Oxidation of the Norditerpenoid Alkaloids Isotalatizidine and 6-Epiforsticine

Oxidation of 1 with KMnO4 in acetone-H2O (1:1) for 1h gave nevadenine 2 (38%). But, 3 was formed in 98% yield when prolonging time and raising temperature (40℃). Reaction of 1 and 10 with Conforth reagent afforded the ketones 11 (55%), 12 (30%), and 13 (13%), 14 (20%), respectively. While oxidation of 7 and 15 with a variety of the oxidizing agents gave 17 only in low 20% of yield besides the minor 16. In addition, 1 was converted to 2 by the fungi Curvularia lunata.