Regioselective coupling reactions of 2,4-diaminopyridine derivatives with aryl halides: the synthesis of elaborated pyridines

The development of a synthetically useful, regioselective cross-coupling of 2,4-diaminopyridines with aryl and heteroaryl halides is reported. Selectivity for coupling through either amine is controlled by a simple change in the reaction conditions. Cross-coupling through the 2-amino group predominates in the presence of a palladium catalyst, whilst the 4-amino coupled product predominates in the absence of palladium.