Cyanobenzaldehydes as key synthons for the construction of fused heterocyclic scaffolds: a mini-review

Cyanobenzaldehydes have emerged as highly valuable and versatile synthons in heterocyclic chemistry owing to the unique coexistence of electrophilic aldehyde and nucleophilic nitrile functionalities within a single molecular framework. This dual reactivity enables diverse annulation and cyclization strategies, providing efficient access to a wide range of fused heterocyclic scaffolds. This mini-review summarizes recent advances in the synthetic applications of 2-cyanobenzaldehydes for the construction of fused heterocycles, with an emphasis on product-oriented classification. The reported heterocyclic skeletons are systematically categorized into five major groups: isoindoline derivatives, isobenzofuran derivatives, isoquinoline derivatives, indole and benzimidazole derivatives, and pyrrolopyrimidine derivatives. Representative synthetic methodologies, key reaction conditions, and mechanistic aspects are discussed to highlight the structural diversity and synthetic potential enabled by 2-cyanobenzaldehydes. This focused overview aims to provide a concise and organized resource for researchers interested in the design and synthesis of fused heterocyclic frameworks using 2-cyanobenzaldehyde-based building blocks.