The amine exchange/biaryl coupling sequence: a direct entry to the phenanthro[9,10-d]heterocyclic framework

Novel phenanthro[9,10-d]pyrimidines and phenanthro[9,10-d][1,2]oxazoles are regioselectively prepared by the application of a straightforward synthetic pathway, starting from new o,o′-dihalogenated and non-halogenated 4,5-diarylpyrimidines and 4,5-diarylisoxazoles, respectively, prepared via a tandem amine exchange/heterocyclization of diarylenaminones. A comparative study of biaryl coupling methodologies provides two highly efficient, complementary procedures to accomplish the final coupling step: an intramolecular Stille–Kelly stannylation/coupling of halogenated diarylpyrimidines and diarylisoxazoles, and a PIFA-mediated non-phenolic oxidative coupling of the corresponding non-halogenated substrates. In addition, other alternative approaches to the same target tetracyclic systems are also examined.