Insecticides stereochemistry

Pyrethrms are a group of naturally occurring insecticidal substances found in the flowers of vanous plants of the chrysanthemum family The following is the structure of a typical pyrethnn cmerin I (exclusive of stereochemistry)... 

The first step is conjugate addition of the highly stabilized anion. The intermediate enolate then closes the three-membered ring by favourable nucleophilic attack on the allylic carbon. The leaving group is the sulfinate anion and the stereochemistry comes from the most favourable arrangement in the transition state for this ring closure. The product is the methyl ester of the important chrysan-themic acid found in the natural pyrethrum insecticides. 

Miyazaki, A. Hotta, T. Marumo, S. Sakai, M., S)Tithesis absolute stereochemistry, and biological activity of optically active cyclodiene insecticides J. Agric. Food Chem. 1978, 26, 975-977. 

S-Bioallethrin (Fig. 5 ]9a]) is a S)mthetic pyrethroid insecticide with three asymmetric centers. The S designation refers to the l-K, 3-R, 4 -S isomer and is not a true designation of stereochemistry. Conversion of the terminal allylic group to —CHjCHjCHjOH, formation of hemisuccinate. 

The usefulness of this transformation first became apparent when it was discovered that some chiral cyclopropane-containing pyrethroids were highly effective insecticides. More importantly, the biological activity of these compounds was directly related to the cyclopropane stereochemistry [4]. One of the most ef-... 

With the aid of decoupling experiments and the INDOR technique, it was possible to define completely the structure and stereochemistry of erythristemine (1) with the exception of the configuration at C-11." In order to obtain the latter information, recourse was taken to A-ray analysis on the 2-bromo-4,6-dinitrophenolate salt of (1). This constitutes a new method and may be applicable elsewhere. Details of the structural and stereochemical elucidation of the interesting insecticidal alkaloid (2), which may be regarded as a ring-D degraded erythroidine structure, have appeared. ... 

Heiiocide H, proved to be four or five times as toxic to insects as hemigossy-polone or heiiocide Hj. This indicates that the insecticidal activity within this class is highly dependent on the stereochemistry of the products. According to Stipanovic et al. (1978), it should be possible to breed cotton varieties that contain the most effective mixture of heliocides. 

JasmoltnS. Active insecticidal constituents of py-rethrum Bowers. Isoln and structure Godin ei at., J. Econ. EntomoL 58, 548 (1965) Godin et at., J. Chem. Soc. (C) 1966, 322. Stereochemistry Begley el aL, Chem. Commun. 1972, 1276. 

Pyrethrins, Active insecticidal constituents of pyrethrum flowers. Isoln Staudinger, Ruzicka, Heh. Chim. Acta 7, 177 (1924). Prepn by reconstitution from pyrethro-lone and chrysanthemic acid Elliott, Janes, Chem. A Ind. (London) 1969, 270. Structure CrOmbie et al. J. Chem. Soc. 1956, 3963 Godin et al, ibid. [Pg.1266]

Quantum yields for the photodechlorination of insecticides of the type (307) have been obtained. Discussion of the mechanism in terms of C—Cl bond fission and the generation of radical pairs was made. Cristol and his co-workers have reported the results of the photolysis of the chloro-compounds (308). The results from this work have given an insight into the stereochemistry of the photochemical reactions. 

Synthetic pyrethroid insecticides are photostable analogs of the natural pyrethrins of botanical origin they consist of a series of related esters derived from alcohols and acids that maintain critical isosteric relations with the natural product prototype. Small changes in substituents and stereochemistry are sufficient... 

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