Special Issue "Metal-free Organocatalysis"

A special issue of Catalysts (ISSN 2073-4344).

Deadline for manuscript submissions: closed (15 April 2017)

Special Issue Editor

Guest Editor
Prof. Dr. Aurelio G. Csákÿ

Instituto Pluridisciplinar, Universidad Complutense, 28040 Madrid, Spain
Website | E-Mail
Interests: metal-free catalysis; boron compounds; radiochemistry

Special Issue Information

Dear Colleagues,

Standard catalysts for organic transformations contain a transition metal. However, the toxicity and cost of transition metals is of particular current concern, especially in large-scale transformations and in the synthesis of pharmaceuticals, where even traces of heavy metals have to be rigorously excluded from the drug product. This is prompting the search for new metal-free chemical transformations under greener conditions. In this context, low-cost and environmentally benign metal-free catalysis constitutes a powerful means for the construction of complex organic molecules. Catalysis by chiral organic molecules (organocatalysis) does also offer the possibility of asymmetric synthesis.

The aim of this Special Issue is to familiarize the reader with recent research and novel trends in the use of metal-free catalysts towards carbon-carbon and carbon-heteroatom bond formation, including examples of chiral organocatalysis.

Prof. Dr. Aurelio G. Csákÿ
Guest Editor

Manuscript Submission Information

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Keywords

  • C–C bond formation
  • C–heteroatom bond formation
  • Chirality
  • Mechanisms
  • Non-metal catalysis
  • Synthesis

Published Papers (6 papers)

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Research

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Open AccessArticle A Recyclable Fluorous Hydrazine‐1,2Bis(Carbothioate) Organocatalyst for the Synthesis of ꞵ‐Chloroethers with N‐Chlorosuccinimide
Catalysts 2017, 7(2), 66; doi:10.3390/catal7020066
Received: 14 January 2017 / Accepted: 15 February 2017 / Published: 16 February 2017
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Abstract
A novel fluorous hydrazine‐1,2‐bis(carbothioate) was prepared. It showed good catalytic activity in the synthesis of ꞵ‐chloroethers with N‐chlorosuccinimide under mild reaction conditions. This fluorous organocatalyst could be recovered and recycled several times with good purity.
[...] Read more.
A novel fluorous hydrazine‐1,2‐bis(carbothioate) was prepared. It showed good catalytic activity in the synthesis of ꞵ‐chloroethers with N‐chlorosuccinimide under mild reaction conditions. This fluorous organocatalyst could be recovered and recycled several times with good purity. Full article
(This article belongs to the Special Issue Metal-free Organocatalysis)
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Open AccessArticle One-Pot Two-Step Organocatalytic Asymmetric Synthesis of Spirocyclic Piperidones via Wolff Rearrangement–Amidation–Michael–Hemiaminalization Sequence
Catalysts 2017, 7(2), 46; doi:10.3390/catal7020046
Received: 14 December 2016 / Revised: 18 January 2017 / Accepted: 22 January 2017 / Published: 4 February 2017
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Abstract
A highly enantioselective organocatalytic Wolff rearrangement–amidation–Michael–hemiaminalization stepwise reaction is described involving a cyclic 2-diazo-1,3-diketone, primary amine and α,β-unsaturated aldehyde. Product stereocontrol can be achieved by adjusting the sequence of steps in this one-pot multicomponent reaction. This approach was used to synthesize various optically
[...] Read more.
A highly enantioselective organocatalytic Wolff rearrangement–amidation–Michael–hemiaminalization stepwise reaction is described involving a cyclic 2-diazo-1,3-diketone, primary amine and α,β-unsaturated aldehyde. Product stereocontrol can be achieved by adjusting the sequence of steps in this one-pot multicomponent reaction. This approach was used to synthesize various optically active spirocyclic piperidones with three stereogenic centers and multiple functional groups in good yields up to 76%, moderate diastereoselectivities of up to 80:20 and high enantioselectivities up to 97%. Full article
(This article belongs to the Special Issue Metal-free Organocatalysis)
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Open AccessArticle Solvent-Free Selective Condensations Based on the Formation of the Olefinic (C=C) Bond Catalyzed by Organocatalyst
Catalysts 2016, 6(7), 106; doi:10.3390/catal6070106
Received: 6 June 2016 / Revised: 4 July 2016 / Accepted: 14 July 2016 / Published: 20 July 2016
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Abstract
Pyrrolidine and its derivatives were used to catalyze aldol and Knoevenagel condensations for the formation of the olefinic (C=C) bond under solvent-free conditions. The 3-pyrrolidinamine showed high activity and afforded excellent yields of α,β-unsaturated compounds. The aldol condensation of aromatic/heterocyclic aldehydes with ketones
[...] Read more.
Pyrrolidine and its derivatives were used to catalyze aldol and Knoevenagel condensations for the formation of the olefinic (C=C) bond under solvent-free conditions. The 3-pyrrolidinamine showed high activity and afforded excellent yields of α,β-unsaturated compounds. The aldol condensation of aromatic/heterocyclic aldehydes with ketones affords enones in high conversion (99.5%) and selectivity (92.7%). Good to excellent yields of α,β-unsaturated compounds were obtained in the Knoevenagel condensation of aldehydes with methylene-activated substrates. Full article
(This article belongs to the Special Issue Metal-free Organocatalysis)
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Open AccessCommunication Brønsted Acid-Catalyzed Direct Substitution of 2-Ethoxytetrahydrofuran with Trifluoroborate Salts
Catalysts 2016, 6(7), 94; doi:10.3390/catal6070094
Received: 29 April 2016 / Revised: 9 June 2016 / Accepted: 10 June 2016 / Published: 25 June 2016
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Abstract
Metal-free transformations of organotrifluoroborates are advantageous since they avoid the use of frequently expensive and sensitive transition metals. Lewis acid-catalyzed reactions involving potassium trifluoroborate salts have emerged as an alternative to metal-catalyzed protocols. However, the drawbacks to these methods are that they rely
[...] Read more.
Metal-free transformations of organotrifluoroborates are advantageous since they avoid the use of frequently expensive and sensitive transition metals. Lewis acid-catalyzed reactions involving potassium trifluoroborate salts have emerged as an alternative to metal-catalyzed protocols. However, the drawbacks to these methods are that they rely on the generation of unstable boron dihalide species, thereby resulting in low functional group tolerance. Recently, we discovered that in the presence of a Brønsted acid, trifluoroborate salts react rapidly with in situ generated oxocarbenium ions. Here, we report Brønsted acid-catalyzed direct substitution of 2-ethoxytetrahydrofuran using potassium trifluoroborate salts. The reaction occurs when tetrafluoroboric acid is used as a catalyst to afford functionalized furans in moderate to excellent yields. A variety of alkenyl- and alkynyltrifluoroborate salts readily participate in this transformation. Full article
(This article belongs to the Special Issue Metal-free Organocatalysis)
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Open AccessCommunication Organocatalytic, Asymmetric [2+2+2] Annulation to Construct Six-Membered Spirocyclic Oxindoles with Six Continuous Stereogenic Centers
Catalysts 2016, 6(5), 65; doi:10.3390/catal6050065
Received: 17 March 2016 / Revised: 13 April 2016 / Accepted: 15 April 2016 / Published: 27 April 2016
Cited by 7 | PDF Full-text (1742 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Lactols and cyclic hemiaminals were directly used in a one-pot organo/organo dual catalytic system induced [2+2+2] tandem reaction for the asymmetric construction of six-membered carbocycles. The enamine-based stereoselective Michael addition of lactols or cyclic hemiaminals to electron-deficient olefinic oxindole motifs provided chiral C4
[...] Read more.
Lactols and cyclic hemiaminals were directly used in a one-pot organo/organo dual catalytic system induced [2+2+2] tandem reaction for the asymmetric construction of six-membered carbocycles. The enamine-based stereoselective Michael addition of lactols or cyclic hemiaminals to electron-deficient olefinic oxindole motifs provided chiral C4 components, which were further combined with triethylamine catalyzed Michael/Henry sequential reactions affording spirocyclic oxindole derivatives containing six continuous stereogenic centers with excellent enantioselectivities as a single diastereoisomer. All these desired products have versatile molecular complexity, which might have potential applications in synthetic organic chemistry and the pharmaceutical industry. Full article
(This article belongs to the Special Issue Metal-free Organocatalysis)
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Other

