Abstract
ABSTRACT Transition metal-catalyzed synthetic methods are the most important tools of modern organic synthesis. Particularly, direct C–H functionalization by uniting readily available π-components is an attractive methodology to synthesize natural products and bioactive skeletons in a single step. It is an atom- and stepeconomical method which is highly urged as one of the green process. In this regard, this thesis describes three new reactions that focus on the intramolecular coupling of enynes with carbonyl compounds, which were successfully achieved by tuning different kinds of ligands in the presence of air stable cobalt catalyst system in a highly atomeconomical manner. These reactions proceed via a novel cobaltacycle prompted C–H functionalization or insertion of carbonyl compounds to afford highly functionalized dihydrofuran and pyrrolidine derivatives which are found in various natural products and biologically active molecules. These reactions are highly stereo- and chemoselective. For better understanding, I divided this thesis into three chapters. These three chapters describe about ligand-controlled cobalt-catalyzed divergent C–H functionalization of carbonyl compounds with enynes. Chapter 1 describes a cobalt-catalyzed hydroarylative cyclization of enynes with esters and ketones. The reaction proceeds via a novel five-membered cobaltacycle induced C–H activation to afford functionalized pyrrolidines and dihydrofurans in good to excellent yields. Chapter 2 deals about cobalt-catalyzed ortho C–H functionalization of aromatic aldehydes with enynes. The reaction is highly step- and atomeconomical process to access cyclic skeletons via a weakly coordinating aromatic aldehyde-assisted C–H activation. Chapter 3 illustrates a cobalt-catalyzed hydroacylative cyclization of enynes with aldehydes. The reaction proceeds well with nonchelating aliphatic, vinylic and aromatic aldehydes to afford vinylic ketones in highly stereo- and chemoselective manner.