2,6‐Piperidinediones, II. Absolute Configuration of the Enantiomers of 3,3‐Disubstituted 2,6‐Piperidinediones

Determination of the absolute configuration of the 2,6‐piperidinediones (+) 3a ‐(+) 3e is achieved by correlation of their CD spectra with the spectrum of R (+)‐glutethimide. It is shown that (+) 3a ‐(+) 3e possess R ‐configuration. The N ‐methyl compounds (+) 7a and (+) 7b , obtained by N ‐methylation of (+) 3a and (+) 3b , possess R ‐configuration, too, and so does (+) 3h which is formed by catalytic hydrogenation of (+) 3e . The absolute configuration of (+) 3g can be deduced from the configuration of the starting compound R (+)‐2‐ethyl‐2‐methylcyanoacetic acid: (+) 3g has S ‐configuration. Compounds (+) 3g and (+) 3f cause opposite Cotton effects. Thus, (+) 3f has R ‐configuration. The hitherto unknown configuration of (−)‐2‐ethyl‐2‐propylcyanoacetic acid, from which R (+)‐ 3f is obtained, can be deduced to be S .