Fe-pillared bentonite-an efficient catalyst for sulfonylation of arenes using aryl and alkyl sulfonyl chlorides

Article abstract of DOI:10.1016/j.tetlet.2004.10.039

Fe-pillared bentonite (Fe-PILC) was shown to be an extremely efficient catalyst for the sulfonylation of activated as well as unactivated carbocyclic aromatic compounds and heterocyclic aromatic compounds. The catalyst was also found to be recyclable.

Full text of DOI:10.1016/j.tetlet.2004.10.039

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 9079–9082
Fe-pillared bentonite—an efficient catalyst for sulfonylation
of arenes using aryl and alkyl sulfonyl chlorides
Devendrapratap U. Singh, Pankajkumar R. Singh and Shriniwas D. Samant*
Organic Chemistry Research Laboratory, University Institute of Chemical Technology, N. M. Parekh Marg,
Matunga, Mumbai 400 019, India
Received 23 June 2004;revised 28 September 2004;accepted 6 October 2004
Available online 22 October 2004
Abstract—Fe-pillared bentonite (Fe-PILC) was shown to be an extremely efficient catalyst for the sulfonylation of activated as well
as unactivated carbocyclic aromatic compounds and heterocyclic aromatic compounds. The catalyst was also found to be recyclable.
ꢀ
2004 Elsevier Ltd. All rights reserved.
Aryl sulfones and sulfoxides are interesting functional
groups possessing manifold reactivity for conversion to
a variety of organosulfur compounds in the field of
tional groups including olefins, amines, and some
nitrogen heterocycles. Very recently, efficient catalytic
protocols have emerged including the use of Fe(III) ex-
1
7a
7b
drugs and pharmaceuticals. In particular, aryl sulfones
have received much attention as powerful anti-HIV-1
changed montmorillonite clay, zeolites, and micro-
7
waves in the presence of FeCl3 as catalysts.
c
2
agents. Indol-3-yl and pyrrolyl aryl sulfones were found
to be highly potent and structurally novel non-nucleo-
side reverse transcriptase inhibitors (NNTRIs), for
However, these reactions often require prolonged heat-
ing, a large amount of a sometimes expensive catalyst
and fail with unactivated substrates. For the sulfony-
lation of unactivated aromatics and indoles the most
3
,4
example, L-737, 126, and PAS.
8
a,b
effective reported catalysts are bismuth(III) triflate,
8
c
8d
8e
indium(III) triflate, sodium perchlorate, and InBr3
but these catalysts are very expensive and are not com-
mercially available.
O
O
NH2
O
O
O
S
O
S
Cl
NH2
N
We have recently reported the high activity of Fe-
exchanged montmorillonite clays for the acylation of
N
O
H
Cl
9
a
sulfonamides, the Friedel–Crafts benzylation of arenes
b,c,d
9
L-737, 126
PAS
with benzyl chlorides,
the Beckmann rearrange-
9
e
9f
ment, and nitrile formation. In the present work,
we demonstrate that Fe-pillared bentonite (Fe-PILC)
functions as an efficient catalyst for the sulfonylation
of activated as well as unactivated carbocyclic aromatic
compounds and heterocyclic aromatic compounds
(Scheme 1).
The common methods for preparing these sulfones
5
include the oxidation of sulfides or sulfonylation of
arenes using an aryl sulfonyl halide or an aryl sulfonic
6
acid in the presence of a strong acid catalyst. Although
these methods are attractive, inherent disadvantages
encountered in the use of conventional soluble acid cata-
lysts are the generation of large amounts of effluent, the
inability to recycle reagents, highly corrosive conditions,
and the low selectivity for para/ortho sulfonylated iso-
mers. They are also incompatible with numerous func-
Fe - PILC
Ar
H
R
SO Cl
Ar SO R
2
+
2
R = CH , C H , p-CH C H
4
3
6
5
3
6
Keywords: Fe-pillared bentonite;Sulfonylation;Sulfones.
*
Corresponding author. Tel.: +91 022 24145616;fax: +91 022
4145614;e-mail: samantsd@udct.org
Scheme 1. Sulfonylation of arenes using aryl and alkyl sulfonyl
chlorides.
2
0
040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.10.039

