Search results for "Diels–Alder"
showing 10 items of 66 documents
Unveiling the Intramolecular Ionic Diels–Alder Reactions within Molecular Electron Density Theory
2021
The intramolecular ionic Diels–Alder (IIDA) reactions of two dieniminiums were studied within the Molecular Electron Density Theory (MEDT) at the ωB97XD/6-311G(d,p) computational level. Topological analysis of the electron localization function (ELF) of dieniminiums showed that their electronic structures can been seen as the sum of those of butadiene and ethaniminium. The superelectrophilic character of dieniminiums accounts for the high intramolecular global electron density transfer taking place from the diene framework to the iminium one at the transition state structures (TSs) of these IIDA reactions, which are classified as the forward electro density flux. The activation enthalpy ass…
Zur Reaktion vonE/Z-N-Benzolsulfonyl-3(2-methoxyvinyl)-indol mit Carbo- und Heterodienophilen: NeueDiels-Alder-Addukte aus der Indol- bzw. Carbazol-R…
1987
E/Z-Benzenesulfonyl-3(2-methoxyvinyl)-indole1 reacts viaDiels-Alder type mechanism with dimethyl acetylendicarboxylate, N-phenyltriazolindione and diethyl mesoxalate to give new cycloadducts2–5 with [b]annellated indole structures.
Studies on the Biosynthesis of Paraherquamide: Synthesis and Incorporation of a Hexacyclic Indole Derivative as an Advanced Metabolite
2001
Mechanism of triplet photosensitized Diels-Alder Reaction between indoles and cyclohexadienes: theoretical support for an adiabatic pathway.
2006
Diels-Alder reactions between indoles (InHs) and 1,3-cyclohexadienes (CHDs) were achieved by using aromatic ketones as photosensitizers. For instance, irradiation of deaerated dichloromethane solutions containing benzoylthiophene (BT, 1 mM), indole (20 mM), and phellandrene (40 mM), in the presence of an acylating agent, led to the N-acetylated Diels-Alder cycloadduct in 46% yield (endo:exo ratio of 1.8:1). Energy transfer from the BT triplet to the CHD gave rise to diene dimers as byproducts. Several combinations of CHDs, InHs, and aromatic ketones were tested; the Diels-Alder reaction was found to be a general process, except when the indole nucleus was substituted at position 2 or 7 and …
Cationic Iron Aminocarbene Complexes as Dienophiles in Diels‐Alder Reaction with Cyclopentadiene
1996
The cationic iron (alkynyl)aminocarbene complexes [Cp(CO)2Fe(C(NHR)CCSiMe3][PF6], (R C6H5, p-CH3C6H4) 1 derived from aromatic amines smoothly react with cyclopentadiene in dichloromethane to yield the cycloadducts 2. No reaction was observed for complexes derived from sterically demanding aliphatic amines, like L-alanine tert-butyl ester. For comparison, the alkynyl-substituted acyl iron compounds Cp(CO)2Fe(CO)CC (R SiMe3, C6H5) 3 were investigated, requiring TiCl4 catalysis to undergo the cycloaddition reaction. The structures of the cycloadducts 4 were determined by X-ray crystallography.
