scholarly journals Microwave Irradiation: Alternative Heating Process for the Synthesis of Biologically Applicable Chromones, Quinolones, and Their Precursors

Molecules ◽  
2021 ◽  
Vol 26 (20) ◽  
pp. 6293
Author(s):  
Hélio M. T. Albuquerque ◽  
Diana C. G. A. Pinto ◽  
Artur M. S. Silva
Keyword(s):  
Energy Consumption ◽  
Microwave Irradiation ◽  
Organic Synthesis ◽  
Heterocyclic Compounds ◽  
Reaction Times ◽  
Heating Process ◽  
Research Groups ◽  
Heating Source ◽  
Microwave Assisted ◽  
Solventless Reactions

Microwave irradiation has become a popular heating technique in organic synthesis, mainly due to its short reaction times, solventless reactions, and, sometimes, higher yields. Additionally, microwave irradiation lowers energy consumption and, consequently, is ideal for optimization processes. Moreover, there is evidence that microwave irradiation can improve the regioselectivity and stereoselectivity aspects of vital importance in synthesizing bioactive compounds. These crucial features of microwave irradiation contribute to its inclusion in green chemistry procedures. Since 2003, the use of microwave-assisted organic synthesis has become common in our laboratory, making our group one of the first Portuguese research groups to implement this heating source in organic synthesis. Our achievements in the transformation of heterocyclic compounds, such as (E/Z)-3-styryl-4H-chromen-4-ones, (E)-3-(2-hydroxyphenyl)-4-styryl-1H-pyrazole, (E)-2-(4-arylbut-1-en-3-yn-1-yl)-4H-chromen-4-ones, or (E)-2-[2-(5-aryl-2-methyl-2H-1,2,3-triazol-4-yl)vinyl]-4H-chromen-4-ones, will be discussed in this review, highlighting the benefits of microwave irradiation use in organic synthesis.

Regioselective Synthesis of Potent 4,5,6,7-Tetrahydroindazole Derivatives via Microwave-assisted Vilsmeier-Haack Reaction and their Antioxidant Activity Evaluation

2019 ◽  
Vol 16 (3) ◽  
pp. 194-201 ◽  
Author(s):  
Renu Bala ◽  
Vandana Devi ◽  
Pratibha Singh ◽  
Navjot Kaur ◽  
Pawandeep Kaur ◽  
...  
Keyword(s):  
Antioxidant Activity ◽  
Microwave Irradiation ◽  
Biological Activities ◽  
Reaction Times ◽  
Conventional Heating ◽  
High Chemical ◽  
Microwave Assisted ◽  
Work Up ◽  
Active Methylene ◽  
By Products

Background: Tetrahydroindazole, a member of the fused-pyrazole system, is a least studied class of heterocyclic compounds owing to its scarcity in nature. However, a large number of synthetically prepared tetrahydroindazoles are known to show a variety of biological activities such as interleukin- 2 inducible T-Cell kinase inhibitors, AMPA receptor positive allosteric modulators, antitumor, antituberculosis, anti-inflammatory and antimicrobial activities. Vilsmeier-Haack reaction is one of the most important chemical reactions used for formylation of electron rich arenes. Even though Vilsmeier- Haack reaction was studied on a wide variety of hydrazones derived from active methylene compounds, literature lacks the examples of the use of 4-substituted cyclohexanones as a substrate for the synthesis of 4,5,6,7-tetrahydroindazoles. The study of the reaction of Vilsmeier-Haack reagent with hydrazones derived from cyclic keto compounds having active methylene has been considered the interested topic of investigation. In the present study, ethyl cyclohexanone-4-carboxylate was treated with one equivalent of various hydrazines for two hours and the resulted hydrazones were further treated with an OPC-VH reagent (Vilsmeier-Haack reagent isolated from phthaloyl dichloride and N,Ndimethylformamide) afforded 4,5,6,7-tetrahydroindazoles in excellent yields. The synthesized compounds 4a-f and 5a-f were screened for their antioxidant activities using the DPPH radical scavenging assay. The target compounds were synthesized regioselectively using 4+1 approach in excellent yields. A number of experiments using both conventional heating as well as microwave irradiation methods were tried and on comparison, microwave irradiation method was found excellent in terms of easy work up, high chemical yields, shortened reaction times, clean and, no by-products formation. Some of the synthesized compounds showed significant antioxidant activity. The microwave assisted synthesis of 4,5,6,7-tetrahydroindazoles from ethyl cyclohexanone-4-carboxylate has been reported under mild conditions in excellent yield. Easy work up, high chemical yield, shortened reaction times, clean and no by-products formation are the major advantages of this protocol. These advantages may make this method useful for chemists who are interested in developing novel 4,5,6,7-tetrahydroindazole based drugs.

scholarly journals Microwave-Assisted Asinger Synthesis of Thiazolines

2020 ◽  
Vol 3 (1) ◽  
pp. 27
Author(s):  
Raúl Eduardo Gordillo-Cruz ◽  
Liliana Gonzalez-Reyes ◽  
Milton Coporo-Reyes ◽  
Nieves Zavala-Segovia ◽  
Bernardo A. Frontana-Uribe ◽  
...  
Keyword(s):  
Microwave Irradiation ◽  
Reaction Times ◽  
Reaction Conditions ◽  
Microwave Assisted

An array of 2,4-disubstituted thiazolines was obtained through Asinger reaction approach from the straightforward treatment of diverse aldehydes/ketones with 1-mercaptopropan-2-one, in the presence of NH3 assisted by microwave irradiation, displaying similar and sometimes higher yields, as well as shorter reaction times that traditional Asinger reaction conditions at room and lower temperatures.

