Catalytic Potential of Pyrazolone Based Dioxidomolybdenum(VI) Complexes for Multicomponent Biginelli Reactions, Epoxidation of Olefins and Oxidative Bromination of Phenol Derivatives

Abstract

Three different types of dioxidomolybdenum(VI) complexes of 4‐acetyl‐3‐methyl‐1‐phenyl‐5‐pyrazolone (Hmp, I)), 3‐methyl‐1‐phenyl‐4‐propionyl‐5‐pyrazolone (Hpp, II), 4‐butyryl‐3‐methyl‐1‐phenyl‐5‐pyrazolone (Hbutp, III), and 4‐isobutyryl‐3‐methyl‐1‐phenyl‐5‐pyrazolone (isobutp, IV) have been isolated and characterized by various spectroscopic (FT‐IR, UV/Vis, 1H and13C NMR) techniques, thermal analysis and single crystal X‐ray analysis. These complexes adopt a distorted six‐coordinated octahedral geometry where ligands act as bidentate, coordinating through the two O atoms. These complexes have been used as catalysts to explore a single pot multicomponent (benzaldehyde or its derivatives, urea/thiourea and ethyl acetoacetate/phenyl acetoacatate) Biginelli reaction producing biologically active 3,4‐dihydropyrimidin‐2‐(1H)‐one and 3,4‐dihydropyrimidin‐2‐(1H)‐thione based biomolecules under solvent‐free conditions. Presence of H2O2 improves the yield of dihydropyrimidin‐2‐(1H)‐one but it acts as poisons for the later molecule. Epoxidation of internal and terminal alkenes mainly resulted in the formation of the corresponding epoxide selectively. The catalytic oxidative bromination of thymol, a reaction facilitated by vanadium dependent haloperoxidases, resulted in the formation of three product namely 2‐bromothymol, 4‐bromothymol and 2,4‐bromothymol. Other phenol derivatives have also been brominated effectively.