Asymmetrische Gegenanion‐vermittelte Katalyse

A synergistic effect is observed for the combination of a neutral dinuclear gold complex with a chiral silver phosphate in the intramolecular hyroalkoxylation of allenes to give furan derivatives in high yields and enantioselectivities. The monocationic dinuclear gold complex affords higher catalytic activity and enantioselectivity than the neutral or dicationic digold complexes. The synergistic effect is thus highly promising to provide a guiding principle in designing an efficient chiral environment for creating an asymmetric catalyst.Keywords: asymmetric activation; chiral anion; chirality control; gold catalyst; hydroalkoxylation; synergistic effectRegarding new frontiers of asymmetric catalyst systems, a variety of highly efficient chiral ligands have been developed that dramatically increase the catalytic activity and enantioselectivity.[1] An asymmetric catalyst is usually constructed by a proper combination of chiral ligand and central metal. An asymmetric catalyst can be further evolved into a more activated catalyst to give higher catalytic activity and enantioselectivity with a chiral activator as an additional chiral source; for this process, we have previously coined the term asymmetric activation.[2] A synergistic effect has been observed where the matched pair with the additional chiral source (R or S) can lead to higher catalytic activity and enantioselectivity than the mismatched one (S or R).Recently, highly efficient asymmetric catalyst systems based on chiral anions, [3] especially those with a binaphthyl backbone, have been reported to induce high levels of enantioselectivity. [4,5,6] List defined the concept as asymmetric counteranion-directed catalysis (ACDC) in a general strategy for asymmetric catalysis.[5] The catalytic systems through the combination of chiral or achiral amines and chiral phosphate anions have been developed in transfer hydrogenation, [5a,b] allylation, [5c] and epoxidation [5d-f] with highto-excellent yield and enantioselectivity. As another important breakthrough, Toste and co-workers have also developed the chiral anion strategy for asymmetric transition metal catalysis for highly enantioselective hydroamination, [6] hydroalkoxylation, [6] and hydrocarboxylation [6a] reactions of allenic fragments by a gold catalyst bearing both chiral or achiral diphosphine ligand and chiral phosphate anion.On the other hand, we have found that the axial chirality of gold complexes bearing tropos BIPHEP ligands [BIPHEP = bis(phosphanyl)biphenyl], [7] which are highly modular, versatile, and easy to synthesize without enantiomer resolution, could be controlled by the phosphate and the corresponding N-triflyl phosphoramide as chiral anions (Scheme 1).[8] The axial chirality of BIPHEP-(AuCl) 2 complexes could also be memorized due to the Au À Au contact even after the dissociation of chiral anions. Treatment of the enantiopure BIPHEP-(AuCl) 2 complexes with two equivalents of Ag salt thus facilitated the intramolecular hydroamination of allenes as an atropos asymmetric...

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“…[4,5,6] List defined the concept as asymmetric counteranion-directed catalysis (ACDC) in a general strategy for asymmetric catalysis.…”

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confidence: 99%

Synergistic Effect: Hydroalkoxylation of Allenes through Combination of Enantiopure BIPHEP‐Gold Complexes and Chiral Anions

2010

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“…For example, electron-poor, sterically hindered, or long alkyl substituted sulfides are often converted with lower selectivity or yield. [6][7][8] Recently, on the basis of our concept of asymmetric counteranion-directed catalysis (ACDC), [9][10][11] we reported a highly enantioselective Jacobsen-Katsuki-type epoxidation reaction catalyzed by an ion-pair consisting of an achiral MnA C H T U N G T R E N N U N G (III)-salen cation and a chiral phosphate counteranion. [12] Now we have discovered and report here a new ironA C H T U N G T R E N N U N G (III)-salen based ion-pair catalyst for the highly chemoselective and enantioselective oxidation of sulfides.…”

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confidence: 99%

“…Remarkably, elevated levels of chemo-and enantioselectivity (up to 98:2 er) were observed with relatively electron-poor sulfides (entries [6][7][8][11][12][13][14]. Sulfides with longer or branched alkyl groups can also be oxidized with generally good enantioselectivity (entries 9,10,[12][13][14]. The chemoselectivity (sulfoxide vs. sulfone) is generally high but can be further improved simply by stopping the reaction at around 90% conversion or by using less than one equivalent of the oxidant.…”

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Asymmetric Counteranion‐Directed Iron Catalysis: A Highly Enantioselective Sulfoxidation

Liao

List

2012

Adv Synth Catal

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A highly active and enantioselective ion-pair sulfoxidation catalyst, consisting of an achiral iron(III)-salen cation and a chiral phosphate counteranion, mediates the oxidization of various sulfides with high yields and enantioselectivities. The enantioselectivities observed, especially for electron-poor substrates, represent the best results so far in manganese and iron-salen systems. This work represents the first application of our concept of asymmetric counteranion-directed catalysis (ACDC) to iron catalysi

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“…[7] This approach uses an alkylphosphine as the Lewis base to initiate the Michael step and a separate bifunctional chiral borate salt as the medium to confer good enantioselectivity via a counterion strategy [8] and H-bonding interactions. [9] These two catalytic models taken together raised the possibility of developing a trifunctional organocatalyst [10] for the azaMBH reaction with motifs of Lewis nucleophilicity, a Brønsted base for ion pairing, and a Brønsted acid for H-bonding interactions all incorporated into one chiral platform (Figure 1 a).…”

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Enantioselective Trifunctional Organocatalysts for Rate‐ Enhanced Aza‐Morita–Baylis–Hillman Reactions at Room Temperature

2009

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A Brønsted acid-activated trifunctional organocatalyst, based on the BINAP scaffold, was used for the first time to catalyze aza-MoritaBaylis-Hillman reactions between N-tosylimines and methyl vinyl ketone with fast reaction rates and good enantioselectivity at room temperature. This trifunctional catalyst, containing a Lewis base, a Brønsted base, and a Brønsted acid, required acid activation to confer its enantioselectivity and rate improvement for both electron-rich and electrondeficient imine substrates. The role of the amino Lewis base of 1a was investigated and found to be the activity switch in response to an acid additive. The counterion of the acid additive was found to influence not only the excess ratio but also the sense of asymmetric induction.

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Asymmetrische Gegenanion‐vermittelte Katalyse

Cited by 205 publications

References 31 publications

Synergistic Effect: Hydroalkoxylation of Allenes through Combination of Enantiopure BIPHEP‐Gold Complexes and Chiral Anions

Synergistic Effect: Hydroalkoxylation of Allenes through Combination of Enantiopure BIPHEP‐Gold Complexes and Chiral Anions

Asymmetric Counteranion‐Directed Iron Catalysis: A Highly Enantioselective Sulfoxidation

Enantioselective Trifunctional Organocatalysts for Rate‐ Enhanced Aza‐Morita–Baylis–Hillman Reactions at Room Temperature

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