Synthesis of bilinones substituted by various nucleophiles at the 19-position and their substituent effects.

Abstract

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. X-ray crystallographic studies revealed that the CF₃COO group coordinated to the zinc. Oxaporphyrin zinc complexes reacted with various nucleophiles such as sodium methoxide, butylamine and aniline to give bilinone zinc complexes. Effects of substituent at the 19-position on spectroscopic properties of bilinones were studied. For example, 19-methoxybilinone was a blue pigment, while 19-anilinobilinone was a green pigment. The UV-visible spectra of various free-base bilinones were affected by the hetero atoms at the 19-position.