Ionic liquid enabled sulfamoylation of arenes: an ambient, expeditious and regioselective protocol for aryl sulfonamides Prashant U. Naik, Jitendra R. Harjani, Susheel J. Nara and Manikrao M. Salunkhe * Department of Chemistry, The Institute of Science, 15-Madam Cama Road, Mumbai 400-032, India Received 10 October 2003; revised 17 December 2003; accepted 23 December 2003 Abstract—The ionic liquid, 1-butyl-3-methylimidazolium chloroaluminate, [bmim]ClAlCl 3 , N ¼ 0:67 mediated syntheses of aro- matic sulfonamides via electrophilic substitution of arenes is reported. The protocol serves as a distinctly expeditious and ambient route towards the syntheses of these pharmaceutically useful compounds, yielding quantitative conversions at room temperature within 5–30 min in most of the cases. The Lewis acidity and molar stoichiometry of the ionic liquid influences the extent of con- version. The method has been used for the syntheses of a diverse range of sulfonamides by variation of arenes and sulfamoyl chlorides. With monosubstituted benzenes, the protocol offers an added advantage of exclusive selectivity towards the formation of para substituted sulfonamides over the ortho products. Ó 2004 Elsevier Ltd. All rights reserved. The utility of ionic liquids in catalysis and as neoteric solvents for various synthetic processes is now well recognised by chemists all over the world. The remark- able attributes possessed by them such as non-volatility, recyclability, thermal stability, diverse solvating ability and tunability have made them popular as environ- mentally benign counterparts to conventional reaction media. 1 The fact that the other ionic liquid-specific properties 2 such as Lewis acidity, viscosity, density, hydrophobicity, hydrophilicity, etc. can be tailored, has provided an enormous scope for innovation in the area of solvent engineering. The realm of these unconventional reaction media began with molten salt chemistry, which subsequently evolved into the ambient temperature ionic liquids very fre- quently referred to as organoaluminates or chloroalu- minate ionic liquids. This interesting class of liquids not only served the purpose of reaction media, but also acted as the catalyst 3 in Lewis acid mediated reactions. The major setback in their development and widespread acceptance is their water sensitive nature. Furthermore, a product of their reaction with water is corrosive HCl, which destroys the very purpose of these liquids being used as environmentally benign alternatives. This fea- ture of chloroaluminates demands that they must be handled with exclusion of moisture-laden atmospheres, usually in a glove box. Despite these disadvantages, the chloroaluminates are often a preferred choice, firstly owing to their diverse solvating ability and variable Lewis acidity, which in an ensemble provides a tunable Lewis acidic medium for execution of reactions in a homogenous phase. Secondly, in certain reactions this conglomerate of properties has demonstrated a pro- found positive effect on the yield 4 or rate 5 or selectivity 6 of the reaction, when compared with the prototypical procedures. Over the past three years, we have been engaged in exploring newer reactions in chloroaluminate ionic liq- uids 7 with emphasis on those reactions where their employment is aptly warranted. 5;8 To this end, we herein report the sulfamoylation of arenes with N,N-dialk- ylsulfamoyl chloride (Scheme 1) in Lewis acidic 1- butyl-3-methylimidazolium chloroaluminate, [bmim]Cl AlCl 3 ,0:50 < N 6 0:67 ionic liquid (N is the apparent N R' R S O O Cl [bmim]Cl.AlCl 3 N R' R S O O Ar + Ar-H 0.50 N 0.67 Scheme 1. Sulfamoylation of arenes in [bmim]ClAlCl 3 , N ¼ 0:50– 0.67. Keywords: Arene; Sulfamoyl chloride; Ionic liquid; Sufamoylation; N,N-Dialkylsulfonamide. * Corresponding author. Tel./fax: +91-22-22816750; e-mail: mmsalun- khe@hotmail.com 0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2003.12.132 Tetrahedron Letters 45 (2004) 1933–1936 Tetrahedron Letters