Efficient and selective conversion of trimethylsilyl and tetrahydropyranyl ethers to their corresponding acetates and benzoates catalyzed by bismuth(III) salts

Article abstract of DOI:10.1007/s706-002-8249-1

A variety of TMS and THP ethers are efficiently converted to their corresponding acetates and benzoates with acetic and benzoic anhydrides in the presence of catalytic amounts of Bi(III) salts such as BiCl₃, Bi(TFA)₃, and Bi(OTf)

Full text of DOI:10.1007/s706-002-8249-1

Monatshefte f uÈ r Chemie 133, 189±193 ꢀ2002)
Ef®cient and Selective Conversion
of Trimethylsilyl and Tetrahydropyranyl
Ethers to their Corresponding
Acetates and Benzoates Catalyzed
by BismuthꢀIII) Salts
IrajMohammadpoor-Baltork
à and Ahmad R. Khosropour
Department of Chemistry, Isfahan University, Isfahan 81744, Iran
Summary. A variety of TMS and THP ethers are ef®ciently converted to their corresponding
acetates and benzoates with acetic and benzoic anhydrides in the presence of catalytic amounts of
BiꢀIII) salts such as BiCl , BiꢀTFA) , and BiꢀOTf) . The present method is also effective for the
3
3
3
selective acetylation and benzoylation of TMS and THP ethers of alcohols in the presence of
phenolic ethers.
Keywords. Acylation; Alcohols; Phenols; BiꢀIII) salts; Lewis acids.
Introduction
Esteri®cation is an important and well-established reaction in organic synthesis.
Esters are useful as solvents, arti®cial ¯avours, and essences; They are usually pre-
pared by esteri®cation of carboxylic acids [1±3], transesteri®cation [4], alkylation
of carboxylate anions [5], acylation of alcohols and phenols [6±13], or cleavage of
ethers [14]. However, little attention has been paid to the esteri®cation of
trimethylsilyl ꢀTMS) and tetrahydropyranyl ꢀTHP) ethers, and only a few reports
are available dealing with the conversion of these ethers to their corresponding
esters [15]. Therefore, the introduction of new methods and catalysts for the
esteri®cation of TMS and THP ethers is of value in synthetic organic chemistry.
The application of bismuth compounds as catalysts in organic transformations
has been investigated extensively [16]. In the course of our research on catalysis by
BiꢀIII) salts [17] and also on reactions of TMS and THP ethers [18], we now report
a simple, ef®cient and selective method for the conversion of TMS and THP ethers
to their corresponding acetates and benzoates using BiCl , BiꢀTFA) , and BiꢀOTf )
3
3
3
as catalysts ꢀScheme 1).
à Corresponding author. E-mail: imbaltork@sci.ui.ac.ir

