Synthesis of some novel carboxylic acids and insecticidal activity of their esters.

Abstract

Various novel acyclic carboxylic acids were prepared and some of their 3-phenoxybenzyl esters were found to have slight insecticidal activity. One of the useful acid moieties of a number of synthetic pyrethroids1) is ƒ¿-isopropyl-4-chlorophenylacetic acid.2) This paper reports the synthesis of some new carboxylic acids in which the phenyl or the isopropyl group of a isopropylphenylacetic acid is replaced with other groups, and the insecticidal activity of their 3-phenoxybenzyl esters. Methyl 3-pentenoate3) and ethyl 3-hexen oate3) were alkylated at a-position with ethyl or isopropyl halides, and the alkylated products were hydrolyzed to acids (1, 2, 3) (Fig. 1). The acids were analyzed by PMR. Alkylation of ethyl crotonate with isopropyl iodide in the presence of LDA gave the ester 4, but hydrolysis of 4 gave a mixture of acids 5 and 6 (2:3). Alkylation of tert-butyl crotonate in the presence of sodium amide gave a mixture of 7 and 8 (2:1), and when 0.8 mol eq. of the base was used the ratio of 7 and 8 was 3:1 (Fig. 1). The nitrile 13, prepared by alkylation of 12, was hydrolyzed to the carboxylic acid 14. The bromide 11 was prepared from the ester 9 via the alcohol 10 and alternatively bromination of dimethylbutene by NBS gave the same bromide.