Current applications of organocatalysts in asymmetric aldol reactions: An update

The aldol reaction is one of the most important carbon–carbon bond formations in synthetic organic chemistry. An enantioselective aldol reaction should provide an enantioenriched product. The organocatalytic asymmetric aldol reaction via an in situ generated enamine intermediate is one of the most powerful synthetic tools to achieve enantiomerically pure products. This approach is often used to obtain chiral β-hydroxycarbonyl compounds with excellent enantioselectivity. In this report, we update our previous review regarding the applications of organocatalysts in asymmetric aldol reactions leading to chiral β-hydroxycarbonyl compounds as versatile synthetic motifs frequently found in pharmaceutically desired intermediates and biologically active naturally occurring compounds.     

Using enantioselective dispersive liquid–liquid microextraction for the microseparation of trans-cyclohexane-1,2-diamine enantiomers

A new chiral separation system effective for the enantioselective extraction of racemic trans-cyclohexane-1,2-diamine is presented. Enantioselective dispersive liquid–liquid microextraction has been used for the chiral microseparation of trans-cyclohexane-1,2-diamine, with a chiral azophenolic crown ether being identified as a versatile chiral selector. The influence of various process conditions on the extraction performance was studied experimentally. It was found that the operational selectivity in one extraction step is mainly related to the type and volume of the solvents, chiral selector concentration, extraction time, temperature of sample solution, and pH. At optimum conditions (300 μL of diethyl ether as the extraction solvent 1 mL of methanol as the disperser solvent, with 5 mmol L^?1 chiral selector concentration, pH of the sample equal to 4.5, 30 min extraction time and a temperature of 10 °C), the distribution ratio of (R,R)- and (S,S)-trans-cyclohexane-1,2-diamine was 18.3 and 1.8, respectively, while the enantioselectivity value of 10.2 was found at the optimum condition.     

Activation of iron-coordinated arenes toward the attack of carbon,nitrogen, and oxygen nucleophiles

Functionally-substituted carbon nucleophiles undergo addition to arenes coordinated to positive iron, but nitrogen and oxygen nucleophiles abstract α protons from iron-coordinated methylated arenes.     

Computer-aided molecular design of (E)-N-Aryl-2-ethene-sulfonamide analogues as microtubule targeted agents in prostate cancer

Microtubules are tube-shaped, filamentous and cytoskeletal proteins that are essential in all eukaryotic cells. Microtubule is an attractive and promising target for anticancer agents. In this study, three-dimensional quantitative structure activity relationships (3D-QSAR) including comparative molecular field analysis, CoMFA, and comparative molecular similarity indices analysis, CoMSIA, were performed on a set of 45 (E)-N-Aryl-2-ethene-sulfonamide analogues as microtubule-targeted anti-prostate cancer agents. Automated grid potential analysis, AutoGPA module in Molecular Operating Environment 2009.10 (MOE) as a new 3D-QSAR approach with the pharmacophore-based alignment was carried out on the same dataset. AutoGPA-based 3D-QSAR model yielded better prediction parameters than CoMFA and CoMSIA. Based on the contour maps generated from the models, some key features were identified in (E)-N-Aryl-2-arylethene-sulfonamide analogues that were responsible for the anti-cancer activity. Virtual screening was performed based on pharmacophore modeling and molecular docking to identify the new inhibitors from ZINC database. Seven top ranked compounds were found based on Gold score fitness function. In silico ADMET studies were performed on compounds retrieved from virtual screening in compliance with the standard ranges.     

