Novel glycol benzyl ether herbicides: Herbicidal activity of 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyran derivatives

Abstract

The structure–activity relationship of novel glycol benzyl ether herbicides, 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyrans (TFBs), was elucidated. Herbicidal activity against Echinochloa crus-galli and rice injury varied with substituents of the benzyloxy group at C-3. When substituents other than the benzyloxy group, such as the cyclohexylmethyloxy group or the benzoyloxy group, were introduced, the herbicidal activity of TFBs was reduced. Introduction of an (S)-methyl group at C-5 increased herbicidal activity but aggravated rice injury. When comparing the herbicidal activity of two stereoisomers, the 5-(S)-isomer showed stronger herbicidal activity than the 5-(R)-isomer. Even when the benzene ring of the fused ring system of TFB was replaced by thiophene or furan, high herbicidal activity was manifested. In particular, TFB partly replaced by thiophene showed the highest herbicidal activity among all compounds examined in this study, with slight injury to rice plants. The 2,6-dioxabicyclo[3,3,0]octane derivative, produced as a by-product, also showed high herbicidal activity.