Olefins and vinylbenzenes react with a-haloalkylbenzenes in the presence of weak Friedel- Crafts catalysts such as ZnClp or SnC14 by addition of the haloalkylbenzenes onto the olefinic double bond and not through alkylation of the aromatic ring. Subsequent dehydrohalogenation allows the preparation of a-aralkylated olefins or vinylbenzenes with high yields.
