Silyl-substituted 1,3-butadienes for Diels-Alder reaction, ene reaction and allylation reaction

Silyl-substituted 1,3-butadienes are useful building blocks and are readily applied in several types of reactions such as Diels-Alder reaction, ene reaction and allylation. They can also participate in different tandem reactions such as Diels-Alder/allylation, ene/allylation, ene/allylation/Diels-Alder reaction, ene/allylation/ene reaction and ene/allylation/Diels-Alder/allylation reaction. This feature article reviews the synthesis of silyl-substituted 1,3-butadienes, and their applications in the reaction types mentioned above, involving a tandem Diels-Alder/ene/allylation process. This article also introduces some reactions of alkenylsilanes and allylsilanes for comparison and discussion about the tandem reaction. The tandem reactions described in this article are a powerful tool to construct complicated multicyclic compounds with high selectivity and high efficiency.     

内分子DIELS-ALDER反应合成DRIMANE类倍半萜化合物DRIMENIN, POLYGODIAL及CINNAMOLIDE的全合成

近年来有不少报道从事于生理活性Drimane类倍半萜的合成,较多采用了分子间Diels-Alder反应来建立Drimane的骨架。本文首次采用内分子Diels-Alder反应作为关键反应合成了Drimane类化合物。同时还在引入了手性诱导基团后,首次完成了从无手性的原料化合物β-紫罗兰酮至光学活性(-)-drimenin1的不对称合成。     

Chemistry and biology of biosynthetic Diels-Alder reactions

Nature's repertoire of biosynthetic transformations has recently been recognized to include the Diels-Alder cycloaddition reaction. Evidence now exists that there are enzymes that mediate the Diels-Alder reaction in secondary metabolic biosynthetic pathways. 2002 marked the 100th anniversary of Alder's birth and 75 years since the discovery of the Diels-Alder reaction. It would appear that living systems discovered and made use of this ubiquitously useful ring-forming reaction eons ago for the construction of complex natural products. In this Review an overview is given of all of the known classes of natural products (polyketides, isoprenoids, phenylpropanoids, alkaloids) that have been speculated to arise by a biological Diels-Alder reaction.     

1,4-Difluoro-2,5-dimethoxybenzene as a precursor for iterative double benzyne-furan Diels-Alder reactions

[reaction: see text] The use of 1,4-difluoro-2,5-dimethoxybenzene as a novel precursor for iterative two-directional benzyne-furan Diels-Alder reactions, using a range of 2- and 3-substituted furans, is reported. Substituted oxabenzonorbornadienes were synthesized following the initial Diels-Alder reaction, which upon ring opening under acidic conditions gave substituted naphthol derivatives. Highly substituted anthracenols were generated in the second benzyne-furan Diels-Alder reaction following acid-catalyzed isomerization of the cycloadducts.     

How Ionization Catalyzes Diels-Alder Reactions

The catalytic effect of ionization on the Diels-Alder reaction between 1,3-butadiene and acrylaldehyde has been studied using relativistic density functional theory (DFT). Removal of an electron from the dienophile, acrylaldehyde, significantly accelerates the Diels-Alder reaction and shifts the reaction mechanism from concerted asynchronous for the neutral Diels-Alder reaction to stepwise for the radical-cation Diels-Alder reaction. Our detailed activation strain and Kohn-Sham molecular orbital analyses reveal how ionization of the dienophile enhances the Diels-Alder reactivity via two mechanisms: (i) by amplifying the asymmetry in the dienophile's occupied π-orbitals to such an extent that the reaction goes from concerted asynchronous to stepwise and thus with substantially less steric (Pauli) repulsion per reaction step; (ii) by enhancing the stabilizing orbital interactions that result from the ability of the singly occupied molecular orbital of the radical-cation dienophile to engage in an additional three-electron bonding interaction with the highest occupied molecular orbital of the diene.     

Reactivity and stereoselectivity of the Diels-Alder reaction using cyclic dienophiles and siloxyaminobutadienes

Several bicyclic compounds were synthesized by the Diels-Alder reaction using aminodiene and a cyclic dienophile. The stereochemistries of the obtained adducts were determined by X-ray crystallography or NMR analysis. The stereoselectivity of this Diels-Alder reaction was based on the interaction of molecular orbitals between the diene and dienophile. The reactivities of these Diels-Alder reactions were estimated, and the generality of this reaction is discussed.     

