E. Juaristi, Heraclio López-Ruiz, D. Madrigal, Y. Ramírez-Quirós y J. Escalante, a-Alkylation of (S)-Asparagine with Self-Regeneration of the Stereogenic Center: Enantioselective Synthesis of a-Substituted Aspartic Acids, J. Org. Chem., 63, 4706-4710 (1998).
A convenient method for the R-alkylation of (S)-asparagine with self-regeneration of the stereogenic center is described. The synthetic protocol involves stereoselective conversion of (S)-asparagine into enantiopure imino ether (2S,6S)-9, which is then alkylated with complete diastereoselectivity to give trans products 10-13 in good yields. Hydrolysis of these alkylated heterocycles is accomplished under mild acidic conditions to give the desired, enantiopure R-alkyl aspartic acids in excellent yields.