Synthesis and Functionalization of Heterocycles via Hydrogen Transfer and Photoredox Catalysis

Das, Sanju (2022) Synthesis and Functionalization of Heterocycles via Hydrogen Transfer and Photoredox Catalysis. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The contents of the thesis entitled “Synthesis and Functionalization of Heterocycles via Hydrogen Transfer and Photoredox Catalysis” have been divided into 7 chapters based on the outcomes of the experimental works accomplished during the complete course of the research period. Over the years, synthetic chemists have focused on the development of new C−C and C−heteroatom bond-forming methods for the construction of valuable cyclic scaffolds. Moreover, functionalization of aromatic and heteroaromatic ring systems using green environmentally methodologies and exclusive applications in pharmaceuticals, medicinal, agrochemicals industries are also in prime attention (Scheme 1). To this end, transition metal-catalyzed borrowing hydrogenation (BH) and acceptorless dehydrogenation (ADC) pathways emerged as powerful synthetic tools for making C−C, C−heteroatom bonds. On the other hand, visible light is a readily available, nonhazardous, environmentally green source of energy. In the last few decades, synthetic organic chemists utilized this green energy source to develop new synthetic methodologies. The first chapter of the thesis presents a general introduction of transfer hydrogenation and photo-redox catalysis synthetic approaches. Chapter 2 describes an earth-abundant transition metal-catalyzed synthesis of benzimidazole derivatives through a hydrogen transfer process. A sustainable method for the construction of quinoline ring via metal-catalyzed acceptorless dehydrogenation is presented in Chapter 3. In Chapter 4, a practical method for the generation of α-carbonyl radical from corresponding bromo-carbonyl compounds using a hybrid catalyst has been described. Synthetic applications of the photochemically generated alkyl radicals from redox-active N-(acyloxy)phthalimides are discussed in Chapters 5-7. Chapter 5 is focused on a cascade radical cyclization to construct chroman-4-one scaffold. Chapter 6 describes an organophotoredox-catalyzed reduction/addition/oxidation cascade of N-protected maleimides and N-(acyloxy)phthalimides. Finally, Chapter 7 presents a redox-neutral radical cascade of N-arylated allenamides and alkyl N-(acyloxy)phthalimides, leading to the synthesis of biologically important indoles. Experimental details and compound characterization data of synthesized compounds are documented in each working chapter. Moreover, the copies of 1H and ¹³C NMR spectra of selected new compounds are also included. Relevant literature references are mentioned at the end of the thesis.

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