Fluoropropenoates as dienophiles in the Diels-Alder reaction

Several fluorinated alkenes were prepared from known ethyl (R)-2-fluoro-4,5-dihydroxyisopropylidine-2-pentenoate (1). The fluoroalkenoates were tested as dienophiles with several dienes and showed cycloaddition only with the very reactive diene, 1,3-diphenylisobenzofuran (5). Fluorobutenolide 2 reacted with 5 to produce the endo-syn adduct 9 in a highly stereoselective manner.     

Investigations of the stereoselectivity of the intramolecular Diels-Alder reaction of a spiculoic acid model system

Model linear precursors to the spiculoic acids were prepared and underwent thermally induced IMDA reactions. The configuration of C5 in the stereotriad was found to dominate any inherent endo/exo selectivity of the IMDA reaction. The isomer (2E,5S)-20 underwent the IMDA to give the spiculoic acid stereochemistry in 84% yield and 94% ds. The required stereotriads were synthesised using stereoselective substrate-controlled aldol reactions; an anti-boron aldol reaction, controlled by the π-facial preference of (S)-2-benzoyloxypentan-3-one ((S)-27) led to (5R)-(22) and a syn-titanium aldol reaction, under the stereocontrol of a chiral N-acylthiazolidinethione (42) led to (5S)-(22). Chain extension using standard Wittig, HWE and ‘modified’ Julia olefinations installed the diene and dienophile components giving the linear precursors to the IMDA reactions.     

A novel Ireland-Claisen rearrangement/Diels-Alder tandem reaction of propargylic acrylates with acyclic dienophiles

A novel DABCO-catalyzed Ireland-Claisen rearrangement/Diels-Alder tandem reaction of propargylic acrylates 3 with dienophiles 4 was developed in the presence of an excess TMSCl and DBU with 1% hydroquinone as polymerization inhibitor in acetonitrile at refluxing temperature under air.This protocol gave cyclicα,β-unsaturated carboxylic acids 5 with complete regioselectivity.     

Diels-Alder reaction of sugar-derived cyclic dienophiles with cyclopentadiene. Factors affecting the reactivity and stereoselectivity

[formula: see text] A sugar-derived cyclic dienophile showed a high exo and face selectivity in the Diels-Alder reaction with cyclopentadiene. Structural modifications on the dienophile structure were made, and the outcomes of the cycloaddition reactions were investigated. These results and the spectroscopic data recorded within a series of analogues were used to analyze the factors affecting the reactivity and exo selectivity.     

A theoretical study of the mechanism and stereoselectivity of the Diels-Alder cycloaddition between difluoro-2-methylencyclopropane and furan

A theoretical study of the molecular mechanism and stereoselectivity of the Diels-Alder cycloaddition reaction between difluoro-2-methylencyclopropane and furan has been carried out at the B3LYP/6-31G+^∗∗ level of theory. The calculation of activation and reaction energies indicates that the 3-endo cycloadduct is favored both kinetically and thermodynamically, which is in agreement with the experimental data. Analysis of the bond order and charge transfer in the transition states shows that this reaction takes place via a synchronous-concerted mechanism.     

亚胺杂Diels-Alder反应的催化剂

综述近年来亚胺的杂Diels-Alder反应各类催化剂的应用。     

Theoretical investigation of the stereoselectivity of some Diels-Alder reactions involving cyclopentadiene

The stereoselectivity of some Diels-Alder reactions was investigated by means of ABEEM-oTr model.Combined with local hard-soft and acid-base(HSAB)principle,we made reasonable explanation by calculating local softness of atom and bond regions for the stereoselectivity of four Diels-Alder reactions involving cyclopentadiene.     

A novel application of the Diels-Alder reaction: nitronaphthalenes as normal electron demand dienophiles

Thermal reactions between nitronaphthalenes and butadienes were studied. It was demonstrated that these reactions are capable of undergoing the normal electron demand Diels-Alder reaction, with a variety of dienes affording the phenanthrene derivatives. The influence of the extension and type of substitution was also discussed. When the electron-withdrawing activation of the naphthalenic nucleus or the donor properties of the dienes were not enough, N-naphthylpyrroles were detected as main product, suggesting that a competitive reaction would probably take place. The results clearly confirmed the dienophilic nature of nitronaphthalenic double bonds and provided an alternative procedure for phenanthrene derivatives and N-naphthylpyrroles' synthesis. The relative reactivity of the reactants and the viability of the reactions were discussed from a theoretical point of view.     

Straightforward hetero Diels-Alder reactions of nitroso dienophiles by microreactor technology

The hetero Diels-Alder reactions of 2-nitrosotoluene and some representative acylnitrosodienophiles with a selected set of 1,3-dienes were studied under microflow conditions. The main assets of the technology, that is, an accurate control of the reaction parameters and continuous operating, led to an increased efficiency of this reaction.     

Comparison of the reaction pathways and intermediate products of a microwave-assisted and high-pressure-promoted cycloaddition of vinyl-moiety-containing dienophiles on 2H-pyran-2-ones

A comparative study of the reaction pathway of the cycloaddition of various vinyl-containing dienophiles on a set of substituted 3-acylamino-2H-pyran-2-ones under microwave-assisted and high-pressure conditions is presented. In the course of the reaction both the intermediate products, i.e., the 2-oxabicyclo[2.2.2]oct-5-ene (the exo/endo selectivity depended upon the dienophile) and the alkoxycyclohexadiene systems, were isolated and comprehensively characterized; this included X-ray diffraction analyses. The role of the base (DABCO) as an organocatalyst was further elucidated.     

