Desymmetrization by Ring-Closing Metathesis Leading to 6,8-Dioxabicyclo[3.2.1]octanes:  A New Route for the Synthesis of (+)-exo- and endo-Brevicomin

[formula: see text] The 6,8-dioxabicyclo[3.2.1]octane skeleton is a common structural subunit in natural products. A conceptionally new strategy affording these structures is described for the syntheses of (+)-exo-brevicomin and rac-endo- and enantiomerically enriched (+)-endo-brevicomin, employing desymmetrization of trienes derived from diols with C2 and meso symmetry via ring-closing metathesis.