Fluorine‐Flanked Congested Sites: Minimal, Though Perceptible Buttressing Effects on the Proton Mobility of Arenes

Heiss, Christophe; Leroux, Frédéric R.; Schlosser, Manfred

doi:10.1002/ejoc.200500552

Cited by 20 publications

(11 citation statements)

References 21 publications

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“…A secondary but still significant buttressing effect exerted by the CH(OMe) 2 group on the adjacent halogen seems to be operative in decreasing the extent of the metalation at the meta-position with respect to it. The concept of a buttressing effect is not new [23] but it was employed only recently to explain the reduced mobility of a proton located ortho to a halogen in some fluoro-(albeit to a small extent), [24] chloro-and bromoarenes bearing adjacent bulky groups such as iodine [25] and trialkylsilyl. [25,26] More advanced studies revealed that this is a purely kinetic phenomenon [27] whose synthetic potential is remarkable.…”

Section: Resultsmentioning

confidence: 99%

Long‐Range Effects in the Metalation/Boronation of Functionalized 1,4‐Dihalobenzenes

2006

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Keywords: Metalation / Long-range inductive effects / Substituent effects / Buttressing effects / Aryl halides / Aryl boronic acidsThe lithiation/boronation of 1,4-dihalobenzenes (Hal = F, Cl, Br) bearing various functional groups in the 2-position was investigated using lithium diisopropylamide (LDA) as the metalating agent and trialkyl borate B(OR) 3 (R = Et, iPr) as the electrophile. It was demonstrated that sufficient steric hindrance precludes effective ortho-lithiation at the 3-position. In such cases, a strong meta-directing effect of an oxygen-or sulfur-based substituent (OMe, OSiMe 3 , SMe), resulting in the preferred formation of 2,6-disubstituted 1,4-di-

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Section: Resultsmentioning

confidence: 99%

Long‐Range Effects in the Metalation/Boronation of Functionalized 1,4‐Dihalobenzenes

2006

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“…In some cases (e.g. with X = SiMe 3 ), buttressing effects [34][35][36][37][38][39][40][41] (steric effects exerted by the X group through the fluoro group) 42 may compromise the reactivity of the 1,2-isomers 2. More importantly, the acidifying effect of substituents at meta positions is no longer the same as at ortho positions.…”

Section: Discussionmentioning

confidence: 99%

Substituent effects on the relative rates and free energies of ortho-lithiation reactions: families of fluorobenzenes as the substrates

Mongin¹,

Curty²,

Marzi³

et al. 2015

Arkivoc

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2-, 3-and 4-substituted fluorobenzenes and 5-substituted 1,3-difluorobenzenes were metalated with sec-butyllithium (LIS) and with lithium 2,2,6,6-tetramethylpiperidide (LiTMP) under irreversible conditions in order to determine the rates of reaction relative to the unsubstituted parent compounds (fluorobenzene and 1,3-difluorobenzene). In addition, the pairs of resulting aryllithiums were subjected to acid-base equilibration to furnish the thermodynamic stabilities (or: basicities) of these species again relative to the parent compounds. Not surprisingly, the effect diminishes with the distance of a given substituent to the lithiation center (ortho > meta > para) and it reaches its maximum at the ground state equilibration of the organometallic intermediate whereas it fades away at transition states, in particular reactant-like ones. Fluorine, the most powerful activator in the entire series if located at an ortho position, increases the rates of LIS-and LiTMP-promoted metalations by respectively 2 and 3 powers of ten, but by 7 to 8 powers of ten the aryllithium equilibrium stability.

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“…[26][27][28] 1 H-and ( 1 H-decoupled) 13 C NMR spectra were recorded at 400 and 101 MHz, respectively. All samples were dissolved in deuterochloroform.…”

Section: Methodsmentioning

confidence: 99%

“…Generalities: Details concerning standard operations and abbreviations have been given in previous publications from this laboratory. [26][27][28] 1 H-and ( 1 H-decoupled) 13 C NMR spectra were recorded at 400 and 101 MHz, respectively. All samples were dissolved in deuterochloroform.…”

Section: Methodsmentioning

confidence: 99%

Metalated 1‐(p‐Methoxybenzyl)pyrazole: A Structural Chameleon

Ondi

Schlosser

2006

Eur J Org Chem

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When treated with either butyllithium or lithium diisopropylamide, 1‐(p‐methoxybenzyl)pyrazole undergoes metalation at the exocyclic α‐position but mutates to the 5‐lithio species in the course of few minutes or hours. Trapping the intermediates with a rapidly reacting electrophile such as chlorotrimethysilane or carbon dioxide offers selective access to either of the two possible regioisomers. On the other hand, the relatively inert 1‐iodobutane and butyl trifluoromethanesulfonate (“triflate”) inevitably give rise to product mixtures, as the 5‐lithio species is more slowly intercepted than it can revert to the α‐metallomer by a rapid, though intermolecular, dynamic equilibration process. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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Fluorine‐Flanked Congested Sites: Minimal, Though Perceptible Buttressing Effects on the Proton Mobility of Arenes

Cited by 20 publications

References 21 publications

Long‐Range Effects in the Metalation/Boronation of Functionalized 1,4‐Dihalobenzenes

Long‐Range Effects in the Metalation/Boronation of Functionalized 1,4‐Dihalobenzenes

Substituent effects on the relative rates and free energies of ortho-lithiation reactions: families of fluorobenzenes as the substrates

Metalated 1‐(p‐Methoxybenzyl)pyrazole: A Structural Chameleon

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