Solvent-Free Tetrahydropyranylation of Alcohols with Sulfamic Acid as Reusable Catalyst

Article abstract of DOI:10.1081/SCC-120026316

An efficient H₂NSO₃H-catalyzed solvent-free tetrahydropyranylation of various alcohols at room temperature was investigated. The features of mild conditions, cost-efficient catalyst, simple work-up, and the recyclability of the catalyst were displayed in this article.

Full text of DOI:10.1081/SCC-120026316

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Solvent-Free Tetrahydropyranylation of Alcohols with
Sulfamic Acid as Reusable Catalyst
a
a
a
Bo Wang , Li-Ming Yang & Ji-Shuan Suo
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of
Chemical Physics, Chinese Academy of Sciences, Lanzhou, China
Published online: 19 Aug 2006.
To cite this article: Bo Wang , Li-Ming Yang & Ji-Shuan Suo (2003): Solvent-Free Tetrahydropyranylation of Alcohols with
Sulfamic Acid as Reusable Catalyst, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 33:22, 3929-3934
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Õ
SYNTHETIC COMMUNICATIONS
Vol. 33, No. 22, pp. 3929–3934, 2003
Solvent-Free Tetrahydropyranylation
of Alcohols with Sulfamic Acid
as Reusable Catalyst
Bo Wang, Li-Ming Yang,* and Ji-Shuan Suo
State Key Laboratory for Oxo Synthesis and Selective
Oxidation, Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou, China
ABSTRACT
An efficient H NSO H-catalyzed solvent-free tetrahydropyrany-
2
3
lation of various alcohols at room temperature was investigated.
The features of mild conditions, cost-efficient catalyst, simple
work-up, and the recyclability of the catalyst were displayed in this
article.
*
Correspondence: Li-Ming Yang, State Key Laboratory for Oxo Synthesis
and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese
Academy of Sciences, Lanzhou 730000, China; Fax: þ86-931-8277088; E-mail:
limy@ns.lzb.ac.cn.
3
929
DOI: 10.1081/SCC-120026316
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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3
930
Wang, Yang, and Suo
INTRODUCTION
Protection of hydroxy groups by their conversion to the corres-
ponding tetrahydropyranyl ethers (THP ethers) is a common and widely
[
1,2]
used transformation in organic synthesis.
The THP ethers are attractive
because they are undoubtedly low expensive, stable enough to a wide range
of reaction conditions, and easy to be deprotected.
In addition to the well known protic and Lewis acid, a variety of
catalysts have been developed for tetrahydropyranylation of hydroxy
[
3]
[4]
functions, such as bis[trimethylsilyl]sulfate,
trimethyliodosilane,
[6]
zirconium sulfophenyl phosphonate,
[
5]
Ru(CH ) -(triphos)](OTf) ,
3
3
2
[
7]
[8]
lithium perchlorate–diethylether,
polyaniline salts,
[10]
vanadyl(IV)
[11]
and lithium triflate ; very
[9]
acetate, tributylammonium bromide,
[
recently, iodinemicrowave irradiation
12,13]
[14]
and ionic liquids as catalysts
have been used to promote the tetrahydropyranylation of alcohols.
Besides, tetrahydropyranylation have been carried out using some hetero-
[
15]
[16–18]
geneous catalysts, e.g., montmorillonite (an acid clay),
heteropolyacids,
zeolites,
etc. Although these methods are suitable for many
[19]
synthetic conditions, most of them have drawbacks such as harsh and
strong acidic conditions, expensive reagents, high temperature, and
nonreusability of catalysts, and also volatile organic solvents or large
amounts of solid supports are usually used, which would eventually
result in the generation of a large amount of toxic waste. Thus, it is
interesting for a solvent-free and catalytically efficient alternative for the
protection of hydroxyl functionality as THP ether.
In our development of new methods for functional group trans-
formations, we are especially interested in developing the potential uses
of various types of low-cost, mild, and efficient catalysts. Sulfamic
acid (H NSO H), which is a common organic acid with mild acidity,
2
3
involatility, and incorrosivity, has been studied as an acid catalyst in
[
20]
acetalization and ketalization reactions.
Particularly, H NSO H is
2 3
insoluble in common organic solvents, and so, its separation and recycling
is very easy in catalytic reaction. Herein, we report an efficient
H NSO H-catalyzed solvent-free tetrahydropyranylation of alcohols at
2
3
room temperature.
H NSO H
R. T.
2
3
+
R
OH
O
O
O
R

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Tetrahydropyranylation of Alcohols
EXPERIMENTAL
Typical Procedure of Tetrahydropyranylation
3931
To a stirred mixture of an alcohol (10 mmol) and 3,4-dihydro-2H-pyran
13 mmol) in a reaction flask, H NSO H (0.19 g) was added. The mixture
was stirring at room temperature (15 C), and the progress of the reaction
was monitored by Hewlett-Packard 6890/5793 GC/MS. After completion
of the reaction, diethyl ether (100mL) was added to the mixture, and a white
solid, sulfamic acid, was precipitated. The catalyst was recovered from the
(
2
3
ꢀ
mixture by filtration. The filtrate was dried over anhydrous Na SO4
2
and then evaporated to give almost pure product. Further purification
was achieved through a short column of silica gel (2 cm in length, 0.5 cm
in diameter) with petroleum ether to obtain the pure THP ether.
RESULTS AND DISCUSSIONS
In the present method, alcohol, 3,4-dihydro-2H-pyran (DHP) and
H NSO H catalyst were mixed together to yield the corresponding
2
3
THP ether at room temperature. It was very interesting that at initial
stage of the reaction, H NSO H catalyst was soluble in the mixture when
short chain alcohols, such as n-propanol, i-propanol, and n-butanol, were
2
3
used. H NSO H could be crystallized from this homogenous solution as
2
3
these alcohols were converted gradually. This dissolution at beginning of
reaction should be attributed to the high polarity of the reaction mixture
dissolving short chain alcohols. With the decrease in concentration of the
alcohols with the reaction, the polarity of the mixture accordingly
decreased, and thus the progressively precipitating of H NSO H was
2
3
reasonable. After the reaction, the catalyst was conveniently recovered
from reaction mixture by filtration and the product was obtained by
simple distillation. A wide variety of alcohols were converted to the
corresponding THP ethers in high yield via this procedure (see Table 1).
Primary, secondary, tertiary, benzylic, allylic, as well as propiolic
alcohols can be conveniently protected to be tetrahydropyranyl ethers
under mild conditions. It is important to note that the acid sensitive
alcohols, such as t-amyl alcohol and t-butanol, undergo protection as
tetrahydropyranyl ethers in 4.5 h without the formation of dehydration
products, indicating the usefulness of this method. The recovered
sulfamic acid could be used directly in next run without any treatment.
Even if sulfamic acid has been reused four times, no considerable activity
loss was observed in the tetrahydropyranylation of butanol.

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932
Wang, Yang, and Suo

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Tetrahydropyranylation of Alcohols
CONCLUSION
3933
Sulfamic acid is effective for tetrahydropyranylation of alcohols with
the features of mild and solvent-free conditions, cost-efficient catalyst,
simple work-up, and the recyclability of the catalyst. Therefore the
present catalytic method is useful in synthetic organic chemistry.
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Received in Japan April 9, 2003