Solvent-free Microwave Irradiation Research Articles

Sulfamic Acid: An Efficient, Cost-Effective, and Reusable Solid Acid Catalyst for the Synthesis of 1,8-Naphthyridines Under Solvent-Free Heating and Microwave Irradiation

An efficient and convenient method is described for the synthesis of 1,8-naphthyridines in excellent yields by condensation of 2-aminonicotinaldehyde with various active methylene compounds in the presence of sulfamic acid as the catalyst in a solvent-free media using both conventional heating and microwave irradiation.

K-10 Clay-Catalyzed Enol-Driven Decarboxylative Ring-Transformation Approach to Dihydro- and Tetrahydroquinolines from Carbohydrates

An original synthetic approach to 4-polyhydroxyal­kylquinolines using unprotected d-glucose/d-xylose as biorenewable resources is reported. The synthetic protocol involves enol-driven Michael-type addition of cyclic ketones to aldose-derived 1,3-oxazin-2-ones followed by decarboxylative ring transformation to yield various novel 5,6-dihydro-/5,6,7,8-tetrahydro-4-polyhydroxyalkylquinolines and their 5-, 6-, or 8-one analogues. This is a one-pot montmorillonite K-10 clay-catalyzed process proceeding under solvent-free microwave irradiation conditions.

Mineral Supported Facile Synthesis of Novel 4-Hydroxybenzoxazin-2-Thione N-Nucleosides

One-pot montmorillonite K-10 clay-supported reactions of substituted/unsubstituted salicylaldehyde and ribosyl/deoxyribosyl thioureas expeditiously yielded novel N-nucleosides, 4-hydroxy-3,4-dihydro-3-(β-D-ribofuranosyl or β-D-2 ′-deoxyribofuranosyl)-2 ″-benz[e]-1,3-oxazin-2-thione via cycloisomerization of aldehyde intermediate under solvent-free microwave irradiation conditions.

Solvent-free synthesis of benzoic esters and benzyl esters in novel Brønsted acidic ionic liquids under microwave irradiation

Fischer esterifications of benzoic acid with a variety of alcohols and a variety of acids with benzyl alcohol could be promoted by four novel Brønsted acidic ionic liquids a–d that bear a benzyl on the imidazolium or pyridinium cation. The reactions were carried out smoothly without the need of added catalyst with good to excellent isolated yields (77–98.5%) under solvent-free microwave irradiation conditions in the presence of 50 mol% ionic liquids. These ionic liquids could be recovered easily and recycled three times without any significant loss in their catalytic activity.

An efficient Bi(NO3)3 · 5H2O catalyzed multi component one-pot synthesis of novel Naphthyridines

An efficient and environmentally friendly multicomponent synthesis of substituted 1,8-naphthyridines catalyzed by bismuth(III) nitrate pentahydrate [Bi(NO3)3 x 5H2O] under solvent-free microwave irradiation is described. This procedure has such advantages as short reaction time, high yields, and simple workup. The catalyst could be reused several times, keeping its initial activity recycled reactions.

A rapid synthesis of isoxazolo[5,4-d]pyrimidin-4(5H)-ones under microwave irradiation with solid acid catalysis in solvent-free conditions

A rapid and efficient method for the synthesis of isoxazolo[5,4-d]pyrimidin-4(5H)-ones has been developed through cyclocondensation of 5-aminoisoxazole-4-carboxamides with orthoesters under conventional heating and solvent-free microwave irradiation with solid acid catalysis. In comparison, the reactions are faster and the yields are higher under microwave irradiation.

An Efficient Method for the Ring Opening of Epoxides with Aromatic Amines by Sb(III) Chloride under Microwave Irradiation

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding β-amino alcohols in high yields with high regioselectivity

Microwave-assisted solvent-free synthesis and spectral properties of some dimethine cyanine dyes as fluorescent dyes for DNA detection

A series of dimethine cyanine dyes were synthesized in a fast, efficient and high yield by the condensation of quaternary salts with 1 H-indole-3-carbaldehyde in the presence of piperidine under solvent-free microwave irradiation. The products were identified by 1H NMR, IR, UV–vis spectroscopy and elemental analysis. The absorption and fluorescence properties of the dyes in both the free state and DNA or BSA were investigated. Significant enhancement of the fluorescent quantum yield was observed for all the dyes in the presence of DNA, with one compound demonstrating excellent sensitivity as a fluorescent probe.

