Light‐Induced Reactions of Small‐Membered Cyclic Carbonyl Compounds

Carbonyl group have long been recognized as one of the most prominent photoreactive groups, and a wide range of photochemical transformations involving carbonyl‐containing compounds has been developed. Among them, cyclic carbonyl compounds such as cyclopropenone and cyclobutenedione, exhibit distinctive physical properties and chemical reactivity attributed to their cyclic structures and inherent ring strain. This review highlights recent advances in the synthesis and photochemical reactivity of these cyclic carbonyl compounds. These compounds undergo photolysis upon direct excitation with ultraviolet or visible light, and in some cases, through indirect excitation mediated by photocatalysts. Notably, cyclopropenones and cyclobutenediones undergo efficient photolysis to yield alkynes and bisketenes, respectively. The resulting photogenerated species exhibit unique reactivity profiles that are strongly influenced by their substituents, enabling diverse applications in synthetic chemistry and chemical biology. This review aims to the advancement of scientific research employing these structurally and functionally unique photoreactive motifs.