Hydride Abstraction from η<sup>3</sup>-Allylic Molybdenum Complexes Exploring Various Diaryl Carbenium Ion Precursors. A Study toward Enantioselective Hydride Abstraction

Bjurling, Emelie; Berg, Ulf; Andersson, Carina

doi:10.1021/om011016g

Cited by 10 publications

(3 citation statements)

References 20 publications

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“…The development of new catalytic motifs remains a frontline in the evolution of asymmetric catalysis . Since the discovery of the first trityl cation in 1901, stable carbocations have been actively pursued as conceptually attractive organic Lewis acid catalysts. − However, progress along this line has been rather slow, and achieving asymmetric carbocation catalysis remains elusive despite the prevalence of organocatalytic concepts and strategies . The primary reason is the limited compatibility of carbocations with many nucleophilic reactants .…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate

Zhang

Zhong

et al. 2015

J. Am. Chem. Soc.

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Stable carbocations such as tritylium ions have been widely explored as organic Lewis acid catalysts and reagents in organic synthesis. However, achieving asymmetric carbocation catalysis remains elusive ever since they were first identified over one century ago. The challenges mainly come from their limited compatibility, scarcity of chiral carbocations, as well as the extremely low barrier to racemization of chiral carbenium ions. We reported here a latent concept for asymmetric carbocation catalysis. In this strategy, chiral trityl phosphate is employed as the carbocation precursor, which undergoes facile ionic dissociation upon mild external stimulation (e.g., acid, H-bonding, polar substrates) to form a catalytically active chiral ion pair for substrate activation and chiral induction. The latent strategy provides a solution for the long sought-after asymmetric carbocation catalysis as illustrated in three different enantioselective transformations.

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Section: Introductionmentioning

confidence: 99%

Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate

Zhang

Zhong

et al. 2015

J. Am. Chem. Soc.

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“…Traditionally, the complexes are prepared either by resolution of racemic complexes or by face-selective π-complexation from enantiopure precursors . Desymmetrization, despite being a powerful tool for the preparation of enantiomerically pure “organic” molecules, has been explored only recently for organometallic π-complexes using hydride abstraction …”

mentioning

confidence: 99%

Enantiocontrolled Synthesis of 2,6-Disubstituted Piperidines by Desymmetrization of meso-η-(3,4,5)-Dihydropyridinylmolybdenum Complexes. Application to the Total Synthesis of (−)-Dihydropinidine and (−)-Andrachcinidine

Shu

Liebeskind

2003

J. Am. Chem. Soc.

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A conceptually new approach to the enantiocontrolled synthesis of 2,6-disubstituted piperidines was achieved by desymmetrization of meso-2,6-dimethoxy-eta-(3,4,5)-dihydropyridinylmolybdenum complexes. After protection of the piperidine nitrogen as a urethane derived from (+)- or (-)-trans-2-(alpha-cumyl)cyclohexyl (TCC), a sequential, one-pot methoxide abstraction/nucleophilic addition/methoxide abstraction/nucleophilic addition generated good yields of 2,6-disubstituted-eta-(3,4,5)-dihydropyridinylmolybdenum complexes. This sequence proceeds by way of a highly diastereoselective methoxide abstraction (>40:1). High yielding protodemetalation and N-deprotection provided a simple and enantiocontrolled synthetic entry to a variety of 2,6-disubstituted piperidines. This new method was used for the total synthesis of (-)-dihydropinidine and (-)-andrachcinidine.

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“…These carbocation-induced oxidations have been used, for example, for the preparation of metalcomplexed cationic π-systems [41][42][43][44][45][46][47], silylium ions [48,49], polycyclic aromatic compounds [50], and the Fig. 5: Oxidations of silyl enol ethers and enamines through hydride abstraction by tritylium ions [15,16].…”

Section: Reactions Of Hydride Donors With Benzhydrylium and Trityliummentioning

confidence: 99%

Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

Ofial

2015

Pure and Applied Chemistry

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The linear free energy relationship log k = s N (N + E) (eq. 1), in which E is an electrophilicity, N is a nucleophilicity, and s N is a nucleophile-dependent sensitivity parameter, is a reliable tool for predicting rate constants of bimolecular electrophile-nucleophile combinations. Nucleophilicity scales that are based on eq. (1) rely on a set of structurally similar benzhydrylium ions (Ar 2 CH + ) as reference electrophiles. As steric effects are not explicitely considered, eq. (1) cannot unrestrictedly be employed for reactions of bulky substrates. Since, on the other hand, the reactions of tritylium ions (Ar 3 C + ) with hydride donors, alcohols, and amines were found to follow eq. (1), tritylium ions turned out to be complementary tools for probing organic reactivity. Kinetics of the reactions of Ar 3 C + with π-nucleophiles (olefins), n-nucleophiles (amines, alcohols, water), hydride donors and ambident nucleophiles, such as the anions of 5-substituted Meldrum's acids, are discussed to analyze the applicability of tritylium ions as reference electrophiles.

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Hydride Abstraction from η³-Allylic Molybdenum Complexes Exploring Various Diaryl Carbenium Ion Precursors. A Study toward Enantioselective Hydride Abstraction

Cited by 10 publications

References 20 publications

Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate

Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate

Enantiocontrolled Synthesis of 2,6-Disubstituted Piperidines by Desymmetrization of meso-η-(3,4,5)-Dihydropyridinylmolybdenum Complexes. Application to the Total Synthesis of (−)-Dihydropinidine and (−)-Andrachcinidine

Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

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Hydride Abstraction from η3-Allylic Molybdenum Complexes Exploring Various Diaryl Carbenium Ion Precursors. A Study toward Enantioselective Hydride Abstraction

Cited by 10 publications

References 20 publications

Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate

Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate

Enantiocontrolled Synthesis of 2,6-Disubstituted Piperidines by Desymmetrization of meso-η-(3,4,5)-Dihydropyridinylmolybdenum Complexes. Application to the Total Synthesis of (−)-Dihydropinidine and (−)-Andrachcinidine

Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

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Hydride Abstraction from η³-Allylic Molybdenum Complexes Exploring Various Diaryl Carbenium Ion Precursors. A Study toward Enantioselective Hydride Abstraction