Practical and stereocontrolled new methods for the synthesis of highly potent synthetic pyrethroids, 2, 2-dimethyl-3- (2-chloro- 3, 3, 3- trifluoro- 2- propenyl) cyclopropanecarboxylates are described. The key of the methods is the transformation of RCHO to RCH=C (Cl) CF
3. This was achieved (1) by aldehyde addition of a zinc carbenoid CF
3CCl
2ZnCl prepared from CCl
3CF
3 and Zn, followed by acetylation and reduction; (2) by one-pot procedure using CF
3CCl
3/Zn (> 2mol) /Ac
2O (1mol); or (3) by conversion to RCH (OH) CX = CF
2 with CF
3CCl
3/Zn (> 2mol) /AlCl
3 (cat.) followed by regio- and stereoselective fluorination. Application of these to 3- formyl- 2, 2- dimethycyclopropanecarboxylates afforded the trans isomer of the target compounds. A series of transformation involving addition of CF
3CCl
2ZnCl to 3- methy- 2- butenal, conversion into Me
2C = CHCH (COCHN
2) CCl
2CF
3, intramolecular carbene addition, and reduction gave the cis acid of the aimed pyrethroids.
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