Die symmetrischen Cyclooctadienine: 1,5‐Cyclooctadien‐3‐in und 1,3‐Cyclooctadien‐6‐in
1985
Die Titelverbindungen 16 und 17, hoch gespannte Kohlenwasserstoffe aus der C8H8-Reihe, konnen auf sechs- bzw. siebenstufigen Synthesewegen aus 1,5-Cyclooctadien (1) bzw. Cyclooctatetraen (2) hergestellt und in reiner Form isoliert werden. Ihre Stabilitat und ihr chemisches Verhalten werden diskutiert. Dabei stehen Di- und Oligomerisierungen einerseits und Diels-Alder-Reaktionen andererseits im Vordergrund. 16 und 17 sind sehr reaktive Dienophile; 17 ist daruber hinaus auch als Dien einzusetzen. The Symmetrical Cyclooctadienynes: 1,5-Cyclooctadien-3-yne and 1,3-Cyclooctadien-6-yne Starting with 1,5-cyclooctadiene (1) and cyclooctatetraene (2), respectively, the title compounds 16 and 17, hig…
Kinetische Untersuchungen zu Diels‐Alder‐Reaktionen des Cyclooctins mit anschließender Aromatisierung
1984
Aus Cyclooctin (1) und den cyclischen Dienen 2a – g entstehen die Tricyclen 3a – g, die ganz unterschiedliche Stabilitat aufweisen. 3a, b, f und g zerfallen spontan. Unter Abspaltung von CO2, SO2, CO und N2 entstehen die aromatischen Verbindungen 4a – c. 3c eliminiert beim Erhitzen C2H4. 3e wird thermisch kaum mehr gespalten, aber ganz effizient bei der Photolyse, und 3d ist schlieslich gegenuber einer Aromatisierung stabil. Die thermische Ethylenabspaltung und die doppelte Photodecarbonylierung werden kinetisch untersucht. Kinetic Investigations of Diels-Alder-Reactions of Cyclooctyne with Consecutive Aromatization The tricyclic compounds 3a – g, generated from cyclooctyne (1) and the cycl…
A retro Diels–Alder method for the preparation of pyrrolo[1,2-a]pyrimidinediones from diexo-aminooxanorbornenecarboxamide
2006
Abstract Through the reactions of diexo-3-amino-7-oxanorbornene-2-carboxamide 1 with the oxocarboxylic acids: 4-oxopentanoic acid, p-chlorobenzoylpropionic acid or 2-formylbenzoic acid, the pyrrolo[1,2-a]pyrimidinediones 2 and 3 or pyrimido[1,2-a]isoindoledione 4 were formed on cyclization and thermolysis, when the parent cycles decomposed via the loss of furan to give 2–4 in a retro Diels–Alder reaction. With cis-or trans-2-aroylcyclohexanecarboxylic acids as starting compounds, the 1-aroylhexahydroisoindol-3-ones (5–8) were formed; the phenyl-substituted derivatives gave diastereomeric mixtures. The structures of the new compounds were established by NMR spectroscopy and, for 3 and 6, als…
A Domino Ring‐Closure Followed by Retro‐Diels–Alder Reaction for the Preparation of Pyrimido[2,1‐ a ]isoindole Enantiomers
2016
A simple method was developed to prepare pyrimido[2,1-a]isoindole derivatives by using di-endo- and di-exo-ethyl 3-aminobicyclo[2.2.1]hept-5-ene-2-carboxylate enantiomers as chiral sources. The method is based on a domino ring-closure reaction of norbornene 2-aminohydroxamic acid followed by microwave-induced retro-Diels–Alder reaction. In the case of enantiomeric starting substances, the chirality is transferred from norbornene derivatives to pyrimido[2,1-a]isoindoles. The configurations of the synthesized compounds were determined by 1D and 2D NMR spectroscopy [based on 2D NOE cross-peaks and 3JH,H coupling constants] and X-ray crystallography.
On the Catalytic Effect of Water in the Intramolecular Diels–Alder Reaction of Quinone Systems: A Theoretical Study
2012
The mechanism of the intramolecular Diels#8211;Alder (IMDA) reaction of benzoquinone 1, in the absence and in the presence of three water molecules, 1w, has been studied by means of density functional theory (DFT) methods, using the M05-2X and B3LYP functionals for exploration of the potential energy surface (PES). The energy and geometrical results obtained are complemented with a population analysis using the NBO method, and an analysis based on the global, local and group electrophilicity and nucleophilicity indices. Both implicit and explicit solvation emphasize the increase of the polarity of the reaction and the reduction of activation free energies associated with the transition stat…