Praseodymium(III)-Catalyzed Regioselective Synthesis of C3‑N-Substituted Coumarins with Coumarins and Azides

A series of C3-N-substituted coumarins were synthesized in good yields directly from coumarins and azides in the presence of Pr­(OTf)3 without any additives or ligands needed. The selected compounds 3a, 3ce, 3g, 3i, 3q, 3u, and 3v exhibited good anticancer activities against MGC-803, A549, and NCI-H460 cell lines with IC50 in the range 8.75–38.54 μmol L–1.