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. Ó 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 drugs and pharmaceuticals. 1 In particular, aryl sulfones have received much attention as powerful anti-HIV-1 agents. 2 Indol-3-yl and pyrrolyl aryl sulfones were found to be highly potent and structurally novel non-nucleo- side reverse transcriptase inhibitors (NNTRIs), for example, L-737, 126, and PAS. 3,4 The common methods for preparing these sulfones include the oxidation of sulfides 5 or sulfonylation of arenes using an aryl sulfonyl halide or an aryl sulfonic acid in the presence of a strong acid catalyst. 6 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- tional groups including olefins, amines, and some nitrogen heterocycles. Very recently, efficient catalytic protocols have emerged including the use of Fe(III) ex- changed montmorillonite clay, 7a zeolites, 7b and micro- waves in the presence of FeCl 3 as catalysts. 7c 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 effective reported catalysts are bismuth(III) triflate, 8a,b indium(III) triflate, 8c sodium perchlorate, 8d and InBr 3 8e but these catalysts are very expensive and are not com- mercially available. We have recently reported the high activity of Fe- exchanged montmorillonite clays for the acylation of sulfonamides, 9a the Friedel–Crafts benzylation of arenes with benzyl chlorides, 9b,c,d the Beckmann rearrange- ment, 9e and nitrile formation. 9f 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). N H S NH 2 O Cl O O O N S NH 2 Cl O O O L-737, 126 PAS 0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2004.10.039 Keywords: Fe-pillared bentonite; Sulfonylation; Sulfones. * Corresponding author. Tel.: +91 022 24145616; fax: +91 022 24145614; e-mail: samantsd@udct.org Ar H R SO 2 Cl Fe - PILC Ar SO 2 R R = CH 3 , C 6 H 5 , p-CH 3 C 6 H 4 + Scheme 1. Sulfonylation of arenes using aryl and alkyl sulfonyl chlorides. Tetrahedron Letters 45 (2004) 9079–9082 Tetrahedron Letters