Copper-mediated synthesis of tertiary diaryl squaramides.

Tertiary aryl squaramides were synthesized by using copper catalyzed C-N bond-formation with L-proline as the ligand. Symmetrical diaryl squaramides could be prepared in a one-pot reaction by using excess aryl bromide with varying yields. Unsymmetrical derivatives were prepared by sequential arylation. Yields of the diarylated products were highly sensitive to steric effects.