Efficient one-step conversion of tetrahydropyranyl ethers into acetates and formates in the presence of potassium dodecatungstocobaltate K 5CoW12O40·3H2O

Article abstract of DOI:10.1007/s11178-005-0176-0

Tetrahydropyranyl ethers derived from primary alcohols were directly and efficiently converted into the corresponding acetates and formates by the action of ethyl acetate, acetic acid, acetic anhydride, and ethyl formate in the presence of a catalytic amount of potassium dodecatungstocobaltate K ₅CoW₁₂O₄₀ ? 3H₂O. Tetrahydropyranyl ethers derived from secondary alcohols and phenols can also be transformed into the corresponding acetates with the use of acetic anhydride, but K₅CoW₁₂O₄₀ ? 3H₂O was ineffective for esterification with ethyl acetate, acetic acid, and ethyl formate.

Full text of DOI:10.1007/s11178-005-0176-0

Russian Journal of Organic Chemistry, Vol. 41, No. 3, 2005, pp. 393–395. From Zhurnal Organicheskoi Khimii, Vol. 41, No. 3, 2005, pp. 403–405.
Original English Text Copyright © 2005 by Rafiee, Tangestaninejad, Habibi, Mohammadpoor-Baltork, Mirkhani.
Efficient One-Step Conversion of Tetrahydropyranyl Ethers
into Acetates and Formates in the Presence of Potassium
Dodecatungstocobaltate K5CoW12O40 ·3H2O*
E. Rafiee, Sh. Tangestaninejad, M. H. Habibi, I. Mohammadpoor-Baltork, and V. Mirkhani
Department of Chemistry, Isfahan University, Isfahan 81744-73441, Iran
fax: +98(311)6689732; e-mail: e.rafiee@sci.ui.ac.ir
Received January 14, 2004
Abstract—Tetrahydropyranyl ethers derived from primary alcohols were directly and efficiently converted into
the corresponding acetates and formates by the action of ethyl acetate, acetic acid, acetic anhydride, and ethyl
formate in the presence of a catalytic amount of potassium dodecatungstocobaltate K5CoW12O40·3H2O.
Tetrahydropyranyl ethers derived from secondary alcohols and phenols can also be transformed into the corre-
sponding acetates with the use of acetic anhydride, but K5CoW12O40·3H2O was ineffective for esterification
with ethyl acetate, acetic acid, and ethyl formate.
Protection and subsequent deprotection of func-
tional groups are important processes in multistep
organic syntheses [1]. Tetrahydropyranyl ethers are
widely used in organic chemistry to protect hydroxy
groups, for these compounds are stable under various
reaction conditions [2]; however, they are unsuitable in
acidic medium. Acetate and formate moieties are also
important hydroxy-protecting groups which are resist-
ant to acidic reagents [2]; acetates and formates are
usually prepared by esterification of the corresponding
acids [3–5], transesterification [6], alkylation of car-
boxylate ions [7], acylation of alcohols and phenols
[8–12], or cleavage of ethers [13]. Thus direct con-
version of tetrahydropyranyl ethers into the corre-
sponding acetates and formates is an important process
in organic synthesis. Only a few reports on this topic
are available from the literature [14, 15]. Therefore,
introduction of new methods and reagents for such
transformation of functional groups is still in demand.
alcohols with ethyl acetate, ethyl formate, acetic acid,
and acetic anhydride [17, 18]. In continuation of our
studies in this line, we now report a convenient method
for direct esterification of tetrahydropyranyl ethers
with the above acylating agents in the presence of
K5CoW12O40·3H2O (Scheme 1).
Treatment of various tetrahydropyranyl ethers with
acetic anhydride in the presence of K5CoW12O40·3H2O
(2 mol %) at room temperature afforded the corre-
sponding acetates in good to excellent yields (Table 1).
In order to extend the scope of application of this
procedure we also examined esterification of tetra-
hydropyranyl ethers with less active acylating agents
such as ethyl acetate, acetic acid, and ethyl formate.
We found that tetrahydropyranyl ethers derived from
primary alcohols were converted to the corresponding
acetates and formates in good to excellent yields under
reflux conditions (Tables 1, 2; run nos. 1–12). Under
the same conditions, tetrahydropyranyl ethers derived
from secondary alcohols and phenols turned out to
be more resistant: they either remained intact or were
transformed into the corresponding acetates and
formates in relatively poor yields (Tables 1, 2; run
nos. 13–15). We also found that the catalyst can be
reused several times without loss in activity. It was re-
generated simply by filtering, washing with acetone,
and drying. The yield of benzyl acetate in the reaction
of benzyl tetrahydropyranyl ether with ethyl acetate,
promoted by five-fold recovered K5CoW12O40·3H2O,
remained equal to 95%.
We recently proposed to use K5CoW12O40·3H2O as
an efficient catalyst for removal of the tetrahydro-
pyranyl protecting group from tetrahydropyranyl
ethers [16] and for acetylation and formylation of
Scheme 1.
K5CoW12O40 ·3H2O
R1OTHP
+
R2C(O)OR3
R2C(O)OR1
For R1, see Tables 1, 2; R2 = CH3, H; R3 = H, Et, CH3CO.
* The original article was submitted in English.
1070-4280/05/4103-0393 © 2005 Pleiades Publishing, Inc.