1
90
I. Mohammadpoor-Baltork and A. R. Khosropour
Scheme 1
Results and Discussion
As shown in Table 1, a series of TMS ethers were treated with acetic and benzoic
anhydrides under catalysis by BiCl , BiꢀTFA) , and BiꢀOTf ) in acetonitrile at room
3
3
3
temperature or under re¯ux to afford the corresponding acetates and benzoates in
excellent yields.
The acetylation and benzoylation of THP ethers were also investigated. The
treatment of a variety of THP ethers with acetic and benzoic anhydrides in the
presence of catalytic amounts of BiCl , BiꢀTFA) , or BiꢀOTf ) in re¯uxing aceto-
3
3
3
nitrile provided the corresponding acetates and benzoates in good to excellent
yields ꢀTable 2). The experimental results show that BiꢀOTf ) is more reactive than
3
BiCl and BiꢀTFA) and works better in terms of reaction times and yields.
3
3
In order to explore further the synthetic utility of this procedure, the com-
petitive acetylation and benzoylation of TMS and THP ethers of alcohols and
phenols were also investigated. As shown in Table 3, TMS and THP ethers of
alcohols are converted to their corresponding acetates and benzoates in the
Table 1. Conversion of TMS ethers to their corresponding acetates and benzoates in the presence of
a
BiꢀIII) salts
b
Yield of acetate/% ꢀt/min)
b
Yield of benzoate/% ꢀt/min)
TMS ether
c
c
BiꢀTFA)3 BiꢀOTf )3
d
c
c
BiꢀTFA)3 BiꢀOTf )3
c
BiCl3
BiCl3
C H CH CH OTMS
2
98 ꢀ20)
96 ꢀ20)
95 ꢀ30)
97 ꢀ20)
96 ꢀ15)
90 ꢀ35)
94 ꢀ40)
94 ꢀ30)
95 ꢀ40)
96 ꢀ20)
97 ꢀ20)
96 ꢀ30)
89 ꢀ60)
90 ꢀ60)
92 ꢀ60)
97 ꢀ20)
95 ꢀ20)
90 ꢀ30)
96 ꢀ20)
95 ꢀ15)
92 ꢀ35)
91 ꢀ40)
90 ꢀ30)
94 ꢀ40)
95 ꢀ20)
94 ꢀ20)
85 ꢀ45)
87 ꢀ50)
85 ꢀ45)
90 ꢀ50)
99 ꢀ15)
98 ꢀ15)
98 ꢀ30)
97 ꢀ20)
97 ꢀ15)
94 ꢀ30)
97 ꢀ20)
95 ꢀ30)
95 ꢀ35)
97 ꢀ15)
98 ꢀ15)
97 ꢀ25)
90 ꢀ30)
92 ꢀ25)
97 ꢀ25)
98 ꢀ60)
94 ꢀ30)
97 ꢀ50)
98 ꢀ30)
98 ꢀ30)
85 ꢀ90)
89 ꢀ90)
91 ꢀ60)
97 ꢀ60)
93 ꢀ30)
96 ꢀ30)
82 ꢀ60)
98 ꢀ60)
94 ꢀ30)
80 ꢀ50)
97 ꢀ45)
97 ꢀ30)
99 ꢀ45)
97 ꢀ30)
97 ꢀ30)
98 ꢀ25)
99 ꢀ20)
6
5
2
C H CH CH CH OTMS
6
5
2
2
2
2
3
4
3
4
4
-MeOC H CH OTMS
6 4 2
-MeOC H CH OTMS
2
6
4
-MeOC H CH OTMS
6
4
2
f
f
-NO C H CH OTMS
2
90 ꢀ105) 95 ꢀ45)
90 ꢀ105) 97 ꢀ45)
6
4
2
-NO C H CH OTMS
2
2
6
4
-ClC H CH OTMS
6
92 ꢀ60)
96 ꢀ60)
95 ꢀ30)
94 ꢀ30)
80 ꢀ60)
98 ꢀ30)
99 ꢀ45)
95 ꢀ30)
97 ꢀ30)
94 ꢀ30)
4
2
f
C H CHꢀCH )OTMS
6
5
3
CH ꢀCH ) OTMS
2 6
3
CH ꢀCH ) OTMS
3 2 7
f
f
f
f
C H COCHꢀC H )OTMS
6
5
6 5
e
e
e
c
c
c
4
-ClC H OTMS
6
85 ꢀ120) 85 ꢀ120) 93 ꢀ90)
82 ꢀ105) 82 ꢀ120) 90 ꢀ90)
85 ꢀ105) 80 ꢀ120) 95 ꢀ90)
4
ꢀ-NaphthylOTMS
ꢁ
-NaphthylOTMS
a
All products were identi®ed by comparison of their physical and spectroscopic data with those of
b
c
d
authentic samples; isolated yields; reaction performed under re¯ux; reaction performed at room
f
temperature; 0.25 mmol of BiCl3; 0.15 mmol of BiꢀTFA)3
e

