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Palladium-Catalyzed Isomerization of Methylenecyclopropanes in Acetic Acid

Min Shi,* Bao-Yu Wang and Jin-Wen Huang

*State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China, Email: mshipub.sioc.ac.cn

M. Shi, B.-Y. Wang, J.-W. Huang, J. Org. Chem., 2005, 70, 5606-5610.

DOI: 10.1021/jo050560m


Abstract

Pd(PPh3)4-catalyzed isomerization of methylenecyclopropanes (MCPs) proceeds smoothly at 80°C in acetic acid and toluene to give 1-substituted or 1,1-disubstituted dienes in good to excellent yields. The mechanism is discussed.

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proposed mechanism



Details

The document discusses the palladium-catalyzed isomerization of methylenecyclopropanes (MCPs) in acetic acid, resulting in the formation of 1-substituted or 1,1-disubstituted dienes. The reaction, catalyzed by Pd(PPh3)4, proceeds efficiently at 80°C in toluene, yielding the desired dienes in good to excellent yields within 3-5 hours. The study highlights the importance of acetic acid in the reaction, as no reaction occurs in its absence. Various solvents and acids were tested, with toluene and acetic acid proving most effective. The mechanism involves hydropalladation of the olefinic moiety of MCPs by AcO-Pd-H, as supported by deuterium-labeling experiments. The reaction's stereochemistry is well-controlled, especially for unsymmetrical MCPs. Other transition metal catalysts were less effective or inactive under similar conditions. The study provides detailed experimental procedures and characterizations of the products, confirming their structures through spectroscopic data and mass spectrometry. The research was supported by various Chinese scientific foundations and aims to further elucidate the mechanistic details and scope of this reaction.


Key Words

Dienes, Isomerizations


ID: J42-Y2005-800