Chemoselective tetrahydropyranylation of alcohols and their detetrahydropyranylation using silicasulphuric acid as a reusable catalyst

Article abstract of DOI:10.1081/SCC-120038489

A simple, mild, and efficient protocol for chemoselective protection of alcohols over phenols as tetrahydropyranyl ethers and their deprotection using silicasulphuric acid as a reusable solid acid catalyst is described.

Full text of DOI:10.1081/SCC-120038489

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Chemoselective Tetrahydropyranylation of
Alcohols and Their Detetrahydropyranylation Using
Silicasulphuric Acid as a Reusable Catalyst
D. M. Pore a , Uday V. Desai a , R. B. Mane a & P. P. Wadgaonkar b
a Department of Chemistry , Shivaji University , Kolhapur, 416004, India
b Polymer Division , National Chemical Laboratory , Pune, India
Published online: 17 Aug 2006.
To cite this article: D. M. Pore , Uday V. Desai , R. B. Mane & P. P. Wadgaonkar (2004) Chemoselective
Tetrahydropyranylation of Alcohols and Their Detetrahydropyranylation Using Silicasulphuric Acid as a Reusable Catalyst,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 34:12,
2135-2142, DOI: 10.1081/SCC-120038489
To link to this article: http://dx.doi.org/10.1081/SCC-120038489
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 12, pp. 2135–2142, 2004
Chemoselective Tetrahydropyranylation
of Alcohols and Their
Detetrahydropyranylation Using
Silicasulphuric Acid as a Reusable Catalyst
1
D. M. Pore,1 Uday V. Desai,1, R. B. Mane, and
*
P. P. Wadgaonkar2
1Department of Chemistry, Shivaji University, Kolhapur, India
2Polymer Division, National Chemical Laboratory, Pune, India
ABSTRACT
A simple, mild, and efficient protocol for chemoselective protection of
alcohols over phenols as tetrahydropyranyl ethers and their deprotection
using silicasulphuric acid as a reusable solid acid catalyst is described.
Key Words: Tetrahydropyranylation; Silicasulphuric acid; Alcohols;
Phenols.
*
Correspondence: Uday V. Desai, Department of Chemistry, Shivaji University,
Kolhapur 416004, India; Fax: 0091-0231-2692333; E-mail: uprabhu_desai@
rediffmail.com.
2135
DOI: 10.1081/SCC-120038489
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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INTRODUCTION
The importance of selective introduction and removal of protecting
groups in organic synthesis is well established. Tetrahydropyranylation is
one of the frequently used methods for the protection of alcohols and phenols
because of low cost, easy installation, and removal but more importantly
its stability towards bases, Grignard reagents, redox reagents, alkylating and
acylating agents.[1,2]
A wide variety of catalysts have been applied for tetrahydropyranyl-
ation of alcohols and phenols including protic acids,[3] Lewis acids,[4]
Lewis acids on silica gel,[5] polystyrene supported aluminium chloride,[6]
expansive graphite,[7] clay materials,[8] CuCl2,[9] NH4Cl,[10] ZrCl4,[11] potas-
sium dodecatungstocobaltate,[12] I2,[13] LiBr,[14] LiBF4,[15] triflate[16] of Sc,
Li, In, ionic liquid,[17] and InCl3.[18]
The protection is normally achieved with catalyst in aprotic solvents like
methylene chloride, tetrahydrofuran, etc., whereas deprotection is effected
with acid catalyst but in polar solvents such as acetonitrile, methanol, or ethanol.
In this communication, we wish to report the usefulness of silicasulphuric
acid[19] (SSA) as a mild, efficient, and chemoselective catalyst for protection
and deprotection of alcohols as tetrahydropyranyl ethers.
When a mixture of an alcohol (1) and 3,4-dihydropyran (2) in
methylene chloride was stirred with a catalytic amount of silicasulphuric
acid (3.9 mol%) corresponding tetrahydropyranyl ether (3) was isolated
after filtration of catalyst and flash chromatography. For deprotection of
THP-group, the THP ether was stirred in methanol at room temperature or
boiled in acetonitrile with excess of catalyst (18.7 mol%) (Sch. 1).
The present protocol is quite general and a wide range of alcohols such as
primary, secondary, tertiary, benzylic, allylic, unsaturated as well as cyclic
alcohols underwent smooth tetrahydropyranylation (Table 1). Interestingly,
phenols failed to undergo tetrahydropyranylation under the conditions
employed (entry 1o and 1p). This chemoselectivity of SSA was demonstrated
through the reaction of 3,4-dihydropyran with a mixture of benzyl alcohol (4)
and phenol (5) as well as with o-hydroxybenzyl alcohol (6) (Sch. 2). The
Scheme 1.

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Pore et al.

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2139
Scheme 2.
catalyst was found to be reusable at least five times with no appreciable change
in the activity.
In conclusion, SSA is a reusable solid acid catalyst effective for the
chemoselective protection and deprotection of alcohols as their tetrahydro-
pyranyl ethers.
EXPERIMENTAL
Procedure for Tetrahydropyranylation
A mixture of benzyl alcohol (10 mmol), 3,4-dihydropyran (11 mmol),
SSA (0.15 g, 0.39 mmol), and methylene chloride (15 mL) was stirred at
room temperature and the progress of reaction was monitored by TLC.
After completion, the reaction mixture was filtered and residue was washed
with methylene chloride. The filtrate was concentrated and subjected to
flash chromatography on silica gel to give the tetrahydropyranyl ether deri-
vative (1.75 g, 91%).
Deprotection of THP Derivative
A mixture of THP ether of benzyl alcohol (1.54 g, 8 mmol), SSA (0.57 g,
1.5 mmol), and methanol (15 mL) was stirred at room temperature till

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completion of deprotection (TLC). The reaction mixture was filtered and
residue was washed with methanol. The filtrate was concentrated to yield
benzyl alcohol (0.73 g, 84%).
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Received in India January 19, 2004

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