Exploring the chemistry of 3-substituted 2-azanorbornyls in asymmetric catalysis

This account summarizes our recent achievements in asymmetric catalysis usi ng 3-substituted 2-azanorbornyl based ligands. Using this structural unit i n ligand synthesis offers several advantages over the analogous proline che mistry, such as equal availability of both enantiomers and increased rigidi ty of the catalysts. The reactions so far performed with good results, incl ude the copper-catalyzed allylic acyloxylation, zinc mediated alkylation of imines, the base-catalyzed rearrangement of epoxides, and the ruthenium-ca talyzed transfer hydrogenation. Other reactions where the results are less satisfactory are described are the oxazaborolidine catalyzed borane reducti on of ketones, and the copper-catalyzed 1.4-addition of alkyl Grignard reag ents to alpha,beta-unsaturated ketones. In the last part of the article, so me intriguing ring-opening reactions are described, leading to syntheticall y very interesting structural units such as alpha-aminoacids and cycloalkyl amines. 1 Introduction 2 The Asymmetric Aza-Diels-Alder Reaction 3 Asymmetric Synthesis Using 2-Azanorbornyl Based Ligands 3.1 Copper-Catalyzed Allylic Acyloxylation the Kharasch-Sosnovsky Reaction 3.2 Dialkylzinc Additions to N-(Diphenylphosphinoyl) Imines 3.3 Oxazaborolidine Catalyzed Borane Reduction of Ketones 3.4 Ruthenium-Catalyzed Transfer Hydrogenation of Ketones 3.5 Catalytic Rearrangement of meso-Epoxides into Chiral Allylic Alcohols 3.6 Copper-Catalyzed 1,4-Addition of Alkyl Grignard Reagents to alpha,beta- Unsaturated Ketones 4 Chemistry of the 2-Azanorbornyl Skeleton 4.1 Allylic C-N-Cleavage Leading to Amino Acid Derivatives 4.2 C-N-Cleavage Leading to Vinyl Functionalized Cyclohexyl and Cyclopentyl Amines 5 Summary.