Rearrangement Of Esters Research Articles

Application of froth flotation in the separation of polyvinyl chloride and polycarbonate for recycling of waste plastic based on a novel surface modification

The complicated stream of waste plastic impedes the recycling of polyvinyl chloride (PVC) and polycarbonate (PC), which can be settled by flotation separation. We proposed a novel chlorine dioxide (ClO2) pretreatment to assist the separation of PVC and PC by froth flotation, and clarified possible surface reactions of hydrophilic PC by contact angles, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The hydrolysis and further rearrangement of carbonic esters (O(CO)O) may be deemed as the main reason for hydrophilic PC, introducing oxygenated functional groups, such as hydroxyl groups (COH), carboxyl groups (COOH), and tiny acyl chloride (ClCO), on PC surfaces. The robustness of this process was proved by efficient flotation separation of PVC and PC under various conditions of size fractions, frother concentration, mass ratio, and flotation time. The optimal pretreatment conditions for flotation separation of PVC and PC are temperature of 70 °C, ClO2 concentration of 0.5 g/L, and treatment time of 70 min. The optimal recovery and purity of PC in sunken plastic can stably maintain 97% and 99%, respectively. Compared with waste plastic, raw PC embraces a high floatability after ClO2 pretreatment, revealing that ageing is conducive to surface modification.

Catalytic Enantioselective Benzilic Ester Rearrangement.

We report the first examples of catalytic enantioselective benzilic ester rearrangement reaction. In the presence of a catalytic amount of Cu(OTf)2 and a chiral box ligand under mild conditions, reaction of 2,3-diketoesters with alcohols afforded structurally diverse α-aryl(alkyl) substituted-α-hydroxy malonates (tartronic esters) in good to excellent yields with high enantioselectivities. Preliminary mechanistic studies indicated that hemiketalization, rather than the dynamic kinetic resolution of hemiketal, was the enantiodetermining step under our reaction conditions.

Catalytic Enantioselective Benzilic Ester Rearrangement

AbstractWe report the first examples of catalytic enantioselective benzilic ester rearrangement reaction. In the presence of a catalytic amount of Cu(OTf)2 and a chiral box ligand under mild conditions, reaction of 2,3‐diketoesters with alcohols afforded structurally diverse α‐aryl(alkyl) substituted‐α‐hydroxy malonates (tartronic esters) in good to excellent yields with high enantioselectivities. Preliminary mechanistic studies indicated that hemiketalization, rather than the dynamic kinetic resolution of hemiketal, was the enantiodetermining step under our reaction conditions.

Substrate substitution effects in the Fries rearrangement of aryl esters over zeolite catalysts

The reaction scheme of the Fries rearrangement of aryl esters over zeolite catalysts strongly depends on the framework type, acidic properties, and substrate identity.

IL@CQD catalyzed active ester rearrangement for the detection and removal of cyanide ions.

Carbon Quantum Dots (CQDs) have been extensively employed in various fields of science such as sensing, catalysis, and drug delivery. In this work, ionic liquid coated CQDs (IL@CQDs) have been used as catalysts for the rearrangement of a 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) amide coupling intermediate. The rearranged product was confirmed by single crystal structure analysis and it was processed into organic nanoparticles (ONPs). An optical detection method was used to scrutinize the anion sensing properties. The ONPs were found to be sensitive and selective for the recognition of highly toxic cyanide ions through enhancement in the fluorescence intensity. The cyanide ion co-ordinates with the -NH groups of the product and restricts the rotation of molecules around the single bond. The ONPs coated over silica-beads were also showing CN- recognition in the solid state. The detection limit for CN- sensing was found to be 3.8 nM, and real sample analysis depicts more than 90% accuracy in detection.

Ir/Phase‐Transfer‐Catalysis Cooperatively Catalyzed Asymmetric Cascade Allylation/2‐aza‐Cope Rearrangement: An Efficient Route to Homoallylic Amines from Aldimine Esters†

Summary of main observation and conclusionHerein, we developed an Ir/phase‐transfer‐catalysis cooperatively catalyzed asymmetric cascade allylation/2‐aza‐Cope rearrangement of aldimine esters to prepare synthetically important homoallylic amines in good yields with excellent enantioselectivities. Compared with the bimetallic catalytic system to realize this transformation, the current cooperative Ir/tetrabutyl ammonium bromide catalytic system provides an alternative but more practical approach, which not only simplify the manipulation process but also increase the cost efficiency.

