Studies on Digitalis Glycosides. XXIV. Ring-opening Reaction of 14, 15-Epoxide with Thiocyanic Acid, and Preparation of 3β-Hydroxy-14β, 15β-epithio-5β-card-20(22)-enolide

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Abstract
Ring-opening reaction of 3[beta]-acetoxy-14[alpha],15[alpha]-epoxy-5[beta]-card-20(22)-enolide with thiocyanic acid proceeded smoothly to afford 3[beta]-acetoxy-14[beta]-thiocyanato-15[alpha]-hydroxy-5[beta]-card-20(22)-enolide and 3[beta]-acetoxy-14[beta]-isothiocyanato-15[alpha]-hydroxy-5[beta]-card-20(22)-enolide. On the contrary, the reaction with 3[beta]-acetoxy-14[beta],15[beta]-epoxy-5[beta]-card-20(22)-enollde did not proceed so smoothly as a result of steric hindrance, giving 3[beta]-acetoxy-14[beta]-hydroxy-15[alpha]-thiocyanato-5[beta]-card-20(22)-enolide together with 3[beta]-acetoxy-15-oxo-5[beta],14[alpha]-card-20(22)-enolide. Ring closure of the mesylate with a weak alkali resulted in the formation of 3[beta]-acetoxy-14[beta],15[beta]-epithlo-5[beta]-card-20(22)-enolide and 3[beta]-acetoxy-14[alpha],15[alpha]-epoxy-5[beta]-card- 20(22)- enolide.