Diels-Alder Reaction Of Diene Research Articles

Synthesis and Application of Chiral 2-Amido and 1-Phenyl-2-amido Dienes in Diels-Alder Reactions to Access Chiral Cyclic Ketones.

The preparation of a focused library of chiral 2-amido and 2-amido-1-phenyl-1,3-dienes from a range of chiral oxazolidinones using palladium-catalysis is reported. This palladium-catalyzed carbon-nitrogen bond-forming reaction provides the corresponding chiral amido-dienes in moderate to excellent yields (12 examples, up to 97%). The resulting chiral amido-dienes are employed as novel dienes in Diels-Alder (DA) reactions (58 examples, up to 93:7 dr, up to 70% yield). A range of chiral cyclic ketones were accessed upon hydrolysis, affording products with high levels of enantioselectivity (up to 92% ee, up to 81% yield).

Phthalazine as a Diene in Diels-Alder Reactions With P- and As-Containing Anionic Dienophiles: Comparison of Possible Reaction Channels.

Phthalazine can behave as a diene in Diels-Alder (DA) cycloadditions, typically at the pyridazine ring, however, its application is somewhat limited because these reactions usually require harsh conditions or sophisticated catalysts. As an unconventional example, phthalazine was reported to undergo cycloaddition with the [PCO]- anion without any catalyst. In this computational study, we scrutinise the mechanism of the DA reactions between phthalazine and the so far known [ECX]- (E: P, As; X: O, S, Se) anions as dienophiles. In principle, the attack of an [ECX]- anion may occur at two different sites of phthalazine, either at the benzene or the pyridazine ring, and both of these possible reaction channels were juxtaposed on the basis of energetic aspects. In all of the investigated cases, the analysis of the energy profiles reveals a clear regioselectivity that favours the attack at the pyridazine ring. As a result, so far unprecedented 2-pnictanaphth-3-olate analogues seem achievable as final products. Comparing the characteristics of these pathways allowed us to clarify the source of this regioselectivity: The pyridazine ring of phthalazine exhibits lower aromaticity than the benzene subring; therefore, in the DA step, the former ring shows a higher affinity toward a dienophile than the latter, leading to lower activation barriers. To further map the electronic and structural features of the cycloaddition steps, the local interactions evolving in the transition states were analysed and compared using global and local descriptors. In most aspects, the characteristics of both pathways were found to be rather similar, in contrast to the markedly differing activation barriers on the two routes.

6-Methylenebicyclo[3.2.1]oct-1-en-3-one: A Twisted Olefin as Diels-Alder Dienophile for Expedited Syntheses of Four Kaurane Diterpenoids.

6-Methylenebicyclo[3.2.1]oct-1-en-3-one, a twisted and highly reactive enone, was prepared for the first time by elimination of its bromide precursor. Its reactions as a dienophile with several dienes in Diels-Alder reactions proceeded smoothly to provide tricyclic and tetracyclic adducts, which allowed short syntheses (10-11 steps) of four kurane diterpenoids including 11β-hydroxy-16-kaurene, 11α-hydroxy-16-kaurene, liangshanin G, and gesneroidin B.

Synthesis of exo-Imidazolidin-2-one Dienes, Their Isomerization, and Selectivity in Diels–Alder Cycloadditions

An efficient and alternative synthesis of exo-imidazolidin-2-one dienes is described. A condensation reaction was carried out with bis-imino derivatives, diacetyl, and triphosgene, affording symmetrically N, N-disubstituted dienes. The use of alkyl methyl α-diketones led to the formation of nonsymmetrical dienes, which underwent isomerization to provide more stable inner-outer-ring dienes under Lewis acid conditions. Evaluation was made of the reactivity as well as regio- and stereoselectivity of these dienes in Diels-Alder reactions. They proved to be highly reactive and selective. DFT calculations of the transition states accounted for their behavior.

Synthesis and Diels-Alder reactions of a benzo[5]radialene derivative.

Apart from their exotic structure, radialenes have been employed as precursors of more complex polycyclic molecules. In this work we report the synthesis of the first compound having the benzo[5]radialene substructure, starting from simple materials. Such a compound proved to be a convenient diene in Diels-Alder reactions, for the preparation of highly functionalized fluorenes and benzo[b]fluorenes in a quimio- and stereocontrolled fashion.

Electron-deficient 1- and 2-azabuta-1,3-dienes: a comprehensive survey of their synthesis and reactivity

Electron-deficient 1- and 2-azabuta-1,3-dienes are reagents intrinsically able to provide a wide range of cyclic and acyclic N-containing building blocks. Depending on their substitution, they behave as dienes for Diels-Alder reactions, as partners for [4+1], [3+2], [2+2]-cycloadditions, for aziridinations and as electrophiles for 1,2 and 1,4-additions. Nowadays, they are a very versatile family of compounds, despite their usual instability and complex reactivity. Four decades of research in this challenging area are reviewed in this critical review: their synthetic aspects and their reactivity towards a wide range of dienophiles, dipoles and nucleophiles are described as well. The introduction focuses on their electronic properties in order to get a clear picture of their reactivity (190 references).

