Bifunctional Catalyst Promotes Highly Enantioselective Bromolactonizations To Generate Stereogenic C–Br Bonds

A novel bifunctional catalyst derived from BINOL has been developed that promotes the highly enantioselective bromolactonizations of a number of structurally distinct unsaturated acids. Like some known catalysts, this catalyst promotes highly enantioselective bromolactonizations of 4- and 5-aryl-4-pentenoic acids, but it also catalyzes the highly enantioselective bromolactonizations of 5-alkyl-4­(<i>Z</i>)-pentenoic acids. These reactions represent the first catalytic bromolactonizations of alkyl-substituted olefinic acids that proceed via 5-<i>exo</i> mode cyclizations to give lactones in which new carbon–bromine bonds are formed at a stereogenic center with high enantioselectivity. We also disclose the first catalytic desymmetrization of a prochiral dienoic acid by enantioselective bromolactonization