Novel versatile synthesis of substituted tetrabenzoporphyrins

A novel general synthetic route to tetraaryltetrabenzoporphyrins (Ar4TBP) with various peripheral functional groups is developed. The procedure includes W 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.