Synthesis of Six-Membered Functionalized Carbocyclic Compounds by One-Pot Reaction of Hydroquinone Derivatives and Dienes

A general method for one-pot reaction of hydroquinone derivatives and dienes has been developed. The system of Pb₃O₄ in tetrahydrofuran–trifluoroacetic acid was found to play dual roles as oxidant for the generation of quinones in situ and as catalyst for the Diels–Alder cycloaddition, which makes the one-pot reaction efficient and easy to carry out. Using this method, a variety of six-membered functionalized carbocyclic compounds can be easily prepared in medium to excellent yields at room temperature.      

Facile Synthesis of Spiro Oxindoles,Azaoxindoles, and Dihydroisoquinolone

Formation of 1-aryl-4-oxo-cyclohexa(e)nonecarboxylates from the Diels–Alder cycloaddition of 2-trimethylsilyloxy-1,3-butadiene and Danishefsky diene with aryl- and pyridylacrylates and further conversion thereof to spirocycles is described. This provides an efficient method for spiro oxindoles, azaoxindoles, and dihydroisoquinolones.

In Situ Enamine Activation in Aqueous Salt Solutions: Highly Efficient Asymmetric Organocatalytic Diels–Alder Reaction of Cyclohexenones with Nitroolefins

Deep‐sea Diels–Alder : The asymmetric organocatalytic Diels–Alder reaction of cyclohexenones with aromatic nitroolefins can be carried out in seawater and brine. The reaction proceeds by an in situ enamine activation involving a one‐step concerted addition pathway (see scheme).

     

Why can the activation volume of the cycloadduct decomposition in isopolar retro‐Diels–Alder reactions be negative?

Rate constants of the Diels–Alder cycloaddition reaction of anthracene with tetracyanoethylene, enthalpy of solution of reactants and adduct, enthalpy of the reaction in solution, enthalpy and entropy of activation of the forward and retro‐Diels–Alder reactions were determined in 14 solvents. Temperature and pressure effects on the rate of the decomposition of the adduct formed from 9‐chloroanthracene and tetracyanoethylene were studied. Since the electrostriction effect can be excluded from the consideration of the isopolar Diels–Alder reaction, negative values of the activation volume in the retro‐Diels–Alder reactions can be caused by the different possibilities of penetration of the solvent molecules to large steric branched structures of the transition states and adducts. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 117–125, 2010     

Efficient Synthesis of Hexahydrocarbazoles

Selective reduction of the nitro group in methyl 1-(2-nitrophenyl)-4-oxo-cyclohex-2-enecarboxylates with zinc-acetic acid forms hexahydrocarbazoles. The reaction is applicable to the corresponding pyridyl analogs to generate azahexahydrocarbazoles. This provides an efficient method for the generation of tricyclic framework.

Facile Polymer Functionalization of Hydrothermal‐Carbonization‐Derived Carbons

A simple and efficient polymer grafting onto hydrothermal carbonization (HTC)‐derived materials is described. The method pertains to the Diels–Alder cycloaddition reaction of furan moieties present on the surface of a HTC material with the maleimide groups stemming from a maleimide protected poly(ethylene glycol) (Me‐PEG‐MI) by a retro Diels‐Alder reaction. The precursor polymer, HTC material, and final product are characterized. Successful grafting is confirmed by elemental analysis, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and dispersion studies.

     

Solvent Influence on the Diels‐Alder Reaction Rates of 9‐(Hydroxymethyl)anthracene and 9,10‐Bis(hydroxymethyl)anthracene with Two Maleimides

The rates of the Diels–Alder reaction of 9‐(hydroxymethyl)anthracene and 9,10‐bis(hydroxymethyl)anthracene with maleic anhydride and two maleimides, N‐ethyl‐ and N‐phenylmaleimide, have been studied at various temperatures and pressures in different solvent media. A rate acceleration in water in comparison with organic solvents is observed. Thermodynamic functions of activation for the reaction of 9,10‐bis(hydroxymethyl)anthracene with N‐ethylmaleimide in binary 1,4‐dioxane–water mixtures are determined. From the observed tendencies, it can be concluded that acceleration of the Diels–Alder reactions in water is linked with an energetically favorable dehydration of the reaction centers of the reactants on the way to the activated complex. Addition of an organic cosolvent makes the desolvation of these centers less favorable.     

