Partialsynthesen von Cardenoliden und Cardenolid‐Analogen. XIII. Synthese substituierter 14,21‐Epoxy‐5β,14β‐card‐20(22)‐enolide

Partial Syntheses of Cardenolides and Cardenolide Analogues. XIII. Synthesis of Substituted 14,21-Epoxy-5β,14β-card-20(22)-enolide The 12-substituted 14,21-epoxy-5β,14β-card-20(22)-enolides 3 and 5 were synthesized by oxidation of the appropriate 17β-(3-furyl) derivatives 2b and 2c, respectively, with chromic acid. 5 was converted to the conjugated Δ9(11)-12-ketone 6 by dehydrogenation with selenium dioxide. The biological activities of the new compounds were investigated and are discussed.