Photocatalytic Transformations of the Resveratrol Derivative in Microflow Reactor

Abstract

A simple and efficient protocol is utilized for the transformation studies of a thiophene analog of E-resveratrol by photocatalytic oxygenation using an anionic and a cationic free-base porphyrin, as well as their manganese(III) complexes. The starting substrate was chosen as a representative of heterostilbenes with proven good antioxidant activity. The experiments were carried out in two photoreactor types (batch and microflow reactor) to investigate the impact of the reactor type and design on conversion and photoproduct composition. NMR spectroscopy and UHPLC/MS analyses were applied for the identification and quantification of four photoproducts (Z-1, 2, 3, and 4), results of isomerization, dimerization, cyclization, and oxygenation. Different yields of photoproducts were obtained in a batch reactor and microflow reactor. In the experiments performed in a microflow reactor, Z-1 was most dominant because it was constantly removed from the reaction mixture. Therefore, the formation of other products (2, 3, 4, and undefined) whose precursor is Z-1 was avoided. This was not the case in the experiments performed in a batch reactor. Additionally, all the reactions tested were significantly accelerated in a microflow reactor, making it the preferred reactor type and design for the photocatalytic transformation of resveratrol derivative.