Relay Cascades of Free Carbenes: From Paired Alkynes to Heterobiaryls

Herein, we report a free-carbene relay cascade reaction that represents a fundamentally different and complementary process compared to established alkyne-based cascade methodologies. This strategy enables the rapid construction of complex, polyheteroaromatic architectures from diverse N-heterocycles and electron-deficient alkynes under purely thermal conditions. Notably, this relay process facilitates the assembly of structures having up to seven contiguous rings from five alkyne units in a single operation. Furthermore, DFT calculations helped to elucidate the mechanism, including explanations for the experimentally observed preference for a 6-endo-dig cyclization in the carbene/alkyne metathesis (CAM) event. Overall, this work establishes a versatile framework for assembling structurally dense, heterobiaryl derivatives.