Cascade Synthesis Research Articles

Bifunctional acidic ionic liquid-catalyzed decarboxylative cascade synthesis of quinoxalines in water under ambient conditions

An acid-functionalized ionic liquid (IL)-catalyzed cascade decarboxylative cyclization of 2-arylanilines with α-oxocarboxylic acids was developed.

Cascade synthesis and optoelectronic applications of intermediate bandgap Cu3VSe4 nanosheets

Two-dimensional (2D) ternary materials recently generated interest in optoelectronics and energy-related applications, alongside their binary counterparts. To date, only a few naturally occurring layered 2D ternary materials have been explored. The plethora of benefits owed to reduced dimensionality prompted exploration of expanding non-layered ternary chalcogenides into the 2D realm. This work presents a templating method that uses 2D transition metal dichalcogenides as initiators to be converted into the corresponding ternary chalcogenide upon addition of copper, via a solution-phase synthesis, conducted in high boiling point solvents. The process starts with preparation of VSe2 nanosheets, which are next converted into Cu3VSe4 sulvanite nanosheets (NSs) which retain the 2D geometry while presenting an X-ray diffraction pattern identical with the one for the bulk Cu3VSe4. Both the scanning electron microscopy and transmission microscopy electron microscopy show the presence of quasi-2D morphology. Recent studies of the sulfur-containing sulvanite Cu3VS4 highlight the presence of an intermediate bandgap, associated with enhanced photovoltaic (PV) performance. The Cu3VSe4 nanosheets reported herein exhibit multiple UV–Vis absorption peaks, related to the intermediate bandgaps similar to Cu3VS4 and Cu3VSe4 nanocrystals. To test the potential of Cu3VSe4 NSs as an absorber for solar photovoltaic devices, Cu3VSe4 NSs thin-films deposited on FTO were subjected to photoelectrochemical testing, showing p-type behavior and stable photocurrents of up to ~ 0.036 mA/cm2. The photocurrent shows a ninefold increase in comparison to reported performance of Cu3VSe4 nanocrystals. This proves that quasi-2D sulvanite nanosheets are amenable to thin-film deposition and could show superior PV performance in comparison to nanocrystal thin-films. The obtained electrical impedance spectroscopy signal of the Cu3VSe4 NSs-FTO based electrochemical cell fits an equivalent circuit with the circuit elements of solution resistance (Rs), charge-transfer resistance (Rct), double-layer capacitance (Cdl), and Warburg impedance (W). The estimated charge transfer resistance value of 300 Ω cm2 obtained from the Nyquist plot provides an insight into the rate of charge transfer on the electrode/electrolyte interface.

Magnetically recoverable copper ferrite catalyzed cascade synthesis of 1,3‐dimethyl‐6‐nitro‐5‐arylpyrido[2,3‐d]pyrimidine‐2,4(1H,3H)‐diones under microwave irradiation and solvent‐less condition

In recent years, magnetically active CuFe2O4 nanoparticles have been gaining significant interest in the field of heterogeneous catalysis as those can be easily prepared and effortlessly recovered from a reaction system. Here, we are reporting our work on cascade syntheses of 1,3‐dimethyl‐6‐nitro‐5‐arylpyrido[2,3‐d]pyrimidine‐2,4(1H,3H)‐diones starting from 6‐[(dimethylamino)methylene‐amino]‐1,3‐dimethyluracil, aromatic aldehydes and nitromethane using magnetically active CuFe2O4 catalyst system under microwave irradiation and solvent‐less condition. The current methodology is a valued addition to the existing procedures of 5‐arylpyrido[2,3‐d]pyrimidines syntheses making best use of the diene behavior of 6‐[(dimethylamino)methylene‐amino]‐1,3‐dimethyluracil. However, heterogeneous catalysis has been employed for the first time to do the syntheses by carrying out [4 + 2]cycloaddition reaction between 6‐[(dimethylamino)methylene‐amino]‐1,3‐dimethyluracil and in situ generated 2‐(2‐nitrovinyl)arenes/heteroarenes. The methodology is highly time‐economic, and along with other features like easy recovery and good reusability of the catalyst, simple operating procedure, wide substrate scope, and good to excellent product yield, it offers the chemists a reaction protocol worth trying for the syntheses of 1,3‐dimethyl‐6‐nitro‐5‐arylpyrido[2,3‐d]pyrimidine‐2,4(1H,3H)‐diones. While laboratory prepared catalyst system was characterized using FT‐IR, XRD, SEM‐EDX, VSM, XPS and TEM analysis, all the synthesized compounds have been characterized using 1H and 13C NMR spectroscopy and HRMS.

