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Special Issue "Microwave-mediated Chemistry"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: 30 April 2019

Special Issue Editor

Guest Editor
Prof. Dr. John Spencer

Department of Chemistry, University of Sussex, Sussex, United Kingdom
Website | E-Mail
Phone: +44 (0)1273 877374
Fax: +44 (0)1273 876687
Interests: palladium catalysis; medicinal chemistry; heterocycle synthesis; cancer; p53

Special Issue Information

Dear Colleagues,

Microwave-mediated chemistry continues to have an impact on chemical synthesis, scale-up, medicinal chemistry, catalysis, material science and many other areas of science. Often, yields are improved and processes can be carried out in minutes compared to their thermal counterparts. Many processes can be carried out in batches or can be solvent-free.

It is a great pleasure to invite you to participate in show-casing your work in microwave-mediated chemistry.

Prof. Dr. John Spencer
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • microwaves
  • catalysis
  • medicinal chemistry
  • flow chemistry
  • materials science

Published Papers (5 papers)

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Research

Open AccessArticle Microwave-Assisted Synthesis of Mono- and Disubstituted 4-Hydroxyacetophenone Derivatives via Mannich Reaction: Synthesis, XRD and HS-Analysis
Molecules 2019, 24(3), 590; https://doi.org/10.3390/molecules24030590
Received: 23 December 2018 / Revised: 31 January 2019 / Accepted: 2 February 2019 / Published: 7 February 2019
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Abstract
An efficient microwave-assisted one-step synthetic route toward Mannich bases is developed from 4-hydroxyacetophenone and different secondary amines in quantitative yields, via a regioselective substitution reaction. The reaction takes a short time and is non-catalyzed and reproducible on a gram scale. The environmentally benign [...] Read more.
An efficient microwave-assisted one-step synthetic route toward Mannich bases is developed from 4-hydroxyacetophenone and different secondary amines in quantitative yields, via a regioselective substitution reaction. The reaction takes a short time and is non-catalyzed and reproducible on a gram scale. The environmentally benign methodology provides a novel alternative, to the conventional methodologies, for the synthesis of mono- and disubstituted Mannich bases of 4-hydroxyacetophenone. All compounds were well-characterized by FT-IR, 1H NMR, 13C NMR, and mass spectrometry. The structures of 1-{4-hydroxy-3-[(morpholin-4-yl)methyl]phenyl}ethan-1-one (2a) and 1-{4-hydroxy-3-[(pyrrolidin-1-yl)methyl]phenyl}ethan-1-one (3a) were determined by single crystal X-ray crystallography. Compound 2a and 3a crystallize in monoclinic, P21/n, and orthorhombic, Pbca, respectively. The most characteristic features of the molecular structure of 2a is that the morpholine fragment adopts a chair conformation with strong intramolecular hydrogen bonding. Compound 3a exhibits intermolecular hydrogen bonding, too. Furthermore, the computed Hirshfeld surface analysis confirms H-bonds and π–π stack interactions obtained by XRD packing analyses. Full article
(This article belongs to the Special Issue Microwave-mediated Chemistry)
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Graphical abstract

Open AccessArticle Microwave-Assisted Stereoselective Heterocyclization to Novel Ring d-fused Arylpyrazolines in the Estrone Series
Molecules 2019, 24(3), 569; https://doi.org/10.3390/molecules24030569
Received: 28 January 2019 / Revised: 1 February 2019 / Accepted: 4 February 2019 / Published: 4 February 2019
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Abstract
Microwave-assisted syntheses of novel ring d-condensed 2-pyrazolines in the estrone series were efficiently carried out from steroidal α,β-enones and hydrazine derivatives. The ring-closure reaction of 16-benzylidene estrone 3-methyl ether with hydrazine in acetic acid resulted in a 2:1 diastereomeric mixture of two [...] Read more.
Microwave-assisted syntheses of novel ring d-condensed 2-pyrazolines in the estrone series were efficiently carried out from steroidal α,β-enones and hydrazine derivatives. The ring-closure reaction of 16-benzylidene estrone 3-methyl ether with hydrazine in acetic acid resulted in a 2:1 diastereomeric mixture of two 16,17-cis fused pyrazolines, which is contrary to the former literature data for both stereoselectivity and product structure. However, the cyclization reactions of a mestranol-derived unsaturated ketone with different arylhydrazines in acidic ethanol furnished the heterocyclic products in good to excellent yields independently of the substituents present on the aromatic ring of the reagents applied. The MW conditions also permitted the ring-closure reaction with p-nitrophenylhydrazine which is unfavorable under conventional heating. Moreover, the transformations led to the heterocyclic compounds stereoselectively with a 16α,17α-cis ring junction without being susceptible to spontaneous and promoted oxidation to pyrazoles. Full article
(This article belongs to the Special Issue Microwave-mediated Chemistry)
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Graphical abstract