Conversion of TMS and THP Ethers to Esters
191
Table 2. Conversion of THP ethers to their corresponding acetates and benzoates in the presence of
a
BiꢀIII) salts
b
Yield of acetate/% ꢀt/min)
b
Yield of benzoate/% ꢀt/min)
THP Ether
BiCl3
BiꢀTFA)3 BiꢀOTf )3
BiCl3
BiꢀTFA)3 BiꢀOTf )3
C H CH OTHP
6
92 ꢀ45)
90 ꢀ60)
82 ꢀ50)
85 ꢀ70)
90 ꢀ60)
90 ꢀ45)
91 ꢀ60)
85 ꢀ50)
80 ꢀ70)
90 ꢀ60)
95 ꢀ30)
93 ꢀ30)
95 ꢀ30)
90 ꢀ45)
95 ꢀ30)
85 ꢀ60)
82 ꢀ60)
89 ꢀ60)
85 ꢀ80)
84 ꢀ75)
83 ꢀ60)
80 ꢀ60)
91 ꢀ60)
88 ꢀ80)
85 ꢀ75)
90 ꢀ50)
91 ꢀ50)
94 ꢀ50)
93 ꢀ50)
90 ꢀ50)
5
2
C H CH CH OTHP
2
6
5
2
C H CH CH CH OTHP
6
5
2
2
2
3
4
2
4
-MeOC H CH OTHP
6 4 2
-MeOC H CH OTHP
4
6
2
-NO C H CH OTHP
2
82 ꢀ100) 84 ꢀ100) 85 ꢀ45)
80 ꢀ120) 82 ꢀ120) 86 ꢀ60)
81 ꢀ100) 80 ꢀ100) 95 ꢀ60)
75 ꢀ120) 72 ꢀ120) 90 ꢀ60)
6
4
2
-NO C H CH OTHP
6
85 ꢀ70)
85 ꢀ60)
94 ꢀ45)
92 ꢀ45)
92 ꢀ45)
85 ꢀ60)
82 ꢀ70)
83 ꢀ60)
90 ꢀ45)
88 ꢀ45)
90 ꢀ50)
83 ꢀ60)
95 ꢀ40)
94 ꢀ45)
96 ꢀ35)
97 ꢀ35)
93 ꢀ30)
87 ꢀ35)
2
4
2
PhCHꢀCH )OTHP
3
CH ꢀCH ) OTHP
3 2 6
94 ꢀ45)
96 ꢀ45)
85 ꢀ45)
87 ꢀ60)
90 ꢀ45)
93 ꢀ45)
87 ꢀ45)
84 ꢀ60)
97 ꢀ35)
98 ꢀ35)
90 ꢀ35)
90 ꢀ45)
CH ꢀCH ) OTHP
3 2 7
CyclohexylOTHP
c
ꢀ
±)-MenthylOTHP
2
-NO C H OTHP
2 6 4
75 ꢀ120) 72 ꢀ120) 80 ꢀ75)
85 ꢀ120) 80 ꢀ120) 90 ꢀ50)
65 ꢀ180) 64 ꢀ180) 75 ꢀ135)
83 ꢀ180) 81 ꢀ180) 85 ꢀ120)
ꢁ
-NaphthylOTHP
a
All products were identi®ed by comparison of their physical and spectroscopic data with those
c
b
of authentic samples; isolated yields; ꢀ±)-menthylacetate and ꢀ±)-menthylbenzoate were obtained
from the reaction mixture
presence of phenolic TMS and THP ethers with high selectivity. Such a selectivity
has not been reported previously and can be considered as a useful practical
achievement in esteri®cation reactions.
In conclusion, we have demonstrated that BiCl , BiꢀTFA) , and BiꢀOTf ) are
3
3
3
practical and useful catalysts for the conversion of TMS and THP ethers to the
corresponding acetates and benzoates. In addition, high yields, short reaction times,
easy workup, availability, stability, and non-toxicity of the catalysts are note-
worthy advantages of this method.
Experimental
BiꢀTFA) and BiꢀOTf ) were prepared according to Ref. [19].
3
3
General procedure for the conversion of TMS ethers to their corresponding
acetates and benzoates
3
To a solution of 1 mmol TMS ether and 1.5 mmol acetic or benzoic anhydride in 3 cm CH CN, the
3
catalyst was added ꢀin the case of acetic anhydride, 0.2±0.25 mmol of BiCl , 0.1±0.15 mmol of
3
BiꢀTFA) , or 0.03 mmol of BiꢀOTf ) ; in the case of benzoic anhydride, 0.25 mmol of BiCl , 0.2 mmol
3
3
3
of BiꢀTFA) , or 0.05 mmol of BiꢀOTf ) ). The reaction mixture was stirred at room temperature or under
3
3
re¯ux for the time indicated in Table 1. The progress of the reaction was monitored by GLC or TLC.
3
The solvent was evaporated, and 20 cm ether were added. The reaction mixture was washed with
5
% aqueous solution of NaHCO , then with H O, and dried over Na SO . Evaporation of the
3 2 2 4
solvent followed by chromatography on silica gel ꢀTLC or CC) afforded the pure product in 80±99%
yield ꢀTable 1).

