Regioselective Synthesis of Angular Isocoumarinselenazoles: A Benzoselenazole-directed, Site-specific, Ruthenium-catalyzed C(sp²)-H Activation

The synthesis of new, angular isocoumarinselenazoles is described, which involves the construction of 2-amino benzoselenazoles and their regioselective C2N-alkylation and alkyne insertion. An expeditious and metal-free synthesis of 2-aminobenzoselenazoles by the reaction of methyl 3-amino-4-fluorobenzoate and isoselenocyanates was achieved. Further N-alkylation of the 2-aminobenzoselenazoles resulted the formation of two regioisomers with different reactivities towards the alkyne insertion. The regioselective construction of the α-pyrone ring on the benzo[1,3-d]selenazole skeleton was achieved via a ruthenium (II)-catalyzed oxidative annulation. It is clear that the selenazole nitrogen plays an important role in the observed selectivity. (Figure presented.).