Preparation of Substituted Dihydrofluorenones by Photoisomerization of Benzotropolone Derivatives

The photoisomerization of the Diels–Alder adduct formed between tetramethylpurpurogallin and maleic anhydride is described. The process is highly stereoselective, involves the β,γ-unsaturated ketone chromophore present in the adduct, proceeds through the formation of allyl and aroyl radical intermediates, and leads to a novel substituted dihydrofluorenone in good yields.

Diels–Alder modification of poly(ethylene terephthalate‐co‐anthracene‐2,6‐carboxylate) with N‐substituted maleimides

Dimethyl 2,6‐anthracene dicarboxylate is used as a comonomer in the synthesis of functional copolymers that are subject to modification with Diels–Alder reactions. The formation of poly(ethylene terephthalate‐co‐2,6‐anthracenate), containing less than 20 mol % of the anthracene‐2,6‐dicarboxylate structural units, provides materials that are tractable and soluble. The anthracene units of the copolymers undergo Diels–Alder reactions with N‐substituted maleimides. The grafting of N‐alkylmaleimides affords soluble, hydrophobic polymers, whereas grafting with maleimide‐terminated poly(ethylene glycol) affords hydrophilic polymers. Because this reaction proceeds below the melting point of the copolymers, the procedure can be applied to thin films, whereby the surface properties are modified. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3256–3263, 2002     

Diels–Alder reactions and transformations of 2-cyclopenten-1-one with a chiral anthracene template

Excellent regio- and diastereoselectivity were achieved in the microwave assisted Diels–Alder reaction between (S)-9-(1-methoxyethyl) anthracene and 2-cyclopenten-1-one. The addition of Grignard reagents to the ketone cycloadduct gave poor levels of diastereoselectivity, however, the reduction was significantly more stereoselective. Flash vacuum pyrolysis of the reduced material furnished the corresponding allylic alcohol in good yield and ee.     

Synthesis of Bicyclo[4.3.0]Non-3-ene-7,9-diones via Solventless Diels–Alder Methodology

Four novel bicyclo[4.3.0]non-3-ene-7,9-diones have been synthesized in moderate to good yields through a solventless Diels–Alder cycloaddition method and characterized. Atom economies after purification ranged from 21% to 32%, and E factors ranged from 2.7 to 3.7. All reaction products exhibited endo selectivity. Dienophiles with heteroatoms that contribute electrons to the π system exhibited faster reaction times than the carbocyclic analog. Hydrogen-bond donating ability in the diene had no noticeable effect on reaction times.

Fused multifunctionalized bridge aromatic hydrocarbons from in situ-generated arynes and anthracene derivatives

This study presents a facile strategy for the formation of highly substituted butterfly 1,4-adducts/9,10-adducts via the Diels–Alder reaction of benzyne intermediates. The method achieves very good to excellent yields of the respective anthracene derivatives under mild conditions. This practical protocol is compatible with a variety of sensitive functional groups and provides access to difunctionalized bridge 1,4-adducts/9,10-adducts.     

Synthetic Studies of the Zoanthamine Alkaloids: The Total Syntheses of Norzoanthamine and Zoanthamine

Highly effective : We report herein the first and highly efficient total syntheses of norzoanthamine and zoanthamine in full detail, which involves stereoselective synthesis of the requisite triene for an intramolecular Diels–Alder reaction via three‐component coupling reactions, the intramolecular Diels–Alder reaction, and subsequent crucial bis‐aminoacetalization as the key steps.

     

SUBSTITUENT EFFECT IN [2+4] DIELS–ALDER CYCLOADDITION REACTIONS OF ANTHRACENE WITH C2X2 (X = H,F, Cl,Me): A COMPUTATIONAL INVESTIGATION

Journal of Structural Chemistry - In the present article, a DFT approach is used at the M06-2X/6-311G(d,p) level of theory to survey [2+4] Diels–Alder cycloaddition reactions of anthracene...     

