A practical chemo-enzymatic process for the preparation of optically active (1 R, cis)-2-(2, 2- dichloro (or dibromo) ethenyl)-3, 3-dimethylcyclopropane carboxylic acids (permethrinic or deltamethrinic acids) from racemic 1, 1, 1-trichloro-2-acetoxy-4-methyl-3-pentene is described. The key intermediate, enantiopure (R)-1, 1, 1-trichloro-2-hydroxy-4-methyl-3- pentene, is prepared by a lipase catalysed kinetic resolution of the racemic acetate. The ...