scholarly journals On the Question of Zwitterionic Intermediates in the [3+2] Cycloaddition Reactions: A Critical Review

Organics ◽  
2020 ◽  
Vol 1 (1) ◽  
pp. 49-69
Author(s):  
Radomir Jasiński ◽  
Ewa Dresler
Keyword(s):  
Critical Review ◽  
Critical Analysis ◽  
Dipolar Cycloaddition ◽  
Cycloaddition Reactions ◽  
Concerted Mechanism ◽  
Academic Literature ◽  
Research Techniques ◽  
One Step ◽  
The One ◽  
Comprehensive Studies

New discoveries require a fundamental revision of the view on the mechanism of the 32CAreaction (according to the older nomenclature defined as 1,3-dipolar cycloaddition reactions). The view of the one-step, “concerted” mechanism of such processes developed in the 20-century is very popular today, both in academic literature and among organic chemists who do not specialize in such transformations. Meanwhile, more and more reports bring examples of reactions that clearly cannot be treated as processes without intermediates. However, these examples are documented very differently. In addition to comprehensive studies using many complementary research techniques, there are also reports in which the presence of intermediates in the cycloaddition environment is postulated on the basis of very unreliable premises. This review is an attempt at a critical analysis and systematization of data in the presented area.

scholarly journals On the Question of Stepwise [4+2] Cycloaddition Reactions and Their Stereochemical Aspects

Symmetry ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1911
Author(s):  
Radomir Jasiński
Keyword(s):  
Twentieth Century ◽  
Reaction Mechanism ◽  
Critical Analysis ◽  
Alder Reaction ◽  
Diels Alder ◽  
Cycloaddition Reactions ◽  
Diels Alder Reaction ◽  
One Step ◽  
The One ◽  
The Way

Even at the end of the twentieth century, the view of the one-step [4+2] cycloaddition (Diels-Alder) reaction mechanism was widely accepted as the only possible one, regardless of the nature of the reaction components. Much has changed in the way these reactions are perceived since then. In particular, multi-step mechanisms with zwitterionic or diradical intermediates have been proposed for a number of processes. This review provided a critical analysis of such cases.

A Critical Analysis of Capitalism, Capital Accumulation and Crisis Theory in David Harvey

2020 ◽  
pp. 097674792095300
Author(s):  
Tanaya Majumder
Keyword(s):  
Business Cycles ◽  
Critical Review ◽  
Critical Analysis ◽  
Capital Accumulation ◽  
Capitalist Economy ◽  
Crisis Theory ◽  
Surplus Labour ◽  
The One ◽  
Rate Of Profit ◽  
Marxist Tradition

This article is a critical review of David Harvey’s essentialist theorisation of a capitalist economy and its crisis from a class focused Marxist perspective. The first part examines Harvey’s immense contribution to the understanding of space and spatiality of capitalism within the Marxist tradition. Capital accumulation in his theorisation serves as the impresario of space and spatiality and the harbinger of capitalist crisis in general. Expanding on a class focused approach, the second part provides a critique of Harvey’s methodology and crisis theory in which the law of capital accumulation reigns supreme. Specifically, using an anti-essentialist methodology of overdetermination with class process of surplus labour as the theoretical entry point, as developed by Resnick and Wolff, I argue that no correspondence of the rate of capital accumulation with those of rate of profit and rate of class distribution can be drawn. This unpredictability renders capitalism inherently unstable, prone to business cycles whose cause cannot be reduced to any chosen causal factor such as the one reducible to capital accumulation.

