Synthesis of (-)-erythrodiene and (+)-7-epispirojatamol via intramolecularPd-catalyzed allylzincation

Two spirobicyclic sesquiterpenoids, (-)-erythrodiene (1) and (+)-7-epispiro jatamol (30),were synthesized in enantiomerically pure form via an intramol ecular allylzincation process. The allylzinc species were formed in the pre sence of Et,Zn via transmetallation of a catalytically generated allylpalla dium intermediate. Several Pd catalysts were tested for this transformation , and [Pd(OAc)(2)/Bu3P(1 equiv.) was found to be, by far, the most effectiv e. Whereas the preparation of 1 involved allylzincation of a tethered termi nal olefin. 30 was formed via a novel intramolecular allylzincation of a me thyl ketone. Both reactions showed the same stereochemical preference. yiel ding the spirobicyclic products in 95:5 and 4:1 diastereoisomer ratios, res pectively.