Chemistry of Unsymmetrical Quarternary Carbon Compounds III. Synthesis of (‐)‐Dimethyl 2‐Cyano‐2‐Methylsuccinate and Determination of Its Absolute Configuration

(−)‐Dimethyl 2‐cyano‐2‐methylsuccinate ((−)‐IIIa) was synthesized from menthyl cyanoacetate ((−)‐I), and the absolute configuration of which was elucidated as (S)‐configuration by chemical correlation to the known (R)(+)‐β‐methylterbic acid ((R)(+)‐VII). (−)‐Dimethyl 2‐carbamoyl‐2‐methylsuccinate ((−)‐IV) and (−)‐methyl 3‐methyl‐2,5‐dioxo‐3‐pyrrolidinecarboxylate ((−)‐V) are also confirmed as belonging to (S)‐configuration and (+)‐3‐(1‐hydroxy‐1‐methylethyl)‐3‐methyl‐2,5‐pyrrolidinedione ((+)‐VI) is belonging to (R)‐configuration. Preliminary experiments on racemic compounds are also described.