An efficient microwave-assisted synthesis of dihydropyrazinones and bis-benzoylketones

Microwave-assisted modified Sandmeyer reactions of oximinoacetanilides, themselves obtained from substituted primary aromatic amines, in concentrated H₂SO₄ give isatins. N-Acetylisatins undergo ring cleavage and subsequent ring closing with alkanediamines in the presence of ethanol under MW irradiation to give the corresponding dihydropyrazinones in excellent yields. Modification of the reaction conditions affords bis-benzoylketones under MW irradiation.     

An eco-friendly protocol for synthesis of thiourea derivatives: 1-benzoyl-3-benzylguanidine and 1-benzoyl-3-benzyl-O-ethylisourea. A possible non-purely thermal microwave assisted reaction

1-Benzoyl-3-benzylguanidine and 1-benzoyl-3-benzyl-O-ethylisourea were synthesized in good yields (68 and 76%, respectively) from 1-benzoyl-3-benzylthiourea and benzoyl-ethylthiocarbamate in dry media conditions using KF-Al₂O₃ under microwave irradiation. Strong nucleophilic amines promoted the sulfur elimination by attack on the thiocarbonyl group in both thiourea and thiocarbamates to afford guanidines and isourea, respectively. Transesterification products were obtained from p-TsOH catalyzed reaction of thiocarbamate with alcohols under MW-solvent-free conditions. Very important non-purely thermal MW specific effects were evidenced and attributed to stabilization by coulombic interactions between materials and waves.     

Rapid Microwave Induced Palladium Catalyzed Amination of Aryl Bromides

Summary.  The palladium-catalyzed coupling reaction of aryl bromides with various amines under microwave irradiation was studied using PdCl₂ [P(o-tolyl)₃]₂ which gave various aryl amines in good yields. The reactions were carried out under normal atmospheric conditions. Received September 3, 2001. Accepted October 10, 2001     

Rapid Microwave Induced Palladium Catalyzed Amination of Aryl Bromides

 The palladium-catalyzed coupling reaction of aryl bromides with various amines under microwave irradiation was studied using PdCl₂ [P(o-tolyl)₃]₂ which gave various aryl amines in good yields. The reactions were carried out under normal atmospheric conditions.     

Facile Synthesis of new 3,5‐Dispiro Substituted Piperidine Analogs via Microwave‐Assisted One Pot Multicomponent Reaction

An eco‐efficient one‐pot three component reaction for the synthesis of 3,5‐dispirosubstituted piperidines is reported by condensing of 2‐thiobarbituric acid, formaldehyde, and aromatic amines in the presence of a catalytic amount of p‐toluenesulfonic acid (1.0 equivalent) in dimethyl sulfoxide. The reactions were examined by two special methods such as classical heating and microwave (MW) irradiation. In general, improvements in rates and yields were observed when reactions were carried out under MW irradiation compared to the conventional method.     

Influence of microwave irradiation on enzyme kinetics

The in vitro effect of 2.45 GHz microwave irradiation on porcine pepsin activity under controlled temperature and absorbed microwave power via kinetic parameters was evaluated. Kinetic study with respect of time of irradiation demonstrated the existence of an inactivation effect of microwaves at pH 2 on pepsin molecule. Bovine serum albumin (BSA)-bromphenol blue (BPB) complex was used as substrate for the assay of pepsin by kinetic method. Depending on absorbed microwave dose, the degree of caused inactivation varies from 39.11 to 45.91% for 5 and 20 min of pepsin MW irradiation, respectively. The V _maxapp and K _mapp were calculated for low (5 min of MW irradiation) and higher specific absorbed dose (20 min of MW irradiation), as well as for untreated enzyme, from double reciprocal Lineweaver-Burk plot. The effect of microwaves on substrate (BSA-BPB complex) was also investigated. For reaction performed with MW irradiated substrate for 5 min the reaction rate was decreased for 15.15%, while for 20 min of substrate irradiation reaction rate was decreased for 25.52% compared to the control reaction. The article is published in the original.     

Microwave-enhanced bismuth triflate-catalyzed epoxide opening with aliphatic amines

In the presence of a catalytic amount of Bi(OTf)₃·4H₂O and under microwave irradiation, neat mixtures of epoxides and amines afforded smoothly the corresponding 2-amino alcohols. A wide variety of aliphatic amines were reacted with cycloalkene oxide, styrene oxide, and stilbene oxide. The reaction proceeded rapidly and afforded the 2-amino alcohols in high up to quantitative yields. All products could be obtained without aqueous work-up by simple filtration.     

