Tandem Reaction Strategy Research Articles

CO2 derived ABA triblock all-polycarbonate thermoplastic elastomer with ultra-high elastic recovery

Although triblock polycarbonate thermoplastic elastomers (TPEs) have recently attracted great interests due to their biodegradability, insufficient attentions have been paid to improving the elastomeric properties. Through a tandem reaction strategy involving CO2 / allyl glycidyl ether (AGE) / cyclohexene oxide (CHO), poly(cyclohexene carbonate)-b-poly(allyl glycidyl ether carbonate)-b-poly(cyclohexene carbonate) (PCAC) is successfully synthesized using a metal-free Lewis acid-base pair catalyst. The synthesized PCACs are pure well-defined ABA triblock all-polycarbonate, which is supported by 1H NMR, gel permeation chromatography (GPC), and diffusion-ordered spectroscopy (DOSY). A simple modification by grafting alkylthiol chains to PCAC results in excellent TPEs named PCAC-g-S-CaH2a+1 (PCASaC). The synthesized TPEs are characterized by atomic force microscopy (AFM), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and mechanical test. They demonstrate a semi-network and semi-domain phase separation structure, wide service temperature range, good strength, high elongation, and extremely high elastic recovery properties. This low-cost, biodegradable, high-performance TPE shows great potential for applications in biomedical, wearable products, sports equipment, and other fields.

Asymmetric Mannich/Cyclization Reaction of 2-Benzothiazolimines and 2-Isothiocyano-1-indanones to Construct Chiral Spirocyclic Compounds.

An efficient and practical organocatalyzed asymmetric Mannich/cyclization tandem reaction strategy of 2-benzothiazolimines and 2-isothiocyanato-1-indanones was developed, and novel spirocyclic compounds containing benzothiazolimine and indanone scaffolds were obtained. This chiral thiourea-catalyzed Mannich/cyclization tandem reaction offers chiral spirocyclic compounds with continuous tertiary and quaternary stereocenters in good to high yields (up to 90%) with excellent diastereoselectivities (up to >20:1 dr) and enantioselectivities (up to 98% ee) at -18 °C. Additionally, the scaled-up synthesis was also performed with retained yield and stereoselectivity, and a reaction mechanism was also proposed.

Lewis Acid-Catalyzed Tandem Reaction Strategy for the Synthesis of Dihydrophenalene-Fused Lactones.

A Lewis acid-catalyzed tandem reaction strategy for the construction of a dihydrophenalene-lactone tetracyclic skeleton has been disclosed. Starting with 2-naphthol-tethered ketones and active methylene esters, the tandem reaction catalyzed by Sc(OTf)3 proceeded well to afford an array of dihydrophenalene-fused lactones with moderate to high efficiency and diastereoselectivity. Moreover, the synthetic utility of this protocol was demonstrated by easy gram-scale preparation and diverse product transformations.

Recent Progress in Palladium Catalysed Sustainable Synthesis of Heterocycles

Background: Palladium metal has been extensively used in the synthesis of organic molecules for the last few decades. Heterocyclic ring synthesis being a significant part of organic synthesis, transition metal catalysis, especially catalysis by palladium, has been actively employed in heterocyclic synthesis. However, since palladium is an expensive metal, there has always been an urge to reuse or recycle the palladium catalyst to make the process economically viable. Modern synthetic chemists are also in constant search for newer sustainable strategies for molecular synthesis, which will lead to eco-friendly synthetic protocols. Thus, in the last few years, palladium catalysed green synthesis of heterocycles has gained importance as these aim to make the synthetic organic chemical world slightly more sustainable. Methods: This review comprises palladium catalysed synthetic strategies that proceed in a sustainable fashion. A few protocols included here involve either organic solvent-free or greener solvents as reaction medium, which is one of the modes adopted towards sustainability. Other modes of sustainability included in this review are recyclability of the palladium catalyst, one pot tandem reaction strategy, use of air as oxidant, etc. All these modes aim at achieving one or the other green chemistry principles like reduction of waste and by-products, increasing atom economy, reduction of cost and use of safer solvents. Results: The review aims to reflect the scope of sustainability in palladium catalysed synthesis of heterocycles so that economically and environmentally viable synthetic methodologies may be selectively identified and applied in academia and industries. Conclusion: Keeping the principles of green chemistry in mind, in this review, we aim to compile the recent advancements in palladium catalysed sustainable synthesis of heterocycles in a single platter that may serve as a piece of reliable literature for further research in this area.

