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Synthesis, X‐Ray Crystal‐Structure Analysis, and NMR Studies of ( η 3 ‐Allyl)palladium(II) Complexes Containing a Novel Dihydro(phosphinoaryl)oxazine Ligand: Application in Palladium‐Catalyzed Asymmetric Synthesis
Author(s) -
Liu Shuangying,
Müller Jürgen F. K.,
Neuburger Markus,
Schaffner Silvia,
Zehnder Margareta
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20000607)83:6<1256::aid-hlca1256>3.0.co;2-5
Subject(s) - chemistry , dimethyl malonate , allylic rearrangement , isomerization , ligand (biochemistry) , stereochemistry , malonate , enantiomer , nuclear magnetic resonance spectroscopy , selectivity , medicinal chemistry , palladium , catalysis , crystallography , organic chemistry , biochemistry , receptor
The novel chiral P,N‐ligand 2‐[2‐(diphenylphosphino)phenyl]‐5,6‐dihydro‐4‐phenyl‐4 H ‐1,3‐oxazine ( 4 ) was synthesized. The corresponding {dihydro[(phosphino‐ ϰ P )aryl]oxazine‐ ϰ N } ( η 3 ‐diphenylallyl)palladium(II) hexafluorophosphate 5 and the analogous [Pd( η 3 ‐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. 1 H‐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%).