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

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 H-1 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. (C) 2014 Elsevier Ltd. All rights reserved.