Generation and characterization of carbonyl ylides from pyrazolinone spirooxiranes

Umrigar, Pesi P.; Griffin, G. W.; Lindig, Barbara A.; Fox, Marye Anne; Das, P. K.; Leslie, Thomas M.; Trozzolo, A. M.; ̄e, Seyhan N. Eg; Thomas, A.

doi:10.1016/0047-2670(93)80010-m

Cited by 5 publications

(3 citation statements)

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“…The degree of active cross-linking is a complex function of the following: (1) the extent of mechanophore activation, (2) the relative rate/efficiency of the cross-linking reaction relative to other deactivation processes, including ring-closing of the activated mechanophore, and (3) the relative probabilities of intra- vs intermolecular addition reactions. A full assessment of the contributions of these factors to the differential behavior of the benzocyclobutenes relative to the alkene-epoxides is beyond the scope of this paper, but we note that o -quinonedimethane intermediates often have long lifetimes that enable intermolecular reactions in other contexts, whereas (force-free) carbonyl ylides often have lifetimes on the order of microseconds or less . In both cases, the formation of a cross-link is in competition with the chain scission.…”

Section: Resultsmentioning

confidence: 99%

“…A full assessment of the contributions of these factors to the differential behavior of the benzocyclobutenes relative to the alkene-epoxides is beyond the scope of this paper, but we note that o-quinonedimethane intermediates often have long lifetimes that enable intermolecular reactions in other contexts, 59 whereas (force-free) carbonyl ylides often have lifetimes on the order of microseconds or less. 60 In both cases, the formation of a cross-link is in competition with the chain scission. The limited amount of gelation for P2 230 suggests that the process of chain scission is occurring more frequently than the formation of new cross-links, which only occurs when a tension-trapped ylide reacts with an alcohol.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Mechanochemical Ring-Opening of Allylic Epoxides

et al. 2019

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Recent successes in covalent polymer mechanochemistry might more easily be translated to stress-responsive bulk materials if easily scalable and minimalist mechanophores were identified. Epoxides represent attractive modifications of unsaturated polymer backbones for this purpose, but they suffer from limited mechanical reactivity. Here, we report that placing alkenes adjacent to cis-epoxide mechanophores along a polymer backbone results in ring-opening to carbonyl ylides during sonication, whereas epoxides with an adjacent saturated, linear alkyl chain do not. Upon release, tension-trapped ylides preferentially close to their trans-epoxides in accordance with the Woodward–Hoffmann rules. The reactivity of carbonyl ylides is exploited to tag the activated species with spectroscopic labels and to facilitate force-induced cross-linking through a reaction with pendant alcohols on co-polymers. The alkene effect is attributed to a combination of lower activation energy of the reaction (ΔG ‡) and greater force-coupled change in the length as the reaction proceeds from the ground to transition state (Δx ‡) relative to epoxides without the alkene. Even with alkene assistance, mechanochemical reactivity remains low; single-molecule force spectroscopy establishes that at ∼2500 pN ring-opening proceeds with a rate constant that is less than approximately 5 s–1 in toluene.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Mechanochemical Ring-Opening of Allylic Epoxides

et al. 2019

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“…In continuation of our interest − in transient-spectral properties and dipolarophilic reactivity of allyl-type 1,3-dipoles and related intermediates in fluid solutions under ambient conditions, we have carried out a nanosecond laser flash photolysis study of azomethine ylides photogenerated from a series of diphenyl aziridines (see Scheme ). The ylides were produced by direct excitation, via energy transfer from acetone triplet, and under singlet-mediated reversible electron-transfer sensitization by 1,4-dicyanonaphthalene (DCN).…”

Section: Introductionmentioning

confidence: 99%

Photochemical Ring-Opening in 2,3-Diphenyl Aziridines. Transient-Spectral and Kinetic Behavior of Azomethine Ylides and Related Photointermediates

