Facile cleavage of the CβCβ′ bond of zirconacyclopentenes. Convenient method for selectively coupling alkynes with alkynes, nitriles, and aldehydes

Takahashi, Tamotsu; Kageyama, Motohiro; Denisov, V. Ya.; Hara, Ryuichiro; Negishi, Ei‐ichi

doi:10.1016/s0040-4039(00)61653-2

Cited by 179 publications

(54 citation statements)

References 19 publications

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“…In the light of the mechanism of the Dzhemilev reaction (Scheme 5), a similar mechanism involving the intermediacy of a zirconacyclopropane 17 and a zirconacyclopentene 19 was considered first (Scheme 7). However, it was soon ruled out since there was no indication of diethylation of Cl 2 ZrCp 2 with Et 3 Al from NMR spectroscopy and since 19, prepared by the reaction of 5-decyne with EtMgBr (2 equiv) and Cl 2 ZrCp 2 [30] and therefore free of Al, did not induce the indicated catalytic cycle in the presence of a 1:1 mixture of 5-decyne and Et 3 Al. [23] RC CH(R 1 ) Eventually, the three sets of results of pertinent stoichiometric reactions shown in Schemes 8 ± 10 were put together to come up with a most intricate bimetallic catalytic cycle, shown in Scheme 11.…”

Section: Discussionmentioning

confidence: 99%

Principle of Activation of Electrophiles by Electrophiles through Dimeric Association—Two Are Better than One

Negishi

1999

Chem. Eur. J.

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Electron-deficient metal compounds can be significantly activated as electrophiles through dimeric (or polymeric) association with either the same or different electrophiles. Although this phenomenon has played an important role in many reactions, such as the Friedel ± Crafts reaction and the Ziegler ± Natta polymerization, it has apparently only recently been fully recognized. Its widespread exploitation promises to lead to many new synthetically useful reactions as well as ready and accurate interpretations of mechanistic and structural phenomena in acid-catalyzed and -promoted reactions.

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Section: Discussionmentioning

confidence: 99%

Principle of Activation of Electrophiles by Electrophiles through Dimeric Association—Two Are Better than One

Negishi

1999

Chem. Eur. J.

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“…[10] Reaction (2) is the first of this kind in which an aldehyde behaves formally as a C 1 unit. It is noteworthy that, when zirconacyclopentadienes were prepared from [Cp 2 ZrCl 2 ]/EtMgBr/alkynes, [11] the above reaction was not observed, even at an elevated temperature. To investigate the scope of the reaction, aliphatic aldehydes were also used.…”

Section: Zhenfeng Xi* and Pixu LImentioning

confidence: 99%

Deoxygenative Cycloaddition of Aldehydes with Alkynes Mediated by AlCl3 and Zirconium: Formation of Cyclopentadiene Derivatives

2000

Angew. Chem. Int. Ed.

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“…The formation of 13 can be understood by assuming that isobutene, generated in the lithiation step, inserts into 3 (Scheme 3). However, the formation of the zirconocycle 13 is inconsequential as it reacts with the same unsatu rated systems as intermediate 3, due presumably to the facile cleavage of the C ß-C ß' bond [5]. Furtherm ore, we have observed that the reaction of 13 with benzophenone at 20 °C leads, after iodinolysis, to the formation of a mixture of 8 and 9, but in a 10:1 ratio of regioisomers.…”

Section: ; R' =R2=h 56%mentioning

confidence: 71%

Regioselective Zirconium-Mediated Cross Coupling of N-Methyl-N-propargyl Aniline and Alkenes

Barluenga

Sanz

Fañanás

1995

Zeitschrift Für Naturforschung B

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Regioselective Cross Coupling, Propargylamine-Zirconocene Complex, Zirconacyclopentene N-(2-bromoallyl)-N-methylaniline 1 is easily converted into the propargylamine-zirconocene complex 3 via loss of m ethane from 2-[zirconocene(methyl)]allyl amine 2. Regioselec tive insertion reactions with alkenes and benzophenone afford, after iodinolysis, products 4 -10.Recently the use of zirconium complexes in o r ganic synthesis has been widely recognized [1]. One of the most interesting transform ations which has been developed is the formation of unsatu rated system-metallocene complexes either by di rect complexation between the unsaturated com pounds and zirconocene [2] or by a /3-hydrogen abstraction process [lb, 3] followed by the inser tion of alkynes, alkenes, carbonyl compounds, or nitriles to generate the corresponding zirconacyclopentanoids. A great limitation of the intermolecular cross-coupling is in most cases the lack of regioselectivity in the coupling reaction when unsymmetrical zirconacyclopropanoids are used [2 a, 3 b, 3e], and the poor coupling in the case of terminal alkynes [3c]. On the other hand, 2-lithioallylamines have been prepared by brominelithium exchange from 2-bromoallylamines [4]. In the present communication we describe the prep aration of ^-propargylam ine-zirconocene com plexes from 2-bromoallylamines and further coup ling with unsaturated compounds followed by iodinolysis. Results and DiscussionTreatment of N-(2-bromoallyl)-N-methylaniline 1 with /erf-butyllithium at -7 8 °C followed by re action with zirconocene methyl chloride at tem peratures ranging between -7 8 and -2 0 °C afReprint requests to Dr. J. Barluenga. r r

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Facile cleavage of the CβCβ′ bond of zirconacyclopentenes. Convenient method for selectively coupling alkynes with alkynes, nitriles, and aldehydes

Cited by 179 publications

References 19 publications

Principle of Activation of Electrophiles by Electrophiles through Dimeric Association—Two Are Better than One

Principle of Activation of Electrophiles by Electrophiles through Dimeric Association—Two Are Better than One

Deoxygenative Cycloaddition of Aldehydes with Alkynes Mediated by AlCl3 and Zirconium: Formation of Cyclopentadiene Derivatives

Regioselective Zirconium-Mediated Cross Coupling of N-Methyl-N-propargyl Aniline and Alkenes

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