Enantioselective Reduction of Ketones and Imines Catalyzed by (CN‐Box)Re<sup>V</sup>–Oxo Complexes

Nolin, Kristine A.; Ahn, Richard W.; Kobayashi, Yusuke; Kennedy‐Smith, Joshua J.; Toste, F. Dean

doi:10.1002/chem.201001164

Cited by 96 publications

(45 citation statements)

References 77 publications

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“…10b The remaining ligands were synthesized from their respective chiral aminoalcohols using the procedure reported by Evans and co-workers. 28,29 The aminoalcohols were prepared either from the reduction of the commercially available amino acid 30 or following Sharpless’ asymmetric aminohydroxylation method 31,32 from the corresponding substituted styrene. The substituted styrene was either commercially available or was readily prepared using the procedure reported by Denmark and Butler.…”

Section: Methodsmentioning

confidence: 99%

Mechanistic Analysis and Optimization of the Copper-Catalyzed Enantioselective Intramolecular Alkene Aminooxygenation

2012

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The catalytic asymmetric aminooxygenation of alkenes provides an efficient and straightforward approach to prepare chiral vicinal amino alcohols. We have reported a copper(II)-catalyzed enantioselective intramolecular alkene aminooxygenation, using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) as the oxygen source, which results in the synthesis of chiral indolines and pyrrolidines. Herein we disclose that kinetics studies indicate the reaction is first order both in substrate and the [Cu(R,R)-Ph-bis(oxazoline)]OTf2 catalyst, and zero order in TEMPO. Furthermore, kinetic isotope effect studies support that the cis aminocupration step, the addition of N-Cu across the alkene, is the rate-limiting step. Subsequent formation of a carbon radical intermediate, and direct carbon radical trapping with TEMPO is the indicated mechanism for the C-O bond formation as suggested by a deuterium labeling experiment. A ligand screen revealed that C(4)-phenyl substitution on the bis(oxazoline) is optimal for high asymmetric induction. The size of the substrate’s N-sulfonyl group also influences the enantioselectivity of the reaction. The preparative scale catalytic aminooxygenation reaction (gram scale) was demonstrated and an unexpected dependence on reaction temperature was uncovered on the larger scale reaction.

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Section: Methodsmentioning

confidence: 99%

Mechanistic Analysis and Optimization of the Copper-Catalyzed Enantioselective Intramolecular Alkene Aminooxygenation

2012

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“…[16] In particular,a part from homogeneous catalysis, [17] significant protocols for the reductiono fa romatic heterocyclic compounds such as quinolines,i ncluding heterogeneous catalytic systems have been developed. [25][26][27][28][29][30] To the best of our knowledge,t here is no study reported on the selective reductiono fa zines to the corresponding benzylh ydrazonesc atalyzed by silver nanoparticles (AgNPs), however, only two reportsa re recorded using magnesium in methanol, andp alladium on carbon in the presence of ethanolicH Cl, leading to the formation of the fully reduced product 1,2-dibenzylhydrazine (Scheme 1a). On the other hand, regarding the reduction of acyclic conjugated imines or 1-azadiene analogues,t here are only ah andful of examples to display the regioselective reductiono ft he C=Nb ond, catalyzed by Re-oxo complexeso rA uNPores in the presence of boron/aluminum hydrides or hydrosilanes.…”

Section: Introductionmentioning

confidence: 99%

Selective Reduction of Azines to Benzyl Hydrazones with Sodium Borohydride Catalyzed by Mesoporous Silica‐Supported Silver Nanoparticles: A Catalytic Route towards Pyrazole Synthesis

