Bi(III) salts as new catalysts for the selective conversion of trimethylsilyl and tetrahydropyranyl ethers to their corresponding acetates and formates

Article abstract of DOI:10.1081/SCC-120006016

Bi(III) salts such as BiCl₃, Bi(TFA)₃ and Bi(OTf)₃ were found to be efficient catalysts for the transformation of trimethylsilyl (TMS) and tetrahydropyranyl (THP) ethers to their corresponding acetates and formates with acetic acid and ethyl formate. Selective acetylation and formylation of TMS and THP ethers of alcohols in the presence of phenolic TMS and THP ethers make this method a useful and practical procedure in organic synthesis.

Full text of DOI:10.1081/SCC-120006016

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Bi(III) SALTS AS NEW CATALYSTS FOR THE
SELECTIVE CONVERSION OF TRIMETHYLSILYL
AND TETRAHYDROPYRANYL ETHERS TO THEIR
CORRESPONDING ACETATES AND FORMATES
a
a
I. Mohammadpoor-Baltork & A. R. Khosropour
a
Department of Chemistry, Isfahan University, Isfahan, 81744, Iran
Version of record first published: 16 Aug 2006.
To cite this article: I. Mohammadpoor-Baltork & A. R. Khosropour (2002): Bi(III) SALTS AS NEW CATALYSTS FOR THE SELECTIVE
CONVERSION OF TRIMETHYLSILYL AND TETRAHYDROPYRANYL ETHERS TO THEIR CORRESPONDING ACETATES AND FORMATES,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 32:15,
2433-2439
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 15, pp. 2433–2439, 2002
Bi(III) SALTS AS NEW CATALYSTS
FOR THE SELECTIVE CONVERSION
OF TRIMETHYLSILYL AND
TETRAHYDROPYRANYL ETHERS TO
THEIR CORRESPONDING ACETATES
AND FORMATES
I. Mohammadpoor-Baltork* and A. R. Khosropour
Department of Chemistry, Isfahan University,
Isfahan 81744, Iran
ABSTRACT
Bi(III) salts such as BiCl , Bi(TFA) and Bi(OTf ) were found
3
3
3
to be efficient catalysts for the transformation of trimethylsilyl
TMS) and tetrahydropyranyl (THP) ethers to their corre-
(
sponding acetates and formates with acetic acid and ethyl
formate. Selective acetylation and formylation of TMS and
THP ethers of alcohols in the presence of phenolic TMS and
THP ethers make this method a useful and practical pro-
cedure in organic synthesis.
*
Corresponding author.
2
433
DOI: 10.1081/SCC-120006016
Copyright & 2002 by Marcel Dekker, Inc.
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2
434
MOHAMMADPOOR-BALTORK AND KHOSROPOUR
Protection and deprotection of functional groups is a common feature
in a multistep organic synthesis. Trimethylsilyl and tetrahydropyranyl ethers
which are protected derivatives of alcohols are considered as important
[
intermediates in organic synthesis. Among the reactions of these ethers,
1]
[
2–7]
their deprotection to alcohols
nyl compounds
and their oxidative deprotection to carbo-
have been widely investigated. However, little attention
[8–14]
has been paid to the esterification of trimethylsilyl and tetrahydropyranyl
ethers and only a few reports are available dealing with the conversion of
[
15]
these ethers to their corresponding acetates and formates.
The applications of bismuth compounds to organic transformations
[
have been extensively investigated. In connection with our ongoing work
16]
[
17]
[7,14]
on Bi(III) catalysis and also on reactions of TMS and THP ethers,
we
now report a mild and efficient method for the conversion of the above
mentioned ethers to their corresponding acetates and formates with acetic
acid and ethyl formate under catalysis of BiCl , Bi(TFA) and Bi(OTf )
3
3
3
(Scheme 1). To the best of our knowledge these is no report on the use of
Bi(III) salts in acetylation and formylation of TMS and THP ethers.
Scheme 1.
As can be seen from Table 1, when a variety of TMS and THP ethers
were treated with acetic acid under reflux conditions in the presence of
catalytic amounts of BiCl , Bi(TFA) and Bi(OTf )3 the corresponding
3
3
acetates were obtained in excellent yields.
Due to the importance of formylation reaction, we also investigated
the possibility of using this method for the formylation of TMS and THP
ethers in ethyl formate. As shown in Table 2, TMS and THP ethers of
alcohols were formylated efficiently with ethyl formate under catalysis of
BiCl , Bi(TFA) and Bi(OTf ) . Phenolic TMS and THP ethers did not
3
3
3
undergo formylation and only deprotection to their corresponding phenols
was occurred under these experimental conditions (Table 2, Entries 8, 9, 18
and 19). The results show that Bi(OTf ) is more reactive thatn BiCl and
3
3
Bi(TFA) in both acetylation and formylation of TMS and THP ethers.
3

