Palladium-Catalyzed Modular Synthesis of Enantioenriched Pyridohelicenes through Double Imidoylative Cyclization

Enantioenriched pyrido[6]helicenes and furan-containing pyrido[7]helicenes have been synthesized through palladium-catalyzed double imidoylative cyclization by applying axially achiral multiaryl bisisocyanides and aryl iodides as coupling components. Two pyridyl rings were constructed sequentially by forming four C-C bonds in one pot with low catalyst loading. A control study using precyclized biaryl monoisocyanides revealed the second pyridine-forming enantiomer-generating step, which also enabled the introduction of different substituents, including trifluoromethyl, on the helical skeleton. This general and convergent approach to structurally diversified optically pure pyridohelicenes paves the way for optical studies and potential applications of this important class of azahelicenes.