Double-Duty Bromocatalyst

By tweaking a classic catalyst scaffold, chemists have developed a route to lactones that feature bromine at chiral centers (J. Am. Chem. Soc., DOI: 10.1021/ja305117m). It’s an addition to the tool kit of halolactonization, a class of reactions organic chemists use to make natural products with therapeutic potential. Stephen F. Martin of the University of Texas, Austin, and coworkers made two modifications to BINOL, a popular chiral catalyst, to promote bromolactonizations of unsaturated carboxylic acids. They added an amidine substituent to stabilize the reaction’s bromonium ion intermediate and a phenyl group to boost stereoselectivity. The method proceeds through ring closure in which the new C–Br bond is formed outside the ring. It’s the first exo-lactonization to generate chiral centers with high enantioselectivity featuring carbon-halogen bonds, Martin says. The team now plans to study the reaction’s mechanism in greater depth.