Copper-Mediated Synthesis of N-Aryl-Oxamic Acids

The Cu-catalyzed Ullmann-Goldberg cross-coupling between aryl iodides and oxamates is shown to afford the corresponding N-aryloxamates with yields ranging from moderate to excellent, when the oxamate precursor incorporates a bulky tertiary alkyl group effectively preventing product degradation under the strongly basic reaction conditions. The final oxamic acids are then generated through the acid hydrolysis of the oxamate in high yields. These acids were then converted into urethanes using PIDA under thermal conditions or a visible-light Fe-LMCT process. While electron-deficient N-aryl oxamic acids provide urethanes with high efficiencies, electron-rich counterparts led to diminished yields due to aryl group over-oxidation induced by PIDA.