Borane‐Induced Dimerization of Arylallenes

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

doi:10.1002/anie.201808436

Cited by 20 publications

(20 citation statements)

References 70 publications

(24 reference statements)

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“…Erker and co‐workers showed that B(C 6 F 5 ) 2 groups are suitable coupling partners in Suzuki‐Miyaura [9,10] cross‐coupling reactions [2a,c,6a,11] . Therefore, we probed if it is possible to develop a one‐pot procedure for a 1,2‐carboboration of allenes by alkenylboranes and a consecutive Suzuki‐Miyaura coupling.…”

Section: Resultsmentioning

confidence: 99%

1,2‐Carboboration of Arylallenes by In Situ Generated Alkenylboranes for the Synthesis of 1,4‐Dienes

Averdunk

Hasenbeck

Müller

et al. 2022

Chemistry A European J

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We herein report a novel method for the coupling of unactivated alkynes and arylallenes, which relies on an unprecedented and regioselective 1,2‐carboboration of the allene by an alkenylborane. The alkenylborane is conveniently prepared in situ by hydroboration of an alkyne with Piers’ borane, i. e., HB(C6F5)2. The boryl‐substituted 1,4‐dienes that are formed by this carboboration are well‐suited for a subsequent Suzuki‐Miyaura coupling with aryl iodides. This allowed us to develop a three‐step, one‐pot protocol for the synthesis of aryl‐substituted 1,4‐dienes. The generality of the reaction was demonstrated by the synthesis of twenty dienes with modular variations of all three reaction partners. The mechanism of the new 1,2‐carboboration was investigated using dispersion corrected double‐hybrid DFT computations that allowed us to rationalize the chemo‐ and regioselectivity of this key step.

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Section: Resultsmentioning

confidence: 99%

1,2‐Carboboration of Arylallenes by In Situ Generated Alkenylboranes for the Synthesis of 1,4‐Dienes

Averdunk

Hasenbeck

Müller

et al. 2022

Chemistry A European J

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“…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.…”

Section: Methodsmentioning

confidence: 99%

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

Zhao

2020

Angew. Chem. Int. Ed.

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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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“…Compound 1 had been synthesized in stoichiometric reaction sequences 4. We recently developed the metal-free, HB(C 6 F 5 ) 2 catalysed formation of isomerically pure 1 by allene cyclotrimerization under mild conditions 5. We also had recently shown that a small series of 1-alkynes could be converted to linear oligomers by treatment with either of the halogenoboranes XB(C 6 F 5 ) 2 2a (X: Cl) or 2b (X: Br).…”

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confidence: 99%

“…We had previously shown that HB(C 6 F 5 ) 2 serves as an efficient metal-free catalyst for the cyclotrimerization of allene to 1,3,5-trimethylenecyclohexane and of cyclohexylallene to cis , trans -2,4,6-tricyclohexyl-1,3,5-trimethylenecyclohexane 5. Our present study shows that the strongly electrophilic halogenoboranes XB(C 6 F 5 ) 2 (X: Cl, Br) in principle can induce the same catalytic reaction.…”

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confidence: 99%

“…We repeated this reaction: treatment of 1 with 5 mol% of p -toluene sulfonic acid in toluene solution at r.t. for 1.5 h cleanly converted 1 to mesitylene (Scheme 5). We also treated the n -octyl- and cyclohexylallene cyclotrimers 14c 14 and 14e 5 with p -toluene sulfonic acid. Compound 14c was fully converted on a preparative scale with 10 mol% of the acid catalyst during 48 h at r.t.…”

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confidence: 99%

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