Enantiospecific synthesis of (+)- and (-)-ferruginine from L-glutamic acid. Synthesis of tropanes via intramolecular iminium ion cyclization

Iminium ions, generated by decarbonylation of N-benzyl-5-[1-(methoxycarbonyl)-4-oxopentyl]-prolines, prolines, undergo intramolecular cyclization to afford 2,4-disubstituted tropanes in good yields. This transformation is also shown to be a stereospecific reaction. The value of these substituted tropanes has been demonstrated by functional group manipulation, leading to the enantiospecific synthesis of (+)-ferruginine, an alkaloid isolated from Darlinga ferruginea, and its unnatural enantiomer, (-)-ferruginine.