Abstract: Halogen-substituted olefin addition compounds that contain a carbonyl group are formed by oxidatively adducting an olefin and a carbonyl compound such as a ketone, aldehyde, or ester. The method consists of reacting the olefin and the carbonyl component, in solution, with an oxidizing ion of manganese, cerium or vanadium in the presence of fluoride, chloride or bromide ion. This ionic component is incorporated in the adduct and appears on the olefin-derived carbon atom gamma to the carbonyl group. The gamma halogen substituted adducts are readily converted to cyclopropane derivatives, including pyrethroid intermediate compounds.