Synthesis of 2-[{2-(1-Acyl-3-aryl-4,5-dihydro-1H-pyrazol-5-yl)phenoxy}methyl]-5-aryl-1,3,4-oxadiazoles and related compounds as potential pesticides

Cyclization of substituted chalkones 3a,b with hydrazine hydrate followed by acylation of the resulting 3-aryl-4,5-dihydro-5-(2-hydroxyphenyl)-1H-pyrazoles (4a,b) with alkanoic acids furnished 1-acyl-3-aryl-4,5-dihydro-5-(2-hydroxyphenyl)-1H-pyrazoles (5a-d). The compounds 5a-d are also directly prepared by refluxing 3a,b with hydrazine hydrate in alkanoic acids. Alkylation of 5a-d with ethyl chloroacetate yields the corresponding aryloxyacetates 6a-d. Aminolysis of the ester 6a-d results in the formation of corresponding substituted aryloxyacetamides 7a-l. Hydrazinolysis of esters 6a-d with hydrazine hydrate followed by cyclization of the resulting aryloxyacetic acid hydrazides 8a-d with aromatic acids in refluxing POCl3 affords the title compounds 9a-t. The compounds 3-9 have been evaluated for their in vitro growth -inhibitory activity against four fungal pests, Alternaria helianthus, Colletotrichum falcatum, fusarium oxysporum and Rhizoctonia solani. Many of the compounds have displayed promising activity at different concentrations ranging from 3.13 - 100 mg L-1.