The reaction of sulphur and nitrogen nucleophiles with [Pt(dien)Cl]+

The reaction of a variety of sulphur nucleophiles [thiourea, S-ethyl mercaptoethylamine (EMEA), glutathione (GSH), dimethylsulphoxide (DMSO) and methionine] with the platinum(II) complex [Pt(dien)Cl]+ has been studied at 25°C using the nucleophiles in large excess. The measurements confirm that the sulphur nucleophiles react directly with the platinum complex and that the solvolytic pathway makes little contribution to the reaction. The reactions were monitored by a combination of conductometric and spectrophotometric methods. The oxygen and nitrogen nucleophiles water and imidazole respectively have also been studied. Reagents such as thiourea, EMEA, methionine and glutathione are some 101–102 more reactive than the nitrogen nucleophile imidazole and some 102–103 more reactive than oxygen nucleophile. In a direct competition between sulphur (kS) and nitrogen (kN) nucleophiles for the platinum substrate, as will occur under biological conditions, the kS/kN ratio is at least 10 so that little of the nitrogen-substituted product will be formed in the reaction.     

A simple,rapid and sensitive method based on modified multiwalled carbon nanotube for preconcentration and determination of lead ions in aqueous media in natural pHs

In this study, multiwalled carbon nanotube (MWCNT) was modified by the pyridine group using a silane agent and characterized by infrared spectroscopy (IR), thermal analysis (TG/DTA), and elemental analysis (CHN) and scanning electron microscopy (SEM). The application of this sorbent was investigated in determination of lead ions in aqueous samples, using flame atomic absorption spectrometry (FAAS). Through this study, different parameters such as pH and sample flow rate on adsorption process and eluent concentration, volume and flow rate were optimized. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 2 ng mL^?1, 1.3% and 99.7%, respectively. Two standard reference materials (NIST 1571 and NIST 1572) were used to verify accuracy of this method. Finally, the sorbent was successfully applied for extraction and determination of low levels of Pb(II) ions in aqueous samples.     

Catalytic asymmetric alkylation in water in the presence of surfactants: influence of the nature of the nucleophile and the allylic acetate on the activity and enantioselectivity

Asymmetric palladium-catalyzed alkylation of 1,3-diphenyl-2-propenyl acetate with carbon and nitrogen nucleophiles occurs in water in the presence of a surfactant, a base, and Binap as the chiral ligand. Enantioselectivities up to 91% were obtained using carbon nucleophiles, and 93% using nitrogen nucleophiles, in the presence of CTHASO₄ as the surfactant. While the efficiency of the catalyst was higher in water in the presence of the surfactant in the case of carbon nucleophiles, no micellar effects were observed using the nitrogen nucleophiles. The alkylation was extended to other allylic acetates, but the efficiency as well the enantioselectivity of the coupling were lower.     

Stereoselective conjugate addition of nitrogen nucleophiles to 3,3,3-trifluoro-1-nitropropene

In order to access 1,2-diamines incorporating perfluorinated groups, the Michael-like addition of nitrogen nucleophiles to 3,3,3-trifluoro-1-nitropropene has been investigated using racemic and optically pure nucleophiles such as amines, amides, oxazolidin(on)es, and thiazolidin(on)es. Complete diastereoselectivity of the addition was achieved with 4-phenylthiazolidine-2-thione.     

Synthesis and Antibacterial Activity of Some New 4(3H)Quinazolin-4-one Derivatives

2-Phenylamino-6,8-dibromo-4H-3,1-benzoxazinone has been reacted with nitrogen nucleophiles, such as hydrazine hydrate, amines, and formamide, yielding 4(3H)quinazolinone derivatives; and with sulfur nucleophiles producing the corresponding thioesters. The behavior of aminoquinazolinone and 4(3H)quinazolinone towards some carbon electrophiles under different conditions has been studied.     

Flexible Stereoselective Functionalizations of Ketones through Umpolung with Hypervalent Iodine Reagents

The functionalization of carbonyl compounds in the α‐position has gathered much attention as a synthetic route because of the wide biological importance of such products. Through polarity reversal, or “umpolung”, we show here that typical nucleophiles, such as oxygen, nitrogen, and even carbon nucleophiles, can be used for addition reactions after tethering them to enol ethers. Our findings allow novel retrosynthetic planning and rapid assembly of structures previously accessible only by multistep sequences.     

