STUDIES IN TRANSITION METAL CATALYZED ORGANIC FUNCTIONAL GROUP TRANSFORMATIONS

Abstract

Organic functional group transformation is one of the most rapidly developing areas of organic chemistry, as it is helpful in efficient synthesis of simple organic molecules, which contain appropriate functional groups for further modification. These simple organic molecules are the basic building blocks of pharmaceuticals, agrochemicals and polymers. Transition metals play very important role in functional group transformations and there are large numbers of organic transformations where transition metals/their complexes are used in catalytic or stoichiometric quantities. Transition metals are keys to catalysis due to their variable oxidation state, ability to form complexes with a variety of ligands, which allow fine-tuning of their catalytic properties. Transition metal catalyzed organic functional group transformations, constitute one of the most powerful strategies as they provide avenues for controlling chemo-, regio-, diastereo- and enantioselectivities as well as achieving high atom economy. In view of the importance of transition metals in organic functional group transformations, the present thesis aimed to develop new efficient catalytic systems for a variety of synthetically important reactions particularly oxidation, oxidative C-H activation, multi-component reaction (MCR) and nucleophilic ring opening reactions. Additionally, synthesis of a variety of new heterocyclic compounds, 7-endo-bromo-3- oxo-2-azabicyclo[4.1.0] heptanes is also presented. For simplicity and clarity, results of the investigation are presented in the thesis as follows: The first chapter consists of general introduction and a brief review of transition metal catalyzed organic functional group transformations relevant to the work presented in this thesis. Activation of environmentally benign oxidants like O2, H2O2 and alkylhydroperoxides by transition metals is discussed in detail as transition metal catalyzed oxidative transformation covers the major part of this dissertation. This chapter also highlights the recent trends such as the use of heterogeneous/heterogenized , homogeneous catalysts, ionic liquids and solvent-free methodologies in organic functional group transformations. Second chapter of thesis describes the development of new synthetic methodologies for the oxidation of imines to oxaziridines, which are among the most versatile intermediates in organic synthesis. They can be used both as oxygenating and aminating agents with a 11 wide variety of nucleophiles. Part A of this chapter describes the use of [bmim]BF4- immobilized rhenium as catalyst and solid peroxides namely UHP, SPB, SPC as oxidant for the oxygenation of aldimines to oxaziridines (Scheme 1). Rhenium-based catalysts used for this study are MTO, HRe04 and Re207. MTO was found to be most active catalyst followed by HRe04 and Re207 for this reaction. Among the various aldimines studied, those substituted with electron-donating groups on the phenyl ring were found to be more reactive and required lesser reaction times than aldimines derived form benzaldehyde and corresponding amine. Aldimines having electron-withdrawing groups on the phenyl ring were in general found to be less reactive.......................