Silica‐Supported P₂O₅ as an Efficient Heterogeneous Catalyst for the One Pot Synthesis of 3‐Amino‐imidazo[2,1‐b](1,3)benzothiazole under Green Conditions

Abstract

The new approach involving the solid supported catalyst for the formation of C–N bond followed by cyclization has been reported. In this work we have reported a facile, efficient, and environment‐friendly protocol for the synthesis of some new 3‐amino‐imidazo[2,1‐b](1,3)benzothiazole derivatives by one‐pot condensation of 2‐aminobenzothiazole, indole‐3‐carbaldehyde, and aryl isocyanide in the presence of silica‐supported P2O5 as a heterogeneous solid acid catalyst. The reaction was performed using conventional method under green conditions. The present approach offers the advantages of simple methodology, inexpensive acid catalyst, short reaction time, easy work up with excellent yield, simple purification and use of green solvent. All the newly synthesized compounds were characterized in details using physical and chemical techniques such as melting point, 1H NMR, 13C NMR, and FTIR spectroscopy.

α-Aminoazoles/azines: key reaction partners for multicomponent reactions

“…S. Keshipour and coworkers 163 used a p -TSOH/ZnCl 2 catalytic system to carry out the GBB reaction, which took 48 h to complete. A comparatively shorter reaction time was taken by the methods catalyzed by HClO 4 , 164 NH 4 Cl, 165 urea-based/choline chloride system, 166 HCl/dioxane 167 glacial acetic acid, 168 β-cyclodextrin-SO 3 H, 169 Yb(OTf) 3 , 170 In(OTf) 3 , 171,172 InCl 3 , 173 P 2 O 5 /SiO 2 , 174 calix[n]arenes-SO 3 H, 175 Cu(OTf) 2 /CuOTf·C 6 H 6 , 176 electrostatically enhanced sulfuric acid (EESA), 177 visible light (24 W CFL), 178 and ZrCl 4 . 179 A brief summary regarding the reaction conditions, time, yields, etc.…”

Modern Approaches to the Synthesis and Transformations of Practically Valuable Benzothiazole Derivatives

“…Up to five turnovers of the catalyst are possible without notable loss of the catalytic activity. Another example of an environmentally friendly process is the multicomponent reaction of 2-aminobenzothiazole or its 6-substituted derivatives, indole-3-carbaldehyde and arylisonitriles, in the presence of P 2 O 5 on SiO 2 as the acidic catalyst (Scheme 31) [61]. The formation of the products, 3-aminoimidazo[2,1-b](1,3)benzothiazoles 39a-l, is facilitated by fast removal of water due to strong dehydrating agent P 2 O 5 /SiO 2 .…”