Purpurin-Promoted Photo-Redox Reduction of Benzyl Selenocyanates as Masked Selenols, Preparative, Electrochemical, Computational, and Mechanistic Study

Abstract

The reduction of substituted benzyl selenocyanates to give the corresponding diselenides was performed by means of photo-redox catalysis using Eosin Y, Rhodamine 6G, Fluorescein, and Purpurin (PP) under LED irradiation. In all cases, diselenides were obtained as the only photoproducts; affording excellent yields when PP was used as photocatalyst under irradiation and air atmosphere in the presence of triethylamine (TEA). Our experimental findings indicate that despite TEA displays an acid-base equilibrium between PP and PP2−, only the former is photoactive. In addition, electrochemical properties of the selenocyanates under study were measured, finding that Se-CN moiety is relatively easy to reduce, around −1 V vs SCE. As a result, RC6H4CH2SeCN can act as masked selenols under photoinduced electron transfer conditions, making this methodology compatible with substituents (R) susceptible to hydrolysis or reduction. DFT calculations lead to a better insight into the reductive process.