9080
D. U. Singh et al. / Tetrahedron Letters 45 (2004) 9079–9082
The catalyst was prepared by treating bentonite clay
with polyoxocations of Fe in an aqueous solution as de-
yields of product in a short reaction time (15min)
whereas the other catalysts took longer and the yields
of the products were less. The Fe -K10 (Fe-exchanged
1
0
3+
scribed earlier. The reaction of m-xylene with p-tolu-
enesulfonyl chloride was selected as a model to test the
activity of different Fe-based catalysts viz. Fe-PILC,
7
a
montmorillonite) (Table 1, entry 5) took 6h for com-
pletion of the reaction. The high activity of Fe-PILC
may be attributed to the presence of a high content
9
b
9b
9d
K10-FeO, K10-FeA, and K10-FePLS at 120ꢁC
Table 1). It was found that the Fe-PILC catalyst was
superior to all other Fe-based catalysts and gave good
3
+
(
of Fe , that is, 20.6%.
To extend the scope of the reaction and to generalize
the procedure, we investigated the reactions of a series
of aromatic hydrocarbons with a variety of sulfonyl
chlorides viz. p-toluenesulfonyl chloride, benzenesulfonyl
chloride, and methanesulfonyl chloride, in the presence
of Fe-PILC as catalyst at different temperatures to
Table 1. Sulfonylation of m-xylene with p-toluenesulfonyl chloride
using different Fe-based catalysts at 120ꢁC
a
Entry
Catalyst
Fe (%)
Time (h)
Yield (%)
1
2
3
4
5
Fe-PILC
20.6
3.6
0.25
7.0
7.0
7.0
6.0
88
No reaction
No reaction
1
1
K10-FeO
K10-FeA
K10-FePLS
obtain the corresponding sulfones (Table 2). Fe-PILC
is capable of catalyzing not only the sulfonylation of
activated arenes but also non- or weakly-activated ones.
In the synthesis of diphenyl sulfone (Table 2, entry j),
an intermediate for the synthesis of Dapsone (4,4-di-
1.12
4.8
22
85
3+
b
Fe -K10
6.32
a
Isolated yield.
As reported in Ref. 7a.
b
12
aminophenyl sulfone), which is effective for leprosy
a
Table 2. Fe-PILC-catalyzed sulfonylation of arenes with aryl and alkyl sulfonyl chlorides
b
Yield (%) [o:m:p]
Entry
Arene 1
Sulfonyl chloride 2
Sulfone 3
Reaction conditions
time/temperature
O
S
O
Me
Me
15min/120ꢁC
88
84
a
Me
Me
Me
Me
Me
S
Cl
Cl
O
O
Me
Me
O
S
O
S
b
Me
15min/120ꢁC
O
O
Me
Me
Me
Me
Me
Me
O
S
O
S
c
Me
Me
Cl
Me
45min/120ꢁC
10min/120ꢁC
76
92
O
O
Me
Me
Me
O
S
O
S
d
Cl
Me
Me
Me
O
O
Me
Me
Me
Me
O
S
O
S
e
f
Me
Me
Me
Me
Cl
Me
45min/120ꢁC
10min/120ꢁC
2h/110ꢁC
78
O
O
Me
Me
OMe
OMe
O
S
O
Cl
Cl
84 [35.2:0:64.8]
80 [38.9:0:61.1]
74 [41.4:0:58.6]
72
S
Me
O
O
Me
Me
Me
Me
O
S
O
S
g
h
i
Me
O
O
O
S
O
S
Cl
2h/110ꢁC
O
O
O
S
O
S
Me
Cl
Me
8h/80ꢁC
O
O

D. U. Singh et al. / Tetrahedron Letters 45 (2004) 9079–9082
9081
Table 2 (continued)
b
Yield (%) [o:m:p]
Entry
Arene 1
Sulfonyl chloride 2
Sulfone 3
Reaction conditions
time/temperature
O
S
O
S
j
8.5h/80ꢁC
70
Cl
O
O
O
S
O
S
c
k
l
Me
Me
Me
Cl
Cl
Cl
Me
Me
Me
20min/120ꢁC
12h/120ꢁC
12h/120ꢁC
88 [63.2:36.8]
O
O
O
S
O
Cl
Br
Cl
Br
S
74
71
O
O
O
S
O
S
m
O
O
O
S
O
S
Me
n
o
Me
Cl
7h/80ꢁC
8h/80ꢁC
88
83
O
N
H
O
N
H
O
O
S
S
Cl
O
N
H
O
N
H
O
O
S
S
Me
Me
p
Me
Me
Cl
Cl
O
6.5h/80ꢁC
92
63
N
H
Me
O
N
H
O
S
Me
O
S
O
q
9h/80ꢁC
N
O
N
Me
Me
a
Arene: 5mL;sulfonyl chloride: 3mmol;Fe-PILC: 0.2g.
Isolated and unoptimized yield.
b
c
1
Isomers distribution based on H NMR, a:b = 63.2:36.8.
treatment, the use of the solid acid (Fe-PILC) offers a
commercially feasible route with control of solid efflu-
ents. Noteworthy results were also observed for the sulfon-
ylation of deactivated chloro- and bromobenzenes
before using for the next cycle. The activity of the cata-
lyst was unaffected even after three cycles.
In summary, Fe-PILC has been found to be a novel
inexpensive and highly efficient catalyst for sulfonyl-
ation of activated as well as unactivated carbocyclic
aromatic compounds and heterocyclic aromatic
compounds.
(
2
Table 2, entries l and m) and indole derivatives (Table
, entries n–q). A variety of indoles reacted smoothly
with sulfonyl chlorides in dichloroethane at reflux with
high regioselectivity. No N-substituted products were
observed under these reaction conditions. This is prob-
ably due to the stabilization of the imine–enamine com-
8e
plex by the Lewis acid during sulfonylation. An
activated indole gave the sulfonylated product in excel-
lent yield (Table 2, entry p). Treatment of the N-pro-
tected indole, N-methylindole with p-toluenesulfonyl
chloride in dichloromethane at 80ꢁC for 9h also
afforded the corresponding sulfone in 63% yield. Furan
and pyrrole were found to be unreactive under identical
conditions.
Acknowledgements
D.U.S. thank CSIR, New Delhi for the award of
fellowship.
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The recyclability of the catalyst, was also studied. After
each cycle the catalyst was filtered and activated at 80ꢁC

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D. U. Singh et al. / Tetrahedron Letters 45 (2004) 9079–9082
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1