- Facile Synthesis of a New Chiral BINOL–Silica Hybrid Catalyst for Asymmetric Diels–Alder and Aza Michael Reactions
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Abstract: A novel chiral BINOL–silica hybrid has been successfully prepared by the reaction of (S)-BINOL and SiCl4 following by gel polymerization under atmosphere condition. The synthesized catalyst was characterized by elemental analysis, Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Catalytic activity of the chiral BINOL–silica hybrid for diastereo- and enantioselective Diels–Alder and aza Michael reactions has been investigated. Mild reaction conditions, high yields, excellent diastereo- and enantiomeric excess make this powerful and effective catalyst as an attractive option for the synthesis of chiral organic compounds. Graphical Abstract: [Figure not available: see fulltext.]
- Saeidian, Hamid,Paghandeh, Hossein,Parvin, Zahra,Mirjafary, Zohreh,Ghaffarzadeh, Mohammad
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p. 1366 - 1374
(2018/05/03)
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- Ruthenium Lewis Acid-Catalyzed Asymmetric Diels–Alder Reactions: Reverse-Face Selectivity for α,β-Unsaturated Aldehydes and Ketones
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Acrolein, methacrolein, methyl vinyl ketone, ethyl vinyl ketone, 3-methyl-3-en-2-one, and divinyl ketone were coordinated to a cationic cyclopentadienyl ruthenium(II) Lewis acid incorporating the electron-poor bidentate BIPHOP–F ligand. Analysis by NOESY and ROESY NMR techniques allowed the determination of conformations of enals and enones present in solution in CD2Cl2. The results were compared to solid-state structures and to the facial selectivities of catalytic asymmetric Diels–Alder reactions with cyclopentadiene. X-Ray structures of four Ru-enal and Ru-enone complexes show the α,β-unsaturated C=O compounds to adopt an anti-s-trans conformation. In solution, enals assume both anti-s-trans and anti-s-cis conformations. An additional conformation, syn-s-trans, is present in enone complexes. Enantioface selectivity in the cycloaddition reactions differs for enals and enones. Reaction products indicate enals to react exclusively in the anti-s-trans conformation, whereas with enones, the major product results from the syn-s-trans conformation. The alkene in s-cis conformations, while present in solution, is shielded and cannot undergo cycloaddition. A syn-s-trans conformation is found in the solid state of the bulky 6,6-dimethyl cyclohexanone-Ru(II) complex. The X-ray structure of divinyl ketone is unique in that the Ru(II) center binds the enone via a η2bond to one of the alkene moieties. In solution, coordination to Ru–C=O oxygen is adopted. A comparison of facial preference is also made to the corresponding indenyl Lewis acids.
- Thamapipol, Sirinporn,Ludwig, Bettina,Besnard, Céline,Saudan, Christophe,Kündig, E. Peter
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p. 774 - 789
(2016/10/17)
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- Enantioselective catalytic diels-alder reactions with enones as dienophiles
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The aqua complexes (SM,RC)-[(η5-C 5Me5)M(PROPHOS)(H2O)][SbF6] 2 [PROPHOS = (R)-propane-1,2-diylbis(diphenylphosphane); M = Rh (1), Ir (2)] are active catalysts for the asymmetric Diels-Alder reaction between ketones and dienes. At low temperatures, enantioselectivities of up to 89% ee are achieved. The intermediate Lewis acid-dienophile complexes (S M,RC)-[(η5-C5Me 5)M(PROPHOS)(MVK)][SbF6]2 (MVK = methyl vinyl ketone; M = Rh (3), Ir (4)) and (SIr,RC)- [(η5-C5Me5)Ir(PROPHOS)(EVK)][SbF 6]2 (EVK = ethyl vinyl ketone (5)) have been isolated and characterized by analytical and spectroscopic means, including the determination of the crystal structure of the iridium complexes 4 and 5 by X-ray diffractometric methods. Structural parameters indicate that the dispositions of the coordinated dienophiles are controlled by the CH/π attractive interactions established between a phenyl group of the PROPHOS ligand and the α-vinyl proton of the ketones. Proton NMR parameters indicate that these interactions are maintained in solution. From these data, the stereoselectivity of the catalytic reaction is discussed.
- Carmona, Daniel,Viguri, Fernando,Asenjo, Ainara,Lahoz, Fernando J.,García-Ordu?a, Pilar,Oro, Luis A.
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experimental part
p. 4551 - 4557
(2012/08/08)
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