Configuration of the ring nitrogen in N-oxides and the conformation of tropanes. Part XVIII

Abstract

The configurations of ring nitrogen in the amine oxides of tropine, oscine, atropine, and scopolamine have been investigated by nuclear magnetic resonance (n.m.r.) spectroscopy. Oxygen function(s) at C-6β (and 7β) were found to deshield the low-field, equatorial N-methyl signal. Analysis of the n.m.r. spectra of epoxides of some tropane bases, in particular the coupling constants, clearly indicates preponderance of the (slightly distorted) chair conformation even in the tropanes with a bulky group in the 3α (endo) position. The protons on the epoxide carbons are magnetically non-equivalent in scopolamine (5b) and its N-oxide while appearing as a singlet in the alkamine, i.e. scopine (5a).