Chlorination of αβ-unsaturated carbonyl compounds. Part II. The mechanism of chlorination of para-substituted methyl cis- and trans-cinnamates in acetic acid
The stereochemistry of addition of chlorine or the elements of chlorine acetate to a series of para-substituted methyl cis- and trans-cinnamates in acetic acid has been determined. At least three different mechanisms have been identified; chloronium ion intermediates are favoured with electron-poor olefins, relatively stable and selective ion-pairs predominate with more nucleophilic olefins, and some direct cis-addition of chlorine is observed over the entire range. A previous interpretation of the mechanism of chlorine addition to methyl trans-cinnamate overestimated the contribution of ion-pair intermediates.