Memory of Chirality

Alkylation of a-Amino Acid Derivatives

抄録

N-Boc-N-MOM-α-amino acid derivatives (Phe, Val, Leu, His, Trp, Tyr, Dopa) underwent asymmetric α-methylation in 76-93% ee by treatment with KHMDS followed by methyl iodide in the absence of any external chiral source. A chiral nonracemic enolate with dynamic axial chirality is proposed as the crucial intermediate whose racemization barrier is 16.0 kcal/mol and the corresponding half-life is 22h at -78°C.