3
99 (5)
98 (15)
11
12
97 (15)
95 (20)
97 (15)
93 (30)
99 (3)
97 (7)
13
97 (25)
96 (25)
98 (7)
14
15
94 (25)
95 (25)
94 (25)
93 (25)
97 (5)
98 (5)
aThe products were characterized by comparison with known samples.
bYields refer to isolated products.
Table 2. Competitive Deprotection Catalyzed by Bi(III) Salts
Yield % (Time, min)
BiCl3 Bi(TFA)3 Bi(OTf )3
Run
1
Substrate
Product
2-MeOC6H4CH2OTHP 2-MeOC6H4CH2OH 99 (15) 98 (15)
PhCH¼
100 (3)
0
PhCH¼
0
0
CHCH2OTBDMS
CHCH2OH
2
Ph2CHOTHP
CH3CO2C7H15
Ph2CHOH
CH3CO2H
98 (15) 98 (15)
0
99 (3)
0
0

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DEPROTECTION OF THP ETHERS
1637
on a silica-gel plate or silica-gel column afforded the pure product in
80–99% yield (Table 1).
ACKNOWLEDGMENT
We are thankful to the Isfahan University Research Council for
partial support of this work.
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Received in Japan February 7, 2001

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