Chemoselectivity in the Pd-catalyzed cyclization of 1,6-enynes and proof of the relative configuration of the new stereogenic centers

The dimerization of dienyne 6 with a palladole catalyst readily provides th e bicyclic enyne rac-7. A second cyclization of the 1,6-enyne substructure in rac-7 works best with a hydropalladation catalyst and delivers rac-8. Di els-Alder reactions of the latter finally lead to a crystalline product rac -12. A crystal structure analysis of rac-12 allowed the determination of th e relative configuration of all stereogenic centers formed in the dimerizat ion or 6.