Slow interconversion of enantiomeric conformers or atropisomers of anilide and urea derivatives of 2-substituted anilines

Abstract

N-Acylated 2-substituted anilines undergo slow Ar–N bond rotation, allowing in some cases isolation of enantiomeric or diastereoisomeric atropisomers and in others the determination of the rate of Ar–N bond rotation by NMR. 2-Iodoanilides bearing a branched N-substituent demonstrate sufficient enantiomeric stability to be resolvable, either by HPLC or by formation of diastereoisomeric lactanilide derivatives. For the first time, the rates of Ar–N rotation in 2-substituted N,N′-diarylureas have been established: they mainly fall in the region of 50–70 kJ mol⁻¹ with a relatively weak dependence on substituent size.