We report a method for addition of α-bromophenylacetic acids to vinyl C![[double bond, length as m-dash]](http://www.rsc.org/images/entities/char_e001.gif)
C bonds in styrenes to afford γ-lactones. Reactions employed a simple cobalt catalyst Co(NO3)2·6H2O in the presence of dipivaloylmethane (dpm) ligand. Many functionalities including halogen, ester, and nitro groups were compatible with reaction conditions. If α-bromoesters were used, vinylacetates were the major products.
