Sulfonamides are a significant class of compounds displaying a wide variety of biological activities such as anti-fungal, anti-bacterial, anti-thyroid, anti-inflammatory and anti-viral etc. (Fig. 1) [1]. Particularly because of the unique functional groups present in their structure, they are extensively utilized in organic materials, agriculture and dyes [2]. They are generally used in veterinary medicines for therapeutic purposes to combat bacterial diseases [3].
Sulfonamides employ their effect by targeting on dihydropteroate synthase (DHPS) enzyme, which catalyzes folic acid pathway in bacteria [4]. Therefore, they are commonly utilized for their broad spectrum of antibacterial activity. Because of the substantial significance of sulfonamides, there are various reports available in literature for their synthesis via different methodologies. However, efficient, environmentally benign, and green approach for the synthesis of sulfonamides from cheap and easily available starting materials is still desirable. One of the most straightforward synthetic approaches for the synthesis of sulfonamides derivatives is via ring opening of aziridines.
Aziridines are three membered heterocyclic compounds, usually employed as intermediates for various organic transformations [5]. Substituted aziridines such as N-arylsulfonyl aziridines in particular, have attracted considerable attention because of their susceptibility towards regio and stereoselective nucleophilic ring opening and ring expansion reactions [6–10]. The nucleophilic ring opening of aziridines has been utilized to synthesize biologically active compounds such as alkaloids, heterocycles and amino acids [11]. Aziridines yield vicinal diamines with nitrogen nucleophiles such as amines, which are components of many biologically important compounds [12]. Therefore, there are several catalytic systems reported in the literature for ring opening of aziridines with various nucleophiles. Very recently, Liu et al. [13] employed zinc based catalytic system for the regioselective ring opening of 2, 3-aziridinyl alcohols using aromatic amines and thiophenols as nucleophiles. Ghorai and co-worker, [14] reported an efficient synthesis of biologically important imidazoline and oxazolidines via ring opening of the activated aziridines and epoxides with various amines, and a subsequent condensation with aldehydes under mild reaction conditions. Bera et al. [15] reported [Ag(COD)2]PF6 catalyzed ring opening reaction of N-tosylaziridines and azetidines with alcohols, amines, thiols and related tethered dinucleophiles. Similarly, Zhang et al. [16] synthesized α-amino aryl ketones via methylquinoline promoted ring opening of N-sulfonyl aziridines with dimethyl sulfoxide (DMSO). Despite their specific selectivity and efficiency for ring opening of aziridines, majority of these methodologies experience several drawbacks such as use of expensive and hazardous reagents, non-recyclable catalysts, use of volatile and toxic solvents, extensive reaction time, long reaction times, harsh reaction conditions, tedious workup procedures and low product yields [17, 18]. Therefore, the exploration of such protocol which is energy efficient, environmentally benign, facile, solvent free, and apparently separable are the current need of hour for the ring opening of aziridines.
In this regard, nano catalysis, which involves nanoparticles as heterogeneous catalysts has came to the forefront for carrying out various organic transformations in an environmentally benign manner. For this purpose, a diverse array of nanomaterials such as transition metals, transition metal oxides, composites of metals with organic moieties and carbon based nanostructures have been employed as versatile heterogeneous catalyst due to the several interesting properties such as high surface to volume ratio, great selectivity, high stability, surface modifiability, great biocompatibility etc. [19, 20].
Nowadays, carbon nanomaterials, in particular, the ones based on graphene have acquired enormous attention from material science and catalysis chemists; as a viable catalyst to carry out several organic transformations. Amongst these materials, reduced Graphene oxide (rGO), has emerged as an excellent heterogeneous catalyst, because of its remarkable characteristics such as large specific surface area, high thermal stability, exceptional structural and electronic properties. Interestingly, rGO possesses several polar functional groups such as hydroxyl, epoxy and carboxyl groups, which imparts hydrophilicity and water solubility to rGO [21–23]. Therefore, rGO has proved to be a competent material for a wide range of catalytic reactions such as Friedel-Craft acylation, hydrogenation, ring opening reaction of epoxides, oxidation-reduction reactions, aerobic oxidation of alcohol etc. [24–26]. However, the separation of rGO from the reaction mixture without causing any secondary pollution has remained a challenge for research community [27]. The recyclability problem can be well addressed by amalgamation of magnetic nanoparticles with rGO, resulting in the fabrication of environmentally benign nanohybrid with simplified isolation of product, facile recovery and recyclability of catalyst [28]. The incorporation of magnetic nanoparticles with rGO not only provides magnetic nature to nanohybrid but also enhances catalytic performance of nanohybrid due to the synergistic interactions between the rGO and magnetic nanoparticles.
In the present work, graphene based magnetically retrievable (CoFe@rGO) nanohybrid has been synthesized via easy and scalable hydrothermal method. For the first time, CoFe@rGO nanohybrid has been utilized as promising heterogeneous catalyst for the one step construction of benzensulfonamides derivatives via ring opening reaction of N-Tosylaziridine and (S)-(+)-2-Benzyl-1-(p-tolylsulfonyl) aziridine with different aromatic amines under solvent free conditions. The catalyst drove the reaction to completion in 9–24 min and afforded good yield (64–92%). As compared to other conventional catalysts, CoFe@rGO nanohybrid exhibited better stability, negligible leaching, good recyclability, and no deactivation of the nanohybrid catalyst.