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.