1
92
I. Mohammadpoor-Baltork and A. R. Khosropour
Table 3. Competitive acetylation and benzoylation of TMS and THP ethers in the presence of BiꢀIII)
salts
a
Yield/% ꢀt/min)
Substrate
Product
BiCl3
BiꢀTFA)3
BiꢀOTf )3
4
-NO C H CH OTMS
2
4-NO C H CH OAc
2
90 ꢀ40)
5
85 ꢀ40)
10
98 ꢀ20)
0
6
4
2
2
6
4
ꢁ
-NaphthylOTMS
ꢁ-NaphthylOAc
4
-NO C H CH OTMS
4
NO C H CH OAc
2
90 ꢀ40)
5
85 ꢀ40)
5
98 ꢀ20)
0
2
6
2
2
6
4
4
-ClC H OTMS
6
4-ClC H OAc
6 4
4
CH ꢀCH ) OTMS
3 2 7
CH ꢀCH ) OAc
3 2 7
95 ꢀ20)
5
93 ꢀ20)
0
100 ꢀ15)
0
ꢁ
-NaphthylOTMS
ꢁ-NaphthylOAc
4
-NO C H CH OTMS
4
4-NO C H CH OCOPh
2
70 ꢀ90)
30
75 ꢀ105)
20
90 ꢀ45)
10
2
6
2
2
6
4
ꢁ
-NaphthylOTMS
ꢁ-NaphthylOCOPh
4
4
-NO C H CH OTMS
4
4-NO C H CH OCOPh
4
82 ꢀ90)
17
85 ꢀ105)
12
94 ꢀ45)
5
2
6
2
2
6
2
-ClC H OTMS
6
4-ClC H OCOPh
6 4
4
CH ꢀCH ) OTMS
2 7
CH ꢀCH ) OCOPh
2 7
89 ꢀ30)
4
95 ꢀ30)
0
98 ꢀ30)
2
3
3
ꢁ
-NaphthylOTMS
ꢁ-NaphthylOCOPh
4
-NO C H CH OTHP
6
4-NO C H CH OAc
4
75 ꢀ70)
10
70 ꢀ70)
20
60 ꢀ40)
37
2
4
2
2
6
2
ꢁ
-NaphthylOTHP
ꢁ-NaphthylOAc
4
2
-NO C H CH OTHP
6
4-NO C H CH OAc
2
88 ꢀ70)
7
85 ꢀ70)
5
84 ꢀ40)
8
2
4
2
2
6
4
-NO C H OTHP
2
2-NO C H OAc
2 6 4
6
4
CH ꢀCH ) OTHP
3 2 7
CH ꢀCH ) OAc
3 2 7
85 ꢀ45)
5
82 ꢀ45)
7
74 ꢀ35)
25
ꢁ
-NaphthylOTHP
ꢁ-NaphthylOAc
4
-NO C H CH OTHP
4
4-NO C H CH OCOPh
2
80 ꢀ100)
10
77 ꢀ100)
7
86 ꢀ60)
8
2
6
2
2
6
4
ꢁ
-NaphthylOTHP
ꢁ-NaphthylOCOPh
4
2
-NO C H CH OTHP
2
4-NO C H CH OCOPh
2
76 ꢀ100)
3
73 ꢀ100)
3
90 ꢀ60)
5
6
4
2
6
4
2
-NO C H OTHP
4
2-NO C H OCOPh
2 6 4
2
6
CH ꢀCH ) OTHP
3 2 7
CH ꢀCH ) OCOPh
2 7
95 ꢀ45)
2
90 ꢀ45)
4
96 ꢀ35)
3
3
ꢁ
-NaphthylOTHP
ꢁ-NaphthylOCOPh
a
GLC yield
General procedure for the conversion of THP ethers to their corresponding
acetates and benzoates
3
A solution of 1 mmol THP ether and 1.5 mmol acetic or benzoic anhydride in 3 cm CH CN was
3
treated with the catalyst ꢀin the case of acetic anhydride, 0.2 mmol of BiCl , 0.15 mmol of BiꢀTFA) ,
3
3
or 0.03 mmol of BiꢀOTf ) ; in the case of benzoic anhydride, 0.3 mmol of BiCl , 0.25 mmol of
3
3
BiꢀTFA) , or 0.06 mmol of BiꢀOTf ) ). The reaction mixture was stirred under re¯ux for the time
3
3
indicated in Table 2. The progress of the reaction was monitored by GLC or TLC. The solvent was
3
evaporated, and 20 cm ether were added. The reaction mixture was washed with 5% aqueous
solution of NaHCO , then with H O, and dried over Na SO . Evaporation of the solvent followed by
3
2
2
4
chromatography on silica gel ꢀTLC or CC) provided the pure product in 64±98% yields ꢀTable 2).
Acknowledgements
We are grateful to the Isfahan University Research Council for partial support of this work.

Conversion of TMS and THP Ethers to Esters
193
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Received May 21, 2001. Accepted June 25, 2001