Hydrotalcite: recyclable, novel heterogeneous catalyst for facile, environmentally benign and high yielding multi-component synthesis and mechanistic study under solvent free conditions

The synthesis of the 4H-pyrimido[2,1-b][1,3] benzothiazole (1a-1h), 1,2,4-triazoloquinazolines (2a,2b), octahydroquinazolinones (3a,3b) and fused thiazolo[2,3-b] quinazolinone (4a,4b) by multicomponent reactions using aldehydes, dicarbonyl and 2-amino benzothiazole/3-amino-1,2,4-triazole/urea/thiorea has been carried out in the presence of Mg-Al-CO3 and Ca-Al-CO3 hydrotalcite as a heterogeneous catalyst. Hydrotalcites need short reaction times, are non-toxic, easy to work up and reusable under solvent free conditions, hence making this process environment friendly. A detailed mechanistic study shows that the reaction using urea proceeds through imine intermediate 6. In addition, we have isolated and characterized the key intermediate of the reaction by using hydrotalcite.