Direct oxidative deprotection of tetrahydropyranyl ethers using hexamethylenetetramine-bromine supported onto silica gel under microwave irradiation in solventless system

Article abstract of DOI:10.1080/10426500490463952

Primary and secondary tetrahydropyranyl ethers (THP ethers) are converted to their corresponding carbonyl compounds efficiently using hexamethylene- tetramine-bromine supported onto silica gel under microwave irradiation in solvent-free conditions.

Full text of DOI:10.1080/10426500490463952

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Phosphorus, Sulfur, and Silicon and the Related
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DIRECT OXIDATIVE DEPROTECTION OF
TETRAHYDROPYRANYL ETHERS USING
HEXAMETHYLENETETRAMINE-BROMINE SUPPORTED
ONTO SILICA GEL UNDER MICROWAVE IRRADIATION IN
SOLVENTLESS SYSTEM
Mahboobeh Behnam Dehkordi a , Majid M. Heravi b , Ahmad Ziafati a , Parviz Khosrofar a &
Mitra Ghassemzadeh c
a Department of Chemistry , Mashhad, Iran
b Department of Chemistry , Tehran, Iran
c Chemistry & Chemical Engineering Research Center of Iran , Tehran, Iran
Published online: 16 Aug 2010.
To cite this article: Mahboobeh Behnam Dehkordi , Majid M. Heravi , Ahmad Ziafati , Parviz Khosrofar & Mitra Ghassemzadeh
(2004) DIRECT OXIDATIVE DEPROTECTION OF TETRAHYDROPYRANYL ETHERS USING HEXAMETHYLENETETRAMINE-BROMINE
SUPPORTED ONTO SILICA GEL UNDER MICROWAVE IRRADIATION IN SOLVENTLESS SYSTEM, Phosphorus, Sulfur, and Silicon and the
Related Elements, 179:8, 1493-1496, DOI: 10.1080/10426500490463952
To link to this article: http://dx.doi.org/10.1080/10426500490463952
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Phosphorus, Sulfur, and Silicon, 179:1493–1496, 2004
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Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490463952
DIRECT OXIDATIVE DEPROTECTION
OF TETRAHYDROPYRANYL ETHERS
USING HEXAMETHYLENETETRAMINE-BROMINE
SUPPORTED ONTO SILICA GEL
UNDER MICROWAVE IRRADIATION IN
SOLVENTLESS SYSTEM
Mahboobeh Behnam Dehkordi,a Majid M. Heravi,b
Ahmad Ziafati,a Parviz Khosrofar,a and Mitra Ghassemzadehc
Department of Chemistry, Ferdowsi University of Mashhad,
Mashhad, Iran;a Department of Chemistry, School of Sciences,
Azzahra University, Vanak, Tehran, Iran;b and Chemistry &
Chemical Engineering Research Center of Iran, Tehran, Iranc
(Received December 22, 2003; accepted March 15, 2004)
Primary and secondary tetrahydropyranyl ethers (THP ethers) are con-
verted to their corresponding carbonyl compounds efficiently using
hexamethylene-tetramine-bromine supported onto silica gel under mi-
crowave irradiation in solvent-free conditions.
Keywords: Carbonyl compounds; microwave irradiation; oxidation;
solvent-free conditions; THP ethers
The use of one-pot reactions offers a great success in organic synthe-
sis today. The combination of the one-pot strategy with the use of eco-
friendly solid-acid catalysts is now the best tool for the synthesis of
specific target compounds with minimum production of pollutants as
well as reduction of the cost.1
Direct oxidation of tetrahydropyranyl (THP) ethers to the corre-
sponding carbonyl compounds has found considerable attention during
recent years.2
Hexamethylenetetramine-bromine is an inexpensive reagent that
has been used for oxidation of alcohols,3 and the cleavage of oximes4
and semicarbazones.5
The authors are thankful to Ferdowsi University of Mashhad for the partial financial
assistance.
Address correspondence to Majid M. Heravi, Department of Chemistry, School of Sci-
ences, Azzahra University, Tehran, Iran. E-mail: Mmheravi@azzahra.ac.ir
1493

