Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 203–205
Cobalt(II) catalyzed tosylation of alcohols with p-toluenesulfonic
acid
Subbarayan Velusamy, J. S. Kiran Kumar and T. Punniyamurthy*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
Received 23 July 2003; revised 7 October 2003; accepted 17 October 2003
Abstract—Cobalt(II) chloride hexahydrate (CoCl2Æ6H2O) has been found to catalyze the tosylation of both aliphatic and aromatic
alcohols with p-toluenesulfonic acid (p-TsOH) in high yields in 1,2-dichloroethane under reflux (ca. 80 ꢀC). In the case of aliphatic
alcohols, secondary alcohols undergo tosylation chemoselectively in the presence of primary hydroxy groups.
ꢁ 2003 Elsevier Ltd. All rights reserved.
The tosylation of alcohols is a frequently used func-
OH
.
5 mol% CoCl2 6H2O
OTs
tional transformation in organic chemistry.1 Typically,
the moisture sensitive and very reactive sulfonyl chloride
or anhydride are usually employed as the tosylating
agents in the presence of bases.2 Sulfonic acids are also
used as tosylating agents but expensive alkylating agents
such as trialkyl orthoformate, alkyl ethers or esters are
needed instead of the alcohol.3 Recently, organic base
adducts of sulfonyls such as 1-phenylsulfonyl benzo-
triazole and aryl sulfonyl methylimidazolium salts have
been employed for sulfonate synthesis, however, signif-
icant amounts of by-products in the form of total
+ H2O
R
R'
R
R'
26-95%
R=alkyl, aryl; R'=alkyl, H
1 equiv p-TsOH
ClCH2CH2Cl
reflux
Scheme 1.
In the presence of a catalytic amount of CoCl2Æ6H2O,
the tosylation of 4-methoxylbenzyl alcohol was first
examined with p-TsOH (Table 1). Toluene, CH2Cl2,
dissolved salts are generated.4 More recently, Fe3þ
–
montmorillonite clay has been reported to catalyze the
tosylation of alcohols with p-TsOH.5 This method
works well with aliphatic alcohols but aromatic alcohols
give rearranged or polymeric products. Herein, we wish
to report a simple and efficient method for the direct
tosylation of both aliphatic and aromatic alcohols with
1 equiv of p-TsOH in the presence of CoCl2Æ6H2Oin
high yields (Scheme 1). This protocol also functions in
the absence of additives and the removal of water is not
warranted. In contrast to the Fe3þ–montmorillonite
catalyzed process,5 this methodology chemoselectively
catalyzes the tosylation of aliphatic secondary alcohols
in the presence of primary hydroxy groups in high
yields.
Table 1. Tosylation of 4-methoxybenzyl alcohol with p-TsOH and
CoCl2Æ6H2O
CH2OH
CH2OTs
.
5 mol% CoCl2 6H2O
p-TsOH
OMe
Solvent
CH2Cl2
Solvent
OMe
Time
(h)
Entry
Temperature
(ꢀC)
Yield
(%)a;b;c
1
2
3
4
Rt
14
1
67
95
41
78
ClCH2CH2Cl Reflux
CH3CN
Toluene
Reflux
Reflux
14
3
a A solution of the substrate (3 mmol), p-TsOH (3 mmol), CoCl2Æ6H2O
(5 mol %), and solvent (10 mL) was stirred for the appropriate time
and temperature.
Keywords: tosylation; alcohol; p-toluenesulfonic acid; catalyst;
cobalt(II) chloride hexahydrate.
b Isolated yield.
* Corresponding author. Tel.: +91-361-2690321; fax: +91-361-2690-
c The identity of the product was ascertained by NMR, IR, and mass
spectrometric analysis.
0040-4039/$ - see front matter ꢁ 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2003.10.106