Sequential cross-coupling on multihalogenated heterocycles is a particularly attractive strategy for the divergent synthesis of polysubstituted heterocycles, but the factors that govern the regioselectivity are not well understood. The present study shows that the selectivity in palladium-catalyzed cross-coupling reactions of heterocycles bearing multiple identical halogens is determined by both the energy to distort the carbon halogen bond to the transition-state geometry (related to BDE) and the interaction of the heterocycle π* (LUMO) and PdL2 HOMO.

Selectivity of the palladium-catalyzed cross-coupling reactions of heterocycles bearing multiple identical halogens is mainly determined by the relative ease of oxidative addition. This is related to both the energy to distort the carbon halogen bond to the transition-state geometry (related to the CX bond-dissociation energy) and to the interaction between the heterocycle π* (LUMO) and PdL 2 HOMO (J. Am. Chem. Soc. 2007, 129, 12664). The computed bond dissociation energies of a larger series of halo-heterocycles have been explored with B3LYP and higher accuracy G3B3 calculations. Quantitative trends in bond dissociation energies have been identified for five-and six-membered chloro and bromo substituted heterocycles with N, O, and S heteroatoms.

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