Pyrethroid insecticides, chiral components

Enantioselection can be controlled much more effectively with the appropriate chiral copper, rhodium, and cobalt catalyst.The first major breakthrough in this area was achieved by copper complexes with chiral salicylaldimine ligands that were obtained from salicylaldehyde and amino alcohols derived from a-amino acids (Aratani catalysts ). With bulky diazo esters, both the diastereoselectivity (transicis ratio) and the enantioselectivity can be increased. These facts have been used, inter alia, for the diastereo- and enantioselective synthesis of chrysan-themic and permethrinic acids which are components of pyrethroid insecticides (Table 10). 0-Trimethylsilyl enols can also be cyclopropanated enantioselectively with alkyl diazoacetates in the presence of Aratani catalysts. In detailed studies,the influence of various parameters, such as metal ligands in the catalyst, catalyst concentration, solvent, and alkene structure, on the enantioselectivity has been recorded. Enantiomeric excesses of up to 88% were obtained with catalyst 7 (R = Bz = 2-MeOCgH4). 

Pyrethroids occupy a central position among insecticides because of their high selectivity and low toxicity [34]. Chrysanthemic esters (33), the carboxylic acid components of this important class of compounds, can be synthesized by asymmetric cyclopropanation of olefins (cf Section 3.1.7) by diazoacetates in the presence of a chiral Schiff base-Cu complex (Scheme 9 and Structures 34 and 35) [35-37]. 

Certain kinds of cyclopropanecarboxylic acids are important in the production of pyrethroid, an insecticide with low mammalian toxicity [1]. For example, chrysanthemic acid is an acid component of allethrin (Fig. 1). Various kinds of alcohols have been developed to produce pyrethroids for special application [2]. Chrysanthemic acid has two chiral centers and there are four optical isomers. There is a close correlation between the chirality of a molecule and its biological activity [3]. In the case of chrysanthemic acid, the most effective isomer is shown to be the d-trans isomer, which is followed by the d-cis isomer whereas... 

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