J. Pesticide Sci. 14, 1-10 (1989) Original Article Synthesis and Insecticidal Activity of Novel Pyrethroids: Silicon-Containing Ethers Atsushl TERUOKA, Toshikazu OHTSUKA, Yoshlo HAYASE, Yusuke FUJITA, Shigetoshi KATAYAMA, Katsuaki OHBA, Akira MIZUTANI, Toshio TAKAHASHI, Takeo ISHIGURO and Yoshiyuki HAYASHI A burahi Laboratories, Shionogi Research Laboratories, Shionogi & Co., Ltd., Koka-cho, Koka-gun, Shiga 520-34, Japan (Received March 18, 1988) We have synthesized a series of pyrethroidal ether compounds which have a dimethyl- (phenyl) silyl moiety and a m-phenoxybenzyl or m-phenoxypyridylmethyl moiety, and studied their insecticidal activity. Of these new pyrethroids, dimethyl(4-ethoxyphenyl)silylmethyl 3- phenoxybenzyl ether was the most effective and broad-spectrum in insecticidal activity and extremely low in fish toxicity. INTRODUCTION A large number of organosilicon compounds with high and specificbiologicalactivity have been synthesized and studied biologically and toxicologically. '' Silicon and carbon both belong to Group IV of the Periodic Table, but there are some important differencesin prop- erty that must be taken into account : they differ in atom size (covalent radii : C = 0.77 A, Si =1. 1710, electronegativity (C = 2. 50, Si= 1. 74) and valence shells (C = 2s2p2, Si= 3s2p2d°). In contrast to carbon, silicon pos- sesses comparatively low-lying, vacant 3d orbitals which can be involved in additional bonding interactions, thus raising its coordina- tion number from 4 to 5 and 6. Sila-substitu- tion (C/Si-exchange) in drugs is one of the approaches currently used in search for new biologically active organosilicon compounds. Organosilicon compounds are often easier to synthesize and less expensive than their cor- respondingorganic carbon compounds. 2-4> With systematic variation in the structure of natural pyrethroids over the past 20 years, synthetic pyrethroids have been developed into highly active compounds with low tox- icity to mammals. 5' Recently a new pyre- throidal ether compound, ethofenprox (2-(4- ethoxyphenyl) -2- methylpropyl 3 - phenoxy- benzyl ether), was introduced as a potent in- secticide against a broad range of insect species. 6) Synthesis and insecticidal activity of or- ganosila-pyrethroids prepared by sila-substi- tution of a quarternary carbon atom in etho- fenprox and its analogs have been reported quite recently. 7' With attention to silicon- containing pyrethroidal ether, we have ex- amined the activity of several dimethylsilyl- substituted synthetic pyrethroids, such as dimethyl (phenyl) silylmethyl 3-phenoxybenzyl ethers and dimethyl (phenyl) silylmethyl 2- phenoxy-6-pyridylmethyl ethers, and their structure-activity relationship. While the former report on organosila-pyrethroids7' mainly refers to insecticidal activity against tobacco cutworms, this paper describes the preparations of new pyrethroids derived from dimethylsilyl-substituted alcohols, and their insecticidal activity against a wider range of pests and fish toxicity.