The synthesis and structural characterization of furanyl-1,2,3-triazole Gold(I) and its application in synthesis of enones from propargylic esters and alcohols

abstract Furanyl-1,2,3-triazole gold(I) was designed, synthesized and characterized by X-ray crystallography, and was found to exhibit high catalytic activity for the synthesis of enones in good to high yields through a propargylic ester rearrangement and subsequent hydration. Notably, excellent E/Z selectivity was observed in these transformations. This catalyst was also effective in catalyzing the rearrangement of propargylic alcohols and hydration of alkynes. Compared to triazole acetyl gold(III) and other gold complexes, the furanyl-1,2,3-triazole gold(I) is able to promote these transformations smoothly at a low temperature with the E isomer of enones as the only product.

Juniperanol: First total synthesis and evaluation in Type 2 Diabetes disease

The first total synthesis of juniperanol, the tricyclic sesquiterpenoid enantiomer of α-cedrol is described. The synthesis relies on stereoselective gold-catalyzed Ohloff-type propargylic ester rearrangement performed on a 10 g scale, and a carbocationic cascade in the presence of acetyl methanesulfonate. The ability of juniperanol to interfere in glucose processes in different cell types is described.

Understanding the Molecular Mechanism of the Rearrangement of Internal Nitronic Ester into Nitronorbornene in Light of the MEDT Study.

The characterization of the structure of nitronic esters and their rearrangement into nitronorbornene reactions has been analyzed within the Molecular Electron Density Theory (MEDT) using Density Functional Theory (DFT) calculations at the B3LYP/6-31G(d) computational level. Quantum-chemical calculations indicate that this rearrangement takes place according to a one-step mechanism. The sequential bonding changes received from the Bonding Evolution Theory (BET) analysis of the rearrangement of internal nitronic ester to nitronorbornene allowed us to distinguish seven different phases. This fact clearly contradicts the formerly-proposed concerted pericyclic mechanism.

Photoinduced cyclization of alkynoates to coumarins with N-Iodosuccinimide as a free-radical initiator under ambient and metal-free conditions

An efficient photoinduced strategy for the preparation of coumarins was developed. In the presence of N-iodosuccinimide (NIS) as a free-radical initiator and under LED (380–385 nm) irradiation and metal-free conditions, the reaction of alkynoates underwent smoothly to afford the corresponding coumarins in high yields at room temperature with broad substrate scope via free radical intramolecular cyclization and ester rearrangement.

Formation of Complex α-Imino Esters via Multihetero-Cope Rearrangement­ of α-Keto Ester Derived Nitrones

A sequential benzoylation and multihetero-Cope rearrangement of α-keto ester derived nitrones has been developed. The reaction furnishes a diverse array of complex α-imino ester derivatives. The products can be transformed into amino alcohols via LiAlH4 reduction.

Stereodivergence in the Ireland-Claisen Rearrangement of α-Alkoxy Esters.

A systematic investigation into the Ireland-Claisen rearrangement of α-alkoxy esters is reported. In all cases, the use of KN(SiMe3)2 in toluene gave rearrangement products corresponding to a Z-enolate intermediate with excellent diastereoselectivity, presumably because of chelation control. On the other hand, chelation-controlled enolate formation could be overcome for most substrates through the use of lithium diisopropylamide (LDA) in tetrahydrofuran (THF).

CASSCF Calculations Reveal Competitive Chair (Pericyclic) and Boat (Pseudopericyclic) Transition States for the [3,3] Sigmatropic Rearrangement of Allyl Esters.

(10,8)CASPT2/6-31G**//(10,8)CASSCF/6-31G** and CCSD(T)/cc-pVDZ//(10,8)-CASSCF/6-31G** calculations have been performed on the potential surface for the [3,3] sigmatropic allyl ester rearrangements of cis-3-penten-2-yl acetate (16) to trans-3-penten-2-yl acetate (17) and 3-buten-2-yl acetate (21) to trans-2-buten-1-yl acetate (22). The results are compared to DFT (B3LYP/6-31G**) calculations on the known 16 → 17 rearrangement that reported it to be concerted and pseudopericyclic through a boat-shaped transition structure ( Birney, D. M. et al. J. Am. Chem. Soc. 2009 , 131 , 528 - 537 ). The CASSCF calculations, on the other hand, uncovered competitive concerted pathways for both the 16 → 17 and 21 → 22 rearrangements, though it was necessary to apply certain approximations in the former case. While one CASSCF pathway in each case involves a boat-shaped transition structure, similar to the one located through DFT calculations, the other pathway involves a chair-shaped transition structure. Preference for chair or boat is shown to be method dependent. Moreover, examination of the CASSCF active-space orbitals clearly confirms that the boat-shaped transition structures are pseudopericyclic but significantly also established that the chair-shaped transition structures are clearly pericyclic. Conclusions based on these results, and regarding our understanding of pericyclic vs pseudopericyclic reactions, are proffered.

