DDQ catalyzed benzylic acetoxylation of arylalkanes: a case of exquisitely controlled oxidation under sonochemical activation

A one-pot ultrasound-assisted regio and stereoselective synthesis of indenoquinoxaline engrafted spiropyrrolidines

A catalyst free ultrasound-assisted regio-/stereoselective modular approach was accomplished for the synthesis of highly constrained indenoquinoxaline engrafted spiro pyrrolidines from easily available substrates. This one-pot strategy utilizes 1,3-dipolar cycloaddition from a four component reaction of ninhydrin, 1,2-phenylenediamine, β-nitrostyrene and benzylamine or amino acids under ultrasound irradiation. The transformation is mild and operationally simple, providing architecturally complex fused spiro polycyclic heterocycles. This synthesis was confined to follow the group-assistant-purification (GAP) chemistry process, which can avoid chromatographic purifications and use of catalysts and allows easy access to a novel class of spiro engrafted polyheterocyclic scaffolds, which may be beneficial in biomedical research/materials science in the near future. This opens an era for the formation of a single exo product, when compared with reported protocols, by merely switching over reaction conditions to US irradiation.

Ultrasound-promoted Green Synthesis of pyrido[2,1-a]isoquinoline Derivatives and Studies on their Antioxidant Activity

Aims & Objective: An efficient procedure for the synthesis of pyrido[2,1-a]isoquinoline derivatives in excellent yields was investigated using catalyst-free multicomponent reaction of phthaladehyde, methylamine, activated acetylenic compounds, alkyl bromides and triphenylphosphine in water under ultrasonic irradiation at room temperature. In addition, Diels- Alder reactions of pyrido[2,1-a]isoquinoline derivatives with activated acetylenic compounds under ultrasonic irradiation are investigated in two procedures. The advantages of this procedure compared to report methods are short time of reaction, high yields of product, easy separation of product, clean mixture of reaction and green media for performing reaction. In addition, because of having isoquinoline core in synthesized compounds, in this research antioxidant activity of some synthesized compounds was studied.

MATERIALS AND METHODS

To a stirred mixture of phthalaldehyde 1 (2 mmol) and methylamine 2 (2 mmol) in water (3 mL) under ultrasonic irradiation was added to activated acetylenic compounds 4 after 20 min. Alkyl bromide 3 and triphenylphosphine 5 react in another pot in water (3 mL) under ultrasonic irradiation for 15 min. After this time, this mixture was added to the first pot. After completion of the reaction, the solid residue was separated by filtration and washed with Et2O to afforded pure title compound 6.

RESULTS

In this work, generation of pyrido[2,1-a]isoquinoline derivatives 6 are performed using phthalaldehyde 1, methylamine 2, α-halo substituted carbonyls 3, activated acetylenic compounds 4 and triphenylphosphine 5 in water under ultrasonic irradiation condition at room temperature in excellent yield at short time.

CONCLUSION

In summary, multicomponent reaction of phthaladehyde, methylamine, activated acetylenic compounds, alkyl bromides and triphenylphosphine in water under ultrasonic irradiation at room temperature produced pyrido[2,1-a]isoquinoline derivatives in excellent yields. Also, Diels-Alder reaction of pyrido[2,1-a]isoquinoline derivatives with activated acetylenic compounds and triphenylphosphine under ultrasonic irradiation is investigated in two procedures. Also, the antioxidant activities of 6a, 6c, 6g and 6i were evaluated by DPPH radical scavenging and ferric reducing power analyzes. The compounds 6a exhibit excellent DPPH radical scavenging activity and FRAP compared to synthetic antioxidants BHT and TBHQ. The chief benefits of our method are high atom economy, green reaction conditions, higher yield, shorter reaction times, and easy work-up, which agree with some principles of green chemistry.

An Efficient Metal-Free Oxidative Esterification and Amination of Benzyl C-H Bond

An esterification and amination of benzylic C-H bonds was developed by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) under metal- and iodide-free conditions. Both carboxylic acids and amines could be used as ideal coupling partners for the oxidative coupling reactions with various diarylmethanes. A close to equal amount of coupling reagents was enough to afford the product in good to high yields.

Selective benzylic C-H monooxygenation mediated by iodine oxides

A method for the selective monooxdiation of secondary benzylic C–H bonds is described using an N-oxyl catalyst and a hypervalent iodine species as a terminal oxidant. Combinations of ammonium iodate and catalytic N-hydroxyphthalimide (NHPI) were shown to be effective in the selective oxidation of n-butylbenzene directly to 1-phenylbutyl acetate in high yield (86%). This method shows moderate substrate tolerance in the oxygenation of substrates containing secondary benzylic C–H bonds, yielding the corresponding benzylic acetates in good to moderate yield. Tertiary benzylic C–H bonds were shown to be unreactive under similar conditions, despite the weaker C–H bond. A preliminary mechanistic analysis suggests that this NHPI-iodate system is functioning by a radical-based mechanism where iodine generated in situ captures formed benzylic radicals. The benzylic iodide intermediate then solvolyzes to yield the product ester.

