I. Trifluoromethylation and Oxidation by Visible Light Photoredox Catalysis II. Hydro-perfluoroalkylation of Alkenes and Alkynes Using an Electride, Dicalcium Nitride (Ca2N)

Abstract

Various approaches to environmentally benign radical-mediated reactions have been studied: i) visible light-induced photoredox catalysis with Ru- and Ir complexes, ii) radical reaction using an inorganic material, two-dimensional electride, dicalcium nitride [Ca2N]+•e-. First, methods for trifluoromethylation of alkenes and oxidation of aldehydes have been developed by visible light-induced photoredox catalysis. Trifluoromethylation of alkenes proceeds with CF3I and DBU in the presence of catalytic amount of Ru(Phen)3Cl2 under visible light irradiation. This process works especially well for terminal alkenes to give alkenyl-CF3 products with only E-stereochemistry. Interestingly, the reaction of allylic amines produced CF3-containing aziridines under similar conditions. A method for oxidation of aldehydes to carboxylic acids has also been developed employing visible light photoredox catalysis. Singlet oxygen, generated by visible light in the presence of a Ru or Ir photocatalyst, reacted with aldehydes to give the corresponding carboxylic acids in excellent yields. The reaction is highly chemo-selective, in which only an aldehyde moiety is reactive even in the presence of other photo-oxidation active sites. This method is an example of an ideal green chemical reaction in the sense that molecular oxygen and visible light are key sources for the transformation. Inorganic electrides, which are stoichiometric ionic crystals, could be used as the efficient electron source for radical mediated reactions. A method for hydrotrifluoromethylation of unactivated alkenes and alkynes with CF3I has been developed using an inorganic electride, [Ca2N]+∙e. In the transformation, anionic electrons were transferred from [Ca2N]+∙e electrides to the trifluoromethylating reagent CF3I to initiate radical-mediated trifluoromethylation. The role of EtOH was observed to be pivotal in the transformation, acting as the solvent, an electron-releasing promoter, and a hydrogen source.