Chiral proton catalysis: development of diastereo- and enantioselective syntheses of vicinal diamines and α,β-diamino acids

Abstract

1,2-Diamines form an important class of compounds, some members of which are valuable for their biological activity. In addition, chiral, non-racemic 1,2-diamines have emerged as an important class of ligands for enantioselective catalysis and have also been a driving force behind the explosive growth of organocatalysis in the last decade. 1,2-Diamines are constituents of α,β-diamino acids, which are nonproteinogenic amino acids that have garnered interest due to their existence in Nature either in the free form or as motifs in complex molecules. These atypical amino acids often display interesting and useful biological properties and have been used as building blocks for the synthesis of amino acid surrogates to modulate their structural profile and biological behavior. The enantioselective synthesis of vicinal diamines and α,β-diamino acids is an actively pursued area in organic synthesis. This dissertation describes the application of chiral proton catalysis for the development of enantio- and diastereoselective aza-Henry reactions of nitroalkane and nitroacetate pronucleophiles as a route towards vicinal diamines and α,β-diamino acids. The development of a working stereochemical model for the polar ionic hydrogen bond- mediated transfer of asymmetry paved the way for the design and synthesis of novel, enantiopure bis(amidine) ligands with diverse structural and electronic properties in order to accomplish the application of various nitroacetate nucleophiles as amino acid equivalents with high diastereo- and enantioselection. A highlight of this work is the development of unsymmetrical Bis(AMidine) (BAM) ligands which are uniquely able to provide high diastereocontrol, in addition to high enantioselection. The use of a proton for activation and stereocontrol in the aza-Henry reactions represents an environmentally friendly (green) method to access useful scaffolds that diversify chemical space while advancing the frontiers of science in the area of asymmetric organocatalysis.