Borostannylation of Alkynes and Enynes. Scope and Limitations of the Reaction and Utility of the Adducts

The utility of the hetero-bismetallating reagent 1,3-dimethyl-2-trimethylstannyl-2-bora-1,3-diazacyclopentane (1) has not been fully realized because of the hydrolytic instability of the products derived from catalyzed vicinal syn-additions to alkynes. The isolation of a variety of such adducts derived from alkynes (and also from hitherto unreported additions to 1,3-enynes) as stable boron pinacolates is reported. Examples of the applications of resulting products in tandem cross-coupling reactions and as dienes in Diels-Alder reactions are illustrated.

Facile Synthesis and Diels-AlderReactions of 2,6-Divinyl-1,4-dithiin

A new and facile synthetic pathway to 2,6-divinyl-1,4-dithiin, involving easily available precursors is reported. The utility of the title compound as a reactive diene in Diels-Alder reactions was demonstrated in the synthesis of various thianthrene derivatives.

Stereoselective Synthesis of 4,5-Diethylidene-Oxazolidinones as New Dienes inDiels-Alder Reactions

The N-substituted isomeric (4Z,5Z)- and (4E,5Z)-4,5-diethylideneoxazolidin-2-ones 5 and 6 were synthesized, the latter being favored during the one-step process from the α-diketone 1c and different isocyanates. The steric interaction between the N-substituent and the Me group attached to the exocyclic diene moiety plays a decisive role in controlling the observed stereoselectivity, as suggested by the calculated free energies of the two isomers. Both dienes undergo efficient additions to symmetric dienophiles in thermal Diels-Alder reactions to yield the adducts 11 and 13, respectively. These molecules displayed interesting C−H⋅⋅⋅π, and C−H⋅⋅⋅X (X=O, Cl) interactions according to their X-ray crystal structures. Isomers 6 suffered highly stereo- and regioselective additions with nonsymmetrical dienophiles such as methyl vinyl ketone or methyl propiolate. Steric interactions, promoted by the inward-pointing Me group in 6, seem to explain such selectivity. These results have also been rationalized by ab initio calculations in terms of the FMO theory.

Preparation of Vinylogous 2-Sulfonylindolines by the Palladium-Catalyzed Heteroannulation of o-Iodoanilines with Dienyl Sulfones and Their Further Transformation to Indoles and Carbazoles

The palladium-catalyzed heteroannulation of o-iodoanilines with dienyl sulfones provides a convenient route to vinylogous 2-sulfonylindolines 3. The reaction proceeds in DMF/water in the presence of potassium carbonate and catalytic palladium(II) acetate and is compatible with both electron-donating and -withdrawing substituents in the para position of the aniline, and with an alkyl substituent at C-2 of the dienyl sulfone. The indolines underwent oxidation with DDQ to afford the corresponding indoles 4. The latter were then employed as dienes in Diels-Alder reactions with dimethyl acetylenedicarboxylate (DMAD), methyl propiolate, or methyl acrylate. In the case of the latter two dienophiles, the cycloadditions were highly regioselective, affording the corresponding 1,3-products (with respect to the relative positions of the sulfone and ester groups), exclusively. The cycloadducts from acetylenic dienophiles were converted to the corresponding carbazoles by elimination of the sulfone moiety with DBU, and that from methyl acrylate was subjected to reductive desulfonylation and oxidation to the corresponding carbazole with DDQ. The method thus provides access to carbazoles with various substituents at the 3-, 4-, and 6-positions.

ChemInform Abstract: 1,2,3,4-Tetrachloro-5,5-dimethoxy-cyclopenta-1,3-diene: Diels-Alder Reactions and Applications of the Products Formed

Readily available 1,2,3,4-tetrachloro-5,5-dimethoxy- cyclopenta-1,3-diene (2) is an excellent cyclic diene for Diels-Alder reaction with a vast variety of dienophiles. The products so formed (norbornene derivatives) constitute important building blocks for the synthesis of diverse complex natural as well as non-natural products. Apart from very high endo selectivity associated with Diels-Alder reactions, there are several other fascinating features associated with these bicyclic products which make them convenient entities in the synthesis of complex molecules. The most important is the rigid framework that act as a powerful template to provide high degree of selectivity and directional nature to various substituents. The proposed article is intended to focus on Diels-Alder reactions of 2 and the applications of norbornene derivatives in organic synthesis.

Stereoselective Diels-Alder reaction of electrogenerated quinones on a PTFE-fiber coated electrode in lithium perchlorate / nitromethane

Diels-Alder reaction of dienes and in situ generated quinones was accelerated on a PTFE-fiber in an electrolytic lithium perchlorate / nitromethane system. In the presence of PTFE-fiber on a glassy carbon electrode, unstable quinones were efficiently generated by electrooxidation and trapped by dienes maintained on the poly-fluorinated fiber to give the desired cycloadducts stereoselectively in excellent yields.

