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.