PROTON MAGNETIC RESONANCE STUDY OF HELIOTRIDENE - A PYRROLIZIDINE DERIVATIVE

The 100 MHz NMR spectrum of heliotridene (IV) in CDCl3 solution has been analysed. The conformation of the title compound has been derived from the vicinal and allylic coupling constants. The pyrrolizidine nucleus of heliotridene (IV) consists of a planar pyrroline ring joined to a pyrrolidine ring existing in two rapidly interconverting exo- and endo-buckled C1 conformers of approximately equal populations. On acidification the ratio of the two conformers is changed in favour of the endo-buckled form (3:1). Unusually large homallylic coupling of 3·6 and 5·0 Hz have been observed. © 1969.