New Developments in Enantioselective Brønsted Acid Catalysis: Chiral Ion Pair Catalysis and Beyond

Rueping, Magnus; Sugiono, Erli

doi:10.1007/2789_2008_085

Cited by 4 publications

(3 citation statements)

References 152 publications

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“…The difference may explain why many substrates were successfully reduced in high yield and ee before the timeframe of this review. Nevertheless, the reduction of endocyclic imines is considered important because they are intermediates for many pharmaceutical drugs and natural products 1n,2e. The reduction of exocyclic imines is considered more difficult and reviewed in the following sections.…”

Section: Asymmetric Imine Oxime and Hydrazone Reductionmentioning

confidence: 99%

Chiral Amine Synthesis – Recent Developments and Trends for Enamide Reduction, Reductive Amination, and Imine Reduction

2010

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The review examines the chiral amine literature from 2000–2009 (May) concerning enantioselective and diastereoselective methods for N‐acylenamide and enamine reduction, reductive amination, and imine reduction. The reaction steps for each strategy, from ketone to primary chiral amine, are clearly defined, with best methods and yields for starting material preparation and final deprotection noted. Categories of chiral amines have been defined in Section 1 to allow the reader to quickly understand whether their specific target amine falls within a difficult to synthesize, or not, structural class. Amino acids are not considered in this work.

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Section: Asymmetric Imine Oxime and Hydrazone Reductionmentioning

confidence: 99%

Chiral Amine Synthesis – Recent Developments and Trends for Enamide Reduction, Reductive Amination, and Imine Reduction

2010

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“…Whereas in metal-catalyzed reactions the activation of the carbonyl or imine group is achieved through coordination to Lewis acids, the basis of organocatalytic methodologies lies either in protonation through chiral Brønsted acids or in hydrogen-bond activation by chiral small-molecule H-bond donor catalysts. [83] Chiral thioureas [84] thus induce enantioselectivity in the nucleophilic addition to the cationic electrophile through hydrogen-bond formation, whereas optically active phosphoric acids or dicarboxylic acids, [85] as well as N-triflylphosphoramides, [86] act as proton donors. Although there are a good number of reports on asymmetric organocatalytic reactions involving intermediary iminium ions (in both inter-and intramolecular processes) [87] and N-acyliminium ions in intermolecular processes, [88] intramolecular α-amidoalkylation reactions with π-electrophiles, and specifically with aromatic and heteroaromatic rings, are still limited to a few examples that take advantage of both activation methods, using chiral Brønsted acids, such as BINOL-derived phosphoric acids or trifylphosphoramides, together with thioureas.…”

Section: Enantioselective α-Amidoalkylation Reactionsmentioning

confidence: 99%

“…[82][83][84][85][86][87][88] Generally, the key to achieving enantioselective catalysis with a chiral Brønsted acid is interaction between a cationic intermediate (protonated substrate) and the chiral conjugate base. The organic transformations thus take place in a chiral environment created by the chiral conjugated base.…”

Section: Enantioselective α-Amidoalkylation Reactionsmentioning

confidence: 99%

Strategies Based on Aryllithium and N‐Acyliminium Ion Cyclizations for the Stereocontrolled Synthesis of Alkaloids and Related Systems

et al. 2011

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The intramolecular α-amidoalkylation reactions of aromatic and heteroaromatic ring systems constitute a versatile approach for the synthesis of nitrogen heterocyles in a diastereoselective or enantioselective fashion. On the other hand, the intramolecular reactions of aryllithium compounds have also been extensively used in the synthesis of carbocycles and heterocycles. The use of imides as internal electrophiles is particularly attractive because of the potential to introduce diverse functionality into the cyclized products by subjecting the resulting α-hydroxylactams to intermolecular IntroductionAryllithium compounds and N-acyliminium ions are extremely versatile intermediates for the formation of carboncarbon bonds in organic synthesis. Cyclization of aryllithium compounds generated by halogen/lithium exchange with internal electrophiles (Parham cyclization) has become a valuable protocol for the stereoselective construction of carbocyclic and heterocyclic systems.[1] Many electrophiles remain inert during halogen/metal exchange reaction at low temperature, but are reactive enough to participate in a subsequent cyclization reaction. Halides, epoxides, or alkenes [2] are thus among the different types of internal electrophiles used in the Parham cyclization. When the internal electrophile is a carboxylate derivative, this anionic cyclization could be considered an anionic Friedel-Crafts equivalent, with the advantage that it lacks the electronic requirements of the classical reaction. Although it is possible to use carboxylic acids [3] or esters, [4] carbamates have proven to be much more effective internal electrophiles in Parham cycliacylations.[5] Amides are also useful electrophiles in Parham cyclizations, and it has been reported that in some cases there is an influence of the natures of the substituents at the nitrogen atom on the course of the cyclization reaction. [6,7] [a] Departamento In connection with our interest in aromatic lithiation, we have developed an anionic cyclization approach directed towards the construction of the pyrrolo[1,2-b]isoquinolone core based on N-(o-halobenzyl)pyrrole-2-carboxamides, showing that Weinreb amides and morpholine amides function as excellent internal electrophiles.[8] This observation could be explained by assuming that halogen/lithium exchange could be favored by a complex-induced proximity effect (CIPE).[9] This concept has been invoked to explain other metal/metal, hydrogen/metal, or halogen/metal [10] exchange reactions. Lithium/halogen exchange would thus be favored first by coordination of the inducing organolithium compound with amide or carbamate groups, and then by stabilization of the resulting aryllithium compound. The better behavior of Weinreb and morpholine amides relative to N,N-diethyl amides could be attributed to the extra stabilization of the intermediate generated after cyclization through the formation of an internal chelate. The scope of these Parham-type cyclizations has been extended to the formation of seven-and eight-membered rings [8b] ...

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ChemInform Abstract: New Developments in Enantioselective Bronsted Acid Catalysis: Chiral Ion Pair Catalysis and Beyond

Rueping

Sugiono

2009

ChemInform

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New Developments in Enantioselective Brønsted Acid Catalysis: Chiral Ion Pair Catalysis and Beyond

Cited by 4 publications

References 152 publications

Chiral Amine Synthesis – Recent Developments and Trends for Enamide Reduction, Reductive Amination, and Imine Reduction

Chiral Amine Synthesis – Recent Developments and Trends for Enamide Reduction, Reductive Amination, and Imine Reduction

Strategies Based on Aryllithium and N‐Acyliminium Ion Cyclizations for the Stereocontrolled Synthesis of Alkaloids and Related Systems

ChemInform Abstract: New Developments in Enantioselective Bronsted Acid Catalysis: Chiral Ion Pair Catalysis and Beyond

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