Metal‐Free, Base‐Promoted, Tandem Pericyclic Reaction: A One‐Pot Approach for Cycloheptane‐Annelated Chromones from γ‐Alkynyl‐1,3‐Diketones

AbstractA microwave‐assisted, base‐promoted, tandem cyclization reaction strategy has been developed for the synthesis of cyclohepta[b]chromones and spiro cyclohepta[b]chromones. Readily accessible γ‐alkynyl‐1,3‐diketones undergo intramolecular cyclization and 7‐endo‐trig carbocyclization to afford various cycloheptane‐annelated chromones in one‐pot reactions. This metal‐free protocol also led to the generation of polycyclic ring with a new C−C bond and a new C−O bond.magnified image

Cationic covalent-organic framework for sulfur storage with high-performance in lithium-sulfur batteries

Covalent organic frameworks (COFs) with pre-designed structure and customized properties have been employed as sulfur storage materials for lithium-sulfur (Li-S) batteries. In this work, a cationic mesoporous COF (COF-NI) was synthesized by grafting a quaternary ammonium salt group onto the pore channel of COFs via a one-pot three components tandem reaction strategy. The post-functionalized COFs were utilized as the matrix framework to successfully construct the Li-S battery with high-speed capacity and long-term stability. The experimental results showed that, after loading active material sulfur, cationic COF-NI effectively suppressed the shuttle effect of the intermediate lithium polysulfide species in Li-S batteries, and exhibited better cycle stability than the as-obtained neutral COF (COF-Bu). For example, compared with COF-Bu based sulfur cathode (521 mA h g−1), the cationic COF-NI based sulfur cathode maintained a discharge capacity of 758 mA h g−1 after 100 cycles. These results clearly showed that appropriate pore environment of COFs can be prepared by rational design, which can reduce the shuttle effect of lithium polysulfide species and improve the performance of Li-S battery.

Enzyme-Free Tandem Reaction Strategy for Surface-Enhanced Raman Scattering Detection of Glucose by Using the Composite of Au Nanoparticles and Porphyrin-Based Metal-Organic Framework.

In this work, an S hybrid nanosheet with multiple functions is synthesized by in situ modification of gold nanoparticles (AuNPs) onto two-dimensional (2D) metalloporphyrinic metal-organic framework (MOF) (Cu-tetra(4-carboxyphenyl)porphyrin chloride(Fe(III)), designated as AuNPs/Cu-TCPP(Fe). Cu-TCPP(Fe) nanosheets contribute peroxidase-like activity, and AuNPs have glucose oxidase (GOx) mimicking performance, which induce the cascade catalysis reactions to convert glucose into hydrogen peroxide (H2O2), and then, by using AuNP catalysis, H2O2 oxidizes the no Raman-active leucomalachite green (LMG) into the Raman-active malachite green (MG). Simultaneously, in the presence of AuNPs, sensitive and selective surface-enhanced Raman scattering (SERS) determination of glucose can be achieved. The bioenzyme-free SERS assay based on such AuNPs/Cu-TCPP(Fe) nanosheets is used for detection of glucose in saliva, showing good recovery from 96.9 to 100.8%. The work paves a new way to design a nanozyme-based SERS protocol for biomolecule analysis.