Development of Silver Nanoparticles Decorated on Functional Glass Slide as Highly Efficient and Recyclable Dip Catalyst

AbstractThe development of a highly reusable and extremely efficient catalyst is still a fundamental as well as technological problem. Here, we report on the preparation and catalytic applications of Silver nanoparticles (AgNPs) immobilized on amine terminated glass slide as a dip catalyst for the transformation of nitrophenol, intramolecular cascade reaction and synthesis of 5‐Phenyl‐1H‐tetrazole. The dip catalyst system consists of AgNPs stabilized on microscopic glass slide as the support. AgNPs were decorated on the glass slide by modifying the glass surface with (3‐Aminopropyl)triethoxysilane (APTES). The dip catalyst was characterized using SEM, EDX, FTIR, and TEM, and AFM. This system is found to be stable in both organic and aquous solvents and exhibits excellent recyclability even at high temperatures. The catalyst was used for 20 cycles of nitrophenol reduction reaction and 5 cycles for other reactions in this study to test its efficiency. No any significant decrease was observed in the activity of the catalyst. We have also investigated the applicability of the AgNPs immobilized on functional glass slide as surface enhanced Raman scattering (SERS) substrate to understand the catalytic reduction reaction mechanism.

Porous aromatic frameworks with precisely controllable conjugation lengths for visible light-driven photocatalytic selective C-H activation reactions

Organic visible light-active porous polymers have been established as a novel promising class of heterogeneous photocatalysts for a variety of important photoredox reactions. To date, given the usually fully conjugated nature of most polymer-based photocatalysts, precise control of the energy band structure and thereby their redox potentials in photocatalytic reactions while retaining highly active surface area is a huge challenge. Here, we design a series of porous aromatic frameworks (PAFs) with precise control of the conjugation length within the polymer architecture as efficient metal-free photocatalysts. The polymers exhibit a high intrinsic surface areas of up to 1070 m2/g as well as tunable optical and redox properties that allow applications in C-H activation reactions driven selectively either by the photogenerated electron or hole species. Furthermore, as an attractive example for high-value chemical conversions, the formation of dantrolene, an active pharmaceutical ingredient, was successfully catalyzed by the PAFs in the simple one-pot cascade synthesis.

Cascade Synthesis of Pyrroles from Nitroarenes with Benign Reductants Using a Heterogeneous Cobalt Catalyst.

A bifunctional 3d‐metal catalyst for the cascade synthesis of diverse pyrroles from nitroarenes is presented. The optimal catalytic system Co/NGr‐C@SiO2‐L is obtained by pyrolysis of a cobalt‐impregnated composite followed by subsequent selective leaching. In the presence of this material, (transfer) hydrogenation of easily available nitroarenes and subsequent Paal–Knorr/Clauson‐Kass condensation provides >40 pyrroles in good to high yields using dihydrogen, formic acid, or a CO/H2O mixture (WGSR conditions) as reductant. In addition to the favorable step economy, this straightforward domino process does not require any solvents or external co‐catalysts. The general synthetic utility of this methodology was demonstrated on a variety of functionalized substrates including the preparation of biologically active and pharmaceutically relevant compounds, for example, (+)‐Isamoltane.

Cascade Synthesis of Pyrroles from Nitroarenes with Benign Reductants Using a Heterogeneous Cobalt Catalyst

AbstractA bifunctional 3d‐metal catalyst for the cascade synthesis of diverse pyrroles from nitroarenes is presented. The optimal catalytic system Co/NGr‐C@SiO2‐L is obtained by pyrolysis of a cobalt‐impregnated composite followed by subsequent selective leaching. In the presence of this material, (transfer) hydrogenation of easily available nitroarenes and subsequent Paal–Knorr/Clauson‐Kass condensation provides >40 pyrroles in good to high yields using dihydrogen, formic acid, or a CO/H2O mixture (WGSR conditions) as reductant. In addition to the favorable step economy, this straightforward domino process does not require any solvents or external co‐catalysts. The general synthetic utility of this methodology was demonstrated on a variety of functionalized substrates including the preparation of biologically active and pharmaceutically relevant compounds, for example, (+)‐Isamoltane.

Hemishell Zeolites Synthesized by Asymmetric Modification as Biphasic Nanoreactors with Tunable Amphiphilicity for Catalysis of Cascade Reactions.