Kinetics of the diels–alder addition of ethene to cyclohexa-1,3-diene and its reverse reaction in the gas phase

The addition of ethene to cyclohexa-1,3-diene has been studied between 466 and 591 K at pressures ranging from 27 to 119 torr for ethene and 10 to 74 torr for cyclohexa-1,3-diene. The reaction is of the “Diels–Alder” type and leads to the formation of bicyclo[2.2.2]oct-2-ene. It is homogeneous and first order with respect to each reagent. The rate constant (in l./mol sec) is given by The retron-Diels–Alder pyrolysis of bicyclo[2.2.2]oct-2-ene has also been studied. In the ranges of 548–632 K and 4–21 torr the reaction is first order, and its rate constant (in sec^?1) is given by The reaction mechanism is discussed. The heat of formation and the entropy of bicyclo[2.2.2]oct-2-ene are estimated.     

Direct Synthesis of Biodegradable Polysaccharide Derivative Hydrogels Through Aqueous Diels‐Alder Chemistry

A robust synthetic strategy where polysaccharide derivative precursors react through aqueous Diels–Alder chemistry without the involvement of catalysts and coupling reagents, allowing for the direct encapsulation of positive and negative proteins within biodegradable hydrogels. The results demonstrated that the aqueous Diels–Alder chemistry provides an extremely selective reaction and proceeds with high efficiency for polysaccharide bioconjugation. This synthetic approach uniquely allows for the direct fabrication of biologically functionalized gels with ideal structures, which provides a competitive alternative to conventional conjugation techniques such as click chemistry.

     

Kinetics of the Diels–Alder addition of acrolein to cyclohexa-1,3-diene and its reverse reaction in the gas phase

The Diels–Alder addition of acrolein to cyclohexa-1,3-diene has been studied between 486 and 571°K at pressures ranging from 55 to 240 torr. The products are endo- and exo-5-formylbicyclo[2.2.2]oct-2-ene (endo- and exo-FBO), and their formations are second order. The rate constants (in l./mole · sec) are given by The retro-Diels–Alder pyrolysis of endo-FBO has also been studied. In the ranges of 565–638°K and 6–38 torr, the reaction is first order, and its rate constant (in sec^?1) is given by The reaction mechanism is discussed. The heat of formation and the entropy of endo-FBO are estimated.     

Enantioselective Synthesis of (+)‐Chamaecypanone C: A Novel Microtubule Inhibitor

A bicycle built for tubulin : The total synthesis of (+)‐chamaecypanone C has been achieved by using a tandem retro‐Diels–Alder/Diels–Alder cascade reaction (see scheme). Initial biological studies demonstrate that (+)‐chamaecypanone C is an inhibitor of tubulin assembly and binds at the colchicine site.

     

Counter anion in Li+‐encapsulated C60 can further enhance the rate of Diels–Alder reaction: A DFT study

Density functional theory calculations were carried out to investigate the Diels–Alder cycloaddition between cyclopentadiene and C₆₀ after the encapsulation of Li⁺ ion with transition states identified and confirmed by intrinsic reaction coordinate calculations. Our results showed that the Li⁺‐encapsulation results in a lower energy barrier and the presence of counter anion can further reduce the energy barrier, making the trend in agreement with the experimental results. In addition, the influencing factors on the reactivity of Li⁺‐encapsulated fullerenes such as counter anion and the position of Li⁺ in C₆₀ were discussed. This study aims to provide a better understanding of Diels–Alder reaction with Endohedral Metallofullerenes to allow more efficient functionalization of fullerenes.     

Highly diastereoselective photochemical Diels–Alder reactions: towards the development of a photoactivated chiral auxiliary

Photochemical Diels–Alder additions of maleic anhydride to a homochiral anthracene derivative occur with excellent diastereoselectivity (>95:5) and faster than the corresponding thermal reactions.