Synthesis of 5-Substituted Benzo[h]quinoline Derivatives via Reactions Involving C(sp2)-Br Bond Activation

In view of literature reports, benzo[h]quinoline and its substituted analogues, due to their structural similarity to 2-phenylpyridine derivatives, appear to be very promising C,N-cyclometalating ligands for iridium-based Phosphorescent Organic Light Emitting Diode technology. 5-bromo-benzo[h]quinoline aroused our particular interest as a convenient precursor for further transformations, and was successfully functionalized in the course of transition metal-promoted exclusive C-C, C-O and C-N bond formation, yielding a series of 5-substituted benzo[h]quinoline derivatives with unique structures and properties. Some of the synthesized compounds seemed to be appropriate starting materials for subsequent transformations, and enabled the preparation of new benzo[h]quinoline-based materials, for instance those with fluorine or silsesquioxane groups, which have not been synthesized by the conventional Scraup protocol. In selected transformations, the assistance of microwave irradiation as a non-conventional energy carrier significantly improved efficiency, leading to the formation of desired products with yields of up to 99%.