Synthesis of [60]fullerene-functionalized rotaxanes

Synthesis of [60]fullerene (C₆₀)-functionalized rotaxanes via Diels-Alder reactions with C₆₀ is described. Diels-Alder reaction of C₆₀ and sulfolene moiety as masked diene attached on the wheels of rotaxanes results in high yields of C₆₀ incorporation. Rotaxanes are prepared by tin-catalyzed urethane-forming end-capping reaction with isocyanate of pseudorotaxane having the wheel carrying C₆₀ functionality as introduced by the Diels-Alder reaction. The Diels-Alder reaction was accomplished as end-capping reaction between C₆₀ and pseudorotaxane bearing sultine moiety as masked diene on the axle terminal. A variety of C₆₀-containing [2]rotaxanes was prepared in moderate to good yields by these Diels-Alder protocols.     

A novel and facile stereocontrolled synthetic method for polyhydro-quinolines and pyridopyridazines via a diene-transmissive Diels-Alder reaction involving inverse electron-demand hetero Diels-Alder cycloaddition of cross-conjugated azatrienes

Cross-conjugated azatrienes bearing an electron-withdrawing sulfonyl or benzoyl group on the nitrogen atom underwent, on heating or in the presence of a Lewis acid (TMSOTf), an initial inverse electron-demand hetero Diels-Alder reaction with electron-rich dienophiles (vinyl ether, vinyl thioether, and allenyl ether) to produce 1:1 cycloadducts with high endo selectivity. The initial cycloadducts thus obtained underwent a second Diels-Alder reaction stereoselectively on the newly formed diene unit with electron-deficient dienophiles to give the crossed bis-cycloadducts, octahydroquinolines, with high diastereo-π-facial selectivity. The N-sulfonylazatrienes tethering an ortho-cinnamyloxyphenyl dienophile at the triene terminal underwent an initial intramolecular hetero Diels-Alder reaction of the inverse electron-demand type. The subsequent second Diels-Alder reaction of the formed mono-cycloadducts completed the diene-transmissive hetero Diels-Alder protocol to give benzopyrano[3,4-c]quinolines in a highly stereoselective manner.     

呋喃环参与的Diels-Alder反应及其应用

呋喃环在作为Diels-Alder反应的二烯组份中得到了广泛的研究.本文就呋喃环参与的分子间和分子内D-A反应及其应用作一综述.     

Aqueous Ti(IV)-catalyzed Diels-Alder reaction

The aqueous Diels-Alder reaction of 1,3-cyclohexadiene with 1,4-benzoquinone was compared and contrasted to the same reaction catalyzed with Flextyl P, a novel Ti(IV) performance catalyst. The catalyst improved conversion by 22% versus the uncatalyzed reaction and represents a rare example of a Ti(IV) catalyzed Diels-Alder reaction in water.     

Lewis acid-catalyzed tandem Diels-Alder reaction/retro-Claisen rearrangement as an equivalent of the inverse electron demand hetero Diels-Alder reaction

A highly stereoselective formal inverse electron demand hetero Diels-Alder reaction (HDA) occurs on reaction of 2-aryl-alpha,beta-unsaturated aldehydes with cyclopentadiene. The major pathway for this transformation is shown to be a Lewis acid-catalyzed tandem Diels-Alder reaction/retro-Claisen rearrangement.     

A substituent effects study reveals the kinetic pathway for an interfacial reaction

This paper describes the use of a substituent effects study to understand the mechanistic basis for an interfacial Diels-Alder reaction that does not proceed with standard second-order kinetics. Cyclopentadiene (Cp) undergoes a Diels-Alder reaction with a chemisorbed mercaptobenzoquinone to yield an immobilized Diels-Alder adduct. The pseudo-first-order rate constants are not linearly related to the concentration of diene, but they reach a limiting value with increasing concentrations of diene. The results of a substituent effects study support a mechanism wherein the electrochemical oxidation of hydroquinone produces two states of quinone. The first form, Q*, either reacts with Cp or isomerizes to Q, a form that is significantly less reactive with the diene. The interfacial reaction reaches a maximum rate when the concentration of diene is sufficiently high so that Q* undergoes complete Diels-Alder reaction and does not isomerize to Q. This work provides an example of the use of physical organic chemistry to understand an interfacial reaction.     

