Ru() catalyzed chelation assisted C(sp)-H bond functionalization along with concomitant (4 + 2) annulation

Efficacious protocols have been established to synthesize a structurally privileged Π-extended coumarin-fused pyridone nucleus by activating the vinylic C(sp 2 )-H bond of coumarin-3-carboxamide under the influence of inexpensive Ru( ii )-metal. Here an N -methoxy carboxamide entity has been exploited as the chelating fragment to manifest C(sp 2 )-H bond functionalization with a concomitant (4 + 2) annulation reaction, resulting in heterocyclic ring-forming protocols along with sulfoxonium ylide and iodonium ylide as representative bench-stable carbene surrogates. This diverse heterocycle formation via carbene insertion strategies, is further expanded to activate the ortho -C(sp 2 )-H bonds of different heterocycles by employing the sp 2 -N moiety as the directing group to develop acyl-alkylated/alkenylated quinazolines, isoxazoles and highly fluorescent pyridone- N -oxides. Intriguingly, during an evaluation of the versatility of the current protocols, a one-pot double C-H activation has been rationalized in the presence of iodonium ylide, which results in biologically potent benzimidazole-fused coumarin-centered bridge-headed polycyclic heteroarenes. Furthermore, a chemo-selective late-stage synthetic transformation is being designed to develop differently substituted pyridone analogues by switching the nature of the reducing agent. In addition, a photophysical experiment was done on one pyridine- N -oxide compound ( 7e ) and delightfully it exhibited fluorescence quenching activity selectively in the presence of Al 3+ ions, which appears to be a unique feature of our methodology. Finally, upon correlation of the merit of the developed pathways, the iodonium ylide mediated strategy appears to be superior. Ru( ii )-assisted C(sp 2 )-H functionalization along with (4 + 2) annulation leads to coumarin-fused pyridone, highly decorated N-heteroarenes and pyridine- N -oxides; the protocol also induces double C-H activation to the benzimidazole-coumarin conjugates.