A mild and efficient tetrahydropyranylation and detetrahydropyranylation of alcohols and phenols by VCl3

Article abstract of DOI:10.1007/s10593-006-0003-8

Vanadium chloride is found to be an efficient catalyst for the tetrahydropyranylation and detetrahydropyranylation of various alcohols and phenols, giving good yields at room temperature and short reaction times. 2005 Springer Science+Business Media, Inc.

Full text of DOI:10.1007/s10593-006-0003-8

Chemistry of Heterocyclic Compounds, Vol. 41, No. 11, 2005
A MILD AND EFFICIENT TETRAHYDRO-
PYRANYLATION AND DETETRAHYDROPYRANYLATION
OF ALCOHOLS AND PHENOLS BY VCl3
P. Narsimha Reddy, B. Sunil Kumar, P. S. Kumar, N. Srinivasulu, Y. Thirupathi Reddy,
and B. Rajitha
Vanadium chloride is found to be an efficient catalyst for the tetrahydropyranylation and
detetrahydropyranylation of various alcohols and phenols, giving good yields at room temperature and
short reaction times.
Keywords: alcohols, phenols, VCl3, detetrahydropyranylation, tetrahydropyranylation.
Tetrahydropyranylation and detetrahydropyranylation of alcohols and phenols is well established in
organic synthesis [1]. Tetrahydropyranylation of hydroxyl groups using 3,4-dihydro-2H-pyran (DHP) has been
recognized as a useful method for the protection of alcohols and phenols [2] due to its ease of introduction and
deprotection. Tetrahydropyranyl ethers are stable under a variety of reaction conditions and reagents like strong
bases, Grignard reagents, redox reagents, metal hydrides, metal alkyls, and catalytic hydrogenation [2, 3].
Several catalysts have been reported for the tetrahydropyranylation and detetrahydropyranylation of
alcohols and phenols, including protic acids [4], Lewis acids like BF3-etherate [5], LiBr [6], LiBF4 [7], LiOTf [8],
LiClO4 [9], Sc(OTf)3 [10], In(OTf)3 [11], I2 [12], InCl3 [13], ZrCl4 [14], CuCl2 [15], NH4Cl [16] and expansive
graphite [17], clay materials [18], silica sulfuric acid [19], and miscellaneous other catalysts [20-26]. Most of the
existing methods are associated with various drawbacks, including long reaction time, low yields, reflux at high
temperature, and tedious experimental procedure. Hence, there is still a need to develop a simple and efficient
method for tetrahydropyranylation and detetrahydropyranylation of alcohols and phenols. In this communication
we report the use of catalytic amounts of VCl3 for protection and deprotection of alcohols and phenols with
DHP.
VCl3 / CH2Cl2 / r. t.
+
R–OH
R
O
O
MeOH / r. t. / VCl3
O
1
3
2
Tetrahydropyranylation and detetrahydropyranylation of alcohols and phenols was achieved in the
presence of a catalytic amount of VCl3 in excellent yields in short reaction times at ambient temperature
(Table 1). A wide range of hydroxyl compounds such as primary, secondary, tertiary, benzylic, and cyclic alcohols
and phenols underwent effective tetrahydropyranylation and detetrahydropyranylation at room temperature.
__________________________________________________________________________________________
Department of Chemistry, National Institute of Technology, Warangal, (A. P) India; e-mail:
rajitabhargavi@yahoo.com. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1634-1636,
November, 2005. Original article submitted August 7, 2005.
0009-3122/05/4111-1371©2005 Springer Science+Business Media, Inc.
1371

TABLE 1. VCl3 Catalyzed Tetrahydropyranylation and Detetrahydro-
pyranylation of Alcohols and Phenols*
Tetrahydropyranylation
Time, min
Detetrahydropyranylation
Time, min
Alcohol
Yields, %*2
Yield, %*2
Benzyl alcohol [7]
10
20
15
10
20
15
10
15
20
25
20
97
94
92
95
96
93
95
97
92
94
90
15
25
20
20
25
25
20
20
25
25
25
95
92
91
93
95
90
91
93
92
91
92
4-Chlorobenzyl alcohol [7]
4-Methoxybenzyl alcohol [19]
Phenol [7]
4-Methoxyphenol [6]
4-Methylphenol [14]
2-Propanol [19]
2-Methyl-2-propanol [14]
Cyclohexanol [7]
1-Naphthol [6]
1-Menthol [7]
_______
* All the tetrahydropyranyl ethers are known compounds.
*2 Yields refer to pure products; all products were characterized by
comparison of their physical and spectral data with those of authentic
samples.
EXPERIMENTAL
General Procedure for Protection of Alcohols and Phenols. VCl3 (0.1 mmol) was added to a solution
of alcohol (1 mmol) and DHP (1 mmol) in dry dichloromethane (20 ml). The mixture was stirred for a specific
period of time (Table 1). The progress of the reaction was monitored by TLC. After disappearance of the starting
material the catalyst was filtered. The solvent was evaporated in vacuo. Water (10 ml) was added and the
mixture was extracted with ether (2 × 20 ml). The separated organic layer was dried over Na2SO4. Solvent
evaporation gave pure THP ethers.
General Procedure for Deprotection of Tetrahydropyranyl Ethers of Alcohols and Phenols. A
mixture of THP-ether (10 mmol) in methanol (20 ml) was added to VCl3 (0.1 mmol) and stirred at room
temperature for a specific period of time (Table 1). The progress of the reaction was monitored by TLC. After
disappearance of the starting material the catalyst was filtered off. The solvent was evaporated in vaccuo. Water
was added (10 ml) and the mixture was extracted with ether (2×20 ml). The separated organic layer was dried
over Na2SO4. Solvent evaporation gave pure alcohols.
The authors are thankful to the director of IICT, Hyderabad for 1H NMR and mass spectral analysis.
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