Tandem C-S Coupling and Debrominative Cyclization Enables an Easy Access to β-Thiazole-Fused Porphyrins.

A catalyst-free synthetic approach to β-thiazole-fused 5,10,15,20-tetraarylporphyrins via a cascade reaction of nickel(II) or copper(II) 2-amido-3-bromo-5,10,15,20-tetraarylporphyrins and Lawesson's reagent is described. During the course of the reaction, 3-bromo-2-thioamido-5,10,15,20-tetraarylporphyrins formed in situ undergo debrominative cyclization in refluxing toluene to provide novel β-thiazole-fused porphyrin macrocycles in good yields. Furthermore, free-base and zinc(II) β-thiazole-fused porphyrins have also been constructed in excellent yields by using standard demetalation and zinc metal insertion procedures. The preliminary photophysical studies revealed a significant bathochromic shift in the electronic absorption and emission spectra of new porphyrins as compared to meso -tetraarylporphyrin precursors.