Synthesis of meso-substituted oxaporphyrins and their acid anhydride like reactivity

Kakeya Kazuhisa, Aozasa Masakatsu, Nakagawa Aya, Mizutani Tadashi

doi:10.11494/kisoyuki.2011.0.59.0

Coupled oxidation of [tetraarylporphyrinato]iron(III) chloride was performed by allowing the iron porphyrin to react with dioxygen, ascorbic acid, and pyridine to give biladienone as the major product and bilindione as a minor one. The meso-substituted bilindione was converted into an oxaporphyrin zinc complex by refluxing it with acetic anhydride and zinc acetate in chloroform, and it was isolated as a CF₃COO^- salt. The oxaporphyrins bearing phenyl, p-methoxyphenyl and p-carbomethoxyphenyl groups were synthesized in yields from 67 % to 99 %. X-ray crystallographic studies revealed that the CF₃COO group coordinated to the zinc, and the Zn-O distance was 2.010 (5) Å. The zinc ion is displaced 0.56 Å out of the oxaporphyrin plane. The phenyl groups are tilted: the dihedral angles of C(pyrrole alpha)–C(meso)–C(phenyl ipso)–C(phenyl ortho) are 60 - 66^o. The oxaporphyrin zinc complex reacted with various nucleophiles such as sodium methoxide, ammonia, butylamine, ethyl acetoacetate enolate and acetylaetone enolate to give bilinone zinc complexes. Additionally oxaporphyrin zinc complexes reacted with weak nucleophiles such as methanol, ethanol and i-propyl alcohol to give bilinone zinc complexes. This reaction depended on steric hindrance of nucleophiles: methanol and ethanol reacted with oxaporphyrins rapidly, while t-butyl alcohol hardly reacted with oxaporphyrins.

Synthesis of meso-substituted oxaporphyrins and their acid anhydride like reactivity

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