Mechanism of the Intramolecular Hexadehydro-Diels–Alder Reaction

Marell, Daniel J.; Furan, Lawrence R.; Woods, Brian P.; Lei, X. L.; Bendelsmith, Andrew J.; Cramer, Christopher J.; Hoye, Thomas R.; Kuwata, Keith T.

doi:10.1021/acs.joc.5b01356

Cited by 51 publications

(35 citation statements)

References 67 publications

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“…Results reported in parallel studies by Kuwata and co-workers strongly support this conclusion. 52 Ultimately, the existence of low energy stepwise reactions must be related to the well-known propensity of polyynes to oligomerize and even to explode. 60 In answer to the second question posed above, there is now ample evidence that the intramolecular 1,3-diyne + yne cycloaddition does occur and can lead to o-benzyne intermediates by both concerted and stepwise reaction mechanisms.…”

Section: Scheme 4 Diyne + Yne Cycloadditions and Cycloreversionmentioning

confidence: 99%

Dehydropericyclic Reactions: Symmetry-Controlled Routes to Strained Reactive Intermediates

2015

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The conceptual dehydrogenation of pericyclic reactions yields dehydropericyclic processes, which usually lead to strained or reactive intermediates. This is a simple scheme for inventing new chemical reactions. Computational results on two novel dehydropericyclic reactions are presented here. Conjugated enynes undergo a singlet-state photoisomerization that transposes the methylene carbon. We previously suggested excited-state closure to 1,2-cyclobutadiene followed by thermal ring opening. CCSD(T)//DFT computations show two minima of similar energy corresponding to 1,2-cyclobutadiene, one chiral and closed shell and the second a planar diradical. The chiral structure has a low barrier to ring opening and may best explain results on enyne photoisomerization. The first examples of 1,3-diyne + yne cycloadditions to give o-benzynes were reported in 1997. Computations on intramolecular versions of this tridehydro (-3H2) Diels-Alder reaction support a concerted mechanism for the parent triyne (1,3,8-nonatriyne); however, a slight electronic advantage in the concerted path may be outweighed by the difference in entropy of activation for sequential vs simultaneous formation of two new ring bonds.

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Section: Scheme 4 Diyne + Yne Cycloadditions and Cycloreversionmentioning

confidence: 99%

Dehydropericyclic Reactions: Symmetry-Controlled Routes to Strained Reactive Intermediates

2015

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“…The open shell singlet and triplet calculation were carried out employing UM06‐2X. In the singlet diradical case wavefunctions of different multiplicity were allowed to mix using the Gaussian keyword “guess = mix”. Triplet contaminations of singlets were accounted for with spin projections and the energy values were corrected using the procedure proposed by Houk and co‐workers .…”

Section: Methodsmentioning

confidence: 99%

Computational studies on the formation of aza‐oxypentadienyl intermediates from alkylidene oxaziridines and keteneimine oxides and their conversion to 1,5‐dihydropyrrolones

Villar

Guillade

González‐Pérez

2018

Int J of Quantum Chemistry

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The rearrangements of alkylidene oxaziridines 1a,b (a, R = Me; b, R = OMe) and keteneimine oxides 1’a,b to 1,5‐dihydropyrrolones 3a,b have been computationally studied at the UM062X/Def2TZVPP(PCM,TFE)//UM062X/Def2SVP(PCM,TFE) level. The mechanism for conversion of 1a‐3a is predicted to be stepwise, with intermediacy of the acyclic aza‐oxypentadienyl species 4a. The stabilization provided by the nitrogen of the oxaziridine makes the ring opening of 1a to diradical/zwitterionic intermediates 4a more feasible than in the case of the vinyl allene oxide counterparts. The formation of aziridinone 2a from 1a showed competing activation energies but 2a was found to be a thermodynamically less stable species than 3a. When the Me group at N is exchanged by the electron‐donating OMe substituent in 1b, the diradical species and the corresponding transition structures are more stabilized and therefore the aziridinones are not required as intermediates in the conversion of 1b to 3b. Keteneimine oxide 1′ is predicted to directly generate diradical 4 by C‐O ring opening although through a less favored transition state.

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“…24 We have observed the same for a series of intra molecular HDDA reactions and found that the (U)B3LYP-D3BJ functional did an excellent job of correlating with our experimentally observed rates. 25 We have not been successful locating transition state structures corresponding to concerted PDDA reactions for 33a–d at this level of theory.…”

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confidence: 93%

The pentadehydro-Diels–Alder reaction

Wang

Naredla

Thompson

et al. 2016

Nature

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In the classic Diels–Alder (DA) [4+2] cycloaddition reaction1, the overall degree of unsaturation of the 4π (diene) and 2π (dienophile) pairs of reactants dictates the oxidation state of the newly formed six-membered carbocycle. For example, in the classic DA reaction, butadiene and ethylene combine to produce cyclohexene. More recent developments include variants in which the hydrogen atom count in the reactant pair and in the resulting product is reduced by2, for example, four in the tetradehydro-DA (TDDA) and by six in the hexadehydro-DA (HDDA3,4,5,6,7) reactions. Any oxidation state higher than tetradehydro leads to the production of a reactive intermediate that is more highly oxidized than benzene. This significantly increases the power of the overall process because trapping of the benzyne intermediate8,9 can be used to increase the structural complexity of the final product in a controllable and versatile manner. In this manuscript, we report an unprecedented net 4π+2π cycloaddition reaction that generates a different, highly reactive intermediate known as an α,3-dehydrotoluene. This species is at the same oxidation state as a benzyne. Like benzynes, α,3-dehydrotoluenes can be captured by various trapping agents to produce structurally diverse products that are complementary to those arising from the HDDA process. We call this new cycloisomerization reaction a pentadehydro-Diels–Alder (PDDA) reaction—a nomenclature chosen for chemical taxonomic rather than mechanistic reasons. In addition to alkynes, nitriles (RC≡N), although non-participants in aza-HDDA reactions, readily function as the 2π-component in PDDA cyclizations to produce, via trapping of the α,3-(5-aza)dehydrotoluene intermediates, pyridine-containing products.

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Mechanism of the Intramolecular Hexadehydro-Diels–Alder Reaction

Cited by 51 publications

References 67 publications

Dehydropericyclic Reactions: Symmetry-Controlled Routes to Strained Reactive Intermediates

Dehydropericyclic Reactions: Symmetry-Controlled Routes to Strained Reactive Intermediates

Computational studies on the formation of aza‐oxypentadienyl intermediates from alkylidene oxaziridines and keteneimine oxides and their conversion to 1,5‐dihydropyrrolones

The pentadehydro-Diels–Alder reaction

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