The question of concerted or consecutive bond formation arises in all types of cycloaddition reactions. Stereochemical investigations and studies of regiospecificity as well as intensive kinetic investigations with regard to substituent and solvent effects, and the dependence of the reaction on temperature and pressure permit in many cases mechanistic conclusions concerning the Diels-Alder reaction. Efforts towards a theoretical interpretation, ab initio and semiempirical calculations, the application of frontier molecular orbital theory (FMO) as well as thermochemical measurements permit a description of the energy hypersurface of these [4+2]-cycloadditions. An attempt is made here to draw a line of distinction between the mechanistic alternatives—one-step reaction versus two-step reaction—considering all experimental and theoretical criteria.

Mechanistic Aspects of Diels‐Alder Reactions: A Critical Survey

Synthetic and mechanistic aspects of 1,3-diene photooxidation

Kinetische Daten fur die Umsetzung substituierter 1,3-Diene mit Tetracyanethylen (TCNE) und anderen Dienophilen werden unter Zugrundelegung des FMO-Modells interpretiert. Wahrend qualitativ die Erwartungen erfullt sind, stellt man ein Versagen quantitativer Korrelationen fest. Dies zeigt, das bei Diels-Alder-Reaktionen neben den HOMO-LUMO-Abstanden weitere Faktoren eine bedeutsame Rolle spielen, z. B. der 1,4-Abstand im Dien, die Gleichgewichtslage cisoide ⇌ transoide Konformation des Diens und andere. Die kinetischen Daten stehen nicht im Widerspruch mit der Vorstellung eines konzertierten Ablaufs der Cycloadditionen.



Reactivity of Substituted 1,3-Butadienes in Diels-Alder-Reactions



Kinetic data for the reaction of substituted 1,3-dienes with tetracyanoethylene (TCNE) and other dienophiles are interpreted in terms of the FMO-model. While the expectations are fulfilled qualitatively, the kinetic data cannot be correlated quantitatively. This shows that in Diels-Alder reactions besides HOMO-LUMO separation other factors play an important role, for instance the 1,4-distance in the diene and the conformational equilibrium cisoid ⇌ transoid of the diene. The kinetic data are in accord with a one-step mechanism of the cycloaddition reaction.

Reaktivität substituierter 1,3‐Butadiene in Diels‐Alder‐Reaktionen

The phosphine-catalysed synthesis of cyclic α-methylene carbonates 2 directly from prop-2-ynyl alcohol derivatives and CO2 is described. These cyclic carbonates 2 are key intermediates for the selective access to β-oxopropyl carbonates 3 by reaction with alcohols under mild conditions, but in the presence of Et2N or KCN as catalyst.

Functional carbonates: cyclic α-methylene and β-oxopropyl carbonates from prop-2-ynyl alcohol derivatives and CO2

Publisher Summary Azodicarbonyl compounds contain a carbonyl function on both sides of the azo bond, in contrast to aliphatic and aromatic azo compounds, possess a highly reactive N=N group. Reactions in which one or both, of the nitrogen atoms of the azo group are retained in the final heterocyclic product are considered, and are classified according to the size of the new ring formed. Other reactions of azodicarbonyl (ADC) compounds, which do not give heterocyclic products, are briefly discussed. Acyclic ADC compounds, which are more correctly named as derivatives of diazene, are generally prepared from hydrazine derivatives. Cyclic ADC compounds are prepared by the oxidation of the corresponding cyclic hydrazine derivatives. The most important aspect of ADC compounds, as far as heterocyclic synthesis is concerned, is the great reactivity of the N=N bond in cycloaddition reactions with dienes, monoenes and 1,3-dipoles, and as an electrophile. Five-membered ring heterocycles can be the result of cycloaddition reactions of ADC compounds acting as 2π components with 1,3-dipoles, or as 4π components in cheletropic reactions. Other major uses of ADC compounds which do not give heterocyclic products are summarized briefly.

Azodicarbonyl Compounds in Heterocyclic Synthesis

Die 4,5-Dimethylen-1,3-dioxolane 1–5 zeigen, obwohl sie s-cis-fixierte Diensysteme darstellen, im Vergleich zu den 1,2-Dimethylencycloalkanen 8–10 und 2,3-Dimethylen-1,4-dioxan (6) sehr geringe Dienreaktivitaten, wie durch die Geschwindigkeitskonstanten und die Aktivierungsparameter belegt wird. Der Einflus der durch Photoelektronenspektroskopie festgelegten Ionisationspotentiale und der nach dem MINDO/3-Verfahren berechneten Molekulgeometrien auf die Reaktivitat wird untersucht. Es zeigt sich, das fur die Reaktivitat der s-cis-fixierten Diene nicht der Interplanarwinkel, sondern die Scherung (1,4-Abstand) des Dien-Systems von entscheidender Bedeutung ist.



On the Diels-Alder Reactivity of s-tis-Fixed 1,3-Dienes



Contrary to the 1,2-dimethylenecycloalkanes 8–10 and 2,3-dimethylene-14-dioxane (6), the 4,5-dimethylene-1,3-dioxolanes 1–5 show very poor diene reactivities in the Diels-Alder reaction though possessing an s-cis-fixed diene system. This is documented by bimolecular rate constants as well as activation parameters. The influence of the ionisation potentials measured by PE spectroscopy and of the molecular geometries calculated by the MINDO/3 method on the reactivity is studied. It is shown that not the dehedral angle but the scissoring (1.4-distance) of the diene system is of decisive importance for the reactivity of the s-cis-fixed dienes.

Zur Diels‐Alder‐Reaktivität s‐cis‐fixierter 1,3‐Diene

Darstellung von 4,5‐Dimethylen‐1,3‐dioxolan‐2‐on

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Helmut Plum

Author Tools

Chat about Author

Papers

Zur Diels‐Alder‐Reaktivität s‐cis‐fixierter 1,3‐Diene

Darstellung von 4,5‐Dimethylen‐1,3‐dioxolan‐2‐on