Cycloadditions Of Norbornadiene Research Articles

Ruthenium-Catalyzed [2 + 2] versus Homo Diels-Alder [2 + 2 + 2] Cycloadditions of Norbornadiene and Disubstituted Alkynes: A DFT Study.

The ruthenium-catalyzed [2 + 2] and homo Diels–Alder [2 + 2 + 2] cycloadditions of norbornadiene with disubstituted alkynes are investigated using density functional theory (DFT). These DFT calculations provide a mechanistic explanation for observed reactivity trends with different functional groups. Alkynyl phosphonates and norbornadiene form the [2 + 2 + 2] cycloadduct, while other functionalized alkynes afford the respective [2 + 2] cycloadduct, in excellent agreement with experimental results. The computational studies on the potential energy profiles of the cycloadditions show that the rate-determining step for the [2 + 2] cycloaddition is the final reductive elimination step, but the overall rate for the [2 + 2 + 2] cycloaddition is controlled by the initial oxidative cyclization. Two distinct mechanistic pathways for the [2 + 2 + 2] cycloaddition, cationic and neutral, are characterized and reveal that Cp*RuCl(COD) energetically prefers the cationic pathway.

Study on the Reactivity of the Alkyne Component in Ruthenium-Catalyzed [2 + 2] Cycloadditions between an Alkene and an Alkyne

The ruthenium-catalyzed [2 + 2] cycloadditions of norbornadiene with a variety of alkynes have been investigated. Electronic effect of the alkyne component has shown to play an important role on the rate of the cycloaddition, and the reactivity of the alkyne component increases dramatically as the alkyne becomes more electron deficient. Increase in the steric bulk of the alkyne component decreases the reactivity of the alkyne component. It was also found that chelation effect of propargylic alcohols greatly enhanced the reactivity of the alkyne component in the ruthenium-catalyzed [2 + 2] cycloadditions.

Cycloaddition of Norbornadiene to Fluorine‐Containing Heteroaddends.

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Influence of the temperature on the enantioselectivity of the cobalt catalysed homo Diels–Alder reactions

Abstract Depending on the variation of the temperature and on the nature of the substituent of alk-1-ynes 2, the enantioselectivity of the deltacyclene formation in the cobalt catalysed [2+2+2] cycloaddition of norbornadiene 1 and acetylenes 2, can be achieved with up to 98%. The best enantioselectivities observed around 14 °C are in agreement with the Isoinversion principle (IIP).

Photoinduced electron transfer reactions across rigid linear spacer groups of high symmetry

A series of highly symmetrical dienes 1– 3 were prepared through [2+2] cyclo-addition of norbornadiene (NBD) in an exo– trans– exo geometry. These molecules can be utilized as spacer groups in donor(D)–spacer(S)–acceptor(A) types of electronic dyads possessing strictly linear rigidity. The electronic coupling between D and A was promoted effectively by the σ-bonds through the all- trans spacer groups so that a highly efficient photoinduced electron transfer process takes place. The even–odd NBD dependent alternation of the D/A orientation is intriguing, which leads to an unusual correlation in the spacer tuning electron transfer process.

Influence of aluminum Lewis acids on the diastereoselectivity of the nickel-catalyzed [2+2+2] cycloaddition of norbornadiene and electron deficient alkenes

The stereoselective formation of 8-substituted deltacyclanes by homo Diels–Alder (HDA) reaction using a phosphine modified nickel catalyst generated by reduction of Ni(acac) 2 with alkylaluminums is discussed. Depending on the nature of the alkene and on the nickel catalytic system, fair to excellent exo selectivity are observed. A switch in selectivity favoring the endo-cycloadduct is observed when the polar methoxycarbonyl group substituted alkene is activated with aluminum species.

Chemistry of Isodrin Derivatives. The Syntheses of 11‐ and 12‐Hydroxy‐1,4,4a,9,9a,10‐Hexahydro‐Endo, Endo‐1,4;9,10‐Dimethano‐Anthracenes

AbstractThe titled compounds are synthesized through multi‐step sequences involving consecutive [n4s + n2s] cycloadditions of norbornadiene with two units of chlorinated cyclopentadiene. A dyotropic double hydrogen migration was observed between two closely located double bonds during the process of aromatization of a cyclohexadiene moiety. A hydroxyl group is introduced onto either of the two methylene bridges in order to provide products suitable for solvolytic analyses.

Homo-Diels–Alder cycloadditions catalysed by cobalt–triphenylphosphine-zinc systems

[Col2(PPh3)n]–zinc systems (n=1 or 2) exhibit high catalytic activity for the homo-Diels–Alder [2 + 2 + 2] cycloadditions of norbornadiene with various alkynes including terminal and internal acetylenes and methyl prop-2-ynyl ether to give the corresponding deltacyclenes in good to excellent yields.

Di-?-trifluoroacetato-bis[norbornadiene-rhodium(I)] in cyclodimerization of bicyclo[2.2.1]hepta-2,5-diene

Di-μ-trifluoroacetate-bis [norbornadiene-rhodium(I)], which serves as a catalyst for cyclodimerization of norbornadiene, in nonpolar solvents, appears as a dimeric, and in polar solvents as a monomeric complex of Rh(I). Depending on the ligand, environment, and the solvent, products of [2+2]-, [4+2]-, or [4+4]-cycloaddition of norbornadiene are obtained in the reaction.