Lewis acid catalysis of the ene addition of chloral and bromal to olefins; product studies

Abstract

The addition of chloral and bromal to a variety of alkyl-substituted alkenes has been investigated. The effect on the reaction of varying the Lewis acid catalyst and the structure of the substrate have been studied. Anhydrous AlCl₃ was found to be the most effective catalyst, and ene-type adducts were the major products in most cases. Side reactions were observed with the less reactive systems leading, variously, to the formation of trihalogenoketones, hydrohalpgenated ene adducts, and cyclic ethers. Conditions for optimising the yield of ene adducts were established in some cases. The trihalogenoketone by-products can be conveniently removed by a Grignard-type reaction.