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).     

An efficient green protocol for the synthesis of chalcones by a Claisen–Schmidt reaction using bismuth(III)chloride as a catalyst under solvent-free condition

Abstract

An environmentally benign protocol for the synthesis of chalcones by the Claisen–Schmidt condensation of aldehydes with ketones using eco-friendly non-toxic bismuth(III)chloride catalyst under solvent-free condition is reported. In this protocol, the reaction time is very short, yields are high, and there are no other pollutants formed.     

An efficient synthesis of β-aminoketone compounds through three-component Mannich reaction catalyzed by calcium chloride

Abstract  

Various β-aminoketones were synthesized in a three-component reaction of ketones, aldehydes, and amines in the presence of calcium chloride as catalyst in ethanol in high yields as compared to other synthetic methods. The advantages of this new method are a short reaction time (2 h), high yields, easy workup, convenience, low cost, and eco-friendly protocol.     

A rapid and efficient synthesis of indoloquinolinone and its analogues under microwave irradiation

A rapid and efficient method was established for the synthesis of indoloquinolinone and its analogues using acid-promoted cyclization in the present of PPA. All the reactions were completed in good yields in lOmin under microwave irradiation.     

An efficient synthesis of 3,4-dihydropyridone via a tandem olefin isomerization–ring-closing metathesis reaction

Novel 3,4-dihydropyridones were efficiently prepared via a tandem olefin isomerization–ring-closing metathesis reaction catalyzed by the second-generation Grubbs catalyst. The products were further functionalized at the 5-position, providing an interesting structural motif to be evaluated in medicinal chemistry.     

An altemative synthetic approach towards erythrinan and homoerythrinan alkaloids by tandem semipinacol/intramolecular Schmidt reaction

An alternative construction of A-B-D ring-system of erythrinan and homoerythrinan alkaloids by TiCl_4-mediated tandem semipinacol/intramolecular Schmidt reaction ofα-siloxyepoxyazide was addressed and the unusual epoxidation stereoselectivity was observed in preparation of the substrate once again.     

An alternative synthetic approach towards erythrinan and homoerythrinan alkaloids by tandem semipinacol/intramolecular Schmidt reaction

An alternative construction of A-B-D ring-system of erythrinan and homoerythrinan alkaloids by TiCl4-mediated tandem semipinacol/intramolecular Schmidt reaction of α-siloxyepoxyazide was addressed and the unusual epoxidation stereoselectivity was observed in preparation of the substrate once again.     

Synthesis of new thioxanthenes by organocatalytic intramolecular Friedel–Crafts reaction

An efficient organocatalytic route has been developed to synthesize novel substituted thioxanthenes (2a–2v) starting from diaryl thioether alcohols (1a–1v) using the intramolecular Friedel–Crafts reaction. The starting materials were obtained in two stages via a coupling reaction followed by the Grignard reaction. In this study, we tried for the first time to use some organic Brønsted acids as organocatalysts (3a–3h) in the intramolecular Friedel–Crafts cyclization reaction of thioether alcohols. The synthesis of original substituted thioxanthenes was achieved within 15?minutes by using N-triflylphosphoramide (3h) with quantitative yields in THF at room temperature.     

Flow synthesis of annulated 5-aryl-substituted pyridines by tandem intramolecular inverse-electron-demand hetero-/retro-Diels–Alder reaction

5-Aryl-substituted annulated pyridines can be accessed directly from the corresponding acetylene substituted pyrimidines through an intramolecular inverse-electron-demand hetero-/retro-Diels–Alder (ihDA/rDA) reaction cascade carried out in continuous flow. Exploiting this new process, a series of cycloalka[c]pyridines that represent useful building blocks for medicinal chemistry were prepared in good to excellent yields with short processing times (<45 min). Importantly, utilizing the ability to superheat solvents in flow permits the replacement of typically employed high boiling solvents (e.g., nitrobenzene or chlorobenzene) with toluene.     

Enantioselective synthesis of benzomorphan analogues by intramolecular oxa-Pictet–Spengler cyclization

A new strategy toward biologically active enantiomerically pure benzomorphan analogues is described. The key steps in the synthesis are the l-proline catalyzed asymmetric α-aminooxylation of an aldehyde and the titanium tetrachloride promoted intramolecular oxa-Pictet–Spengler cyclization of (4R)-2-(bromomethyl)-4-(2,5-dimethoxybenzyl)-1,3-dioxolane. In the intramolecular oxa-Pictet–Spengler cyclization, cis-pyran 8a (71%) formed over the trans-pyran 8b (14%). Computational modeling studies provided an insight into the stereoselectivity of the products. Docking studies of benzomorphan derivatives indicated that compound 6c had the best binding efficiency, and that it formed extensive hydrogen bonding with TYR148 on transmembrane (TM) helix 3 and HIS297 on TM6 of the μ-opioid receptor, which belong to the G-protein coupled receptor super family.     

