Chiral Trisimidazoline Catalyzed Bromolactonization

Significance

The authors report an enantioselective bromolactonization of 5-substituted 5-hexenoic acids, catalyzed by the chiral C ₃-symmetric trisimidazoline 1. By using 1,3-dibromo-5,5-di­methylhydantoin (DBDMH) as the Br⁺ source, a variety of 5-hexenoic acids, preferentially 5-aryl-substituted, were converted into the corresponding δ-lactones in high yields and enantioselectivities. The proposed mode of action involves the formation of a 1:3 complex of 1 and the substrate, at the same time embedding the substrate in a chiral environment and activating the carboxylic acid function. This proposal is supported by mechanistic studies and the utility of the products is underlined by derivatizations of the obtained bromolactones.