Some aspects of polybenzimidazoles’ synthesis in Eaton reagent under different temperatures and microwave irradiation

Solution polycondensations of 3,3′-diaminobenzidine with two dicarboxylic acids, 4,4′-oxybis(benzoic acid) and hexafluoroisopropylidene bis(benzoic acid) to obtain two different polybenzimidazoles, OPBI and CF₃PBI, correspondingly, were studied in terms of formation of processable polymers and insoluble crosslinked gel. The syntheses were conducted in Eaton’s reagent using conventional heating (CH) at 100, 140 and 180?°C and microwave irradiation (MW) at 90 and 100?°C. The content of gel fraction was lesser using high temperature conditions under CH. The MW-assisted syntheses resulted in acceleration of polycondensations, but an abrupt growth of the insoluble gel was also observed under these conditions. The FTIR data showed that MW irradiation stimulated the side acylation reactions, and OPBI suffered more from the side acylation than CF₃PBI.     

Synthesis and antibacterial evaluation of new pyrido[3',2':4,5]thieno[3,2-d ]pyrimidin-4(3H)-one hybrids linked to different heteroarene units

A three-component protocol involving the reaction of 3-aminothieno[2,3-b]pyridine-2-carboxylate, Me₂NCH(OMe)₂ and heteroaryl (bis)amines in dioxane under microwave irradiation yielded a new series of pyrimidinones. The target hybrids were formed by an initial formamidine formation,Pyrazole-linked pyrimidinones displayed the best antibacterial activity against all the gram-positive and negative strains tested.     

Microwave acceleration in DABAL-Me3-mediated amide formation

Facile direct coupling of esters and secondary amines to afford tertiary amides proceeds under microwave irradiation using the air-stable trimethylaluminium source DABAL-Me₃ [(DABCO)(AlMe₃)₂]. Excellent yields (88-98%) are attained for cyclic secondary amines in reactions that are complete in 5-16 min. The process can be extended to the formation of Weinreb amides (upto 76% from commercial MeNHOMe·HCl) in a one-pot procedure using NaH to liberate the free methoxyamine.     

Facile amidation of esters with aromatic amines promoted by lanthanide tris (amide) complexes

The development of catalysts capable of catalyzing amidation of esters with amines to construct amides under mild conditions is of great importance. Compared to aliphatic amines, the direct catalytic amidation of esters with less nucleophilic aromatic amines is rather difficult. Employing simple lanthanide tris (amide) complexes Ln[N (SiMe₃)₂]₃(μ-Cl)Li (THF)₃ as the catalysts, it was found a broad range of aromatic amines and esters were efficiently converted into various amides in good yields under mild conditions. A plausible mechanism for this transformation was experimentally supported as starting from an amide exchange reaction between the lanthanide tris (amide) complex and the substrate amine.     

[Bmim]NO2/H3BO3 as an effective nitrosonium source for electrophilic aromatic nitrosation under MW-promoted solvent-free conditions

[Bmim]NO₂/H₃BO₃ was used as a nitrosonium source for the efficient synthesis of nitrosoarenes. The reaction was accomplished under MW irradiation at 60 W in a solventless system. Side processes such as oxidation or dealkylation were not observed during the nitrosation of alkyl phenyl ethers in the presence of this new reagent. The satisfactory results were obtained with very short reaction time, simplicity in the experimental procedure and good to excellent yields.     

Solid–liquid phase alkylation of P=O–functionalized CH acidic compounds utilizing phase transfer catalysis and microwave irradiation

Optimum conditions for the solid–liquid phase alkylation of methylenebis(diphenylphosphine oxide) (MBDPPO) and ethyl cyanomethylphosphonate (ECMP) were explored studying the role of phase transfer catalysis and microwave (MW) irradiation, as well as the effect of the cation of the alkali carbonate. It was found that the alkylation of MBDPPO may be best accomplished in acetonitrile, in the presence of a quaternary ammonium salt and Cs₂CO₃, while that of ECMP in the absence of catalyst and solvent using K₂CO₃. MW irradiation was beneficial in both cases. During the alkylation of ECMP, by‐products coming from the alcoholysis of the diethyl ester were also identified. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:174–179, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20673     

Microwave‐Assisted Solid‐Phase Synthesis of a 1,2‐Disubstituted Benzimidazole Library by Using a Phosphonium Linker

An efficient and rapid microwave‐assisted solid‐phase method for the synthesis of 5‐methyl‐1,2‐disubstituted benzimidazoles derivatives has been developed. The phosphonium linker, obtained by reaction between polymer‐supported triphenylphosphine and 4‐fluoro‐3‐nitrobenzyl iodide, underwent aromatic substitution with primary amines, followed by one‐pot reaction with aldehydes in the presence of SnCl₂·2H₂O, yielded the benzimidazole system under microwave irradiation. The final products were released from the resin with NaOH under microwave irradiation and were obtained in high purity and good overall yield.     

