Relationship between rotational barriers and structures in N–C axially chiral 3,4-dihydroquinolin-2-one and 3,4-dihydrobenzoquinolin-2-one

Abstract The rotational barrier around the N–C chiral axis in N -(2- tert -butylphenyl)-3,4-dihydrobenzoquinolin-2-one was found to be 6 kcal/mol lower than that in N -(2- tert -butylphenyl)-3,4-dihydroquinolin-2-one. X-ray crystal structures and 1 H NMR spectra of both compounds indicate that the significant decrease in the rotational barrier in benzoquinolinone is brought about by destabilization of the ground state which is highlighted by a considerable distortion of the N-C chiral axis.