Enantioselective Brønsted Acid Catalyzed Transfer Hydrogenation:  Organocatalytic Reduction of Imines

Rueping, Magnus; Sugiono, Erli; Azap, Cengiz; Theissmann, Thomas; Bolte, Michael

doi:10.1021/ol0515964

Cited by 474 publications

(245 citation statements)

References 25 publications

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“…For Type I Z reactions the correct catalyst is dependent on the nature of the imine and nucleophile. Reactions involving acyclic imines require a catalyst that has large proximal sterics to disfavor Type II pathways and small AREA(θ) to disfavor competing Type I E pathway 6, 7, 14b, 23, 54, 55, 56, 57, 58, 59, 60. If the imine is cyclic, the optimal catalyst is dependent on the nature of the nucleophile.…”

Section: Resultsmentioning

confidence: 99%

Selecting Chiral BINOL‐Derived Phosphoric Acid Catalysts: General Model To Identify Steric Features Essential for Enantioselectivity

Reid

Goodman

2017

Chemistry A European J

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Choosing the optimal catalyst for a new transformation is challenging because the ideal molecular requirements of the catalyst for one reaction do not always simply translate to another. Large groups at the 3,3′ positions of the binaphthol rings are important for efficient stereoinduction but if they are too large this can lead to unusual or poor results. By applying a quantitative steric assessment of the substituents at the 3,3′ positions of the binaphthol ring, we have systematically studied the effect of modulating this group on enantioselectivity for a wide range of reactions involving imines, and verified this analysis using ONIOM calculations. We have shown that in most reactions, the stereochemical outcome depends on both proximal and remote sterics. Summarising detailed calculations into a simple qualitative model identifies and explains the steric features required for high selectivity. This model is consistent with seventy seven papers reporting reactions (over 1000 transformations in total), and provides a straightforward decision tree for selecting the best catalyst.

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Section: Resultsmentioning

confidence: 99%

Selecting Chiral BINOL‐Derived Phosphoric Acid Catalysts: General Model To Identify Steric Features Essential for Enantioselectivity

Reid

Goodman

2017

Chemistry A European J

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“…[12][13][14][15][16][17] Recently some fascinating reports on asymmetric imine reduction using substituted chiral binaphthyl hydrogen phosphate as catalyst were reported by List (5h), [18] and Rueping (5g). [19] Extensive [20] and Kočovský [21] using trichlorosilane and a Lewis base organocatalyst. However, only MacMillan et al (5i) [22] have reported the synthesis of enantioselective amines via reductive amination using an ortho-triphenylsilyl variant of the Terada-Akiyama catalyst.…”

Section: Introductionmentioning

confidence: 99%

Single Nucleotide‐Catalyzed Biomimetic Reductive Amination

2010

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Abstract:We have successfully developed a single nucleotide (adenosine 5'-diphosphate)-catalyzed enantioselective direct reductive amination of aldehydes and ketones using a Hantzsch ester as reducing agent. The process is a simple, efficient and a real mimic of the NADH reduction approach for the synthesis of structurally diverse amines. This reaction is the first report demonstrating the ability of a single nucleotide as catalyst and one of the most genuine biomimetic reactions of organic chemistry.

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“…Figure 2b shows metal-free organocatalysts. These depend on strong imine activation by protonation, which allows use of weaker nucleophiles such as the Hantzsch ester [30][31][32][33] . Recently, strong Brønsted-acid activation and organometallic hydride catalysis have been combined 34,35 .…”

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confidence: 99%

Imine hydrogenation with simple alkaline earth metal catalysts

et al. 2018

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W ith molecular hydrogen being one of the cleanest reducing agents, catalytic hydrogenation using the more noble transition metals is among the most studied of all chemical processes 1 . Increasing social pressure towards a sustainable society, however, dictates replacement of costly, and often harmful, precious metals by more abundant first-row transition metals or even biocompatible redox inactive main group metals [2][3][4][5][6] . The alkaline earth metal calcium does not possess partially filled d orbitals for substrate activation, but has recently shown catalytic activities in the hydrogenation of C= C double bonds with molecular H 2 (ref. 7 ). Although restricted to conjugated C= C bonds, this example strikingly broke the dogma that transition metals are needed for alkene hydrogenation. This was followed by the development of metal-free frustrated Lewis pair (FLP) catalysts [8][9][10][11] and, most recently, cationic calcium hydride catalysts that are also able to hydrogenate unactivated alkenes 12 . Figure 1a shows a working hypothesis for styrene hydrogenation with a dibenzylcalcium catalyst (CaBn 2 ) 7 . The first step is the generation of a calcium hydride species, for which ample precedence exists [13][14][15][16][17] . Further reaction with H 2 may cause precipitation of insoluble (CaH 2 ) n , but catalyst loss is partly prevented by aggregation to soluble but undefined Ca x Bn y H z species. Despite a lack of d orbitals, alkene activation proceeds through a weak electrostatic calciumalkene interaction, recently shown to be of importance in calcium catalysis 18 . The benzylic calcium intermediate formed after insertion may, after successive styrene insertions, form polystyrene 19 , but high H 2 pressure (20-100 bar) can prevent this side reaction by promoting σ-bond metathesis. The latter step in the cycle is, like the initiation reaction, formally a deprotonation of H 2 by a resonance-stabilized benzylic carbanion. Considering the high pK a of H 2 (≈ 49) 20 , this reaction seemed questionable. Stoichiometric conversions of model systems, however, underscored the feasibility of this pathway 7 . Independent theoretical calculations illustrate that the final σ-bond metathesis step is indeed highly endergonic: Gibbs free energy of activation Δ G ‡ (60 °C, 20 bar) = 25.7 kcal mol −1 (ref. 21 ).As the highly atom-efficient catalytic reduction of imines by H 2 received much less attention than alkene or ketone hydrogenation [22][23][24] , it remained an important question whether calcium-catalysed hydrogenation can be extended to imine reduction. Current stateof-the-art imine hydrogenation catalysts can be divided into four categories that vary in terms of substrate activation and nucleophilic power ( Fig. 2a-d). Figure 2a shows organometallic metal hydrides that rely on hydride nucleophilicity. Apart from few early transition metal catalysts (Ti 25 , lanthanides 26 ), these are generally based on late transition metals (Rh, Ir) 22 . The aluminium hydride compound (iso-butyl) 2 AlH is an odd example of a ...

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Enantioselective Brønsted Acid Catalyzed Transfer Hydrogenation: Organocatalytic Reduction of Imines

Cited by 474 publications

References 25 publications

Selecting Chiral BINOL‐Derived Phosphoric Acid Catalysts: General Model To Identify Steric Features Essential for Enantioselectivity

Selecting Chiral BINOL‐Derived Phosphoric Acid Catalysts: General Model To Identify Steric Features Essential for Enantioselectivity

Single Nucleotide‐Catalyzed Biomimetic Reductive Amination

Imine hydrogenation with simple alkaline earth metal catalysts

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