Iridium(III) Photocatalysis: A Visible‐Light‐Induced Dearomatizative Tandem [4+2] Cyclization to Furnish Benzindolizidines

A photocatalytic dearomatizative tandem [4+2] cyclization between N‐(2‐iodoethyl)indoles and a variety of alkenes leads to tri‐ and tetracyclic benzindolizidines with high diastereoselectivity and yield. The intermolecular annulation reaction is performed under visible‐light irradiation and employs [Ir(ppy)₃] or [Ir(dtbbpy)(ppy)₂] PF₆ as photocatalysts, in combination with tertiary amines as electron and hydrogen atom donors.     

Solvent-free conjugated addition of thiols to citral using KF/alumina: preparation of 3-thioorganylcitronellals, potential antimicrobial agents

A general, clean and easy method for the conjugated addition of thiols to citral promoted by KF/Al₂O₃ under solvent-free conditions at room temperature or under MW irradiation is described. It was found that the same protocol is applicable to the direct reaction of thiophenol with essential oil of lemon grass (Cymbopogon citratus) to afford directly 3-thiophenylcitronellal, a potential bactericide agent. The method was extended to others electron-poor alkenes with excellent results. The catalytic system can be reused up to three times without previous treatment with comparable activity.     

Microwave‐assisted alkylation of diethyl ethoxycarbonylmethylphosphonate under solventless conditions

The reaction of diethyl ethoxycarbonylmethylphosphonate with a series of alkyl halides, under microwave (MW) and solventless conditions at 120°C, in the presence of Cs₂CO₃ and in the absence of a phase transfer catalyst afforded the corresponding monoalkylated products in yields of >70%. The thermal variant carried out in boiling acetonitrile was slow and led to incomplete conversions. In the MW method, the phase transfer catalyst is substituted by MW irradiation and there is no need for a solvent. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:241–246, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21009     

Reversed-phase high performance liquid chromatographic separation of diastereomers of β-amino alcohols and microwave assisted synthesis of Marfey's reagent,its chiral variants and diastereomers

Ten chiral derivatizing reagents (CDRs) were synthesized by replacing the l-Ala–NH₂ moiety in Marfey's reagent (MR) by seven l-amino acid amides and three l-amino acids employing microwave irradiation (MW) and were characterized. Ten racemic amino alcohols were derivatized with these CDRs under MW. The diastereomers were separated on a reversed-phase C₁₈ column using binary mixtures of acetonitrile with aqueous trifluoroacetic acid (TFA) and triethylammonium phosphate buffer (TEAP). In general, amino acid variants of MR provided better separation of diastereomers in comparison to amino acid amide variants. The method was also found successful for the separation of 20 diastereomers from a mixture.     

A comparative study using conventional methods,ionic liquids,microwave irradiation and combinations thereof for the synthesis of 5-trifluoroacetyl-1,2,3,4-tetrahydropyridines

This study reports a comparison between conventional methods, ionic liquids, microwave (MW) irradiation, and combinations thereof for the synthesis of a series of fourteen 1-aryl-2-arylamino-5-trifluoroacetyl-1,2,3,4-tetrahydropyridines. In all of the reactions tested, the products were obtained at very good yields (87–97%), but the reaction times were very different, depending on the method used. Comparing to other methods, the time decreased to 1?min when [BMIM]BF₄ under MW irradiation was used, thus evidencing a synergic effect.     

Synthese und Eigenschaften von Bis(Dimethylarsino)-aminen

Synthesis and Properties of Bis(dimethylarsino) Amines Primary amines react with cacodyl halides (CH₃)₂AsX (X = Cl, J) under formation of Bis(dimethylarsino)amines RN[As(CH₃)₂]₂. Nine amines were prepared. The compounds were characterized by IR, ¹H-nmr and mass-spectroscopy. In the reactions with acid molecules cleavage of the As? N bond was observed. Formation of amine RNH₂ or ammoniumsalt (RNH₃)X and cacodyl derivates took place in all cases. The reactions of the arsinoamines with some carbonyles are reported.