Catalytic Transformations of Aza-Cyclobutenes, Fused Cyclobutenes, and Cyclobutenones.

Cyclobutenes, four-membered cyclic compounds with a carbon-carbon double bond, are valuable intermediates in organic synthesis, offering unique reactivity due to their ring strain. This review focuses on three major types including aza-cyclobutene, fused cyclobutene, and cyclobutenone, highlighting their synthetic versatility and reactivity. Aza-cyclobutenes enable diverse functionalization strategies for constructing complex N-heterocyclic structures. Fused cyclobutenes with their bicyclic nature are explored for applications in stereoselective chemical transformations, polymer, and materials science, while cyclobutenones, with their electrophilic carbonyl group, serve as key intermediates in polyfunctionalized frameworks. We discuss recent advancements in catalysis, including transition metal- and photoredox-mediated transformations, which enable selective, enantioselective, and regioselective reactions. The review also addresses emerging challenges and future directions, emphasizing the scalability of these methods for industrial applications. This comprehensive overview underscores the transformative potential of cyclobutenes in synthetic organic chemistry.