Directive Effects in Free Radical Oxidation by Fe(III). Reductive Decarboxylation of Peroxy Acids

Treatment of peroxycyclohexanecarboxylic acid with ferrous perchlorate in acetonitrile has been found to afford a 25% yield of cyclohexanol. Similar treatment of cis- or trans-3-hydroxyperoxycyclohexanecarboxylic acid yields largely cis-1,3-cyclohexanediol, revealing a directive effect for free radical oxidation by iron(III) analogous to that observed for the stereospecific cis-1,3 hydroxylation of cyclohexanol by ferrous ion-hydrogen peroxide. Preference for cis diol formation is also observed for w-4-hydroxyperoxycyclohexanecarboxylic acid, but the cis- and trans-1,2 isomers give a cis/trans diol ratio near unity. Analysis of the stereoisomeric mixture of 1,2-cyclohexanediols from the reaction of cyclohexene with ferrous ion-hydrogen peroxide leads to the conclusion that, in acetonitrile, the predominant mode of olefin hydroxylation does not proceed via addition of hydroxyl radical to the double bond.