Metal-Free Synthesis\nof <i>meso</i>-Aminoporphyrins\nthrough Reduction of <i>meso</i>-Azidoporphyrins Generated <i>in Situ</i> by Nucleophilic Substitution Reactions of <i>meso</i>-Bromoporphyrins

Abstract

A facile\nand metal-free method for the preparation of free base <i>meso</i>-aminodiarylporphyrins from readily available <i>meso</i>-bromodiarylporphyrins is described. Simple treatment\nof <i>meso</i>-bromoporphyrins with sodium azide and sodium\nascorbate in DMF affords the corresponding <i>meso</i>-aminoporphyrins\nin very good yields. This method involves the aromatic nucleophilic\nsubstitution (S_NAr) of a bromo group with an azido group\nand the subsequent <i>in situ</i> reduction of the introduced\nazido group by sodium ascorbate. This amination reaction can be scaled\nup to gram scale without any decrease of the product yield. The amination\nreaction of free base <i>meso</i>-dibromoporphyrin affords\na monoaminated product selectively, whereas that of the Ni­(II) complex\nfurnishes a diaminated product that is oxidized by air under ambient\nconditions but isolable as a trifluoroacetyl ester. Metal-insertion\nreactions of the obtained free base aminoporphyrins afford the corresponding\nmetal complexes (Ni­(II), Cu­(II), Zn­(II), and Pd­(II)) all in good yields\nexcept the Pd­(II) complex. Synthetic methods for the preparation of <i>N</i>-mono- or dialkylaminoporphyrins from the free base <i>meso</i>-aminoporphyrins have been also established.