Deprotonation of Furans Using Lithium Magnesates.

Mongin, Florence; Bucher, Aurélien; Bazureau, Jean Pierre; Bayh, Omar; Awad, Haçan; Trécourt, François

doi:10.1002/chin.200607114

Cited by 2 publications

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“…Pioneered by Knochel, the magic potions that effect these unlikely regioselective magnesiations have formulas such as TMPMgCl·LiCl (dianionic−dicationic) or (TMP) 2 Zn·2MgCl 2 ·2LiCl (dianionic−tricationic), but when they are utilized in situ in THF solution, details of how their different components interact with each other are sketchy. Mongin has also reported success in direct magnesiation applications of furans with more standard ate formulations (for example, Bu 4 MgLi 2 ) …”

Section: “Complex” Metalators: Ates Mixed-metal Superbases Unimetal S...mentioning

confidence: 99%

“…Mongin has also reported success in direct magnesiation applications of furans with more standard ate formulations (for example, Bu 4 MgLi 2 ). 13 From this brief survey, the key to finding new improved metalating agents appears to lie in mixing together two or more distinct components to combine different anions with the same cation, different cations with the same anion, or a combination of different anions and different cations. It is said that "l'union fait la force" ("union makes strength"), and in the examples discussed here, this certainly applies as the union of components produces stronger metalators.…”

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confidence: 99%

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Avant-Garde Metalating Agents: Structural Basis of Alkali-Metal-Mediated Metalation

2009

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Metalation, one of the most useful and widely used synthetic methodologies, transforms a relatively inert carbon-hydrogen bond to a more labile carbon-metal bond. Until recently, most organometallic reagents that facilitate this process have combined strongly electropositive metals, such as lithium, with organic reagents to form highly polar and, by implication, highly reactive carbon-metal bonds. For example, the alkyllithium reagents and bulky lithium amides that are commonly employed for this purpose can suffer from low functional group tolerance. Lithio-products of these reactions generally have low kinetic stabilities. More recently, several groups around the world have pioneered alternative metalation reagents, complex metalators, which can be interpreted as composite molecules or mixtures made up of two or more distinct compound types. Several examples include magnesiate complexes, Lochmann-Schlosser superbases, Kondo and Uchiyama's 2,2,6,6-tetramethylpiperidide (TMP)-zincate complexes, and Knochel's turbo-Grignard and related salt-supported reagents. This Account describes our rational development of novel complex metalators based on existing structural templates and designed to execute alkali-metal-mediated metalations (AMMMs). By changing the nonalkali metal in these structures, we have produced tailor-made dianionic-dicationic structures such as [(TMEDA).Na(mu-TMP)(mu-(n)Bu)Mg(TMP)], [(TMEDA).Na(mu-TMP)(mu-(t)Bu)Zn((t)Bu)], and [(TMEDA).Li(mu-TMP)Mn(CH(2)SiMe(3))(2)] (TMEDA = N,N,N',N'-tetramethylethylenediamine). These compounds can perform unprecedented magnesiations, zincations, or manganations on aromatic substrates that are generally inert toward conventional Mg, Zn, or Mn(II) reagents. Although the alkali metal is an essential component of these new complex metalators, interestingly, the less electropositive, less polar nonalkali metal [Mg, Zn, or Mn(II)] actually carries out the deprotonation. We view this unique behavior as a mixed-metal synergic effect: intramolecular communication through metal-ligand-metal bridges directs special regioselectivities or polydeprotonations. We demonstrate structurally defined alkali-metal-mediated magnesiations (AMMMg), zincations (AMMZn), and manganations [AMMMn(II)] of representative aromatic substrates (including benzene, toluene, anisole, and ferrocene). In addition, we present remarkable meta-orientated metalations of toluene and N,N-dimethylaniline. We also review 2-fold metalations of arenes, in which an arenediide guest is encapsulated within a 12-atom polymetallic cationic (NaNNaNMgN)(2) host ring to form inverse crown structures. Furthermore, using X-ray crystallography of a turbo-Grignard reagent, we establish a link between our complex metalators and turbo-Grignard reagents. Armed with this accruing knowledge of complex metalators, we think rapid progress in "low polarity metalation" should now be possible. The greatest remaining challenge is to develop methodologies that shift these processes from stoichiometric reactions into more economical catal...

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Section: “Complex” Metalators: Ates Mixed-metal Superbases Unimetal S...mentioning

confidence: 99%

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confidence: 99%

Avant-Garde Metalating Agents: Structural Basis of Alkali-Metal-Mediated Metalation

2009

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“…Interestingly the higherorder magnesiate yielded a sodiated benzyl complex while the lower order complex gave a DABCO-and toluene-solvated contact-ion pair in which no deprotonation to benzyl anions takes place. Mongin also noted and quantified a reactivity difference between higher-order Li2MgBu4 and lower-order LiMgBu3 in the regioselective deprotonation of furan; while both bases deprotonated at the same site, the higher order magnesiate gave an improved yield under identical reaction conditions (Figure 30b) [89]. Likewise, Marsais and co-workers saw a similar yield increase under identical conditions on moving from lower order to higher order magnesiate in the deprotonation of 2chloro-N-tert-butylisonicotinamide (Figure 30c) with the yield improving from 42 (39) to 80 (66) % upon electrophilic interception with D2O (or I2) [90].…”

Section: Contrasting Reactivity Of Higher-order and Lower-order Alkylmentioning

confidence: 89%

Alkaline-Earth Metal Compounds

Mulvey

Robertson

2013

Topics in Organometallic Chemistry

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This year (2012) commemorates the 100 th anniversary of the award of the Nobel Prize to Victor Grignard for his development of Grignard reagents (at the simplest level expressed as "RMgX" where R is an organic group and X is a halogen), one of the most widely utilized classes of synthetic reagent. A century on but only in the past decade or so has magnesium reagent chemistry entered a new and exciting phase, surpassing the limitations of what traditional Grignard reagents can do. Modern magnesium reagents have been designed to possess essentially comparable reactivity to their great rivals, organolithium reagents (traditional Grignard reagents are orders of magnitude less reactive than organolithium reagents) but at the same time to maintain the superior selectivity and broader functional group tolerance of their traditional ancestors. The key to the design of these new reagents is their multi-component constitution with the organomagnesium engine powered by an activating alkali metal additive, often a halide salt or another organometallic entity. This chapter outlines some of the most significant advances in this emerging field.

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Deprotonation of Furans Using Lithium Magnesates.

Cited by 2 publications

References 1 publication

Avant-Garde Metalating Agents: Structural Basis of Alkali-Metal-Mediated Metalation

Avant-Garde Metalating Agents: Structural Basis of Alkali-Metal-Mediated Metalation

Alkaline-Earth Metal Compounds

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