10.1002/chem.200600725
The research focuses on the development of a direct catalytic asymmetric a-aminomethylation of aldehydes, a significant advancement in organic chemistry. This reaction provides a pathway to ?-amino aldehydes, which are valuable precursors to ?2-amino acid derivatives and ?-amino alcohols, important in pharmaceuticals. The study explores the use of chiral amine and amino acid catalysts to facilitate the reaction between unmodified aldehydes and a formaldehyde-derived imine precursor. The reactions were conducted under various conditions, with the addition of lithium halide salts found to enhance enantioselectivity. The experiments involved screening different catalysts, such as proline and its derivatives, as well as chiral pyrrolidines, using dibenzylamine-derived aminomethyl ether and isovaleraldehyde as reactants. The enantioselectivity and conversion rates were determined through NMR spectroscopic analyses and chiral-phase HPLC analysis. The results showed that the reactions were fast, highly chemoselective, and yielded the corresponding ?-amino alcohols with high enantiomeric excess (up to 98% ee) after in situ reduction. The research also proposed transition-state models to account for the stereochemical outcomes of the reactions catalyzed by different chiral pyrrolidines and proline derivatives.