Solvent-free DABCO-catalyzed one-pot conversion of tetrahydropyranyl ethers into acetates by the action of bismuth(III) nitrate under microwave irradiation

Full text of DOI:10.1134/S1070428009070215

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 7, pp. 1110–1111. © Pleiades Publishing, Ltd., 2009.
Published in Russian in Zhurnal Organicheskoi Khimii, 2009, Vol. 45, No. 7, pp. 1121–1122.
SHORT
COMMUNICATIONS
Solvent-Free DABCO-Catalyzed One-Pot Conversion
of Tetrahydropyranyl Ethers into Acetates by the Action
of Bismuth(III) Nitrate under Microwave Irradiation*
K. Asadolah, M. M. Heravi, and R. Hekmatshoar
Department of Chemistry, School of Sciences, Azzahra University, Vanak, Tehran, Iran;
e-mail: mmh1331@yahoo.com
Received September 28, 2005
DOI: 10.1134/S1070428009070215
Acetylation of alcohols is an important transforma-
tion frequently used in organic synthesis [1]. Selective
protection of functional groups and their subsequent
deprotection are common processes in multistep organ-
ic syntheses, and conversion of one functional group
into another is useful in day-to-day synthetic practice.
Among protecting groups for alcohols, tetrahydropyr-
anyl (THP) ethers are used most frequently due to
their easy formation, reasonable stability, and compati-
bility with various reaction conditions [1, 2]. Although
several methods have been reported for deprotection of
THP ethers [2], as well as for the transformation of
alcohols into acetates [3], procedures for direct conver-
sion of THP ethers into acetates are few in number, and
they suffer from serious disadvantages. These proce-
dures make use of the following reagents: FeCl /Ac O
lyst in the direct conversion of THP ethers into the
corresponding acetates in the presence of bismuth(III)
nitrate under microwave irradiation without a solvent.
Development of clean and efficient catalytic proce-
dures is important from both economic and environ-
mental points of view. Our experience in performing
catalytic transformations of THP ethers [16] under eco-
logically friendly conditions [13–15] prompted us to
elaborate a direct and fast one-pot procedure for the
transformation of THP ethers into acetates. We re-
cently described a mild and efficient method for the
conversion of alcohols and phenols into the corre-
sponding tetrahydropyranyl ethers [16]. For direct
deprotection and acetylation, tetrahydropyranyl ether
derived from benzyl alcohol was applied onto silica
gel, bismuth(III) nitrate and acetic anhydride were
added, and the mixture was thoroughly stirred and
placed in microwave oven. The reaction gave benzal-
dehyde as the major product and benzyl acetate as
minor one. When benzyl alcohol was used instead of
its THP ether, benzaldehyde was formed in quantita-
tive yield. These findings indicated that oxidative de-
protection of THP ether must be minimized to ensure
direct one-pot transformation of benzyl THP ether into
benzyl acetate. In other words, the oxidative ability of
bismuth(III) nitrate should be suppressed.
3
2
[
4], AcCl/AcOH [5], Ti/Ac O [6], bismuth salts [7],
2
Cu(OTf) /Ac O [8], and ZrCl [9]. In the recent years,
2
2
4
microwave irradiation has become popular in organic
synthesis due to acceleration of a wide variety of trans-
formations [10]. Examples of microwave-assisted syn-
thesis utilizing supported reagents under solvent-free
conditions have been reported very recently; here,
a combination of the convenience of supported re-
agents and the gain in reaction rate produced by micro-
waves gave excellent results in the preparation of vari-
ous organic compounds [11]. The utility of bismuth
compounds in organic transformations has been exten-
sively studied [12].
It is known that bismuth(III) nitrate readily forms
complexes with amines [17] and that such complex
formation should reduce the oxidative power of
Bi(NO ) [18]. For this purpose, we used a catalytic
In continuation of our studies on catalytic reactions
3
3
[13, 14] and the use of bismuth compounds in organic
transformations [15] we now report that 1,4-diazabi-
cyclo[2.2.2]octane (DABCO) is an effective co-cata-
Me
OR
Ac O, Bi(NO ) , DABCO, MW
2
3 3
O
*
The text was submitted by the authors in English.
O
OR
1
110

SOLVENT-FREE DABCO-CATALYZED ONE-POT CONVERSION
1111
amount of DABCO in the above reaction. A large num-
ber of structurally different THP ethers were subjected
to deprotection–acetylation with acetic anhydride in
the presence of DABCO and bismuth(III) nitrate under
microwave irradiation. Below are listed the R group in
the substrate, reaction time (min), yield (%, isolated
ide and water, dried over MgSO , and evaporated to
dryness, and the residue was purified by column chro-
matography.
4
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1
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We can conclude that the proposed procedure for
the direct one-pot transformation of tetrahydropyranyl
ethers into acetates is simple, efficient, and general. It
requires no solvent and utilizes accessible, inexpen-
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Typical procedure for the transformation of
tetrahydropyranyl ethers into the corresponding
acetates. A mixture of 0.5 mmol of THP ether [16],
0
0
.5 mmol of bismuth(III) nitrate pentahydrate,
.1 mmol of DABCO, and silca gel was thoroughly
1
1
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stirred and ground in a mortar. The mixture was trans-
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was added, the mixture was thoroughly stirred with
a spatula, and the beaker was placed into a microwave
oven and irradiated for a time indicated above. The
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product was extracted into methylene chloride, the
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 7 2009