Oxidative deprotection of amino protecting groups and oxidative brominations using tetrabutylammonium peroxydisulfate

Abstract

Tetrabutylammonium peroxydisulfate has been prepared from tetrabutylammonium hydrogen sulfate and potassium persulfate in water. This peroxide shows strong oxidizing abilities and high solubilities in various organic solvents such as dichloromethane, chloroform, acetonitrile, and methanol, etc. in contrast to poor solubilities of other metal peroxy disulfates such as potassium persulfate and sodium persulfate. Tetrabutylammonium peroxydisulfate has turned out to be a good source of tetrabutylammonium sulfate radical in organic solvents. ρ-Methoxybenzyl amines which is the amino protected groups could be successfully cleaned to the corresponding amines in good yield by tetrabutyl ammonium peroxydisulfate. Activated aromatic compounds substituted with electron releasing groups such as methoxy or hydroxy groups were brominated with tetrabutylammonium peroxydisulfate and lithium bromide in acetonitrile. Bromination has ocurred regioselectively at the activated ρ-position of methoxy or hydroxy groups. Only monobrominated products were obtained in good yields. Regioselective mono-brominations utilizing tetrabutylammonium peroxydisulfate / LiBr can be achieved under mild reaction conditions.