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

Three different types of dioxidomolybdenum(VI) complexes of pyrazolone based ligands have been isolated and used them as catalysts for 3,4-dihydropyrimidin-2-(1H)-one and 3,4-dihydropyrimidin-2-(1H)-thione based biomolecules under solvent-free conditions, epoxidation of internal and terminal alkenes, 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 and ¹³C NMR) techniques, thermal analysis and single crystal X-ray analysis. These complexes adopt a distorted six-coordinate 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 poison for the later molecule. Epoxidation of internal and terminal alkenes mainly resulted in the formation of the corresponding epoxide. 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.

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