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)-gamma-bisabolenes

Highly efficient stereoselective syntheses of both (Z)- and (E)-gamma -bisa bolenes (1) were achieved by ring closing metathesis of stereodefined tetra substituted alkenes. Both (Z)and (E)-tetrasubstituted alkene precursors wer e obtained by Cu-catalyzed stereoselective addition of allylmagnesium bromi de to propargyl alcohols, followed by Pd-catalyzed cross coupling of alkylz inc derivatives. This represents the first application of ring-closing meta thesis to the stereoselective synthesis of exocyclic alkenes.