Bis-porphyrin arrays. Part 1. The synthesis of meso-halophenyl porphyrin-α-diones

Abstract

meso-Functionalised porphyrin-α-diones have been prepared as the basic building blocks for bis-porphyrin arrays. meso-Halophenyl porphyrins 4 and 7 were prepared by condensation of 3,5-di-tert-butylbenzaldehyde with dipyrromethanes 1, 2, and 3. Conversion of 4 and 7 to the corresponding meso-halophenylporphyrin-α-diones was achieved in five steps in overall yields of up to 58%. The reaction sequence consisted of chelation of the porphyrin with copper(II), nitration, hydroxylation with the benzaldoximate anion, demetallation, followed by oxidation with the Dess–Martin periodinane. The key hydroxylation step was found to proceed chemoselectively, displacing the β-pyrrolic nitro group whilst leaving the meso-halophenyl group intact.