Mechanism and regioselectivity of 1,3-dipolar cycloaddition reactions of bicyclic monoterpenes with aryl and heteroaryl nitrile oxides: a DFT study

2015 ◽  
Vol 93 (7) ◽  
pp. 749-753 ◽  
Author(s):  
Hossein Eshghi ◽  
Amir Khojastehnezhad ◽  
Farid Moeinpour ◽  
Mehdi Bakavoli
Keyword(s):  
Gas Phase ◽  
Density Functional ◽  
Energy Surface ◽  
Dipolar Cycloaddition ◽  
Cycloaddition Reactions ◽  
Functional Theory ◽  
Nitrile Oxides ◽  
Reactivity Indices ◽  
One Step ◽  
Step Mechanism

The reactivity and regioselectivity of 1,3-dipolar cycloaddition reactions of aryl and heteroaryl nitrile oxides (1a–1c) with bicyclic monoterpenes (R)-(+)-a-pinene (2a) and (S)-(–)-b-pinene (2b) have been investigated by using density functional theory based on reactivity indices and activation energy calculations at the B3LYP/6-31G(d) level of theory in the gas phase. The potential energy surface analyses for both reactions are in agreement with the experimental observations. Moreover, our calculations on the geometries, bond orders, and global electron density transfers at the transition state structures shows that these 1,3- dipolar cycloaddition reactions occur via an asynchronous one-step mechanism.

Multicomponent 1,3-Dipolar Cycloaddition Reactions in the Construction of Hybrid Spiroheterocycles

2013 ◽  
Vol 17 (18) ◽  
pp. 1929-1956 ◽  
Author(s):  
Natarajan Arumugam ◽  
Raju Kumar ◽  
Abdulrahman Almansour ◽  
Subbu Perumal
Keyword(s):  
Dipolar Cycloaddition ◽  
Cycloaddition Reactions

A Study on the Rearrangement of Dialkyl 1-Aryl-1-hydroxymethylphosphonates to Benzyl Phosphates

2020 ◽  
Vol 24 (4) ◽  
pp. 465-471 ◽  
Author(s):  
Zita Rádai ◽  
Réka Szabó ◽  
Áron Szigetvári ◽  
Nóra Zsuzsa Kiss ◽  
Zoltán Mucsi ◽  
...  
Keyword(s):  
Quantum Chemical ◽  
Room Temperature ◽  
Phase Transfer ◽  
One Pot ◽  
Substrate Dependence ◽  
Triethylbenzylammonium Chloride ◽  
One Step ◽  
The Pudovik Reaction ◽  
The One ◽  
Solid Liquid

The phospha-Brook rearrangement of dialkyl 1-aryl-1-hydroxymethylphosphonates (HPs) to the corresponding benzyl phosphates (BPs) has been elaborated under solid-liquid phase transfer catalytic conditions. The best procedure involved the use of triethylbenzylammonium chloride as the catalyst and Cs2CO3 as the base in acetonitrile as the solvent at room temperature. The substrate dependence of the rearrangement has been studied, and the mechanism of the transformation under discussion was explored by quantum chemical calculations. The key intermediate is an oxaphosphirane. The one-pot version starting with the Pudovik reaction has also been developed. The conditions of this tandem transformation were the same, as those for the one-step HP→BP conversion.

Therapeutic role of vegetables in Respiratory Diseases – A critical review from Ayurvedic classics.

2016 ◽  
Vol 1 (3) ◽  
Author(s):  
Dr. Raghavendra Naik ◽  
Shweta Vekariya ◽  
R. N. Acharya ◽  
Sneha D. Borkar
Keyword(s):  
Clinical Practice ◽  
Respiratory Disease ◽  
Respiratory System ◽  
Critical Review ◽  
Critical Analysis ◽  
Respiratory Diseases ◽  
Unique Contribution ◽  
Pharmacological Activities ◽  
The Family

