Boron Trifluoride Etherate-catalyzed Backbone Rearrangement of 13β,18β-Epoxybaccharan-3β-yl Acetate. A Sequential Migration of Two Methyl Groups and a Hydride in Biogenetic Direction

Abstract

13β,18β-Epoxybaccharan-3β-yl acetate was treated with boron trifluoride etherate in acetic anhydride to afford a complex mixture, in which a formation of backbone rearrangement products, D:C-friedobacchar-9(11)-en- and -7-en-3β-yl acetates together with 3β-acetoxy-D-friedo-13,18-secobacchar-13-en-18-ylidene diacetate was observed. The D:C-friedobacchar-9(11)-ene derivative is the first example of the backbone rearrangement product formed by a sequential migration of two methyl groups and a hydride towards the biogenetic direction in baccharene-shionene series.