A novel skeletal rearrangement of the A ring of the immonium salt derived from norditerpenoid alkaloid yunaconitine

Treatment of 3-acetylyunaconitine from yunaconitine with NBS at 40°C for 12 h afforded the 3-acetylyunaconitine azomethine (48%). Reaction of with CH3I in MeOH at room temperature overnight gave the iminium salt (100%). Unexpectedly, treatment of with 5% NaOH in methanol at room temperature for 20 min produced the rearrangement alkaloid (38%) besides other unidentified compounds. Acetylation of with Ac2O/pyridine containing a small amount of TsOH gave its two derivatives (28%) and (56%). The structure of was confirmed using 2D NMR spectra and single crystal X-ray analysis of its acetyl derivative .