Accessing pharmaceutically relevant maleimide scaffolds through C-H bond functionalization

Maleimides are important scaffolds in medicinal chemistry and versatile substrates for transition-metal-catalyzed C-H functionalization. Over the past decade, C-H alkylation, alkenylation/arylation, and annulation have emerged as effective strategies for synthesizing diverse succinimide derivatives, including fused and spirocyclic structures, thereby expanding the chemical space accessible to pharmaceutical research. These approaches enable efficient synthesis of structurally complex molecules and facilitate the late-stage functionalization of bioactive compounds. This review provides a comprehensive and critical overview of recent advances in transition-metal-catalyzed C-H functionalization of maleimides, organized according to major reaction classes, including alkylation, alkenylation/arylation, and annulation. Beyond summarizing synthetic methodologies, the review comparatively evaluates catalyst systems, directing-group strategies, substrate scope, regioselectivity, functional-group tolerance, and mechanistic factors governing reactivity and selectivity. Particular emphasis is placed on the potential pharmaceutical relevance of maleimide- and succinimide-derived scaffolds, including their biological significance, application in analogue synthesis and scaffold diversification, and potential utility in the late-stage functionalization of bioactive molecules. The review also critically evaluates current limitations in the field, including reliance on noble-metal catalysts and strongly coordinating directing groups, limited compatibility with free N-H maleimides and structurally complex substrates, the lack of enantioselective methodologies, the absence of comprehensive green-chemistry metrics, and limited integration of C-H functionalization with biological evaluation and structure-activity relationship (SAR) studies. Finally, future directions are considered, with emphasis on earth-abundant metal catalysis, directing-group-free and asymmetric C-H functionalization, electrochemical and photoredox strategies, machine-learning-assisted catalyst design, and the integration of these methodologies into medicinal chemistry, late-stage functionalization of complex pharmaceuticals, and sustainable drug discovery.