Meso-mechanics simulation analysis of microwave-assisted mineral liberation

2015 ◽  
Author(s):  
Qin Like ◽  
Dai Jun ◽  
Yuan Liqun
Keyword(s):  
Energy Consumption ◽  
Microwave Irradiation ◽  
Power Density ◽  
Microwave Power ◽  
Mineral Content ◽  
Crystal Size ◽  
Irradiation Time ◽  
Mineral Crystal ◽  
Microwave Assisted ◽  
Time And Energy

Microwave-assisted crushing and grinding can improve efficiency and reduce energy consumption. This paper takes rock grains with galena and calcite as the research object to establish a two-dimensional computational model through the finite difference software FLAC2D. It analyzes the process and law of mineral boundary failure under microwave irradiation, and assesses the effects of four factors, namely, microwave irradiation time, power density, mineral crystal size, and mineral content, on mineral boundary failure. Results indicate an optimal microwave irradiation period for the rapid failure of mineral boundary. Moreover, irradiation time and energy consumption can be reduced by increasing the microwave power density. However, irradiation time and energy consumption are basically unchanged when the microwave power density is above a certain threshold. Mineral content slightly affects the microwave irradiation time, whereas mineral crystal size significantly affects the microwave irradiation time. In addition, a larger-sized mineral crystal requires less irradiation time and energy consumption to reach the same failure rate. However, irradiation time and energy consumption slightly change when the crystal size is larger than a certain value.

Microwave-assisted Carbon-carbon and Carbon-heteroatom Cross-coupling Reactions in Organic Synthesis

2020 ◽  
Vol 7 (2) ◽  
pp. 86-98
Author(s):  
Rammyani Pal ◽  
Chhanda Mukhopadhyay
Keyword(s):  
Microwave Irradiation ◽  
Organic Synthesis ◽  
Cross Coupling ◽  
Side Reactions ◽  
Coupling Reactions ◽  
Considerable Effort ◽  
Microwave Assisted ◽  
External Heat Source ◽  
Cross Coupling Reactions ◽  
Metal Catalyzed

Conventionally, the organic reactions are accomplished by conductive heating with an external heat source like an oil bath. On the contrary, since its inception, the application of microwave irradiation is growing as a suitable alternate heating method in organic synthesis. Microwave heating considerably reduces the reaction time without promoting any side reactions. The fundamental synthetic organic chemistry majorly deals with transition-metal-catalyzed C–C and C–heteroatom bond formation reactions. It is one of the most important methods in contemporary chemistry resulting in a tremendous increment in the applications of these reactions during the last few years. This field has been acknowledged with a number of Nobel Prizes during the last decade (2001, 2005 and 2010). A considerable effort has been done on the continuous development of new ligands and catalysts as well as an increased understanding of the mechanisms for the improvement of the reaction condition. This review focuses on some of the latest developments in the area of cross-coupling reactions aided by microwave irradiation.

scholarly journals Orthoamide, LXII [1]. – Mikrowellen-unterst ¨ utzte Formylierung schwach CH2-acider Verbindungen mit dem Bredereck-Simchen Reagenz – Umwandlung der Kondensationsprodukte in Heteroaromaten / Orthoamides, LXII [1]. – Microwave Assisted Formylation of Weak CH2-Acidic Compounds with the Bredereck-Simchen Reagent – Preparation of Heteroaromatic Compounds from the Condensation Products

2005 ◽  
Vol 60 (2) ◽  
pp. 231-241 ◽  
Author(s):  
Willi Kantlehner ◽  
Gerhard Simchen ◽  
Jochen Mezger ◽  
Edmont V. Stoyanov ◽  
Ralf Kreß ◽  
...  
Keyword(s):  
Microwave Irradiation ◽  
Reaction Times ◽  
Conventional Heating ◽  
Methyl Anthranilate ◽  
Prolonged Heating ◽  
Heteroaromatic Compounds ◽  
Microwave Assisted ◽  
Condensation Products ◽  
Acidic Compounds ◽  
Isoxazole Derivatives

The diformylation of the dinitriles 4 and diesters 7 with the Bredereck-Simchen reagent HC[N(CH3)2]2[OC(CH3)3] (1) under microwave irradiation give the bis-enamines 6 and 8 with dramatically reduced reaction times and improved yields compared to conventional heating. The condensation products formed can be easily converted to bis-pyrazole and bis-isoxazole derivatives 13 and 20, respectively. Methyl anthranilate reacts on prolonged heating with the orthoamide 21 to give ketene aminal 23 in low yield (8 %). Under microwave irradiation the same reagents lead to a mixture of 23 (14 %) and dihydropyrane 24 (28 %).