Directing activator-assisted regio- and oxidation state-selective aerobic oxidation of secondary C(sp(3))-H bonds in aliphatic alcohols

The regioselective conversion of an unactivated C(sp(3))-H bond of a methylene carbon (CH2) into a C-O single bond is an attractive reaction in organic synthesis. Herein, we present a strategy for a regio- and oxidation state-selective aerobic C-H oxidation based on an N-hydroxyamide-derived directing activator (DA), which is attached to a hydroxy group in alcohol substrates. The DA reacts with NOx species generated in situ from NaNO2, a Brønsted acid, and aerobic oxygen, and effectively generates an amidoxyl radical from the N-hydroxy moiety of the DA. Then, the amidoxyl radical promotes site-selective intramolecular C-H abstraction from methylenes with γ- (or δ-) selectivity. The thus-generated methylene radicals are trapped by molecular oxygen and NO. This process results in the predominant formation of nitrate esters as products, which suppresses undesired overoxidation. The products can be easily converted into alcohols after hydrogenolysis.

Novel ionic liquid supported on Fe3O4 nanoparticles and its application as a catalyst in Mannich reaction under ultrasonic irradiation

A family of novel ionic liquid with l-alanine and choline chloride as environmentally benign materials have been synthesized and grafted on Fe₃O₄ nanoparticles using easy preparation techniques. The structure of ionic liquid supported on Fe₃O₄ nanoparticles (IL-Fe₃O₄ NPs) characterized by various analyses such as FE-SEM, EDX, XRD, NMR, FTIR and VSM. The catalytic activities of this catalyst are examined in the Mannich reaction for synthesis of β-aminocarbonyl compounds under ultrasonic irradiation. The recyclability of catalyst is investigated, and the results have indicated that the catalyst can be recycled six times without obvious activity decreasing.

One-pot synthesis of new Pyrido [2,3-d] Pyrimidine derivatives under ultrasonic irradiation using organo catalyst 4-Dimethylaminopyridine (DMAP)

The one-pot synthesis of pyrido[2,3-d] pyrimidine derivatives has been reported via Knoevenagel-Michal addition pathways using substituted aromatic aldehydes, Cyanoacetamide and 6-aminouracil in N,N-dimethylformamide (DMF) solvent, with 4-dimethylaminopyridine (DMAP) as new organo catalyst catalyst under ultrasonic irradiation. The results showed that a series of aromatic aldehydes were effectively used to prepare the targeted pyrido [2, 3-d] pyrimidine derivatives with good to excellent yields (81-93 %) with no major effect on the yield of product by electron donating/withdrawing substituents. Short reaction time, environment friendly procedure, excellent yields, inexpensive and readily available catalyst are the advantages of this procedure. All synthesized compounds were characterized by IR, 1HNMR, 13CNMR and mass spectral data.

Efficient photolytic C-H bond functionalization of alkylbenzene with hypervalent iodine(iii) reagent

A practical approach to radical C-H bond functionalization by the photolysis of a hypervalent iodine(iii) reagent is presented. The photolysis of [bis(trifluoroacetoxy)iodo]benzene (PIFA) leads to the generation of trifluoroacetoxy radicals, which allows the smooth transformation of various alkylbenzenes to the corresponding benzyl ester compounds under mild reaction conditions.

Synthesis of esters via sp3 C–H functionalisation

This review describes various methods for the synthesis of eleven classes of esters involving sp³ C–H functionalisation.

