Development of tandem reactions for efficient synthesis of (Hetero)acene and phenanthridin-6(5H)-one derivatives

Abstract

Part 1. Pd(II)-Catalyzed Tandem Synthesis of Acenes Using Carboxylic Acids as Traceless Directing Groups A straightforward synthetic strategy for generating useful anthracene derivatives was developed involving palladium(II)-catalyzed tandem transformation with carboxylic acids as traceless directing groups. Carboxyl-directed C-H alkenylation, carboxyl-directed secondary C-H activation and rollover, intramolecular C-C bond formation, and decarboxylative aromatization are proposed as the key steps in the tandem reaction pathway. This novel synthetic route utilizes a broad range of substrates and provides a convenient synthetic tool that allows access to acenes. Keywords Acene, C-H Functionalization, Decarboxylation, Palladium, Tandem reactions

Part 2. Efficient Synthesis of Anthraquinone Derivatives from Diaryl Carboxylic Acids via Pd(II)-Catalyzed and Visible Light-Mediated Transformations Irradiation of 9-ester-substituted anthracenes with visible light results in the formation of endoperoxides in the absence of a photocatalyst, which further undergo base-assisted fragmentation to afford anthraquinones. The excited state species of anthracene generated by energy transfer, interacts with $^3O_2$ to afford $^1O_2$ by energy transfer and undergoes cycloaddition with $^1O_2$. By employing palladium(II)-catalyzed and visible light-mediated transformations, I have developed an efficient synthetic protocol for accessing diverse anthraquinones from readily available diaryl carboxylic acids. Keywords Palladium, Visible light, Anthraquinone, Singlet oxygen, Photooxidation

Part 3. Visible Light-Mediated Tandem Annulation for the Synthesis of Phenanthridin-6(5H)-one Derivatives Without External Photocatalyst Visible light-promoted tandem reactions were developed through the photochemical activity of quinolinones containing alkyne or alkene appendages without the need for an external photocatalyst. Dissociation of N-O bond of pyridinium salt, enabled by single electron transfer from excited quinolinones, allows the transformations for divergent and efficient construction of dihydro- or tetrahydrophenanthridin-6(5H)-ones through generation of phosphine or sulfur-centered radicals, subsequent radical addition, intramolecular cyclization, and hydrogen atom transfer (or electron transfer) sequence. Keywords Phenanthridin-6(5H)-one, External photocatalyst-free, Visible light, Electron transfer, Hydrogen atom transfer, Tandem reaction, Pyridinium salt