Electrocyclic Ring Opening of <i>cis</i>‐Bicyclo[<i>m.n</i>.0]alkenes: The Anti‐Woodward–Hoffmann Quest

López, Carlos Silva; Faza, Olalla Nieto; Lera, Ángel R. de

doi:10.1002/chem.200601151

Cited by 23 publications

(9 citation statements)

References 35 publications

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“…Collectively, the spectroscopic data indicated that trans -poly(acetylene) was obtained as the only detectable product from the methodology described above, which was a surprising result and prompted us to postulate potential mechanisms (see Scheme ). Although previous reports have shown that certain cyclobutenes and related polyladderenes can undergo selective electrocyclic ring-opening, − mixtures of cis and trans products may result when the precursors feature assorted stereoisomers. , Because the spectroscopic data recorded for 9 indicated that the material was composed of a single stereoisomer, an alternative route wherein ring-opening proceeds through a radical intermediate that isomerizes to the thermodynamically favored ( trans ) polymer product was considered.…”

Section: Results and Discussionmentioning

confidence: 99%

Unveiling a Masked Polymer of Dewar Benzene Reveals trans-Poly(acetylene)

2019

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A dibromo derivative of Dewar benzene, trans-5,6-dibromobicyclo[2.2.0]hex-1-ene, was polymerized using ring-opening metathesis polymerization (ROMP). The reaction proceeded in a controlled manner as changing the initial monomer-to-catalyst ratio afforded monodispersed polymers with tunable molecular weights and growing polymer chains were extended upon subsequent exposure to additional monomer. Treatment of the halogenated polymers with an alkyllithium reagent resulted in elimination followed by isomerization to afford trans-poly(acetylene). Based on a series of mechanistic and spectroscopic studies, the transformation was proposed to proceed through a cyclobutenyl intermediate that undergoes rearrangement. The methodology was found to be versatile as triblock copolymers containing the halogenated homopolymer were prepared and converted to their poly(acetylene)-containing derivatives. The polymers were characterized using gel permeation chromatography as well as a range of spectroscopic (NMR, FT-IR, UV−vis, and Raman) and analytical techniques.

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Section: Results and Discussionmentioning

confidence: 99%

Unveiling a Masked Polymer of Dewar Benzene Reveals trans-Poly(acetylene)

2019

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“…26–29 No such transition structure was found using spin-restricted B3LYP; however, use of broken symmetry, spin-unrestricted B3LYP successfully yielded structure 8a (Figure 5). This result clearly indicates diradical character, which is known to exist in transition structures of π-bond rotation.…”

Section: Resultsmentioning

confidence: 99%

A Theoretical Study of Cyclohexyne Addition to Carbonyl–C_α Bonds: Allowed and Forbidden Electrocyclic and Nonpericyclic Ring-Openings of Strained Cyclobutenes

Sader

2012

J. Org. Chem.

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The mechanism of cyclohexyne insertion into a C(O)-Cα bond of cyclic ketones, explored experimentally by the Carreira group, has been investigated using density functional theory. B3LYP and M06-2X calculations were performed in both gas phase and THF (CPCM, UAKS radii). The reaction proceeds through a stepwise [2+2] cycloaddition of cyclohexyne to the enolate, followed by three disparate ring opening possibilities of the cyclobutene alkoxide to give the product: 1) thermally-allowed conrotatory electrocyclic ring opening, 2) thermally-forbidden disrotatory electrocyclic ring opening, or 3) non-pericyclic C-C bond cleavage. Our computational results for the model alkoxide and potassium alkoxide systems show that the thermally-allowed electrocyclic ring opening pathway is favored by less than 1 kcal/mol. In more complex systems containing a potassium alkoxide (e–f), the barrier of the allowed conrotatory ring opening is disfavored by 4–8 kcal/mol. This suggests that the thermodynamically more stable disrotatory product can be formed directly through a “forbidden” pathway. Analysis of geometrical parameters and atomic charges throughout the ring opening pathways provides evidence for a non-pericyclic C-C bond cleavage, rather than a thermally-forbidden disrotatory ring opening. A true forbidden disrotatory ring opening transition structure was computed for the cyclobutene alcohol; however, it was 19 kcal/mol higher in energy than the allowed conrotatory transition structure. An alternate mechanism in which the disrotatory product forms via isomerization of the conrotatory product was also explored for the alkoxide and potassium alkoxide systems.

