Heck reactions of 2-substituted enol ethers with aryl bromides catalysed by a tetraphosphine/palladium complex

• Published in: Tetrahedron letters Vol. 47; no. 4; pp. 459 - 462
• Main Authors: Battace, Ahmed, Zair, Touriya, Doucet, Henri, Santelli, Maurice
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 23.01.2006; Elsevier
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; HALIDES; ALKENES; IODIDES; ACIDS; ARYLATION; DERIVATIVES; PALLADIUM CATALYSTS; CONJUGATE ADDITION
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/j.tetlet.2005.11.071

cis, cis, cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C 3H 5)] 2 efficiently catalyses the Heck reaction of β-substituted enol ethers with aryl bromides. Employing β-methoxystyrene, 3-ethoxyacrylonitrile or methyl 3-methoxyacrylate, the regioselective α-arylation of these enol ethers was observed in all cases, and mixtures of Z and E isomers were generally obtained, which in many cases yielded a single ketone product after acid treatment. The stereoselectivity of this reaction depends on steric and electronic factors, and better stereoselectivities in favour of Z isomers were observed with electron-rich or sterically congested aryl bromides. Better yields were obtained for this reaction with electron-rich or sterically congested aryl bromides than with electron-poor aryl bromides. This observation suggests that with these β-substituted enol ethers the rate-limiting step of the catalytic cycle is not the oxidative addition of the aryl bromide to the palladium complex.