Blue Light-Driven [4+2]-Cycloaddition: Diastereoselective Synthesis of Chromeno[4,3-b]quinoline and Chromeno[4,3-b][1,8]naphthyridine Scaffolds

A one-pot, metal-free, light-driven [4+2]-cycloaddition reaction is described by accessing a diverse collection of chromeno[4,3-b]quinoline and chromeno[4,3-b][1,8]naphthyridine scaffolds in a diastereoselective manner. This process delivered stereoisomers, which were challenging to produce by an inverse-demand Diels–Alder reaction. The tetracyclic products were provided in good yields, promoted by rose bengal and blue light in a single operation. The developed protocol proceeded efficiently without the need for expensive photosensitizers such as Ir or Ru complexes. The cascade is modular and step-economic, and the substrate scope is wide. Polycyclic architectures can be assembled from readily available aniline, aminoazine, indole, and salicylaldehyde derivatives.