Facile Synthesis of Meso-Aminoporphyrins and Their Oxidative Oligomerization

Porphyrins and their metal complexes have been attracting significant attentions due to their characteristic chemical, or physicochemical properties derived from their 18π aromaticity.  Recently, nitrogen-based substituents (e.g., amino, amido, imido, imino, and azo groups) have been energetically introduced on the porphyrin periphery because of their strong influence of the p-electron system of the porphyrin.  Among them, meso-aminoporphyrins are the simplest nitrogen-substituted porphyrins.  Because of a wide variety of reactivities of the amino groups, meso-aminoporphyrins have been utilized as useful precursors for other nitrogen-substituted porphyrins.  Despite their synthetic usefulness, there have been only a few practical methods for the preparation of meso-aminoporphyrins. 

In this presentation, we present a facile and efficient synthetic method for meso-aminoporphyrins from meso-bromoporphyrins.¹  This method involves the aromatic nucleophilic substitution (S_NAr) of a bromo group with azide² and the following in-situ reduction of the introduced azide group by sodium ascorbate.  A simple treatment of 10 equiv. of sodium azide and sodium ascorbate with meso-bromodiarylporphyrins affords the corresponding meso-aminoporphyrins almost quantitatively.  This reaction is easily scalable up to a gram scale without the decrease of the product yield. 

We also performed the oxidative oligomerization of meso-aminoporphyrins to afford the polyaniline-like π-conjugated oligomers.³  We will also report the synthesis, structural characterization, and redox behavior of the obtained oligomers.

 

References

(1) K. Yamashita, K. Kataoka, S. Takeuchi, M. S. Asano, K. Sugiura, in preparation.

(2) K. Yamashita, K. Kataoka, M. S. Asano, K. Sugiura, Org. Lett. 2012, 14, 190–193.

(3) K. Yamashita, S. Takeuchi, M. S. Asano, K. Sugiura, in preparation.