A new palladium(I1) complex containing an amido-substituted P-chiral phosphine ligand is prepared efficiently by the asymmetric Diels-Alder reaction between N,N-dimethylacrylamide and l-phenyl-3,4-dimethylphosphole; the chelating properties of the functionalised ligand and the absolute configurations of the four newly generated stereocentres are determined by single-crystal X-ray analysis, and the optically active phosphine ligand displaced from the palladium template with 1,2-bis(diphenylphosphino)ethane.
An asymmetric Diels-Alder reaction between 1-phenyl-3,4-dimethylphosphole and ethyl vinyl ketone promoted by a chiral organopalladium complex gives the corresponding keto-substituted phosphine ligands in which the keto group can be stereospecifically located in the endo-or exo-positions of the phosphanorbornene skeleton.
The organopalladium complex containing ortho-metalated (S)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary has been used successfully to promote the asymmetric
[4 + 2] Diels−Alder reaction between 3,4-dimethyl-1-phenylphosphole and 2-vinylpyridine.
The pyridyl group in the resulting phosphanorbornene cycloadducts can be located stereospecifically in the exo or endo position by controlling the electronic properties of the
organopalladium promoter. In the exo-cycloaddition process, the P−N bidentate ligand (−)-2-[(1α,2α(S),4α,7S)-5,6-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-5-ene-2-yl]pyridine was
produced stereoselectively. In the endo-cycloaddition process, however, a pair of separable
diastereomeric palladium template complexes containing the naphthylamine auxiliary and
the enantiomeric forms of 2-[(1α,2β(R/S),4α,7(R/S)-5,6-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-5-ene-2-yl]pyridine were obtained. In these diastereomeric complexes, the endo-cycloadducts coordinated on palladiun as monodentate ligands via only their phosphorus
donor atoms. The pyridyl-nitrogen atoms are not involved in metal complexation. The
absolute configurations and the coordination properties of the exo- and endo-pyridylphosphines have been established by single-crystal X-ray analyses.
The chiral palladium complex (+),,,-di-p-chloro-bis{(S)-1 -[I -(dimethylamino)ethyl]-2-naphthyl-C2,N}dipalladium(II) has been used successfully to promote the asymmetric [4 + 21 Diels-Alder reaction between 3,4-dimethyl-1 -phenylphosphole and phenyl vinyl sulfide. The cycloaddition product ( -)-( 1 a,4a,5~,7R)-2,3-dimethyl-7-phenyl-5-(phenylsulfanyl)-7-phosphabicyclo[2.2.l]hept-2-ene was formed stereoselectively on the chiral palladium template and behaves as a bidentate ligand uia its phosphorus and sulfur donor atoms. The chiral naphthylamine auxiliary and the new P,S bidentate ligand can be selectively released with retention of chirality by treatment with hydrochloric acid or 1,2-bis(diphenylphosphino)ethanerespectively. The optical purity of the liberated heterobidentate compound has been confirmed by NMR spectroscopic studies. The absolute stereochemistries and the co-ordination properties of the enantiomerically pure P,S compound and its oxidized derivative have been established by single-crystal X-ray analyses.
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