Efficient and facile synthesis of heterocycles and their mechanistic consideration using kaolin

A kaolin catalyzed solvent-free synthesis for new heterocyclic compounds is described. A series of heterocyclic compounds can be readily obtained using the three-component reaction of diketones, aldehydes and 2-amino benzothiazole, urea or thiourea. The mechanism of the three component kaolin catalyzed Biginelli (using urea and thiourea) and Biginelli like (using 2-amino benzothiazole) reaction has been investigated. This is the first time that we have isolated and characterized the key intermediates using H-1 NMR, C-13 NMR and ESI-mass spectral characterization. Imine 3 and Knoevenagel type intermediate 4 were strongly suggested as key intermediates by mechanistic study. The reaction is simple, clean and good yield is obtained within minutes.