Cascade Radical Pathway-Enabled Nitrogen-Sulfur Coupling: Access to Isothiazolo[3,4- b ]- meso -tetraarylporphyrins.

A catalyst-free radical-mediated domino strategy for the construction of isothiazolo[3,4- b ]- meso -tetraarylporphyrins was developed. During the course of the reaction, 2-benzothioylamino-3-thioformyl- meso -tetraarylporphyrins generated in situ after the addition of Lawesson's reagent to a solution of 2-benzoylamino-3-formyl- meso -tetraarylporphyrins in refluxing toluene underwent a homolytic cleavage to produce nitrogen-sulfur radicals. Subsequently, the formation of a new N-S bond through an intramolecular cascade radical coupling provided direct access to novel β-isothiazole-fused porphyrins.