Conformational study of the 4,9‐dihetero‐(Z,Z)‐cyclodeca‐1,6‐diene ring system; the mono‐ and di‐benzo analogues

Abstract

The dynamic 'H and 13C NMR spectra of a series of mono-and bis-annelated 4,9-dihetero-(Z,.Z)-cycloaece-1,6 dienes were obtained and are discussed with respect to ground-state conformers and the barriers to ring inversion, and to the restricted rotation about exocyciic partial C,N double bonds. The ten-membered rings are, with one exception, anancomeric chair conformers and interconvert via a combination of single bond rotations and bond angle bendings. Depending on the heteroatoms present, the series of decreasing barriers to ring inversion S > NH > 0 was obtained. Benzannelation decreases the free energy of activation of the same dynamic process owing to greater intramolecular transannular H,H interactions.