Microwave-assisted synthesis of asymmetric thiocarbonohydrazones under solvent-free conditions

Six new asymmetric thiocarbonohydrazones 3a-3f were synthesized from following steps:firstly hydrazine hydrate reacted with carbon disulfide to form thiocarbonohydrazide(1) under microwave irradiation.Then compound(1) reacted with ketone and different aldehydes step by step to give 3a-3f with excellent yields under solvent-free conditions using microwave irradiation.Their structures have been determined by elemental analysis,IR,MS and ~1H NMR data.     

Aromaticity in azlactone anions and its significance for the Erlenmeyer synthesis

Azlactone anions—the key intermediates in the classical Erlenmeyer synthesis of amino acids—apparently possess aromatic stabilization, as indicated by the relative rate of base catalyzed deuterium exchange in the following analogs: 1-methyl-2-phenyl-5(4H)-imidazolone > 2-phenyl-5(4H)-oxazolone (azlactone) > 3,3-dimethyl-2-phenyl-4(3H)-pyrrolone. This is paralleled by the relative rate of condensation of these compounds with hexadeuteroacetone. Reported pK_a data also suggest that the azlactone products of the Erlenmeyer synthesis are analogs of the fulvenes.     

Microwave-assisted simple, one-pot, four-component synthesis of 2,4,6-triarylpyrimidines under solvent-free conditions

2,4,6-Triarylpyrimidines are synthesized via a simple, one-pot, four-component reaction between aryl methyl ketones, benzaldehydes, aromatic nitriles, and hydroxylamine under microwave irradiation and solvent-free conditions in good to excellent yields.     

An efficient and solvent-free one-pot synthesis of dihydropyrimidinones under microwave irradiation

An efficient synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives using formic acid as catalyst, from aldehydes,β-ketoester and urea(thiourea) without solvent under the irradiation of microwave is described. Compared with the classical Biginelli reaction, this new method has the advantage of good yields (77-94% for aromatic aldehydes) and short reaction time (3-8 min).     

Catalyst-free and solvent-free method for the synthesis of quinoxalines under microwave irradiation

A facile procedure for the synthesis.of quinoxalines is being reported starting from benzil and 1,2-diaminobenzene. Thereactions were carried out catalyst-free, solvent-free and under microwave irradiation conditions in high yield (84-98%) with short time (3-6 rain) and environmental benign, as well as convenient operation. The structures of all the compounds have been confirmed on the basis of their IR, 1H NMR, and/or 13C NMR, mass spectral data.     

An expeditious and one-pot synthesis of unsymmetrical 2,5-disubstituted-1,3,4-oxadiazoles under microwave irradiation and solvent-free conditions

A one-pot synthesis of some unsymmetrical 2,5-disubstituted-1,3,4-oxadiazoles via cyclocondensation of benzoylhydrazines with orthoesters under solvent-free and microwave conditions are described here. The reaction is efficiently catalyzed by silica- supported sulfuric acid as it provided the title compounds in high yields and relatively short times. The catalyst is reusable and can be applied several times without considerable decrease in the yields and rates of the reactions.     

Microwave-assisted efficient, one-pot, three-component synthesis of 3,5-disubstituted 1,2,4-oxadiazoles under solvent-free conditions

A novel synthesis of 1,2,4-oxadiazoles is described from a one-pot, three-component reaction between nitriles, hydroxylamine, and aldehydes under microwave irradiation and solvent-free conditions in excellent yields.     

Immobilized ionic liquid on superparamagnetic nanoparticles as an effective catalyst for the synthesis of tetrasubstituted imidazoles under solvent-free conditions and microwave irradiation

The ionic liquid 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride was immobilized on superparamagnetic Fe₃O₄ nanoparticles (IL-MNPs) and used as an efficient heterogeneous catalyst for the one-pot synthesis of 1,2,4,5-tetrasubstituted imidazoles under solvent-free conditions using microwave irradiation. The reactions in conventional heating conditions were compared with the microwave-assisted reactions. The combined merits of microwave irradiation and immobilized ionic liquid on superparamagnetic nanoparticles make the four-component condensation with safe operation, low pollution, and rapid access to products and simple work-up.     

NHC triggered cascade metal-free synthesis of 2,3-diarylated indoles under solvent-free conditions

A new cascade strategy to the synthesis of 2,3-diarylated indoles via the metal-free reaction of aryl aldehyde and aryl amine triggered by N-heterocyclic carbene (NHC) under solvent-free conditions, has been disclosed. The protocol has the advantages of easy work-up, high yields, wide application scope, and an environmentally benign procedure compared with the reported methods.     

The first synthesis of β-phenylchalcogeno-α,β-unsaturated esters via hydrochalcogenation of acetylenes using microwave and solvent-free conditions

A simple, clean, and efficient solvent-free protocol was developed for hydrochalcogenation of methyl propiolate derivatives with phenylchalcogenolate anion generated in situ from the respective diphenyl dichalcogenide (S, Se, Te) using alumina supported sodium borohydride. This efficient and improved method is general and furnishes the (Z)-β-phenylchalcogeno-α,β-unsaturated esters in yields and with selectivity comparable to those using organic solvent and inert atmosphere. The use of MW irradiation facilitates the procedure and accelerates the reaction.     

