Quantitative determination of conformational equilibrium in quinolizidine-piperidine alkaloids. Part 2: Synthesis and conformational study of N-methylalbine

N-methylalbine () was synthesized for the first time. The structure is other than the one bearing hitherto its name. The fraction of the conformer with the boat ring C in the conformational equilibrium in in benzene solution was determined to be ca. 22% using coupling constant J9–11β. The reason of the occurrence of a significant amount of the boat conformer is, similarly to N-methylangustifoline (), the interaction of an axial allyl group with the bridge H8α hydrogen atom. The smaller fraction of the boat conformation in than in is caused by the repulsion of one of the H14 hydrogen atoms of the allyl group with the axial H5α proton in the boat conformer of .