Synthesis and Functionalization of N/O - Heterocycles through Redox and Thermal Activations

Halder, Atreyee (2023) Synthesis and Functionalization of N/O - Heterocycles through Redox and Thermal Activations. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Atreyee Halder (15IP001)) 15IP001.pdf - Submitted Version Restricted to Repository staff only Download (18MB)

Abstract

The contents of the thesis entitled “Synthesis and Functionalization of N/O - Heterocycles through Redox and Thermal Activations” have been distributed into 6 chapters based on the consequences of the experimental works done throughout the research tenure. Organic chemists have devoted significant attention towards the formation and functionalization of valuable versatile N/O-heterocycles through the development of novel methodologies. Apart from the classical transition metal catalysis approach, mechanochemistry and electrochemistry have become powerful sustainable, and economical tools for the ring-making-breaking strategies of these prevalent heterocycles. Despite several sustainable methodologies, transition metal catalysis via thermal activation is necessitous to design various significant heterocyclic fragments. Herein, utilizing these three strategies, the construction and functionalization of quinolines, dihydro-benzoimidazothiazines, furans, imidazopyridines, and benzofurans have been accomplished. The first chapter, Chapter 1 of the thesis describes an overall outline of the three sections. First overview of mechanochemistry, its evolution through the ages, and its significance in organic chemistry has been discussed. Next, iodine and diselenide-mediated oxidative annulation has been depicted. Thereafter basic aspects of organic electrochemistry, its advancement, and different modes of electrolysis have been elaborated. In the last part, the importance of dual catalysis, especially Cu-Fe dual catalysis has been portrayed. Chapter 2 represents a solvent free mechanochemical technique for functionalized quinoline synthesis by iodine-mediated oxidative annulation. By this transition metal free mild methodology, an active iodine moiety remains in the final molecule which opens up the possibility for further functionalization. Chapter 3 proposes a highly diastereoselective and regioselective synthesis of dihydro- benzoimidazo-[1,3]-thiazines via electro-oxidative selenocyclization of thioallyl benzoimidazoles. This metal free mild electrochemical strategy involves the electrochemical generation of phenyl selenyl cation followed by a loose transition state which decides the exclusive 6-membered regioselectivity as well as the trans-diastereoselectivity of the final product. Chapter 4 demonstrates electro-oxidative synthesis of unsymmetrical but-2-yne-1,4- diones via sequential ring formation and cleavage starting from easily accessible homopropargylic alcohols. Chapter 5 focuses on the electro-oxidative generation of trifluoromethyl radical from Langlois’ reagent by desulfurative manner and follow up C-3 trifluoromethylation of imidazo[1,2-a]pyridines. In Chapter 6, synthesis of C-3 enyne benzofuran analogues with 3- carbon homologation has been achieved via annulation of easily accessible ortho-iodopropargylic phenols using Cu-Fe dual catalysis. Experimental findings and characterization data of synthesized compounds are documented at the end of each chapter. Moreover, the copies of ¹H and ¹³C NMR spectra of selected new compounds are also involved. Relevant literature are cited at the end of the thesis.

Actions (login required)

View Item