Reactivity In Diels-Alder Reactions Research Articles

Theoretical study on the mechanochemical reactivity in Diels-Alder reactions.

Mechanochemical reactions sometimes give different yields from those under solvent conditions, and such mechanochemical reactivities depend on the reactions. This study theoretically elucidates what governs mechanochemical reactivities, taking the Diels-Alder reactions as an example. Applying mechanical force can be regarded as the deformation of molecules, and the deformation in an orthogonal direction to a reaction mode can lower the reaction barrier. Here, we introduce a dimensionless cubic force constant, a mechanochemical reaction constant. It tells us how easily the deformation can lower a reaction barrier and enables us to compare the mechanochemical reactivities of different reactions. The constants correlate positively with the yields of the mechanochemical Diels-Alder reactions.

Substituent Effects in Bioorthogonal Diels-Alder Reactions of 1,2,4,5-Tetrazines.

1,2,4,5-Tetrazines are increasingly used as reactants in bioorthogonal chemistry due to their high reactivity in Diels-Alder reactions with various dienophiles. Substituents in the 3- and 6-positions of the tetrazine scaffold are known to have a significant impact on the rate of cycloadditions; this is commonly explained on the basis of frontier molecular orbital theory. In contrast, we show that reactivity differences between commonly used classes of tetrazines are not controlled by frontier molecular orbital interactions. In particular, we demonstrate that mono-substituted tetrazines show high reactivity due to decreased Pauli repulsion, which leads to a more asynchronous approach associated with reduced distortion energy. This follows the recent Vermeeren-Hamlin-Bickelhaupt model of reactivity increase in asymmetric Diels-Alder reactions. In addition, we reveal that ethylene is not a good model compound for other alkenes in Diels-Alder reactions.

Orbital-Weighted Dual Descriptor for the Study of Local Reactivity of Systems with (Quasi-) Degenerate States.

An alternative response function, based on the dual descriptor in terms of Koopmans' approximation, is hereby proposed for the description of chemical reactivity in systems with (quasi-) degenerate frontier molecular orbitals. This descriptor is constructed from Fukui functions that include contributions from different orbitals, i.e., orbital-weighted Fukui functions. The methodology is applied to three case studies: the first case consists of a series of benchmark organic and inorganic molecules from which the dual descriptor, based only on frontier orbitals, is not appropriate to describe their reactivity. The second case deals with the proper description of chemical reactivity in Diels-Alder reactions between fullerene C60 and cyclopentadiene (CP), revealing the importance of considering secondary orbital interactions for an adequate regioselectivity description. The third, and last case, consists of a series of polycyclic aromatic hydrocarbons (PAHs) possessing molecular orbital degeneracy. By means of analyzing of this descriptor, an alternative approach to the description of aromaticity is proposed. In all cases, the proposed index called "orbital-weighted dual descriptor" has proven to accurately describe the chemical reactivity and aromaticity of the studied systems.

Gold-catalyzed synthesis of β-trifluoromethylated α,β-unsaturated ketones from CF3-substituted propargylic carboxylates and their reactivity in Diels-Alder reactions

The synthesis of fluorinated synthetic intermediates has become a field of intense research in organic chemistry. In this article, we report the application of a gold-catalyzed rearrangement to the synthesis of β-trifluoromethylated α,β-unsaturated ketones. The scope of the reaction, as well as the valorization of the products in subsequent transformations has been investigated. This study allowed for the preparation of various CF3-substituted enones and fluorinated Diels-Alder adducts from easily accessible starting materials.

Modulation of Reactivities of Dienophiles for DielsAlder Reactions via Complexation of α,β‐Unsaturated Chelating Amides

AbstractWe describe the modulation of reactivities of dienophiles for DielsAlder reactions via a new principle based on chelating amides positioned adjacent to their CC bond. It is demonstrated for modified acrylic acid derivatives and related dienophiles with three different chelating entities. Complexation of the chelators leads to an intensified electron‐withdrawing effect leading to an enhancement of reactivity in DielsAlder reactions depending on the complexed metal ion. The application of this new approach might be extended to other reactions with reacting entities adjacent to chelating amides.

