A 1H, 13C, and 19F nuclear magnetic resonance study of rotational isomerism and long-range coupling in methyl (1S,5R,7R)-1-ethyl-3-oxo-6-trifluoroacetyl-2,8-dioxa-6-azabicyclo[3.2.1]octane-7-carboxylate

Abstract

The ¹H, ¹³C, and ¹⁹F n.m.r. spectra of the title compound show that it exists in solution as a mixture of rotamers about the amide bond. Each rotamer possesses a distinct pattern of long-range ¹H, ¹⁹F, ¹³C and ¹⁹F couplings. Proton spin–lattice relaxation time experiments have been used to assign the n.m.r. spectra of each rotamer. These assignments show that large values of the long-range couplings are associated with a close spatial approach of the nuclei involved. The title compound was obtained via degradation of methyl clavulanate with acid followed by hydrogenation.