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

Abstract

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 growthinhibitory 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.