Catalyst‐Free Enantiospecific Olefination with In Situ Generated Organocerium Species

Music, Arif; Hoarau, Clément; Hilgert, Nicolas; Zischka, Florian; Didier, Dorian

doi:10.1002/anie.201810327

Cited by 22 publications

(25 citation statements)

References 34 publications

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“…In contrast, the mixed species n Bu 2 SmMe⋅5 LiCl ( 2 , 0.70 equiv), inspired by our previous work on lanthanum, reacted at −30 °C, leading to full conversion of 4‐bromoanisole ( 7 a ) into the corresponding diaryl(methyl)samarium reagent 8 within 1 h. Subsequent reaction with ketone 9 provided the tertiary alcohol 10 a in 69 % yield (Table , entry 2). Interestingly, we noticed that n Bu 3 Sm⋅5 LiCl ( 3 ) exchanged all three of its butyl residues, whereas the related n Bu 3 La⋅5 LiCl was able to exchange only one butyl residue ,. Indeed, the exchange of n Bu 3 Sm⋅5 LiCl ( 3 , 0.40 equiv) with 7 a led to full conversion into the corresponding triarylsamarium derivative 11 a within only 15 min at −30 °C.…”

Section: Methodsmentioning

confidence: 91%

The Halogen–Samarium Exchange Reaction: Synthetic Applications and Kinetics

et al. 2019

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Fast I/Sm and Br/Sm exchanges take place when various aromatic or heterocyclic iodides and bromides are treated with nBu 2 SmCl·4 LiCl and nBu 3 Sm·5 LiCl, respectively.The resulting organosamarium reagents were efficiently quenched with aldehydes,k etones,a nd imines.A lso,t hey undergo acylations when treated with N,N-dimethylamides leading to ketones.The rate of the Br/Sm exchange for atypical aryl bromide was determined and found to be 8.5 10 5 faster than the Br/Mg exchange,i ndicating that the rate of am etalexchange is related to the ionic character of the carbon-metal bond and to the metal electronegativity.Organometallics are key nucleophilic reagents for organic synthesis, [1] and their efficient preparation is an important synthetic task. Besides the oxidative addition [2] of am etal to an organic halide,the halogen-metal exchange reaction [3][4][5] is one of the most important synthetic routes to aryl and heteroaryl organometallics.T he halogen/lithium exchange [3] is certainly the most used in synthesis;h owever,t he functional group tolerance of aryllithiums is rather moderate. [4] As an alternative,the halogen/magnesium exchange [5] is compatible with large number of functional groups;nevertheless,this exchange reaction is considerably slower than the halogen/ lithium exchange. [6] Further,t he iodine/zinc exchange proceeds at an even slower rate. [7] Besides ate-metal reagents such as manganates [8] and cuprates [9] undergo an exchange, but the atom economy [10] of these reactions is moderate.Recently,w eh ave reported an ew halogen/lanthanum exchange reaction and have found that this exchange is at least 10 6 faster than the halogen/magnesium exchange.A lso, the I/La or Br/La exchange displays better functional group tolerance than the halogen/lithium exchange. [11] This led us to postulate that the rate of the halogen/metal exchange depends on the ionic character of the carbon-metal bond of the exchange reagent, and that the functional group compat-ibility also depends on this ionic character and therefore on the electronegativity [12] of the metal (Scheme 1).Forp roving this relation, we turned our attention to samarium which has an electronegativity of 1.17 compared to 1.10 for lanthanum. We therefore predicted that the halogen/ samarium exchange should be slower than the halogen/ lithium, the halogen/lanthanum, and the halogen/cerium exchanges,a nd that the functional group tolerance of the resulting arylsamarium(III) reagent should be better than that of the corresponding lanthanum(III) reagents.Moreover, organosamarium reagents already proved their utility as nucleophiles,b ut only few preparation methods of these organometallics have been reported. [13] Ah alogen/samarium exchange will then provide an ew access to these reagents.Herein, we report the preparation of halogen/samarium exchange reagents and their use for performing efficient I/Sm and Br/Sm exchanges.W edescribe also the reaction of these new aryl-and heteroarylsamarium reagents with various electrophiles and provide an appr...

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Section: Methodsmentioning

confidence: 91%

The Halogen–Samarium Exchange Reaction: Synthetic Applications and Kinetics

et al. 2019

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“…Man beachte,d ass das aus der Reaktion von CeCl 3 •2 LiCl (Cer-Turbo-Chlorid) mit drei ¾quivalenten n-BuLi in THF bei À30 8 8Ce rhaltene Produkt zuvor durch Raman-Spektroskopie als "n-Bu 3 Ce" analysiert wurde (Abwesenheit signifikanter Raman-Linien von CeCl 3 und n-Bu-Li). [15] Die Aktivierung des carbonylischen Substrats und dessen Umwandlung (hier Reduktion zum Alkoxyrest) findet am selben Cer-Metallzentrum statt und kçnnten dreimal ablaufen. Solche 1,2-Additionsreaktionen wurden sowohl für die Yttriummethyle [YMe 3 ] n , [57] [YMe 2 (thf) 5 ][BPh 4 ]u nd [YMe(thf) 6 ][BPh 4 ] 2 [24] als auch die Neosilyle [Y(CH 2 SiMe 3 ) 2 -(thf) 4 ][A] (A = BPh 4 ,A l(CH 2 SiMe 3 ) 4 )u nd [Y(CH 2 SiMe 3 )-(thf) 5 ][BPh 4 ] 2 [58] nachgewiesen, unter Verwendung von Fluorenon und Benzophenon.…”

