Asymmetric Synthesis of Amines and Alkaloids Through Novel Organocatalytic Transformations

Abstract

The field or organocatalysis has enabled numerous types of new asymmetric bond formations through very few modes of activation. Within the organocatalytic paradigm, SOMO catalysis has emerged as a unique mode of activation able to accomplish bond formations previously unattainable through typical polar catalytic pathways. By exploiting the umpolung reactivity pattern exhibited in SOMO catalysis, we have demonstrated a new asymmetric method to form α,β-disubstituted β-nitroaldehydes from simple aldehyde and silyl nitronate starting materials. Most interesting is that the diastereomeric outcome is entirely dependent on the identity of the nitronate silyl group. Accumulated evidence has allowed us to propose a divergence in the mechanistic pathway, involving two distinct SOMO-activated intermediates for each major diastereomer formed. Utility of the β-nitroaldehyde products has been demonstrated by an efficient two-step synthesis of β-amino acids.

Organocascade catalysis has been combined with a common intermediate approach to address the exponential losses associated with traditional total synthesis. The successful design and execution of an asymmetric organocatalytic triple cascade that forms Büchi-type ketone common intermediates is described. A Büchi-type ketone was successfully employed in the eight-step total synthesis of ochrosamine B. Substantial precedence establishing the utility of Büchi-ketones for the synthesis of <italic>Strychnos</italic> and <italic>Aspidosperma</italic> alkaloids highlights the impact of these highly advanced intermediates.