Rh(III)‐Catalyzed Redox‐Neutral Cascade Annulation of Benzamides withp‐Quinone Methides

Herein, we demonstrate a [RhCp*Cl2]2catalyzed synthesis of isoindolo[2,1‐b]isoquinolin‐5(7H)‐one derivatives fromN‐(pivaloyloxy)benzamides andp‐quinone methides under redox neutral conditions.p‐Quinone methide derivatives were engaged for the first time as precursors in C–H activation reactions and the cascade sequence consists of Rh(III)‐catalyzed C–H activation, alkyne insertion followed by an intramolecular 1,6‐conjugate addition. This novel tandem reaction strategy offers a rapid and straightforward access to complex fused isoquinolinone derivatives in an efficient manner.

Cu(II)-Catalyzed 6π-Photocyclization of Non-6π Substrates

This research successfully achieved a Cu(II)-catalyzed 6π-photocyclization of non-6π substrates. The photoenolization converts ortho-alkylphenyl alkynl ketones into a triene-type intermediate which undergoes the subsequent 6π-photocyclization to give naphthol as the final product. Cu(II) catalyst facilitates both photoenolization and 6π-photocyclization. This research highlighted the tandem reaction strategy and the importance of metal catalysis in photochemistry.

Tandem reaction strategy of the Passerini/Wittig reaction based on the in situ capture of isocyanides: One-pot synthesis of heterocycles

This paper reports the tandem reaction strategy of the Passerini/Wittig reaction based on the in situ capture of isocyanides. According to this strategy, plenty of isocyanides have been synthesized, which is immediately used for the tandem reaction of Passerini/Wittig reaction in one pot. Compared to the previous work, this strategy avoids the separation, purification, and storage of isocyanides, which prominently solves the problems of isocyanide-based multicomponent reaction such as: (a) The environmentally unfriendly (strong foul odor), (a) the labile of Isocyanides, (c) high toxicity of isocyanides. In the meantime, in order to expand the application scope of our strategy, 1H-isochromenes and 3H-2-benzoxepin-1-ones have also been synthesized, which undergoes four-step transformations in one-pot. In addition, a relatively credible reaction mechanism has also been proposed, based on a series of control experiments. Furthermore, preliminary testing was performed on biological activity of some obtained compounds; These results showed that the synthesized compounds exhibited certain activity over P. digitatum and P. italicum. © 2019 Elsevier Science. All rights reserved.

Odorless Isocyanide Chemistry: One-Pot Synthesis of Heterocycles via the Passerini and Postmodification Tandem Reaction Based on the in Situ Capture of Isocyanides.

This paper reports the tandem reaction strategy of the Passerini/Staudinger/aza-Wittig reaction based on the in situ capture of isocyanides. According to this strategy, isocyanides are synthesized in situ and immediately work as the substrate for the Passerini reaction and postmodification tandem reaction in one pot. In addition, two types of new compounds, 5-oxo-3,5-dihydrobenzo[ e][1,4]oxazepines and 6-oxo-5,6-dihydro-2 H-1,4-oxazines, were synthesized using the tandem reaction strategy that includes five-step transformations in one pot.

Procedure for the Synthesis of Polysubstituted Carbazoles from 3-Vinyl Indoles.

A simple Brønsted acid catalyzed tandem reaction, including intermolecular nucleophilic addition, substitution and intramolecular cyclization, in a one-pot manner is described. Thirty two 2-indolyl substituted carbazoles are generated in good to excellent yields. Based on this tandem reaction strategy, the poly(1,4-carbazole) is prepared for the first time. Preliminary studies indicate that the poly(1,4-carbazole) has good thermostability and optical properties.

Efficient biosynthesis of β-alanine with a tandem reaction strategy to eliminate amide by-product in the nitrilase-catalyzed hydrolysis

An efficient biosynthesis of β-alanine from 3-aminopropionitrile at high concentration has been developed using a one-pot bienzymatic cascade of a nitrilase and an amidase. The nitrilase BjNIT3397 from Bradyrhizobium japonicum strain USDA110 catalyzes the hydrolysis of 3-aminopropionitrile to β-alanine at the concentration up to 3.0mol/L with the formation 23% of 3-aminopropanamide. In order to eliminate the by-product 3-aminopropanamide, we cloned and characterized a new amidase from Pseudomonas nitroreducens through gene mining. Under the optimal conditions (50mmol/L Na2HPO4-NaH2PO4 buffer, pH 6.0, 40°C), 2.0mol/L (176g/L) of 3-aminopropanamide was completely hydrolyzed within 12h. A tandem reaction system was then established to eliminate the by-product 3-aminopropanamide and increase the production of β-alanine to 90% isolated yield with 15.02g/(L.h) space-time-yield. These results demonstrated that the tandem reaction strategy was an effective method of eliminating the amide by-products in the nitrilase-catalyzed hydrolysis at high substrate concentration.

