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(Z)-pentenoic acids. These reactions represent the first catalytic
bromolactonizations of alkyl-substituted olefinic acids that proceed
via 5-exo 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.