Zeofen: A user-friendly catalyst for oxidative cleavage of tetrahydropyranyl ethers under non-aqueous conditions

Article abstract of DOI:10.1007/s007060170076

Primary and secondary tetrahydropyranyl ethers are efficiently converted to carbonyl compounds in excellent yields by zeofen under non-aqueous conditions.

Full text of DOI:10.1007/s007060170076

Monatshefte f uÈ r Chemie 132, 871±873 (2001)
Zeofen: A User-Friendly Catalyst for Oxidative
Cleavage of Tetrahydropyranyl Ethers Under
Non-Aqueous Conditions
Bagher Mohajerani1 , Majid M. Heravi , and Dariush Ajami2
;Ã
2;Ã
1
Chemistry and Petrochemical Division, Research Institute of Petroleum Industry, Tehran, Iran
2
Chemistry and Chemical Research Center of Iran, Tehran, Iran
Summary. Primary and secondary tetrahydropyranyl ethers are ef®ciently converted to carbonyl
compounds in excellent yields by zeofen under non-aqueous conditions.
Keywords. THP ethers; Zeofen; Oxidative deprotection; Carbonyl compounds.
Introduction
The tetrahydropyranyl group is one of the most widely employed protecting groups
in organic synthesis [1]. Because of the remarkable stability of tetrahydropyranyl
ethers towards a variety of conditions such as strongly basic media, reactions
involving Grignard reagents and lithium alkyls, reduction with hydride, oxidation,
oxidative alkylation, and acylation reactions, tetrahydropyranylation is one of the
methods of choice to protect a hydroxy group in a multi-step organic synthesis [2].
Many catalysts have been reported for the tetrahydropyranylation of alcohols and
the cleavage of tetrahydropyranyl ethers to the parent alcohols [3]. Direct oxidation
of tetrahydropyranyl ethers to the corresponding carbonyl compounds has been
relatively less considered. Although a number of reagents are known for such a
transformation [4], there is still a need either to improve the existing oxidative
deprotection methods or to introduce new reagents to permit better selectivity and,
most importantly, to be environmentally benign. Most of the reagents used for
oxidative dehydropyranylation are based on chromium [4]. Chromium compounds
are toxic, corrosive, and they are irritants for the skin and for sensitive parts of body
such as eyes [5]. Chromium(VI) compounds are suspected to be carcinogens [6].
In this communication we report that zeofen can ef®ciently oxidatively de-
protect tetrahydropyranyl ethers to yield the corresponding carbonyl compounds.
Results and Discussion
Zeofen (zeolite HZSM-5 and ferric nitrate) has been used for the oxidation of
alcohols to the corresponding carbonyl compounds by classical heating and micro-
à Corresponding authors