Diversity oriented synthesis of fused-ring 1,3-oxazines from carbohydrates as biorenewable feedstocks

Microwave enhanced diversity oriented synthesis (MEDOS) of various N- and O-heterocyclic systems fused with 1,3-oxazine ring is reported. The synthesis represents a new montmorillonite K-10 clay-catalyzed green protocol, which utilizes d-glucose/ d-xylose as biorenewable feedstocks. d-Glucose/ d-xylose-derived 1,3-oxazin-2-ones(thiones) either directly undergo K-10 clay-catalyzed cyclization to yield pyrano-/furo-1,3-oxazine systems under solvent-free microwave irradiation conditions or afford azolo-/azino-1,3-oxazines when subjected to Malaprade reaction followed by cyclization with appropriate reagents, viz. phenylhydrazine, hydroxylamine, acetamidine, phenylurea and semi(thiosemi)carbazide.

A route to functionalized pyrimidines from carbohydrates via amine-driven dehydrative ring transformations

A novel and expeditious synthetic protocol for functionalized pyrimidines using unprotected aldoses as biorenewable resources is reported. The synthesis involves aza-Michael addition of aromatic amines to aldose-derived 1,3-oxazin-2-ones(thiones) followed by dehydrative ring transformation to afford 4-polyhydroxyalkylpyrimidin-2-ones(thiones) in excellent yields. This is a one-pot Montmorillonite K-10 clay-catalyzed amine-driven process proceeding under solvent-free microwave irradiation conditions.

Carbohydrates to Functionalized Pyridines: A New Synthetic Approach via Enol-Driven Ring Transformations

An expeditious synthetic protocol for polyhydroxyalkyl­pyridines and their 3-amino/mercapto-2-pyridinone analogues using unprotected aldoses as biorenewable resources is reported. The synthesis involves enol-driven Michael-type addition of lactones/ketones to aldose-derived 1,3-oxazin-2-ones followed by decarboxylative ring transformation to yield various novel polyhydroxyal­kylpyridines. This is a one-pot nanoclay (K-10 clay)-catalyzed process proceeding under conditions of solvent-free microwave irradiation.

Microwave-assisted Solvent-free Synthesis of Some Dimethine Cyanine Dyes, Spectral Properties and TD-DFT/PCM Calculations

A series of dimethine cyanine dyes were synthesized in a fast, efficient and high yield by the condensation of quaternary salts with 1H-indole-3-carbaldehyde in the presence of piperidine under solvent-free microwave irradiation. The products were identified by 1H NMR, IR, UV-Vis spectra and elemental analysis. The absorption and fluorescence properties of these dyes were investigated both experimentally and theoretically. Calculations performed at a combination of time-dependent density functional theory (TD-DFT) and the polarizable continuum model (PCM) reproduced the π-π* type absorption bands of the dyes. Regression analysis was used for studying theoretical results of the absorption maxima in different solvents. Compared with experimental counterparts, estimated overall uncertainties in the absorption maxima were about ±2%.

One‐Pot Solvent Free Synthesis and DNA Binding Studies of Thieno[2,3‐b]‐1,8‐Naphthyridines

With the aim of evaluating interaction between double‐stranded calf thymus (ds)DNA and sulphur containing fused planar rings, the derivatives of 1,8‐naphthyridine containing thiono groups were synthesized by the condensation of 2‐mercapto‐3‐formyl[1,8]naphthyridines using 1‐chloroacetone, 2‐chloroacetamide, chloroaceticacid, and 2‐chloro‐1‐phenylethanone in the presence of anhydrous potassium carbonate as s catalyst under solvent free microwave irradiation. The structures of the compounds were elucidated on the basis of elemental analysis, IR, 1H NMR, and mass spectra. The interaction of thieno[2,3‐b]‐1,8‐naphthyridine‐2‐carboxylic acid (TNC) (3a) with ct‐DNA was studied by UV‐Vis spectrophotometry, viscosity, thermal denaturation, as well as cyclic voltammetry experiments. On binding to DNA, the absorption spectrum underwent bathochromic and hypochromic shifts. Binding parameters, determined from spectrophotometric measurements indicated a binding constant of K b =2.1×106 M−1. The thieno[2,3‐b]‐1,8‐naphthyridine‐2‐carboxylic acid (3a) increases the viscosity of sonicated rod‐like DNA fragments. The binding of TNC to DNA increased the melting temperature by about 4°C. The decrease in peak current heights and shifts of peak potential values are observed by the addition of calf thymus DNA in cyclic voltammetry studies.