Synthesis of 3-vinylpiperidines, 3-ethylidenepiperidines and 5-functionalized-1,2,3,4-tetrahydropyridines

Reaction of 1-azapentadienyl anions, generated by deprotonation of N-(2-buten-1-ylidene)-alkylamines, with 1-bromo-3-chloropropane led to the formation of N-[2-(3-chloropropyl)-3-buten-1-ylidene]alkylamines. By reaction with nucleophiles and bases, the latter functionalized imines were converted into unsaturated piperidines, i.e. 3-vinylpiperidines, 3-ethylidenepiperidines, 5-vinyl-1,2,3,4-tetrahydropyridines and 5-(2-cyanoethyl)-1,2,3,4-tetrahydropyridines. 5-Vinyl-1,2,3,4-tetrahydropyridines proved to be suitable dienes in Diels-Alder reactions with N-phenylmaleimide, giving rise to octahydro-1 H-pyrrolo[3,4 h]quinoline-1,3-diones.

A New Strategy for the Stereoselective Synthesis of Olefins Based on Selenophosphates

: New selenophosphates 2 containing the α,β-unsaturated carbonyl moiety have been prepared and applied as intermediates in the synthesis of novel 1,3-dienes 7 with an alkylselenosubstituent in position 1 and the diethoxyphosphoryloxy substituent in position 2. Diels-Alder reactions of dienes 7 with some dienophiles have been investigated; they are fully regio-and endo-stereospecific. The Diels-Alder cycloadducts 8 and 9 have been transformed by oxidationinto the corresponding functionalizedallylicalcohols 12

D-glucose bound dienes in diels-alder reactions

D-glucose bound dienes in diels-alder reactions

Cycloaddition reactions of conjugated dienoic carboxylic acids and esters with N-substituted maleimides and Schiff bases

Sorbic acid and its esters were investigated as potential dienes in Diels-Alder reactions with N-substituted maleimides. The purpose was to characterise such Diels-Alder adducts by means of NMR, and to provide reference compounds to identify the formation of related products in model food systems. These reactions occur both in aqueous and non-aqueous systems and it is possible that the CN bond of Schiff bases could act as a dienophile towards sorbic acid. In general, the 1 H chemical shifts for the olefinic protons, originally at C 3 and C 4 of sorbic acid, are to be found at δ 5.7–5.9 and 6.3–6.5, respectively in the adduct. Those at C 2, C 5 and C 6 are at δ 2.4–2.6, 3.4–4.2 and 1.4–1.5, respectively. All these values are characteristically different from the corresponding proton chemical shifts in sorbic acid.

A theoretical study of acetylene, ethylene, and cyclopropene additions to benzo[b]- and benzo[c]-fused heterocycles

The reactivity of benzo[b]- and benzo[c]-fused heterocycles as dienes for Diels-Alder reactions were evaluated on the basis of Frontier Molecular Orbital (FMO) energy gaps between reactants, necessary FMO changes for the transformation of reactants into transition state structures, uniformity of bond orders of heterocyclic rings, and uniformity of bond orders of the six-membered cyclic transition state structures All of these values were obtained with AM1 semiempirical methods. The selectivity of the cycloaddition reaction was also judged with Secondary Orbital Interactions (SOI) between two reactant moieties in isomeric transition state structures. For every possible reaction pathway, AM1 and B3LYP/AM1 energies were evaluated. The relative reactivity and selectivity obtained by computing activation barriers for these reactions were in full agreement with our qualitative studies as well as with experimental results. The usefulness of the FMO and bond order uniformity approach for the study of the Diels-Alder reaction was discussed.

2,4-Dimethoxy-1,3-diazaanthracene, a Diels-Alder Diene for the Preparation of Polyalicyclic Structures Functionalised with Uracil Subunits

2,4-Dimethoxy-1,3-diazaanthracene (DDA) has been prepared from the known 2,4-dichloro-1,3-diazaanthracene by methoxide displacement of the chloro-substituents and shown to react as a diene in Diels-Alder reactions with electron-deficient and ring-strained dienophiles. Sodium hydroxide fusion is used to transform the DDA adducts to uracil derivatives.

The Formation of Thiocarbonyl Compounds by The Thermal Decomposition of Heteroaryl Substituted Sulfoxides

The thermal reaction of phenacyl sulfoxide bearing some heterocycles in the presence of butadiene afforded the thiapyarn derivatives, which is considered to be formed by the Diels Alder reaction of diene with thiocalbonyl compound.

(2 E)-4-methoxy-2,4-pentadienamides as new dienes in the Diels-Alder reaction

(2 E)-4-Methoxy-2,4-pentadienamides have been stereoselectively prepared by treatment of (2 E,4 E)-5-tosyl-2,4-pentadienamides with IM methanolic potassium hydroxide in good yields. They behave as new electron-rich dienes in Diels-Alder reactions to give stereoselectively highly functionalized adducts 3 mainly with endo-selectivity and, after hydrolysis, only their corresponding cyclohexanone derivatives 4. Semi-empirical calculations corroborate their reactivity.