Open AccessArticle Synthesis of Chromium Carbide Nanopowders by Microwave Heating and Their Composition and Microstructure Change under Gamma Ray Irradiation
Received: 3 November 2018 / Revised: 11 December 2018 / Accepted: 16 December 2018 / Published: 20 December 2018
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Abstract
Chromium carbide nanopowders were synthesized by mechanical alloying-assisted microwave heating. The effect of gamma irradiation on phase composition and microstructure of chromium carbide nanopowders synthesized by the microwave heating method was analyzed. The samples were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy [...] Read more.
Chromium carbide nanopowders were synthesized by mechanical alloying-assisted microwave heating. The effect of gamma irradiation on phase composition and microstructure of chromium carbide nanopowders synthesized by the microwave heating method was analyzed. The samples were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) techniques. The results showed that well-dispersed chromium carbide nanopowders can be synthesized by maintaining the temperature at 1000 °C for 1 h. Gamma ray irradiation had an important effect on the microstructure of chromium carbide nanopowders. The interplanar spacings of chromium carbide (110) crystal faces before and after gamma ray irradiation were 0.3725 nm and 0.3824 nm, respectively. The crystal structure of chromium carbide was changed by gamma ray irradiation. Gamma ray irradiation can also increase the binding energy of chromium carbide, which is beneficial to improve the thermal stability and mechanical properties of chromium carbide at high temperature. Full article
(This article belongs to the Special Issue Microwave-mediated Chemistry)
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Open AccessArticle Microwave Irradiation Assists the Synthesis of a Novel Series of bis-Arm s-Triazine Oxy-Schiff Base and Oxybenzylidene Barbiturate Derivatives
Molecules 2018, 23(11), 2976; https://doi.org/10.3390/molecules23112976
Received: 13 October 2018 / Revised: 7 November 2018 / Accepted: 10 November 2018 / Published: 14 November 2018
PDF Full-text (909 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A novel series of s-triazines incorporating 4-hydroxybenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde was prepared and fully characterized. The reaction was carried out via stepwise nucleophilic aromatic substitution of chlorine atoms in cyanuric chloride. The first chlorine was substituted by different amines (morpholine, piperidine, or diethylamine) [...] Read more.
A novel series of s-triazines incorporating 4-hydroxybenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde was prepared and fully characterized. The reaction was carried out via stepwise nucleophilic aromatic substitution of chlorine atoms in cyanuric chloride. The first chlorine was substituted by different amines (morpholine, piperidine, or diethylamine) to afford 2,4-dichloro-6-substituted-1,3,5-triazine. The second and third chlorines were substituted by benzaldehyde derivatives in the presence of Na2CO3 as a HCl scavenger to afford the target products: s-triazine oxyaldehyde derivatives (dipodal). The dipodal derivatives were reacted with acid hydrazide, hydralazine, barbituric, or thiobarbituric acid derivatives using conventional heating or microwave irradiation to afford the di-arm s-triazine oxy-Schiff base and oxybenzylidene barbiturate derivatives in good yields. Microwave irradiation done in less solvent afforded the target product in less reaction time with good yield and purity. These types of derivatives might have special interest in coordination and medicinal chemistry. Full article
(This article belongs to the Special Issue Microwave-mediated Chemistry)
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Open AccessArticle Microwave-Assisted Expeditious Synthesis of 2-Alkyl-2-(N-arylsulfonylindol-3-yl)-3-N-acyl-5-aryl-1,3,4-oxadiazolines Catalyzed by HgCl2 under Solvent-Free Conditions as Potential Anti-HIV-1 Agents
Molecules 2018, 23(11), 2936; https://doi.org/10.3390/molecules23112936
Received: 30 September 2018 / Revised: 3 November 2018 / Accepted: 9 November 2018 / Published: 10 November 2018
PDF Full-text (2122 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A series of 2-alkyl-2-(N-arylsulfonylindol-3-yl)-3-N-acyl-5-aryl-1,3,4-oxadiazolines were expeditious prepared under microwave-assisted, catalyzed by HgCl2 and solvent-free conditions. This method has the advantage of low catalyst loading and recovering catalyst, ease reaction and repaid reaction times, easy separation products and excellent [...] Read more.
A series of 2-alkyl-2-(N-arylsulfonylindol-3-yl)-3-N-acyl-5-aryl-1,3,4-oxadiazolines were expeditious prepared under microwave-assisted, catalyzed by HgCl2 and solvent-free conditions. This method has the advantage of low catalyst loading and recovering catalyst, ease reaction and repaid reaction times, easy separation products and excellent yields, and more conducive to the large-scale synthesis products. Furthermore, compounds 3s, 3y, 3a′, 3b′, 3f′, 3i′, 3q′, and 3r′ exhibited more potent anti-HIV-1 activity with EC50 values of 3.35, 6.12, 3.63, 9.54, 1.79, 0.51, 3.00, and 4.01 μg/mL, and TI values of 32.66, >32.68, 31.22, 13.94, 24.27, 39.59, 26.01, and 24.51, respectively. Especially compound 3i′ displayed the highest anti-HIV-1 activity with TI values of 39.59. Full article
(This article belongs to the Special Issue Microwave-mediated Chemistry)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Advantages of Green CuAAC Methodologies: Microwave and Solvent-less
Authors: Clayton J. Hull-Crew, Marissa N.Trujillo, Andrew D. Outlaw, Christopher M. Clements, Ashleigh A. Zeller, Loren J.Taylor, Kevin A. Stewart and Allen M. Schoffstall*
Affiliation: Department of Chemistry and Biochemistry, University of Colorado Colorado Springs (UCCS), Colorado Springs CO80918, United States
Abstract: Numerous modifications of the original conditions reported for successful copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) have added new choices when performing CuAAC click chemistry. Four different methods were chosen as being representative for comparison in terms of overall efficiency of the synthetic method, including time required for the synthesis and yield, ease of isolation and purity of the
1/H/-1,2,3-triazole product. The methods were those first reported (conventional heating), the microwave method, a method using a copper-carbene catalyst (solvent-less) and a method employing a CuI catalyst. Reactants for this study are non-fluorinated and fluorinated components. Results lead to a conclusion that a microwave method for the CuAAC reaction should be considered among others. The less general solvent-less method often gave comparable results.
Keywords: organic synthesis, triazole, copper-catalyzed azide-alkyne cycloaddition (CuAAC), microwave heating, solvent-less reaction, green chemistry

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