1494
M. B. Dehkordi et al.
Microwave irradiation in organic synthesis is a useful technique
nowadays.6 Dry media using microwave heating have attracted much
attention.7
Oxidation reactions are less considered under microwave irradiation
due to unsafe and uncontrollable experimental conditions.8 Impregna-
tion of reagents on solid supports have circumvented this problem and
provides an attractive alternative in organic synthesis in view of selec-
tivity and ease of manipulation.9
We have recently reported the oxidation of alcohols3b and deoxi-
mation4 and desemicarbonzation5 using hexamethylenetetramine-
bromine under microwave irradiation in solvent-free conditions. In
continuation of manipulation of the above supported reagent and in
connection with our investigations on organic reactions in solventless
system under microwave irradiation,9 herein we report our results for
the mild, facile, fast, and high-yielding reaction of the direct oxidative
deprotection of THP ethers using hexamethylenetetramine-bromine
supported onto silica gel under microwave irradiation in solventless
system.
The reaction is conducted by mixing hexamethylenetetramine-
bromine with silica gel, and adding the neat THP ethers and grinding
them thoroughly to make an intimate mixture. By placing the mixture
in a microwave oven the reactions are completed in a couple of seconds.
In a typical procedure THP ethers of benzyl alcohol were mixed with
2 equivalent of hexamethylenetetramine-bromine supported onto sil-
ica gel. The mixture was placed in a microwave oven, the progress of
the reaction was monitored by TLC (thin layer chromatography) (us-
ing petroleum either: ethyl acetate 8:2 as eluent). The reaction was
completed in 2 min with an 83% yield. To establish the generality of
the method, various THP ethers were converted to their carbonyl com-
pounds (Table I). No over-oxidation to carboxylic acid was observed.
In conclusion, we have developed a solid-state method for facile,
mild, and rapid one-pot oxidative deprotection of THP ethers

Deprotection of Tetrapyranyl Ethers
1495
TABLE I Direct Oxidative Deprotection of THP Ethers Using
Hexamethylenetetramine-Bromine Under Microwave Irradiation
in Solventless System
Entry
Substrate
Time (s)
Product
Yield (%)
1
2
3
4
5
6
7
PhCH2OTHP
120
110
110
120
120
90
PhCHO
83
75
73
82
85
72
65
CH3(CH2)2CH2OTHP
CH3(CH2)6CH2OTHP
C6H13CH2OTHP
c-C6H11OTHP
CH3(CH2)2CHO
CH3(CH2)6CHO
C6H13CHO
Cyclohexanone
Menthone
(−)-Menthol-THP
Cholestroil-THP
90
Cholostenone
using hexamethylenetetramine-bromine supported onto silica gel. The
reagent is prepared by adding bromine to a chloroform solution of com-
mercially available amine.3b This homogenous nonhygroscopic solid is
very stable at room temperature and is not affected by ordinary expo-
sure to light, air, or water, and has no offensive odour of bromine or
amine.
EXPERIMENTAL
All compounds are known and were identified with authentic samples.
Yields refer to isolated products. Hexamethylenetetramine-bromine
was prepared by the reported procedure.3b THP ethers were prepared
by the described method.10
Typical Procedure
Hexamethylenetetramine-bromine (2 mmol) was mixed thoroughly
with an equivalent weight of silica gel (mesh 60) in a beaker using
a spatula. To this mixture neat benzyl THP ether (1 mmol) was added
and mixed to make an intimate mixture. The beaker was placed in a
household microwave oven and irradiated for 2 min. The progress of re-
action was monitored by TLC using petroleum ether: ethyl acetate 8:2
as eluent. Upon completion of the reaction, CH2Cl2 (5 ml) was added.
The mixture was filtered and the filtrate was evaporated to afford the
benzaldehyde, yield 83%. Caution: although we did not encounter any
accident, the use of a microwave oven in an efficient hood is highly
recommended.

1496
M. B. Dehkordi et al.
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