Studies on oxidations with IBX: oxidation of alcohols and aldehydes under solvent-free conditions

A variety of allylic and benzylic alcohols are oxidized to their respective carbonyl compounds with IBX under solvent-free conditions at ca. 60-70 °C. It has also been found that some of the aromatic aldehydes also undergo oxidation when heated with IBX at 90 °C under solvent-free conditions; notably, this transformation does not occur under the otherwise identical but heterogeneous conditions.     

A rapid and efficient method for synthesis of new 3-arylideneisobenzofuran-1(3H)-one derivatives catalyzed by acetic anhydride under solvent-free and microwave conditions

In this study we have described the synthesis of new 3-arylidene isobenzofuran-1(3H)-one derivatives. Condensation reaction of phthalic anhydride and quinoline derivatives under solvent-free condition and microwave irradiation in the presence of acetic anhydride as catalyst in good excellent yield is reported.     

Iodination of alcohols using triphenylphosphine/iodine under solvent-free conditions using microwave irradiation

A straightforward and effective procedure for the conversion of benzylic, allylic and aliphatic alcohols to the corresponding iodides using Ph₃P/I₂ under solvent-free conditions using microwave irradiation is reported.     

Solvent-free synthesis of 2-amino-4-arylthiazoles under microwave irradiation

2-Amino-4-arylthiazoles were prepared in a one-pot solvent-free procedure by reaction of p-substituted acetophenones with thiourea and iodine under microwave irradiation.     

Ionic liquid/potassium hydroxide catalyzed solvent-free, one-pot synthesis of diarylglycolic acids from aromatic aldehydes under microwave

Ionic liquid in conjugation with KOH brings about an efficient, one-pot, green synthesis of α,α-diarylglycolic acids in reasonably high yields from aromatic aldehydes under solvent-free condition using conventional heating as well as microwave irradiation.     

Microwave-assisted effi cient synthesis of azlactone derivatives using 2-aminopyridine-functionalized sphere SiO2 nanoparticles as a reusable heterogeneous catalyst

In the present work, the highly efficient Erlenmeyer synthesis of azlactones catalyzed by 2- aminopyridine, supported on nano-sphere SiO2 is reported. First, the silica nanoparticles were modified with triethoxysilylpropyl chloride and then 2-aminopyridine was attached to the support via covalent linkages. This new heterogenized catalyst was used for efficient microwave-assisted synthesis of azlactone derivatives with Ac2O as a condensing agent under solvent-free conditions. The present method offers advantages including high yields, short reaction times and simple work-up. Also, the catalyst can be easily recycled and reused several times, which makes this method attractive, economic and environmentally-benign.     

One-pot synthesis of pyrimidines under solvent-free conditions

N,N,N’,N’-Tetrabromobenzene-1,3-disulfonamide was used as an efficient catalyst for the one-pot synthesis of pyrimidine derivatives in excellent yields from triethoxymethane, ammonium acetate, and various ketone derivatives at 100–110 °C under solvent-free conditions.     

Efficient synthesis of heterophosphole-2-sulfides by solvent-free microwave reaction

Microwave irradiation of a stoichiometric amount of Lawesson’s reagent in the presence of o-aminophenols, o-aminothiophenols, o-phenylenediamines, or catechols leads to benzoxazaphosphole-, benzothiazaphosphole-, benzodiazaphosphole-, and benzodioxaphosphole-2-sulfides, respectively, in good yields in a fast and direct way under solventless conditions. The procedure requires short reaction times and is similar for all reagents; thus it may be used in parallel synthesis.     

A novel and efficient strategy for the synthesis of various carbamates using carbamoyl chlorides under solvent-free and grinding conditions using microwave irradiation

We present an efficient,fast and simple strategy of generating the intermediate carbamoyl chlorides from secondary amines using stoichiometric amounts of bis(trichloromethyl)carbonate(BTC) in solution and solvent-free conditions with excellent yields.The results obtained showed the yield increasing on whether a base was used.Finally,an efficient and rapid synthesis of variety carbamate derivatives was developed by the reaction with a high variety of different alcohols,phenols,diols and this intermediate at room temperature with grinding and in solvent-free conditions under microwave irradiation.The presence of various safe bases is shown to be effective in reducing the reaction times,increasing the yields and easing purification.The present method does not involve any hazardous phosgene.     

无溶剂条件下离子液体催化香豆素衍生物的绿色合成(英文)

Brnsted acidic ionic liquids, namely 2-pyrrolidonium hydrogen sulfate, N-methyl-2-pyrrolidonium hydrogen sulfate, N-methyl-2-pyrrolidonium dihydrogen phosphate, (4-sulfobutyl)tris(4-sulfophenyl)phosphonium hydrogen sulfate, and triphenyl(propyl-3-sulfonyl)phosphonium toluenesulfonate, catalyzed efficient Pechmann condensation of phloroglucinol with β-keto ethyl/ methyl esters. 5,7-Dihydroxy-4-methylcoumarin and 5,7-dihydroxy-4-phenylcoumarin were prepared in good to excellent yields under mild, ambient, and solvent-free conditions. Pyrano[2,3-h] coumarins were then prepared by one-pot three-component reactions of 5,7-dihydroxy-4-subsituted coumarin, malononitrile, and aldehydes in the presence of catalytic amounts of Br nsted basic ionic liquids, namely 2-hydroxyethylammonium formate, 3-hydroxypropanaminium acetate, 1-butyl-3-methylimidazolium hydroxide, pyrrolidinium formate, and pyrrolidinium acetate, under thermal solvent-free conditions. The catalysts are environmentally benign and can be easily prepared, stored, and recovered without significant loss of activity.