A simple and eco-friendly method for the synthesis of novel imidazo[2,1-b][1,3] thiazin derivatives has been developed via the one-pot, three-component and solvent-free reaction of thiohydantoins, aromatic aldehyde and 5,5-dimethylcyclohexane-1,3-dione in the presence of catalytic amount of p-toluene sulfonic acid, in good and excellent yields. [GRAPHICS] .