Section: Methodsunclassified

CeCl₃/n‐BuLi: Enträtselung von Imamotos Organocer‐Reagenz

2021

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CeCl 3 (thf) reagiert bei niedrigen Temperaturen mit MeLi, t-BuLi und n-BuLi zu isolierbaren Organocer-Komplexen.E ine lçsemittelabhängige,z .T .s tark ausgeprägte Dissoziation von n-BuLi konnte durch 7 Li-NMR-Spektroskopie aufgeklärt werden. Dieses Verhalten deutet darauf hin, dass "Ce(n-Bu) 3 (thf) x "o der Solvens-separierte Ionenpaare wie "[Li(thf) 4 ][Ce(n-Bu) 4 (thf) y ]" die dominanten Spezies des Imamoto-Reagenzes sind. Die Stabilitätder Komplexe Li 3 Ln-(n-Bu) 6 (thf) 4 steigt mit der Abnahme der Ln III -Grçße deutlich. Untersuchungen zum Lçsungsverhalten von kristallinem Li 3 Lu(n-Bu) 6 (thf) 4 und Mischungen von LuCl 3 (thf) 2 /n-BuLi in THF deuten darauf hin, dass eine merkliche Dissoziation von n-BuLi nur bei Molverhältnissen von < 1:3erfolgt. Der an n-BuLi abgereicherte Komplex LiLu(n-Bu) 3 Cl(tmeda) 2 wurde durch Behandlung von Li 2 Lu(n-Bu) 5 (tmeda) 2 mit ClSiMe 3 gewonnen, jedocha uf Kosten einer Einlagerung von LiCl. Imamotos Transformation von Ketonen zu tertiären Alkoholen wurde mit 1,3-Diphenylpropan-2-on untersucht und lieferte 99 %d es Alkohols. Abbildung 1. Die Ce III -Carbonylkoordination kontrolliert die hochselektive nukleophile Addition von binären CeX 3 /RLi-Mischungen (X = Halogenido;R= Alkyl).

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“…After optimizations, n-Bu 3 Ce•5LiCl showed the best results, furnishing triaryl cerium species through an advantageous, unprecedented and quantitative triple halogen-cerium exchange reaction. 27 The reaction of triaryl cerium species with sterically hindered ketones such as camphor or ditert-butyl ketone furnished the corresponding tertiary alcohols 8a and 8c in good yields, and ,-unsaturated ketones gave exclusively the products resulting from 1,2-additions (8b). Noteworthy, deprotonation was not observed when enolizable ketones were used.…”

Section: Synpacts Syn Lettmentioning

confidence: 99%

“…Noteworthy, deprotonation was not observed when enolizable ketones were used. 27 On the basis of these successful experiments, in situ generated triaryl cerium species were engaged in Zweifel olefinations with alkenyl boron pinacol reagents. Selected…”

Section: Synpacts Syn Lettmentioning

confidence: 99%

Organocerium: A New Contender for Halogen–Metal Exchanges

Music¹,

Didier

2019

Synlett

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In the context of our current research on dependable and sustainable methods for C–C bond-forming reactions, we have recently developed new strategies to generate organocerium reagents through simple bromide–cerium exchanges. n-Bu3Ce enabled a fast and general access to functionalized triaryl- and alkenyl cerium species from the corresponding aryl- and alkenyl bromides. A broad range of these new organocerium species was engaged in Zweifel’s olefination, allowing for the synthesis of widely substituted alkene derivatives in a stereospecific way. Herein, we place the formation of organocerium species in the context of known organometallic reagents (Li, Mg, Zn, Cu, Ca, La, and Sm) generated through halogen–metal exchange reactions and their application in further transformations.

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Catalyst‐Free Enantiospecific Olefination with In Situ Generated Organocerium Species

Cited by 22 publications

References 34 publications

The Halogen–Samarium Exchange Reaction: Synthetic Applications and Kinetics

The Halogen–Samarium Exchange Reaction: Synthetic Applications and Kinetics

CeCl₃/n‐BuLi: Enträtselung von Imamotos Organocer‐Reagenz

Organocerium: A New Contender for Halogen–Metal Exchanges

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Catalyst‐Free Enantiospecific Olefination with In Situ Generated Organocerium Species

Cited by 22 publications

References 34 publications

The Halogen–Samarium Exchange Reaction: Synthetic Applications and Kinetics

The Halogen–Samarium Exchange Reaction: Synthetic Applications and Kinetics

CeCl3/n‐BuLi: Enträtselung von Imamotos Organocer‐Reagenz

Organocerium: A New Contender for Halogen–Metal Exchanges

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CeCl₃/n‐BuLi: Enträtselung von Imamotos Organocer‐Reagenz