Organocatalytic Asymmetric Transferhydrogenation of β-Nitroacrylates: Accessing β2-Amino Acids
摘要:
We describe a highly efficient and enantioselective Hantzsch ester mediated conjugate reduction of beta-nitroacrylates that is catalyzed by a Jacobsen thiourea catalyst as a key step in a new route to optically active beta2-amino acids.
A powerful catalyst: Quaternary stereogenic centers adjacent to tertiary stereocenters were formed with high diastereoselectivities and enantioselectivities in conjugateadditionreactions between aldehydes and β,β‐disubstituted nitroolefins by using a peptidic catalyst (see scheme). γ‐Amino acids and heterocyclic compounds bearing quaternary stereogenic centers are easily accessible from the products
Enantioselective Michael Reactions of β, β-Disubstituted Nitroalkenes: A New Approach to β<sup>2,2</sup>-Amino Acids with Hetero-Quaternary Stereocenters
An atom-economic organocatalytic asymmetric Michaelreaction of α,β,β-trisubstituted olefins has been successfully developed. The reaction exhibits excellent enantioselectivities under low loading of catalysts, and the conjugate addition products are valuable for the synthesis of novel β2,2-amino acids and β-peptides.
Epi-quinine-catalyzed asymmetric nitro-Michaeladdition of furanones to β,β,-disubstituted nitroalkenes is described. The reaction proceeded smoothly with 1–5 mol % loadings of epi-quinine catalysts at room temperature, giving the corresponding Michael adducts in high yields (72–93%) with extremely high diastereo- and enantioselectivities (>98/2 dr, syn major; 95–99% ee). This reaction provides an