Diels-Alder reaction of maldoxin with an isopropenylallene

The Diels-Alder reaction of maldoxin with an isopropenylallene at 60-75 °C afforded an adduct closely related to chloropestolide A (24%) and a second adduct (0-11%) that underwent an ene reaction to generate the chloropupukeanolide D (11-22%) skeleton. The Diels-Alder reaction occurred with good selectively (>5:1) from a single face of maldoxin under much milder conditions than previously reported for the analogous dimethoxycyclohexadienone. Furthermore, the ene reaction took place under mild conditions, whereas the analogous Diels-Alder adduct from the dimethoxycyclohexadienone did not undergo an ene reaction.     

Studies towards a postulated biomimetic Diels-Alder reaction for the synthesis of himgravine

The possible role of an iminium ion mediated Diels-Alder reaction on the biosynthetic pathway to himgravinc is discussed. The results of a preliminary investigation of a related oxycarbenium ion mediated Diels-Alder reaction are reported and are in accord with the stereochemistry of the natural product.     

Brønsted-acid and Brønsted-base catalyzed Diels-Alder reactions

The enantioselective Diels-Alder reaction is one of the most important reactions for the synthesis of complex molecules. It provides access to chiral six-membered carbocyclic compounds containing up to four stereogenic centers in a single step. Asymmetric catalysis in the Diels-Alder reaction has mainly been realized using chiral Lewis acids. In this perspective, we describe several cases of chiral Br?nsted-acid and Br?nsted-base catalyzed Diels-Alder reactions, providing an overview of this rapidly growing field.     

应用Diels-Alder反应制备聚合物的研究进展

由于Diels-Alder反应具有一系列重要特点(原子经济性、热可逆性、立体选择性、立体专一性和区域选择性等),自从1928年被发现以来,该反应就一直是人们研究的热点。将其应用于聚合物的合成中,可制备一些具有特殊性能的Diels-Alder聚合物,人们在这方面作了大量的研究工作,取得了许多研究成果。本文首先根据不同的分类标准,对应用Diels-Alder反应制备聚合物的研究进行了分类,然后结合本课题组的相关研究工作,综述了近年来人们在该领域的研究进展,最后展望了其研究前景。     

Diels-Alder reactions of masked o-benzoquinones: new experimental findings and a theoretical study of the inverse electron demand case

Diels-Alder reactions of the masked o-benzoquinone (MOB) 2 with vinylene carbonate (3), the bicyclic derivatives 4, 5, and 6, and the intramolecular version of the 2-hydroxymethylfuran-MOB Diels-Alder reaction are described. In addition, a theoretical study of the Diels-Alder reactions of MOBs with enol and thioenol ethers is presented.     

Efficient synthesis of a 4,5-epoxy-2-cyclohexen-1-one derivative bearing a spirolactone via a Diels-Alder reaction with high pi-facial selectivity: a synthetic study towards scyphostatin

The Diels-Alder reaction of spirolactones with cyclopentadiene afforded the adduct with high pi-facial selectivity; a hydrophilic analogue of scyphostatin was synthesized from the Diels-Alder adduct.     

The cosolvent-directed Diels-Alder reaction in ionic liquids

The rate constants of a bimolecular Diels-Alder reaction in binary mixtures of ionic liquids prepared in molecular solvents were analyzed to investigate the effect of viscosity of the medium and solvent effect. In this connection, we have carried out the Diels-Alder reaction of anthracene 9-carbinol with N-ethyl maleimide in binary mixtures of pyridinium-based ionic liquids, 1-butyl-pyridinium tetrafluoroborate, 1-butyl-3-pyridinium tetrafluoroborate, and 1-butyl-4-methyl pyridinium tetrafluoroborate in water, methanol, and chloroform at 298.15 K. The rates of reaction decreased, caused by gradually increasing the volume fraction of ionic liquids in solvents for all three ionic liquids. The kinetic results demonstrate a successful application of the pairwise interaction model built upon the concept of enforced hydrophobic hydration. A temperature-dependent study of kinetics of the Diels-Alder reaction was carried out in the binary mixtures of ionic liquids in water and was explained by the entropy-enthalpy compensation effect based upon activation parameters. Kinetics of the Diels-Alder reaction in highly aqueous medium was noted to be entropically driven.     

Intramolecular ionic Diels-Alder reactions of alpha-acetylenic acetals

The intramolecular ionic Diels-Alder reaction of alpha-acetylenic acetals as a precursor of the propargyl cation has been investigated in the presence of Lewis acids and in protic acids. The reaction of diene-tethered alpha-acetylenic acetals (1-2) with formic acid yielded the regioselective intramolecular ionic Diels-Alder reaction products, bicyclodienal (9) and bicyclodienone (11) derivatives, in good yields.