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CONVERSION OF TMS AND THP ETHERS
2435
Table 1. Acetylation of TMS and THP Ethers with Acetic Acid Catalyzed by
a
Bi(III) Salts
b
Yield % of Acetate (Time/min)
Run
Substrate
CH CH OTMS
2-MeOC H CH OTMS
BiCl
3
Bi(TFA)
3
Bi(OTf )
3
1
2
3
4
5
6
7
8
9
C
6
H
5
2
2
90 (30)
95 (30)
95 (30)
92 (35)
90 (35)
91 (40)
95 (30)
97 (100)
96 (100)
98 (60)
95 (40)
90 (40)
93 (60)
90 (60)
98 (45)
95 (60)
80 (65)
80 (150)
90 (100)
90 (30)
93 (30)
96 (30)
90 (40)
85 (35)
90 (40)
95 (30)
90 (120)
95 (100)
95 (75)
90 (50)
85 (70)
90 (75)
80 ( 100)
98 (50)
95 (65)
80 (70)
75 (180)
80 (120)
98 (25)
98 (30)
98 (30)
96 (30)
98 (30)
97 (25)
98 (25)
98 (60)
98 (60)
98 (45)
98 (30)
91 (40)
95 (45)
92 (60)
99 (45)
98 (50)
87 (50)
6
4
2
4-MeOC
4-NO
4-ClC H CH OTMS
6
4
H CH
2
OTMS
2 6 4 2
C H CH OTMS
6
4
2
C
CH
6
H
5
CH(CH
(CH OTMS
4-ClC H OTMS
3
)OTMS
3
2 7
)
6
4
b-NaphthylOTMS
10
11
12
13
14
15
16
17
18
19
C
6
H
5
CH
2
OTHP
C
4-MeOC H CH OTHP
6
H
5
CH
2
CH OTHP
2
6
4
2
4-NO
CH(CH
CH (CH ) OTHP
2
C
6
4
H CH
2
OTHP
C
6
H
5
3
)OTHP
3
2 7
CyclohexylOTHP
(À)-MenthylOTHP
2-NO C H OTHP
c
82 (100)
90 (80)
2
6
4
b-NaphthylOTHP
a
Products were identified by comparison of their physical and spectral data with
b
c
those of authentic samples; Isolated yields; (À)-Menthyl acetate was obtained
from the reaction mixture.
To explore the generality and scope of the described method, we
have also investigated the competitive acetylation and formylation of
TMS and THP ethers of alcohols and phenols. The experimental results
show that TMS and THP ethers of alcohols are selectively converted to
their corresponding acetates and formates in the presence of phenolic TMS
and THP ethers. Such a selectivity has not been reported previously
and could be considered as a useful practical achievement in acylation
reactions.
In conclusion, we believe that the present methodology offers an
attractive alternate method for the selective acetylation and formylation
of TMS and THP ethers. Moreover, high yields of the products, short
reaction times, easy workup, availability, stability and non-toxicity of the
catalysts are noteworthy advantages of this method.

