- Sulfone Group as a Versatile and Removable Directing Group for Asymmetric Transfer Hydrogenation of Ketones
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The sulfone functional group has a strong capacity to direct the asymmetric transfer hydrogenation (ATH) of ketones in the presence of [(arene)Ru(TsDPEN)H] complexes by adopting a position distal to the η6-arene ring. This preference provides a
- Clarkson, Guy J.,Vyas, Vijyesh K.,Wills, Martin
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supporting information
p. 14265 - 14269
(2020/07/04)
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- Enantio- and regioselective epoxidation of olefinic double bonds in quinolones, pyridones, and amides catalyzed by a ruthenium porphyrin catalyst with a hydrogen bonding site
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An array of differently substituted 3-alkenylquinolones was synthesized, and the enantio- and regioselectivity of their Ru-catalyzed epoxidation were studied. A precursor ruthenium(II) complex with a chiral tricyclic γ-lactam skeleton (octahydro-1H-4,7-methanoisoindol-1-one) was available by Sonogashira cross-coupling with a monobromo-substituted ruthenium(II) porphyrin. Enantioselective epoxidation reactions (60-83% yield, 85-98% ee) were achieved with this catalyst, and it was shown that the enantioselectivity depends critically on the presence of a two-point hydrogen bond interaction between the γ-lactam site of the catalyst and the δ-lactam (quinolone) site of the substrate. DFT calculations support the hypothesis that the reaction occurs via a hydrogen-bound transition state, in which the 3-alkenylquinolone adopts an s-trans conformation. The calculations further revealed that this transition state is preferred over a competing s-cis transition state because it exerts less strain in the rigid backbone and because the hydrogen bond interaction is more stable. The catalyst loading required for complete conversion was low (0.2 mol %), and turnover numbers exceeding 4000 were recorded. It was shown that there is little, if any, inhibition of the catalytic process by other quinolones, which could potentially compete with the binding site. A mechanistic model for the catalytic reaction is presented. In accordance with this model 3-alkenylpyridones reacted with similar enantioselectivities as the respective quinolones. The epoxidation products were unstable, however, and the enantiomeric purity (77-87% ee) of the products could be established only after derivatization. Primary alkenoic acid amides also underwent the epoxidation but gave the respective products in lower enantioselectivities (70% and 45% ee), presumably because the enantioface differentiation is hampered by the increased flexibility of the substrates, which exhibit two or three rotatable single bonds between the binding site and the reactive olefinic double bond.
- Fackler, Philipp,Huber, Stefan M.,Bach, Thorsten
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supporting information; body text
p. 12869 - 12878
(2012/09/22)
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- Synthesis of Enantiomerically Pure 2,5-Disubstituted Teterahydrofurans Using Readily Prepared (2S)-1-Phenylsulphonylalkan-2-ols
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Enantiomerically pure (2S)-1-phenylsulphonylalkan-2-ols have been prepared from 1-chloro-3-phenylsulphonylpropan-2-one (2) by the folloving successive procedures: reduction with baker's yeast, epoxidation with silver(I) oxide, and alkylation with
- Tanikaga, Rikuhei,Hosoya, Ken,Kaji, Aritsune
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p. 1799 - 1804
(2007/10/02)
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- Reactions of (2S)-1-Arenesulfonyl-2-alkanol Dianions with Aldehydes. Application to the Synthesis of Enantiomerically Pure (3S)-1-Alken-3-ols and (2E,4S)-4-hydroxy-2-alkenenitriles
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Enantiomerically pure (2S)-1-arenesulfonyl-2-alkanols (1) were prepared by yeast reduction of 1-arenesulfonyl-3-chloro-2-propanones, followed by epoxydation and alkylation.Reaction of dianions of 1 with aldehydes occurred at the pro(R) position of C(1) to give 1,3-diols, which were converted to (3S)-1-alken-3-ols or (2E,4S)-4-hydroxy-2-alkenenitriles in 100percent e.e.
- Tanikaga, Rikuhei,Hosoya, Ken,Kaji, Aritsune
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p. 829 - 832
(2007/10/02)
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- Synthesis of Enantiomerically Pure (4S)-2-Alken-4-olides via (2S)-1-Phenylsulfonyl-2-alkanols
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Reduction of 1-chloro-3-phenylsulfonyl-2-propanone with baker's yeast, followed by epoxidation and alkylation with Grignard reagents, yields enantiomerically pure (2S)-2-phenylsulfonyl-2-alkanols, which are converted into (4S)-2-alken-4-olides in 100perce
- Tanikaga, Rikuhei,Hosoya, Ken,Kaji, Aritsune
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p. 389 - 390
(2007/10/02)
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- Ready Nucleophilic Ring Opening of β-Epoxy-sulphone, -sulphoxide, and -ester with Grignard Reagents
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Treatment of β-epoxy-sulphone, -sulphoxide, and -ester with Grignard reagents and copper(I) iodide in diethyl ether-tetrahydrofuran at low temperature leads to rapid ring opening without loss of chirality.
- Tanikaga, Rikuhei,Hosoya, Ken,Kaji, Aritsune
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p. 836 - 837
(2007/10/02)
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