Spectroscopic analysis of imidazolidines Part V: 1H and 13C NMR spectroscopy and conformational analysis of N-acylimidazolidines

Abstract

The conformational features of a series of 1-acyl-3-arylimidazolidines 1-14 were correlated with their 1 H and 13 C-NMR spectra. Due to the hindered rotation around the N-CO bond, these compounds exist in solution as a mixture of non-isolable Z/E diastereomers, the Z-isomer being the most abundant in all cases. The analysis of NOESY spectra confirmed the complete assignment of the 1 H-NMR resonances of each rotamer. Two-dimensional heteronuclear HMQC and HMBC spectra of selected compounds permitted the assignment of 13 C-NMR signals. We analyzed the influence of the imidazolidine ring substituents on the equilibrium abundance of Z/E isomers. We also studied the spectroscopic and conformational properties of a 1-acyl-2,3-diarylimidazolidine 15, which revealed the effect of the C-2 substitution.