A New Chiral Axis due to N(open-chain imide)—Ar Bond: Unexpected Racemization Effect of an Acyl Group.

The first example of optically active compound 3c which possesses axial chirality based on the N(open-chain imide)Ar bond rotation, is described. Furthermore, a quite interesting result is also described, namely, that 3a bearing a bulky acyl group rather than a small one racemized more rapidly. To explain this phenomenon, 13C NMR experiments and the reaction with benzylamine of 3a-d were undertaken. These preliminary results suggest that the t-BuCON bond in 3a which racemized easily, is more twisted, compared with the CON bonds in 3b-d which were relatively stable to racemization.