Palladium-Catalyzed Dehydrogenative Annulation of Indolizines with Maleimides: Synthesis and Photophysical Studies of Maleimide-Fused Pyrrolo[2,1,5-cd]indolizines

A palladium(II)-catalyzed (3+2) dehydrogenative annulation of indolizines with maleimides, providing a tetracyclic heterocyclic framework, is described. The developed protocol provides a variety of maleimide-fused pyrrolo[2,1,5-cd]indolizines in moderate to good yields from both substituted indolizines and maleimides. The method is scalable, is compatible with a repertoire of substrates, and exhibits high functional group tolerance. The resulting annulated product demonstrates promising potential as a fluorescent molecular scaffold. Photophysical studies revealed solvatochromism and further showed efficient fluorescence quenching in the presence of picric acid, highlighting the potential for selective nitroaromatic sensing.