Functionalization of Carbon Materials using the Diels‐Alder Reaction

A simple and efficient Diels-Alder (DA) reaction on carbon material has been demonstrated. The present work involves single and multiwall carbon nanotubes (CNTs), as well as Herringbone carbon nanofiber. The CNTs show a dual nature of reactivity in DA reaction, i.e., they behave both as dienophile and diene with furfuryl groups and maleic anhydride derivatives, respectively. Various functional groups, including alcohol, amine, epoxy, carboxylic and ester, have been introduced on the carbon materials. The results suggest that the reactivity of CNT in DA reaction may resemble the chemistry of small molecules.

Diels-Alder Cycloadditions of Ethyl 2-Carbomethoxyethenesulfinates with Cyclopentadiene. Lewis Acid Enhancement and Adduct Identification with the Assistance of Competitive Stereodifferentiating Iodolactonization and Iodosultinization Reactions.

Ethyl (Z)-2-carbomethoxyethenesulfinate (1) and ethyl (E)-2-carbomethoxyethenesulfinate (2) were each subjected to cyclopentadiene (ca. 3 equiv) in order to determine their reactivity in Diels-Alder reactions. Thermal reactions proceeded in less than 4 h, while Lewis Acid enhanced reactions were substantially faster and demonstrated greater selectivity. In particular, the BF(3).Et(2)O-mediated cycloaddition of 1 gave syn/endo cycloadduct 3a as a major diastereomer in about 90% yield. The reactions of 2 were less synthetically useful. The structures of the cycloadducts were established through a combination of X-ray crystal structure determinations and through exposure of the compounds to an electrophilic iodine reagent. Each cycloadduct underwent an iodocyclization reaction with either the carboxylic ester or the sulfinate ester participating in the formation of a polycyclic lactone or sultine, respectively. The iodocyclization reactions allowed further elucidation of the cycloadduct structures.

A comparison of the benzo[b]furan and benzo[c]furan reactivity in diels-alder reactions through an AM1 computational study

The aromaticity of benzo[c]furan was evaluated based on the uniformity of the CC bond distances and their deviation from the ideal aromatic CC bond distance. The AM1 computed values were compared to those of furan and benzo[b]furan. The goal was to determine the relative stability and reactivity of benzo[b]furan. The reactivity of benzo[c]furan as a diene for the Diels-Alder reaction was estimated through its HOMO energy and activation barriers using several dienophiles.

Synthesis and Diels-Alder reactions of 3-methylene-2-ferrocenylmethylenequinuclidine

The synthesis and chemical reactivity in Diels-Alder reactions of the title compound 6 is described. When 6 was reacted with N-phenylmaleimide, a 3:1 mixture of isomers exo 14a and endo 14b was found, while with triazolinedione 13, a novel ferrocenyl heterocycle 15 was formed. The structures for 14b and 15 were confirmed by X-ray diffraction analysis.

2-Trimethylsilyloxy-1,3-butadiene, a new reactive diene. Preparation and reactions

reactions in the hands of synthetic chemists today. The thorough understanding of the stereochemical (Alder endo transition state rules') and regiochemical (concerted but non-synchronous formation of bondFselectivity of the Diels-Alder reaction which exists today allows one to construct a large variety of specifically substituted cyclohexene derivatives. However the applicability Of this reaction to the construction of highly useful cyclohexanone derivatives is rather limited. Because the usual reagent developed for this process, E-ethoxy-1,3-butadiene, 1, is cumbersome to prepare3 and possesses very low synthetic flexibility, there existed a need for a new reagent of this type which would circumvent these problems. We report now a solution to this problem with the development of the compound E-trimethylsilyloxy-1,3-butadiene 1. as a reactive diene comonent in Diels-Alder reactions? In particular we wish to indicate four important points about this 2-oxygenated-1,3-butadiene: a) the ease of preparation of the diene; b) its reactivity in Diels-Alder reactions; c) the susceptibility of its adducts 3 to various hydrolytic conditions; and d) the synthetic versatility of the adducts 3 especially with regard to the silyl enol ether functionality.