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Exo- and Endocyclic Oxazolinyl−Phosphane Palladium Complexes:  Catalytic Behavior in Allylic Alkylation Processes

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posted on 21.06.2004, 00:00 by Delphine Franco, Montserrat Gómez, Francisco Jiménez, Guillermo Muller, Mercè Rocamora, Miguel Angel Maestro, José Mahía
The new bidentate chiral N,P-donor oxazolinyl−phosphane ligands 715 are described. Upon coordination to the palladium metal, ligands 712 gave endocyclic oxazolinyl−phosphane complexes having seven-membered rings, while ligands 1315 afforded exocyclic oxazolinyl−phosphinite complexes with six-membered rings, depending on the relative CN oxazoline bond and metal ring position. Ionic palladium(II) complexes containing N,P-bidentate ligands and allyl groups (η3-C3H5 for 1622 and η3-1,3-Ph2-C3H3 for 2326) were prepared and fully characterized. X-ray structures were determined for complexes 18 and 19. Pd catalytic systems containing ligands 715 were tested in the asymmetric allylic alkylation of the racemic substrates rac-3-acetoxy-1,3-diphenyl-1-propene (I) and rac-3-acetoxy-1-cyclohexene (III). The endocyclic systems show better activites and selectivites (ee values up to 82%) than the exocyclic ones (ee values up to 72%) for substrate I. In particular, palladium endocyclic oxazoline−phosphinite systems containing the PCy2 group (20, 21) give the highest activities, but the best enantioselectivities were observed for those containing PPh2 (18, 19).

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