The incorporation of alkene bonds into aromatic heterocyclic skeletons offers an efficient and straightforward strategy for molecular splicing and extension of conjugated systems, while also paving the way for the development of novel functional molecules. However, conventional approaches often depend on aldehyde or ketone precursors, involve multistep sequences, or require harsh reaction conditions, which considerably restrict their applicability. Herein, we present a single-step photoinduced alkene coupling reaction using quinoxalinones and indoleones that proceeds in high yield within a recyclable ionic liquid medium. This process exploits the inherent photosensitivity of the substrates to achieve autocatalysis, eliminating the need for an external photocatalyst, and proceeds under mild conditions with only a stoichiometrically minimal amount of oxidant. The method demonstrates strict stereoselectivity, broad substrate scope, and good functional group tolerance. Mechanistic investigations indicate a radical-based mechanism, wherein photoexcitation generates radical species that are regenerated via hydrogen atom transfer between the photoactive substrate and the radical intermediate. Given the significance of aromatic heterocyclic conjugated systems in pharmaceuticals and energy-related materials, this photocatalytic alkene coupling strategy holds considerable potential for practical applications.
Liu et al. (Mon,) studied this question.