[reaction: see text] Ligand-free Pd(OAc)(2) can be used as a catalyst in the Heck reaction of aryl bromides as long as the amount of catalyst is kept between 0.01 and 0.1 mol %. At higher concentrations palladium black forms and the reaction stops. The actual catalyst is monomeric. Palladacycles merely serve as a source of ligand-free palladium in Heck reactions of aryl bromides.

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Polyphenylalkene derivatives Polyphenylalkene derivatives Q 0740Homeopathic Ligand-Free Palladium as a Catalyst in the Heck Reaction. A Comparison with a Palladacycle. -The novel procedure for the Heck reactions with aryl bromides can be conveniently performed with ligand-free palladium, added as Pd(OAc)2, as long as the amount is kept as low as 0.01-0.1 mol%. This method is more reliable than previous methods using higher concentrations of palladium catalysts, where palladium black forms and the reaction stops. Comparison with the Hermann-Beller catalyst (VII) reveals that both catalysts have a similar kinetic profile. -(DE VRIES*, A. H. M.; MULDERS, J. M. C. A.; MOMMERS, J. H. M.; HENDERICKX, H. J. W.; DE VRIES*, J. G.; Org. Lett. 5 (2003) 18, 3285-3288; DSM Pharma Chem.-Adv. Synth., Catal. Dev., NL-6160 MD Geleen, Neth.; Eng.) -Steudel 51-102

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Methyl 2-Acetamido Acrylate and Aryl Bromides as Key Step in the Synthesis of Enantiopure SubstitutedPhenylalanines. -A number of substituted phenylalanines are prepared in good yields with high enantioselectivity using a cost-effective ligand free Pd-catalyzed arylation of the acetamido acrylate (I) followed by asymmetric hydrogenation of the resulting products. -(WILLIANS, C. E.; MULDERS, J. M. C. A.; DE VRIES, J. G.; DE VRIES*, A. H. M.; J. Organomet. Chem. 687 (2003) 2, 494-497; DSM Pharma Chem.-Adv. Synth., Catal. Dev., NL-6160 MD Geleen, Neth.; Eng.) -Jannicke 16-166