Epoxide Opening of a 7,17-Seco–7,8-Epoxy-C₁₉-Diterpenoid Alkaloid

A new and effective approach toward epoxide opening of a 7,17- seco–7,8-epoxy-C19-diterpenoid alkaloid is herein described. The starting epoxide was prepared from naturally occurring yunnaconitine via a nine-step transformation. Treatment of this epoxide with trifluoroacetic anhydride in dioxane at 110oC followed by reduction with sodium boron hydride generated two epoxide opening compounds 7 and 8. Each of their structures is characteristic of a Δ8,15 bridgehead double bond and a 7β-oxygen-substituted group.