Stereoselective Synthesis of Exocyclic Alkenes by Cu-Catalyzed Allylmagnesiation, Pd-Catalyzed Alkylation, and Ru-Catalyzed Ring-Closing Metathesis: Highly Stereoselective Synthesis of (Z)- and (E)-γ-Bisabolenes

Highly efficient stereoselective syntheses of both (Z)- and (E)-γ-bisabolenes (1) were achieved by ring closing metathesis of stereodefined tetrasubstituted alkenes. Both (Z)- and (E)-tetrasubstituted alkene precursors were obtained by Cu-catalyzed stereoselective addition of allylmagnesium bromide to propargyl alcohols, followed by Pd-catalyzed cross coupling of alkylzinc derivatives. This represents the first application of ring-closing metathesis to the stereoselective synthesis of exocyclic alkenes.