Palladium-Catalyzed Asymmetric Allylic Amination Using Ferrocenyl Pyrazole Ligands: Steric Control of 3-Allyl Configuration
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- 作者：Antonio Togni ; Urs Burckhardt ; Volker Gramlich ; Paul. S. Pregosin ; and Renzo Salzmann
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：February 7, 1996
- 年：1996
- 卷：118
- 期：5
- 页码：1031 - 1037
- 全文大小：254K
- 年卷期：v.118,no.5(February 7, 1996)
- ISSN：1520-5126
文摘
The reaction of 1,3-diphenylallylethyl carbonate (1)with benzylamine to afford the secondary amine 2iseffectively catalyzed by Pd-complexes containing chiral ferrocenylpyrazole ligands. The highest enantioselectivity(99% ee) was obtained using ligand 3a,1-{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl}-3-(1-adamantyl)-1H-pyrazole. Four different cationic Pd-allyl intermediates,4a, 4c, 4j, and 4k(containing ligands 3a, 3c, 3j, and3k,respectively), formed during the catalytic reaction were studied insolution by 2D-NMR spectroscopy, with the aimof clarifying configurational aspects. Depending on the size andshape of the substituent in position 3 of the pyrazolering, it was found that the major diastereoisomeric form of thesecomplexes either adopts an exo-syn-syn (ligands3aand 3c,1-{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]-ethyl}-3-phenyl-5-methyl-1H-pyrazole)or an exo-syn-anticonfiguration (ligands 3j,1-{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl}-3-(9-anthryl)-5-methyl-1H-pyrazoleand 3k,1-{(S)-1-[(R)-2-(diphenylphosphino)ferrocenyl]ethyl}-3-(9-triptycyl)-1H-pyrazole).This analysis allows thesite of nucleophilic attack on the allyl ligand to be establishedunequivocally, i.e., the carbon atom trans to phosphorus.The reasons responsible for this pronounced site-selectivity arediscussed. The Pd-allyl complexes[Pd(
3-PhCHCHCHPh)(3c)]PF6, 4c,and[Pd(3-PhCHCHCHPh)(3k)]PF6,4k, were characterized by X-ray diffraction.4ccrystallizes with 1 equiv of Et2O in the orthorhombic spacegroup P212121:a = 13.026(2) Å, b = 14.784(2) Å,c= 25.124(5) Å, Z = 4. Crystals of4k contain 3 equiv of hexane and 1 equiv of acetone andH2O in the unit cellbelonging to the trigonal system, space group P3221:a = 24.07(3) Å, c = 22.48(3) Å,Z = 6.
3-PhCHCHCHPh)(3c)]PF6, 4c,and[Pd(3-PhCHCHCHPh)(3k)]PF6,4k, were characterized by X-ray diffraction.4ccrystallizes with 1 equiv of Et2O in the orthorhombic spacegroup P212121:a = 13.026(2) Å, b = 14.784(2) Å,c= 25.124(5) Å, Z = 4. Crystals of4k contain 3 equiv of hexane and 1 equiv of acetone andH2O in the unit cellbelonging to the trigonal system, space group P3221:a = 24.07(3) Å, c = 22.48(3) Å,Z = 6.