Novel Metal-Free Synthetic Approaches Using Triarylfluoroboranes as Efficient Main-Group Lewis Acid Catalysts

Abstract

This thesis explores the development of sustainable, metal-free synthetic methodologies by utilizing the strong Lewis acid catalyst B(C6F5)3 across a range of organic transformations. In Chapter 1, the importance of Lewis acidic boranes as sustainable alternatives to traditional metal-based catalysts is introduced, with particular emphasis on B(C6F5)3. A comprehensive discussion on Lewis acidity is presented, covering both computational and experimental methods for its evaluation, alongside synthetic strategies for triarylboranes. In Chapter 2, a metal-free synthetic method for the C3-carboxamidation of N-methylindoles and N-methylpyrroles with phenyl isocyanates is discussed using B(C6F5)3. This method achieves synthetically useful yields without pre-functionalization of starting materials or hazardous waste generation. Chapter 3 describes the successful C3-alkylation of 2-phenylimidazo[1,2-a]pyridines with α,β-unsaturated ketones under mild conditions with mechanistic insights supported by Density Functional Theory (DFT) calculations. Chapter 4 demonstrates the regioselective sulfenylation of alkenes using N-thiosuccinimide, producing a wide variety of allylic and vinylic sulfides and enabling further post-synthetic transformations. Extensive DFT calculations were carried out to gain insight into the reaction mechanism. Finally, Chapter 5 presents a green, atom-efficient method for the synthesis of symmetrical thioethers directly from arenes and heteroarenes, providing an environmentally friendly alternative to conventional approaches. These studies show the versatility of B(C6F5)3 in metal-free organic synthesis and highlight opportunities for further expansion in sustainable catalysis and substrate scope.