Formal [5 + 2] cycloaddition of ortho-indolizinyl anilines with cyclopentenediones: access to planar indolizine-fused azepines†

An efficient and straightforward approach to planar indolizine-fused azepines via Brønsted acid catalyzed [5 + 2] cycloaddition of ortho-indolizinyl anilines with cyclopentenediones has been established. This reaction involves a Friedel–Crafts addition/oxidation/Schiff-base condensation tandem process and features mild conditions, broad substrate scope and diverse further transformations. Furthermore, the intriguing planar azepines exhibited favorable photoluminescence properties, which indicated their potential as fluorescent materials.