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“…As a guess geometry, we used the TS geometry computed in ref. 178. This guess geometry has C s symmetry, and we note that the reactant and product have a common (i.e.…”

Section: A Woodward-hoffmann Violating Reactionmentioning

confidence: 94%

“…8). Theoretical ground-state studies 177,178 have shown that the added carbon atom, which starts off in a cyclopropyl group, serves to force the molecule into a ring-opening disrotatory motion that entails a TS.…”

Section: A Woodward-hoffmann Violating Reactionmentioning

confidence: 99%

Restricted Hartree Fock using complex-valued orbitals: A long-known but neglected tool in electronic structure theory

Small

Sundstrom

Head‐Gordon

2015

The Journal of Chemical Physics

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Restricted Hartree Fock using complex-valued orbitals (cRHF) is studied. We introduce an orbital pairing theorem, with which we obtain a concise connection between cRHF and real-valued RHF, and use it to uncover the close relationship between cRHF, unrestricted Hartree Fock, and generalized valence bond perfect pairing. This enables an intuition for cRHF, contrasting with the generally unintuitive nature of complex orbitals. We also describe an efficient computer implementation of cRHF and its corresponding stability analysis. By applying cRHF to the Be + H2 insertion reaction, a Woodward-Hoffmann violating reaction, and a symmetry-driven conical intersection, we demonstrate in genuine molecular systems that cRHF is capable of removing certain potential energy surface singularities that plague real-valued RHF and related methods. This complements earlier work that showed this capability in a model system. We also describe how cRHF is the preferred RHF method for certain radicaloid systems like singlet oxygen and antiaromatic molecules. For singlet O2, we show that standard methods fail even at the equilibrium geometry. An implication of this work is that, regardless of their individual efficacies, cRHF solutions to the HF equations are fairly commonplace.

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Electrocyclic Ring Opening of cis‐Bicyclo[m.n.0]alkenes: The Anti‐Woodward–Hoffmann Quest

Cited by 23 publications

References 35 publications

Unveiling a Masked Polymer of Dewar Benzene Reveals trans-Poly(acetylene)

Unveiling a Masked Polymer of Dewar Benzene Reveals trans-Poly(acetylene)

A Theoretical Study of Cyclohexyne Addition to Carbonyl–C_α Bonds: Allowed and Forbidden Electrocyclic and Nonpericyclic Ring-Openings of Strained Cyclobutenes

Restricted Hartree Fock using complex-valued orbitals: A long-known but neglected tool in electronic structure theory

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Electrocyclic Ring Opening of cis‐Bicyclo[m.n.0]alkenes: The Anti‐Woodward–Hoffmann Quest

Cited by 23 publications

References 35 publications

Unveiling a Masked Polymer of Dewar Benzene Reveals trans-Poly(acetylene)

Unveiling a Masked Polymer of Dewar Benzene Reveals trans-Poly(acetylene)

A Theoretical Study of Cyclohexyne Addition to Carbonyl–Cα Bonds: Allowed and Forbidden Electrocyclic and Nonpericyclic Ring-Openings of Strained Cyclobutenes

Restricted Hartree Fock using complex-valued orbitals: A long-known but neglected tool in electronic structure theory

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A Theoretical Study of Cyclohexyne Addition to Carbonyl–C_α Bonds: Allowed and Forbidden Electrocyclic and Nonpericyclic Ring-Openings of Strained Cyclobutenes