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

meso-Functionalised porphyrin-alpha-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-alpha-diones was achieved in five steps in overall yields of up to 58%. The reaction sequence consisted of chelation of the porphyrin with copper(Ir), 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 beta-pyrrolic nitro group whilst leaving the meso-halophenyl group intact.