Efficient, microwave-assisted intramolecular 1,3-dipolar cycloadditions of oximes and N-methylnitrones derived from o-alkenylmethoxy-acetophenones

2005 ◽  
Vol 83 (3) ◽  
pp. 260-265 ◽  
Author(s):  
Surinderjit Singh ◽  
M PS Ishar ◽  
Gajendra Singh ◽  
Rajinder Singh
Keyword(s):  
Microwave Irradiation ◽  
Microwave Heating ◽  
Reaction Times ◽  
Solvent Free ◽  
Dipolar Cycloadditions ◽  
Microwave Assisted ◽  
Solvent Free Conditions ◽  
A Minor ◽  
Acetophenone Oxime

Contrary to literature reports, the o-allyloxy- and crotyloxy-acetophenone-oximes (2a, 2b) are transformed to nitrones, which undergo regio- and stereoselective intramolecular 1,3-dipolar cycloadditions, both on microwave heating under solvent free conditions and refluxing in toluene, to afford novel cycloadducts (5a, 5b); the oxazepine-N-oxide (3a) reported to be formed in 98% yield was obtained only as a minor product (~10%). However, o-cinnamyloxy-acetophenone-oxime (2c) under similar conditions undergoes intramolecular N-alkylation to afford nitrone (3c). The reactions carried out under microwave irradiation are cleaner, require shorter reaction times, and have higher yields. Corresponding intramolecular 1,3-dipolar cycloadditions of N-methylnitrones (B), generated in situ from o-alkenylmethoxy-acetophenones (1a–1c) and N-methylhydroxylamine under solvent-free microwave irradiation conditions, are completely regio- and stereoselective, require much shorter reaction times, and afford adducts (4a–4c) in higher yields, as compared with their thermal counterparts.Key words: cycloadditions, nitrones, oximes, o-alkenylmethoxy-acetophenones, microwave, isoxazolidines.

Microwave-Assisted Tandem Processes for the Synthesis of N-Heterocycles

2009 ◽  
Vol 62 (3) ◽  
pp. 208 ◽  
Author(s):  
Mohammed Abid ◽  
Béla Török ◽  
Xudong Huang
Keyword(s):  
Organic Synthesis ◽  
Heterocyclic Compounds ◽  
Significant Contribution ◽  
Solid Phase Synthesis ◽  
Solid Phase ◽  
Reaction Rates ◽  
Phase Synthesis ◽  
Microwave Assisted ◽  
Solvent Free Conditions ◽  
Reaction Media

Over the years, microwave-assisted organic synthesis (MAOS) became a commonly applied mainstream tool for the synthesis of heterocyclic compounds. The broad range of emerging applications in this field is mainly due to the significant contribution of MAOS to the development of ecofriendly processes. Various transformations have been developed for the synthesis of N-heterocycles under microwave conditions, including fast and selective processes. Tandem reactions involving greener reaction media, solvent-free conditions, and solid-phase synthesis are of exceptional interest in this area. In most transformations, microwave conditions dramatically enhanced reaction rates, as well as provided improved yields. This account highlights the most recent advancements in MAOS-based tandem processes for the synthesis of N-heterocycles.

scholarly journals Gold film-catalysed benzannulation by Microwave-Assisted, Continuous Flow Organic Synthesis (MACOS)

2009 ◽  
Vol 5 ◽  
Author(s):  
Gjergji Shore ◽  
Michael Tsimerman ◽  
Michael G Organ
Keyword(s):  
Microwave Irradiation ◽  
Functional Groups ◽  
Organic Synthesis ◽  
Continuous Flow ◽  
Metal Film ◽  
Silver Film ◽  
Gold Film ◽  
Microwave Assisted ◽  
Glass Capillaries ◽  
Inner Surface

Methodology has been developed for laying down a thin gold-on-silver film on the inner surface of glass capillaries for the purpose of catalysing benzannulation reactions. The cycloaddition precursors are flowed through these capillaries while the metal film is being heated to high temperatures using microwave irradiation. The transformation can be optimized rapidly, tolerates a wide number of functional groups, is highly regioselective, and proceeds in good to excellent conversion.

Microwave-Assisted Synthesis of Azo Aromatic Diacyl Chlorides

2012 ◽  
Vol 524-527 ◽  
pp. 1702-1705
Author(s):  
Qing Chao Jia ◽  
Yan Jun Chen ◽  
Hong Min Hou
Keyword(s):  
Microwave Irradiation ◽  
Ultrasonic Irradiation ◽  
Reaction Times ◽  
Microwave Assisted Synthesis ◽  
Microwave Assisted

Six azo aromatic diacyl chlorides were synthesized under microwave irradiation. The method offers better yields in shorter reaction times compared to classical heating approaches and ultrasonic irradiation.

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