Borane‐Induced Dimerization of Arylallenes

Tao, Xin; Daniliuc, Constantin G.; Dittrich, Dustin; Kehr, Gerald; Erker, Gerhard

doi:10.1002/ange.201808436

Cited by 10 publications

(6 citation statements)

References 70 publications

(6 reference statements)

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“…As the formation of 10 was accompanied by the formation of small amounts of regioisomers, an excess of 10 was used (for details, see Section S8 in the Supporting Information). As reported by Erker and co-workers, the formation of intermediate 11 can be observed within minutes . Diene 11 then interconverts slowly within hours to 12 .…”

Section: Resultssupporting

confidence: 66%

“…To substantiate the assumption that 12 is an intermediate of the catalytic reaction, we performed a reaction with 3a as the substrate and 10 mol % 12 , prepared, and isolated, according to the procedure reported by Erker and co-workers, as a catalyst (Scheme ). This reaction yielded 4a in 69% yield, indicating that the transborylation between 12 and 2 releases the catalyst HB(C 6 F 5 ) 2 1 . However, the transborylation requires an excess of allene to proceed.…”

Section: Resultsmentioning

confidence: 92%

“…5 A notable example is the Piers' borane (HB(C 6 F 5 ) 2 1)-induced dimerization of arylallenes that Erker and co-workers reported in 2018 (Scheme 1). 6 According to their mechanistic proposal, this reaction commences with the hydroboration of an allene to yield an allylborane that adds to a second equivalent of the allene yielding a boryl-substituted diene. This diene then undergoes a Cope rearrangement.…”

Section: ■ Introductionmentioning

confidence: 99%

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Piers’ Borane-Catalyzed Dimerization of Arylallenes via Transborylation: A Synthetic and Mechanistic Study

et al. 2022

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Herein, we report a Piers’ borane-catalyzed dimerization of arylallenes. Catalytic turnover is achieved by a transborylation with pinacolborane (HBpin) that releases Piers’ borane and promotes the catalytic reaction, thereby giving convenient access to a range of synthetically versatile bench-stable pinacolborane-substituted 1,5-dienes. The synthetic utility of these pinacolborane-substituted 1,5-dienes was demonstrated by Suzuki–Miyaura coupling, the synthesis of azide and halogen-substituted 1,5-dienes, and the oxidation to γ,δ-unsaturated aryl ketones. The mechanism of the reaction was investigated experimentally as well as by dispersion-corrected double-hybrid density functional theory (DFT) computations. These investigations indicate that Piers’ borane mediates the allene dimerization and a subsequent Cope rearrangement to yield a B(C6F5)2-substituted 1,5-diene. This diene then undergoes a transborylation via a concerted σ-bond metathesis at the final stage of the catalytic reaction.

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Section: Resultssupporting

confidence: 66%

Section: Resultsmentioning

confidence: 92%

Section: ■ Introductionmentioning

confidence: 99%

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Piers’ Borane-Catalyzed Dimerization of Arylallenes via Transborylation: A Synthetic and Mechanistic Study

et al. 2022

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“…Interestingly, the reaction of Piers' borane 6 with arylallenes 20 takes a different course. [13] In this case, dimerization, and the formation of the boryl substituted 1,6-diaryl-1,5-hexadiens 21 a-21 d was observed (Scheme 10).…”

Section: Reactions Initiated By the Hydroboration Of Allenes By Electrophilic Boranesmentioning

confidence: 89%

Reactions of Allenes with strong Borane‐Based Lewis Acids

Gellrich

2021

Eur J Org Chem

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In recent years, reactions of unsaturated organic molecules with strong boron-based Lewis acids have attracted considerable attention. In this review, reactions of allenes with boron-based Lewis acids, especially such ones equipped with perfluorophenyl rings, are discussed. It is shown that depending on the substitution pattern of the allene and the borane, a surprisingly broad variety of chemical transformations can be observed.These transformations often include unexpected skeletal rearrangements of the former allene. Furthermore, some transformations require only catalytic amounts of the borane-based Lewis acid. Within this minireview, emphasis is given to the mechanistic aspects of these transformations, and similarities in the initial reaction steps are outlined.

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“…[12] Nevertheless, none of these catalysts have been shown to promote dimerization of allenes during hydroboration reactions. There is one example of a borane-mediated dimerization of arylallenes reported by Erker (Scheme 1 B), [13] and this stoichiometric reaction employs a highly reactive and electrophilic hydroborane (C 6 F 5 ) 2 BH and affords a boryl-functionalized (E,E)-1,5-diene product.…”

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confidence: 99%

Chromium‐Catalyzed Selective Dimerization/Hydroboration of Allenes to Access Boryl‐Functionalized Skipped (E,Z)‐Dienes

Zhao

2020

Angewandte Chemie

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A chromium-catalyzed dimerization/hydroboration of allenes is developed to access synthetically versatile borylfunctionalized skipped dienes with a catalyst generated in situ from CrCl 2 and a pyridine-2,6-diimine ligand mes PDI. A variety of allenes reacted with pinacolborane (HBpin) to afford the corresponding boryl-functionalized (E,Z)-1,4-dienes in high yields and with excellent selectivity. Electron paramagnetic resonance (EPR) spectroscopic studies suggest that this chromium-catalyzed reaction probably proceeds through a chromium(I) hydride intermediate. Catalysts based on first-row transition metals, such as iron, cobalt, nickel, and copper, have been extensively studied in reaction discovery and development over past decades partially because of their low price, high abundance, and low toxicity. [1] Chromium, a first-row early transition metal in Group 6, is an abundant element in the Earths crust. Although Cr VI compounds are highly toxic, Cr II and Cr III compounds, such as CrCl 2 and CrCl 3 , have low toxicity. [2] Chromium compounds have shown unique catalytic reactivities in Nozaki-Hiyama-Kishi reactions, [3] various crosscoupling reactions, [4] and the polymerization and oligomerization of olefins. [5] However, chromium-catalyzed hydroboration reactions of unsaturated hydrocarbons that can afford synthetically versatile organoboron compounds [6] have remained unknown. Skipped dienes are valuable structural motifs in numerous bioactive natural products and synthetic compounds (Scheme 1 A). [7] Several synthetic approaches, such as hydroallylation of alkynes, [8] hydroalkenylation of 1,3-dienes, [9] and coupling of vinyl metallic reagents with various allylic electrophiles, [10] have been developed to prepare skipped dienes. However, systematic approaches to access borylfunctionalized skipped dienes from readily accessible starting materials are still lacking. Considering broad applications of organoboron compounds in chemical synthesis, [6] we are interested in developing selective approaches to synthesize boryl-functionalized skipped dienes because they can be further converted to other unsaturated hydrocarbons via selective C À B bond transformations. Scheme 1. Boryl-functionalized skipped dienes generated by coupling of two allenes with boron reagents.

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Borane‐Induced Dimerization of Arylallenes

Cited by 10 publications

References 70 publications

Piers’ Borane-Catalyzed Dimerization of Arylallenes via Transborylation: A Synthetic and Mechanistic Study

Piers’ Borane-Catalyzed Dimerization of Arylallenes via Transborylation: A Synthetic and Mechanistic Study

Reactions of Allenes with strong Borane‐Based Lewis Acids

Chromium‐Catalyzed Selective Dimerization/Hydroboration of Allenes to Access Boryl‐Functionalized Skipped (E,Z)‐Dienes

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