Electro-oxidative Radical-Polar Crossover Enabled Construction of Heterocycles

Saha, Suman Kumar (2025) Electro-oxidative Radical-Polar Crossover Enabled Construction of Heterocycles. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Suman Kumar Saha (20RS027)) 20RS027.pdf - Submitted Version Restricted to Repository staff only Download (19MB)

Abstract

The thesis entitled “Electro-oxidative Radical-Polar Crossover Enabled Construction of Heterocycles” illustrates the development of innovative and sustainable electrochemical synthetic strategies for the construction of five- and six-membered heterocycles. The content of the thesis has been described in 3 chapters based on the experimental works done throughout the research tenure. Five- and six-membered heterocycles are of paramount importance in various scientific and industrial fields due to their diverse chemical properties and biological activities. This motivates synthetic chemists to develop environmentally friendly, sustainable, and efficient pathways for the synthesis and functionalizat ion of various heterocycles. In recent times, synthetic organic chemists have increasingly utilized electrochemistry as an alternative to traditional redox processes, to expand the scope of environmentally benign, sustainable, and greener chemical processes. Additionally, fine-tuning reaction parameters like applied potential boosts selectivity and efficiency, preventing unwanted side reactions. Herein, my doctoral research delves into the electro-oxidative synthesis of pivotal functionalized five- and six-membered heterocyclic compounds, employing radical addition followed by polar cascade cyclization or radical annulation followed by polar addition on electrode surfaces. Introductory Chapter 1 covers the importance of heterocyclic compounds, the basic concept of organic electrochemistry, an understanding of radical-polar crossover strategy in organic synthesis, and its appliance in the synthesis of important heterocyclic compounds. In Chapter 2, Synthesis of diversely functionalized quinoline-2-carboxylates is illustrated through electrochemical cross-dehydrogenative coupling between N-aryl glycinates and methylenecyclopropanes. Cyclic voltammetric measurements and control experiments suggested a formal [4 + 2] cycloaddition involving radical intermediates, followed by a cyclopropyl ring opening through nucleophilic polar addition, consecutively fabricating C−C and C−N bonds. Chapter 3 describes an environmentally benign protocol for electro-oxidative CF3-radical generation, followed by cascade cyclization fabricating an isoxazoline scaffold from a β,γ- unsaturated oxime. Consecutive C–O and C–C bond formations through this method feature mild, robust, and scalable reaction conditions and broad substrate scope.

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