The partial or total hydrolysis of
(3R,4S,5S,6S,9R,10R,11R)-9,13-diangeloyloxylongipinan-1-one
(1), isolated from the roots of Stevia viscida, gave alcohols 2 or 3, respectively, which
were subjected to molecular rearrangements with boron trifluoride
etherate. Compound 2 afforded (3R,4R,5R,6S,9R,10S,11S)-11,13-oxyneomorelian-1-one
(10) and (4S,5R,6S,8S,10R)-10,13-oxyneojiquilp-2-en-1-one
(11), both possessing novel sesquiterpenoid skeletons.
In turn, 3 provided (3R,4R,5S,6S,9R,11R)-13-hydroxymoreli-10(14)-en-1-one (7) and 10. Acetylation of 3 gave 4, thus
allowing reduction of the C-1 carbonyl group to yield 5, which was rearranged to (1S,3R,4S,5S,6S,9R,10R,11R)-13-acetoxy-9,11-epoxyjiquilpane
(6), while an attempt to mesylate 3 directly
gave rearranged (3R,4R,5S,6S,9R,11R)-13-mesyloxymoreli-10(14)-en-1-one (8) through expulsion
of the C-9 mesylate group by the antiperiplanar C-4–C-10 bond
migration to C-4–C-9. In addition, treatment of 1 with boron trifluoride etherate generated (3R,4R,5S,6S,9R,11R)-13-angeloyloxymoreli-10(14)-en-1-one (9). The structures of 2–11 were elucidated by 1D and 2D NMR experiments and those of 2, 3, 8, 10, and 11 were confirmed by single-crystal X-ray diffraction analysis.