Novel Sesquiterpenoid Skeletons by Wagner-Meerwein Rearrangements of Longipinane-9,13-diol-1-one Derivatives.

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