Origin of Regioselectivity Switch in Pyridinium Functionalizations with Phosphinoyl and Carbamoyl Radicals

The origins of regioselectivity switch in pyridinium phosphinoylation and carbamoylation were computationally investigated using energy decomposition analysis. The results reveal that the preference for regioselectivity arises from distinct intermolecular interactions between phosphinoyl/carbamoyl radicals and pyridinium derivatives. The ortho‐methoxy group on pyridinium remodulates different types of intermolecular interactions, exhibiting an opposite trend in its influence on para versus ortho selectivity.