Development of organic synthetic methods using cobalt carbony reagents

Abstract

This thesis deals with the results of the investigations carried out on the quotDevelopment of Organic Synthetic Methods Using Cobalt Carbonyl Reagents.quot It comprises of three chapters. Each chapter is subdivided into three parts. quotIntroduction,quot quotResults and Discussionquot and quotExperimental sectionquot along with references. The work described in this thesis is exploratory in nature and the chapters are arranged in the order the investigations were executed. Chapter 1 describes the preparation of alkyne-Co2(CO)6 complexes via reduction of CoBr2 with Zn in the presence of CO in CH2CI2/t-BuOH or toluene/t-BuOH for applications in Pauson-Khand cyclopentenone synthesis (Scheme 1). Recent developments in the Pauson-Khand reaction are briefly reviewed in the Introductory section. To facilitate the discussion, methods of preparation of (alkyne)Co2(CO)6 complexes are also briefly reviewed. Scheme 1 It has been observed tha. the amines/amides promote the Pauson-Khand reaction (alkyne)Co2(CO)6 complexes prepared in this way in CH2CI2/t-Bu0H solvent system at 25 °C (Scheme 2). Whereas the use of norbornylene gave the corresponding cyclopentenones in 52-58% yields, cyclopentene afforded the products in 30-32% yields. Scheme 2 The Pauson-Khand reactions were also carried out in CH2CI2 in the presence of amines such as TMEDA, ct-methylbenzylamine. The yields of cyclopentenones obtained were similar to the reactions that were carried out using CH2CI2 and t-BuOH. The Pauson-Khand reactions carried out using sub-stoichiometric amounts of CoBr2 and Zn (Scheme 3) are also described in chapter 1. The cyclopentenones were obtained in good yields when norbornylene was used as olefin. In the case of cyclopentene, the products were obtained in 30-35% yields. Scheme 3 In chapter 2, results of the Investigations carried out on the reactions of (alkyne)Co2(CO)6 complexes without using an externally added olefin are described.