2013

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By employing laser pulses at various wavelengths for nanosecond flash photolysis, a comprehensive time-resolved study has been performed on transient azomethine ylides photogenerated from several 2,3-diphenyl aziridines in fluid solutions under three different conditions, namely, by direct 266 nm excitation, under reversible electron-transfer sensitization by 1,4-dicyanonaphthalene singlet excited state, and via energy transfer from acetone triplet. Under each of the three conditions of photoexcitation, azomethine ylides are readily formed as transient species, characterized by broad, structureless absorption spectra with maxima at 470-500 nm and mostly complex decay kinetics in μs-ms time domain. Under acetone triplet sensitization, a second, shorter-lived transient species with absorption maximum at ∼360 nm is observed to grow and decay in the same time range as that of the growth of ylides. This species has been identified as the ring-opened precursor ylide triplet. The azomethine ylides are practically nonquenchable by oxygen, except that under acetone triplet sensitization in air-saturated acetonitrile, their decay is significantly enhanced. The latter is explained in terms of quenching through dipolarophilic reaction with singlet oxygen. A value of 1.6 × 10(9) M(-1) s(-1) has been estimated for the rate constant for reaction between singlet oxygen and ylide from trans-2,3-diphenylaziridine. We also report rate constants, in the range 2 × 10(3) to 4 × 10(9) M(-1) s(-1), for the quenching of azomethine ylides by two dipolarophiles, namely, maleic anhydride and dimethyl acetylene dicarboxylate. The dipolarophilic reactivity of ylides carrying bulky substituents on the N atom is relatively subdued. Acetic acid proved to be a modest quencher of ylides with rate constants close to 10(6) M(-1) s(-1).

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Competitive Formation of Ylide and Carbene Intermediates from ¹π,π*‐Excited α,β‐Unsaturated γ,δ‐Epoxyketones

Bischofberger

Frei

Wirz

1983

Helvetica Chimica Acta

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SummaryLaser flash photolyses (A = 265mm) of the y,d-epoxyenones 1-3, 7 and 8, the M , P-unsaturated y,d-epoxy ester 6, and the epoxytriene 9 at ambient temperature produced short-lived transients with broad absorption maxima in the visible region, which are identified as carbonyl ylides. Comparison of the rather long-wavelength absorption maxima with the results of standard PPP SCF SCI calculations suggests that some degree of twisting is present in all the ylides studied. The lifetimes of the order of hundreds of ns of these intermediates and Stern-Volmer analysis of the trapping of the carbonyl ylide derived from 2 with CH,COOH provide conclusive evidence that the carbene products are not formed via the carbonyl-ylide intermediate (Scheme 3 ) .

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Generation and characterization of carbonyl ylides from pyrazolinone spirooxiranes

Cited by 5 publications

References 36 publications

Mechanochemical Ring-Opening of Allylic Epoxides

Mechanochemical Ring-Opening of Allylic Epoxides

Photochemical Ring-Opening in 2,3-Diphenyl Aziridines. Transient-Spectral and Kinetic Behavior of Azomethine Ylides and Related Photointermediates

Competitive Formation of Ylide and Carbene Intermediates from ¹π,π*‐Excited α,β‐Unsaturated γ,δ‐Epoxyketones

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Generation and characterization of carbonyl ylides from pyrazolinone spirooxiranes

Cited by 5 publications

References 36 publications

Mechanochemical Ring-Opening of Allylic Epoxides

Mechanochemical Ring-Opening of Allylic Epoxides

Photochemical Ring-Opening in 2,3-Diphenyl Aziridines. Transient-Spectral and Kinetic Behavior of Azomethine Ylides and Related Photointermediates

Competitive Formation of Ylide and Carbene Intermediates from 1π,π*‐Excited α,β‐Unsaturated γ,δ‐Epoxyketones

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Competitive Formation of Ylide and Carbene Intermediates from ¹π,π*‐Excited α,β‐Unsaturated γ,δ‐Epoxyketones