Lighting the way to diverse cyclic architectures: expanding the horizons with photogenerated ketenes in sustainable chemistry

Light is a fundamental energy source that has considerably driven scientific progress, especially in the fields of synthetic chemistry and pharmaceuticals. Visible-light-mediated synthetic chemistry has revolutionized conventional bond formation and enabled previously inaccessible chemical processes under mild conditions. However, the continuous consumption of photocatalysts and corresponding additives has led to system complexity and cost escalation, making the development of photoactivated substrates a promising yet challenging research frontier. Recently, emerging photogenerated ketenes as a potent class of organic compounds has provided a promising solution to the challenges associated with classic ketene preparation and application, with reduced preparative costs and simplified processes. This review highlights how photogenerated ketenes have simplified and accelerated the synthesis of diverse cyclic architectures through [2 + n ] cyclization reactions and complex natural products through Danheiser benzannulation. Significantly, their successful application in flow chemistry has demonstrated remarkable potential for industrialization. Despite challenges in terms of limited cyclic architectures, elusive mechanisms, and challenging chiral control, ongoing efforts in investigating the chemical behaviors of photogenerated ketenes and exploring their potential applications hold promise for breakthrough discoveries, propelling the field forward sustainably.