Lactones of the formula ##STR1## wherein R is hydrogen or a CX.sub.3 group, and each X is a chlorine or bromine atom, are converted to the known cis-3-(2,2-dihalovinyl)-2,2-dimethylcyclopropanecarboxylic acids or lower alkyl esters, from which pyrethroid insecticides are obtained.
公式为 ##STR1## 的内酯,其中R是氢或CX.sub.3基团,每个X都是
氯或
溴原子,被转化为已知的顺式-3-(2,2-二卤
乙烯基)-2,2-二
甲基环丙烷羧酸或较低的烷基酯,从中获得拟
除虫菊酯类杀虫剂。