Baccharis oxide structure

Baccharis Oxide.—The interesting structure (79) has been proposed for baccharis oxide, from Baccharis halimifolia. In biogenetic terms baccharis oxide is readily derivable from the cation (80), which leads to ebelin lactone (81) and shionone (82). On treatment with boron trifluoride dihydro-baccharis oxide rearranged to (83). 

The structure of Baccharis oxide has been revised biosynthetically this is close to the previous structure (Vol. 2, p. 168) and therefore of comparable interest. The total laboratory synthesis of lupeol is a notable further achievement in the synthesis of unsymmetrical triterpenoids. 

The structure of baccharis oxide (see Vol. 2, p. 168) has been revised to (95) on the basis of a direct A"-ray analysis. Baccharan-3-one (96) was found to be identical with 18,19-secolupan-3-one, prepared via cleavage of (97), the mercuric acetate oxidation product of lupenyl acetate. This provides direct chemical proof of the configuration at C-17 in baccharis oxide. 

Mo, F., T. Anthonsen, and T. Bruun Revised Structure of the Triterpenoid Baccharis Oxide. Acta Chem. Scand. 26, 1287 (1972). 

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