meso-Reactivity of porphyrins and related compounds. Part 9. Photo-oxygenation of octaethyloxophlorin

Abstract

The photo-oxygenation of octaethyloxophlorin has been investigated under basic and under neutral conditions. In both cases unstable intermediate stages are observed spectroscopically. In methanolic sodium methoxide the solution becomes bleached and tetraethyl(methanol)propentdyopent is a significant product. In neutral solutions (e.g. benzene–methanol) the major products are octaethyl-l5,15-dioxo-5,15-dihydroporphyrin (4) and octaethyl-19-formyl-21H,24H-bilin-1,15-dione (7), the formation of octaethyl-21H,24H-bilin-1,19-dione (6) being a minor pathway. A mechanistic rationalisation is proposed.