ChemInform Abstract: SILYL‐, GERMYL‐, AND STANNYLALKOXYACETYLENES IN REACTIONS WITH CARBONYL COMPOUNDS AND CARBOXYLIC ACID CHLORIDES

Baukov, Yu. I.; Зайцева, Г. С.; Livantsova, L. I.; Bekker, R. A.; Savost'yanova, I. A.; Oleneva, G. I.; Lutsenko, I. F.

doi:10.1002/chin.198149284

Cited by 3 publications

(4 citation statements)

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“…Lewis acid catalyzed or photochemical condensations of carbonyl compounds with alkynes, producing α,β-unsaturated ketones, are well documented . Intermediacy of a highly labile 2 H -oxete has been firmly established by the isolation in a low-temperature reaction of hexafluoroacetone with ethoxyacetylene ).…”

mentioning

confidence: 99%

Difluoro-λ³-Bromane-Induced Oxidative Carbon−Carbon Bond-Forming Reactions: Ethanol as an Electrophilic Partner and Alkynes as Nucleophiles

et al. 2008

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Reported here for the first time are the oxidative couplings of alkynes and primary alcohols yielding conjugated enones. Although the BF3-catalyzed reaction of terminal alkynes with p-trifluoromethylphenyl(difluoro)-lambda3-bromane results in the fluoro-lambda3-bromanation of triple bonds to afford (E)-beta-fluorovinyl-lambda3-bromanes, reaction of an alkyne with the difluoro-lambda3-bromane in the presence of an alcohol and BF3-Et2O affords directly conjugated enones in good yields. The reaction proceeds in a highly stereo- and regioselective manner under metal-free conditions. Interestingly, no formation of enones was detected, when difluoro-lambda3-iodane p-CF3C6H4IF2 was used instead of the lambda3-bromane. A mechanism involving a lambda3-bromane-induced oxidation of an alcohol to an aldehyde, [2 + 2] cyclization with alkynes yielding 2H-oxetes, and finally the electrocyclic ring opening is discussed.

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mentioning

confidence: 99%

Difluoro-λ³-Bromane-Induced Oxidative Carbon−Carbon Bond-Forming Reactions: Ethanol as an Electrophilic Partner and Alkynes as Nucleophiles

et al. 2008

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“…The high Z -selectivity obtained from the isomerization of 3-silyloxetenes has been previously observed by Baukov et al when α-silyl-α,β-unsaturated esters were formed . Both steric and electronic effects have been shown to influence torquoselectivity in 4 e ‑ electrocyclic ring-openings; however, electronic effects play a greater role .…”

Section: Resultsmentioning

confidence: 55%

“…In an attempt to improve the yields for the tandem alkene isomerization/electrocyclic ring-opening of 2-methyleneoxetanes, 3-silyl-2-methyleneoxetane 1d was prepared (Scheme and Table ). Baukov et al reported in 1981 that 2-ethoxy-3-silyloxetenes 5 (R = TMS) gave α-silyl-α,β-unsaturated esters in higher yields than the corresponding unsilylated systems ( 5 , R = H). Compound 1d was heated at 160 °C; after 5–10 min, it was completely isomerized to enone 3d in an isolated yield of 80% (Scheme and Table , entry 3).…”

Section: Resultsmentioning

confidence: 99%

Silicon Acceleration of a Tandem Alkene Isomerization/Electrocyclic Ring-opening of 2-Methyleneoxetanes to α,β-Unsaturated Methylketones

et al. 2013

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The first rearrangement of 2-methyleneoxetanes to α,β-unsaturated methylketones is reported. It is proposed that when these substrates are heated, the corresponding oxetenes are formed and subsequently undergo electrocyclic ring-opening to methyl vinylketones. In particular, α-silyl-α,β-unsaturated methylketones were isolated in moderate to high yields and with high stereoselectivities. Based on the proposed mechanism, density functional theory explains the differential kinetics and stereoselectivities among substrates.

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“…Operating under the assumption that oxocarbenium ion formation preceded oxetene formation, we postulated that a silicon on C3 would stabilize the positive charge at C2 via hyperconjugation and, perhaps, provide an improved outcome . In fact, silyl substituents on C3 led to increased dienone yields and enhanced reaction rates, even at lower temperatures (Table , entries 3–10).…”

Section: Preparation and Reactivity Of 2-methyleneoxetanesmentioning

confidence: 99%

Unusual Transformations of Strain-Heightened Oxetanes

Riel

Howell

2021

Acc. Chem. Res.

