Microwave-assisted solvent-free organic reactions: Synthesis of β-lactams from 1,3-azadienes (original) (raw)
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Solvent-free accelerated organic syntheses using microwaves
Pure and Applied Chemistry, 2001
A solvent-free approach for organic synthesis is described which involves microwave (MW) exposure of neat reactants (undiluted) either in the presence of a catalyst or catalyzed by the surfaces of inexpensive and recyclable mineral supports such as alumina, silica, clay, or "doped" surfaces, namely, Fe(NO 3 ) 3 -clay (clayfen), Cu(NO 3 ) 2 -clay (claycop), NH 2 OH-clay, PhI(OAc) 2 -alumina, NaIO 4 -silica, MnO 2 -silica, and NaBH 4 -clay. A variety of deprotection, condensation, cyclization, oxidation, and reduction reactions are presented including the efficient one-pot assembly of heterocyclic molecules from in situ generated intermediates such as enamines and α-tosyloxyketones. The application of this solvent-free MW approach to multicomponent reactions is highlighted that can be adapted for high-speed parallel synthesis of the library of dihydropyrimidine-2(1H)-ones and imidazo [1,2-a]annulated pyridines, pyrazines, and pyrimidines.
Microwave-assisted synthesis of benzoxazinediones under solvent-free conditions
Green Chemistry Letters and Reviews, 2016
Benzoxazinediones exhibit potential as versatile synthons in the synthesis of wide variety of heterocyclic compounds with biological activity. In this work, an efficient and eco-friendly onestep synthesis of benzoxazine-2,4-diones from phthalic anhydrides derivatives and trimethylsilyl azide using the microwave technique was developed and compared with conventional heating. Microwave irradiation plays a critical role in driving the reaction and providing access to products and/or regioisomers not available from conventional heating. Thus, the regioselectivity of the reaction may be modulated by the irradiation time. Depending on the method employed the benzoxazinediones were isolated with yields in the range of 30-90%.
Australian Journal of Chemistry, 2009
The use of emerging microwave (MW)-assisted chemistry techniques in conjunction with benign reaction media is dramatically reducing chemical waste and reaction times in several organic syntheses and chemical transformations. The present review summarizes recent developments in MW-assisted synthesis, name reactions and organic transformations, and rapid generation of nanoparticles with uniform size distribution. Greener protocols have been developed for the synthesis of various bio-active heterocycles, namely 1,3,4-oxadiazoles, 1,3,4-thiadiazoles, 1,3-dioxanes, pyrazoles, hydrazones and 3,4-dihydropyrimidin-2(1H)-ones, which proceed under the influence of microwaves and using eco-friendly conditions. These high-yielding methods were catalyzed efficiently by solid-supported Nafion NR50 under solvent-free conditions and polystyrene sulfonic acid in aqueous media. The eco-friendly nucleophilic substitution chemistry in water to generate cyclic amines via double N-alkylation of primary a...
Solvent-free organic syntheses using supported reagents and microwave irradiation
Recent developments in microwave-accelerated solventless organic syntheses are summarised. This expeditious and solventfree approach involves the exposure of neat reactants to microwave (MW) irradiation in conjunction with the use of supported reagents or catalysts which are primarily of mineral origin. The salient features of these high yield protocols are the enhanced reaction rates, greater selectivity and the experimental ease of manipulation. Among other reagents recently described in the literature on this eco-friendly green approach, the use of recyclable mineral oxides or supported reagents from our laboratory such as Fe(NO 3 ) 3 -clay (clayfen), Cu(NO 3 ) 2 -clay (claycop), NH 4 NO 3 -clay (clayan), NH 2 OH-clay, PhI(OAc) 2 -alumina, NaIO 4 -silica, CrO 3 -alumina, MnO 2 -silica, NaBH 4 -clay, etc. are highlighted in MW-promoted deprotection, condensation,
ChemInform Abstract: Microwave-Assisted Organic Synthesis: An Alternative Synthetic Strategy
ChemInform, 2011
Pharmaceutical companies have made major investments in high-throughput technologies for genomic and proteomic research, combinatorial chemistry and biological screening in order to identify more potential drug candidates at a faster pace. However, synthesis and lead compound optimisation remain the bottlenecks in the drug discovery process. Developing chemical compounds with the desired biological properties is time-consuming and expensive. Consequently, increasing interest is being directed towards technologies that allow more rapid synthesis and screening of chemical substances to identify compounds with functional qualities. Microwave heating is a process within a family of electroheat techniques, such as induction, radio frequency, direct resistance or infra-red heating, all of which utilise specific parts of the electromagnetic spectrum. These processes supplement, and in specific cases totally replace, conventional heating or drying systems used in industry. There is hardly any reaction type or name reaction that has not yet been tested in the microwave field. This is because some conventional systems are very bulky, not easy to operate, can pollute the environment due to harmful omissions and above all can be very inefficient. The major advantages of using microwaves are rapid heat transfer, volumetric and selective heating, compactness of equipment, speed of switching on and off and pollution-free environment as there are no products of combustion. Microwave leakage can certainly be kept well below government recommended levels. It has long been established that a dielectric material can be processed with energy in the form of high-frequency electromagnetic waves. The present review article describes the mechanism of microwave heating and comparison of the conventional and microwave assisted organic synthesis to improve the synthesis of the organic molecules.
General characteristics and applications of microwaves in organic synthesis
2009
This review focusses upon the key achievements made in organic synthesis using microwave-assisted reactions in the solid phase, with neat reactants and under solvent-free conditions. It also highlights the general characteristics of microwave applications in organic synthesis. It shows that reactions under microwaves are fast, with often increased reaction rates and lead to better selectivity. Some of the microwave-assisted reactions can even be carried out under neat conditions therefore leading to the area of green chemistry.
Microwave-Promoted Ring Opening Reaction of Azalactones
Letters in Organic Chemistry, 2007
α,β-Dehydroamino amides are important intermediates for the synthesis of biologically active molecules. A rapid procedure is reported for the synthesis of α,β-dehydroamino amides from azalactones under MW radiation. Azalactones were produced via Erlenmeyer reaction and submitted to ring opening reactions under MW during 15-30 min. Over 90% yields were obtained.
Microwave-Assisted Syntheses in Organic Chemistry
SpringerBriefs in Molecular Science, 2016
The second part focuses on the summary of typical organic chemical reactions selected, such as coupling reactions (C-C bond formation reactions, carbon-heteroatom bond formations),