Abstract: 4-.beta., .beta.-dichlorovinyl (or dibromovinyl)-3,3-dimethylbutyrolactones are prepared from 1,1-dichloro (or dibromo)-4-methylpenta-1,3-diene by reacting with an acid of formula CH.sub.2 R.CO.sub.2 H in presence of a salt of a metal in one of its higher valency states, especially manganese (III), cerium (IV), or vanadium (V). Higher yields are obtained in the presence of the anhydride of the acid and of the sodium or potassium salt of the acid. Treatment of the lactones with an inorganic acid halide opens the lactone ring with formation of the corresponding 4-haloacid halide, which with alcohols affords the corresponding 4-haloacid ester, cyclised by bases to a 3-.beta.,.beta.-dichloro (or dibromo)vinyl-2,2-dimethylcyclopropanecarboxylic ester, intermediate for insecticides such as the m-phenoxybenzyl ester.

Abstract: 2,2-Dichloro-5-methyl-1,1,1-trifluorohex-4-ene, an intermediate in the synthesis of pyrethroid insecticides, is obtained by continuous distillation, preferably under sub-atmospheric pressure, of a mixture of 5-methyl-2,2,4-trichloro-1,1,1-trifluorohexane, dimethylformamide and lithium bromide, precipitating the chlorofluorocarbons from the distillate with water and separating the desired product from starting material by a further distillation.

Abstract: Halogenated hydrocarbons of formula:RR.sup.1 C.dbd.CH--CH.sub.2 CYZQandRR.sup.1 C.dbd.CH--CH.dbd.CYQ,and mixtures thereof, wherein Y is F, Cl or Br, R is hydrogen or a lower alkyl group, R.sup.1 is a lower alkyl group, Z is Y or Q and Q is W(CF.sub.2).sub.m -- in which W is hydrogen, F or Cl and m is 1 or 2, and a process for their preparation which comprises heating in a polar aprotic solvent, preferably in the presence of an alkali metal halide, a halogenated hydrocarbon of formula RR.sup.1 C--CHX--CH.sub.2 CYZQ wherein R,R.sup.1,Y,Z and Q have the previously defined meanings and X is Cl, Br or I, provided that X is always Br or I when at least one of Y and Z is Br.