Conformational Studies of Marine Polyhalogenated ?-Chamigrenes Using Temperature-dependent NMR spectra inverted-chair and twist-boat cyclohexane moieties in the presence of an axial halogen atom at C(8)
α-Chamigren-3-one (+)-8 bearing an axial CI-atom at C(8) exists as a largely dominant conformer with Me—C(5) at the envelope-shaped enone ring pointing away from CIax−C(8) at the cyclohexane ring (= B) in the ‘normal’ chair conformation, as shown by 1H-NMR. In contrast, the α-chamigren-3-ols (+)-9 and (+)-10, obtained from hydride reduction of (+)-8, show a temperature-dependent equilibrium of conformers where