BIOGENETIC-LIKE BACKBONE REARRANGEMENT. A FORMATION OP<i>D</i>:<i>C</i>-FRIEDOBACCHAR-9(11)-ENE-3β,18β-DIYL LIACETATE FROM 13β,18β-EPOXYBACCHARAN-3β-YL ACETATE
13β,18β-Epoxybaccharan-3β-yl acetate was treated with BF3·Et2O in acetic anhydride to yield a complex mixture, in which the presence of D:C-friedobacchar-9(11)-ene-3β,18β-diyl diacetate (2) was shown; the product (2) was converted into 18-oxo-D:C-friedobacchar-9(11)-en-3β-ylacetate, the structure of which was confirmed by X-ray diffraction analysis.