Selenoxides as catalysts for the activation of hydrogen peroxide. Bromination of organic substrates with sodium bromide and hydrogen peroxide

Diphenyl selenoxide (7), dibenzyl selenoxide (8), and several aryl benzyl selenoxides (9-13) are catalysts for the bromination of organic substrates in two-phase systems of CH2Cl2 and pH 6 phosphate buffer containing 2.0 M NaBr and 2.6 M H2O2. The catalysts are effective at 2.5 mol % relative to the organic substrates. In the bromination of 4-pentenoic acid, electron-donating substituents in the selenoxides accelerate the reaction, while electron-withdrawing substituents slow the reaction. Benzyl 2-((dimethylamino)methyl)phenyl selenoxide (13), with a chelating dimethylamino group, was the most effective catalyst and was used in the preparative bromination of 4-pentenoic acid, 2,2-diphenyl-4-pentenoic acid, 1,3,5-trimethoxybenzene, N,N-dimethylaniline, and N-phenylmorpholine.