ALIPHATIC HYDROXYLATION CATALYZED BY IRON(III) PORPHYRINS

Hydroxylation of aliphatic hydrocarbons with oxidants such as iodosobenzene can be effectively catalyzed with highly halogenated iron(III) porphyrins such as iron(III) tetrakis(2,6-dichlorophenyl)octabromoporphyrin. Hydroxylation of norbornane and tetraexodeuterionorbornane using this catalyst afforded good yields of products which consisted of 86:13: < 1 and 84:16: < 1 ratios of exo-norbornan-2-ol, endo-norbornan-2-ol, and 2-norbornanone, respectively. In the latter case both D3 and D4 exo and endo alcohols but only D3 ketone were obtained. The primary isotope effect is 5. These results show that the reaction involves loss of stereochemistry and has a large isotope effect; the results are in agreement with those from a previous study of the same compounds using the enzyme cytochrome P-450. As in that case, this hydroxylation proceeds through a free-radical cage process. The hemin catalysis leads to a loss of stereospecificity similar to that in the enzyme-catalyzed reaction.