Organoboranes for synthesis. 6. : A convenient,general synthesis of alkylhydroperoxides via autoxidation of organoboranes

The low temperature autoxidation of organoboranes in tetrahydrofuran leads to the formation of diperoxyboranes, which provide the corresponding alkylhydroperoxides in excellent yields, upon treatment with hydrogen peroxide. However, only two of the three alkyl groups on boron are used for the formation of hydroperoxides. This difficulty was solved by employing alkyldichloroborane etherates instead of trialkylboranes. The alkyldichloroborane etherates react cleanly with one molar equivalent of oxygen in ether solvent. The product is readily hydrolyzed to form the corresponding hydroperoxides in excellent yields. The autoxidation of organoboranes is inhibited by iodine or such free-radical scavengers. A study of the inhibition by iodine of the oxidation of representative trialkylboranes indicates that the rate of initiation decreases with an increase in the steric crowding about the boron atom. The rate of inhibition of the autoxidation of trialkylboranes by iodine reveals that the reaction involves a relatively slow rate of radical initiation, followed by a very fast rate of chain propagation.