Novel Products from Oxidation of the Norditerpenoid Alkaloid Pseudaconine with HIO₄

Abstract

Oxidation of pseudaconine 8, a norditerpenoid alkaloid, with HIO₄ led to a series of novel interesting products, depending greatly on reaction medium and work-up conditions. Treatment of 8 in MeOH-H₂O (1:1) with NaIO₄ gave compounds 10 and 11, but compound 12 was obtained quantitatively when the final reaction solution was alkalized with conc. NH₄OH. The imine 12 was also obtained in 100% yield by treating 8 in 5% HCl solution with NaIO₄ followed by alkalizing the reaction products to pH>9 with conc. NH₄OH. When the work up pH was 7-8, only N, O-mixed acetal-ketal 13 was formed in 96% yield, which was converted quantitatively to 12 by further alkalizing. When the reaction mixture was alkalized to pH 7-8 with Na₂CO₃, a hemiacetalketal 14 was afforded quantitatively, which was converted to 15 in 87% yield by further treatment with Na₂CO₃ or 5% NaOH methanol. Compound 15 could be converted back to 14 by treatment with 10% HCl solution. Acetylation of the imine 12 gave the compounds 16 and 17 in 15% and 19% yields, respectively. All of the new compounds were isolated and fully characterized.