Nonselective bromination-selective debromination strategy: Selective bromination of unsymmetrical ketones on singly activated carbon against doubly activated carbon

[GRAPHICS] We have found a new synthetic method for the preparation of the alpha-bromoketones that are brominated in the less activated terminal position of unsymmetrical ketones. Brominations in short reaction times (kinetically controlled) provided internally brominated compounds as a major product. However, brominations in longer reaction times (thermodynamically controlled) gave more of the terminally brominated compound through the reversible reaction by Br-2 and produced hydrogen bromide. Several brominated compounds at the terminal position were successfully prepared through the new synthetic route.