Procedure:  150 mL 1-neck flask, stirbar, septum, N₂ inlet

                  Prepared a suspension of 1.507 g of L-aspartic acid (I) in 25 mL of absolute MeOH.  Stirred; cooled to 0 C.  Carefully added 1.80 mL of SOCl₂ dropwise.  The reaction mixture was then warmed to 40 C.  After 3.5 h, the reaction mixture was then cooled to rt.  The solvent was removed by rotary evaporation to afford the product as a white solid. 

 

¹H NMR (CDCl₃, 400 MHz) d 8.76 (br, NH₃), 4.63 (br, H2), 3.86 (s, CO₂CH₃), 3.76 (s, CO₂CH₃), 3.32 (br, H3).