Photoinduced fragmentation-rearrangement sequence of cycloketoxime esters

A novel rearrangement of cycloketoxime esters to cyano-containing benzoates beyond the traditional Beckmann and Neber rearrangement process has been established in the presence of photocatalysis catalysis.

Synthesis of 2-alkenyl-3-hydroxyquinolin-4(1H)-ones as promising antimicrobial and fluorescent agents

2-Alkenyl-3-hydroxyquinolin-4(1H)-ones were prepared by the rearrangement of anthranilic acid esters synthesized by two alternative methods. The prepared derivatives were screened for their antimicrobial activities against representative Gram-positive and Gram-negative bacteria, displaying notable minimum inhibitory concentration values against specific strains. The emission spectra of the target quinolines exhibited two well-separated emission bands, and the maximum excitation wavelengths of the selected compounds were detected at relatively high values.

Investigation of polycyanurate/benzoxazine curing system

In this study, we investigated the curing system between polycyanurate and benzoxazine derivatives which could be a useful system for producing low-k thermoset materials. This curing reaction contains the following steps: (1) the ring-opening reaction of benzoxazine, (2) the insertion of benzoxazine into the triazine ester, and (3) the rearrangement of the triazine ester to the isocyanurate. During the curing reaction, the self-polymerization of benzoxazine also occurs, resulting in the formation of phenol groups (Ph-OH). To avoid this side reaction, all the reactive sites need to be blocked by methyl substituents. As a result, there was no Ph-OH generation during the model reaction which is important for preparing low-k thermoset materials.

Synthesis of α-(Pentafluorosulfanyl)- and α-(Trifluoromethyl)-Substituted Carboxylic Acid Derivatives by Ireland-Claisen Rearrangement.

Earlier studies have shown that [3,3]-sigmatropic rearrangements of allyl esters are useful for the construction of fluorine-containing carboxylic acid derivatives. This paper describes the synthesis of 3-aryl-pent-4-enoic acid derivatives bearing either a pentafluorosulfanyl (SF5) or a trifluoromethyl (CF3) substituent in the 2-position by treatment of corresponding SF5- or CF3-acetates of p-substituted cinnamyl alcohols with triethylamine followed by trimethylsilyl triflate (TMSOTf). This Ireland-Claisen rearrangement delivered approximate 1:1 mixtures of syn/anti diastereoisomers due to tiny differences (<0.5 kcal/mol) both in the energy of (Z)/(E)-isomeric ester enolates and in the alternative Zimmerman-Traxler transition states of model compounds as shown by DFT calculations. Acidic reaction conditions have to be avoided since addition of the reagents in opposite sequence (first TMSOTf then Et3N) led to oligomerization of the cinnamyl SF5- and CF3-acetates. Treatment of the corresponding regioisomeric 1-phenyl-prop-2-en-1-yl acetates under the latter conditions resulted in [1,3]-sigmatropic rearrangement and subsequent oligomerization of the intermediately formed cinnamyl esters. When Et3N was added first followed by TMSOTf, no further reaction of the formed ester was detected.

Stereoselective synthesis of the viridiofungin analogue NA808 from a chiral tetrahydrofuran-carboxylic acid.

The viridiofungin analogue NA808 was synthesized by the stereoselective Ireland-Claisen rearrangement of dienylmethyl ester, regioselective bromolactonization of β-divinylpropanoic acid and retro-bromolactonization.

ChemInform Abstract: Ligand‐Controlled Gold‐Catalyzed Cycloisomerization of 1,n‐Enyne Esters Toward Synthesis of Dihydronaphthalene.

We describe herein a gold-catalyzed rearrangement of propargyl esters followed by allene–ene cyclization to afford substituted bicyclic [4.4.0] dihydronaphthalene compounds. This method is also applied to vinylethers and vinylamines of 1,7-enyne esters to form dihydroquinoline and dihydrobenzopyran structures. The basis of this transformation is the ligand-controlled preferential activation of the alkene over the allene, affording the desired aromatic bicyclic structures in moderate to excellent yields.

ChemInform Abstract: Gold(I) Catalyzed Tandem Cyclization of Propargylic Esters to 4‐Acyloxy‐1,2‐dihydroquinolines.

AbstractA facile method to synthesize 4‐acyloxy‐1,2‐dihydroquinolines is established through a gold(I)‐catalyzed tandem [3,3]‐rearrangement and intramolecular hydroamination of propargylic esters, giving the desired products in good yields under mild conditions.