Synthesis and Herbicidal Activity of Optically Active Ethyl 2-[4-(6-Chloro-2-quinoxalinyloxy) phenoxy] propanoate

Abstract

Optically active ethyl (R)-(+) and (S)-(-)-2-[4-(6-chloro-2-quinoxalinyloxy) phenoxy]-propanoate ((R)-(+)-1 and (S)-(-)-1) were synthesized from (S)-(+)-lactic acid: (S)-(+)-lactic acid was converted to ethyl O-(p-toluenesulfonyl)-(S)-(-)-lactate, ethyl O-methane-sulfonyl-(S)-(-)-lactate, ethyl (R)-(+)-2-chloropropanoate and ethyl-(R)-(+)-2-bromopro-panoate, respectively. Each intermediate was condensed with 4-(6-chloro-2-quinoxalinyloxy)-phenol (2) to afford (R)-(+) and (S)-(-)-1. Optical purities were determined by the 200MHz ¹H NMR spectroscopic measurement using shift reagent, Eu(HFC)₃. It was assumed that optically pure (R)-(+)-1 would have [α]²⁰_D+35.2°(CHCl₃, c=1.20%). The growth inhibiting activity against rice plants in petridish and the post-emergence herbicidal activity against Setaria viridis were examined. The strong correlation was observed between the content of (R)-(+)-isomer and biological activity. It was assumed that optically pure (R)-(+)-1 was approximately two fold more active than the racemate and optically pure (S)-(-)-1 was low active or inactive.