Terminal moieties cyano groups

Pyrethroid insecticides are generally classified into one of two large groups on the basis of the central neurotoxic syndrome that they produce [5, 6]. Type I pyrethroids are esters of chrysanthemic acid and an alcohol, having a furan ring and terminal side chain moieties, and absence of a cyano moiety. Allethrin was the first pyrethroid identified in 1949. Allethrin and other pyrethroids such as phenothrin and permethrin with the basic cyclopropane carboxylic ester structure are type I pyrethroids. The insecticidal activity of these synthetic pyrethroids was enhanced further by the addition of a cyano group to give ot-cyano type II pyrethroids such as deltamethrin, fenvalerate, cyfluthrin, cyhalothrin, and lambda-cyhalothrin (Fig. 137.2). 

Although the synthesis of each chromophore material is to some extent unique (and hence requires individual description which is beyond the scope of this review), most chromophores used for device prototyping involve amine donor moieties. Thus, once a large quantity of aldehyde-terminated amine do-nor/partial bridge material has been synthesized, it can be reacted via Knoeve-nagel condensation with a variety of acceptor groups to form different series of chromophores. The acceptor in Schemes 1-4 is 3-cyano-5,5-dibutyl-2-dicy-anomethylene-4-methyl-2,5-dihydrofuran (which we refer to as the cyanofuran, CF, acceptor). This is synthesized by a literature method [213]. 

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