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436
MOHAMMADPOOR-BALTORK AND KHOSROPOUR
Table 2. Formylation of TMS and THP Ethers with Ethyl Formate Catalyzed by
a
Bi(III) Salts
b
Yield % of Formate (Time/min)
Run
Substrate
CH CH OTMS
2-MeOC H CH OTMS
BiCl
3
Bi(TFA)
3
Bi(OTf )
3
1
2
3
4
5
6
7
8
9
C
6
H
5
2
2
95 (45)
90 (60)
92 (60)
91 (60)
92 (60)
90 (50)
98 (40)
0 (25)
90 (45)
90 (65)
94 (60)
85 (65)
85 (60)
88 (50)
95 (40)
0 (25)
95 (20)
91 (40)
95 (30)
94 (40)
93 (35)
95 (30)
98 (25)
0 (20)
6
4
2
4-MeOC
4-NO
4-ClC H CH OTMS
H
6 4
CH
2
OTMS
2 6 4 2
C H CH OTMS
6
4
2
C
CH
6
H
5
CH(CH
(CH OTMS
4-ClC H OTMS
3
)OTMS
3
2 7
)
c
6
4
c
b-NaphthylOTMS
0 (25)
0 (25)
0 (20)
10
11
12
13
14
15
16
17
18
19
C
C
6
H
H
5
CH
2
OTHP
90 (60)
95 (40)
92 (40)
90 (50)
85 (80)
98 (45)
95 (60)
86 (80)
0 (55)
90 (65)
95 (50)
90 (50)
80 (60)
80 (100)
97 (50)
93 (65)
80 (90)
0 (65)
95 (45)
97 (35)
95 (40)
92 (50)
89 (60)
99 (30)
96 (45)
90 (60)
0 (40)
6
5
CH
CH OTHP
2 2
4-MeOC H CH OTHP
6
4
2
4-NO
CH(CH
CH (CH ) OTHP
2
C
6
4
H CH
2
OTHP
C
6
H
5
3
)OTHP
3
2 7
CyclohexylOTHP
(À)-MenthylOTHP
d
c
2-NO C H OTHP
2
6
4
c
b-NaphthylOTHP
0 (50)
0 (80)
0 (40)
a
Products were identified by comparison of their physical and spectral data with
b
those of authentic samples;
c
Isolated yields; The corresponding phenol was
d
obtained in 90–99% yields; (À)-Menthyl formate was obtained from the reaction
mixture.
EXPERIMENTAL
Bi(TFA) and Bi(OTf ) were prepared according to the described
3
3
[18]
procedures.
General Procedure for the Conversion of TMS and
THP Ethers to Their Corresponding Acetates
To a solution of TMS or THP ether (1 mmol) in acetic acid (3 mL) was
added the catalyst (in the case of TMS ether, 0.3 mmol of BiCl , 0.3 mmol of
3
Bi(TFA) and 0.03 mmol of Bi(OTf ) ; in the case of THP ether, 0.4 mmol of
3
3

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CONVERSION OF TMS AND THP ETHERS
2437

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MOHAMMADPOOR-BALTORK AND KHOSROPOUR
BiCl , 0.4 mmol of Bi(TFA) and 0.5 mmol of Bi(OTf ) ). The reaction mix-
3
3
3
ture was stirred under reflux conditions for the appropriate time according
to Table 1. The progress of the reaction was monitored by GLC or TLC.
Acetic acid was removed under reduced pressure and ether (20 mL) was
added. The reaction mixture was washed with 5% aqueous solution of
NaHCO , then with water and dried with Na SO . Evaporation of the
3
2
4
solvent followed by chromatography on a silica-gel plate or silica-gel
column afforded the pure acetate in 75–99% yields (Table 1).
General Procedure for the Conversion of TMS and THP Ethers to
Their Corresponding Formates
A solution of TMS or THP ether (1 mmol) in ethyl formate (3 mL) was
treated with the catalyst (in the case of TMS ether, 0.35 mmol of BiCl3,
0.35 mmol of Bi(TFA) and 0.04 mmol of Bi(OTf ) ; in the case of THP
ether, 0.5 mmol of BiCl , 0.5 mmol of Bi(TFA) and 0.07 mmol of
3
3
3
3
Bi(OTf ) ). The reaction mixture was stirred under reflux conditions for
3
the appropriate time according to Table 2. The progress of the reaction
was monitored by GLC or TLC. The solvent was evaporated and ether
(
dried with Na SO . Evaporation of the solvent followed by chromatography
20 mL) was added. The reaction mixture was washed with water and
2
4
on a silica-gel plate or silica-gel column afforded the pure formate in
0–99% yields. In the case of phenolic TMS and THP ethers only deprotec-
tion to their corresponding phenols was occurred under these conditions
Table 2).
8
(
ACKNOWLEDGMENT
We are thankful to the Isfahan University Research Council for
partial support of this work.
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Received in Japan May 12, 2001

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