Synthesis of Cyhalothric Acid

The ( )cis-Z-isomer of cyhalothric acid 217 is the acid moiety for the commercial pyrethroids cyhalothrin, biphenthrin and tefluthrin. One CF3-group exchanged for 

However, another copper-catalyzed carbon-C -addition across the double bond as shown in Reaction scheme 143 provides twice as much of the cis-isomer 219 than the trans one [408]. 

Intramolecular diazoester addition similar to Reaction scheme 128 (page 64) only yields the cis-isomeric acid after reduction with zinc [411]. 

The olefine 218 was also subjected to the Faworski-reaction [410]. Separation of the pure racemic or optically active, stereoisomeric acid succeeds, as described for permethric acid, with the selective precipitation with certain amines [409]. 

An adapted version of the Sagami-synthesis (Reaction scheme 65) allows the use of the interesting 3,3-dimethylpentenic ester IIL If one chlorine atom in carbonte-trachloride is substituted by CF3 or CH3, or if 1,1-dibromotetrafluoroethane is used, the radical addition to this olefinic bond is still feasible. As in the case of 1,1,1-trichloroethane, more drastic conditions are required. l,l,l-trichloro-2-tri-fluoroethane, on the other hand, behaves almost normally, thus providing an efficient starting point to produce the desired acid as shown in Reaction scheme 144, particularly if the 1,3-cyclo-elimination is carried out with potassium carbonate in dimethylacetamide at 140 °C, giving predominantly the cis-Z-isomer [411]. 

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