Syntheses of ficuseptine, juliprosine, and juliprosopine by biomimetic intramolecular Chichibabin pyridine syntheses.

[structure: see text] Biomimetic intramolecular Chichibabin pyridine syntheses using two molecules of an aldehyde and 4-aminobutanal dimethyl acetal (6) proceed efficiently in AcOH at 95 degrees C to give 2,3-dihydro-1H-indolizinium salts. Reaction occurs at 25 degrees C if 1-pyrroline (5) is used instead of 6. This reaction has been used for a one-step synthesis of ficuseptine (1) and the first syntheses of juliprosine (2) and juliprosopine (17t), which is now assigned as the trans stereoisomer.