Synthesis and fungitoxic activity of 5-aryl-1-formyl-4,5-dihydro-3-(2-hydroxyphenyl)-1H-pyrazoles and their complexes

Cyclization of 3-aryl-1-(2-hydroxyphenyl)prop-2-en-1-ones with hydrazine hy drate in refluxing formic acid afforded the title ligands, 5-aryl-1-formyl- 4,5-dihydro-3-(2-hydroxyphenyl)-1H-pyrazoles (HL1-HL4, Ar=Ph, 4-CH3O-C6H4-, 2-furyl, 2-thienyl). Reaction of HL1-HL4 with the divalent metal ions, Mn2 +, Co2+, Ni2+, Cu2+, and Zn2+, afforded novel complexes of the type [ML2] ( M=metal ion; L=deprotonated ligand) which were characterized by elemental a nalyses, molecular weight determinations, molar conductances, magnetic mome nts and electronic and infrared spectral data. The ligands behaved as tride ntate, coordinating through. the phenolic oxygen after deprotonation, N-2 o f the pyrazole ring and oxygen of the 1-formyl group. The ligands and their complexes were evaluated for growth-inhibiting activity against four phyto pathogenic fungi. Macrophomina phaseoli was generally most sensitive follow ed by Alternaria alternata and Colletotrichum falcatum while Fusarium oxysp orum was least sensitive to the tested compounds. The ligand HL1 and its co mplexes showed the best activity against the fungi tested. (C) 2000 Society of Chemical Industry.