Organophotocatalyzed E and Z stereoselective C_sp³-C_sp² bond forming cross coupling reactions of carboxylic acids with β-aryl-vinyl halides

Owing to their importance in organic synthesis, transition metal catalyzed cross-coupling reactions have been the focus of many studies. Recently, it was recognized that merged transition metal and photoredox catalysis is a powerful strategy for the design of challenging C_sp³-C_sp² bond forming cross coupling reactions. However, these reactions require metals (e.g., Ni) to activate C_sp²-halogen bonds. In the current investigation, we developed a new, photocatalysis based, metal free approach to accomplish C_sp³-C_sp² bond formation between an alkyl fragment, derived from a carboxylic acid, and a vinyl moiety of a,β-aryl-substituted vinyl halide. The cross coupling process, which is activated by using the simple organic dye 4CzIPN, acting as a single electron transfer type photocatalyst, and visible light, is chemoselective, E-stereoselective and efficient. Moreover, upon prolonged irradiation of the reaction mixture, 4CzIPN serving as an energy transfer photocatalyst, promotes isomerization of the initially formed alkenes into mixtures enriched in the Z-isomers.