On the Origin of Asymmetric Induction of the Palladium-Catalyzed Allylic Substitution Reaction with Chiral 4,4-Disubstituted 4,5-Dihydro-2-(phosphinoaryl)oxazole Ligands

The X-ray analyses of (η3-allyl){4-benzyl-2-[2-(diphenylphosphino-κP)phenyl]-4,5-dihydro-4-4-methyloxazole-κN}palladium(II) hexafluorophosphate (5) and the analogous [Pd(η3-1,3-diphenylallyl)] complex 6 are presented. A comparison with the (η3-allyl)- and (η-1,3-diphenylallyl)palladium complexes 2 and 3, respectively, containing the 4-monosubstituted 4,5-dihydro-2-(phosphinoaryl)oxazole ligand 1a reveals important structural differences (Fig. 3). 1H-NMR Spectroscopic investigation confirm that the 4,4-disubstituted 4,5-dihydro-2-(phosphinoaryl)oxazole ligand 4 of 5 and 6 shows the same conformation in solution as in the solid state (Table 2). The application of ligand (S)-4 in the Pd-catalyzed allylic substitution demonstrates a configurational relationship between the orientation of the allyl ligand in the intermediate (cf. complex 6) and the absolute configuration of the allylic-substitution product (Table 3).

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