Synthesis of (−)-Erythrodiene and (+)-7-Epispirojatamolvia Intramolecular Pd-Catalyzed Allylzincation
摘要:
Two spirobicyclic sesquiterpenoids, (-)-erythrodiene (1) and (+)-7-epispirojatamol (30),were synthesized in enantiomerically pure form via an intramolecular allylzincation process. The allylzinc species were formed in the presence of Et,Zn via transmetallation of a catalytically generated allylpalladium intermediate. Several Pd catalysts were tested for this transformation, and [Pd(OAc)(2)/Bu3P(1 equiv.) was found to be, by far, the most effective. Whereas the preparation of 1 involved allylzincation of a tethered terminal olefin. 30 was formed via a novel intramolecular allylzincation of a methyl ketone. Both reactions showed the same stereochemical preference. yielding the spirobicyclic products in 95:5 and 4:1 diastereoisomer ratios, respectively.
A highly diastereoselective synthesis of (-)-Erythrodiene was achieved via an intramolecular Pd-catalyzed Znene reaction as the key step. It was found that Pd(OAc)(2)/Bu3P was a superior catalyst for this reaction to Pd(PPh3)(4). (C) 1998 Elsevier Science Ltd. All rights reserved.