The meso-reactivity of porphyrins and related compounds. Part VII. Benzoyloxylation of phenylpyrroles and of octaethylporphyrin

Abstract

Benzoyl peroxide reacts with phenylpyrroles under mild conditions to give mixtures of which benzoyloxy-derivatives are the major components. 2,5-Diphenyl-, 1,2,5-triphenyl-, and 2,3,5-triphenyl-pyrroles give β-benzoyloxy-derivatives, and 2,3,4,5-tetraphenylpyrrole gives 2-benzoyloxy-2,3,4,5-tetraphenyl-2H-pyrrole. These reactions do not appear to involve substitution by benzoyloxyl radicals, although the substrate radicals (or radical cations) are possible intermediates.

With octaethylporphyrin at 95 °C substitution at meso-positions (giving mono-, bis-, tris-, and tetrakis-benzoyloxy-derivatives) and at side chain ‘benzylic’ positions is observed. The latter reaction is quenched by oxygen, and in iron porphyrin substrates, and is regarded as a radical-chain process.

Phenylation was not detected in any of these reactions and can be no more than a minor pathway under the conditions employed.