Synthesis of (−)-Erythrodiene and (+)-7-Epispirojatamol via Intramolecular Pd-Catalyzed Allylzincation

• Published in: Helvetica chimica acta Vol. 84; no. 2; pp. 416 - 430
• Main Authors: Oppolzer, Wolfgang, Flachsmann, Felix
• Format: Journal Article
• Language: English
• Published: Basel Verlag Helvetica Chimica Acta 28.02.2001; Wiley
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; PI-ALLYLPALLADIUM; REAGENTS; ACTIVE ACYLATION CATALYST; ENE-TYPE CYCLIZATIONS; TRIFLUOROMETHANESULFONATE; ERYTHRODIENE; STEREOSELECTIVE PREPARATION; CERIUM(III) CHLORIDE; SPIROJATAMOL; ZINC
• ISSN: 0018-019X; 1522-2675
• DOI: 10.1002/1522-2675(20010228)84:2<416::AID-HLCA416>3.0.CO;2-K

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 Et2Zn 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 allyl zincation of a methyl ketone. Both reactions showed the same stereochemical preference, yielding the spirobicyclic products in 95 : 5 and 4 : 1 diastereoisomer ratios, respectively.