Abstract
ABSTRACT The development of new and highly efficient synthetic approaches for the preparation of valuable intermediates and industrially important products are more interesting and remains as a fundamental objective in the synthetic chemistry. In this regard, the present thesis has described six chapters; the first two chapters focused on utilizing singlet oxygen as a mild oxidant system for oxidative functionalization of ethers and direct oxidation of cyclicketones to dicarboxylic acids. In the chapters 3-6, visible light mediated organic functional group transformations using simple copper (I) chloride as catalyst has been described. Chapter 1 and 2: Selective and direct C-H functionalization of readily available starting materials for the synthesis of useful fine chemicals and complex natural products remains an elusive goal in synthetic chemistry. Particularly, selective oxidative functionalization α-C-H bond of aliphatic ether is one of the most important reaction pathways in organic synthesis. Since, this direct synthetic potential has easily allowed in synthesizing lactones or esters, which were considered to be as major functional groups found in fine chemicals, pharmaceuticals and synthesis of natural products. Although, several new oxidation methods have been demonstrated typically by using transition metal catalysts along with several additional reagents, have revealed the selective oxidation of α-C-H bond of ethers. In chapter 1, we utilized singlet oxygen (1O2) as an oxidation system to selectively oxidize the α-C-H bond of aliphatic ethers. Since, singlet oxygen (1O2) is a very important molecule in organic reactions as well as in biological pathways; this was extensively studied for organic functional group transformation. Moreover, the reaction of singlet oxygen mediated α-C-H bond oxidation of ethers was enhanced by addition of mild Lewis acid and this strategy has allowed in synthesizing several natural products and complex molecules. Adipic acid and their family of other dicarboxylic acids are playing important role in chemical process, pharmaceutical and food industries. As known as, nitric acid mediated oxidation of KA oil (cyclohexanone & cyclohexanol) to Adipic acid, is one of the classical approaches used for the industrial production; and still this method has applicability in worldwide. However, in this protocol, a series of problems have been documented during the oxidation of KA-oil to Adipic acid, in which the stoichiometric amount of HNO3 is reduced to NO2, NO, N2O. N2O is a greenhouse gas and ~ 300 times stronger than CO2 which cause the depletion of ozone layer. To overcome these problems, later new routes were developed for the industrial production of adipic acid mainly using H2O2 as oxidant in presence of metal catalyst. In chapter 2, we report an efficient method for direct oxidation of cyclohexanone to industrially important adipic acid in the presence of weak Lewis acid (i.e. Et3B or gamma Al2O3) via singlet oxygen. Moreover, this system has facilitated for the synthesis of industrially valuable adipic acid under mild conditions, without any usage of powerful oxidants (HNO3, metal oxides and peroxides). Chapter 3-6: Visible-light mediated organic functional group transformation reactions have emerged as one of the most attractive and powerful strategies in organic synthesis. Visible light is more attractive because most of the organic molecules lack of absorbance in the visible region and hence possess high natural abundance. Compared to traditional stepwise methods, visible light induced one-pot synthetic strategies have more potential towards avoiding extra steps, high reaction efficiency, atom-economical process and simplicity in operation. However, usage of expensive ruthenium and iridium photo-redox catalysts poses severe limitations in terms of feasibility and scalability. Later, organic dyes were utilized as cost-effective photo-catalyst for organic reactions and their achievements have been documented in the literature. Recently, photoactive copper complexes have emerged as a novel and powerful tool for organic reaction in terms of copper catalysed alkyne-azide cycloaddition (CuAAC) click reactions and coupling reactions. In this regard, chapter 3-6 was mainly focused on the simple copper (I) salt catalyzed direct C-C and C-N coupling reactions of terminal alkynes and aryl/alkyl halides or aryl-amines without any usage of expensive palladium and ligands under visible-light irradiation. The detailed reaction schemes for each chapter have described below. Chapter 3: Photo-induced copper (I) chlorite catalyzed Sonogashira cross coupling reaction without any palladium and ligands at room temperature. Chapter 4: Visible-light-mediated Higly Selective Csp-Csp Homo and Cross-Coupling Reaction using Copper (I) catalyst : Without Palladium, Ligands and Base Chapter 5: Visible-light-induced Simple Copper (I) Catalyzed Oxidative Coupling of Aromatic Amines with Terminal Alkynes: One-Pot Synthesis α-Ketoamides. Chapter 6: Visible-light-induced Copper(I)-Catalysed Oxidative direct coupling of o-Phenylenediamine and Terminal Alkynes: One-Pot Synthesis 3-phenyl-2-Hydroxy-Quinoxaline.