Details

Autor(en) / Beteiligte

• Zanoni, Giuseppe
• Porta, Alessio
• Meriggi, Alessia
• Franzini, Maurizio
• Vidari, Giovanni

Titel

1,2-Oxopalladation versus π-Allyl Palladium Route. A Regioconvergent Approach to a Key Intermediate for Cyclopentanoids Synthesis. New Insights into the Pd(II)-Catalyzed Lactonization Reaction

Ist Teil von

• Journal of organic chemistry, 2002-08, Vol.67 (17), p.6064-6069

Ort / Verlag

Washington, DC: American Chemical Society

Erscheinungsjahr

2002

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Regioconvergent synthesis of the key lactone 1 from an equimolar mixture of the two olefins 4 and 5 was achieved by unique Pd(II) chemistry. The synthetic versatility of lactone 1 has been demonstrated in the synthesis of iridoids and of the endo-Corey lactone 2, which is a key intermediate for the F2-isoprostane synthesis. Upon exposure of the sodium salts of 4 and 5 to a catalytic amount of Pd(OAc)2 under oxygen, in the presence of AcOH, an isomeric lactone 12 was obtained in addition to the title compound 1. The Pd(II) lactonization was optimized by fine-tuning all the factors participating in the catalytic cycle:  solvent, oxidant, co-oxidant, and Pd(II) source. The Hosokawa's heterobimetallic couple emerged as the catalyst of choice. With a Cu(II)−Pd(II) couple, the redox process was transferred to copper, and the formal oxidation state of palladium remained constant during the reaction. By virtue of this new methodology, lactone 1 was obtained in a rewarding 60% yield, along with isomeric lactone 12 in 30% yield. A detailed mechanistic study was carried out in order to elucidate the formation of lactones 1 and 12. Lactone 1 was formed from either olefin 8 or olefin 10; on the other hand, lactone 12 was formed exclusively from olefin 10. An intramolecular 1,2-acyloxypalladiation was invoked for the transformation of 8 into 1, whereas the π-allyl complexes 13 and 11 were involved in the transformation of olefin 10 into 12 and 1, respectively.