Proline-Catalyzed Asymmetric α-Amination in the Synthesis of Bioactive Molecules

Abstract

The direct α-amination of carbonyl compounds using organocatalysts represents a powerful and atom-economical tool for asymmetric C–N bond formation. We describe a complete account of α-functionalization of carbonyl compounds, through iterative sequential α-aminoxylation/amination using electrophilic O and N sources, as well as sequential α-amination/HWE reaction for enantio- and diastereoselective synthesis of both syn- and anti-1,3-aminoalcohols and 1,3-diamines. Additionally this protocol is further extended for the easy construction of alkaloids such as indolizidine, pyrrolizidine, and quinolizidine fused-ring systems just by tuning the chain length of the aldehyde used as a starting material. This methodology provides further scope to extrapolate it for a variety of naturally occurring hydroxylated monocyclic and fused bicyclic pyrrolidine and piperidine based alkaloids such as lentiginosine, epi-lentiginosine, dihydroxypyrrolizidine, (+)-deoxoprosophylline and (–)-deoxoprosopinine alkaloids. Furthermore, we have also uncovered proline-catalyzed anti-selectivity for the synthesis of 1,2-amino alcohols in α-amination of aldehyde and one-pot indium-mediated Barbier type allylation of α-hydrazino aldehydes to accomplish the total synthesis of clavaminols, sphinganine and spisulosine with reduced number of steps and with high overall yields. 1 Introduction 2 Application in the Total Synthesis of Alkaloids 3 Conclusion