Tandem oxidation-bromination of allylic alcohols with a TEMPO-Oxone-Et₄NBr reactant system

Allylic alcohols may be converted directly to α-bromo-α, β-unsaturated ketones in a single reaction with a mixture of TEMPO, Oxone and tetraethylammonium bromide. The process proceeds first through the oxidation of the alcohol to the ketone, followed by dibromination of the alkene with bromine that is generated from Oxone and tetraethylammonium bromide. Quenching the reaction with triethylamine then facilitates an elimination and forms the vinyl bromide. The presence of electron-donating groups on the aromatic ring leads to faster reactions and higher yields. Alternatively, substrates decorated with electron withdrawing groups on the aromatic ring are slower to oxidize. This method provides a rapid means to access these bromoalkenes using conditions that are operationally simple with reagents that are stable and easy to handle.