cyhalothrin

Cyhalothrin (ISO common name) is an organic compound that, in specific isomeric forms, is used as a pesticide. It is a pyrethroid, a class of synthetic insecticides that mimic the structure and properties of the naturally occurring insecticide pyrethrin which is present in the flowers of Chrysanthemum cinerariifolium. Pyrethroids, such as cyhalothrin, are often preferred as an active ingredient in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. λ-and γ-cyhalothrin are now used to control insects and spider mites in crops including cotton, cereals, potatoes and vegetables.

== Structure and stereochemistry == 600px|class=skin-invert-image|γ-cyhalothrin and λ-cyhalothrin Gamma-cyhalothrin and lambda-cyhalothrin are the active ingredients in the current commercial products based on cyhalothrin. Both are cyanohydrin esters of cis-3-[(Z)-2-chloro-3,3,3-trifluoropropenyl]-2,2-dimethylcyclopropanecarboxylic acid. All of the insecticidal activity is due to the proportion of absolute stereochemistry (1R) in the mixture. The active isomer of deltamethrin, (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylic acid, has the same stereochemistry. 450px|class=skin-invert-image|Cyhalothrin and deltamethrin acids. γ-cyhalothrin (a single chiral isomer) is indeed twice as active as λ-cyhalothrin on a weight-for-weight basis. The latter is racemic and contains the (1R) and inactive (1S) isomers in equal amounts.