Practical, Stereocontrolled Synthesis of Polyfluorinated Artificial Pyrethroids

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Abstract
Practical and stereocontrolled approaches to polyfluorinated synthetic pyrethroids based on aldehyde addition of CF3CCl2ZnCl are described. The zinc reagent was allowed to react with 3-formyl-2,2-dimethylcyclopropanecarboxylates (6) to give the corresponding adducts. These were acetylated and then reduced again with zinc to afford (1R*, 3S*)-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylates (12). The (1R*, 3R*)-isomer was derived from 2,2-dichloro-1,1,1-trifluoro-5-methyl-4-hexen-3-ol by diazoacetylation, Cu(II)-catalyzed intramolecular carbene addition, and finally by the zinc reduction. An alternative access to 12 and its halogen homologues of the (Z)-pyrethroids involves addition of 1-halo-2,2-difluoroethenyl group across the CHO group of 6 and subsequent regio- and stereoselective halogenation.