Circular dichroism studies of some 13-oxosparteines

Abstract

C. d. data for 1 3-oxosparteines and related compounds provide direct evidence for the process of protonation, involving possible transannular interaction of the carbonyl and amine functions in the ring D boat form. Transannular interactions are found to occur both in the 11α- and in the more rigid 11β-series. In the 11α-series transannular interaction in ring D requires ring C to adopt a boat conformation. The ring D bridged forms are evidently stabilized in water and presumably in other protic solvents. In the absence of a 2-oxo-function the process of transannular interaction upon acidification is retarded due to intramolecular hydrogen bonding between N(1) and N(16).