On a seamlessly replicable circular photoreactor for lab-scale continuous flow applications

A cost effective and replicable continuous flow circular photoreactor system is introduced. All body parts of the reactor are 3D-printed and the electronics are purchased from various mainstream suppliers. The reactive path of the reactor features a low-cost PFA coil assembly, which provides comfortable chemical resistance and a wide wavelength window for scouting diverse photochemical reactions. The internal volume can be easily adapted from exploratory microscale experiments to multigram scale preparation of small libraries of compounds. The fabrication of the circular photoreactor was successfully reproduced and operated at 2 different locations. We showcase the versatility of the setup and its utility, as well as its suitability to both academic and industrial environments. A total of 4 case studies relevant to pharmaceutical and medicinal chemists are demonstrated. The first case study is a photocatalyzed singlet oxygen oxidation of a thioether, using methionine as model substrate and affording complete and selective conversion into the corresponding sulfoxide. Next, a photoredox application for the α-functionalization of a model tetrahydroisoquinoline is successfully optimized, with process conditions outclassing previous batch reports. Then, the preparation of a small library of arylcycloamines through a XAT cross-electrophile coupling is carried out. Finally, a photocatalyzed difluoroamidation of indoles is optimized and scaled up.