Daisy-Chaining Photo- and Thermal Chemistry: Multi-Step Continuous Flow Synthesis of Visible-Light Mediated Photo-chemistry 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 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 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.