text: NBS can α-brominate carbonyl derivatives via either a radical pathway (as above) or via acid-catalysis. For example, hexanoyl chloride 1 can be brominated in the alpha-position by NBS using acid catalysis.
  The reaction of enolates, enol ethers, or enol acetates with NBS is the preferred method of α-bromination as it is high-yielding with few side-products.