Biomimetic iron porphyrin-catalysed oxidation of cyclopenta [a] phenanthrenones

Abstract

Peracid oxidation of two cyclopenta[a]phenanthrenones occurs at the chemically active K-region to yield the cis-6,7-epoxides. Biomimetic oxidation of these compounds as substrates in an iron porphyrin–iodosylbenzene system produces similarly high yields of these oxidation products. The steric hindrance around the periphery of the porphyrin has been increased to the extent that access of the K-region to the active iron centre is impossible. However, these steric constraints do not encourage stereoselective substrate oxidation at the more accessible terminal rings, the site of attack with the natural enzymatic system. Methoxy substitution around the porphyrin periphery produces a highly effective catalyst for these substrates. Cyclohexene oxidation is not so encouraged, suggesting a ‘pocket’ attractive to the cyclopenta[a]phenanthrenones.