Diels-Alder reaction of eight-membered cyclic siloxydienes

Eight-membered cyclic siloxydienes, 2-(tert-butyldimethylsiloxy)-1-methyl-5-oxacycloocta-1,3-diene and 2-(tert-butyldimethylsiloxy)-5-oxacycloocta-1,3-diene, were prepared from δ-valerolactone, and their Diels-Alder reactions with various dienophiles are reported.     

由Diels-Alder反应合成四氢咔唑

采用W.E.Noland等人提出的咔唑合成路线,以吲哚、醛或酮、丁烯二酰亚胺为原料,在酸催化下经缩合和Diels-Alder反应而形成四氢咔唑。本研究采用乙酸乙酯为溶剂,对甲苯磺酸为催化剂,提高了反应速度和产物质量。共合成11个新的四氢咔唑化合物,进行了^1HNMR和IR测试及元素分析,确认了其结构。     

Synthesis of cyclic peptides using a palladium-catalyzed enyne cycloisomerization

In this letter, we report a palladium-catalyzed enyne cycloisomerization of linear peptides to generate small cyclic peptides embedded with a conjugated 1,3-diene. The utility of these resulting macrocyclic dienes is demonstrated by carrying out [4+2] cycloadditions with dienophiles to generate constrained cyclic peptides with cyclic linkers.     

Stereoselective construction of the octalin unit of symbioimine using an intramolecular Diels-Alder reaction

The octalin unit of symbioimine (1) has been synthesized stereoselectively via an intramolecular Diels-Alder reaction.     

Diels-Alder reaction in protic ionic liquids

Protic imidazolium ionic liquids have been tested as reaction media in the Diels-Alder reaction between cyclopentadiene and two dienophiles (dimethyl maleate and methyl acrylate). Good conversions and endo/exo selectivities were achieved. The activation of the dienophile by hydrogen bonding with protic imidazolium ILs was demonstrated.     

Synthesis of poly(4-vinylbenzocyclobutene) and its reaction with dienophiles

4-Vinylbenzocyclobutene ( 1 ) was prepared by the nickel-catalyzed coupling reaction of 4-bromobenzocyclobutene with vinylbromide in 70% yield. Radical homopolymerization of 1 at 60°C for 24 h afforded poly(4 vinylbenzocyclobutene) [poly( 1 )] in 89% yield and radical copolymerizations of 1 with styrene (St) or methyl methacrylate (MMA) were carried out to obtain the corresponding copolymers. The Q = 1.07, e = 0.046. As a model reaction of the polymer reaction of the polymer reaction of poly( 1 ) and poly(4-vinylbenzocyclobutene-co-styrene) [copoly( 1 -St)] with dienophiles, the Diels-Alder reaction of benzocyclobutene with N-phenylmaleimide (MI) or maleic anhydride (MANH) was carried out to determine the optimum reaction conditions. Under the optimum condition, the Diels-Alder reaction of poly( 1 ) and copoly( 1 -St) with MI and MANH in the presence of 4-tert-butyl-catechol as an inhibitor were carried out to yield the corresponding polymers in good yields. The properties (solubilities, T_g, and temperature of 10% weight loss) of the products obtained from the polymer reaction were different from these of poly( 1 ). © 1995 John Wiley & Sons, Inc.     

A study of solvent effects on the stereoselectivity of Diels-Alder reactions through molecular surface electrostatic potentials

Statistical models for the study of solvent effects on the endo/exo selectivity of Diels-Alder reactions using molecular surface electrostatic potentials was obtained. The models show that hydrogen bond interactions of solvent molecules favor the predominance of the endo isomer for the reaction of methyl acrylate, methyl methacrylate and methyl trans-crotonate with cyclopentadiene whereas the effect of solvophobicity seems to be negligible.     

Diastereoselective synthesis of β-aminocyclopentene sulfonic acid via hetero Diels-Alder reaction

A new cyclopentene GABA analogue was synthesized as a conformationally rigid analogue of the epilepsy drug vigabatrin. N-Sulfinyl dienophile Diels-Alder methodology, followed by alkaline hydrolysis of the corresponding dihydrothiazine oxide, oxidation and deprotection of the amino group gave cis-4-aminocyclopent-2-ene-1-sulfonic acid. The corresponding N,N-dimethylsulfinamide was also obtained.     

The enantioselective high-pressure Diels-Alder reaction of 1-methoxybuta-1,3-diene with tert-butyldimethylsilyloxyacetaldehyde catalyzed by (salen)Co(II) and (salen)Cr(III)Cl complexes

The high-pressure (10-11 kbar) reaction of 1-methoxybuta-1,3-diene (1) with tert-butyldimethylsilyloxyacetaldehyde (2), catalyzed by the chiral (salen)Co(II) 4 or (salen)Cr(III)Cl 5 complexes, has been studied. We found that the reaction afforded, in good yield (up to 90%) and both with very good diastereoselectivity (up to 92%) and enantioselectivity (up to 94% ee), the [4 + 2]cycloadducts 3, which are compounds of significant synthetic interest.