Cross-dehydrogenative coupling for the intermolecular C-O bond formation

The present review summarizes primary publications on the cross-dehydrogenative C-O coupling, with special emphasis on the studies published after 2000. The starting compound, which donates a carbon atom for the formation of a new C-O bond, is called the CH-reagent or the C-reagent, and the compound, an oxygen atom of which is involved in the new bond, is called the OH-reagent or the O-reagent. Alcohols and carboxylic acids are most commonly used as O-reagents; hydroxylamine derivatives, hydroperoxides, and sulfonic acids are employed less often. The cross-dehydrogenative C-O coupling reactions are carried out using different C-reagents, such as compounds containing directing functional groups (amide, heteroaromatic, oxime, and so on) and compounds with activated C-H bonds (aldehydes, alcohols, ketones, ethers, amines, amides, compounds containing the benzyl, allyl, or propargyl moiety). An analysis of the published data showed that the principles at the basis of a particular cross-dehydrogenative C-O coupling reaction are dictated mainly by the nature of the C-reagent. Hence, in the present review the data are classified according to the structures of C-reagents, and, in the second place, according to the type of oxidative systems. Besides the typical cross-dehydrogenative coupling reactions of CH- and OH-reagents, closely related C-H activation processes involving intermolecular C-O bond formation are discussed: acyloxylation reactions with ArI(O2CR)2 reagents and generation of O-reagents in situ from C-reagents (methylarenes, aldehydes, etc.).

Direct transformation of arylpropynes to acrylamides via a three-step tandem reaction

A novel and metal-free acrylamides formation between arylpropynes and hydroxylamine hydrochloride through sp(3) C-H and C-C bond cleavage has been achieved with DDQ as an oxidant. The mechanistic study shows that the acrylamides are formed through a three-step tandem sequence, including cross-dehydrogenative-coupling (CDC) reaction, aza-Meyer-Schuster rearrangement and Beckmann rearrangement.

Relevance of sonochemistry or ultrasound (US) as a proficient means for the synthesis of fused heterocycles

Medicinal chemistry has been benefited by combinatorial chemistry and high throughput parallel synthesis. The use of sonochemistry under controlled conditions has been proved beneficial for medicinal chemistry and drug discovery process since it dramatically reduces reaction times, from days or hours to minutes. In addition, sonochemistry synthesis provides higher yields, lower cost, easy workups and greater purity as compared to lower yields, tedious workups, longer reaction times, lesser purity and termination of many by-products in the conventional thermal methods.

Ultrasonic synthesis, characterization of β-aminoketones by bismuth(III) triflate and determination of antigenotoxic properties

Direct-type catalytic Mannich reaction for the synthesis of β-aminoketones from cyclohexanone, substituted aromatic amines and aromatic or hetero-aromatic aldehydes has been applied in water with bismuth triflate under ultrasound. Good yields of the expected β-aminoketones were obtained from available substrates, at room temperature in 1–2 hours. This study was designed to evaluate the mutagenic and antimutagenic potential of synthesized β-aminoketones compounds using Ames/ Salmonella and Escherichia coli WP2 bacterial reverse mutation assay systems.

Experimental and DFT studies on the vibrational and electronic spectra of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

Vibrational and electronic spectral measurements were made for 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Optimized geometrical structure and harmonic vibrational frequencies were computed by DFT(B3LYP, CAMB3LYP, B3P86, M062X, mPW3PBE and PBE1PBE) using 6-311++G(d,p) basis set. Complete assignments of the observed spectra were proposed. The absorption spectra of the compound were computed both in gas-phase and in CH(2)Cl(2) solution using TDCAMB3LYP/6-311++G(d,p) and PCM-TDCAMB3LYP/6-311++G(d,p) approaches, respectively, the calculated results provide a good description of positions of the bands maxima in the observed electronic spectrum.

Ultrasound-promoted solvent-free aza-Michael addition of p-toluenesulfonamide to fumaric esters by potassium carbonate: Synthesis of p-toluenesulfonamide derivatives

An efficient, mild, inexpensive and eco-friendly protocol for the synthesis of p-toluenesulfonamide derivatives by aza-Michael addition reaction of p-toluenesulfonamide to fumaric esters using potassium carbonate under ultrasound irradiation was developed. This method is simple, convenient and the desired compounds are produced in good to excellent yield. The bulkiness of alkoxy group (-OR) of fumaric esters did not affect significantly on the yields and reaction times. This reaction worked well on linear and nonlinear alkyl fumarates. The reaction, surprisingly, was not successful on methyl fumarate. In this case methyl fumarate has been hydrolyzed to fumaric acid under reaction conditions.

Poly(4-vinylpyridinium)hydrogen sulfate: a novel and efficient catalyst for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under conventional heating and ultrasound irradiation

A simple and convenient procedure for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes is described through a one-pot condensation of 2-naphthol with aryl aldehydes in the presence of poly(4-vinylpyridinium)hydrogen sulfate as an efficient, cheap, readily synthesized and eco-friendly catalyst in a solvent free media using conventional heating and ultrasound irradiation.

