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We report the efficient carboxylation of bromides and triflates with K₂CO₃ as the source of CO₂ using an organic photocatalyst in combination with a nickel complex under visible light irradiation at room temperature. The reaction is compatible with a variety of functional groups and has been successfully applied to the synthesis and derivatization of biologically active molecules. Particularly, the carboxylation of unactivated cyclic bromides proceeds well under our protocol extending the scope of this transformation. Spectroscopic and spectroelectrochemical investigations indicate the generation of a Ni(0) species as catalytic reactive intermediate.

Herein we establish, for the first time, a straightforward access to stable oxonium-doped polycyclic aromatic hydrocarbons (PAHs) through the rhodium-catalyzed cascade C-H activation/annulations of naphthalene-type aldehydes with internal alkynes. This protocol provides four divergent reaction types (categorized as IA, IB, IIA and IIB), including two unexpected annulations with an oxygen transposition process, which lead to diverse types of phenalenyl-fused pyrylium cations comprising a four, five or six-ring-fused π-conjugated core. The annulations exhibit an exquisite regioselectivity and a high tolerance of sensitive functional groups. These PAHs feature the intriguing photophysical properties such as full-color tunable fluorescence emission, high quantum yield and positively charged core, and can be reduced easily to the phenalenyl radicals.

Unmet Potential. Electrochemistry is the most simple and basic way of altering the redox-states of organic molecules. Despite extensive studies and its demonstrated promise, it has yet to take off in mainstream synthesis. The reason, we argue, is due to engineering challenges in instrument design.

Along with amide bond formation, Suzuki cross-coupling, and reductive amination, the Buchwald-Hartwig-Ullman type amination of aryl halides stands as one of the most employed reactions in modern medicinal chemistry. This Communication demonstrates the potential of utilizing electrochemistry to provide a complementary avenue to access such critical bonds using an inexpensive nickel catalyst under mild conditions. Of note is the scalability, functional group tolerance, rapid rate, and the ability to employ a variety of aryl donors (Ar-Cl, Ar-Br, Ar-I, Ar-OTf), amine types (primary and secondary), and even alternative X-H donors (alcohols and amides).