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-aroy l-N-(2-t-butylphenyl)acetamides 2a-g (X=NMe2, OMe, Me, H, F,CI, CF3), depen ding 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 bet ween the DeltaG(double dagger) and Hammett's sigma (p) para-substituent con stant 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 fr om (R-a,2S)-N-(2-t-butylphenyl)-N-(4-trifluoromethylbenzoyl)-2-acetoxypropi onamide (4b), whose absolute configuration was determined by X-ray analysis . (C) 2001 Elsevier Science Ltd. All rights reserved.