Ultrasound-assisted synthesis of 2,2'-(2-oxoindoline-3,3-diyl)bis(1H-indene-1,3(2H)-dione) derivatives

A simple and efficient procedure for the synthesis of 2,2'-(2-oxoindoline-3,3-diyl)bis(1H-indene-1,3(2H)-dione) derivatives, 2,2'-(2-oxo-1,2-dihydroacenaphthylene-1,1-diyl)bis(1H-indene-1,3(2H)-dione) and 2,2'-(1,3-dioxo-2,3-dihydro-1H-indene-2,2-diyl)bis(1H-indene-1,3(2H)-dione) by the reaction of 1,3-indandione and isatins or acenaphthylene-1,2-dione or ninhydrine in ethanol under ultrasonic irradiation in the presence of p-TSA is reported. The advantages of this method are the use of an inexpensive and readily available catalyst, easy work-up, good yields, and the use of ethanol as a solvent that is considered to be relatively environmentally benign.

Ultrasonic irradiation and its application for improving the corrosion resistance of phosphate coatings on aluminum alloys

In this paper, ultrasonic irradiation was utilized for improving the corrosion resistance of phosphate coatings on aluminum alloys. The chemical composition and morphology of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effect of ultrasonic irradiation on the corrosion resistance of phosphate coatings was investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Various effects of the addition of Nd(2)O(3) in phosphating bath on the performance of the coatings were also investigated. Results show that the composition of phosphate coating were Zn(3)(PO(4))(2).4H(2)O(hopeite) and Zn crystals. The phosphate coatings became denser with fewer microscopic holes by utilizing ultrasonic irradiation treatment. The addition of Nd(2)O(3) reduced the crystallinity of the coatings, with the additional result that the crystallites were increasingly nubby and spherical. The corrosion resistance of the coatings was also significantly improved by ultrasonic irradiation treatment; both the anodic and cathodic processes of corrosion taking place on the aluminum alloy substrate were suppressed consequently. In addition, the electrochemical impedance of the coatings was also increased by utilizing ultrasonic irradiation treatment compared with traditional treatment.

A convenient synthesis of bis(indolyl)alkanes under ultrasonic irradiation using silica-supported Preyssler nanoparticles

Bis(indolyl)alkanes have been synthesised in excellent yields in the presence of catalytic amount of silica-supported Preyssler nano particles as green, reusable and efficient catalyst under ultra sonic irradiation.

Ultrasound-promoted greener synthesis of 2H-chromen-2-ones catalyzed by copper perchlorate in solventless media

Copper perchlorate is found to be a heterogeneous catalyst for an efficient and greener synthesis of 4-substituted 2H-chromen-2-ones via von Pechmann condensation of substituted phenols and beta-keto esters in solventless media with excellent yields using ultrasound irradiation. The present methodology offers several advantages such as excellent yields, simple procedure and milder conditions.

Ultrasound-promoted access to Baylis-Hillman amines

It is surveyed that the amination of the Baylis-Hillman acetates with primary amines can be dramatically promoted in improved yields and shortened reaction time under ultrasound irradiation than those under conventional stirring. The extensive scope of both amines and acetates are screened to investigate the relationship between substituents and their performance in such transformation.

Ultrasound-promoted a green protocol for the synthesis of 2,4-diarylthiazoles under ambient temperature in [bmim]BF(4)

A mild, efficient, facile and eco-friendly procedure for the synthesis of 2,4-diarylthiazoles from arylthioamides and alpha-bromoacetophenones in 1-n-butyl-3-methylimidazolium tetrafluoroborate as a "green" media under ultrasound irradiation at room temperature is described. It is interesting to mention that only one product was obtained when two different alpha-bromoacetophenones were reacted with 1,3-phenyl dithioamide as the substrate. Work-up is very simple and there is no need to purify the product. A recycling study confirmed that the ionic liquid can be reused multiple times without a significant loss in its activity.

Ultrasound-promoted greener synthesis of aryl-14-H-dibenzo[a,j]xanthenes catalyzed by NH4H2PO4/SiO2 in water

Silica supported ammonium dihydrogen phosphate (NH(4)H(2)PO(4)/SiO(2)) is found to be a recyclable heterogeneous catalyst for a rapid and efficient synthesis of various aryl-14-H-dibenzo[a,j]xanthenes with excellent yields using ultrasonic irradiation. The present methodology offers several advantages such as excellent yields, simple procedure, short reaction times and milder conditions.

Ultrasound-promoted greener synthesis of 2,4,5-trisubstituted imidazoles catalyzed by Zr(acac)4 under ambient conditions

A simple, efficient and green procedure has been developed for the synthesis of 2,4,5-trisubstituted imidazoles catalyzed by zirconium (IV) acetylacetonate using ultrasonic irradiation. The present methodology offers several advantages such as excellent yields, simple procedure, short reaction times and milder conditions.