served for the u-peroxylactones (2) and that the electron exchange mechanism does not operate [2].On the basis of our preliminary results, we conclude that the 3-imino-I ,2-dioxetanes (3) are thermally much less stable than the u-peroxylactones and are inefficient sources for chemi-energizing electronically excited products. In this context, it is of interest that the 3-imino-1,2-dioxetanes (3) derived from N-phenyl-and N-p-tolyl-diphenylketenimines and N-p-tolyl-tert-butylketenimine via singlet oxygenation were too unstable for 'H-NMR observation even at -60 "C; only the carbonyl compound and isocyanate produced by fragmentation could be detected.

Several rare phenylpropanoids of the genus Pimpinella were tested for biological activity. Compounds with epoxy groups have a negative effect on the growth of plants, and they also show insecticidal and acaricidal activities.

No abstract

Als reaktive Zwischenstufe eindeutig nachgewiesen wurde das Silabenzol (2) jetzt durch nebenreaktionsfreie Erzeugung aus (1) und Dimerisierung zu (3) oder Diels‐Alder‐Addition an Diene. magnified image

Some highly active and broad‐spectrum representatives of the phenoxyphenyl‐ and carboxyphenyl urea groups of compounds are described. The products are relatively easily accessible, simple and economical to produce in high yield. Excellent biological activity has been detected using S. littoralis and a broad‐spectrum activity has been found on Lepidoptera, Diptera, Coleoptera and Hemiptera. Using two examples of phenoxyphenyl acylureas the high level of selectivity to certain larval stages has been shown in various noctuids. By altering the ester function to an ether group some indications of systemic activity could be achieved. Disturbances caused in cuticle formation have been investigated in ultrastructural studies of regenerating cockroach legs.