The concept of Pathya (wholesome diet) is an unique contribution of Ayurveda, which plays an important role in prevention and management of many diseases. “Shakavarga”, a category under dietetics in classical texts of Ayurveda enlisted different vegetables with their properties and indications in different disease conditions. These vegetables can be prescribed as Pathya (wholesome diet) in clinical practice. In the present review, plants described under Shakavarga, indicated as Pathya in different diseases related to Pranavaha Srotas (Respiratory system) were compiled from 15 different Ayurvedic classical texts. Critical analysis of the compiled data reveals that out of 332 vegetables described under Shakavarga, 44 are indicated in respiratory disease like Shvasa (Dyspnoea/Asthma), Kasa (Cough), Peenasa (Chronic rhinitis) and Hikka (Hiccup). Among them, botanical identity of 42 classical plants has been established and maximum number of vegetables belongs to the family cucurbitaceae (10) followed by solanaceae (4). Some of these vegetables have been reported for their various pharmacological activities related to prevention and management of diseases related to Pranavaha Srotas (Respiratory system). These vegetables are reported for their anti-inflammatory (16), antioxidant (14), anti-allergic (6) and antitussive (3) activities. The observed result may be helpful in use of vegetables as Pathya (wholesome diet) and planning further scientific studies about the efficacy of these plants on prevention as well as management of respiratory diseases.

π-Facial Selectivity in 1,3-Dipolar Cycloaddition Reactions of α-Methylidene-γ-lactone Substituted by 4-Methyl-2,6,7-trioxabicyclo[2.2.2]octan-1-yl Group in γ-Position

2002 ◽  
Vol 67 (3) ◽  
pp. 353-364 ◽  
Author(s):  
Petr Melša ◽  
Ctibor Mazal
Keyword(s):  
Double Bond ◽  
Carboxylic Acid ◽  
Nitrile Oxide ◽  
Dipolar Cycloaddition ◽  
Cycloaddition Reactions ◽  
Enantiomerically Pure ◽  
Nitrile Imine ◽  
Facial Selectivity ◽  
Excellent Selectivity

Diastereoselectivity of 1,3-dipolar cycloaddition reactions of benzyl azide, diazomethane, a nitrile oxide and a nitrile imine to α-methylidene-γ-lactone dipolarophile was effectively controlled by a bulky γ-substituent, 4-methyl-2,6,7-trioxabicyclo[2.2.2]octan-1-yl in γ-position of the dipolarophile. The dipoles added from the less hindered face of the double bond with an excellent selectivity. Enantiomerically pure dipolarophile was prepared from the easily available (S)-5-oxotetrahydrohydrofuran-2-carboxylic acid.

scholarly journals One-Year Clinical Evaluation of the Bonding Effectiveness of a One-Step, Self-Etch Adhesive in Noncarious Cervical Lesion Therapy

2015 ◽  
Vol 2015 ◽  
pp. 1-5 ◽  
Author(s):  
Babacar Faye ◽  
Mouhamed Sarr ◽  
Khaly Bane ◽  
Adjaratou Wakha Aidara ◽  
Seydina Ousmane Niang ◽  
...  
Keyword(s):  
Clinical Performance ◽  
Retention Rate ◽  
Recall Rate ◽  
Acid Etching ◽  
Significant Difference ◽  
Usphs Criteria ◽  
One Step ◽  
One Year ◽  
The One ◽  
Self Etch

This study evaluated the one-year clinical performance of a one-step, self-etch adhesive (Optibond All-in-One, Kerr, CA, USA) combined with a composite (Herculite XRV Ultra, Kerr Hawe, CA, USA) to restore NCCLs with or without prior acid etching. Restorations performed by the same practitioner were evaluated at baseline and after 3, 6, and 12 months using modified USPHS criteria. At 6 months, the recall rate was 100%. The retention rate was 84.2% for restorations with prior acid etching, but statistically significant differences were observed between baseline and 6 months. Without acid etching, the retention rate was 77%, and no statistically significant difference was noted between 3 and 6 months. Marginal integrity (93.7% with and 87.7% without acid etching) and discoloration (95.3% with and 92.9% without acid etching) were scored as Alpha or Bravo, with better results after acid etching. After one year, the recall rate was 58.06%. Loss of pulp vitality, postoperative sensitivity, or secondary caries were not observed. After one year retention rate was of 90.6% and 76.9% with and without acid conditioning. Optibond All-in-One performs at a satisfactory clinical performance level for restoration of NCCLs after 12 months especially after acid etching.

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