Sustainable Synthesis and Functionalization of Heteroand Carba-cycles through Electrochemical and Thermal Activations

Maiti, Debabrata (2022) Sustainable Synthesis and Functionalization of Heteroand Carba-cycles through Electrochemical and Thermal Activations. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Debabrata Maiti (15RS060)) 15RS060.pdf - Submitted Version Restricted to Repository staff only Download (13MB)

Abstract

The contents of the thesis entitled “Sustainable Synthesis and Functionalization of Hetero- and Carba-cycles through Electrochemical and Thermal Activations” have been divided into 7 chapters based on the outcomes of the experimental works accomplished during the complete course of the research period. Realizing the advancement of greener and the efficient synthetic process has displayed an important target in research. In recent years, new sustainable methodologies, especially environmentally benign protocols, have captured the attention of synthetic community. Electrochemical synthesis is a tool that has been widely studied because of its practical applications in chemical reactions and it observes the principles of sustainable chemistry. In this context, electro-organic synthesis was utilized as an environmentally benign and scalable approach for the construction of different carbon-carbon and carbon-heteroatom bonds. Here, electrosynthesis has allowed to be a greener, highly versatile and effective platform for carrying out the different nonclassical bond disconnections via formation of radical intermediates under mild protocols. Over the decades, various chemical oxidative methods have been introduced successfully employed for radical cascade addition. However, the exploitation of the electrode process remains in general interest as they are a safe and efficient alternative, is achieved for large applications, approving controlled reactions to be performed via radical anion or radical cation intermediates in the organic process. In this thesis, direct electrochemical oxidations as well as indirect (mediated) oxidations at anode surface were employed for the generation of crucial radical intermediate from cheap and easily accessible starting materials to synthesize the valuable molecular scaffolds. On the other hand, oxidation of alcohols to synthesize the corresponding carbonyl compounds represents the essential functional group conversion in modern synthetic chemistry. Various transition metal catalysts for alcohol activation via borrowing hydrogen concept or classical oxidants were well surveyed to prepare the complex molecules. In this context, base-mediated aerobic oxidation of alcohols under thermal activation, which is a more sustainable approach from a synthetic point of view, was utilized to construct the different important moieties. The first chapter of the thesis presents a general introduction to the electrochemical and thermal activation process. In chapter 2, an electrochemical method for the synthesis of polysubstituted selenofuran derivatives through seleno-cyclization of homo propargyl alcohols has been presented. In chapter 3, the electrochemical di-selenide activation has utilized to access the highly regioselective selenylated benzothiophene derivatives. The synthetic application of manganese catalyzed electrochemical azide radical generation from cheap sodium azide starting material are discussed in chapter 4-5. Chapter 4 describes a tandem radical cyclization to produce Azido-oxindole and quinolinone scaffolds. Chapter 5 presents electrochemical azide functionalization of 2-H indazole followed by coarctate fragmentation process to provide the 2-azo-benzonitrile motif. In Chapter 6-7, base promoted aerobic oxidation of alcohols through the thermal activation process. Chapter 6 is focused on sequential oxidation of alcohol and direct condensation reaction with the amine resulting in a C–N bond formation followed by a radical C–C coupling in a cascade sequence to construct the polysubstituted phenanthridines. Chapter 7 describes the synthesis of alkyl containing symmetrical 1,3,5- substituted benzenes from easily accessible and cheap starting material like aliphatic alcohols and acetophenone derivatives. 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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