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 pyrrolo2,1,5-cdindolizines 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.
Dhyani et al. (Tue,) studied this question.