Iminium ion activation is a rapidly expanding and contemporary area of synthetic chemistry in which a number of enantio- and diastereoselective transformations have been developed. Despite the substantial attributes of the area, high catalyst loadings, aldehyde substrate specificity and incomplete understanding of the catalytic process detracts from iminium ion activation being fully competitive with metal-based alternatives. Within this Thesis a series of investigations are presented to address some of these perceived shortcomings. In Chapter 2, a novel imidazolidinone containing an α-electron withdrawing group is evaluated as an asymmetric catalyst for Diels-Alder cycloaddition reactions. A substrate and reaction scope is presented and the conformational preference of the imidazolidinone is probed to rationalise the origins of enantioselectivity. In Chapter 3, further understanding of the conformational preference of the MacMillan first generation imidazolidinone is gained using chiral optical spectroscopic measurements. For the first time each proposed intermediate in the full catalytic cycle is observed using mass spectrometry. In Chapter 4, a hybrid secondary amine is designed based upon the diarylprolinol ether and imidazolidinone scaffold. In Chapter 5, the 3-position of the imidazolidinone ring is investigated as a potential site to install electron withdrawing groups to influence the catalytic cycle. In Chapter 6, efforts are made to tackle α,β-unsaturated aldehyde substrate specificity through the design of C2 symmetric amines suitable for use in iminium activation of α,β-unsaturated ketones. Chapter 7 and Chapter 8 are both outside the immediate subject area of this thesis. In Chapter 7 a novel amino acid amide dimer architecture is revealed. Investigations into substrate scope, stability and conformational rigidity are presented. In Chapter 8 a mechanistic investigation into the malonoyl peroxide mediated alkene dioxygenation reaction is made. DFT calculations and a mechanistic probe substrate are used to define the nature of the interaction between the peroxide and alkene. Chapter 9 summarises the work contained within Chapters 2-8 and suggests some avenues along which research could be continued.