Dynamic kinetic resolution in the asymmetric synthesis of β-amino acids by organocatalytic reduction of enamines with trichlorosilane

A new methodology based on the organocatalytic asymmetric hydrosilylation of enamines that allows a direct access to a range of β and β -amino acid derivatives was presented. The results show a successful reduction of aromatic substrates, a sterically more hindered ortho-substituted derivatives, and the thiophenyl analogue exhibiting lower reactivity. Fast enamine-imine equilibration is crucial as imines are chiral but racemic, while α-alkyl β-amino acids can be accessed by the symmetrical Mannich reaction. The α-alkyl derivatives have relative and absolute configuration due to their reduction with LiAlH into a known amino alcohols. Predominant formation of the anti isomer in 3o is consistent with conformation of the imine intermediate in the catalytic reduction.