It is strongly desired to design and synthesize amphiphilic nanoreactors with tunable compatibility, which are stable at the biphasic interface in both acidic and alkaline environments. Herein, a novel amphiphilic R1-ZSM-5-R2 nanoreactor with adjustable hydrophilic-lipophilic balance (solid) (HLB(S)) values has been successfully synthesized by hydrophilic/lipophilic asymmetric modification of the surface of hemishell zeolites. The hemishell zeolites obtained by alkali etching have different surfaces for this asymmetric modification. Owing to the unique hemishell structures and asymmetric modification, the R1-ZSM-5-R2 nanoreactors with an optimized type and amount of modified organosilanes show excellent stability and emulsifying properties under extreme environments, which is important for cascade reactions in a biphasic system. The modified amino groups on the surface of the nanoreactors not only enhance the hydrophilicity of the hemishell zeolites and stabilize ultrasmall Pt nanoparticles (1.90 nm) but also used for the catalytic synthesis of trans-cinnamaldehyde. The Pt@R1-ZSM-5-R2 amphiphilic catalysts fabricated through a one-step reduction of Pt nanoparticles present outstanding performances in the biphasic cascade synthesis of cinnamic acid, achieving a very high turnover frequency (TOF) of 978 h-1. The TOF values of the catalysts correspond well to the HLB(S) values of the R1-ZSM-5-R2 nanoreactors.

A transition metal-free cascade reaction using heterogeneous tin(IV)oxide catalyzed and iodine promoted synthesis of 3-aroylimidazo[1,2-a]pyridines

The cascade synthesis of 3-aroylimidazo[1,2-a]pyridines using chalcones and 2-aminopyridine was achieved over the SnO2/I2 catalytic system in toluene at ambient air atmosphere. The catalyst shows high activity towards the broad substrate scope of the various aromatic and heterocyclic chalcones with 2-aminopyridine, 4-methyl 2-aminopyridine, and 5-methyl 2-aminopyridine in good yields during the synthesis of 3-aroylimidazo[1,2-a]pyridines. The methodology was further extended for the one-pot three-component synthesis of 3-aroylimidazo[1,2-a]pyridines using acetophenone, benzaldehyde, and 2-aminopyridine derivatives. The present protocol describes the easy purification methodology in the synthesis of 3-aroylimidazo[1,2-a]pyridines.

One-pot bi-enzymatic cascade synthesis of puerarin polyfructosides

Enzymatic glycosylation is an efficient way to increase the water solubility and the bioavailability of flavonoids. Levansucrases from Bacillus subtilis (Bs_SacB), Gluconacetobacter diazotrophicus (Gd_LsdA), Leuconostoc mesenteroides (Lm_LevS) and Zymomonas mobilis (Zm_LevU) were screened for puerarin (daidzein-8-C-glucoside) fructosylation. Gd_LsdA transferred the fructosyl unit of sucrose onto the glucosyl unit of the acceptor forming β-d-fructofuranosyl-(2→6)-puerarin (P1a), while Bs_SacB, Lm_LevS and Zm_LevU synthesized puerarin-4’-O-β-D-fructofuranoside (P1b) and traces of P1a. The Gd_LsdA product P1a was purified and assayed as precursor for the synthesis of puerarin polyfructosides (PPFs). Bs_SacB elongated P1a more competently forming a linear series of water-soluble PPFs reaching at least 21 fructosyl units, as characterized by HPLC-UV-MS, HPSEC and MALDI-TOF-MS. Simultaneous or sequential Gd_LsdA/Bs_SacB reactions yielded PPFs directly from puerarin with the acceptor conversion ranging 82–92 %. The bi-enzymatic cascade synthesis of PPFs in the same reactor avoided the isolation of the intermediate product P1a and it is appropriate for use at industrial scale.

Palladium-catalyzed cascade synthesis of spirocyclic oxindoles via regioselective C2-H arylation and C8-H alkylation of naphthalene ring

A simultaneous C2-H arylation and C8-H alkylation of naphthalene ring has been achieved by palladium-catalyzed cascade reaction of N-(2-halophenyl)-2-(naphthalen-1-yl)acrylamides with aryl iodides, which provides an efficient method for synthesizing various aryl-substituted spirocyclic oxindoles. The protocol enables three CC bonds formation via an intramolecular Heck reaction and sequentially regioselective CH bond activation.

Triethyl Phosphite/Benzoyl Peroxide Mediated Reductive Dealkylation of O‐Benzoylhydroxylamines: A Cascade Synthesis of Secondary Amides

A new triethyl phosphite/benzoyl peroxide (BPO) mediated system has been developed for the synthesis of secondary amides with good to excellent yields in a single step. This unprecedented cascade process involves sequential reduction of N–O bond and benzoylation followed by dealkylation of N–C bond of O‐benzoylhydroxylamines (O‐BHA). The methodology is versatile as it tolerates a variety of aromatic and aliphatic O‐BHA as substrates to access secondary amides.

One-pot cascade ring enlargement of isatin-3-oximes to 2,4-dichloroquinazolines mediated by bis(trichloromethyl)carbonate and triarylphosphine oxide

An efficient and convenient one-pot cascade synthesis of 2,4-dichloroquinazolines directly from isatin-3-oximes with the addition of bis(trichloromethyl)carbonate and triarylphosphine oxide was developed, leading to substituted quinazolines in moderate to excellent yields. The efficiency of this transformation was demonstrated by compatibility with a range of functional groups. Thus, the method represents a convenient and practical strategy for the synthesis of substituted 2,4-dichloroquinazolines.

