Novel Versatile Synthesis of Substituted Tetrabenzoporphyrins

A novel general synthetic route to tetraaryltetrabenzoporphyrins (Ar₄TBP) with various peripheral functional groups is developed. The procedure includes (i) Barton−Zard condensation of 1-nitro- or 1-phenylsulfonylcyclohexenes with isocyanoacetic acid esters, (ii) condensation of the resulting 4,5,6,7-tetrahydroisoindoles with aromatic aldehydes to give fused tetraaryltetracylohexenoporphyrins (Ar₄TCHP), and (iii) aromatization of the metal complexes of Ar₄TCHP's into the corresponding Ar₄TBP's. Cu and Zn complexes of Ar₄TBP's are further demetalated to give the corresponding Ar₄TBP free bases. The overall yields for the sequence range from 15% to 40%, making the method suitable for the preparation of gram quantities of Ar₄TBP's in a single run. The scope of the method, the selection of the peripheral substituents, the choice of the metal ions, and their influence on the yields of aromatization are discussed. The basic spectroscopic properties of newly synthesized Ar₄TBP's and Ar₄TCHP's are reported together with the first X-ray crystallographic structure of the NiAr₄TBP complex.