Process for stereoselectively synthetizing cyclopropane carboxylates as intermediates for pyrethroids.

摘要

Stereoselective process for preparing lower alkyl esters of the cis-2,2-dimethyl-3-( beta -trifluoromethyl- beta - fluorovinyl)-cyclopropane carboxylic acid of formula:
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(wherein R = an alkyl C1-C4) in which a compound of formula:
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(wherein R has the meaning specified hereinabove and substituent Y is an atom of chlorine or of bromine) is monodehydrohalogenated in the presence of a primary or secondary amine and in an apolar solvent or in a low-polarity solvent, so selectively obtaining a compound of formula:
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(wherein Y and R have the meanings specified hereinabove), which, in its turn, is dehydrohalogenated by the action of an alkaline base in an apolar solvent or in ether maintaining, in the latter case, a temperature below 50 DEG C.
<??>The compounds thus obtained are intermediates for the preparation of pyrethroids.