| Abstract: | Silicon effectively substitutes for quaternary carbon in etofenpr ox-type insecticides; the resulting dimethyl-4-ethoxyphenyl-3-(4-fluoro-3-phenoxyphenyl)propylsilane is a broad-spectrum insecticide with extremely low toxicity to fish. Four regions of this new silane insecticide have been systematically altered. The methyl groups on silicon appear to be critical for activity. Replacement of the fluorine with hydrogen results in a substantial loss of activity. The aromatic rings of the phenoxyphenyl fragment are best tethered by oxygen or carbonyl, the methylene and nitrogen analogs being of very low toxicity to the test species. The activity ranking of the methylene and carbonyl tethers is opposite to that found for ester pyrethroids. The relationship of insecticidal activity to the aromatic substituent para to the silicon atom has been found to correlate with the molar refractivity of the substituent. Replacement of a tetra-substituted carbon atom with a silicon atom can simplify construction of test compounds and thus be advantageously used in the exploration of structure—activity relationships. A novel method for preparing allylbenzenes from aromatic aldehydes was also developed. |
