Synthesis and Herbicidal Activity of 1H-2, 3-Benzoxazine Derivatives

Abstract

A series of 1H-2, 3-benzoxazine derivatives were synthesized and their herbicidal activity against upland weeds and selectivity against crops were assessed. Studies of the structure-activity relationship revealed that the strongest herbicidal activity was achieved when position-4 in the benzoxazine ring was substituted with a 3-chloro-4-fluorophenyl or a 3-bromo-4-fluorophenyl group. The treated weeds showed a strong bleaching symptom. Among the compounds examined, 4-(3-chloro-4-fluorophenyl)-1H-2, 3-benzoxazine (23) and 4-(3-bromo-4-fluorophenyl)-6-fluoro-1H-2, 3-benzoxazine (34), applied at 1.0kg a. i./ha, showed strong pre-emergence herbicidal activity against upland weeds such as Echinochloa crus-galli and Digitaria ciliaris without affecting soybean.