- Organocatalytic asymmetric aldol reaction using protonated chiral 1,2-diamines
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Organic-catalyzed stereoselective reactions have gained attention because they avoid the problems associated with metal catalysts, but existing catalysts based on proline have limitations. Therefore, (R,R)-(+)-1,2-diphenylethylenediamine (DPEN) was select
- Shim, Jae Ho,Kim, Min-Joon,Lee, Ji Yeon,Kim, Kyoung Hoon,Ha, Deok-Chan
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supporting information
(2020/08/14)
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- Stable ruthenium olefin metathesis catalysts bearing symmetrical NHC ligands with primary and secondary: N -alkyl groups
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Four novel stable Hoveyda-Grubbs-type catalysts containing N,N′-dineopentyl- and N,N′-dicyclohexyl-substituted N-heterocyclic carbene (NHC) ligands with syn and anti phenyl groups on the ring backbone were synthesized and fully characterized. The catalytic potential of these complexes was investigated in metathesis reactions of both standard and renewable substrates. Compared to the Hoveyda-Grubbs second generation catalyst (HGII), all of the new catalysts showed high performances in most of the examined metathesis transformations. In particular, N,N′-dicyclohexyl catalysts gave improved results in the challenging ring-closing metathesis (RCM) reaction to form tetrasubstituted olefins, while catalysts with neopentyl N-groups were found to be more active and Z-selective in cross-metathesis (CM) reactions. Modest enantioselectivities in the asymmetric ring-closing metathesis (ARCM) of achiral trienes with different steric hindrance were observed in the presence of catalysts bearing chiral C2-symmetric NHC ligands.
- Ambrosio, Chiara,Paradiso, Veronica,Costabile, Chiara,Bertolasi, Valerio,Caruso, Tonino,Grisi, Fabia
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p. 6615 - 6627
(2018/05/23)
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- Expanding the Family of Hoveyda-Grubbs Catalysts Containing Unsymmetrical NHC Ligands
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A series of Hoveyda-Grubbs second-generation catalysts containing N-alkyl/N′-aryl N-heterocyclic carbene (NHC) ligands were synthesized and investigated in representative olefin metathesis reactions. Steric perturbations of unsymmetrical NHCs were achieved through modulation of the hindrance of alkyl (neopentyl, neophyl, cyclohexyl) and aryl (2-isopropylphenyl, mesityl) substituents at the nitrogen atoms in combination with different backbone configurations (syn and anti). The NHC substitution patterns strongly influence the stability and reactivity of the corresponding complexes. In general, complexes bearing an anti NHC backbone are more stable and more active than their corresponding syn isomers. In both the series, the presence of bulky, highly branched N-alkyl groups tends to give reduced catalytic differences between syn and anti isomers, whereas the nature of the N′-aryl substituent (2-isopropylphenyl or mesityl) gives rise to different activity and/or selectivity. Of note, an N′-mesityl catalyst with anti backbone was found to be highly competent in the ethenolysis of ethyl oleate, achieving up to 90% selectivity for the formation of terminal olefins.
- Paradiso, Veronica,Bertolasi, Valerio,Costabile, Chiara,Caruso, Tonino,D?browski, Micha?,Grela, Karol,Grisi, Fabia
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p. 3692 - 3708
(2017/10/13)
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- Asymmetric Hydroazidation of Nitroalkenes Promoted by a Secondary Amine-Thiourea Catalyst
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Chiral β-nitro azides are obtained by asymmetric addition of azides to nitroalkenes, with an enantioselectivity of up to 82% ee. The reaction, promoted by an easily accessible secondary amine-thiourea catalyst, is performed with azidotrimethylsilane in th
- Bellavista, Tiziana,Meninno, Sara,Lattanzi, Alessandra,Della Sala, Giorgio
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p. 3365 - 3373
(2015/11/03)
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- Novel olefin metathesis ruthenium catalysts bearing backbone-substituted unsymmetrical NHC ligands
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Stable Ru-based catalysts containing unsymmetrical N-heterocyclic carbene (NHC) ligands with phenyl substituents on the backbone in syn and anti stereochemical relationships have been easily prepared and fully characterized. Preliminary investigation reve
- Paradiso, Veronica,Bertolasi, Valerio,Grisi, Fabia
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supporting information
p. 5932 - 5935
(2015/02/19)
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- Asymmetric synthesis of trisubstituted tetrahydrothiophenes bearing a quaternary stereocenter via double michael reaction involving dynamic kinetic resolution
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The stereoselective synthesis of highly functionalized tetrahydrothiophenes bearing three contiguous stereocenters, one of them quaternary, can be achieved by reacting trans-α-cyano-α,β-unsaturated ketones and trans-tert-butyl 4-mercapto-2-butenoate in the presence of a readily available amine thiourea. The products are obtained in high yield, good diastereoselectivity, and excellent enantioselectivity. The overall formation of tetrahydrothiophenes occurs via a cascade double Michael reaction involving a highly efficient process of dynamic kinetic resolution.
- Meninno, Sara,Croce, Gianluca,Lattanzi, Alessandra
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supporting information
p. 3436 - 3439
(2013/07/26)
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