Thiourea to Dithiazolopyrimidines: Highly Regio- and Stereoselective Synthetic Routes via Mercaptoacetylative Cyclization

The Michael addition of 3-imino-1,4,2-dithiazoles to 4-arylidene-1,3-oxathiolan-5-one afforded isolable adducts regio- and diastereoselectively, which underwent mercaptoacetylative annulation of the mercaptopyrimidine ring onto the dithiazole under solvent-free microwave irradiation conditions. Alternatively, similar conjugate addition of [(methylsulfinyl)methyl]isothioureas to 4-arylidene-1,3-oxathiolan-5-one diastereoselectively afforded Michael adducts that underwent mercaptoacetylative ring transformation followed by heterocyclization via deoxygenative demethyl-ation with thionyl chloride to yield the same products, 7-aryl- or 2,7-diaryl-6,7-dihydro-6-mercapto-5 H-[1,4,2]dithiazolo[2,3- A]pyrimidin-5-ones, regio- and diastereoselectively.

Knoevenagel condensation of α,β-unsaturated aromatic aldehydes with barbituric acid under non-catalytic and solvent-free conditions

An efficient route for the synthesis of 5-(arylpropenylidine)-2,4,6-pyrimidinetrione 3 from an appropriate α,β-unsaturated aromatic aldehydes 1 and barbituric acid 2 under both non-catalytic and solvent-free microwave irradiation conditions was described. In this way, a range of biologically important compounds 3 was obtained in good to excellent yields (86–98%) in a very short reaction time (30–80 s).

A Novel Three‐Component Tandem Protocol for the Regioselective Synthesis of 1‐(2‐Arylmethyl‐5‐aryl‐3‐thienyl)pyrrolidines and ‐piperidines

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

A Facile Synthesis and Highly Atom Economic 1,3‐Dipolar Cycloaddition of Hexahydropyrido[3,4‐c][1,5]benzothiazepines with Nitrile Oxide: Stereoselective Formation of Hexahydro[1,2,4]oxadiazolo[5,4‐d]pyrido[3,4‐c][1,5]benzothiazepines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Efficient glycosydation and/or esterification of d-glucuronic acid and its 6,1-lactone under solvent-free microwave irradiation

2,3,4-Tri- O-acetyl- d-glucurono-6,1-lactone was obtained ‘one-pot’ from d-glucuronic acid. The lactone opening with different alcohols in the presence of a variety of catalysts was studied. All reactions were performed under microwave irradiation in solvent-free conditions.

Novel environmentally benign procedures for the synthesis of styryl dyes

A series of styrylpyridinium, styrylquinolinium and styrylbenzothiazolium dyes have been synthesized by novel environmentally benign procedures. The condensation of 4-methylpyridinium methosulphate, 2- or 4-methylquinolinium methosulphate or 2-methylbenzothiazolium methosulphate with aromatic aldehydes was performed under solvent-free conditions or microwave irradiation in the presence of different basic or acidic reagents. The chemical structures of the derived styrylcyanine dyes were confirmed by 1H NMR and UV–vis spectroscopies and elemental analysis.

A novel four-component tandem protocol for the stereoselective synthesis of highly functionalised thiazoles

The reaction of bis(aroylmethyl) sulfides with aromatic aldehydes and ammonium acetate in 1:2:1 molar ratio under solvent-free microwave irradiation afforded predominantly a series of thiazoles, viz., 1-aryl-2-[5( Z)-5-arylmethylidene-2,4-diaryl-2,5-dihydrothiazol-2-yl]ethanones stereoselectively. This reaction presumably occurs via a Knoevenagel condensation–Michael addition–cyclocondensation–ring opening–ring closing Michael addition sequence. The intermediacy of ( Z, Z)-2,2′-thiobis(1,3-diarylprop-2-en-1-ones) in the above transformation is demonstrated by their conversion to the thiazoles upon reaction with ammonium acetate under solvent-free microwave irradiation.