Photoredox-Catalyzed Difunctionalization of Unsaturated Carbon Compounds with CO2 for the Synthesis of Unnatural Amino Acids

Abstract

Unnatural amino acids have a special function not seen in natural amino acids. Therefore, Unnatural amino acids are introduced into peptides and proteins and widely used as important monomers in drug development and protein processing. High-value-added unnatural amino acids can’t be obtained in nature, so chemical processes are essential. For this reason, the synthesis of various unnatural amino acid derivatives has been considered important in the pharmaceutical field. The synthetic routes of unnatural amino acid have the disadvantage of using multistage reactions or toxic substances. To overcome these drawbacks, the photochemical reactions are very useful to convert carbon dioxide into high-value-added unnatural amino acids. In this research, we developed various unnatural amino acid synthetic methods of unsaturated carbon compounds with CO2 and amines via visible-light catalysis. Chapter 2 discusses the photoredox-catalyzed carbocarboxylation of various alkenes with CO2 to give γ-aminobutyric ester. (2,3,4,6)-3-benzyl-2,4,5,6-tetra(9H-carbazol-9-yl)benzonitrile (4CzBnBN) is an efficient photocatalyst for the carbocarboxylation of various electron-donating and electron-withdrawing group-substituted styrenes with CO2. Chapter 3 describes the photoredox-catalyzed intermolecular α-aminoalkylcarboxylation of aryl allenes with CO2 and amines for the synthesis of β-substituted γ-aminobutyric ester. In the case of the electron-deficient substituted aryl allenes, good regioselectivity was observed. Chapter 4 explores the photoredox-catalyzed intramolecular aminocarboxylation of alkenes with CO2 for the synthesis of the β-amino acids. The key step is the olefin addition of aminium radical cation via 5-exo-cyclization. The benzyl anion attacks CO2 faster than proton transfer. This process is a novel synthetic method for the heterocyclic β-amino acids.