Rhodium‐Catalyzed Asymmetric Hydrogenation of Unprotected NH Imines Assisted by a Thiourea

Zhao, Qingyang; Wen, Jialin; Tan, Renchang; Huang, Kexuan; Metola, Pedro; Wang, Rui; Anslyn, Eric V.; Zhang, Xumu

doi:10.1002/anie.201404570

Cited by 126 publications

(52 citation statements)

References 71 publications

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“…31 The corresponding chiral amines products were obtained in high yields and enantioselectivities. We proposed that the anion-binding interaction between the thiourea and chloride counterion played a crucial role in the catalytic system based on the control experiments and 1 H NMR studies.…”

Section: Xumu Zhangmentioning

confidence: 99%

Metalorganocatalysis: cooperating transition-metal catalysis and organocatalysis through a covalent bond

Dong

Zhao

et al. 2015

Org. Chem. Front.

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Asymmetric catalysis has grown rapidly and made considerable progress in last decades, but there still remain significantly unachievable reactions through either organocatalysis or transition-metal catalysis alone. The concept of combination transition-metal catalysis with organocatalysis was emerged as a powerful strategy for developing asymmetric catalysis, and has attracted great attention. In order to avoid the incompatibility existing in catalysts, substrates, intermediates and solvents through combining transition-metal catalysis and organocatalysis, it is urgently necessary to develop a new catalytic strategy to resolve these problems. Therefore, we are devoted to design a series of novel bifunctional catalysts based upon the synergistic activation strategy via cooperating transition metal-catalysis and organocatalysis through a covalent bond forming a bifunctional molecule. In this critical review, this momentous strategy is illustrated with several recent outstanding examples and prospectively promising application, with the aim of elaborating the synthetic utilities and potentialities of this concept as a powerful tool in organic synthesis.

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Section: Xumu Zhangmentioning

confidence: 99%

Metalorganocatalysis: cooperating transition-metal catalysis and organocatalysis through a covalent bond

Dong

Zhao

et al. 2015

Org. Chem. Front.

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“…[10] Ap ractical and commonly applied method to access oxocarbenium ions is the elimination of al eaving group.I nt his equilibrium, if the leaving anion could be trapped by another molecule by molecular recognition, the formation of oxocarbenium ions would be favored. We recently developed ab ifunctional ligand, ZhaoPhos, [11] aiming to incorporate athiourea moiety on ab isphosphine ligand to render as econdary interaction with as ubstrate.A nion binding by thiourea with substrates assists to achieve high efficiencies and high enantioselectivities in homogeneous hydrogenation of cationic C=Nb onds present in iminium, [12] (iso)quinolinium, [13] and indolinium ions. [14] We envisioned that this type of highly reactive intermediate could be captured by thiourea [15] and be reduced by metal hydride complexes in an ionic hydrogenation manner.…”

Section: Introductionmentioning

confidence: 99%

Iridium‐Catalyzed Enantioselective Hydrogenation of Oxocarbenium Ions: A Case of Ionic Hydrogenation

et al. 2020

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Ionic hydrogenation has not been extensively explored, but is advantageous for challenging substrates such as unsaturated intermediates. Reported here is an iridium‐catalyzed hydrogenation of oxocarbenium ions to afford chiral isochromans with high enantioselectivities. A variety of functionalities are compatible with this catalytic system. In the presence of a catalytic amount of the Brønsted acid HCl, an α‐chloroether is generated in situ and subsequentially reduced. Kinetic studies suggest first‐order kinetics in the substrate and half‐order kinetics in the catalyst. A positive nonlinear effect, together with the half kinetic order, revealed a dimerization of the catalyst. Possible reaction pathways based on the monomeric iridium catalyst were proposed and DFT computational studies revealed an ionic hydrogenation pathway. Chloride abstraction and the cleavage of dihydrogen occur in the same step.

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“…[8a] If ac arbocation could be stabilized by either adjacent heteroatoms or substituents and therefore exist in considerable concentration,t he feasibility of being captured and subsequently reduced by am etal hydride would create an opportunity to form as tereogenic center.T his strategy offersa na lternative approacht op reparing chiral acetals by asymmetric hydrogenation.F ortunately,o ur group hasr ecently developed at hiourea-containing bis-phosphine ligand, ZhaoPhos, [9] which has the potential to bind with ionic substrates throughh ydrogen bonding. This catalytic system tolerates acidic conditions, [10] and has been successfully applied in the asymmetrich ydrogenation of imines, [11] quinolines/isoquinolines, [12] indoles, [10] and conjugated olefins. [13] Guided by these rationales, we envisioned that this catalytic system has the potential to achieve the asymmetric hydrogenation of cationic sp 2 carbon atoms to generate chiral acetal compounds.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Hydrogenation of Cationic Intermediates for the Synthesis of Chiral N,O‐Acetals

Sun

Zhao

Wang

et al. 2020

Chemistry A European J

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For over half a century, transition‐metal‐catalyzed homogeneous hydrogenation has been mainly focused on neutral and readily prepared unsaturated substrates. Although the addition of molecular hydrogen to C=C, C=N, and C=O bonds represents a well‐studied paradigm, the asymmetric hydrogenation of cationic species remains an underdeveloped area. In this study, we were seeking a breakthrough in asymmetric hydrogenation, with cationic intermediates as targets, and thereby anticipating applying this powerful tool to the construction of challenging chiral molecules. Under acidic conditions, both N‐ or O‐acetylsalicylamides underwent cyclization to generate cationic intermediates, which were subsequently reduced by an iridium or rhodium hydride complex. The resulting N,O‐acetals were synthesized with remarkably high enantioselectivity. This catalytic strategy exhibited high efficiency (turnover number of up to 4400) and high chemoselectivity. Mechanistic studies supported the hypothesis that a cationic intermediate was formed in situ and hydrogenated afterwards. A catalytic cycle has been proposed with hydride transfer from the iridium complex to the cationic sp2 carbon atom being the rate‐determining step. A steric map of the catalyst has been created to illustrate the chiral environment, and a quantitative structure–selectivity relationship analysis showed how enantiomeric induction was achieved in this chemical transformation.

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Rhodium‐Catalyzed Asymmetric Hydrogenation of Unprotected NH Imines Assisted by a Thiourea

Cited by 126 publications

References 71 publications

Metalorganocatalysis: cooperating transition-metal catalysis and organocatalysis through a covalent bond

Metalorganocatalysis: cooperating transition-metal catalysis and organocatalysis through a covalent bond

Iridium‐Catalyzed Enantioselective Hydrogenation of Oxocarbenium Ions: A Case of Ionic Hydrogenation

Asymmetric Hydrogenation of Cationic Intermediates for the Synthesis of Chiral N,O‐Acetals

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