Further study of axial chirality due to an acyclic imide N–Ar bond: control of rotational barrier by electronic effects of acyl groups

Studies on stability to racemization in a series of optically active N-aroyl-N-(2-t-butylphenyl)acetamides 2a–g (X=NMe2, OMe, Me, H, F,Cl, CF3), depending on the electronic effect of their aroyl groups, are described. It has been revealed that the stability of 2 bearing stronger electron-withdrawing groups on the aroyl benzene ring was enhanced, with linear correlation between the ΔG‡ and Hammettʹs σp para-substituent constant of 2a–g. Furthermore, the absolute configuration of optically active imides 2a–g has been determined by comparison with the CD spectrum of (S)-N-(2-t-butylphenyl)-N-(4-trifluoromethylbenzoyl)propionamide (5b) derived from (Ra,2S)-N-(2-t-butylphenyl)-N-(4-trifluoromethylbenzoyl)-2-acetoxypropionamide (4b), whose absolute configuration was determined by X-ray analysis.