Trimethylenemethane diyl mediated tandem cycloaddition reactions: mechanism based design of synthetic strategies.

Several criteria for the measure of synthetic strategies toward "ideal synthesis" are available to guide the design and evaluation of the synthetic strategies toward the target molecules. One strategy toward "ideal synthesis" is developing a multistep reaction that involves dramatic change in complexity. Biogenesis of natural products and mechanistic investigation of complicated organic transformation provide good inspiration for design of new synthetic strategies. Trimethylenemethane diradical (TMM diyl), first introduced only as a theoretically interesting structure 60 years ago, gained interests of physical organic chemistry when it was first detected by Dowd. Study of characteristics and properties of TMM diyl was accelerated in a great deal when Koebrich observed dimeric hydrocarbon products from the reaction of 1,1-dibromo-2-methylhexa-1,5-diene with MeLi. Berson followed the mechanistic investigation of the reaction that involved 2-methylenecyclopentane-1,3-diyl, and thoroughly studied physical and chemical properties of the TMM diyl. This lead to the development of intramolecular [2 + 3] TMM diyl cycloaddition reaction for the construction of linearly fused triquinanes by Little. We envisioned that the generation of a TMM diyl through cycloaddition reaction discovered by Koebrich and [2 + 3] cycloaddition reaction of the TMM diyl could be combined together to form polyquinane structures. A cycloaddition reaction sequence of generating a TMM diyl from a alkylidene carbene of 2-methylhexa-1,5-diene structure in the presence of another olefin was designed and executed to produce linearly fused and angularly fused triquinanes depending on the connectivity of the second double bond. The successful transformation also inspired design of a tandem cycloaddition reaction strategy of using unprecedented tetrahydrocyclopentapyrazole to TMM diyl transformation. The new design involves two [2 + 3] cycloaddition reactions of 6-diazohexa-1,2-diene with an olefin attached at a proper position. When a diazo functionality is produced, the initial [2 + 3] cycloaddition reaction generates the TMM diyl, which undergoes the second [2 + 3] cycloaddition reaction to form triquinanes with high efficiency. The first tandem strategy involves a massive reorganization of molecular connectivity as one C═C double bond was cleaved and four C-C bonds were formed. The second tandem strategy connected two double bonds with one carbon center to form four C-C bonds without breaking any bond. The developed tandem strategies were readily applied to the total synthesis of natural products, especially triquinanes. Thus, the total syntheses of hirsutene, ceratopicanol, pentalenene and panaginsene with structural revision were achieved and the strategy was extended to the total synthesis of crinipellins (tetraquinane natural products). The newly designed tandem strategies not only demonstrated the efficiency and effectiveness of the process but also provided future opportunity of studying TMM diyl mediated reactions for designing variety of synthetic strategies.

Nitrilase-catalyzed hydrolysis of 3-aminopropionitrile at high concentration with a tandem reaction strategy for shifting the reaction to β-alanine formation

Given the importance of β-alanine, the nitrilase BjNIT3397 from Bradyrhizobium japonicum strain USDA110 was examined toward the hydrolysis of 3-aminopropionitrile. It has been found that nitrilase BjNIT3397 effectively hydrolyzed 3-aminopropionitrile with substrate concentration up to 3M (210g/L) at the pH 7.3 and temperature 30°C. With the increase of substrate concentration from 0.6 to 3M, 3-aminopropanamide was formed and its percentage in the products was increased up to 33%. In order to reduce the formation of 3-aminopropanamide, aspartate ammonia-lyase and fumaric acid were added into the reaction system to consume the byproduct ammonia. As expected, the reaction was shifted toward the formation of β-alanine, resulting in the decrease of 3-aminopropanamide from 33% to 3%. Therefore, a tandem reaction strategy was developed to effectively prevent the formation of 3-aminopropanamide. This might also offer a possibility of producing β-alanine and l-aspartic acid in one process.

