Delineating the mechanistic features of C-H activation in aryl-heteroaryl coupling is an important step in the design of selective, catalytic processes. Herein we use the intramolecular dehydrogenative coupling of 4-phenoxy-2-coumarins as a model study. Computational results and experimental studies suggest that CMD is operative in the cleavage of both C-H bonds, and that the heteroaryl C-H is cleaved initially.