Isomerization of E-Cinnamamides into Z-Cinnamamides Using a Recycling Photoreactor

The photocatalytic synthesis of thermodynamically less-stable Z-alkenes has received considerable research attention in recent years. In this study, a recycling photoreactor was applied to the photoisomerization of E-alkenes (cinnamamide and Weinreb amide derivatives) to produce Z-alkenes. The closed-loop recycling system comprises an immobilized photosensitizer to achieve rapid photoisomerization and a high-performance liquid chromatography instrument for separation of the Z/E diastereomers. After 4-10 cycles, the desired pure Z-alkenes were obtained efficiently. In the photoreactor system, a photosensitizer (thioxanthone) was covalently immobilized on silica gel via amide bonding, which led to an enhanced photocatalytic activity compared to the parent thioxanthone. This recycling photoreactor shows promise as an alternative system for the production of Z-alkenes.