Investigations into new methods for the efficient and environmentally benign catalytic asymmetric epoxidation of alkenes

Abstract

This thesis presents our investigations into the catalytic asymmetric epoxidation of alkenes. An introductory chapter highlights the importance of chirality in nature and industry. It focuses on a few relevant examples of syntheses in which the use of optically pure epoxides as building blocks is fundamental to the overall stereochemistry of the product. The introduction then continues describing the advances in the field of asymmetric epoxidation of olefins; it contains a review of a wide range of the ligands and metals employed in the recent literature together with a range of different oxidants. A section on organocatalytic epoxidations concludes this chapter. A second chapter presents attempts to impart enantioselectivity in the epoxidation of olefins by employing chiral additives (BINOL derivatives) in conjunction with a known oxidising system, TMTACN/manganese with hydrogen peroxide as the oxidant. A brief electrochemical study of the redox potential of the catalytic systems described in this chapter and a study of the effect of the electronic properties of the substrates on the reaction is also reported. The third and fourth chapters describe the synthesis of a series of tri- tetra- and pentadentate ligands based on the backbone of L-proline and trans-diaminocyclohexane. The chapters contain the results of the screening of the above mentioned ligands in the epoxidation of alkenes with a number of metal salts using either hydrogen peroxide or peracetic acid as the oxidant. Single crystal X-ray structures of some of the new ligands are also presented herein. A final experimental chapter presents the supporting characterisation data associated with the compounds synthesised.