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

Abstract 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.