A New Class of Herbicides that are Derivatives of 8-Oxabicyclo[3.2.1]oct-6-en-3-one

Abstract

Treatment of 8-oxabicyclo[3.2.1]oct-6-en-3-one with a catalytic amount of osmium tetraoxide and excess hydrogen peroxide resulted in the formation of the acetonide exo-6,exo-7-isopropylidenedioxy-8-oxabicyclo[3.2.1]oct-3-one (2), in 96% yield. This acetonide was converted into several aromatic alcohols (4a–k) through a Grignard reaction. The alcohols were treated with aqueous HCl in acetone, and the corresponding alkenes (5a–c,e–g, j,k) were obtained in 26–46% overall yield, from the ketone (2). The herbicidal activity of the alkenes was evaluated at a concentration of 6.6 µg g−1. All compounds showed an inhibitory effect (21–66%) on the Sorghum bicolor radicle growth. The inhibition of the accumulation of fresh and dried weight of the aerial parts of Cucumis sativus, after 14 days, varied from 7.1 to 60.7% and from 0.0 to 41.6%, respectively. Compounds (5a,e–g) caused 100% mortality of C. sativus, after 20 days. Compound (5g) (exo-6,exo-7-isopropylidenedioxy-3-(3-methylphenyl)-8- oxabicyclo[3.2.1]oct-2-ene) was evaluated against several weeds, and it caused 100% mortality of Desmodium tortuosum and Pennisetum setosum.