Pd(ii)-catalyzed direct arylation of chromones and enaminones gives divergent site-selectivities. Computational and experimental studies reveal a switch in mechanism, from a C3-selective CMD mechanism to a C2-selective carbopalladation pathway. This model accounts for the opposite selectivities of enaminone and chromone, and also correctly predicts selectivities for the C–H functionalization of heteroaromatic substrates as a function of the coupling partner.

An efficient method for the C4-regiocontrolled C-H functionalization of coumarins to enable facile oxidative cross-couplings with simple arene components is disclosed.

Light-promoted phosphonation of quinolinones and coumarins was developed without the need for an external photocatalyst. Investigations support a mechanism whereby both starting materials and products act as photosensitizers upon excitation using compact fluorescent light sources to photochemically promote the dissociation of the N-O bond in the pyridinium salt by a single electron transfer pathway. A wide range of quinolinone and coumarin substrates can be utilized in the phosphonation process under mild reaction conditions.