RAPID, HIGH‑YIELDING AND RECYCLABLE CeO2‑CATALYZED PROTOCOL FOR THE SYNTHESIS OF 4‑PHENYL‑1,3‑THIAZOLE‑2‑AMINES: A GREEN ALTERNATIVE TO CONVENTIONAL METHODS
The present study describes a CeO2-catalyzed heterogeneous protocol for the synthesis of substituted 4-phenyl- 1,3-thiazol-2-amine derivatives under recyclable and environmentally preferable reaction conditions. It uses theheterogeneous catalyst cerium oxide under mild conditions. The cyclo-condensation of different substitutedphenacyl bromides and thiourea was carried out in ethanol at 80 0C in the presence of 10 mol%CeO2. Thebifunctional acid-base nature of the oxide surface coupled with the dual redox character of ceriumwhichswitches between its +3 and +4 state jointly with the bifunctional acid-base nature of the oxide surface promotethe simultaneous activation of the electrophilic and nucleophilic partners and hence the efficient constructionof the C-S and C-N bonds required to close the ring. The streamlined process provided the respective thiazole-2- amine products in isolated yields between 86 and 91 within a mere 3 hours. Ten structurally different congeners, substituted with electron-rich and electron-deficient substituents distributed across ortho-, meta-, and para- positions of the phenyl ring, were successfully accessed, which highlights the broad functional-groupcompatibility of the approach. The catalyst was easily separated by simple filtration and could be reused infour consecutive runs with insignificant attenuation of activity. The use of ethanol as a non-toxic solvent alsocontributes to the environmental merits of the protocol. This plan provides a cost-saving, green and easilyimplementable platform to assemble biologically relevant thiazole frameworks and preludes the further functional and pharmacological studies of the resulting frameworks. Furthermore, the developed methodologyaligns with United Nations Sustainable Development Goal (SDG) 12: Responsible Consumption and Productionthrough the use of a recyclable heterogeneous catalyst, environmentally benign ethanol as solvent, reducedreaction time, and minimized waste generation.
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