Conformation of aromatic rings in isolable atropisomers of 2-arylindoline derivatives and kinetic evidences for π-π interaction

The equilibrium constants [K=anti/syn] of a pair of atropisomers; due to restricted rotation about CSp(3)-Csp(2) bond for [2-(2-hydroxynaphthalen-1-yl)-3,3-dimethylindolin-1-yl](4-substituted phenyl)methanone were determined in some solvents. The presence of the effective pi-pi interaction was demonstrated by the correlation between the equilibrium constants (K) and the substituent effect of the phenyl groups (sigma(p)), suggesting that the 'neutral-type' interaction is operative. (C) 2009 Elsevier Ltd. All rights reserved.