Photolytic <i>ortho</i>-Selective Amino Pyridylation of Aryl Isocyanates with <i>N</i>-Amino Pyridinium Ylides for the Synthesis of <i>N</i>-Arylsulfonyl Ureas

Herein, we report an expedient synthesis of aryl sulfonyl ureas <b>4</b> and <b>5</b> from <i>N</i>-amino pyridinium ylides and aryl isocyanates. <i>N</i>-Aminopyridinium ylides <b>3</b> are synthesized via blue light-emitting diode irradiation of pyridine/isoquinoline and appropriate iminoiodinanes. The strategy involved a hitherto unknown carboamination of imine moieties (of aryl isocyanates) via a three-component reaction of pyridine derivatives/isoquinoline <b>1</b>, <i>N</i>-aryl sulfonyl iminoiodinanes <b>2</b>, and numerous aryl isocyanates at room temperature in 2-methyl tetrahydrofuran to afford the target compounds in moderate to excellent yields. <i>N</i>-Arylpyridinium ylides <b>3</b> (as intermediates) undergo a [3+2] cycloaddition with the aryl isocyanates followed by the aromatization of the pyridine/isoquinoline moiety to afford compounds <b>4</b>. On the basis of the substitution pattern among the reactants, in some cases pyridine extrusion occurs during the reaction to afford depyridinylated aryl sulfonyl ureas <b>5</b>. In general, isocyanates are used as dipolarophiles in [3+2] cycloaddition reactions. However, regioselective amino pyridylation of these species is a first. Control experiments and density functional theory calculations elucidate the reaction mechanism. The batch process of the protocol could be seamlessly transferred to the photoflow synthesis.