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Open AccessFeature PaperLetter Organocatalysis: Fundamentals and Comparisons to Metal and Enzyme Catalysis
Catalysts 2016, 6(9), 128; doi:10.3390/catal6090128
Received: 19 June 2016 / Revised: 16 July 2016 / Accepted: 22 July 2016 / Published: 26 August 2016
Cited by 1 | PDF Full-text (21118 KB) | HTML Full-text | XML Full-text
Abstract
Catalysis fulfills the promise that high-yielding chemical transformations will require little energy and produce no toxic waste. This message is carried by the study of the evolution of molecular catalysis of some of the most important reactions in organic chemistry. After reviewing the
[...] Read more.
Catalysis fulfills the promise that high-yielding chemical transformations will require little energy and produce no toxic waste. This message is carried by the study of the evolution of molecular catalysis of some of the most important reactions in organic chemistry. After reviewing the conceptual underpinnings of catalysis, we discuss the applications of different catalysts according to the mechanism of the reactions that they catalyze, including acyl group transfers, nucleophilic additions and substitutions, and C–C bond forming reactions that employ umpolung by nucleophilic additions to C=O and C=C double bonds. We highlight the utility of a broad range of organocatalysts other than compounds based on proline, the cinchona alkaloids and binaphthyls, which have been abundantly reviewed elsewhere. The focus is on organocatalysts, although a few examples employing metal complexes and enzymes are also included due to their significance. Classical Brønsted acids have evolved into electrophilic hands, the fingers of which are hydrogen donors (like enzymes) or other electrophilic moieties. Classical Lewis base catalysts have evolved into tridimensional, chiral nucleophiles that are N- (e.g., tertiary amines), P- (e.g., tertiary phosphines) and C-nucleophiles (e.g., N-heterocyclic carbenes). Many efficient organocatalysts bear electrophilic and nucleophilic moieties that interact simultaneously or not with both the electrophilic and nucleophilic reactants. A detailed understanding of the reaction mechanisms permits the design of better catalysts. Their construction represents a molecular science in itself, suggesting that sooner or later chemists will not only imitate Nature but be able to catalyze a much wider range of reactions with high chemo-, regio-, stereo- and enantioselectivity. Man-made organocatalysts are much smaller, cheaper and more stable than enzymes. Full article
(This article belongs to the Special Issue Metal-free Organocatalysis)
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