An efficient ultrasonic-assisted synthesis of ethyl-5-(aryl)-2-(2-alkokxy-2-oxoethylidene)-7-methyl-3-oxo-3, 5-dihydro-2H-thiazolo [3, 2-a] pyrimidine-6-carboxylate derivatives

Dihydropyrimidinone derivatives were prepared by tri-component reaction of ethyl aceto acetate, aldehydes and thiourea in the presence of modified montmorillonite nanostructure as a catalyst and used as key intermediates for the synthesis of ethyl-5-(aryl)-2-(2-alkokxy-2-oxoethylidene)-7-methyl-3-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyri midine-6-carboxylate derivatives with use of diethyl and dimethyl acetylene dicarboxylate by two methods: (a) in methanol as a solvent under ultrasonic irradiation at ambient temperature (b) in methanol as a solvent at ambient temperature (conventional magnetic stirring). Ultrasound-assisted synthesis provides excellent yields in short reaction times (15–25 min) at room temperature.     

Silver(I)‐Catalyzed Tandem 1,3‐Acyloxy Migration/Mannich‐type Addition/Elimination of the Sulfonyl Group of N‐Sulfonylhydrazone‐propargylic Esters to 5,6‐Dihydropyridazin‐4‐one Derivatives

The addition of nucleophiles to C?N bonds offers a highly efficient synthetic strategy for accessing nitrogen‐containing molecules. 1 Among the well‐developed addition reactions, such as the highly efficient Mannich reaction, various C? H bond‐activated compounds including carboxylic acid derivatives, nitroalkanes, and terminal alkynes have been applied as nucleophiles to achieve different classes of amines. 2 However, employing new nucleophiles without activated C? H bonds, such as internal alkynes and allenic esters are limited when using metal catalysts. 3 Herein, we wish to report a new addition of allenic esters to C?N bonds initiated by a silver‐catalyzed 1,3‐migration of propargylic esters.     

Iron(III) phosphate catalyzed synthesis of 1,4-dihydropyridines

Novel 1,4-dihydropyridines (1,4-DHPs) are prepared efficiently via Hantzsch reaction using aldehydes, benzylacetoacetate and catalytic amount of iron(III) phosphate under solvent-free conditions in good yields.     

Utility of 3-Chlorobenzothiophene-2-Carbonylisothiocyanate for the Synthesis of Some Novel Biheterocycles of Expected Biological Activity

The behavior of 3-chlorobenzothiophene-2-carbonylisothiocyanate 2 towards nitrogen nucleophiles such as primary amines, substituted hydrazines, aryl hydrazines, glycine, anthranilic acid; sulfur nucleophiles such as thioglycolic acid; and oxygen nucleophiles such as substituted phenols has been investigated and found that it proceeds via isothiocyanate heterocyclization to furnish noncondensed heterocyclic compounds containing thiourea, triazole, oxazole, thiazole, and benzoxazole nuclei besides the benzo[b]thiophene nucleus. The structures of the newly synthesized compounds were elucidated on the basis of IR, ¹H NMR, and mass spectral data of the compounds, and they have been screened for antimicrobial, analgesic, and anti-inflammatory activities.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Synthesis of the four enantiomers of diethyl 1,2-di(N-Boc-amino)propylphosphonates

A simple and efficient synthetic strategy to all four enantiomerically pure diethyl 1,2-di(N-Boc-amino)propylphosphonates has been elaborated starting from the corresponding N-[(R)-(1-phenylethyl)]aziridine-(2S)- and N-[(S)-(1-phenylethyl)]aziridine-(2R)-carboxaldehydes, employing a one-pot three-components Kabachnik-Fields reaction followed by the hydrogenolytic removal of the chiral auxiliary and aziridine ring opening with simultaneous protection of the amino groups as the N-Boc derivatives.     