872
B. Mohajerani et al.
Table 1. Oxidative cleavage of THP ethers with zeofen in CH2Cl2 at re¯ux temperature
ꢁ
ꢁ
Substrate
t/h
Product
Yield/%
m.p./ C or b.p./ C(torr)
Found
Ref. [11]
PhCH2OTHP
6
6
PhCHO
91
98
80
85
88
78
82
85
88
177±178(760)
58±59
178±179(760)
59±61
4
2
-MeC6H4CH2OTHP
4-MeC6H4CHO
2-NO2-5-MeCH3CHO
PhCOMe
-NO2-5-MeC6H3OTHP
10
6
66±67
66±67
PhCH(Me)OTHP
Ph2CHOTHP
201±202(760)
46±47
202(760)
49±59
8
PhCOPh
PhCH=CHCH2OTHP
Cyclohexyl-THP
Me-Cyclohexyl-THP
10
12
10
10
PhCH=CHCHO
Cyclohexanone
2-Me-Cyclohexanone
(� )-Menthone
247±248(760)
156±157(760)
163±164(760)
207±208(760)
248(760)
155(760)
165(760)
200±210(760)
(
� )-Menthyl-THP
wave irradiation [7]. The association of ferric salts with clay had been pioneered in
the 1980s, leading to the design of clayfen [8] as a versatile reagent [9] including the
oxidative cleavage of tetrahydropyranyl ethers to carbonyl compounds.
A variety of tetrahydropyranyl ethers were treated with catalytic amounts of
zeofen [7]. The corresponding aldelydes and ketones were obtained in high to
excellent yields. The results are summarized in Table 1. To prepare zeofen,
FeꢀNO † Á 9H O and a weight equivalent of HZSM-5 zeolite were crushed together
3
2
3
to form an intimate mixture. In a typical procedure, 1±1.2 equivalents of zeofen
were re¯uxed with a tetrahydropyranyl ether in dichloromethane.
In conclusion, zeofen represents a convenient reagent for the one-pot oxidative
deprotection of tetrahydropyranyl ethers to the corresponding carbonyl compounds.
The notable advantages of this methodology are use of non-toxic ferric nitrate, mild
conditions, and high to excellent yields.
Experimental
Zeofen was prepared by a reported method [7]. Yields refer to isolated products which were
identi®ed by comparison of their physical and spectroscopic data with those of authentic samples
[
11]. THP ethers were prepared according to Ref. [3b].
Oxidative deprotection of tetrahydropyranyl ethers; general procedure
3
In a round-bottomed ¯ask (5 cm ) equipped with stirrer and condenser, 1 mmol THP ether was
3
dissolved in 15 cm CH2Cl2 was prepared. Zeofen (equivalent to 1.2 mmol ferric nitrate) was added
to this solution and re¯uxed for the time indicated. The progress of the reaction was monitored by
TLC (eluent: petroleum ether:ethyl ˆ acetate 8:2). After completion of the reaction the mixture was
®ltered, and the solid material was washed with CH2Cl2. The ®ltrate was combined and evaporated

Dehydropyranylation by Zeofen
873
to dryness. The crude residue was subjected to column chromatography using petroleum ether:ethyl
acetate ˆ 8:2 as eluent to afford the corresponding carbonyl compounds (Table 1).
Acknowledgements
The authors are grateful to Dr. A. R. Garakani for a generous gift of zeolite.
References
[
1] a) Green TW, Wutz PGM (1991) Protective Groups in Organic Synthesis, 2nd edn. Wiley, New
York, p 68; b) Reese CB (1973) Protective Groups in Organic Chemistry. Plenum, London, chapt 3
2] Hoger S, Laszlo P, Orlovi M, Polla E (1986) Synthesis 655
[
[
3] a) Ballini R, Bigi F, Carlose S, Maggi R, Sartori E (1997) Tetrahedron Lett 38: 4169; b) Heravi
MM, Ajami D, Ghassemzadeh M (1999) Synth Commun 29: 1013; c) Cha KH, Kang TW, Lee
HW, Kim EN, Choi NH, Kim JW, Hong Ch (1998) Synth Commun 28: 2131; d) Heravi MM,
Bigdeli MA, Nahid N, Ajami D (1999) Indian J Chem 1285
[
[
[
4] a) Heravi MM, Ajami D (1998) J Chem Res 718; b) Heravi MM, Ajami D, Tabar-Hyder K (1999)
Monatsh Chem 130: 337; c) Heravi MM, Ajami D, Ghassemzadeh M (1999) Synthesis 393
5] Page BJ, Loar GW (1988) In: Kirk-Othmer (ed) Encyclopedia of Chemical Technology, vol 6.
Wiley, New York, pp 263±311
6] Nriagu JO, Nuboor E (1988) Chromium in the Natural and Human Environments. Wiley, New
York
[
[
[
7] Heravi MM, Ajami D, Aghapoor K, Ghassemzadeh M (1999) J Chem Soc Chem Commun 833
8] Fieser M, Fieser (1984) Reagents for Organic Synthesis, vol 11. Wiley, New York, p 237
9] Cornelis A, Laszlo P (1985) Synthesis 909
[
10] Heravi MM, Ajami D, Mojtahedi MM, Ghassemzadeh M (1999) Tetrahedron Lett 40: 561
11] Aldrich Catalogue / Handbook of Fine Chemicals 1990±1991
[
Received November 21, 2000. Accepted (revised) January 9, 2001