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Allylic Alkylations Catalyzed by Palladium Systems Containing Modular Chiral Dithioethers. A Structural Study of the Allylic Intermediates

2005; American Chemical Society; Volume: 24; Issue: 16 Linguagem: Inglês

10.1021/om050190s

1520-6041

F. Fernandez, Montserrat Gómez, Susanna Jansat, Guillermo Muller, Erika Martin, L. Flores-Santos, Paula X. García, Alberto de Lago Acosta, Ali Aghmiz, M. Gimenez-Pedros, Anna M. Masdeu‐Bultó, Montserrat Diéguez, Carmen Claver, M.A. Maestro,

Chemical Synthesis and Analysis

Palladium allylic systems containing modular chiral dithioether ligands were chosen as catalysts for a systematic study of homodonor ligands in allylic alkylation reactions. For this purpose, new type-DMPS (4−6) and -DEGUS (8, 9) ligands were synthesized. Dithioethers 4−6 afforded high activities and excellent selectivities in all Pd-catalyzed allylic reactions. Particularly the Pd/6 catalytic system provided b-VIII with an ee > 99% and a regioselectivity l/b (VIII) = 1/1.6. A family of intermediate complexes containing several allyl groups (symmetrical, 13−16 and 20, and nonsymmetrical, 17−19, moieties) and dithioether ligands (4−6, 8, 9, 11, and 12) is described. The complexes were fully characterized both in solution and in the solid state. X-ray structures of four of these complexes (16−18 and 20) were determined. The diastereomers present in solution were studied by NMR spectroscopy, and in some cases it was possible to establish a relationship between the diastereomeric excesses and the selectivities found in the catalytic process.