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Conspectus Oxetanes are important motifs for drug discovery and are valuable templates in organic synthesis. Much of their use as synthetic intermediates exploits their inherent strain, often resulting in chain extensions at the expense of the heterocycle. Modifications on the carbon alpha to the oxygen of oxetanes, such as the CO of β-lactones, extend the modes of reactivity. Nevertheless, the outcomes are still largely predictable. On the other hand, other alpha modifications, such as a CH2, a spiro-oxiranyl moiety, or a spiro-cyclopropyl group, increase strain and open pathways not available to simple oxetanes or β-lactones. Methods in generating 2-methyleneoxetanes, 1,5-dioxaspiro[3.2]hexanes, and 4-oxaspiro[2.3]hexanes have been developed by us and others. To date, reactions of these systems have sometimes been predictable, but often the outcomes have been unexpected. This has provided fertile ground for thinking about what controls reactivity and what other reaction pathways might be accessible to these strain-heightened oxetanes. This Account summarizes the published literature on the most straightforward approaches to 2-methyleneoxetanes, dioxaspirohexanes, and oxaspirohexanes and on their reactivity. In contrast to simple oxetanes, reactions of 2-methyleneoxetanes with nucleophiles at C4 release an enolate rather than an alkoxide. Also, 2-methyleneoxetanes can be converted to homopropargyl alcohols or undergo a silicon accelerated isomerization/electrocyclic ring opening, processes accessible only because of the exocyclic double bond. In addition, oxetane oxocarbenium ions, derived from protonation of the enol ether, can react with nucleophiles to provide 2,2-disubstituted oxetanes. Oxaspirohexanes are readily prepared by Simmons–Smith cyclopropanation of 2-methyleneoxetanes. These unusual systems undergo a variety of substituent dependent rearrangements in the presence of the Lewis acid BF3·Et2O. In addition, upon treatment with Zeise’s dimer, oxaspirohexanes are transformed to synthetically useful 3-methylenetetrahydrofurans. Dioxaspirohexanes are easily accessed by dimethyldioxirane oxidation of 2-methyleneoxetanes. Predictably, dioxaspirohexanes react with many nucleophiles to give α-functionalized-β′-hydroxy ketones. Unexpectedly, 2,2-disubstituted oxetanes can also be selectively produced. This latter pathway has led to further unusual transformations, illuminating computational studies, and novel routes to biologically relevant molecules.

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ChemInform Abstract: SILYL‐, GERMYL‐, AND STANNYLALKOXYACETYLENES IN REACTIONS WITH CARBONYL COMPOUNDS AND CARBOXYLIC ACID CHLORIDES

Abstract: Läßt man auf elementorganische Ethoxyacetylene Aldehyde einwirken, dann entstehen α‐elementorganische Ester ungesättigter Säuren.

Cited by 3 publications

References 0 publications

Difluoro-λ³-Bromane-Induced Oxidative Carbon−Carbon Bond-Forming Reactions: Ethanol as an Electrophilic Partner and Alkynes as Nucleophiles

Difluoro-λ³-Bromane-Induced Oxidative Carbon−Carbon Bond-Forming Reactions: Ethanol as an Electrophilic Partner and Alkynes as Nucleophiles

Silicon Acceleration of a Tandem Alkene Isomerization/Electrocyclic Ring-opening of 2-Methyleneoxetanes to α,β-Unsaturated Methylketones

Unusual Transformations of Strain-Heightened Oxetanes

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ChemInform Abstract: SILYL‐, GERMYL‐, AND STANNYLALKOXYACETYLENES IN REACTIONS WITH CARBONYL COMPOUNDS AND CARBOXYLIC ACID CHLORIDES

Abstract: Läßt man auf elementorganische Ethoxyacetylene Aldehyde einwirken, dann entstehen α‐elementorganische Ester ungesättigter Säuren.

Cited by 3 publications

References 0 publications

Difluoro-λ3-Bromane-Induced Oxidative Carbon−Carbon Bond-Forming Reactions: Ethanol as an Electrophilic Partner and Alkynes as Nucleophiles

Difluoro-λ3-Bromane-Induced Oxidative Carbon−Carbon Bond-Forming Reactions: Ethanol as an Electrophilic Partner and Alkynes as Nucleophiles

Silicon Acceleration of a Tandem Alkene Isomerization/Electrocyclic Ring-opening of 2-Methyleneoxetanes to α,β-Unsaturated Methylketones

Unusual Transformations of Strain-Heightened Oxetanes

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Product

Resources

About

Difluoro-λ³-Bromane-Induced Oxidative Carbon−Carbon Bond-Forming Reactions: Ethanol as an Electrophilic Partner and Alkynes as Nucleophiles

Difluoro-λ³-Bromane-Induced Oxidative Carbon−Carbon Bond-Forming Reactions: Ethanol as an Electrophilic Partner and Alkynes as Nucleophiles