et al. 2017

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Thec atalytic activity of supported silver nanoparticles on mesoporous silica was studied, for the selectiver eduction of azines into benzyl hydrazones using sodium borohydride as mild reducing agent. Different sizes of silver nanoparticles supported on mesoporous silica (Ag/HMS) were successfully prepared by two methods,i .e., wet impregnationf ollowed by reductionw ith hydrogena t3 50 8 8Ca nd in situ deposition/reduction with am ixture of amines (ethanolamine and ethylenediamine).T he Ag/HMS (amines) catalyst was found to promote the selective 1,2-reduction of aryl-substituted azines, comparedt o the corresponding 1,4-reductiont hat occurs in general reduction processes. This catalytic transfer hydrogenation process found to be clean, fast andq uantitative (> 99% yields and selectivity) towards benzyl hydrazone synthesis under mild conditions.O fg reat importance is that under the presentc atalytic condi-tions reducible functional groups remain intact. Formal kinetics, support the in situ formation of silver hydride species being responsible for the reductionp rocess.T he presence of protic polarm ethanol enhanced the catalytic activity of Ag/HMS. Basedo nt he recycling studies the catalytic system Ag/HMS-NaBH 4 wasf ound to catalyze the selective reductiono fa zines nine times without significant loss of its activity.F inally,ao ne-pot reactionb etween the in situ produced benzylh ydrazones and a series of nitrostyrenes readilyp rovided the regioselective synthesiso f1 ,3,5-subtituted pyrazoles,h ighlightingau seful synthetic application of the catalytic protocol.

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“…N-phosphinyl imines have found a variety of synthetic applications in asymmetric processes [10,24,25]. For instance, the preparation of chiral amines can be achieved by stereoselective reduction of N-phosphinyl ketimines through different synthetic approaches such as hydrogenation [26][27][28], hydrosilylation [29][30][31][32][33], Meerwein-Schmidt-PonndorfVerley (MSPV) reaction [34] or the use of boron [35] and aluminium hydrides [36].…”

Section: Open Accessmentioning

confidence: 99%

Chiral β-Amino Alcohols as Ligands for the Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of N-Phosphinyl Ketimines

2012

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Some chiral β-amino alcohols have been evaluated as potential ligands for the ruthenium-catalyzed asymmetric transfer hydrogenation (ATH) of N-phosphinyl ketimines in isopropyl alcohol. The ruthenium complex prepared from [RuCl 2 (p-cymene)] 2 and (1S,2R)-1-amino-2-indanol has shown to be an efficient catalyst for the ATH of several N-(diphenylphosphinyl)imines, affording the reduction products in very good isolated yields and enantiomeric excesses up to 82%. The inherent rigidity of the indane ring system present in the ligand seems to be very important to achieve good enantioselectivities.

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Enantioselective Reduction of Ketones and Imines Catalyzed by (CN‐Box)Re^V–Oxo Complexes

Cited by 96 publications

References 77 publications

Mechanistic Analysis and Optimization of the Copper-Catalyzed Enantioselective Intramolecular Alkene Aminooxygenation

Mechanistic Analysis and Optimization of the Copper-Catalyzed Enantioselective Intramolecular Alkene Aminooxygenation

Selective Reduction of Azines to Benzyl Hydrazones with Sodium Borohydride Catalyzed by Mesoporous Silica‐Supported Silver Nanoparticles: A Catalytic Route towards Pyrazole Synthesis

Chiral β-Amino Alcohols as Ligands for the Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of N-Phosphinyl Ketimines

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Enantioselective Reduction of Ketones and Imines Catalyzed by (CN‐Box)ReV–Oxo Complexes

Cited by 96 publications

References 77 publications

Mechanistic Analysis and Optimization of the Copper-Catalyzed Enantioselective Intramolecular Alkene Aminooxygenation

Mechanistic Analysis and Optimization of the Copper-Catalyzed Enantioselective Intramolecular Alkene Aminooxygenation

Selective Reduction of Azines to Benzyl Hydrazones with Sodium Borohydride Catalyzed by Mesoporous Silica‐Supported Silver Nanoparticles: A Catalytic Route towards Pyrazole Synthesis

Chiral β-Amino Alcohols as Ligands for the Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of N-Phosphinyl Ketimines

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Enantioselective Reduction of Ketones and Imines Catalyzed by (CN‐Box)Re^V–Oxo Complexes