- Enantioselective N-heterocyclic carbene-catalysed intermolecular crossed benzoin condensations: Improved catalyst design and the role of in situ racemisation
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The enantioselective intermolecular crossed-benzoin condensation mediated by novel chiral N-heterocyclic carbenes derived from pyroglutamic acid has been investigated. A small library of chiral triazolium ions were synthesised. Each possessed a tertiary alcohol H-bond donor and a variable N-aryl substituent. It was found that increasing both the steric requirement and the electron-withdrawing characteristics of the N-aryl ring led to more chemoselective, efficient and enantioselective chemistry, however both quenching the reaction at different times and deuterium incorporation experiments involving the product revealed that this is complicated by product racemisation in situ (except in the case of benzoin itself), which explains the dependence of enantioselectivity on the electrophilicity of the reacting aldehydes common in the literature. Subsequent protocol optimisation, where one reacting partner was an o-substituted benzaldehyde, allowed a range of crossed-benzoins to be synthesised in moderate-good yields with moderate to excellent enantioselectivity.
- Delany, Eoghan G.,Connon, Stephen J.
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supporting information
p. 248 - 258
(2021/01/14)
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- N-Heterocyclic carbene triazolium salts containing brominated aromatic motifs: Features and synthetic protocol
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In this work, we provide a brief overview of the role of N-aryl substituents on triazolium N-heterocyclic carbene (NHC) catalysis. This synopsis provides context for the disclosed synthetic protocol for new chiral N-heterocyclic carbene (NHC) triazolium salts with brominated aromatic motifs. Incorporating brominated aryl rings into NHC structures is challenging, probably due to the substantial steric and electronic influence these substituents exert throughout the synthetic protocol. However, these exact characteristics make it an interesting N-aryl substituent, because the electronic and steric diversity it offers could find broad use in organometallic- A nd organo-catalysis. Following the synthetic reaction by NMR guided the extensive modification of a known protocol to enable the preparation of these challenging NHC pre-catalysts.
- Raed, Anas Abo,Dhayalan, Vasudevan,Barkai, Shahar,Milo, Anat
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p. 878 - 882
(2020/12/25)
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- Highly chemoselective intermolecular cross-benzoin reactions using an: Ad hoc designed novel N-heterocyclic carbene catalyst
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The design of a novel N-heterocyclic carbene catalyst incorporating a bulky yet highly electron-deficient N-aryl substituent has allowed the development of an efficient protocol for the first highly chemoselective intermolecular benzoin condensations between two non-identical aromatic aldehydes.
- Delany, Eoghan G.,Connon, Stephen J.
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supporting information
p. 780 - 786
(2018/02/09)
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- Comments on a Conversion of Epoxides to Halohydrins with Elemental Halogen Catalyzed by Phenylhydrazine: Tandem Electrophilic Halogenation of Aromatic Compounds and Epoxide Ring Opening to Halohydrins
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The halogenation of aromatic compounds by bromine or chlorine in the presence of an epoxide gives the corresponding halogenated aromatics and 2-halohydrins, both with good yields.
- Soroka, Miroslaw,Goldeman, Waldemar,Malysa, Piotr,Stochaj, Monika
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p. 2341 - 2344
(2007/10/03)
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- Novel chemoselective reduction of aryldiazonium fluoroborates with Zn- NiCl2·6H2O-THF
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Substituted aryldiazonium fluoroborates are selectively reduced to the corresponding phenylhydrazines by using Zn-NiCl2·6H2O in THF as a reducing agent.
- Bandgar,Uppalla
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p. 714 - 715
(2007/10/03)
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- Selective reduction of aryl diazonium fluoroborates
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Substituted aryl diazonium fluoroborates have been selectively reduced to the corresponding phenylhydrazines by using borohydride exchange resin (BER).
- Bandgar,Thite
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p. 635 - 639
(2007/10/03)
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- Process for producing 3-anilino-5-pyrazolones
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A process for producing a 3-anilino-5-pyrazolone which comprises reacting a β-anilino-β-alkoxy-acrylate with a hydrazine in the presence of a compound having a pKa of about 8 up to about 14.
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