An efficient synthesis of β-ketoesters via transesterification and its application in Biginelli reaction under solvent-free,catalyst-free conditions

A simple and efficient transesterification process for the synthesis of β-ketoester derivatives has been achieved by the reaction of methyl β-ketoester with higher alcohols at 110 °C under solvent-free, catalyst-free conditions and its application in synthesis of 3,4-dihydropyrimidin-2(1H)-ones C-5 ester derivatives via Biginelli reaction has been described.     

Facile synthesis of α-methylidene-γ-butyrolactones: intramolecular Rauhut–Currier reaction promoted by chiral acid–base organocatalysts

The acid–base organocatalyzed intramolecular Rauhut–Currier (RC) reaction of the dienone enolates has been developed. The enantioselective RC process produces the highly functionalized α-methylidene-γ-butyrolactones as a single diastereomer with up to 98% ee.     

An efficient green MCR protocol for the synthesis of 2,4,5-trisubstituted imidazoles by Selectfluor™ under ultrasound irradiation

A simple, efficient and eco-friendly procedure has been developed using Selectfluor™ (15% mol) as a novel catalyst under ultrasound irradiation and solvent-free conditions for the synthesis of 2,4,5-triaryimidazole by a three-component, one-pot condensation of benzil, aryl aldehydes and ammonium acetate. The present methodology offers several advantages such as excellent yields, shorter reaction times (10–15 min) and environmentally benign milder reaction conditions and easy work-up.     

An efficient synthesis of substituted benzene-1,2-dicarboxaldehydes

Substituted-benzene-1,2-dicarbaldehydes were synthesized by the reaction of substituted-1,2-bis(dibromomethyl) benzenes with fuming sulfuric acid,followed by hydrolysis. The yields were signifi-cantly improved by introducing solid sodium bicarbonate into the reaction mixture before hydrolysis and workup.     

An efficient synthesis of novel pyridothieno-fused thiazolo[3,2-α]pyrimidinones via Pictet–Spengler reaction

An efficient method for the synthesis of novel pyrido[3',2':4',5']thieno[3',2':2,3]pyrido [4,5:d][1,3]thiazolo[3,2-a]pyrimidine-4-one derivatives(5) has been developed using a Pictet–Spengler reaction between 2-(3-aminothieno[2,3-b]pyridin-2-yl)thiazolo[3,2-a] pyrimidin-5-one(3), which could be obtained from the condensation of 7-(chloromethyl)-5H-thiazolo[3,2-a]pyrimidin-5-one(1) with3-cyanopyridine-2-thione(2) via Thorpe–Ziegler isomerization, and aromatic aldehydes under NH_2SO_3 H as catalysis in good yields.     

An efficient synthesis of diquinane-based bis-γ-lactones

An efficient stereoselective synthesis of both the diastereomers of diquinane-based conformationally constrained symmetric bis-γ-lactones starting from tricyclic derivative 9 is reported. The key step involves the intramolecular ring opening of an epoxide by the in situ formed hydrate of a diketone leading to the tetracyclic hemiacetal 10, which directly leads to the exo-hydroxy bis-γ-lactone derivatives 2 and 4 under basic hydrogen peroxide cleavage conditions. Conversion to the endo-hydroxy bis-γ-lactone derivatives 1 and 3 was accomplished through lithium hydroxide mediated S_N2 displacements in dimesylate 7, or more expeditiously, via trimesylate 21 through alkaline H₂O₂ mediated cleavage.     

Studies of manufacturing controlled-release graphene acid and catalyzing synthesis of chalcone with Claisen–Schmidt condensation reaction

In the paper, graphene acid (GA) was manufactured, using flake graphite as raw material, and the acidity and the structure of GA were characterized as well as. Then, chalcone was synthesized in the presence of GA, using acetophenone and benzaldehyde as the reactant. The results showed that the acidity of GA was for pH = 1.12 in aqueous solution, and it was structured by the graphene sheets with the spaces between the graphene sheet and the graphene sheet and sulfuric acid (H₂SO₄) and acetic acid (CH₃CO₂H) inside the spaces. At the same time, the results also exhibited that the chalcone yield was able to reach 60.36% when GA dosage was 5 g, and the chalcone yields could attain apart 60.36, 52.05 and 31.16% when 5 g of GA was used thrice. This shows that GA is not only a high-performance catalyst, but also a controlled-release catalyst.     

An efficient and simple synthesis of (−)-wine lactone

A, short and efficient diastereoselective synthesis of (−)-wine lactone (−)-4a involving FeCl₃/NaI-mediated iodolactonization of γ,δ-unsaturated acid 7 as the key step is described.