Introducing the Staudinger phosphazene reaction to porphyrin chemistry

The syntheses, characterizations and transformations of three tetraphenylporphyrins derived from methoxymethylated benzaldehyde 3 are described. Benzaldehyde 3 reacted with pyrrole under Lewis acid catalysis to give dipyrromethane 4 which was used as precursor in porphyrin syntheses. Porphyrins 6, alpha alpha-7 and alpha beta-7 were obtained using conditions for sterically encumbered benzaldehydes, with alpha alpha-7 and alpha beta-7 being atropisomers. The methoxymethyl groups of 6, alpha alpha-7 and alpha beta-7 were transformed into bromomethyl substituents (porphyrins 8, alpha alpha-9 and alpha beta-9) which were easily modified by nucleophilic reaction with the azide anion. Porphyrin azide 10 was subjected to a Staudinger phosphazene formation with triphenylphosphine. Subsequent reaction of the porphyrin phosphazene 12 with carboxylic acids gave acetamide 13, benzamide 14, and ferrocene carboxamide 15, respectively. Kornblum oxidation of monobromomethyl porphyrin 8 gave the formyl derivative 16. Copyright (c) 2004 Society of Porphyrins & Phthalocyanines.