Reactivity of conformationally constrained bispropargyl sulfones: complete preference for 6π-electrocyclization process

Ghosh, Dulal C.; Jana, Saibal; Panja, Arpita; Anoop, Anakuthil; Basak, Amit

doi:10.1016/j.tet.2013.07.099

Cited by 9 publications

(4 citation statements)

References 22 publications

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“…The barrier for the first cyclization (ΔG ⧧ B1 ) follows the order sulfone > methane > sulfide > amine > ether. The resulting diradical intermediate (9) forms an aromatic ring for X = S, O, and NH, but not for X = SO 2 or CH 2 , and hence, the barriers are relatively higher for sulfone and methane. The barrier for the first cyclization (ΔG ⧧ B1 ) is higher than that of the second in all the cases.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The barrier for the first cyclization (ΔG ⧧ B1 ) is higher than that of the second in all the cases. The reactive diradical intermediate (9) prefers to undergo second cyclization rapidly. ΔG ⧧ B1 for X = O is almost half that of the sulfone (X = SO 2 ).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The mechanism of the GB cyclization involves three basic steps: − (1) base-mediated isomerization of alkyne to allene, (2) cyclization via a diradical intermediate, and (3) aromatization through H-rearrangements. There is only one variation proposed in this major route, namely, [4 + 2] cycloaddition from an allenyne intermediate . Selectivity of GB cyclization of unsymmetrical substrates , is even more exciting for synthetic chemists as a route to complex biologically important molecules, but at the same time the increased complexity is challenging for theoretical studies.…”

Section: Introductionmentioning

confidence: 99%

“…There is only one variation proposed in this major route, namely, [4 + 2] cycloaddition from an allenyne intermediate. 9 Selectivity of GB cyclization of unsymmetrical substrates 6,10 is even more exciting for synthetic chemists as a route to complex biologically important molecules, but at the same time the increased complexity is challenging for theoretical studies.…”

Section: ■ Introductionmentioning

confidence: 99%

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Does the Mechanism of the Garratt–Braverman Cyclization Differ with Substrates? A Computational Study on Bispropargyl Sulfones, Sulfides, Ethers, Amines, and Methanes

Jana

Anoop

2016

J. Org. Chem.

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We studied the variation in mechanism among different bispropargyl substrates-sulfone, sulfide, ether, amine, and methane-toward Garratt-Braverman (GB) cyclization using density functional theory calculations. Isomerization and cycloaddition are the key steps in the GB cyclization. To compare the reactivity among the various substrates, we computed the free energy of activation (ΔG(⧧)) for the cycloaddition and the cyclization steps, whereas we used the theoretically computed pKa values for the isomerization steps. Our results suggest that the sulfones undergo a relatively fast isomerization followed by slower cyclization, while the ethers undergo a slow isomerization followed by easy cyclization. The methanes and amines are similar to the ethers, and the sulfides showed intermediate behavior. We extended our study to unsymmetrical substrates and compare the results with experiments that suggest the isomerization to be the rate-limiting step for bispropargyl ethers, while cyclization through a diradical intermediate is crucial to the rate for the bispropargyl sulfones. On the basis of these findings, we made predictions on the selectivity of unsymmetrical bispropargyl sulfones, amines, methanes, and sulfides. This is the first detailed mechanistic study on the GB cyclization of bispropargyl substrates other than sulfones.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Does the Mechanism of the Garratt–Braverman Cyclization Differ with Substrates? A Computational Study on Bispropargyl Sulfones, Sulfides, Ethers, Amines, and Methanes

Jana

Anoop

2016

J. Org. Chem.

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Molecular Rearrangements

Coxon¹

2016

Organic Reaction Mechanisms · 2013

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Benzannulation of Triynes to Generate Functionalized Arenes by Spontaneous Incorporation of Nucleophiles

et al. 2015

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The thermal reaction of ester-tethered 1,3,8-triynes provides novel benzannulation products with concomitant incorporation of an ucleophile.E vidence suggests that this reaction proceeds via an allene-enyne intermediate generated by an Alder-ene reaction in the first step.D epending on the substituent of the alkyne moiety on the allene-enyne intermediate,t he subsequent transformation can take one of two different paths,e achl eading to discrete aromatization products.T he benzannulation of as ilane-substituted 1,3,8-triynes provides arene products with an ucleophile incorporated onto the newly formed benzene core,w hereas an aryl substituent leads to nucleophile trapping at the benzylic carbon atom connected to the aryl substituent. The formation of these two different products results from the involvement of two regioisomeric allene-enyne intermediates.

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Reactivity of conformationally constrained bispropargyl sulfones: complete preference for 6π-electrocyclization process

Cited by 9 publications

References 22 publications

Does the Mechanism of the Garratt–Braverman Cyclization Differ with Substrates? A Computational Study on Bispropargyl Sulfones, Sulfides, Ethers, Amines, and Methanes

Does the Mechanism of the Garratt–Braverman Cyclization Differ with Substrates? A Computational Study on Bispropargyl Sulfones, Sulfides, Ethers, Amines, and Methanes

Molecular Rearrangements

Benzannulation of Triynes to Generate Functionalized Arenes by Spontaneous Incorporation of Nucleophiles

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