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.

Visible light mediated iron-catalyzed addition of oxamic acids to imines.

Oxamic acids where shown to add to imines, providing a broad range of α-aminoacid amides in generally good yields. The process is efficient on pre-formed imines but may also be conducted using a 3-component strategy by simply mixing aldehydes, amines and oxamic acids in the presence of ferrocene, acting both as a photocatalyst under visible light and as a Lewis acid. The reaction proceeds through the addition onto the imine of a carbamoyl radical intermediate generated through a charge transfer from the carboxylate ligand to a Fe(iii) species (LMCT).