Terpenoids. Part V. Rearrangement of ent-kaurane 15β,16β-epoxide to ent-(16R)-atisan-15-one

Abstract

Treatment of ent-kaurane 15β,16β-epoxide (5) with boron trifluoride–ether complex in benzene yields ent-(16R)-atisan-15-one (11) and small amounts of the 16S-epimer (4) of ent-kauran-15-one. In the conversion of ent-(16R)-atisan-15-one (11) into ent-atis-15-ene (16), the 15-tosylates (13) and (15) of the epimeric ent-atisan-15-ols (12) and (14) were found to rearrange to the olefin (18) in high yield.