Copper-Catalyzed Hydroarylation: Synthesis of 4-Arylcoumarins

Significance

Reported here is a high-yielding synthesis of 4-arylcoumarins via the copper-catalyzed hydroarylation of MOM-protected ortho-phenol-derived propiolates with arylboronic acids followed by cyclization under acidic work-up. Unprotected ortho-phenol-derived propiolate gave mixtures of compounds under hydroarylation conditions, the reason for which is unclear. The scope of the method has been reasonably well defined. Unfortunately, three equivalents of aryl boronic ­acids appear to be required. The current method was used for the synthesis of seven naturally occurring neoflavones that contain medicinal properties.