Synthesis and herbicidal activity of 2 alpha,4 alpha-dimethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one derivatives

The catalytic oxidation of 2 alpha,4 alpha-dimethyl-8-oxabicyclo[3.2.1]oct- 6-en-3-one with osmium tetraoxide and excess hydrogen peroxide resulted in the formation of 2 alpha,4 alpha-dimethyl-6,7-exo-isopropylidene- dioxy-8-o xabicyclo[3.2.1]octan-3-one (2), with 91% yield. Addition of aryllithium re agents to this compound resulted in the formation of the aromatic alcohols (6a-h) with 48-76% yield. These alcohols were treated with thionyl chloride in pyridine, and the corresponding alkenes (7a-h) were obtained with 46-80 % yield. The effect of compounds 6a-h and 7a-h on the root growth of Sorghu m bicolor was evaluated at a concentration of 6.6 mu g g(-1). The alcohols 6a-h caused an inhibitory effect (8-100%) on the S. bicolor radicle growth. The three most active compounds were 6e (aryl = p-methylphenyl), 6g (aryl = p-chlorophenyl), and 6h (aryl = p-fluorophenyl) and caused 100% inhibitio n. The effect of alkenes 7a-h was less pronounced and varied from 15% to 46 % inhibition. Another experiment was carried out in a greenhouse to evaluat e the effect of alcohols 6e, 6g, and 6h, at a 6.6 mu g g(-1) dose, against Cucumis sativus, S. bicolor and the weeds Bidens pilosa, Desmodium tortuosu m, and Pennisetum setosum. All three compounds showed an inhibitory effect on the development of the aerial parts (26-73%) and roots (13-79%) of the w eeds and crops.