Three-Component Cascade Synthesis of Fully Substituted Trifluoromethyl Pyrroles via a Cu(II)/Rh(III)-Promoted Aza-Michael Addition/Trifluoromethylation Cyclization/Oxidation Reaction

A three-component cascade reaction of 1,3-enynes, anilines, and Togni-II reagent has been developed to give fully substituted trifluoromethyl pyrroles with high regioselectivity under mild conditions. The transformation proceeds through a Cu(II)/Rh(III)-promoted cascade aza-Michael addition/trifluoromethylation cyclization/oxidation reaction, affording trifluoromethyl pyrrole derivatives as primary products.

One-pot cascade synthesis of benzopyrans and dihydropyrano[c]chromenes catalyzed by lipase TLIM.

Lipase TLIM was reported to be an efficient, commercially available and reusable catalyst for the Knoevenagel-Michael cascade reactions of aldehydes, malononitrile/ethyl cyanoacetate and 4-hydroxycoumarin/1, 3-cyclohexanedione/dimedone in aqueous DMSO. This methodology presents many superiorities such as simple procedure, mild reaction conditions, commercially available and reusable catalyst, high substrate applicability, the ability to be scaled up, and good to excellent yields.

Copper-Mediated Cascade Synthesis of Open-Cage Fullerenes

An open-cage fullerene bearing an eight-membered ring orifice has been synthesized in one pot by the reaction of C60 with propargylic phosphate in the presence of CuCl. The reaction cascade involves the transformation of the phosphate to the 1,3-dienyl phosphate, which enables the reaction with C60 by [4 + 2] cycloaddition to form the cyclohexene-annulated intermediate, and subsequent intramolecular syn-elimination of the phosphodiester affords the cyclohexadiene-annulated fullerene derivative as the precursor for the open-cage fullerene.

Palladium-Catalyzed Cascade Synthesis of Novel Quinolone- Bis(indolyl)methane Hybrids as Promising α-Glucosidase Inhibitors

An unexpected cascade reaction is developed for the construction of functionalized 3-bis(indol-3-yl)methylquinoline-2(1H)-ones. Three C–C bonds and one ring are created in one pot triggered by Pd-catalyzed C-3 alkenylation of indole with 2-acyl-N-acrylaniline derivatives. A series of complex and specific quinoline-2(1H)-ones were produced, most of them showed significant α-glucosidase inhibitory activities.

Iron‐Mediated Ring‐Opening and Rearrangement Cascade Synthesis of Polysubstituted Pyrroles from 4‐Alkenylisoxazoles

AbstractAn iron‐mediated ring‐opening and rearrangement cascade from 4‐alkenylisoxazoles to polysubstituted pyrroles is described. The cascade reaction conditions are compatible with a variety of functional groups, including ketones, esters, amides, and aryl halides. High reactivity is maintained even if the reaction scale is expanded to 0.5 grams. It is the first iron‐catalyzed rearrangement of 4‐alkenylisoxazoles to pyrroles that is independent of the presence of the alkoxy or amino group at position 5 of the isoxazole substrates. A plausible mechanism of the iron‐mediated cascade reaction is proposed.magnified image

Characterization of alditol oxidase from Streptomyces coelicolor and its application in the production of rare sugars

A synthetic platform for the cascade synthesis of rare sugars using Escherichia coli whole cells was established. In the cascade, the donor substrate dihydroxyacetone phosphate (DHAP) was generated from glycerol by glycerol kinase (GK) and glycerol phosphate oxidase (GPO). The acceptor d-glyceraldehyde was directly produced from glycerol by an alditol oxidase. Then, the aldol reaction between DHAP and d-glyceraldehyde was performed by l-rhamnulose-1-phosphate aldolase (RhaD) to generate the corresponding sugar-1-phosphate. Finally, the phosphate group was removed by fructose-1-phosphatase (YqaB) to obtain the rare sugars d-sorbose and d-psicose. To accomplish this goal, the alditol oxidase from Streptomyces coelicolor (AldOS.coe) was expressed in E. coli and the purified AldOS.coe was characterized. Furthermore, a recombinant E. coli strain overexpressing six enzymes including AldOS.coe was constructed. Under the optimized conditions, it produced 7.9 g/L of d-sorbose and d-psicose with a total conversion rate of 17.7% from glycerol. This study provides a useful and cost-effective method for the synthesis of rare sugars.

N-Functionalized Azaheterocycles through PIII/PV=O-Catalyzed Cascade Synthesis

N-Functionalized Azaheterocycles through PIII/PV=O-Catalyzed Cascade Synthesis