292140-03-5Relevant articles and documents
Synthesis, X-ray crystal-structure analysis, and NMR studies of (η3- allyl)palladium(II) complexes containing a novel dihydro(phosphinoaryl)oxazine ligand: Application in palladium-catalyzed asymmetric synthesis
Liu, Shuangying,Mueller, Juergen F. K.,Neuburger, Markus,Schaffner, Silvia,Zehnder, Margareta
, p. 1256 - 1267 (2000)
The novel chiral P,N-ligand 2-[2-(diphenylphosphino)phenyl]-5,6-dihydro- 4-phenyl-4H-1,3-oxazine (4) was synthesized. The corresponding {dihydro[(phosphino-κP)aryl]oxazine-κN} (η3-diphenylallyl)palladium(II) hexafluorophosphate 5 and the analogous [Pd(η3-1,3-dimethylallyl)] complex 6 were investigated by X-ray analysis and 1D- and 2D-NMR spectroscopy. The complex 5 exists as 'exo'-syn-syn isomer in the solid state (Fig. 1). In solution, the same isomer exceeds with 90%. The X-ray crystal structure of 6 reveals that the dihydro(phosphinoaryl)oxazine ligand coordinates in a pseudo-enantiomeric conformation compared with that of 5 (Fig. 3). A syn-anti arrangement of the allyl substituents of 6 is favored in the solid state. 1H-NMR Spectroscopic investigations suggest that the auxiliary 6 adopts two conformations. This conformational instability together with 'exo'/'endo' and syn/anti isomerization leads to the formation of 6 isomers (Fig. 4). The asymmetric allylic substitution reaction of 1,3-diphenylallyl acetate with dimethyl malonate in the presence of 4 proceeds with a selectivity of 99% ee. The ee induced by 4 in the catalytic allylic substitution of 1-methylbut-2- enyl acetate is moderate (54%).
