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).