Daisy-Chaining Photo- and Thermal Chemistry: Multistep Continuous Flow Synthesis of Visible-Light-Mediated Photochemistry with a High-Temperature Cascade Reaction

A highly efficient visible-light-mediated photochemical [2 + 2] cycloaddition is coupled with an atom economic thermal cascade reaction in a continuous flow process. By moving the photochemistry from ultraviolet (UV) to visible, it is made more energy-efficient and can be conducted with readily available equipment. The application of high-temperature flow chemistry to the thermal cascade step allows for safe and reliable scale-up with short reaction times. Thus, we demonstrate a rare example of a photo/thermal daisy-chained process and, specifically, the first visible-light-mediated excited state to the thermal cascade reaction as a fully continuous process (20 g/h). The synthetic utility of flow chemistry is further showcased by the isolation of a reactive intermediate at quantities not possible under batch conditions.