RAFIEE et al.
394
Table 1. Conversion of tetrahydropyranyl ethers into the corresponding acetates in the presence of K5CoW12O40·3H2O
Yield of acetate,a %
acetic acidb (time, h) acetic anhydridec (time, min)
Run no.
Initial ether
ethyl acetateb (time, h)
94 (10)
98 (6)
01
02
03
04
05
06
07
08
09
3-MeOC6H4CH2OTHP
4-ClC6H4CH2OTHP
PhCH=CHCH2OTHP
PhCH2CH2OTHP
PhCH2CH2CH2OTHP
PhCH2OTHP
96 (2.5)
97 (2.25)
98 (0.4)
95 (3.5)
96 (2)
90 (20)
98 (3)
75 (0.5)
98 (6)
94 (8)
91 (15)
94 (3)
98 (5)
98 (6)
95 (2)
94 (20)
70 (13)
84 (45)
03 (25)
CH3(CH2)6OTHP
CH3(CH2)8OTHP
95 (6)
96 (2)
90 (7)
92 (2.5)
95 (2)
CH3(CH2)3CH(Et)CH2OTHP
88 (8)
OTHP
10
32 (8)
32 (2)
95 (7)
11
12
13
14
15
2,3-(MeO)2C6H4CH2OTHP
4-O2NC6H4CH2OTHP
4-BrC6H4CH(CH3)OTHP
Ph2CHOTHP
61 (1)
53 (2)
20 (2)
90 (3.5)
90 (1)
95 (30)
50 (10)
93 (17)
97 (10)
80 ( 120)
45 (1)
20 (1)
96 (0.25)
30 (4)
2-C10H7OTHP
a
b
c
According to the GLC data.
The reactions were carried out under reflux.
The reactions were carried out at room temperature.
Table 2. Conversion of tetrahydropyranyl ethers into the corresponding formates in the presence of K5CoW12O40 ·3H2O
(under reflux conditions)
Run
no.
Time,
min
Run
no.
Time,
min
Initial ether
Yield,a %
Initial ether
Yield,a %
40
1
2
3
4
5
6
7
8
9
3-MeOC6H4CH2OTHP
4-ClC6H4CH2OTHP
PhCH=CHCH2OTHP
PhCH2CH2OTHP
40
60
20
45
20
05
30
30
20
83
97
94
91
91
90
94
93
94
OTHP
10
20
PhCH2CH2CH2OTHP
PhCH2OTHP
11
12
13
14
15
2,3-(MeO)2C6H4CH2OTHP
4-O2NC6H4CH2OTHP
4-BrC6H4CH(CH3)OTHP
Ph2CHOTHP
60
91
50
50
90
00
30
CH3(CH2)6OTHP
09 h
45
CH3(CH2)8OTHP
CH3(CH2)3CH(Et)CH2OTHP
2-C10H7OTHP
10 h
a
According to the GLC data.
Thus we have proposed a convenient procedure for
EXPERIMENTAL
acetylation and formylation of alcohols through the
corresponding tetrahydropyranyl ethers. The procedure
is advantageous due to easy isolation of the products
and relatively low toxicity and reusability of the
catalyst.
Potassium dodecatungstocobaltate K5CoW12O40·
3H2O was prepared by the procedure described in [17].
Typical procedure for the conversion of tetrahy-
dropyranyl ethers into the corresponding acetates
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 3 2005

EFFICIENT ONE-STEP CONVERSION OF TETRAHYDROPYRANYL ETHERS
395
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and formates. To a solution of 1 mmol of tetra-
hydropyranyl ether and 4 ml of acylating agent we
added K5CoW12O40 ·3H2O in an amount of 0.05 mmol
for ethyl acetate, 0.01 mmol for acetic acid or ethyl
formate, or 0.02 mmol for acetic anhydride. The mix-
ture was stirred at room temperature or at the boiling
point for a time indicated in Table 1 or 2. The progress
of the reaction was monitored by GLC or TLC. The
catalyst was filtered off, the filtrate was evaporated,
20 ml of diethyl ether was added to the residue, and the
solution was washed with 5% aqueous NaHCO3 and
water, dried over Na2SO4, and evaporated. The prod-
ucts were isolated by chromatography on silica gel and
were characterized by the IR and 1H NMR spectra.
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The authors are thankful to the Isfahan University
Research Council for partial support of this work.
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