Hierarchical nanocomposite composed of layered V2O5/PEDOT/MnO2 nanosheets for high-performance asymmetric supercapacitors

We present here a tandem redox reaction strategy for building layered V2O5 (LVO), conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT), and layered MnO2 (LMO) into a sandwich structure LVO\\PEDOT\\LMO. The fabrication process consists of two redox reactions: (i) the oxidizing polymerization of PEDOT on LVO nanosheets to form a conformal coating (LVO\\PEDOT); and (ii) the reduction of KMnO4 by PEDOT to generate LMO nanoplates that stacked onto the LVO\\PEDOT (LVO\\PEDOT\\LMO). This approach to the fabrication of a complex structure eliminates the use of any extra toxic oxidizing/reducing agents. Using LVO aerogel as the starting material, the total reaction time can be as short as 10min. Asymmetric supercapacitors built from LVO\\PEDOT\\LMO cathode and active carbon (AC) anode (LVO\\PEDOT\\LMO||AC) using Na2SO4 aqueous electrolyte showed an energy density of 39.2Wh kg−1 (based on active materials), which is among the highest reported for supercapacitors with neutral aqueous electrolytes. The LVO\\PEDOT\\LMO||AC supercapacitors also offered high rate capability (21.7Wh kg−1 at 2.2kW kg−1) and good cycle stability (93.5% capacitance retention after 3000 cycles). These results demonstrate that the green tandem redox reaction strategy is promising for the development of complex nanocomposite materials for advanced energy storage.

Tandem Cycloaddition Reactions of Allenyl Diazo Compounds Forming Triquinanes via Trimethylenemethane Diyls

A tandem reaction strategy for forming triquinanes from linear allenyl diazo compounds through an intramolecular 1,3-dipolar cycloaddition reaction of an allenyl diazo group that generates a trimethylenemethane (TMM) diyl followed by an intramolecular [2 + 3] TMM diyl cycloaddition reaction has been developed. The new tandem cycloaddition reaction is readily applicable to the synthesis of complex molecules with high versatility and efficiency.

Electrocatalytic tandem Knoevenagel–Michael addition of barbituric acids to isatins: Facile and efficient way to substituted 5,5′-(2-oxo-2,3-dihydro-1 H-indole-3,3-diyl)bis(pyrimidine-2,4,6-(1 H,3 H,5 H)-trione) scaffold

Electrocatalytic transformation of isatins and barbituric acids in ethanol in an undivided cell in the presence of sodium bromide as an electrolyte results in the formation of substituted 5,5′-(2-oxo-2,3-dihydro-1 H-indole-3,3-diyl)bis(pyrimidine-2,4,6(1 H,3 H,5 H)-triones) in 89–95% substance yields and 890–950% current yields. The developed efficient electrocatalytic approach to medicinally relevant 5,5′-(2-oxo-2,3-dihydro-1 H-indole-3,3-diyl)bis(pyrimidine-2,4,6(1 H,3 H,5 H)-trione) scaffold is 10 times faster than general chemical method, is beneficial from the viewpoint of diversity-oriented large-scale processes and represents novel example of facile environmentally benign synthetic concept for electrocatalytic tandem reaction strategy.

Investigation of a Unified Strategy for the Synthesis of Anatoxin Analogues: Scope and Limitations

Syntheses of the potent neurotoxins and biochemical probes anatoxin-a and homoanatoxin and several analogues by a combined two-directional synthesis―tandem reaction strategy are presented. Key steps include an oxidative desymmetrisation and a tandem Michael―intramolecular Mannich cyclisation.