Electroauxiliary-assisted sequential introduction of two carbon nucleophiles on the same alpha-carbon of nitrogen: application to the synthesis of spiro compounds

The sequential introduction of two carbon nucleophiles on the same alpha-carbon of nitrogen by using selective oxidative cleavage of two silyl groups as electroauxilialies has been accomplished. The combination of this expedient transformation and ring-closing metathesis enables reliable and straightforward syntheses of nitrogen-containing spiro compounds, such as cephalotaxine.     

Water-promoted unprecedented chemoselective nucleophilic substitution reactions of 1,4-quinones with oxygen nucleophiles in aqueous micelles

Unique nucleophilic substitution and addition reactions of nitrogen and sulfur nucleophiles with 1,4-quinones in aqueous suspension with amines and thiols have recently been demonstrated by us.² However, the reactivity of oxygen nucleophiles toward nucleophilic substitution compared to nitrogen and sulfur nucleophiles ‘on water’ is not facile. An unprecedented economical, green methodology approach using ordinary laundry detergent (LD; washing powder, 0.5 mol %, reusable)/SDS as surfactant ‘in water’ for nucleophilic substitution by oxygen nucleophiles in 1,4-quinones in excellent yields has been demonstrated.     

Synthesis and reactivity of 5-methylenehydantoins

5-Methylenehydantoin, as well as the N-mono- and N,N-di-protected derivatives, can be obtained by different synthetic routes. These compounds can undergo a large variety of reactions, such as Diels-Alder, epoxidation, methanol addition and conjugate addition reactions of different types of nucleophiles, including carbon (cyanide), nitrogen (piperidine) and sulfur (thiols, thioacetate) nucleophiles. The reactivity with electrophilic reagents, such as m-CPBA or methanol in acidic medium, and the need for Lewis acids to promote the conjugate addition reactions indicate that hydantoin is a poor electron-withdrawing group.     

Chiral benzimidazoles and their applications in stereodiscrimination processes

Chiral aspects of benzimidazoles have been over-shadowed for a long time due to the large number of reports on benzimidazoles in the medical field in numerous categories of therapeutic agents. The vigorous research activity in chiral applications of benzimidazole derivatives started after bifunctional benzimidazoles made their appearance especially in the last 2–3 decades. Thus, chiral benzimidazoles form a comparatively young branch of chiral chemistry. The presence of pyridine and pyrrole type of nitrogens along with the fused benzene ring confer on this class of molecules, special properties including useful nucleophilicity, hydrogen bonding ability and a rigid backbone, all of which play decisive roles in proven chiral applications. The present review aims to cover the synthetic routes to access chiral benzimidazoles and their applications in a plethora of chiral fields including enantioselective organocatalysis, metal-based catalysis, asymmetric transformations involving benzimidazole-N-heterocyclic carbenes, kinetic resolution, benzimidazole-based macrocyclic hosts in chiral supramolecular chemistry and other miscellaneous chiral applications.     

Optimization of profenofos organophosphorus pesticide degradation by zero-valent bimetallic nanoparticles using response surface methodology

This study synthesized bimetallic Fe/Ni nanoparticles and used them for catalytic degradation of profenofos, an organophosphorus pesticide. This novel bimetallic catalyst (Fe/Ni) was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray analysis spectroscopy (EDAX) and X-ray diffraction (XRD). The bimetallic nano-catalyst was prepared at diameters of 20–50 nm and was shown to effectively degrade profenofos. A three-factor central composite design combined with response surface methodology was used to maximize profenofos removal using the bimetallic system. A quadratic model was built to predict degradation efficiency. ANOVA was used to determine the significance of the variables and interactions between them. Good correlation between the experimental and predicted values was confirmed by the high F-value (16.38), very low P-value (<0.0001), non-significant lack of fit, an appropriate coefficient of determination (R² = 0.936) and adequate precision (14.75). The highest removal rate attained was 94.51%.